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Detection of Alkylideneoxophosphoranes by Cycloaddition of Carbonyl Compounds.

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PPP ~ a l c u l a t i o n sthe
~ ~electron
~
spectra of the acepleiadylenes (5a)-(5f)-alI
strongly fluorescent-depend little
on the nature of the substituents R'-R4. Not unexpectedly
the UV spectrum of the non-fluorescent ( 5 9 ) is distinctly
different.
Received: September 1 I . 1973 [Z 912b IE]
German version. Angew. Chem 85. 11 13 (1973)
161
[ I ] Cyclic Cross-Conjugated Bond Systems. Part 27.--Part 16: H . Prinzbach and H.-W Schwider, Angew Chcm. 85. 1112 (1973): Angew. Chem.
internat. Edit. /2,1007( 1973).
[2] V Boekelherdr, W E . Lunqefand, and C.-T Liu, J. Amer. Chem.
SOC.73, 2432 (1951); V Boekelheide and G . K . Vick, ihid. 78, 653 (1956).
[3] A. J . Jones, P. D. Gardner, D. M . Grant, W M . Litchman, and
V Boekelheide, J. Amer. Chem. SOC.92. 2395 (1970).
[4] For the segment C'-C'ob-C'o'-C'o
a "butadienoid character
order" (0.E. Polansky and G. Derflinger, Internal. J. of Quantum Chemistry, Vol. I, 379 (1967)) of p=0.7005 has been calculared (0.E . Polansky,
personal communication).
[ S ] With comparable ease 1 2 a ) reacts with 3- and 8-styrylpiperidine
t o give unsymmetrically substituted acepleiadylenes [ 6 ] : see also the
addition of ADM t o pyridiniocyclopentadienylides ( R . Gomppw, Angew.
Chem. 81, 348 (1969); Angew. Chem. internat. Edit 8, 312 (1969)).
[6] H.-W Sckneider, Dissertation, UniversitPt Freiburg 1973.
[7] In contrast thereto,addition of 1-( I-propeny1)piperidine and of methyl
3-piperidinocrotonate t o ( 2 c ) is not regiospecific [6].
[8] In co-operation with Miss B. Berjer. University of Goteborg
[9] Thc n-clcctron denaitiea and ic-bond ordera calculated for 1,2dicyanoacepleiadylene deviate only slightly from the values obtained
for ( I ) ( R . Zahradnik, personal communication; R. ZahradnrX, H . Prinzhach, et a/., unpublished work).
=4.8 and 5.0 d, ,JH,,=23 and 26 Hz, respectively]. A
fragment M + -C,H,PO, appearing in the mass spectrum
of (5a') and ( 5 b ) is not consistent with the alternative
orientation of the aldehyde in the cycloaddition. Furthermore, alkaline ring fission of (5a) to the 0-hydroxy
phosphinic acid (6) [m-p. 140°C; NMR (CDCI,):
GCH-0=5.42 d, 3J,,,,=8 Hz] accords with the structure
assigned to the cycloadducts.
The a-benzoylbenzylideneoxophosphorane (3b) is obtained by analogous photochemical reaction in a melt
of p-dichlorobenzene (60'C), this product being expected
because of the 1,4-dipolar reactivity due to the differing
electronegativities of phosphorus and oxygen. In agreement
therewith,theproduct [yield 15%; m.p. 182--183-C (from.
ethyl acetate/ether); no C O absorption in the IR spectrum]
trapped by benzophenone has the 1,5,2-dioxaphosphorin
structure (7).
Detection of Alkylideneoxophosphoranes by
Cycloaddition of Carbonyl C o m p o u n d s [ * * ] [ ' ]
By Manfred Regitz, Hans Scherer, Walter Illger, and
Helmut Eckes"'
Irradiation of (dipheny1phosphoryl)diazomethanes ( I ) in
methanol affords phosphinic esters (4) in amounts that
vary with the nature of the group R ; their formation
is readily explained as occurring by way of the carbene
(2) and the alkylidenephosphorane intermediates (3)l21.
p
!2)
1)
(rr),
K
= C6H5
( h i , R = COC6115
$b1'5
P-C<<
0" \0CI13
,011
/C6115
R
14)
To trap the hitherto unknown heterocumulenes ( 3 ) , they
were prepared in the presence of carbonyl compounds.
