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Heterocycles Containing Phosphorus.

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found the force constant of the Si-S bond to be ksi.s -2.28 mdyne/A, and the absorption region of the Si-S
bond (see also 1561 and 1601) was found to be from 520 to
400 cm-1. The force constant was determined for
C13SiSH with the aid of the value of ksi-ci -= 2.46
mdyne/A calculated by Siebert 1681for (CH,)3SiSCI. It was
concluded from the close resemblance of the spectra that
ksi.s == 2.28 mdyne/A is valid for all silicon-sulfur compounds, any deviations being only slight. This value
agrees closely with the theoretical value of 2.22 mdyne/A
calculated by Siebert (691 for the Si-S single bond, showing that Si-S bonds possess n o appreciable double-bond
character. These results were fully corroborated by subsequent investigations 170-731.
[ 6 8 ] H . Siebert, Z. anorg. allg. Chem. 268, 177 (1952).
[69] H . Siebert, 2. anorg. allg. Chem. 273, 170 (1953).
[70] H. R . Linton and E. R . Nixon, J. chem. Physics 29,921 (1958).
1711 E. A. V. Ebsworth, R. Taylor, and L . A. Woodward, Trans.
Faraday SOC. 55, 21 I (1959).
[72] H. Kriegsmnnn, Z. Elektrochem., Ber. Bunsenges. physik.
Chem. 61, 1088 (1957).
1731 H. Kriegsrnnnn and H . Clnusr, Z. anorg. allg. Chem. 300,
210 (1959).
The Si-S distance as found by electrot? diffraction measurements 1741 on CI3SiSH is 2.14 5 0.02 A, compared
with the sum of the covalent radii of 2.338 A given by
Pauling. This contraction, however, is not attributed to
any double-bond character of the Si-S bond, but to the
polarity of the o-bond. Thus, in agreement with thc
force constants, p,-d,
bonds play only a minor part
in the chemistry of silicon-sulfur compounds, which is
in contrast with the chemistry of silicon-oxygen and
silicon-nitrogen compounds. It is still uncertain, however, why the Si-S bond, unlike the C-S bond, cannot
form adducts (e.g. [(HsC,)~S]+I-).
I am very gratejiul to Prof. 0. Glemser for encouragement and discussions. I am also deeply indebted to Prof.
M. Schmeisser for permission to use unpublished results
obtained by his research group.
Received: February 4th, 1965.
[A 470/257 IE]
German version: Angew. Chem. 77, 1066 (1965)
Translated by Express Translation Service, London
[74] C. J . W . Wilkins and L . F. Sirtton, Trans. Faraday SOC.50,
783 (1954).
Heterocycles Containing Phosphorus
BY PR1V.-DOZ. DR. G. MARKL
CHEMISCHES INSTITUT DER UNIVERSITAT WURZBURG (GERMANY)
The preparation of heterocycles containing phosphorus is described. The chemical behavior
of ring systems containing trivalent phosphorus is niainly determined by their phosphine
character; heterocyclic behavior in the ordinary sense is shown by rings containingfunctional
groups. Syntheses and reactions of cyclic compounds of’pentavalent and hexavaIent phosphorus are particularly interesting.
Introduction
A. General Methods of Preparation
B. Heterocycles Containing On e Phosphorus Ato m
I . Phosphacylopropanes an d Phosphacyclobutanes
2. Five- Membered Rings (phospholanes, phospholenes,
phospholes, five-membered rings containing pentavalent phosphorus, phosphindolines, isophosphindolines, phosphofluorenes, phosphafluorenes containing
pentavalent an d hexavalent phosphorus, spiro compounds)
3. Six-Membered Rings (phosphorinanes, 1,l-diphenyl-lphosphabenzene, I,l-diphenyl-1-phosphanaphthalene,
tetrahydrophosphinoline, tetrahydroisophosphinoline,
spirophosphonium salts, phospha-anthracene a n d
phosphdphenanthrene)
4. Seven- and Eight-Membered Rings
Introduction
Almost 98 % of all papers dealing with heterocycles containing phosphorus were published within the last
fifteen years, and more than 80% since 1959. This
development is the result of the rapid progress made in
Angew. Chem. internat. Edit.
VoI. 4 (1965) No. I 2
C. Heterocycles Containing Two or More Phosphorus
Atoms
1. 1,3-Diphosphacyclohexane. Cyclic Phosphacyanins
2. 1,4-Diphosphacyclohexane. 9,IO-Dihydrophosphanthrene
3. 1,4-Diphosphabicyclo[2.2.2]octane
4. 1,2-Diphosphacycles a n d 1,2,3-Triphosphacycles
D. Phosphorus Heterocycles t h at also Contain Oxygen o r
Nitrogen Atoms in the Ring
I . I-Oxa-3-phosphacyclopentanes
2. 1,3-Dioxa-5-phosphacycIohexanes
3. 9-Phosphaxanthene an d 9,lO-Dihydrophenophosphazine
4. 1-Aza-4-phosphacyclohexane a n d 1,2-Diaza-4-phosphacyclohexane
the organic Chemistry of phosphorus, which ceased to
be a specialized field with the discovery of the phosphorylide olefinations.
What quantitative or qualitative differences should we
expect to find between the heterocyclic systems of nitrogen and of phosphorus? The single-bond covalent
1023
radius [11 of phosphorus (1.1 A) is 0.4 A greater than
that of nitrogen. The greater bulk of the phosphorus
atom is shown by the P-C distances of 1.83 to 1.94 A
(as compared with an N-C distance of 1.47 A in tertiary
amines) found by electron-diffraction and X-ray measurements [21 on tertiary phosphines. The C-N-C
valence angle in tertiary amines (107 to 108 ") is close to
the terahedral angle, whereas the phosphorus atom in
tertiary phosphines (valence angle 98.9 to 99.1 ") is
situated at the apex of a much more acute trigonal
pyramid 121. The fact that, in contrast to nitrogen, the
phosphine pyramid inverts only at high temperatures
(activation energy 29 to 31 kcal/mole), as is shown by
Homer's isolation and racemization of optically active
phosphines [31, must have stereochemical consequences
for cyclic phosphines. The electronic configurations of
nitrogen and phosphorus are 2 ~ 2 2 ~
and
3 3 ~ 2 3 ~respec3,
tively. Experimental evidence shows that trivalent phosphorus does not form double bonds either with itself
(3p,-3p,)
or with carbon (3pn-2p,) or nitrogen [41.
Thus we cannot to find a branch of phosphorus chemistry corresponding to that of the aromatic N-heterocycles.
The unique ability of phosphorus to expand its valence
shell to include 3d orbitals, i.e. to form pentaorganophosphorus compounds, promises new chemical results.
In heterocycles in which the phosphorus has five covalent sd,-2p,
single bonds, it should be possible to
observe stereochemical variation, depending on the dorbitals involved in the hybridization 151. Finally, ring
systems containing pentavalent phosphorus with
3d,-2p,
double bonds should be obtainable in the
form of cyclic methylenephosphoranes.
Th e difficulties encountered in th e nomenclature of organic
phosphorus compounds, which have been discussed b y
Susse161, a r e particularly serious in t h e case of t h e heterocycles.
A. General Methods of Preparation
Method I. The monosodium phosphides ( I ) , which
result from the reaction of primary phosphines or PH3
with sodium (in liquid ammoniac71 or organic solvents [*]), react with dihalogenoalkanes to form cyclic
[ I ] L. Pauling: The Nature of the Chemical Bond. 2nd ed.,
Cornell University Press, Ithaca 1948, p. 164-167.
[2] L. Maier, Progr. inorg. Chem. 5, 136 (1963); J. J. Duly,
J . chern. SOC.(London) 1964, 3799.
[3] L. Horner, H. Winkler, A . Rapp, A . Mentrup, H . Holfmann
and P. Beck, Tetrahedron Letters 1961, 161; L. Horner and H.
Winkler, ibid. 1964,461; L. Horner, P . Schedlbauer, and P . Beck,
ibid. 1964, 1421.
[4] See, however, K . Dimroth and P. Hoffmann, Angew. Chern.
76, 433 (1964); Angew. Chem. internat. Edit. 3, 384 (1964).
[5] R . F. Hudson and M . Green, Angew. Chem. 75, 47 (1963);
Angew. Chem. internat. Edit. 2, 1 1 (1963).
[6] K . Sasse in Houben-Weyl: Methoden der organischen Chemie. Georg Thieme, Stuttgart 1963, Vol. 12, I.
171 US.-Pat. 3086053 (Apr. 16th, 1963), inventor: R . I. Wagner,
Chem. Abstr. 59, 10124 (1963); US.-Pat. 3086056; Chem. Abstr.
60, 559 (1964).
181 F. Pass, E. Steininger, and H . Schindlbauer, Mh. Chem. 90,
148, 792 (1959).
1024
phosphines (2) [7,91. The reaction also (or in some cases
even exclusively [9l) yields w,w'-diphosphinoalkanes
RHP-(CHz),-PHR,
which can be easily separated by
distillation.
Method ZI. Dilithium phosphides (3), which can be
readily obtained by the introduction of the metal into
primary phosphines, also react with dihalogenoalkanes
(applying the Ruggli-Ziegler dilution principle) to form
(2) 1101. Even the primary phosphines themselves react
slowly at 80 to 130 "C [ I l l .
Method I
Method I1
(2)
R = H, Alkyl, A r y l
n
X = C1, Br, I
= 4.5
R = Alkyl, A r y l
X = C1, Br
Method 111. Secondary aliphatic phosphines react with
dihalogenoalkanes to form bis(dialky1phosphino)alkanes RzP-(CHz),-PR2 Ill]. Potassium diphenylphosphide 1131, and even diphenylphosphine itself under
forcing conditions ~ 1 , 1 2 1 form
,
the cyclic phosphonium
salts (4). The reaction of tetraphenyldiphosphine with
dihalogenoalkanes 1141 is particularly simple.
Method ZV. The acid-catalysed nucleophilic addition of
secondary phosphines or PH3 to dialdehydes provides
an elegant synthesis of the a,u'-dihydroxyphosphonium
salts (5)
15bI
and spirophosphonium salts
(6) 115b-16b1, respectively.
