Stereoselectivity and stereospecificity of cyclopropanation reactions with stable (phosphanyl)(silyl)carbenes

Article abstract of DOI:10.1021/ja994408b

The stable (phosphanyl)(silyl)carbenes 1a,b react efficiently with various electron-poor alkenes [methyl acrylate, 3,3,4,4,5,5,6,6,6- nonafluorohex-1-ene, styrene, (Z)- and (E)-2-deuteriostyrene, (E)-t- BuOC(O)CH=CHC(O)OEt, and (E)-Me₂NCOCH=CHC

Full text of DOI:10.1021/ja994408b

4464
J. Am. Chem. Soc. 2000, 122, 4464-4470
Stereoselectivity and Stereospecificity of Cyclopropanation Reactions
with Stable (Phosphanyl)(silyl)carbenes
Ste´phanie Goumri-Magnet, Tsuyoshi Kato, Heinz Gornitzka, Antoine Baceiredo, and
Guy Bertrand*
Contribution from the Laboratoire d’He´te´rochimie Fondamentale et Applique´e, UniVersite´ Paul Sabatier,
118 route de Narbonne, 31062 Toulouse Cedex 04, France
ReceiVed December 16, 1999
Abstract: The stable (phosphanyl)(silyl)carbenes 1a,b react efficiently with various electron-poor alkenes [methyl
acrylate, 3,3,4,4,5,5,6,6,6-nonafluorohex-1-ene, styrene, (Z)- and (E)-2-deuteriostyrene, (E)-t-BuOC(O)CHd
CHC(O)OEt, and (E)-Me2NCOCHdCHCO2Me] giving the corresponding cyclopropanes in good yields. The
stereochemical outcome was such that all monosubstituted alkenes gave exclusively the syn isomer (with
respect to the phosphanyl group), and the addition of disubstituted alkenes was totally stereospecific. The high
stereoselectivity observed was ascribed to a secondary orbital interaction (LUMOcarbene-HOMOalkene) similar
to that explaining the endo-rule in Diels-Alder reactions.
Introduction
Scheme 1
In a recent paper,1 Krogh-Jespersen, Yan, and Moss wrote:
“The addition of a carbene to an alkene with the formation of
a cyclopropane is perhaps the most fundamental of cycloaddition
reactions, as well as a basic component of the synthetic
armamentarium.” Indeed, cyclopropanation reactions involving
transient carbenes2 or even transition metal carbene complexes
have been widely studied.3 Both singlet and triplet transient
carbenes undergo cyclopropanation reactions, although with a
totally different mechanism, which is apparent from the stereo-
chemistry of the reaction: with singlet carbenes the stereo-
chemistry about the original carbon-carbon double bond is
maintained, while with triplet carbenes the stereochemical
information is lost.4 Additionally, for all types of carbene,
including transition metal-carbene complexes, intermolecular
cyclopropanation usually occurred in poor to moderate diastereo-
selectivity (syn- versus anti-attack).5
To date, two types of stable singlet carbene are known:6 the
phosphanylcarbenes I and the aminocarbenes II. For derivatives
of type II, no cyclopropanation reactions have been reported,
most probably because of the strong donation of the amino
substituent, which makes the vacant orbital too high in energy.7
For example, the 1,2,4-triazol-5-ylidene IIa reacts with diethyl
fumarate and diethyl maleate to give methylenetriazoline
derivatives and not the corresponding cyclopropanes.8 In
contrast, we have already shown that the (phosphanyl)(silyl)-
carbenes 1a,b react with dimethyl fumarate with retention of
the stereochemistry about the double bond to give the corre-
sponding trans-cyclopropane.9 However, since 1 does not react
with dimethyl maleate no conclusion could be drawn on the
stereospecificity of the reaction (Scheme 1). The difference in
reactivity between cis and trans alkenes toward carbenes has
(1) Krogh-Jespersen, K.; Yan, S.; Moss, R. A. J. Am. Chem. Soc. 1999,
121, 6269.
(2) (a) Moss, R. A. Acc. Chem. Res. 1989, 22, 15. (b) Minkin, V. I.; Ya
Simkin, B.; Glukhovtsev, M. N. Russ. Chem. ReV. 1989, 58, 1067. (c)
Regitz, M. Carbene (Carbenoide); Methoden der Organische Chemie
(Houben-Weyl); Thieme Verlag: Stuttgart, 1989; Vol. E19b, Parts 1 and
2. (d) de Meijere, A. Carbocyclic Three-Membered Ring Compounds;
Methoden der Organische Chemie (Houben-Weyl); Thieme Verlag: Stut-
tgart, 1996; Vol. E17a.
(3) (a) Brookhart, M.; Studabaker, W. B. Chem. ReV. 1987, 87, 411. (b)
Harvey, D. F.; Sigano, D. M. Chem. ReV. 1996, 96, 271. (c) Fru¨hauf, H.
W. Chem. ReV. 1997, 97, 523.
(4) (a) Skell, P. S.; Garner, A. Y. J. Am. Chem. Soc. 1956, 78, 3409 and
5430. (b) Skell, P. S.; Woodworth, R. C. J. Am. Chem. Soc. 1956, 78, 4496
and 6427. (c) Skell, P. S. Tetrahedron 1985, 41, 1427. (d) Gaspar, P. P.;
Hammond, G. S. In Carbenes; Moss, R. A., Jones, M., Jr., Eds., Wiley-
Interscience: New York, 1973; Vol. II, p 153.
(5) ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds;
Pergamon Press: New York, 1991; Vol. 4.
(6) For reviews on stable singlet carbenes see: (a) Bourissou, D.; Guerret,
O.; Gabbai, F. P.; Bertrand, G. Chem. ReV. 2000, 100, 39. (b) Herrmann,
W. A.; Ko¨cher, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2162. (c)
Bourissou, D.; Bertrand, G. AdV. Organomet. Chem. 1999, 44, 175.
