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Optically Active Selenoxomethylphenylpropylphos-phoranes and Their Transformations.

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view of our results, however, this does not seem to be a true
reversal of aromatic substitution by way of o-complexes;
an alternative route via tautomeric quinonoid intermediates
is rather more likely. The efficiency of substituents in
stabilizing a positive charge in the transition state is given
Our results show the electronic influence of the NR, group
to be decisive for isomerization and dealkylation. Due to
steric hindrance of mesomerism, ortho-substituents favor
N-protonation and thus dealkylation, as shown by the
reactions of ( 4 ) and ( 6 ) .
Products (mot-%) [a]
-N-meth ylaniline
Hydrobromide of
-N,N-dimethylaniline
2,4-Dibromo-N,N-dimethylaniline
(3)
2,4-Br2
4-Br
35.4
14.3
2,4-Br2
50.3
2,6-Dibromo-N,N-dimethylaniline
(4)
2,6-Br,
30.0
2,6-Br2
2-Br
54.3
5.6
2,4-Br2
6.6
2,6-Me,
24.4
2,4-Dibromo-N-ethyl-N-methylaniline
(5)
2.6,N,N-Tetramethylaniline(6)
2,6-Me,
75.6
-aniline
2,6-Br,
10.1
2,4-Br,-N-Et-N-Me
4-Br-N-Et-N-Me
2,4-Br2-N-El
aniline
33
20
30
8
[a] The bases were liberated by passing in NH,; the product composition was determined by gas chromatography, the individual compounds being
identified by comparison of the retention times with those of pure substances. W. BIum has confirmed the assignments by a GC-MS combination Finnigan
system DA-150.
[b] Product compositions in parentheses are those obtained after heating for 160 hours at 120°C.
by the o,' values which are -0.92 for OH and -1.70 for
N(CH,),"'. Thus, reversibility of electrophilic bromination
of phenols should be achieved only under appreciably
more vigorous conditions than those required for N,Ndialkylanilines.
We assume the anilines obtained to be formed via cationic
intermediates (7)-(9), as formulated for reaction of ( I )
in the above scheme. In an S,2 reaction cation (7) is
dealkylated by the Br@. C-Protonation of ( I ) affording
( 8 ) is followed by dehalogenation to dimethylaniline which
then gives the isomerization product (2) via ( 9 ) . Incorporation of labeled *Br in the course of the reaction of
N,N-dimethyl-p-bromoaniline. H'Br is proof that (2) may
be dehalogenated again by way of ( 9 ) , and that free Br,
must occur during the overall reaction. The large proportion of starting material recovered when (2) is heated must
be ascribed to preferential rebromination of dimethylaniline at the para-position. Longer reaction times favor
dealkylation, as shown by the product composition after
160 hours' heating of ( 1 ) at 120°C. These also are not
equilibrium concentrations, though, since irreversible
oxidations (discoloration) become more and more pronounced with longer reaction times.
[I] This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
[2] R. 0. C. Norman: Principles of Organic Synthesis. Methuen, London 1968, p. 347.
(31 For a review, see H . J . Shine: Aromatic Rearrangements. Elsevier,
New York 1967, pp. 32ff.
[4] Ph. C. Myhre, Acta Chem. Scand. 14,947 (1960).
[S] R. Niess, K . Nagel, and F. Effenberger, Tetrahedron Lett. 1968,
4265.
[6] E. J . O'Bara, R. B. Balsley,and J . Starer, J. Org. Chem. 35,16(1970).
[7] J . March: Advanced Organic Chemistry. Reactions, Mechanisms,
and Structure. McGraw-Hill, New York 1968, p. 241.
494
Since CH, rather than C,H, is lost preferentially from ( S ) ,
the dealkylation is indicated to be of S,2 type. If HBr is
replaced by acids with less nucleophilic anions, the share
of isomerization and dealkylation products decreases ;
N,N-dialkylbromoanilinium perchlorates remain practically unchanged under our experimental conditions.