O n irradiation of (1 a) in benzene containing benzaldehyde
or I -naphthaldehyde the solvent was first cyclopropanated
by the carbene (2 a), yielding 7-(exo-diphenylphosphoryl)7-endo-phenylnorcaradiene [IS% yield; m. p. 179 to
180°C ; NMR (CDCI,): GCH-cyclopropane= 3.46, d ,
= 14 Hz['*~]].
However, at least 18% of ( 2 a ) was
3JH,r(~is)
rearranged by a PIC-phenyl shift, yielding (3a) which
undergoes [2 21-cycloaddition with the aldehydes, thus
forming the 1,2-oxaphosphetanes (5a') and ( 5 b ) [m. p.
246 and 249 "C, respectively ; NMR (CDCl,) : GCH-ring
+
____['I Prof. Dr. M. Regitz, Dr. H. Scherer, DiplLChem. W. Illger, and
Dipl.-Chem. H. Eckes
Fachbereich Chemie der Universitit
675 Kaiserslautern. Pfaffenbergstrdsse 95 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
1010
C € I C6H5
I 6
I
P-CH-C-CblI,
0" 'OH
A
+
FI
fC\
Ii5CS C6H5
(8)
Thermal fragmentation (215"C, 5.10-3 torr) of (7) to
diphenylacetylene, benzophenone and the hypothetical
fragment C,H,P0,141 also supports formula (7), as does
hydrolysis by 20% potassium hydroxide in ethanollwater at
room temperature to the phosphinic acid ( 8 ) [yield 83%;
m.p. 148'C; IR (KBr): 2225, 2560 (OH, br), 1675 cm-'
(CO); NMR (CDC13): 6CH-x=5.50 d, 'J~.p=20Hz] and
benzophenone. O n use of acetophenone as trapping agent
for ( 3 b ) there is formed, analogously to (7), a 30% yield
of an oily mixture of diastereoisorners that could not hitherto be separated. In its NMR spectrum (CDCI,) the methyl
signals occur at 2.47 and 2.04 ppm (the latter is split,
4J~.p
= 2 Hz, rel. areas 2 : 1).
Correct analytical data were obtained for all the products.
2-0xo-2,3,3,4-terraphenyi-I,23,5-oxaphosphetan ( 5 a') and 4(a- naphthyl) - 2-0x0 -2,3,3- triphenyl- I , 2 E. - oxaphosphetan
(5b'):
30mmol (9.54g) of ( I a) and 100mmol of benzaldehyde
or I -naphthaldehyde in benzene (750ml) were irradiated
(Duran-50 filter, Philips HPK 125 W) until at least 50%
of the theoretical amount of nitrogen was liberated. Evaporation, dissolution of the residue in methanol (50ml)
and crystallization at -20°C gave ( 5 a ' ) or (5b'). The
filtrate was evaporated and the residue chromatographed
in benzene (1000ml) on Woelm silica gel (300 g, 0.05 to
Anqew. Chem. internat. Edit.
Vol. 12 (lY73) 1 No. 12
0.2 mm) to remove unchanged aldehyde. Further elution
with ether (2500ml) afforded 7-(exo-diphenylphosphoryl)7-endo-phenylnorcaradiene.
R
Eu..
C -N\
/
CH-COOCH3
k-i
H
I
R
R
I
O,\
C -N\
CH-COOCH3
4C -N,
k,
/
A
7
H
/
k - ~ +O/
H
+Of
CH-COOCH3
I
R
2
(I), R
Highly resolved NMR spectra are extremely well suited
for demonstration of intramolecular mobility. The method
fails, however, when the NMR spectra of the isomers d o
not differ sufficiently (accidental equivalence) and when
the equilibrium lies greatly to one side. We have found
that the use of lanthanoid shift reagents such as E ~ ( f o d ) ~
[tris(6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octane-dionato)europium(~~~)]
can lead to success in such cases.
The 'H-NMR spectra of Boc-glycine methyl ester ( I )
and Boc-L-alanine methyl ester (2) in CDCI3 at 90 MHz
are independent of temperature and it is not possible to
recognize any hindrance to rotation around the urethane
N-C bond from these spectra. Nevertheless all the signals
are doubled in the spectrum of ( I ) or (2) in C2D2C14
at 0 'C after addition of Eu(fod),r2I, showing the presence
of the two rotamers side by side. The complexation occurs
preferentially with the E-isomer that is present in smaller
amounts. Its signals are more strongly shifted and become
more intense as the concentration of E ~ ( f o dis) ~increased.
Only if the molar ratio of Eu(fod), to substrate approaches
unity d o the signals of the 2-isomer, now present in
smaller amount, follow the same pattern.