(7) This is well illustrated by the structure of the radical anion IIa•-
obtained by reduction of the corresponding stable carbene IIa. According
to ESR spectroscopy and ab initio calculations, the additional electron is
not located at the carbene carbon atom but delocalized into the PhCN
fragment: Enders, D.; Breuer, K.; Raabe, G.; Simonet, J.; Ghanimi, A.;
Stegmann, H. B.; Teles, J. H. Tetrahedron Lett. 1997, 38, 2833.
(8) Enders, D.; Breuer, K.; Raabe, G.; Runsink, J.; Teles, J. H.; Melder,
J. P.; Ebel, K.; Brode, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1021.
10.1021/ja994408b CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/22/2000

Reactions of the Stable (Phosphanyl)(silyl)carbenes
J. Am. Chem. Soc., Vol. 122, No. 18, 2000 4465
Table 1. Crystallographic Data for Cyclopropanes 2a, 6b, 7a, 7b, 8a, and 15a
2a
6b
7a
7b
8a
15a
formula
formula wt
cryst system,
space group
a, Å
b, Å
c, Å
C20H43N2O2SiP
402.62
monoclinic,
P21/c
15.147(8)
9.852(4)
C36H61N2SiP(C7H8)0.5 C24H45N2SiPS
C36H61N2SiPS
612.99
monoclinic,
C26H53N2O4SiP C23H48N3O3SiPS
627
triclinic,
452.74
monoclinic,
516.76
monoclinic,
P21/c
36.818(5)
9.5963(12)
18.765(2)
505.76
orthorhombic,
Pna21
10.233(1)
17.265(2)
16.354(2)
90
P1h
P21/n
P21/c
10.013(2)
10.937(2)
17.832(3)
79.51(2)
76.75(2)
89.38(2)
1868.1(6)
2
10.293(2)
13.027(2)
19.551(3)
12.552(1)
16.173(2)
17.548(1)
18.554(8)
R, deg
â, deg
114.04(2)
94.96(2)
97.72(1)
104.749(6)
90
90
γ, deg
V, Å3
2529(2)
4
1.058
2611.7(8)
4
3530.0(6)
4
1.153
0.198
28238
5328
6411.5(15)
8
1.071
0.152
14359
5699
2889.3(6)
4
1.163
0.236
23935
4580
Z
d(calcd), Mg/m3
1.115
0.134
10001
5065
1.151
0.244
20109
3875
absorp coeff, mm-1 0.171
no of total reflcns
no of unique reflcns 3403
22045
R1 (I > 2σ(I))
wR2a (all data)
0.0523
0.1392
0.0385
0.1021
0.0331
0.0825
0.0354
0.0875
0.994
0.2832
0.0395
0.0913
(∆/F)max [eÅ-3
]
0.204 and -0.163 0.190 and -0.248
0.250 and -0.264 0.235 and -0.365 0.443 and 0.401 0.175 and -0.132
a wR2 ) {[Σw(Fo2 - Fc2)2]/[Σw(Fo2)2]}1/2
.
Scheme 2
Figure 1. Solid-state structure of cyclopropane 2a.
4
by the large JPF coupling constant (178.5 Hz), which cannot
readily be explained without involving a through space cou-
pling.12 Treatment of a thf solution of 3a with a stoichiometric
amount of hydrated tetrabutylammonium fluoride gave rise to
the syn-cyclopropane 4a (95% yield) which also showed a large
4JPF coupling constant (145.9 Hz).
The phosphanylcarbene 1c is unavailable because of its
instability.11a Its diazo precursor 5a is stable toward dinitrogen
elimination on heating at 40 °C for 3 h. Interestingly, under the
same experimental conditions, but in the presence of the
perfluoroalkyl-substituted alkene, cyclopropane 4′a was obtained
in 95% yield (Scheme 2). The anti-configuration was apparent
from the 31P and 19F NMR spectra: no JPF coupling constants
were observed.
The reaction of carbene 1a with styrene was monitored by
31P NMR spectroscopy. After 30 min at room temperature, the
reaction was over, and two new signals at +73 and +61 ppm
in a 90/10 ratio were observed, arguing for the presence of two
diastereomers. A white solid was obtained after treatment with
elemental sulfur, and purification by column chromatography.
Although one single spot was apparent on the TLC, two signals
(+93 and +86 ppm; 60/40 ratio) were observed in the 31P NMR
spectrum of a CDCl3 solution of the solid. The 1H and 13C NMR
spectra confirmed the presence of two species, but the similari-
ties of their spectroscopic data (Table 2) were surprising for
two diastereomers. Slow evaporation of a pentane solution of
the solid gave single crystals suitable for an X-ray diffraction
study. The molecular structure of the molecule is depicted in
already been noted by Moss et al. with the methoxy(phenyl)-
carbene.10 On the other hand, we have reported that 1a reacted
with methyl acrylate to give the corresponding cyclopropane
as only one diastereomer 2a.9 However, the total selectivity of
the reaction was quite surprising, and the structure only based
on questionable NMR data.
Here, we report a detailed study of the reactions of the stable
(phosphanyl)(silyl)carbenes 1a and 1b with various electron-
poor alkenes, focusing particularly on their diastereoselectivity
(syn- versus anti-attack) and diastereospecificity.
Results
We first reproduced the synthesis of the phosphanylcyclo-
propane 2a9 by addition of methyl acrylate to the carbene 1a
(Scheme 1).11a The total syn-selectivity (with respect to the
phosphanyl group), according to NMR spectroscopy, was
confirmed by a single-crystal X-ray diffraction study (Figure
1, Table 1).
