Synthesis of a donor-stabilized silacyclopropan-1-one

Article abstract of DOI:10.1002/anie.201210010

As intriguing as the Bermuda Triangle: The synthesis and characterization of an isolable silacyclopropan-1-one (see structure; red O, blue N, green Si, yellow P) was made possible by stabilization through intramolecular coordination by a Lewis base. However, this silacyclopropan-1-one, which contains a significantly elongated endocyclic C-C σ bond, remains highly reactive and underwent an unprecedented silanone-silenol rearrangement under mild conditions. Copyright

Full text of DOI:10.1002/anie.201210010

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Angewandte
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DOI: 10.1002/anie.201210010
Small-Ring Systems
Synthesis of a Donor-Stabilized Silacyclopropan-1-one**
Ricardo Rodriguez, Thibault Troadec, David Gau, Nathalie Saffon-Merceron,
Daisuke Hashizume, Karinne Miqueu, Jean-Marc Sotiropoulos, Antoine Baceiredo,* and
Tsuyoshi Kato*
Cyclopropanones I are highly reactive ketones that display
unusual properties due to the incorporation of a carbonyl
group in a strained three-membered ring. In particular,
substituted cyclopropanones may undergo ring opening to
form oxyallyl zwitterions II,[1] which can behave as 1,3-
dipoles.[2] Inherently reactive, oxyallyl zwitterions II have
been implicated as intermediates in a number of organic
reactions,[3] although there have been very few reports of the
direct experimental observation of oxyallyl intermediates.[4]
The bicyclobutanone III, with increased ring strain, has
The synthesis of the silicon analogue of I, silacyclopropan-
1-one IV, remained elusive. Indeed, in contrast to stable
organic carbonyl compounds, silanones are highly reactive
À
intermediates owing to a weak and strongly polarized Si O
p bond.[6] Therefore, they readily oligomerize to give poly-
siloxanes.[7,8] The stabilization of such species is possible by
the coordination of electron-donating ligands to the silicon
center. This approach enabled the isolation of the first
examples of base-stabilized silaureas V[9] and silacarbamates
VI.[10] Several donor/acceptor-stabilized silacarbonyl com-
pounds have been reported.[11] However, no silicon analogue
of ketones (a silaketone or silanone VII) has previously been
reported, and only one example of a transition-metal–
silanone complex has been described.[12] Herein, we report
the synthesis of the first donor-stabilized silacyclopropan-1-
one 2 (Scheme 1), which has a hybrid structure with an
a unique hybrid structure between a cyclopropanone and an
[5]
À
oxyallyl zwitterion, with a long endocyclic C C bond.
Scheme 1. Synthesis of the base-stabilized silacyclopropan-1-one 2.
important oxyallyl character, and its unprecedented isomer-
ization to a stable silenol derivative.
[*] Dr. R. Rodriguez, Dr. T. Troadec, Dr. D. Gau, Dr. A. Baceiredo,
Dr. T. Kato
We recently reported the synthesis of the first stable base-
supported silacycloprop-1-ylidene 1.[13] Silylene 1 readily
reacts at room temperature with nitrous oxide (N2O) to
afford the corresponding silacyclopropan-1-one 2, with the
elimination of N2 (Scheme 1). Colorless crystals of the
silanone 2 were obtained in 85% yield from a solution in
CHCl3/Et2O (1:5). The diastereoselectivity of the reaction was
indicated by the presence of a singlet in the 31P NMR
spectrum (d = 46.6 ppm). The 29Si NMR spectrum revealed
a doublet (d = À69.1 ppm, 2JP, S i = 6.8 Hz) at a lower field than
that at which the doublet for 1 appeared (d = À87.5 ppm,
2JPSi = 2.9 Hz), but approximately in the range observed for
previously reported Lewis base stabilized silacarbonyl com-
pounds Vand VI (d = À71 to À86 ppm).[9,10] The signal for the
hydrogen atom on the cyclopropanone ring appeared in the
1H NMR spectrum as a doublet at d = 3.02 ppm with a rela-
Universitꢀ de Toulouse, UPS, and CNRS
LHFA UMR 5069, 31062 Toulouse (France)
E-mail: baceired@chimie.ups-tlse.fr
kato@chimie.ups-tlse.fr
Homepage: http://hfa.ups-tlse.fr
Dr. N. Saffon-Merceron
Universitꢀ de Toulouse, UPS, and CNRS, ICT FR2599
118 route de Narbonne, 31062 Toulouse (France)
Dr. R. Rodriguez, Dr. D. Hashizume
Advanced Technology Support Division, RIKEN Advanced Science
Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)
Dr. K. Miqueu, Dr. J.-M. Sotiropoulos
Universitꢀ de Pau et des Pays de l’Adour and CNRS IPREM UMR
5254, Technopꢁle Hꢀlioparc
2 avenue du Prꢀsident Angot, 64053 Pau (France)
[**] We are grateful to the CNRS and the ANR (NOPROBLEM, LEGO)
for financial support of this research. R.R. acknowledges the JSPS
for a postdoctoral fellowship. For the theoretical studies, access to
the HPC resources of Idris was granted by GENCI (Grand Equipe-
ment National de Calcul Intensif) under allocation 2012
(i2012080045).
tively large phosphorus–proton coupling constant (3JP, H
=
29.1 Hz).
The structure of 2 was confirmed unambiguously by X-ray
diffraction analysis (Figure 1).[14] The short Si1–O distance
(1.547 ꢀ) is very similar to those in the previously reported
base-stabilized silanones (1.532–1.579 ꢀ).[9,10] As a result of