RzPH
+
OHC-(CHz),-CHO
R = Alkyl, A r y l
-
JCHA
(S),
n = 2,3
HO OH
[9] K . lssleib and D . Jakob, Chem. Ber. 94, 107 (1961); K . Issleib
and F. Krech, ibid. 94, 2656 (1961).
[I01 K . Issfeib and S. Hausler, Chem. Ber. 94, 113 (1961).
[I11 K. Issleib, K. Krech, and K . Gruber, Chern. Ber. 96, 2186
( 1963).
1121 S. 0. Grim arid R . Schaaff, Angew. Chem. 75, 669 (1963);
Angew. Chern. internat. Edit. 2, 436 (1963).
1131 G. Murkl, Angew. Chem. 75, 669 (1963); Angew. Chem.
internat. Edit. 2, 479 (1963).
[I41 G. Murkl, Angew. Chern. 75, 859 (1963); Angew. Chem.
internat. Edit. 2, 620 (1963).
[15a] Sh. A . Buckler and M . Epstein, J. org. Chemistry 27, 1090
(1962); Tetrahedron 18, 1231 (1962); French. Pat. 1348669;
Chem. Abstr. 60, 15912 (1964).
[15b] M . Grayson, Chem. Engn. News No. 49, 40, 90 (1962).
Angew. Chem. internat. Edit.
Vul. 4 (1965) / No. I2
Method V. Reactions of bifunctional Grignard compounds with halogenophosphines (a reversal of Methods I and 11) were used by Griittner 1171 in the first synthesis of cyclic phosphines. Contrary to earlier belief [201,
c1
R-P(
c1
(CH2)n
+ BrMg-(CH2),-MgBr
LJ
-+
R
R = Alkyl[l8], ArylIl?], N(CH,)z[19]
(2), n = 4,5
n = 0, m = 2,3[27-291; p=m = 1 j30,31];
n = 2, m = 1[32]
R = c 2 H 3 , C&5
the o-position as the alkylating agent (331. With 2 moles
of base, the cyclic methylenephosphoranes (13) are
formed directly from the open-chain salts.
ring closure evidently does not take place with phosphonic chlorides R-POC12 [R = N(CzH5)2, C ~ H Sor
]
phosphites [211.
Method Vf. The use of bifunctional lithium compounds
in reactions corresponding to method V is restricted to
the 2,2-dilithiumdiphenyl derivatives (7), which can be
readily obtained by reaction of the 2,2'-dibromides with
lithium. This method can, however, be adapted for the
synthesis of a very wide range of ring systems (8) by
variation of the bridging group Y .
B. Heterocycles Containing One Phosphorus Atom
1. Phosphacyclopropanes and Phosphacyclobutanes
R
Y = -122a-22~1, (CH&[23].
R = Alkyl, A r y l
PR[241, NR[25a,25h], O[ZS];
Method VII. Intramolecular formation of quaternary
salts ( L O ) from w-bromoalkylphosphines, which are
readily available from tertiary phosphines (9) containing a n w-alkoxy side chain by cleavage of the ether
linkage.
Method VIIf. Formation of (12) by intramolecular Calkylation of the ylides (11) derived from the phosphonium salts, using the w-bromoalkyl side chain in
[16a] Sli. A . Buckler and V. P. Wystrach, .I.
Arner. chem. S O C .
80, 6454 (1958); 83, 168 (1961).
[16b] US.-Pat. 2969398 (Jan. 24th, 1961), inventor: Sh. A .
Buckler; Chern. Ahstr. 55, 17660 (1961); Sh. A. Buckler and M .
Epstein, Tetrahedron 18, 121 1 (1962).
[17] G. Griittner and M . Wiernik, Ber. dtsch. chern. Ges. 48, 1473
(1915); G. Griittner and E . Krause, ibid. 49, 437 (1916).
[I81 US.-Pat. 2853518 (Sept. 23rd, 1958), inventor: W. J . Balon;
Chern. Abstr. 53, 5202 (1959).
[I91 A. B. Burg and P. J. Slota Jr., J . Arner. chern. S O C . 82, 2148
( 1960).
[20] G. M . KosolapoJ and R. F. Struck, J. chern. Soc. (London)
1957, 3739.
[21] G. Hilgetag, H.-G. Henning, and D. Gloyna, 2. Chem. 4 , 341
(1 964).
[22a] G. Wittig and G. Geissler, Liebigs Ann. Chern. 580, 44
(1953).
[22 h] G. CVittig and A. Maerker, Chem. Ber. 97, 747 (1964).
[22c] A. F. Bedlord, D. M . Heinekey, J. T. Millar, and C. Mortimer, J . chem. SOC. (London) 1962, 2932.
[23] F. G. Mann, I. T . Millar., and B. B. Smith, J . chem. SOC.(London) 1953, 1130.
[24] M. Davis and F. G. Mann, Chern. and Ind. 1962, 1539;
J . chern. SOC. (London) 1964, 3770.
[25a] E. R. H . Jones and F. G. Mann, J . chem. SOC. (London)
1956,786.
[25b] G. Baum, H. A. Lloyd, and C . Tamburski, J. org. Chemistry 29, 3410 (1964).
1261 F. G. Mann and I. T. Millar, J . chern. SOC. (London) 1953,
3746.
Angew. Chem. internut. Edit. 1 Vol. 4 (1965)
No. I 2
As is shown by the examples of the tetrahedral P4 (14)
(valence angle 60 ") and the cyclotetraphosphines (15),
phosphorus forms very stable small rings with itself.
The ring strain may be reduced by spd hybridization [34J,
and stabilization of (15) by p,-d,
double bonds between the phosphorus atoms has been suggested 1351.
Small phosphorus-carbon rings are difficult to prepare.
1-Substituted phosphacyclopropanes (16) (R = H, CH3)
and unsubstituted phosphacyclobutane (17), R = H,
can be synthesized by Method I (for n = 3 and R = alkyl
or aryl, only the open-chain phosphines are obtained [7J).
Formation of the four-membered ring is also suppressed
in Methods 11, 111, and VII in favor of polymer formation [lo, 141 or cyclodimerization [12,29J. An unusual
cycloaddition of PC13 (as PC12@/AIC14") to 1,4,4-trimethylpent-2-ene yields the phosphinic acid (18) 1361.
[27] F. G. Mann and I. T. Millar, J . chern. SOC. (London) 1951,
2205.
[28] M . H . Beeby and F. G. Mann, J . chern. Soc. (London) 1951,
41 1 .
[29] G. Murkl, Angew. Chern. 75, 168 (1963); Angew. Chem.
internat. Edit. 2, 153 (1963).
[30] F. G. Mann, I. T. Millar, and F. H. C. Stewart, J . chern. SOC.
(London) 1954, 2832.
[31] F. G. Mann, I. T. Millar, and H. R. WatJon, J. chern. SOC.
(London) 1958,2516.
[32] F. G. Holliman and F. G. Mann, J. chern. SOC. (London) 1947
1634.
[33] G. Murkl, 2. Naturforsch. 186, 84 (1963).
1341 L. Pauling and Simonetta, J. chern. Physics 20, 29 (1952).
[35] W. Mahler and A. B. Burg, J. Arner. chem. SOC. 79, 251
(1957); 80, 6161 (1958).
[36] J. J. McBride Jr., E. Jungermann, .
I
.
V . Killheffer, and R. J .
Clutrer, J . org. Chemistry 27, 1833 (196%);see also [20].
1025
The four-membered ring is not opened even under
extreme conditions (e.g. boiling conc. HNO3 or boiling
aqueous conc. NaOH), indicating that there is no internal strain.
’.
( C H S ) ~ C = C H - C ( C H ~2,) ~
PCI~/AIC1,p
H,O
CH3
H3&H3
H3
with alkyl halides, sometimes in an exothermic reaction, to form the phosphoniuni salts (22) (R = alkyl) by
an SN2 mechanism. In accordance with Ingold’s
rule [411, diaryl-substituted salts (which can be prepared
by Method 111) are degraded by aqueous alkali to the
oxide (21) (R - aryl) without suffering ring cleavage.
H3
A
H
b) P h o s p h o l e n e s
(18)
COOR
(CGH5)S
On t h e basis of considerations regarding th e reaction
mechanism, the reaction of alkylidenetriphenylphosphoranes
with esters of acetylenedicarboxylic acid [37Jor with arynes [381
must proceed via 1,1,1-triphenylphosphacycIobut-2-enes(19).
McCormack [421 discovered in 1955 that, in the presence
of polymerization inhibitors (e.g. Cu stearate), aryldihalogenophosphines add onto dienes in a quasi-DielsAlder reaction to form 1-aryl- I , 1-dihalogenophospholenes (26), which are readily hydrolysed to 1-arylphospholene oxides (27). Modifications of this synthesis
were achieved by the use of PCl3, PBr3c43a-441, and
Diene
2. Five-Membered Rings
a) P h o s p h o l a n e s
Phospholanes (20) have been prepared by Methods I,
11, and V. Another interesting preparation is the reduction of dimethylamide (20) [R = N(CH&] to 1Hphospholane (20’) by the pyrolysis of the BH3 adduct
(23) [19,391.
RO-PHal2 [451. Diene = butadiene, isoprene, 2,3-dimethylbutadiene, chloroprene, dicyclohexylidene, erc.;
R” = phenyl, p-tolyl, mesityl, CH3, C2H5, OC2H5,
OC6H5, C1, Br, etc.
Th e diene component must b e able to assume a cisoid conformation (1,l-disubstituted dienes do not react) an d 1substituted dienes must be in t h e trans form. Phosphorus
bromides a r e more reactive t h an t h e chlorides. T h e average
reaction time (1 t o 10 days at 25 “ C )is increased by bulky and
electronegative substituents in t h e diene. T h e ring cIosure
probably starts with the nucleophilic addition o f t h e phosphine t o t h e I-position of t h e diene.