According to multinuclear NMR spectroscopy, the (phos-
phanyl)(silyl)carbene 1a quantitatively reacts with 3,3,4,4,5,5,6,6,6-
nonafluorohex-1-ene, affording the cyclopropane 3a as a single
diastereomer (Scheme 2). The total syn-selectivity was suggested
(9) (a) Igau, A.; Baceiredo, A.; Trinquier, G.; Bertrand, G. Angew. Chem.,
Int. Ed. Engl. 1989, 28, 621. (b) Gillette, G. R.; Igau, A.; Baceiredo, A.;
Bertrand, G. New J. Chem. 1991, 15, 393.
(10) Moss, R. A.; Shen, S.; Hadel, L. M.; Kmiecik-Lawrynowicz, G.;
Wlostowska, J.; Krogh-Jespersen, K. J. Am. Chem. Soc. 1987, 109, 4341.
(11) (a) Igau, A.; Gru¨tzmacher, H.; Baceiredo, A.; Bertrand, G. J. Am.
Chem. Soc. 1988, 110, 6463. (b) Alcaraz, G.; Reed, R.; Baceiredo, A.;
Bertrand, G. J. Chem. Soc., Chem. Commun. 1993, 1354.
(12) Spectroscopic Methods in Organic Chemistry; Hesse, M., Meier,
H., Zeeh, B., Eds; Georg Thieme Verlag: Stuttgart, 1997; pp 202-204.

4466 J. Am. Chem. Soc., Vol. 122, No. 18, 2000
Goumri-Magnet et al.
1
Table 2. Selected H NMR Resonance Values and Coupling Constants for Cyclopropanes 7a, 10a, 12a, and 15a
δ
31P (ppm)
δ Ha (2JHH, 3J(HH)trans, 3JPH
)
δ Hb (2JHH, 3J(HH)cis, 3JPH
)
δ Hc (2J(HH)cis, 3J(HH)trans, 3JPH
)
7a
85.9 major
93.2 minor
85.9 major
93.0 minor
85.9 major
93.1 minor
90.8
1.73 (4.2, 7.3, 19.6)
2.43 (3.9, 8.6, 20.6)
not observed
2.53 (7.8, 7.3, 17.6)
2.69 (8.0, 8.6, 17.2)
2.52 (7.8, -, 17.6)
2.69 (8.5, -, 16.8)
2.50 (-, 7.3, 18.6)
2.68 (-, 7.9, 16.8)
3.35 (-, 5.4, 16.4)
10a
12a
15a
not observed
1.71 (-, 7.3, 19.4)
2.42 (-, 8.0, 22.4)
2.9 (-, 5.4, 18.8)
Figure 2. Solid-state structure of cyclopropane 6b.
Scheme 3
Figure 3. Solid-state structure of cyclopropane 7a.
Figure 2. In the unit cell, the two enantiomers corresponding
to the syn-cyclopropane 7a were observed, suggesting that a
diastereoselective crystallization occurred. However, the room
temperature 31P NMR spectrum of a CDCl3 solution of the single
crystal showed the two signals previously observed at +93 and
+86 ppm in the same 60/40 ratio! On cooling this solution to
240 K only the signal at +86 ppm was observed, while heating
at T > 363 K led to the decomposition of the product. These
results as a whole strongly suggest that a stereoselective syn-
cyclopropanation occurred leading to 6a, which exists as two
rotamers in a slow equilibrium (Scheme 3).
Figure 4. Solid-state structure of cyclopropane 7b.
Very similar results were observed using the [bis(dicyclo-
hexylamino)phosphanyl](silyl)carbene 1b.11b However, in this
case, single crystals of both the phosphanyl-substituted cyclo-
propane 6b and thioxophosphoranyl-substituted cyclopropane
7b, suitable for analysis by X-ray diffraction, were obtained
(Figures 3 and 4). These studies confirmed the exclusive
formation of the syn-cyclopropanes 6b and 7b and that
unexpected isomerization does not occur in the sulfuration
process (Scheme 3).
The phosphanylcarbene 1a also reacts with the unsymmetri-
cally substituted olefin (E)-t-BuOC(O)CHdCHC(O)OEt to give
a 9/1 mixture of cyclopropanes 8a and 8′a. The major isomer
8a was isolated by selective recrystallization as colorless crystals
in 40% yield. An X-ray diffraction study (Figure 5) unambigu-
ously established the anti-position of the tert-butyl group with
respect to the phosphanyl group.
Addition at room temperature of 3 equiv of (Z)- and (E)-2-
deuteriostyrene to the carbene 1a afforded the cyclopropanes
9a and 11a, respectively. Addition of elemental sulfur, followed
by column chromatography gave rise to the thioxophosphoranyl
Figure 5. Solid-state structure of cyclopropane 8a.
analogues 10a and 12a in 95 and 96% yield, respectively
(Scheme 5). Again, in both cases two rotamers were observed.
The relative configuration of the three stereogenic centers of
10a and 12a was determined based on the 1H NMR spectra of
cyclopropanes 7a, 10a, and 12a (Table 2). By comparing the
spectra of 7a and 10a, it is clear that Ha has been substituted
by a deuterium atom: its signal is not present and the JH H
a
c

Reactions of the Stable (Phosphanyl)(silyl)carbenes
J. Am. Chem. Soc., Vol. 122, No. 18, 2000 4467
Scheme 4
Scheme 5
Figure 6. Solid-state structure of cyclopropane 15a.
we obtained exclusively the isomer featuring the amido and
phosphanyl substituents syn to one another.
Discussion
The total syn-stereoselectivity (with respect to the phosphanyl
group) observed in the reaction of the carbenes 1 with methyl
acrylate, styrene, and the perfluoroalkene was quite surprising
(Schemes 1, 2, and 3). Indeed, looking at the molecular
structures (Figures 1-4), it is hard to believe that steric factors
could govern the observed selectivity since the bis(amino)-
phosphanyl group appears to be roughly as sterically demanding
as the trimethylsilyl group. The definitive proof that the
phosphanyl group is in fact more sterically demanding than the
trimethylsilyl group is given by the results observed with the
alkene substituted by the ethyl and tert-butyl ester groups: the
major isomer 8a features the bulkier ester group anti with respect
to the phosphanyl group.