Received: April 2, 1971 [ Z 408 IE]
German version : Angew. Chem. 83,535 (1971)
OpticaIly Active SeIenoxomethylphenylpropyIphosphoranes and Their Transformations
By W Stec, A. Okruszek, and J a n Michalski"'
We have found that the previously unreported"] optically
active selenoxotriarylalkyl(triary1-)phosphanescan be readily obtained by addition of elemental selenium to optically
active tertiary phosphanes. Since the stereochemistry of the
addition of selenium to phosphanes was obscure, some
additional studies on the transformation of optically active
selenoxotriarylalkyl(triary1-)phosphanes were considered
necessary. Correlation of known absolute configurations of
phosphanes[2' and oxophosphoranes['] with those of
selenoxophosphoranes was therefore undertaken. Optically
active selenoxophosphoranes can be readily converted
into the corresponding oxophosphoranes by two stereoselective routes, as well as reduced stereoselectively to
the parent phosphanes (Scheme 1).
[*] Dr. W. Stec, A. Okruszek, and Prof. J. Michalski
Institute of Organic Chemistry
Polish Acadern) of Sciences
Zwirki 36, Lodi 40 (Poland)
Angew. Chem. internat. Edit. / Vol. I0 (1971) / No. 7
Treatment of ( + )-(S)-methylphenylpropylphosphane
[a]::8 = + 17.3" (toluene) with stoichiometric amounts of
elemental seleniumin benzene gave(+)-(R)-selenoxomethylphenylpropylphosphane (2)[41,[a]::x = + 16.9"I51, m. p.
Close analogy of the stereochemical transformations is
observed in the case of the corresponding thioxophosphoranes, except for the oxidation with N,O,. Since only little
is known about the mechanism of oxidation cf phosphanes
and the thioxo- and selenoxophosphoranes with the oxidizing agents mentioned above, interpretation of this
observation is difficult.
cis - ( 5 )
trans-(5)
Scheme 2.
6@75"C, while addition of selenium to (-)-(R)-(l),
[a]::8 = -9.0" (toluene), produced (-)-(S)-(2), [a]::8
= - 8.8", m. p. 55-75°C. Multiple fractional crystallization
of compounds (2) from cyclohexane improved their optical
purity. Both enantiomers of ( 2 ) have m. p. 75-76°C and
[a]$:x( + or - ) 20.2".
The compound (+)-(R)-(2),[a]:;8= + 19.7", is readily
reduced by LiAlH, in boiling THF to (+)-@)-(I), [a]::x
= + 17.8" (toluene). The same reduction of (-)-(S)-(2),
[a]::8= -20.2",gave(-)-(R)-(I), [a]::8= - 18.65"(toluene). The yields of both reactions were over 80%. An
attempt to reduce the selenoxophosphoranes ( 2 ) with
other reducing agents such asRaney-Ni or SiHCI,/(C,H,),N
were partially successful only in the former case161.
Oxidation of the optically active selenoxophosphoranes
(2) with nitric acid['I and with potassium permanganate
via stereochemically differin aqueous ~ y r i d i n e [proceeds
~]
ent courses. When (-)-(S)-(2), [a]$8 = - 11.3", was treated
with KMnO, in pyridine/water (2 :1) v/v), (-)-(S)-oxomethylphenylpropylphosphorane ( 3 ) , [a]::x= - 9.7 was
formed. The same enantiorner ( 2 ) . [cx]?",=
-20.2'.
oxidized with HNO, gave (+)-(R)-(3),[a]:&= 17.9'.
Treatment of (+)-(R)-(2),[a]::x= +20.2", with 'HNO,
produced (-)-(S)-(-?), [a]:;8 = - 17.9'. Oxidation with
N 2 0 , followed a similar stereochemical course to that
with HNO,. Thus, from (+)-(R)-(2),[a]::x=+20.2" the
oxophosphorane ( - ) - ( S ) - ( 3 ) , [a]:!x= - 3.2" was isolated
after treatment with a 10% solution of N,O, in CH,Cl,.