CzHs
CoHs
(20)
b.p. [ “C/mrnl
(20 a)
b.p. [ “C/rnml
145-147/760
9713
1071760
124114
The use of a dihalide R”PHal2 is not absolutely necessary, as is shown by the addition of cyclic monochlorophosphites (24) to dienes to form the spiro intermediates (25), which then undergo rearrangement to (27),
1411 G. W . Fenton and C. K. Ingold, J. chem. SOC.(London) 1929,
2342.
[42] W . B. McCormack: US.-Pat. 2663736 (Dec. 22nd, 1953),
and 2663737 (Dec. 22nd, 1953); Chem. Abstr. 49, 7601 (1955);
US.-Pat. 2663738 (Dec. 22nd, 1953); Chem. Abstr. 49, 7602
(1955).
[37] S. T. D. Cough and S . Trippett, Proc. chem. SOC.(London)
1961, 302; J . B. Hendrickson, J. Amer. chem. SOC. 83, 2018
( I 96 1) ; J . B. Hmdrickson, R . Rees, J. F. Templeton, ibid. 86, 107
(1964); H. J . Bestmann and 0. Rothe, Angew. Chem. 76, 569
(1964); Angew. Chem. internat. Edit. 3, 512 (1964); C. W.
Brown, R . C. Cookson, and I. D. Stevens, Tetrahedron Letters
1964, 1263.
[381 E. Zbiral, Tetrahedron Letters 1964, 3963.
1391 US.-Pat. 3025326 (March 12th, 1962), inventors: A . B.
Burg and R. I. Wagner; Chern. Abstr. 57, 8619 (1962).
[40] W. A. Henderson and Sh. A. Buckler, J. Amer. chem. SOC.
82, 5794 (1960).
1026
(43aI (1. Hnsserodt, K. Hunger, and F. Korte, Tetrahedron 19,
1563 (1963).
[43 b] K . Hunger, U. Hasserodt, and F. Korte, Tetrahedron 20,
1593 (1964)
[43c] Belg. Pat. 631416 (Nov. 18th, 1963); Chem. Abstr. 61, 688
(1964).
1441 B. A. Arbuzov and A. 0. Vizrl, Dokl. Akad. Nauk U . S . S . R .
I58 (S), 1105 (1964); Chem. Abstr. 62, 2791 (1965).
[45] B. A . Arbuzov and L . .4. Shapshinskaya, Izv. Akad. Nauk
U.S.S.R., Otdel. khim. Nauk 1962, 65; Chem. Abstr. 57, 13791
(1962).
[46] N. A. Razumova and A. A . Petrov, Zh. obshch. Khim. 31,
3144 (1961); 33, 783 (1963); 33, 3858 (1963); 34, 1886 (1964);
Chem. Abstr. 56, 12720 (1962); 59, 8738 (1963); 60, 10711
(1964); 61, 8336 (1964).
Angew. Chem. internat. Edit. 1 Vol. 4 (1965) No. 12
R”
O-(CH2)2CI, O-(CH2)3CI, by an intramolecular
Michaelis-Arbusow reaction 146,471.
~
Kortc L43bl recognized that the hydrolysis of the primary
adduct (26) to yield (27) may be accompanied by
migation of the double bond to the 2-position. The two
possible products can be distinguished on the basis of
ultraviolet, infrared, and NMR data L48J. The PC13 adducts (26a) (R = H ; R’ = H, CH3) undergo complete
rearrangement in all their reactions, whereas a mixture
of both isomers is formed in the case of R = R’ =: CH3.
The reactivity of the adducts (26a) is similar to that of
R
Oxophospholanes can be obtained by catalytic hydrogenation of the double bond in (27) with Raney nickel,
Adams’ catalyst, or noble metal catalysts 142,43fI. He&rich [521 achieved an independent synthesis of l-alkoxyI-oxophospholane (30) by an intramolecular MichaelisArbuzov reaction [R
C2H5, (CH2)3CH3; yield ~
75 XI.
The primary adducts (26) are dehalogenated by M g
turnings in tetrahydrofuran 1531 or by LiAIH4 118,53J to
I-substituted phospholenes (31), [R = R’ = H, CH3;
R” = CH3, C6Hs; yield = 20-40 %I, with retention of
R’
C,H,OH
-4
\
HO’r*O
(28)
CYr*O
(29)
0 (27a), R = R’ = H
R = H; R’ = CH3
PCI5. Thus alcohols are chlorinated by (26a), which is
itself converted into the phosphinic acid (28) and the
acid chloride (29). Reactions with S02, acetic anhydride,
and above all, orthoesters of carbocylic acids 1491 permit
the direct preparation of the acid chlorides (29), which
can then be converted into esters, thioesters, amides,
and (by reaction with Grignard reagents) tertiary
phospholene oxides (27u) (R” -= alkyl, ary];. The double
bond never migrates in the PBr3[43bi and CH3PC12
adducts 1501.
The tendency of the double bond to migrate I S increased by a
high concentration of strongly efectronegative substituents o n
the phosphorus, and decreased by the presence of CH3 groups
in positions 3 and 4 (stabilization by hyperconjugation).The
first step of the rearrangement is probably the removal of a
strongly acidic a-proton to form a carbanion (266) or an
ylide ( 2 6 ~ ) .
Partial interconversion of the A2- and A3-phospholene
oxides (27) occurs on heating at 200 to 300 “C or in the
presence of strong bases such as KOC(CH& L43b,50,511.
the double bond (the position of which, however, must
be checked). The phosphinic acids and their esters (27)
[R” =: OH, O(CH2)2CI] are reduced to (31) by
LiAIH4 [541.
c) P h o s p h o l e s
The reason for the great interest shown in the phosphole
ring system is the question whether it behaves like
pyrrole, i.e. whether the phosphorus atom in (32) makes
its lone electron pair available for the formation of an
aromatic system of 6 i~electrons(33). Phosphole oxides
(34) were obtained by Howardr551 (R
R’ == H, CH3;
R == H, R’ = CH3; R” = C6H5) by dehydrobromination
of the bromine adducts of (27) with organic bases, and
by Westheinier[561 (R = R’ == H ; R” = OC2H5) from
the ally1 bromide (35)or by Hofmann degradation of the
methylphosphonium iodide prepared from (35). As
expected, the phosphole oxides (34) behave as cyclic
3
(32)
Q
by
p
R
- ‘UR’
I . (CH,),NH
2. CH,I
3. NaOC>H,
~
Rr,~p*o
(35)
[471 B. A . Arbrtzov, I.. A . Shapshinskaya, and V . M . Erokhtna,
Izv. Akad. Nauk U.S.S.R., Otdel. khim. Nauk 1962, 2071;
Chem. Abstr. 58, I 1 396 (1963); B. A . Arbuzov and I-. A. Shap~hinsku.rv7,Jzv. Akad. Nauk U.S.S.R., Otdel. khim. Nauk /964,
581 ; Chem. Abstr. 60, 15903 (1964).
1481 H . Weitkainp and F. Korte, Z.analyt. Chem. 204, 245 (1964).
[49] K. Hunger and F. Korte, Tetrahedron Letters 1964, 2855.
[SO] L . D.Quinn and J . A . Peters, Tetrahedron Letters 1964, 3689.
[SI] E. W. Miiller and F. Korte, Tetrahedron Letters 1964, 3039.
A n g e w . Clieni. intermit. Edit.
Vol. 4 (1965)
1 No. I2
(33)
R
1. Br,
2. ore. Base
(341
[52] B. Helferich and E. Aufderhaar, Liebigs Ann.
(1962).
[53] L .
(1964);
(27)
Chem. 658, 100
D.Quinn and D. A . Marhews, J . org. Chemistry 29, 836
Dissertat. Abstr. 24, (3)
997 (1963).
[54] G. M . Bogolynbov, N . A . Razumova, and A . A . Pelrov, Zh.
obshzh. Khim. 33, 2419 (1963); Chem. Abstr. 59, 1408 (1963).
[ 5 5 ] E. Howard Jr. and R . E . Donadio, Abs:r. Papers, Amer.
chem. SOC. 1959, 100-P.
[561 D. A . Usher and F. Westheimer,J. Amer. chem. SOC. 86,4732
(1964).
1027
dienes. They form crystalline dimers (for R" = C6Hs)
on standing at room temperature. The tendency to
dimerize is so great in the case of 1-ethoxyphosphole
oxide that this compound can only be detected by ultraviolet spectroscopy or by interception as the DielsAlder adduct.
The phospholes themselves are obtained by a number of
syntheses that are both simple and elegant. Campbell [571
prepared I ,3,5-triphenylphosphole [yellow needles,
m.p. 186.5-187.5"CI in a single step by the cycloaddition of C6H5PC12 to 1,4-diphenylbutadieneat 226 to
230 "C (thermal dehydrochlorination after migration of
the halogen in (26) from the phosphorus to the double
bond ?).
Hiibel and Braye [581 and Leavitt [593 discovered about
simultaneously that 1,4-dilithio-l,2,3,4-tetraphenylbuta1,3-diene (36) [GO], which is readily obtainable by the dimerization of diphenylacetylene with lithium, is a useful
starting material for the synthesis of phospholes. It
reacts with dihalogenophosphines to form P-alkyl- or Paryl-2,3,4,5-tetraphenylphospholes(37), [R = C6Hs:
light yellow needles; m.p. 255-256 "C; UV: Amax (log€)
= 357.5 mp (3.945), 320 mp (3.94), 247.5 mp (4.51);
strong fluorescence with maximum at 480 mp], while
the phosphole oxide is obtained directly by the reaction
of (36) with C6HsP(O)C12.
which result in the loss of the C6H5P group and formation of the phthalate esters. The availability of the lone
electron pair on the phosphorus becomes obvious with
the quantitative formation of the o-complex (39) with
Fe(CO)5 ;reaction with [Fe(C0)4]3in addition yields the
x-complexes (40) characteristic of conjugated dienes
and (41).
Pentaphenylphosphole oxide forms a x-complex corresponding to (40),whereas the sulfide, surprisingly, yields the complex (39). The tendency of the P=S bond to undergo cleavage
is observed even in the reaction of (36) with C&#(S)C12,
which yields 45 of pentaphenylphosphole together with 1 %
of the sulfide.