Table 3. Philicity of Phosphino(silyl)carbene 1b toward Styrenes
X
X
kX/kH
Since the syn-selectivity observed with the carbenes 1 is not
due to steric factors, the obvious other possibility is to invoke
orbital-controlled reactions. Thus, it was first necessary to check
that the cyclopropanation reactions were concerted (or at least
quasiconcerted). Although the total stereospecificity observed
in the reaction of 1a with (Z)- and (E)-2-deuteriostyrene is not
a definitive proof for the concerted nature of the cyclopropa-
nation reactions, this is a strong argument13 (Scheme 5).
CH3O
H
F
H
H
H
H
0.88
1
1.7
7
CF3
Scheme 6
Before drawing a reasonable hypothesis to explain the
observed syn-selectivity, it was necessary to check whether
carbenes 1 are nucleo- or electrophilic in character.2a Indeed,
although their nucleophilic character appears from the calcula-
tions,14 we recently reported that 1b reacted with phosphines
to give the correspnding phosphorus ylides,15 which suggests
that 1b features an accessible vacant orbital and therefore could
behave as an electrophile. The results observed with different
styrene derivatives (Table 3) leave no doubt that the carbenes
1 are the nucleophilic partners in the cycloaddition reaction with
olefins. For example, using the same set of styrene derivatives,
but the electrophilic H-C-CO2Et carbene generated by copper-
catalyzed decomposition of the corresponding ethyl diazoacetate,
coupling constant is not observed. In the spectrum of 12a, the
signals of both Ha and Hc are present, but no coupling constants
with Hb are observed. In both cases, no trace of other isomers
was detected.
Interestingly, photolysis at 300 nm of the diazo precursor 13a
in the presence of (Z)-2-deuteriostyrene led after sulfuration to
a 9/1 mixture of cyclopropanes 10a and 12a (Scheme 5).
However, we have checked that irradiation of (Z)-2-deuteri-
ostyrene under the same experimental conditions (during the
same period of time) gave a 9/1 mixture of (Z)- and (E)-2-
deuteriostyrene.
(13) The stereochemical results are most compatible with concerted
addition of 1a to styrene, in accord with typical singlet carbene behavior,
and with the lack of theoretical prohibition of concerted nucleophilic
carbene-olefin [1+2] cycloadditions. However, there is no spin-inversion
barrier to rapid closure of a 1,3-dipole, so that a two-step singlet carbene
addition is not as certain to occur nonstereospecifically as in a triplet carbene
addition, which proceeds via a triplet 1,3-diradical. Moss, R. A.; Huselton,
J. K. J. Chem. Soc., Chem. Commun. 1976, 950.
(14) (a) Nguyen, M. T.; McGinn, M. A.; Hegarty, A. F. Inorg. Chem.
1986, 25, 2185. (b) Hoffmann, M. R.; Kuhler, K. J. Chem. Phys. 1991, 94,
8029. (c) Dixon, D. A.; Dobbs, K. B.; Arduengo, A. J., III; Bertrand, G. J.
Am. Chem. Soc. 1991, 113, 8782. (d) Nyulaszi, L.; Szieberth, D.; Reffy, J.;
Veszpremi, T. J. Mol. Struct. (THEOCHEM) 1998, 453, 91.
Competitive reactions of phosphinocarbene 1b with various
para-substituted styrenes have been carried out, and the results
are summarized in Table 3.
The carbene 1a also readily reacts at room temperature with
(E)-Me2NCOCHdCHCO2Me to give the corresponding cyclo-
propane 14a, in near quantitative yield. Treatment with elemen-
tal sulfur gave the corresponding thioxophosphoranyl derivative
15a (45% yield) (Scheme 6), which was fully characterized
including by an X-ray diffraction study (Figure 6). Interestingly,
(15) Goumri-Magnet, S.; Polishchuk, O.; Gornitzka, H.; Marsden, C. J.;
Baceiredo, A.; Bertrand, G. Angew. Chem., Int. Ed. Engl. 1999, 38, 3727.

4468 J. Am. Chem. Soc., Vol. 122, No. 18, 2000
Goumri-Magnet et al.
Scheme 7
somerization of the alkene, while using the stable carbene 1a,
only 9a is formed.
Figure 7. Schematic representation of the cycloaddition of phosphino-
(silyl)carbene to acroleine.
the reverse relative rate of cyclopropanation has been observed.16
It is important to note that in the latter case a range of syn/anti
isomers from 1:1 to 1:15 was obtained.16
Conclusion
These results present convincing evidence for the concerted
nature of cyclopropanation reaction and therefore the genuine
singlet carbene nature of stable phosphanylsilylcarbenes. To
date, the observed diastereoselectivity (where present) of
cyclopropanation reactions involving transient nucleophilic
singlet carbenes has been rationalized by steric factors.22 Here,
we demonstrate that the diastereoselectivity is due to second-
order orbital interactions, in a manner analogous to the well-
known endo rule for the Diels-Alder reaction. These reactions
allow the diastereoselective synthesis of various cyclopropanes
with simultaneous control of two or even three stereogenic
centers. The enantioselective version of this reaction is under
active investigation.
At this point, it seems clear that the (phosphanyl)(silyl)-
carbenes have to be compared with methoxymethylcarbene17
for which the nucleophilic character is strongly expressed but
its electrophilicity not totally suppressed (as observed for the
dimethoxycarbene).18 Therefore, in the transition state, the more
dominant orbital interaction is between the HOMOcarbene and
the LUMOalkene (Figure 7a), but this set of orbitals does not
explain the observed syn-selectivity. However, in the course of
computational and experimental19 work on the addition of
carbenes to alkenes the significance of a second pair of orbital
interactions in the addition geometry has been pointed out. Thus,
our hypothesis was that the secondary orbital interaction
LUMOcarbene-HOMOalkene (Figure 7b) should explain the
selectivity observed. Due to donation of the phosphorus lone
pair, the LUMOcarbene has some π*(PC) character and shows
significant bonding overlap between the phosphorus center and
the alkene substituent, as indicated schematically in Figure 7b.