(-)-(S)-(2), [a]:!?8= -20.2", gave (+)-(R)-(2), [E]::~
= + 5.6". The considerable racemization is undoubtedly
caused by action of N,O, on the resulting oxide (.?)Ix1.
O,
+
Since the stereochemistry of the oxidation of phosphane
( I ) with HN0,[8' and with H,0,[21 is well established we
conclude from our experiments that addition of selenium
to optically active tertiary phosphanes proceeds with
retention of configuration. The absolute configuration R
has been therefore assigned for dextrorotatory selenoxophosphorane (2).A retention mechanism is also proposed
for reduction of the selenoxophosphorane (2) to parent
phosphane as well as for its oxidation with KMnO, in
pyridinelwater solution to the corresponding oxophosphorane, while oxidation of ( 2 ) with HNO, or N20, proceeds uia inversion.
Angew. Chem. internat. Edit./ Vol. 10 (1971) 1 N o . 7
In contrast to the oxidation of acyclic selenoxophosphoranes (2) described above oxidation ofdiastereomeric 2-methoxy-4-methyl-4H-5,6-dihydro-1,3,2-dioxaphosphorin
2selenides ( 4 ) to the oxides (5)r91is highly stereoselective;
an epimerization was not observed"'!
trans-(4)
cis-(4)
(%I
(%)
83.5
16.5
16.5
78.0
78.0
83.5
22.0
22.0
Reagent
N,O4
HNO,
N204
HNO,
trans-iS)
cw(S)
(%I
(;a
79.0
81.0
25.0
25.0
21.0
19.0
75.0
75.0
Received: March 15. 1971 [Z 411 IE]
German version: Angew. Chem. 83,491 (1972)
[I] A racemic asymmetric selenoxotriarylphosphorane containing an
amino group has been prepared by W C . Daries and F . G . Mann, J.
Chem. SOC.1944,274.
[2] L. Horner, Pure Appl. Chem. 9, 225 (1964).
[3] Optically active phosphanes ( I ) were prepared by alkaline hydrolysis of diastereoisomeric benzylmethylphenylpropylphosphonium dibenzoyltartrates ( K . F. Kumli, W E. McEwen, and C. A . Vander Werf.
J. Amer. Chem. SOC.81,248, 3805 (1959)) followed by reduction of the
oxophosphoranes ( 3 ) with SiHCI,/(C,H,)3N (L. Horner and W D.
Balzer, Tetrahedron Lett. 196S, 1157).
[4] Both selenoxophosphoranes (2) gave the correct elemental analysis and NMR spectra and their purity was checked by thin-layer
chromatography.
[ 5 ] Rotations refer to solvent methanol unless otherwise stated.
[6] The reduction of racemic ( 2 ) with 5-fold excess of Ni-Raney in
boiling ethanol for 7 hours yielded only 27% of ( I ) .
[7] Retention of configuration during oxidation of methylphenylpropylthioxophosphorane with KMnO, in pyridine has been described
by L. Horner [2].
[XI The procedure for oxidation with HNO, and N,04 was identical
to that described for transformation of the corresponding optically
active thioxophosphoranes (J. Michalski, A . Okruszek, and W Stec.
Chem. Comm. 1970,1495).
[ 9 ] W Stec. A . Okruszek, and M . Mikohjczyk, 2. Naturforsch., in press.
[lo] (41 was prepared by addition ofelemental selenium to 2-methoxy4-methyl-4H-5,6-dihydro-l,3,2-dioxaphosphorin
;
cis-(4) :
b. p.
85-87'C/0.2
torr, NMR (CDCI,): 6(OCH,)= 3.8 ppm,
= 14.4
Hz; trans-(4): b.p. 100-102"C/0.2 torr. NMR (CDCI,): 6(OCH,)
= 3.7 ppm, JpoCH
= 14 4 Hz. The ratio of the diasrei-comeric dioxaphosphorins ( 4 ) and ( 5 ) (+5%) was determined by gas-liquid chromatography.
495
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