Using the LCAO and SCFMO methods, respectively,
Brownrs*I calculated conjugation energies of 1.37 and 1.49 p
for pyrrole and for the unsubstituted phosphole. The ease
of oxidation of 1,3,5-triphenylphospholeand (37), in comparison with pyrrole, can be explained by the fact that the PO
bond energy is 70-90 kca1,'mole greater than the NO bond
energy, so that the loss of conjugation energy is more than
compensated.
As is shown by a comparison of the experimental P = O dissociation energies [22aI (Table 2), the conjugation energy in
L1 L1
(36)
Related to this in principle is a second synthesis described by Hiibe2[581: The Fe(CO)3 complex (38) of
butadiene [611, which is obtained by the reaction of
[Fe(CO)& with diphenylacetylene in boiling petroleum
ether, reacts with C6H5PC12 at 140°C to form pentaphenylphosphole.
The stability of triphenylphosphole and pentaphenylphosphole towards oxygen is the same as that of tertiary
aromatic phosphines; benzylphosphole and methylphosphole are more liableto autoxidation. The diene character
of pentaphenylphospholeoxide is shown by the formation
of an adduct with maleic anhydride (yield = 67 %); the
pentaphenylphosphole itself, on the other hand, gives
only a 3 % yield of this adduct, so that prior oxidation
appears to be possible and essential. Diethyl acetylenedicarboxylate, however, forces even 1,3,5-triphenylphosphole and (37) (R = C6H5) into diene reactions,
[57] I. M . Campbell, R . C. Cookson, and M . B. Hocking, Chem.
and Ind. 1962, 359.
[58] E. H . Braye and W. Hiibel, Chem. and Ind. 1959, 1250;
E. H. Braye, W . Hiibel, and I. Capier, J. Amer. chem. SOC. 83,
4406 ( I 96 1).
[59] F. C. Leavitr, T. A. Manuel, and F. Johnson, J. Amer. chem.
So;. 81,3163 (1959); F. C. Leavitt, T . A . Manuel, F. Johnson, L . U .
Matternas, and D . S. Lehmann, ibid. 82, 5099 (1960).
[60] L . I. Smifh and H . H. Hoelin, J. Amer. chem. SOC.63, I184
(1 94 1 ).
[61] W. Hiibel and E. H . Braye, J. inorg. nuclear Chem. 10, 250
(1959).
1028
the phosphole, as compared with the corresponding oxide, is
much greater than in all other phosphines. The decrease in
the Dpo value has been explained by increasing participation
of the 3px-orbital in the conjugation.
Table 2. Dissociation energies of the P = O bonds in some
phosphine oxides.
I Dp=o
Phosphine oxide
[kcal/mole]
100.4 F 9.5
Pentaphenylphosphole oxide
9-Phenyl-9-phosphafluorene oxide
126.0
+ 9.0
Triphenylphosphine oxide
128.4
+ 5.5
Trimethylphosphine oxide
139.3 k 3.0
Since the Dps values are about 50 kcal mole lower than the
DPO valuesr21, the formation of the phosphole from the
sulfide could also be "financed" by the gain in conjugation
energy. The difference of 39 13 kcal/mole in comparison
with trimethylphosphine oxide is regarded as a measure of
the conjugation energy of the phosphole [22al. The discussion
of the bonding system in the phospholes is not yet closed.
d) F i v e - M e m b e r e d R i n g s C o n t a i n i n g
Pentavalent Phosphorus
Triphenylphosphine reacts with esters of acetylenedicarboxylic acid at -50 "C to form an unstable yellow
1 :2 adduct, which undergoes rearrangement to (4 3 )
1621 D . A. Brown, J. chem. SOC.(London) 1962, 929.
Angew. C h i n . internot. Edit.
/
Vol. 4 (1965)
1 No. I 2
even at room temperaturet631. On the basis of PMR
measurements and the observation that the migration
of the phenyl group is catalysed by H@,the primary
adduct is assumed by Hendrickson [641 to possess the
structure (42a), in which the phosphorus forms five
covalent 3p,-2p,
bonds. The red acetylenedicarbonitrile adduct, for which structure (42b) has been
postulated by Reddy and Weis1651, is unusually stable
(dec. point 245 "C) in comparison with (42a), as is the
1,l,l-triphenyloctacyanophosphole (44) (dec. point
230 "C) obtained in an exothermic reaction with tetracyanoethylene.
aldehydes in normal Wittig olefinations, with ring
cleavage, to form the olefins (47) '331.
a
RZ
(45a). R' = H; R = C2H5
(45b), R' = H; R = C&15
(45~),R = R' = C&5
As expected [681, I-ethylphosphindoline (48) (b.p. 102
to 104"C/13 mm) is formed on pyrolysis of (45a) at
350 to 375 "C (yield 75 %); 2-phenylisophosphindoline
(49) is obtained in a similar manner 1311. The phosphine
(49) possesses the unusual ability to form stable complexes having abnormal coordination numbers with
transition metals of group VIII. Whereas the complexes
T h e 3fP-NMR spectrum o f (44) shows a chemical shift 6 of
-22 p p m [65J. Since according t o recent N M R studies, 6-31P
values of +25 t o 100 p p m a r e t o be expected f o r c o m p o u n d s
of pentavalent phosphorus (phosphoranes) (see T a b l e 3), a t
least t h e structure of (44) appears uncertain.
+
Table 3. Chemical shifts of J'P-NMR signals for compounds containing pentavalent phosphorus, based o n 85 % H,P04 as external
standard.
Compound
formed by aliphatic and aromatic phosphines, as well as
by (48), are normal (50), covalent or ionic (depending
on the solvent) complexes (51) with the coordination
number 5 are also formed from (49) 1691.
Ref.
[(Phosphine)zPdCl~]
+97i 2
(50)
A = (49); M
163d)
+85&
p(0cZH5)5
2
+70.9
=
[ A ~ M X Z ]+ [A3MXloXc3
(51)
Pd, Pt, Ni, Co; X = C1, Br, I, SCN
T h e explanation for this is probably t h e combination of
favorable steric (quinuclidine character) a n d electronic factors (favorable relationship between o p t i m u m P + M 6bonding a n d x-back donation).
+27.9
f) 9 - P h o sp h af lu o r ene s
- 16.9
-22
Of theoreticalinterestis the formation of 9-phenyl-9-phosphafluorene (52) on thermal decomposition of pentaphenylphosphorane either in the melt or in boiling benzene
[22b970,717.Theringclosurernaybeinitiated by theremoval
of hydrogen atoms from the o-position by phenyl radicals. According to Razuvaev 1711, the yield of 9-phospha-
e) P h o s p h i n d o 1i ne s a n d I sop h o s p h i n d o 1in e s
The phosphindolinium salts (45) are readily obtainable
by methods VII 127,291 and VII 1331. Cyclic ylides (46)
prepared by the reaction of (4Sb) and (45c) with potassium t-butoxide [or directly from ( I I ) , n = I ] react with
2
c6H6
+
Polyc ondensates
[63] A. W. Johnson and J. C . Tebby, J. chem. SOC. (London) 1961,
2126.
1641 J . B. Hendrickson, R. E. Spenger, and J. J . Sims, Tetrahedron Letters 1961, 447; Tetrahedron 9, 707 (1963).
(651 G. R . Reddv, and C. D. Weis, 5. org. Chemistry 28, 1822
(1963).
[66a] D.B. Denney and S. T . D.Cough, J. Amer. chem. SOC.87,
138 (1965).
[66b] F. Ramirez, A . V . Patwardhan, and S . R. Heller, J. Amer.
chem. SOC.86, 519 (1964); F. Ramirez, 0.P. Madan, and C . P.
Smith, Tetrahedron Letters 1965, 201.
[67] D.Hetlwinktl, Chern. Ber., in the press; personal communication.
Angew. Cliem. interntit. Edit.
/
Vul. 4 (1965) 1 No. I 2
[68] G . F. Fenton, L. Hey, and C . K . Ingold, I. chem. Soc. (London) 1933, 989.
[69] J. W . Collier, F. G . Mann, D. G. Watson, and H . R. Wajsari,
J. chem. SOC. (London) 1964,1803; J . W. Coliier and F. G. Mann,
ibid. 1964, 1815; J . W. Collier, A. R. Fox, 1. G. Hinton, and F. G .
Mann, ibid. 1964, 1819.
1701 G. Witjig and M . Rieber, Liebigs Ann. Chem. 562, 187
(1949).
[71] G. A . Razuvaev and N . A . Osanova, Dokl. Akad. Nauk
U.S.S.R. 104, 552 (1955); Chem. Abstr. 50, 1 1 2 6 8 ~(1956); Zh.
obshch. Khirn. 26, 2531 (1956); Chem. Abstr. 51, 1875 (1957);
2 h . obshch. Khim. 27, 1466 (1957); Chem. Abstr. 52,3715 (1958).
1029
fluorene increases to 60 % if the reaction is carried out in
pyridine at room temperature (1 50 hours) (see also 122bl).
The tetraphenylphosphonium cation reacts with methyl-lithium [22b, 731 or lithium diethylamide (yield
60 %) 1721 to form (52). The cyclization, which is facilitated by the inductive and mesomeric effects of the cation, is preceded by the introduction of the metal into
the o-position to form (53); the ylide (53a) then loses
benzene to form (52).
The fact that, even in (54), the o-attack by the metal is
preferred to attack on the P-hydrogen atoms of the tbutyl group is shown by the formation of (52) [42 %,
together with 8 % of ( C ~ H S ) ~on
P ] reaction of (54) with
lithium piperidide1731. A second route to (52) via the
intermediate (53) is the addition of benzene to triphenylphosphine, discovered by Wittig and Benz
(53) was intercepted as the B(C6H5)3 adduct (55). This
reaction became preparatively important as a result of
Zbirul's work 1751. The surprising formation of (52)
(yield 10 %) from (C&5)3P and phenylsodium [701 undoubtedly proceeds by an o-deprotonation, although
this reaction is not favored.
The conventional Method VI 122a-22cI was found to be
particularly useful for the synthesis of (56) and of 9(p-dimethylaminopheny1)-9-phosphafluorene.