In other words, like the endo selectivity in the Diels-Alder
reaction,20 the high stereoselectivity observed could be rational-
ized on the basis of favorable “secondary orbital interactions”.
Experimental Section
All manipulations were performed under an inert atmosphere of
argon using standard Schlenk techniques. Dry, oxygen-free solvents
1
were employed. H, 13C, 19F, and 31P NMR spectra were recorded on
1
Brucker AC80, AC200, WM250, or AMX400 spectrometers. H and
13C chemical shifts are reported in ppm relative to Me4Si as external
standard. 31P and 19F NMR downfield chemical shifts are expressed
with a positive sign, in ppm, relative to external 85% H3PO4 and CF3-
CO2H, respectively. Infrared spectra were recorded on a Perkin-Elmer
FT-IR Spectrometer 1725 X. Mass spectra were obtained on a Ribermag
R10 10E instrument.
The effectiveness of the secondary orbital interactions on the
selectivity of cyclopropanation reactions is demonstrated by the
exclusive formation of 14a (Scheme 6). Not surprisingly, simple
Hu¨ckel calculations show that the highest coefficient of the
HOMO of the alkene is located at the amido group, and thus
despite the smaller steric demand of the ester group, the amido
substituent lies syn with respect to the phosphanyl group.
Preparation of the Carbenes 1a,b. In a typical experiment,
phosphanyl(silyl)carbenes 1a,b were obtained by irradiation (300 nm,
8 h) of a pentane solution (3 mL) of the corresponding phosphanyl-
(silyl)diazomethane11 (0.30 mmol). According to 31P NMR spectroscopy
the reactions were quantitative and the carbenes 1a,b were used without
any further purification.
On the other hand, the synthetic importance of having stable
carbenes is nicely illustrated by the reaction of the phospha-
nyldiazomethane 5a with the perfluoro-substituted alkene, which
leads to the anti-cyclopropane 4′a, while desilylation of 3a
affords the syn-cyclopropane 4a (Scheme 2). Since in the
absence of olefin the diazo derivative 5a is stable toward
nitrogen elimination, it is quite clear that the formation of 4′a
does not involve the carbene 1c but results from a [3+2]-
cycloaddition process giving the transient pyrazoline 16a, which
undergoes a classical nitrogen elimination21 (Scheme 7). Note
also that when the carbene 1a is generated under irradiation in
the presence of (Z)-2-deuteriostyrene, a mixture of cis- and
trans-cyclopropanes 9a and 11a is obtained due to the photoi-
General Procedure for Cycloaddition Reactions with the Car-
benes 1a,b. To a pentane solution (3 mL) of the carbene 1 (0.3 mmol)
was added at room temperature 3 equiv of alkene. The resulting mixture
was stirred at room temperature and the progress of the reaction was
monitored by 31P NMR spectroscopy. After the reaction was complete
(1-3 h), volatile components were removed under reduced pressure,
and the phosphanylcyclopropanes were analyzed without any further
purification. Treatment of a thf solution of phosphanylcyclopropanes
with an excess of elemental sulfur gave the corresponding thioxophos-
phoranyl derivatives, which were purified as indicated for each
compound by column chromatography on silica gel.
3a: Yellow oil. 31P{1H} NMR (CDCl3) δ 78.2 (d, 4JPF ) 178.5 Hz);
19F{1H} NMR (CDCl3: δ -51.3 and -46.0 (m, CF3-CF2-CF2-),
2
2
-34.2 (dd, JFF ) 265.1 Hz, JPF ) 178.5 Hz, CF2-CH), -25.9 (s,
(16) Diaz-Requejo, M. M.; Pe´rez, P. J.; Brookhart, M.; Templeton, J. L.
Organometallics 1997, 16, 4399.
(17) Sheridan, R. S.; Moss, R. A.; Wilk, B. K.; Shen, S.; Wlostowski,
M.; Kesselmayer, M. A.; Subramanian, R.; Kmiecik-Lawrynowicz, G.;
Krogh-Jespersen, K. J. Am. Chem. Soc. 1988, 110, 7563.
(18) Dunn, J. A.; Pezacki, J. P.; McGlinchey, M. J.; Warkentin, J. J.
Org. Chem. 1999, 64, 4344 and references therein.
(19) (a) Keating, A. E.; Merrigan, S. R.; Singleton, D. A.; Houk, K. N.
J. Am. Chem. Soc. 1999, 121, 3933. (b) Rondan, N. G.; Houk, K. N.; Moss,
R. A. J. Am. Chem. Soc. 1980, 102, 1770.
3
CF2-CH), -5.0 (t, JFF ) 9.0 Hz, CF3).
4a: To a thf solution (3 mL) of the cyclopropane 3a (0.1 g, 0.18
mmol) was added at room temperature 1 equiv of Bu4NF (0.05 g, 0.18
mmol). The reaction was monitored by 31P NMR spectroscopy, and
the cyclopropane 4a was obtained after 3 h in near-quantitative yield
(according to NMR spectroscopy). 31P{1H} NMR (CDCl3) δ 44.1 (d,
4JPF ) 145.9 Hz); 19F{1H} NMR (CDCl3) δ -49.7 and -47.1 (m, CF3-
2
2
CF2-CF2-), -43.1 (dd, JFF ) 268.1 Hz, JPF ) 145.9 Hz, CF2-
CH), -28.7 (s, CF2-CH), -5.1 (m, CF3).