H
k
1
,
+O/
[ I ] Carbencs l'art 6 . Part 5 : H . S</ic,rvr. I f!ortni<rnii. .if. R q i t z ,
B. D. E r r i q y d . and H. (,ii!r{/wr. Chcm. Ber. i0i. 3357 (1972).
123 M Rcqrr:. 4. LiCdhqcm,r. W. Ansihirrz, and H . E c k m . Chem. Ber.
104. 2177 (1971).
131 H . Giinrhar. B . D. Tunggul, M . Rrgrtz, H. Sckrrer, and T Kellrr,
Angew. ('hem. X3. 585 (1971): Angew. Chem. internat. Edit. 10. 563
( I 97 I ).
141 All three fragments appear in the mass spectrum.
By Horst Kessler and Michurl Molter[*]
- t o%'
,,CH-COOCH3
C-N,
Received: September 21, 1973 [7 933 IE]
German version. Angew. Chem 85, I115 11973)
Dynamic NMR Measurements of Boc-amino Esters
with Application of Lanthanoid Shift
Reagents [ '"**I
Eu..
I
'O*
E
= H;
(2), R
= CH3;
(3), R = CHZ-CGH,
Assignment of the rotamers is effected by comparing
the lanthanoid-induced shifts A[41. It can be assumed
that complexation occurs at the urethane-carbonyl group.
The signals of the tert-butyl group are thus relatively
strongly shifted in both rotamers. Although the C,protons are further away from the europium ion in the
E- than in the 2-conformation, the signal of the former
is at first more shifted because of its greater complex
formation. However, with increasing Eu(fod)3 concentration [e.g., for ( 1 ) > 38 mol-%] the strength of this signal is,
as expected, overhauled by that of the 2-C,H signal because
of the increased complexation of the 2-form that now
clearly occurs. If the shifts of the C,H-protons are referred
to those of the tert-butyl groups, the values shown in Table 1
are obtained, whence the assignments follow unambiguously. Extrapolation of the Eu(fod), concentration to zero
shows that the Boc-a-amino acids studied exist in CDCl, or
C2D,C1, preferentially in the 2-conformation, but the
E-conformations are clearly better complexed so that their
contribution increases with increasing Eu(fod), concent ration.
If the solution of ( 1 ) containing Eu(fod)3 is warmed one
observes coalescence of four groups of signals, corresponding to occurrence of rotation around the urethane bond.
The chemical shifts Av (without exchange) in the low-temperature region are only slightly temperature-dependent,
so they can be extrapolated without much difficulty. The
Table I . Data for Boc-L-n-amino acid methyl esters calculated from the 'H-NMR spectra of solutlons in C2D2C14
after addition of Eu(fod),.
(1)
Buc-Gly-OCH .~
z
[moI-%] Eu(fod),
referred to the sub5trate
Proportions of the isomers at 7 C
0
> 88
< 12
> 92
<8
20
40
60
36
17
40
74
83
71
49
32
29
51
68
60
& J I ' A H < ~[b]
<
__
1:
~
.~
__
AG;-.L [kcal/molJ[c]
3.9
0.33
(31
Boc-Phe-OCH,
E
(2)
Boc-Ala-OCH,
Z
E
22
0.18
z
["/.I
90
68
52
37
[d]
10 [d]
22
48
63
0.1 1
13
. ..
16.1 kl.0
1 5 . 4 i 1.0
15.92 1.0
ral
[a] In this compound the proportions of the two conformations can be recognized from the signal of the trrt-butyl
group even without addition of Eu(fod)3. The other signals are not split.
[b] Ratio of the Eu(fod),-induced splitting at concentrations of Eu(fod), up t o 30 mol-% reffered lo the substrate.
[c] Line widths evaluated at 32 C ; 34 mol-% of Eu(fod), referred t o the substrate.
[*] Prof. Dr. H. Kessler and DipLChem. M. Molter
lnstitut fur Organische Chemie der Universltat
6 Frankfurt (Main), Sandhofstrasse (Germany)
[**I This work was supported by the Deutsche Forschungsgemetnschaft
and the Fonds der Chemischen Industrie.
A n g r w . Chrm. infrrnar. Edit. J Vol. I 2 ( 1 9 7 3 ) J No. 12
free activation enthalpies of rotation around the urethane
bond can be determined from the line broadenings in
the usual Way and are found to lie in the expected range
(see Table 1)[1.51.
1011
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carbonyl, compounds, cycloadditions, detection, alkylideneoxophosphoranes
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