The bright
yellow phosphine (56) and its orange-red methylphosphonium salt clearly indicate that the phosphorus
participates in the conjugation of the biphenyl system.
Many derivatives, particularly containing substituents
in the nucleus, have been obtained by the intramolecular
electrophilic substitution of substituted biphenyl
derivatives ( M a ) and (58b) [prepared from the
diazonium fluoroborates by reaction with PCl3 and
[72] H . Hoffmanti, Chem. Ber. 95, 2563 (1962).
(731 D. Seyterth, M . A . Eisert, and J. K . Heeren, J. organornet.
Chemistry 2, 101 (1964).
[74] G. Wittig a n d E. Ben?, Chern. Ber. 92, 1999 (1959).
[75] E. Zbiral, Tetrahedron Letters 1964, 1649.
1030
C6H5P(O)C12] 176a,76b,77J. 2-Carboxy-9-phosphafluorene 9-oxide (60) [m.p. 250-251 OC; [a]%= 126 f2 "),
which is prepared from the 2-methyl derivative of (596),
has been resolved into its optical antipodes by Campbe// [771, using the amide of (+)- or (-)-wphenylethylamine; both antipodes are fully racemized to the phosphine on reduction with LiAIH4.
Finally, another variant is the application of Busch's [78J
biphenyl synthesis to phosphinic acids such as (57),
particularly for derivatives of the phosphinic acid
(59a) [791.
(58a), A = PC1,
(Jab), A = PO(OH)2
g) 9 - P h o s p h a f l u o r e n e s C o n t a i n i n g P e n t a valent and Hexavalent Phosphorus. Spiro
Compounds
This field was pioneered by Wittig and his school. In an
adaptation of the synthesis of (C6H5)sP to 9-phosphafluorenes, the salts (62) of the latter are treated
with phenyl-lithium. For example, 9,9,9-triphenyl9-phosphafluorene (61) [m.p. 155.5-1 56.5 'C; yield
84 %] is obtained by the addition of phenyl-lithium and
displacement (SN2 reaction) of the methylaniline residue
by a second mole of phenyl-lithium; the reaction with
2,2'-dilithiobiphenyl leads to the spiro compound (63a)
[m.p. 201.5-202.5 OC; yield 68 %I, and that with 2,Ydilithio-4,4'-bis(dimethylamino)biphenyl to (636)
The tosylimines of the 9-phosphafluorenes, too, are
suitable starting materials for the synthesis of (63)
[(63a)-(63c) from 9-(p-dimethylaminophenyl)-9-phosphafluorene] and are more readily obtainable than
[76a] G. 0.Duak, L . D. Freedman, and J. B. Lev.v, J . org. Chernistry 29, 2382 (1964).
[76b] L. D. Freedman, G . 0. Doak, and I. R. Ediiiisten, J. org.
Chemistry 26, 284 (1961).
[77] I . G. M . Campbell and J . K. Way, J. chem. SOC. (London)
1961, 2133.
[78] M . R~scliand W. Weber, J. prdkt. Chern. 146, 1 (1936).
[79] L . D. Freedinon an3 G . 0. Doak, J. or%.Chemistry 21, 238
( I 956); 24, 638 ( I 959).
1801 G. M'ittig and E . KoclienduerJer, Chern. Ber. 97, 741 (1964).
Angew. Cliem. intertiat. Edit. 1. Vol. 4 (1965) Nu. 12
(62) 122bl. Corresponding to the behavior of the phosphole (42a), cGmpound (61) rearranges to the tertiary phosphine ( 6 / a ) with migration of the phenyl
group, but only at temperatures above the melting
point [i.e. 250 "C higher than in the case of (42a)l. The
analogous rearrangement of (63) yields derivatives of
the 1-substituted phosphacyclononatetraene (64). The
stereochemical behavior of (61) and (63) must be interpreted in accordance with the trigonal-bipyramid arrangement of the phenyl groups in (C6H5)5F"811.
Q-p-QO
P
D
Compound (651, which is stable in boiling ethanol or
water, is decomposed by Nal into the sparingly soluble
phosphonium iodide (66b) and sodium trisbiphenylylenephosphate (66a). The octahedral structure of the
anion B' is clearly demonstrated by the resolution of
potassium trisbiphenylylenephosphate ([XI::; - 1920
t 30 ").
The iodide (66b), which is directly obtainable (yield
87 oh) by the action of 2,2'-dilithiobiphenyI on triphenyl
phosphate, is a valuable starting material for the synthesis of the phosphoranes (63) and (with dilithiobiphenyl) of the ate-complex itself. Compound (63)
(R r 2-biphenylyl) is formed by acid cleavage and (64)
(R . 2-biphenyly1, R
H) by pyrolysis (270°C) of
lithium trisbiphenylylenephosphate.
~
3. Six-Membered Rings
a) P h o s p h o r i n a n e s
Phosphorinanes (phosphacyclohexanes) and their phosphonium salts, which are synthesized by Methods I, IT,
111, and V, present no new features in comparison with
the phospholanes. The parent compound (69) is a
readily oxidizable liquid (b.p. 110 " C ; m.p. 19 "C) and
was prepared by HowardIs21 by the reduction of (68),
which is obtained by an intramolecular Grignard reaction with a phosphonate (67).
Heterocycles containing hexavalent phosphorus were
first prepared by Hellwinkel 1671. The reaction of 2,2.'dilithiobiphenyl with PCl5 leads directly to the onium-ate
complex A"'B 9 (65), which crystallizes as yellow needles.
The JIP-NMR values are 8 -26.5 ppm for A" (in
agreement with the values for other phosphonium salts,
cf. Table 3) and 8 .:= +186.5 ppm for B E , as compared
with +118ppm and +305ppm for PF? and PCIX,
respectively .
7
Two simple and valuable syntheses of I-substituted
phosphorinan-4-ones were developed by Welcher. The
bis-(2-cyanoethyl)phosphines (70), which are obtained
in good yields by the thermal 183al or base-catalysed 183bl
addition of primary phosphines to acrylonitrile, can be
cyclized by the Thorpe-Ziegler method to (71) (the
enamine structure is confirmed by infrared and P M R
spectra); the hydrolysis of (71) leads directly to
(72) [84,851.
[PCl,lQ[PCl,f
After numerous unsuccessful attempts to prepare I phenyl- I-phospha-4-tetralone (73) by intramolecular
[ S l ] P. J . Whetrtlyv, J. chem. SOC.(London) 1964, 2206.
[82] E. I-Iowcrrd Jr. and M. BrL?id,Abstr. Papers, 140th ACSMeeting, 1961, 4 0 0 ; Dissertat. Abstr. 23,434 (1962).
[83a] F. G. Mann and 1. T . Millor., J. chern. SOC. (London) 1952,
4453.
[83b] M . M . Rnuhrri, G. B. Borowii?, and t f . C. Gi//htrnr,J. Amer.
chem. SCC.81, I103 (1959).
[84] R. P. Welcher, G. A . Johnson, a n d V . P. Wystrach, J. Amer.
chem. SOC.82, 4437 (1960); German Pat. 1162840 (Febr. 13th,
1964), inventors: R. P. Wekher, G. A . Johnson, a n d V. P.
W.vJlrach; Chern. Abstr. 60, P 14542a (1964).
[SSl M. J . Gollrrgher and F. G. Mntnr, J. chern. SOC.( L o n d o n )
1962, 5 I 10.
Angew. Cliern. intcrncif. Edit. 1 VoI. 4 (1965) 1 No. 12
1031
AB
NeI
[BQNaQ] + [AoIo]
(651
(63)
*
R = CHs,
C4Hgr CsH5
(66a)
(666)
-
[AQIo]
[B"LiQ]
(66b)
Li Li
acylation on the benzene nucleus 1861, Mann succeeded
in preparing this compound from the benzonitrile
derivative corresponding to (70), which is difficult to
obtain [87aJ. The formation of phosphonium salts and
A
H
N
NC
1,)
N~OC(CHJ),/CHJ-C&
110°C; 3h
R (71)
(70) R
dOOH
The yellow color of the hydrochloride of the colorless compound (77) has been interpreted by Mann as being due to a
small contribution by the limiting structure in which phosphorus forms a px-prc double bond :
normal carbonyl derivatives and the position of the
C=O band [1695 and 1680cm-1 for (72b) and (73),
respectively] indicate that there is no interaction between the carbonyl group and the phosphine part of
the molecule.
PH3 and primary and secondary phosphines add onto
olefins by a free-radical mechanism; however, the addition can also be catalysed by H@ions or, in the case of
strongly polar double bonds, by OHO ionsrssl. The
possibility of cycloadditions was proved by the preparation of the phosphorinanones (74) from primary phosphines and phorone [(CH3)zC=CH]zCO, dibenzalacetone, etc.[*91. In some cases the initial products are
open-chain or macrocyclic polymers, which form (74)
on thermal decomposition (sublimation at 220 "C/
0.1 mm).
..
)P-C=C-CH=NH-0
tf
..
)P=C-C=CH-NHeJ
In the corresponding N series, these salts are deep red L*7bl,
owing to the formation of a delocalized x-electron system in a
phenylogous trimethinecyanin.
Compound (72a) was used for the synthesis of the phosphine
(78), which undergoes self-alkylation in boiling benzene to
l-ethyl-4-hydroxy-l-phosphoniabicyclo[2.2.2~octane
form
bromide (79) 1901. The theoretically interesting bicyclic phosphine could not be obtained from (79).
Reduction of (74) with LiAlH4 yields the cyclic alcohols,
b) 1 , l -Diphenylphosphabenzene a n d
whereas Wolf-Kishner reduction leads to the phos1,l -Diphenylphosphanaphthalene
phorinanes. Chemical reactions at the ring became possible for the first time with the phosphorinanoThe trimeric phosphonitrilic chlorides (80) are ring systems of
nes [85,*7a, 87bl. The Fischer indole synthesis when applied
pentavalent phosphorus which contain only double bonds of
to the phenylhydrazone of (72a) leads to the indole
the prr-d, type. MO calculations taking into account only
derivative (75); compound (73) reacts similarly, in
the d,, orbital of the phosphorus (81) led Craig[91] to
contrast to the formation of the yellow, conjugated !I?-postulate the existence of a new type of aromatic system
(4n rc-rule). Dewarr921, on the other hand, believes that each
indoles I*] from the tetralones. The Pfitzinger condensaphosphorus atom uses two orthogonal d orbitals, d,, and
tion of (72b) yields (76), and the Friedlander condensadxb, ( 8 I ) (from a linear combination of dyz and drz) in
tion of (73) yields (77).
localized three-center x-bonds.