(20) “Endo rule”: Woodward, R. B.; Hoffmann, R. The conserVation of
Orbital Symmetry; Verlag Chemie: Weinheim, 1971.
(21) Regitz, M.; Heydt, H. In 1,3-Dipolar Cycloaddition Chemistry;
Padwa, A., Ed.; Wiley: New York, 1984; Vol. 1, pp 393-558.
(22) See, for example: Brahms, D. L. S.; Dailey, W. P. Chem. ReV.
1996, 96, 1585.

Reactions of the Stable (Phosphanyl)(silyl)carbenes
J. Am. Chem. Soc., Vol. 122, No. 18, 2000 4469
4′a: A pentane solution (3 mL) of the diazo compound 5a11a (0.1 g,
0.37 mmol) and nonafluoro-1-hexen (193 µL, 1.11 mmol) was heated
at 40 °C. The reaction was monitored by 31P NMR spectroscopy, and
the cyclopropane 4′a was obtained after 2 h in near-quantitative yield
(according to the NMR spectroscopy). 31P{1H} NMR (CDCl3) δ 50.6;
19F{1H} NMR (CDCl3) δ -50.1 and -46.2 (m, CF3-CF2-CF2-),
95%). Mp 163-164 °C; 31P{1H} NMR (CDCl3) δ 85.9 and 93.1 (2
1
rotamers 60/40); H NMR (CDCl3) major rotamer δ 0.25 (s, 9 H,
3
3
SiCH3), 1.07-1.54 (m, 24 H, CHCH3), 1.71 (dd, JHH ) 7.3 Hz, JPH
) 19.4 Hz, 1 H, CHD), 2.50 (dd, 3JHH ) 7.3 Hz, 3JPH ) 18.6 Hz, 1 H,
CH), 3.85 (m, 4 H, CHCH3), 7.19-7.80 (m, 5 H, Harom), minor rotamer
2.42 (dd, 3JHH ) 8.0 Hz, 3JPH ) 22.4 Hz, 1 H, CHD), 2.68 (dd, 3JHH
7.9 Hz, JPH ) 16.8 Hz, 1 H, CH).
)
3
3
-35.4 (m, CF2-CH), -5.0 (t, JFF ) 8.7 Hz, CF3).
6a: 31P{1H} NMR (C6D6) δ 76.6 and +61.0 ppm (2 rotamers, 90/
10 ratio).
Reaction of the Diazo 13a in the Presence of (Z)-2-Deuteriosty-
rene. A pentane solution (3 mL) of phosphanyl(silyl) diazomethane
(13a, 0.10 g, 0.30 mmol) and 3 equiv of (Z)-2-deuteriostyrene (0.09 g,
0.90 mmol) was irradiated at 300 nm for 18 h. According to 31P NMR
spectroscopy the reaction was quantitative (δ 73.5). Treatment of the
solution mixture with an excess of elemental sulfur gave the thioxo-
phosphoranyl derivatives 10a and 12a in a 90/10 ratio (according to
1H NMR spectroscopy).
7a: (pentane/ether, 98/2, RF ) 0.6). (0.12 g; 90%). Mp 163-164
°C; 31P{1H} NMR (C6D6) δ 85.9 and 93.2 (2 rotamers, 60/40); 1H NMR
3
(C6D6) major rotamer δ 0.33 (s, 9 H, SiCH3), 0.50 (d, 6 H, JHH
)
3
7.0 Hz, CHCH3), 1.13 (d, 6 H, JHH ) 6.8 Hz, CHCH3), 1.29-1.50
2
3
3
(m, 12 H, CHCH3), 1.73 (ddd, JHH ) 4.2 Hz, JHH ) 7.3 Hz, JPH
)
3
3
19.6 Hz, 1 H, CH2), 2.53 (td, JHH ) 7.8 Hz, JPH ) 17.6 Hz, 1 H,
CH), 3.54-4.11 (m, 4 H, CHCH3), 7.17-7.61 (m, 5 H, Harom), one of
the CH2 protons was not observed, minor rotamer δ 0.30 (s, 9 H,
SiCH3), 1.27-1.51 (m, 24 H, CHCH3), 2.43 (ddd, 2JHH ) 3.9 Hz, 3JHH
1
14a: Yellow oil. 31P{1H} NMR (C7D8) δ 94.0; H NMR (C7D8) δ
4
3
0.65 (d, JPH ) 1.0 Hz, 9 H, SiCH3), 1.45 (d, 6 H, JHH ) 6.8 Hz,
3
3
CHCH3), 1.49 (d, 6 H, JHH ) 6.8 Hz, CHCH3), 1.55 (d, 6 H, JHH
)
) 8.6 Hz, 3JPH ) 20.6 Hz, 1 H, CH2), 2.69 (td, 3JHH ) 8.0 Hz, 3JPH
)
3
6.8 Hz, CHCH3), 1.71 (d, 6 H, JHH ) 6.8 Hz, CHCH3), 2.81 (s, 3 H,
CH3N), 2.84 (s, 3 H, CH3N), 3.00 (dd, 3JHH ) 6.4 Hz, 3JPH ) 4.8 Hz,
17.2 Hz, 1 H, CH), 3.54-4.11 (m, 4 H, CHCH3), 7.17-7.61 (m, 5 H,
arom), one of the CH2 protons was not observed; 13C{1H} NMR (C6D6)-
3
3
H
1 H, CHring), 3.50 (dd, JHH ) 6.4 Hz, JPH ) 11.4 Hz, 1 H, CHring),
3.59 (s, 3 H, CH3O), 3.80 (sept d, 3JHH ) 6.8 Hz, 3JPH ) 9.0 Hz, 4 H,
CHCH3); 13C{1H} NMR (C7D8) δ 1.9 (d, 3JPC ) 8.8 Hz, SiCH3), 24.8
(d, 3JPC ) 4.9 Hz, CHCH3), 24.9 (d, 3JPC ) 3.5 Hz, CHCH3), 34.6 (d,
2JPC ) 3.4 Hz, CHring), 35.8 (s, CH3N), 35.9 (d, 2JPC ) 7.2 Hz, CHring),
36.7 (d, 1JPC ) 100.0 Hz, PCSi), 37.5 (s, CH3N), 51.6 (s, CH3O), 52.4
(d, 2JPC ) 15.9 Hz, CHN), 170.8 (d, 3JPC ) 6.5 Hz, CO), 174.1 (d, 3JPC
) 5.2 Hz, CO).
2
major rotamer δ 0.6 (s, SiCH3), 15.1 (d, JPC ) 5.1 Hz, CH2), 21.0
1
3
(d, JPC ) 91.6 Hz, PC), 23.7 (d, JPC ) 6.9 Hz, CHCH3), 24.0 (s,
3
CHCH3), 25.5 (s, CHCH3), 26.6 (d, JPC ) 1.2 Hz, CHCH3), 29.6 (d,
2
4
2JPC ) 5.9 Hz, CH), 48.2 (d, JPC ) 6.0 Hz, CHN), 126.9 (d, JPC
)
17.4 Hz, Co), 128.2 (s, Cp), 130.8 (d, 4JPC ) 8.5 Hz, Cm), 137.5 (s, Ci).
Anal. Calcd for C24H45N2SiPS: C, 63.67; H, 10.02; N, 6.19. Found:
C, 64.01; H, 10.15; N, 5.98.
6b: Yellow crystals from a pentane solution at -20 °C (0.16 g,
95%). Mp 210-211 °C; 31P{1H} NMR (CDCl3) δ 76.4 and +67.4 ppm
(2 rotamers, 95/5 ratio). Anal. Calcd for C36H61N2SiP: C, 70.43; H,
10.58; N, 4.82. Found: C, 70.23; H, 10.45, N, 4.65.
7b (hexane/ether, 95/5, RF ) 0.8): Pale yellow crystals were obtained
by slow evaporation of a pentane solution (0.16 g; 90%). Mp 196-
197 °C; 31P{1H} NMR (CDCl3) δ 84.4. Anal. Calcd for C36H61N2-
SiPS: C, 70.54; H, 10.03; N, 4.57. Found: C, 70.14; H, 9.83, N, 4.71.
15a: White crystals obtained by slow evaporation of a ether solution
(0.06 g; 45%). Mp 191-192 °C dec; 31P{1H} NMR (C7D8) δ 90.8; 1H
NMR (C7D8) δ 0.76 (s, 9 H, SiCH3), 1.20-2.17 (m, 24 H, CHCH3),
3
3
2.90 (dd, JHH ) 5.4 Hz, JPH ) 18.8 Hz, 1 H, CHring), 2.89 (s, 3 H,
3
CH3N), 3.07 (s, 3 H, CH3N), 3.34 (s, 3 H, CH3O), 3.35 (dd, JHH
)
5.4 Hz, 3JPH ) 16.4 Hz, 1 H, CHring), 4.23, 4.44, 4.50, and 4.63 (m, 4
H, CHCH3); 13C{1H} NMR (C7D8) δ 4.3 (s, SiCH3), 23.0 (s, CHCH3),
3
23.8 (s, CHCH3), 25.6 (s, CHCH3), 25.8 (s, CHCH3), 25.9 (d, JPC
)
8a and 8′a: 31P{1H} NMR (CD2Cl2, 293 K) δ 89.7 very large. By
cooling the sample, two rotamers were observed for each compound,
31P{1H} NMR (CD2Cl2, 223 K) δ 96.5 and 88.0 (major isomer 8a),
87.8 and 87.0 (minor isomer 8′a). At 193 K, only one rotamer was
detected for each isomer,31P{1H} NMR (CD2Cl2, 193 K) δ 88.0 (8a),-
and 87.8 (8′a) (90/10 ratio). The major isomer 8a precipitated from a
pentane solution at -50 °C as colorless crystals (0.04 g; 40%). Mp
2
2
4.2 Hz, CHCH3), 29.2 (d, JPC ) 3.1 Hz, CHring), 33.6 (d, JPC ) 2.7
1
Hz, CHring), 34.9 (d, JPC ) 79.7 Hz, PCSi), 35.6 (s, CH3N), 39.3 (s,
CH3N), 53.1 (s, CH3O), 47.3 (s, CHN), 47.8 (d, 2JPC ) 7.4 Hz, CHN),
50.1 (s, CHN), 51.7 (d, 2JPC ) 8.2 Hz, CHN), 166.2 (d, 3JPC ) 6.6 Hz,
CO), 171.9 (d, 3JPC ) 4.4 Hz, CO). Anal. Calcd for C23H48N3O3SiPS:
C, 54.62; H, 9.57; N, 8.31. Found: C, 54.83; H, 9.70; N, 8.41.