8
0
((CH,)~C=CH),C=O
*
110-130%; 6-8h
(C6H5CH=CH)zC=0
RPHz
120-125?l!;
15 mi"%
1861 F. G. Mann and 1. T. Millar, J. chem. SOC.(London) 1952,
4453; R . C. Hinron, F. G. Mann, and D. Todd, ibid. 1961, 5454.
[87a] M . J . Gallagher, E. C. Kirby, and F. G. Mann, J . chem. SOC.
(London) 1963, 4846.
[87b] M. J . Gallagher and F. G. Mann, J . chem. SOC.(London)
1963,4855.
[881 See 161, p. 25.
[89] R. P. Welcher and N. E. Dfly, J . org. Chemistry 27, 1824
(1962); US.-Pat. 3105096 (Sept. 24th, 1963), inventor: R. P.
Welcher, Chem. Abstr. 60, 5553d (1964).
1032
[*I Y-Indoles are conjugated, yellow products which are formed
o n dehydrogenation of indoles.
[90] L. D.Quin and D . A. Mathews, Chem. and Ind. 1963, 210;
D. A. Mathews, Dissertat. Abstr. 24, ( 3 ) 977 (1963); G. A. Wiley,
Abstr. Papers, 145th ACS-Meeting, 1961, 40Q; W. E. McEwen,
ef at., ibid. 96Q.
[91] 0. P. Craig and N . L. Paddock, J. chem. SOC. (London) 1962,
4118.
[92] M. J. S. Dewar, E. A. C. Luckqr, and M. A. Whitehead,
J. chem. SOC.(London) 1960,2423.
Angew. Chem. internut. Edit.
1 Vol. 4 (1965) 1 No. 12
The question of the consequence of replacing one
2p,-2p,
double bond in benzene with a 2p,-3d,
double bond led to the synthesis of 1,l-diphenylphosphabenzene (82) [29,933. This compound possesses the
structural characteristics of a methylenephosphorane,
for which two Kekule structures can formally be written.
The ether linkage of 1,l-diphenyl-4-methoxy-l-phosphoniacyclohexane bromide (83) (prepared by Method
1111131) can be cleaved to form the alcohol; this is then
dehydrated to obtain (84), the double bond being formed in the 3,4-position [v,--, = 1637 cm-11. Intermediate
ylide formation permits the ready dehydrobromination
of the Br2 adduct (85) to the vinylphosphonium salts
(86) [vcCc = 1596 cm-11. Since (86) is a vinylogous y.bromophosphonium salt[94Jtboth the hydrogen and the
bromine at position 4 are active (Ha, Br”), and since
it is also an ally1 bromide, it also possesses SN1 reactivity. The introduction of the second double bond to
form a 1,l-diphenyl-l-phosphoniacyclohexa-2,4-diene
salt (87) (perchlorate: m.p. 117-119°C; v,--~ -=
1626, 1572, 1550cm-1) is possible only with the catalytic action of hot H3P04.
“insulator” owing t o the orthogonality of the d-orbitals) has
not yet been settled (see also 1951).
Price [96,971 adapted the classic synthesis of pyridine
from pyrilium salts to the preparation of phosphorus
heterocycles. C G H ~ P Hreacts
~
with 2,4,6-triphenylpyrylium fluoroborate in boiling pyridine to form t w o
compounds, one being amorphous and the other
crystalline (m.p. 257 “C, colorless). The structure (88)
has been assigned to the former on the basis of infrared,
PMR and 31P-NMR measurements; no protonation
of the “quasi-ylide” corresponding to (82) F+ (87) can
be observed.
The deep red ylides of the 3,4-dihydro-l,l-diphenyl-1phosphanaphthalenes (90) 129,331 are formed from the
salts (89) (obtained by Methods VII and VIII) on treatment with strong bases in aprotic solvents. With these
ylides, as with compounds (46), normal Wittig reactions can be carried out. Moreover, (90), R -= H, can be
methylated or acylated to the stable cc-acylylide (91).
The bromination of (89) to (92) with N-bromosuccinimide, followed by H3P04-catalysed dehydrobromination, leads to almost quantitative yields of the diene
salts (93) (perchlorates: R := H, m.p. 173 OC; R CH3,
m.p. 197-199°C; R = C6H5, m.p. 182-183°C). In
agreement with the structure (82), the ylides (94) can
be deposited from the aqueous solutions of their salts
(R == H ;, , ,A
L:
439mp; strong infrared band at
1550 cm-1; PMR doublet at 4.467, J = 9 cis, 1 proton;
complex spectrum from 2.3 to 3.3 7). Attempted Wittig
olefinations have so far been unsuccessful. Thus (94)
cannot form betaines with the carbonyl component (by
participation of the free electron pair on the ylide carbon
-:
methylated at position 4 (according to infrared and
PMR measurements) to give (95); with R = CH3 o r
C6H5 it couples with diazonium salts to form 4-azo compounds (96) and, in the case of R -. H, the 2,4-bisazo
compounds (961, R = -N=N-R‘, is obtained; the
cation (95) forms the isomeric 2-azo compound [9*1.
The cation (87) is deprotonated by dilute alkalis even in
aqueous solution. Compound (82) is formed as a yellow
(A,,
= 409 m p in ether), non-crystalline precipitate
which is stable in water; (87) is re-formedinacidic solution. Similar open-chain phosphonium salts, as well as
(84), form ylides only with strong bases, and these
ylides are extremely readily hydrolysed.
The question of whether this stabilization of (82) is due to the
formation of a delocalized rr-electron system (through conjw
gation at the phosphorus atom) or to resonance stabilization as postulated by Dewor (the phosphorus atom acts as an
1931 G. Murk/, Habilitation Thesis, Universitiit Wurzburg, 1963.
[94] D. Seyfertk, J. K . Herren, and S . 0 . Grimnz, J. org. Chemistry 26, 4783 (1961).
Atigew. Chem. i n f e r m t . Edit. / Vol. 4 (1965) 1 No. 12
The phosphanaphthalenes with R = H, CH3 and phosphabenzene (82) are extremely susceptible to autoxidation. A mixture of high-molecular weight colored salts
(A,,
= 460-600mp),
which are vinylogues of the
simplest phosphacyanin ( C ~ H S ) ~ P - = C H - P ( C ~1991,
HS)~
are formed, probably via free-radical cations such as
(97). The ease of formation of (98) also indicates a
[95] G. Murkl, Angew. Chern. 75, 1121 (1963).
[96] C1i. C. Price, Chern. and chern. Ind. ( J a p m ) 16, 10) (1963).
[97] Ch. C. Price, T . Parosaran, and T . Lnkshiniiinro~~oii,
Abstr.
Papers, 148th ACS-Meeting 1964.
[98] See also G. Mark/, Tetrahedron Lcttcrs 1961, 807; 2. Naturforsch. 176, 782 (1962).
I991 F. Ratnirez, N . B. Desai, B. Haiwrii, and N . M c Kelvir,
J. Amcr. chern. SOL 83, 3539 (1961).
1033
considerable gain in x-electron delocalization energy in
the transition from the phosphanaphthalene to a phosphacyanin system r13,931.
9,9-Dipheny]-9.phosphaphenanthreneI1001 is obtained in the
same way a s (82) a n d (94), from the corresponding phosphonium salt (prepared by Method VII) in aqueous solution.
Once again, no Wittig reactions have been observed.
1,5,7,11 -Tetrahydroxy-6-phosphoniaspiro[5,5]undecane
salts (99) and the spiro compound (6), n = 2, with fivemembered rings are formed in a single step by Method
Iv [15b-16b1. In the paddle-wheel arrangement Of the
OH groups which is postulated for steric reasons, the
~ ~
11031.
molecule has the m c structure
CH3
cyanin
dyes
G
(98), R = H
c) T e t r a h y d r o p h o s p h in o 1 i n e , T e t r a h y d r o i so phosphinoline, and Spirophosphonium Salts
P-Ethyltetrahydrophosphinolineand P-ethyltetrahydroisophosphinoline, like the phosphines (48) and ( 4 9 ) .
can be obtained in good yields as oils which are relatively stable in air, by thermolysis of the diethylphosphonium
salts (obtained by Method VII) [28,32,1011. The first
optically active phosphonium salt was prepared by
Mann 1321 by the resolution of the camphorsulfonate of
the asymmetrically substituted isophosphinolinium salt
(100) (m.p. 268-270 "C, [MI, = +32.9 ").
d) P h o s p h a - a n t h r a c e n e a n d P h o s p h a phenanthrene
The dichlorophosphine ( / 0 2 ) , which i s prepared in the
same way as (%a), undergoes ring closure in the presence of ZnCl2 to form 9-chloro-9-phospha-anthracene
(l03), which is converted by hydrolysis and oxidation
into the phosphinic acid 1761. The acid (104), which can
be obtained from 2-bromomethylbiphenyl by an Arbuzov reaction, cannot be cyclized by the usual methods
(with PzOs, PC15, AlC13); it is, however, cyclized to 9hydroxy-9-0x0-9-phosphaphenanthrene(105)simply on
heating at 350 "C 11041.
f 100)
I
c1
,, ,,
11041
P-OH
d 'OH
The phosphonium iodide (101) [1*21, which is obtained
by twofold intramolecular salt formation (Method VII)
exhibits molecular asymmetry, and has been resolved
into its optical antipodes by means of the (-)-menthy1
acetate (iodide: m.p. 246-248"C, [MI, = -65" and
4 6 in CHC13).
[loo] P. C . Crofts, personal communication.
[ l o l l See also F. G. Holliwan and F. G. Mnnn, J. chem. SOC.
(London) 1943, 547, 550.
[I021 F. A. Hnrt and F. G . Mann, J . chcrn. SOC. (London) 1955,
4107
1034
ilO_Ci
P-OH
D
0
4. Seven- and Eight-Membered Rings
1-Benzyl-1 -phosphacycloheptane and 1-phenyl- l-phosphacyclooctane have been synthesized by Method I 171.
Attempted syntheses by other methods led only to
polymeric products. The phosphacycloheptadiene (106)
[I031 McCaslilandand S. Proskow, J. Amer. chern. Soc. 77, 4688
(1956).
[I041 E . R . Linch, J. chem. Soc. (London) IY52, 3729; Brit. Pat.
933800 (Aug. 14th, 1963); Chem. Abstr. 60, 1796 (1964).
Angew. Chem. internat. Edit. 1 Vol. 4 (1965) No. 12
(m.p. 75-75.5 " c ) is practically identical to (C6Hs)jP
in its chemical behavior and in its ultraviolet spectrum11051. The phosphonium salt (107) has been obtained by intramolecular ylide alkylation in accordance
with Method V I I I 3 3 l .
ethane LY~,108-1111;
1,2-bis(diethylphosphino)benzene
reacts to form (114). 1,3-Dibromopropane and obis(bromomethy1)benzene react to form seven- and
eight-membered bisphosphonium salts, respectivelyI11zx1131. A second method is by the free-radical addition of secondary phosphines to vinyl acetate or vinyl
bromide at 80°C. This leads to the phosphines (113).
With R - R'
CHzCH2CN and X
OAc, Br, these
dimerize even during the preparation to form (111).
Temperatures between 120 and 150 "C are required for
the dimerization when R - - R'
butyl, isobutyl, or
CbHl 1 (yield . 21 - 59 %) [1091; linear polymers are first
formed at 80 to 12O"C, and these then rearrange at
higher temperatures to form (111).
:
C. Heterocycles Containing Two or More
Phosphorus Atoms
1. 1,3-Diphosphacyclohexane and Cyclic
Phosphacyanins
Bisphosphonium salts containing the ring system ( I 10)
can be readily obtained by the reaction of bis(dipheny1phosphino)methane 11071 with 1,3-dihalogeno compoundsrlo61. The salts (110) lose a proton in aqueous
sodium carbonate solution to give a quantitative yield
of the resonance-stabilized phospha-amidinium salts
(109). A double bond can be introduced by the dehydration of the alcohol (11Oc) with polyphosphoric
acid. The resulting compound (108), like ( I I O ) , is deprotonated to the resonance-stabilized cyclic trimethinephosphacyanin (1086) [perchlorate: m.p. 236-237 "C,
vcZc = 1620 cm-1, A,,,
(log E )
268 m p (3.954),
274 mp (3.967), 340 mp (4.086)]. A second proton is removed by stronger bases such as aqueous sodium hydroxide, and 1,1,3,3-tetraphenyl-1,3-diphosphabenzene
(108c) separates out from aqueous solution as a bulky,
yellow, non-crystalline precipitate (A,,
=
28 1 and
384 mp).
t
Diphenylvinylphosphine dimerizes quantitatively to
( 1 I I), R = R' = C6H5, in the presence of proton donors
[HOAc, (CzH&NH SCl:', sc-halogenohydrins]; besides
the protonated phosphine, another possible intermediate
is the cyclic bis-ylide1114J.On thermolysis of (111) (R ==
CzH5, R' -= CsH5), ethylene is split off to reform the
original phosphine (112).
The reductive debenzylation of phosphonium salts with
LiAlH4 was found to be an excellent method of preparing 1,4-diphosphacyclohexanes(116a) (m.p. 90-92 "C)
and (116b) (m.p. 128-130°C) [10*bl. The availability of
secondary bis(phosphin0)ethanes and their lithium
salts (115) enabled Issleib[1151 to develop a direct synthesis of the compound (116) without first forming the
phosphonium salts. The remarkable octafluoro derivative
(127) (m.p. 73-73.5 OC, yellowish crystals) is formed,
together with a little phospholane (118),in the reaction
2. 1,4-Diphosphacyclohexaneand
9,lO-Dihydrophosphanthrene
The bis-quaternary salts (111) are again very easy to
prepare. One method is by salt formation between 1,2bis(phosphin0)ethanes (112)"071 with I ,2-dibromo[I051 F. G. Mann, I . T. Millar, and B. B. Smith, J. chem. SOC.
(London) 1953, 1130.
[lo61 G. Markl, Z . Naturforsch. 18h, 1136 (1963).
[lo71 K. Issleib and F. Kreclr, Chem. Ber. 94, 2656 (1961).
Angew. Chem. internat. Edit. I Vol. 4 (1965)
1 No. I 2
[1G8a] C. H . Hitchrock and F. G. Mann, J. chem. SOC.(London),
1958,2081.
[108b] R . C . Hinton and F. G. Mann, J. chern. SOC. (London),
1959,2835.
[lo91 R. C. Hintor7 and F. G. Mann, J. chem. Soc.(London) 1959,
2835.
[110] M . M . Rnuhut, G . B. Borowitz, and H. C. Gillham, J. org.
Chemistry 28, 2565 (1963); Brit. Pat. 898759 (June 14th, 1962);
Chern. Abstr. 57, 12539 (1962).
f l l l ] A . M . Aguinr, H . Aguiar, and D. Daigie, J. Arner. chem.
SOC.87, 671 (1965).
[ I 12 F. A. Hart and F. G. Mann, Chem. and Ind. 1956, 574,
J. chem. SOC.(London) 1957,3939.
[113] E. R. H . Jones and F. G. Mann, J . chem. SOC. (London)
1955, 4472.
[ I 141 G. Murkl, unpublished work.
[ I 151 K . Issleib and G. Ddll, Chem. Ber. 96, 1544 (1963).
1035
of tetrafluoroethylene with elementary red phosphorus( !)
in the presence of stoichiometric quantities of iodine 11161.
The stability of the phosphines against inversion, as
discussed in the Introduction, suggests that (116) should
exist in two stereoisomeric forms (116') and (116").
Compounds (116a) and (1166) have sharp melting
points; they form the complexes (119) and (120) with
Kz[PdC141, give bicyclic salts (121) with dibromoethane, and form uniform oxides on oxidation [109J. The
existence of the cis structure (116"') thus appears to be
certain. On the other hand, the oily product with R =
C6H5 which was obtained by Issleib 11151 by distillation
at 300 to 310 "C/7 mm was probably the isomer mixture
of (116). Thisalso holdsfor theproducts with R = C2H5,
CHzCsHs, and CYCIO<~H~I.
Since the uptake of oxygen
0
(116')
a' Emp3
\p
0
I
'
The 9,10-diethyl-9,10-dihydrophosphanthrene (122)
with R = CzHs, which was prepared by Mann [1181 using
Method VI, fulfils these stereochemical expectations.
The compound is separated from the reaction mixture
by precipitation as the bisbenzylphosphonium bromide
(123); the expected salts (123a) [m.p. 346'CI and
(123b) [m.p. 319 "C] with cis-trans isomerism about the
tetrahedral phosphorus atom were found.
-
phospha-10-arsaphenanthrene form only o n e of t h e two
possible stereoisomers, probably because of t h e greater bulk
of the phenyl group[llsl.
3. 1,4-Diphosphabicyclo[2.2.2]octane
The first phosphine with the phosphorus in a bridgehead position, i.e. 1,4-diphosphabicyclo[2.2.2]octane
(124) (colorless needles, m.p. 252 "C), was prepared by
Mann[lo*bl by the debenzylation of (121) (R =
CHzC6Hs) with LiAIH4. Even in boiling benzene, (124)
is not oxidized by atmospheric oxygen, and quaternization with CH31 occurs only on heating. The ease of
sublimation of this compound is reminiscent of the
behavior of quinuclidine and triethylenediamine.
T h e low nucleophilicity of this compound a s compared with
normal phosphines may be d u e to the resistance of t h e phosphine (124) t o t h e widening of t h e valence angle associated
with t h e change from spz to sp3 hybridization.
The unexpected formation of the 1,4-diphosphabicyclo[2.2.2]octatriene derivative (125) from hexafluorobut-2yne and elementary red phosphorus (200 OC, 8 hours, I2
as catalyst) again shows the special position occupied by
perfluorinated compounds, even in the chemistry of
phosphorus [1193. The evidence for the structure of the
colorless and, like (124), readily sublimable product
(125) (m.p. 119-120°C) is based mainly on infrared
and 19F-NMR measurements.
.-
[ I 161 C. G. Krespan and C. M . Langkammerer, J. org. Chemistry
27, 3584 (1962); US.-Pat. 2931 803 (Apr. 5th, 1960), inventor:
C. G. Krespan; Chern. Abstr. 55, 12436 (1961).
[117] L . Horner and H . Winkler, Tetrahedron Letters 1964, 175.
[I181 M. Davis and F. G. Mann, Chem. and Ind. 1962, 1539;
J . chem. SOC. (London) 1964,3770.
1036
the benzene rings about the P-P aixs without loss of isomerism [cf. Formula (122")J Since (122a) readily
reacts with dibromoethane and o-bis(bromomethy1)benzene to form bicyclic phosphonium salts, and forms
a 1:l complex with K2[PdC14], for which only a bimolecular cis structure is possible, this is probably the
cis isomer (122"').
Compound (122) with R = C&5 a s well a s 9,10-diphenyl-9-
(]16!!)
or sulfur is not accompanied by inversion of the configuration [1171, the formation of two isomeric sulfides
and of oxides with very indistinct melting points supports this belief.
~
The debenzylation of (123a) gives rise to two phosphanthrenes, i.e. (122a) [m.p. 52-53 "C] and a little
(1226) [m.p. 96-97"CI; the isomerism of these compounds is due to the stable cis and trans arrangements
of the substituents R in the molecule, which is folded
about the P-P axis [(122') and (122")j. This "butterfly conformation" permits a synchronous oscillation of
[119] C. G. Krespan, B. C . McKusick, and T . L. Cairus, J. Amer.
chem. SOC.82, 1515 (1960); C. G. Krespan, ibid. 83, 3432 (1961);
US.-Pat. 2996527 (Aug. 15th, 1961); Chem. Abstr. 56, 1483
(1962).