Competition Experiments (p-X-C6H4-CHdCH2 vs C6H4-CHd
CH2) Using Carbene 1b. In a typical experiment, 1 equiv of styrene
and 1 equvi of para-substituted-styrene (X ) CH3O, F, CF3) was added
at room temperature to a pentane solution (3 mL) of phosphanyl(silyl)-
carbene 1b. When the reaction had reached completion (1-3 h), volatile
components were removed in vacuo, and the ratios of the resulting
cyclopropanes were determined by 1H NMR spectroscopy without any
further purification. The phosphanylcyclopropanes resulting from the
reaction of 1b with the different para-substituted-styrenes were
independently prepared. X ) CH3O: 31P{1H} NMR (CDCl3) δ 76.7
and +68.5 (2 rotamers, 90/10 ratio); 1H NMR (CDCl3) δ 0.11 (s, 9 H,
SiCH3), 0.53-1.64 (m, 41 H, CH2 and CHring), 2.51-2.89 (m, 6 H,
CHN and CHring), 3.64 (s, 3 H, CH3O), 6.54-7.17 (m, 5 H, CHarom). X
) F: 31P{1H} NMR (CDCl3) δ 76.2 and +67.7 (2 rotamers, 90/10
ratio); 1H NMR (CDCl3) δ 0.12 (s, 9 H, SiCH3), 0.81-1.63 (m, 41 H,
CH2 and CHring), 2.52-3.04 (m, 6 H, CHN and CHring), 6.73-7.15
(m, 5 H, CHarom). X ) CF3: 31P{1H} NMR (CDCl3) δ 76.3 and +67.9
1
147-148 °C; H NMR (CD2Cl2, 193 K) δ 0.23 (s, 9 H, SiCH3), 1.22
(d, 12 H, 3JHH ) 6.7 Hz, CHCH3), 1.23 (d, 6 H, 3JHH ) 6.7 Hz, CHCH3),
3
1.29 (d, 3 H, JHH ) 7.2 Hz, OCH2CH3), 1.43 (s, 9H, tBu), 2.56 (tlike
,
3JHH ) 3JPH ) 6.1 Hz, 1 H, CHring), 2.73 (dd, 1 H, 3JHH ) 6.0 Hz, 3JPH
) 12.2 Hz, CHring), 3.50 (m, 4 H, CHCH3), 4.00 (dq, 1 H, 3JHH ) 7.2
Hz, 2JHH ) 10.8 Hz, OCH2CH3), 4.22 (dq, 1 H, 3JHH ) 7.2 Hz, 2JHH
10.8 Hz, OCH2CH3); 13C{1H} NMR (CD2Cl2, 193 K) δ 0.9 (d, 3JPC
)
)
9.6 Hz, SiCH3), 14.5 (s, OCH2CH3), 24.5 (d, 3JPC ) 17.5 Hz, CHCH3),
26.9 (d, 3JPC ) 15.3 Hz, CHCH3), 28.1 (s, OC(CH3)3), 34.8 (d, 2JPC
)
2
1
2.3 Hz, CHring), 35.7 (d, JPC ) 9.0 Hz, CHring), 38.1 (d, JPC ) 91.8
2
2
Hz, PCSi), 45.1 (d, JPC ) 37.9 Hz, CHN), 51.1 (d, JPC ) 10.0 Hz,
3
CHN), 61.4 (s, OCH2CH3), 81.0 (s, OC(CH3)3), 172.8 (d, JPC ) 5.4
3
Hz, CO), 174.8 (d, JPC ) 8.0 Hz, CO). Anal. Calcd for C26H53N2O4-
PSi: C, 60.43; H, 10.34; N, 5.42; Found: C, 60.22; H, 10.28; N, 5.36.
9a: 31P{1H} NMR (C6D6) δ 73.5.
10a (pentane/ether, 98/2, RF ) 0.6): Colorless crystals of 10a were
obtained by slow evaporation of a dichloromethane solution (0.13 g;
95%). Mp 161-162 °C; 31P{1H} NMR (C7D8) δ 85.9 and 93.0 (2
rotamers, 60/40); 1H NMR (C7D8) major rotamer δ 0.51 (s, 9 H,
1
(2 rotamers, 90/10ratio); H NMR (CDCl3) δ 0.14 (s, 9 H, SiCH3),
0.43-1.99 (m, 41 H, CH2 and CHring), 2.56-2.96 (m, 6 H, CHN and
CHring), 7.24-7.39 (m, 5 H, CHarom).
SiCH3), 1.11 (d, 12 H, 3JHH ) 7.0 Hz, CHCH3), 1.13 (d, 12 H, 3JHH
)
X-ray Crystallographic Studies of Compounds 2a, 6b, 7a, 7b,
8a, and 15a. Crystal data for all structures are presented in Table 1.
Data for 6b, 7a, 7b, and 15a were collected at low temperatures on a
Stoe-IPDS diffractometer and data for 2a and 8a were collected at room
temperature on a Bruker-CCD with Mo KR (λ ) 0.71073 Å). The
structures were solved by direct methods by means of SHELXS-9723
7.0 Hz, CHCH3), 2.52 (dd, 3JHH ) 7.8 Hz, 3JPH ) 17.6 Hz, 1 H, CH),
the proton of CDH was not observed, 4.32 (m, 4 H, CHCH3), 7.22-
3
3
7.71 (m, 5 H, Harom), minor rotamer δ 2.69 (dd, JHH ) 8.5 Hz, JPH
) 16.8 Hz, 1 H, CH), the proton of CDH was not observed.
11a: 31P{1H} NMR (C6D6) δ 73.5.
12a (pentane/ether, 98/2, RF ) 0.5): Colorless crystals of 12a were
obtained by slow evaporation of a dichloromethane solution (0.13 g;
(23) Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467.

4470 J. Am. Chem. Soc., Vol. 122, No. 18, 2000
Goumri-Magnet et al.
and refined with all data on F2 by means of SHELXL-97.24 All non-
hydrogen atoms were refined anisotropically. The hydrogen atoms of
the molecules were geometrically idealized and refined using a riding
model. Refinement of an inversion twin parameter25 [x ) -0.16(9); x
) 0 for the correct absolute structure and x ) +1 for the inverted
structure] confirmed the absolute structure of 15a.
Acknowledgment. Thanks are due to the French Embassy
in Tokyo for a grant (to T.K.) and to the CNRS for financial
support of this work.
Supporting Information Available: X-ray crystallographic
data for compounds 2a, 6b, 7a, 7b, 8a, and 15a (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
(24) Sheldrick, G. M., SHELXL-97, Program for Crystal Structure
Refinement, Universitat Gottingen, 1997.
(25) Flack, H. D. Acta Crystallogr. Sect. A 1983, 39, 876.
JA994408B