Ang e w . Chem. intermit.
Edit. Vol. 4 (I965) 1 No. I2
T h e decrease i n the basicity a n d nucleophilicity is even more
pronounced in (125) th an in (124): co m p o u n d (125) is insoluble in concentrated HzS04, does n o t react with CH31 or
benzyl bromide, a n d does n o t ad d on Brz. Beside th e change
in the valence angle, there a r e other factors th at co n tr i b u t e
t o the decrease in basicity, i.e. steric hindrance by th e CF3
groups, electron deficiency o n th e phosphorus owing t o t h e
attraction of electrons by th e CF3 a n d vinyl groups, a n d possible stabilization of t h e trivalent phosphorus by d,-p,
overlap with the adjacent double bonds.
4. 1,2-Diphosphacycles and 1,2,3-Triphosphacycles
Interaction of the d-orbital of the phosphorus with the
p,-orbitals of adjacent double bonds is also indicated
by ultraviolet measurements on the 1,2-diphosphacyclobutene and 1,2,3-triphosphacyclopentene derivatives
(126) and (127), which are formed from hexafluorobut2-yne and the cyclopolyphosphines [P(CF3)], (n =
43)“201. These phosphines, which are stable in a nitrogen atmosphere, ignite spontaneously on contact with
Compound (130), which like (124) is a tertiary phosphine with a bridgehead phosphorus atom, cannot be
protonated even in HC104/nitromethane, and does not
react with CH31, H202, or sulfur. Therefore, the rigid
polycyclic system appears to be incapable of tolerating a
tetrahedral phosphorus atom at the bridgehead.
The reaction of acetylacetone with PH3 has also been
known for a long time [1231. Epstein and Buckler found
that the product (as well as the products obtained with
other 1,3-diketones and secondary phosphines) has
the phospha-adamantane structure (131). These compounds behave as normal phosphines “251.
RCOCHzCOR
air. The structurally related 1 ,Zdiphenyl-1,2-diphosphacyclopentane (128) (b.p. 184-190°C) is formed by an
exchange reaction
1221 :
+
R’PH2
4-6NHCl
2 8%
R = Alkyl, CF3
R’ = H, Alkyl, C&15
(1311
I
2. 1,3-Dioxa-5-phosphacyclohexane
D. Phosphorus Heterocycles which also Contain
Oxygen or Nitrogen as Ring Atoms
The nucleophilic addition of PH3 to cc-branched aldehydes leads to 2,4,6-trialkyl-1,3-dioxa-5-phosphacyclohexanes [124b, 1271, and not to the expected 11261 phosphonium salts (132). For steric reasons, only the 1:2
adduct (133) is formed, and this is then cycloacetalized
to (124). The accumulation of bulky substituents favors
both the ring closure and the stability of (134), which is
1. 1-Oxa-3-phosphacyclopentanes
Unusual phosphorus heterocycles have been obtained
by unexpected reactions. An example is the reaction between PH3 and pyruvic acid, which was carried out as
early as 1888[1231, and which was shown by BuckZer[124a-l24c] to yield the product (134). The H @
catalysed nucleophilic addition of PH3 to the C=O
groups to form (129) is followed by closure of the ylactone ring to form (130).
[I201 W . Mahler, J. Amer. chem. SOC.86, 2306 (1964).
[I211 K. Issleib and F. Krech, Chem. Ber. 94, 2656 (1961).
[I221 K. Issleib and D . Jakob, Chem. Ber. 94, 107 (1961).
[I231 J. Messinger and C . Engels, Ber. dtsch. chem. Ges. 21, 326,
2919 (1888).
[124a] Sh. A. Buckler, J . Amer. chern. SOC.82,4215 (1960).
[124b] Sh. A. Buckler and M . Epstein, Tetrahedron 18, 1211
(1 962).
[124c] US.-Pat. 2845454 (July 29th, 1958), inventors: Sh. A .
Budder and V . P . Wystrach; Chem. Abstr. 53, 3061 (1959).
Angcw. Chem. intermit. Edit.
1 VoI. 4 (1965) 1 No. I2
R,,CH-CHO
R’
+ PH3
kF/HCI
[I251 M . Epstein and Sh. A. Buckler, J. Amer. chem. SOC.83,3279
(1961); US.-Pat. 3050531 (Aug. 21st, 1962); Chem. Abstr. 57,
16659c (1962).
[I261 H. Hellmann, J . Bader, H . Birkner, and 0 . Schumarher,
Liebigs Ann. Chem. 659,49 (1962).
[I271 Sh. A. Buckler and V . P. Wystrach, J. Amer. chem. SOC. 80,
6454 (1958); 83, 168 (1961); US.-Pat. 2984683 (May 16th, 1961).
inventor Sh. A . Buckler; Chem. Abstr. 55,22347 (1961).
1037
not decomposed even in boiling concentrated HCI. The
similarity to normal secondary phosphines is only
slight. The 1,3-dioxa-5-phosphacyclohexaneshave a
mild, not unpleasant odor (!), and are more stable
towards oxygen than other secondary phosphines.
T he generally lower sensitivity t o oxygen ofcyclic as compared
with open-chain phosphines indicates th at autoxidation is
probably hindered by th e conformational change accompanying the P + PO transition, as well as by steric shielding of the
cr-orbital of the phosphorus.
The sc-hydroxyalkylphosphonium salts (135) obtained
from primary phosphines (R = alkyl, aryl) and aliphatic
aldehydes can be readily degraded by bases to the x,.,5c'dihydroxyphosphines (136), the acetalization of which
with any aldehyde ( R ' = alkyl, aryl) also leads to cyclic
compounds (137) [*2*1. Aromatic aldehydes also react
directly with aryl-substituted secondary phosphines
(benzaldehyde even reacts with PH3 [124b71301) to give
(137) ( R = R") '1291.
Michnelis an d Schenk 11321 reported a phenophosphazine
derivative, i.e. t h e secondary phosphine oxide (140) (m.p.
214- 216"C, yield 40"6), which they had prepared by the
reaction of diphenylamine with PCI3/ZnC12 (in a sealed tube)
followed by hydrolysis. This was later confirmed, in particular by Haring[1331. Compound (140) is oxidized t o the
phosphinic acid by atmospheric oxygen, whereas the reaction with bromine surprisingly leads t o a dibrominated product in which no attack o n t h e phosphorus has taken place.
Whereas di-p-tolyl ether reacts in a similar manner with ring
closure 176b1, the unsubstituted phosphinic acid (140n) is
obtainable only by the cyclization o f dichloro-o-phenoxyphenylphosphine, which proceeds o n heating [76al.
4. 1-Aza-4-phosphacyclohexane
The applicability of Method I1 in cases in which the
dibromoalkane chains also contain heteroatoms is
shown by the synthesis of 1,4-diphenyl-l-aza-4-phosphacyclohexane (141) (colorless crystals; m.p. 89 to
9OoC)[1341. CH3Br and C2HsBr attack only on the
phosphorus atom, due to the greater nucleophilicity of
the phosphine; a bis-salt of (/4i),which is thermally
very unstable, is formed only in boiling methyl iodide.
Compound (141) is stable towards oxygen at room
temperature, i.e. substantial deactivation has taken
place in comparison with 1-phenylphosphorinane,owing
to the presence of the nitrogen atom in the ring.
3. 9-Phosphaxanthene and
9,lO-Dihydrophenophosphazine
9-Phenyl-9-phosphaxanthene(138) (m.p. 94-94.5 "C)
has been prepared from 2,T-dibr~modiphenylether by
Method VI 1261. 2,2'-Dibromodiphenylamine, which is
difficult to prepare, gives only polymerization products,
owing to metalation of the NH groupL25al. The alkylation of the amine via the Li compound11311 led to
(139) [R - CH3: pale yellow crystals, m.p. 154 to
157 "C] r2sb1. Compounds (138) and (139) are almost
identical in their chemical behavior and in their ultraviolet spectra to (C6H5)3P. The valence angles ( C - 0 - C :
116 = 4 O ; C-N-C: 107 ") indicate a folded structure, as
in (122).
Cycloadditions onto vinylphosphines promise interesting methods for the preparation of phosphorus
heterocycles. The 1,3-dipolar nitrilimine (142) adds onto
triphenylphosphine to form the azophosphorus ylide;
with diphenylvinylphosphine, on the other hand, (142)
undergoes ring closure to the 1,3,4,4-tetraphenyl-1,2diaza-4-phosphoniacyclohex-2-ene
cation (143) [1*4J.
dk
(J38), Y = 0
(139), Y = NR
(140),
(140a),
Y
Y
=
NH; R = H
R = OH
= 0;
[I281 US.-Pat. 300.50201 (March 3rd, 1959). inventor: Sh. A .
Buckler; Chem. Abstr. 56, 6002 (1962).
[I291 Franz. Pat. 1333818 (Aug. 2nd, 1963), inventors: M.
Grayson and P. T. Keough; Chem. Abstr. 60, 3013 (1964); Sh. A .
Buckler and M . Epstein, Tetrahedron 18, 1231 (1962).
[I301 V. Etteland J . Hardk, Collect. czechoslov. chem. Commun.
25, 2192 (1960).
[I311 H . Gilnian and E. A. Zuech, Chern. and lnd. 1958, 1227.
[I321 A. Michaelis and A . Schenk, Liebigs Ann. Chem. 260, 1
(1890).
1038
The author's own investigations mentioned in this review
have been supported by the Deutsche Forschungsgemeinschaft and by the Fonds der Chemischen Industrie.
Received: March Ist, 1965
[ A 463/261 IE]
German version: Angew. Chem. 77, 1109 (1965)
Translated by Express Translation Service, London
[ I 3 3 1 M . Huring, Helv. chim. Acta 43, 1826 (1960).
[I341 F. G. Mann and I. T . Millar, J. chem. SOC.(London) 1952,
3039.
Angew. Chem. internnt. Edit. Vol. 4 (1965) 1 No. 12
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containing, heterocyclic, phosphorus
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