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201210010.
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Figure 1. Molecular structure of 2. Thermal ellipsoids represent 50%
probability. Hydrogen atoms are omitted for clarity. Selected bond
lengths [ꢂ] and angles [8]: Si1–O 1.5467(6), Si1–C1 1.9177(7), Si1–C2
1.8358(6), C1–C2 1.6671(9), Si1–N1 1.7641(6), C1–P1 1.7777(6), P1–
C3 1.7351(7), C3–C4 1.3799(9), C4–N1 1.3658(8); C1-Si1-C2 52.68(3),
Si1-C1-C2 61.13(3), Si1-C2-C1 66.18(3), C1-P1-C3 107.16(3), O-Si1-C1
127.76(3), O-Si1-C2 127.48(3), O-Si1-N1 114.97(3), N1-Si1-C1
109.01(3), N1-Si1-C2 110.38(3).
the oxidation of the Si atom, a significant shortening of the
À
bonds around the silicon atom was observed (Si1 C1 1.918,
À
À
À
À
Si1 C2 1.836, Si1 N1 1.764 ꢀ for 2; Si1 C1 1.996, Si1 C2
À
1.929, Si1 N1 1.8525 ꢀ for 1). The most striking feature of 2 is
the very long endocyclic C1 C2 bond (1.667 ꢀ), which is
significantly longer than the corresponding C C bond in the
starting silacycloprop-1-ylidene 1 (1.568 ꢀ). This bond is
À
À
À
considerably longer than the corresponding s C C bond in
cyclopropanones (1.592 ꢀ)[15] and is similar in length to that
observed in the more highly strained bicyclobutanone III
(1.69 ꢀ).[4] In fact, this value is close to the lengths of the
3
3
Figure 2. Static model maps[17] for the silacyclopropanone ring: a) map
in the Si1-C1-C2 plane with bond paths and bond critical points;
À
longest C(sp ) C(sp ) single bonds known to date (1.72–
1.78 ꢀ).[16]
À
b) map on the cross-section at the bond critical point of the C1 C2
bond. Contours drawn with unbroken and dashed lines indicate
positive and negative densities, respectively. The interval is 0.05 eꢂ3.
Bold dashed lines and points indicate bond paths and bond critical
points, respectively.
To gain more insight into the electronic situation in 2, we
derived the experimental electron-density distribution from
the X-ray diffraction data.[18] The double-bond character of
À
the Si1 O bond is indicated by a significantly large density at
the bond critical point (BCP; 0.213 eauÀ3); for comparison,
a Si O single bond has a density of 0.135 eauÀ3 at the BCP.[19]
À
[21]
À
As suggested by the unusual length observed in the X-ray
for Si1 C2)
relative to those for the starting material
À3
À
À
À
crystal structure, the bond density of the endocyclic C1 C2
1 (0.093 for Si1 C1 and 0.097 eau for Si1 C2) clearly
indicate their enhanced multiple-bonding character. The
s bond is highly deformed towards the Si1 atom (the BCP is
À
located inside the three-membered ring), in contrast to the
higher electron density of the Si1 C2 bond relative to that
À
À
Si C bonds, for which the BCP is found outside the ring, as is
of the Si1 C1 bond suggests a greater contribution of the
typical for strained s bonds in three-membered rings
canonical structure 2B (Scheme 2).
(Figure 2).[20] These results strongly suggest an electron
These experimental observations were supported by
theoretical calculations performed at the M06/6-31G** level
of theory. Indeed, the optimized structure of 2 agrees quite
À
delocalization of the C C s bond towards the silicon atom.
Furthermore, as a result of this delocalization, the electron
À
density at the BCP (C1 C2) is significantly lower
(0.164 eauÀ3) than that of classical C C single bonds
À
À3
À
(0.262 eau ). The C C s-bond electrons probably interact
through negative hyperconjugation by an in-plane p inter-
action with low-lying vacant orbitals on the silicon atom.
Indeed, the significantly increased electron densities at the
À3
À
À
BCPs of the Si C bonds (0.113 for Si1 C1 and 0.138 eau
Scheme 2. Canonical structures of 2.
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Angewandte
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well with the experimental data, particularly the calculated
C C endocyclic bond length (1.655 ꢀ).[22] Furthermore, AIM
À
(“atoms in molecules”) calculations revealed a very small
À
electron density 1(r) at the BCP of the long endocyclic C C
bond (0.185 eauÀ3). This value is much smaller than the
typical value for
a classical s bond, such as that in
1 (0.217 eauÀ3). More interestingly, natural bonding orbital
(NBO) analysis indeed revealed an interaction between the
À
endocyclic C C s bond and the antibonding orbitals at the
silicon center of 2 of considerable strength (33 kcalmolÀ1).
À
As expected, the very long C1 C2 bond in 2 is thermally
labile. This property was demonstrated by the facile isomer-
ization of 2 under mild conditions (808C) with the quantita-
tive formation of an unprecedented Lewis base supported 1-
silenol derivative 3 (Scheme 3). The 29Si NMR spectrum of 3
Figure 3. Molecular structure of 3. Thermal ellipsoids represent 30%
probability. Only hydrogen atoms on the O and C2 atoms are shown
for clarity. Selected bond lengths [ꢂ] and angles [8]: Si1–O 1.644(11),
Si1–N1 1.747(12), Si1–C2 1.890(14), Si1–C1 1.794(14), C1–P1
1.677(14), P1–C3 1.764(14), C3–C4 1.371(18), C4–N1 1.381(17), C1–
C5 1.466(19), C2–C6 1.529(19), C5–C6 1.427(19); C5-C1-P1
132.12(10), Si1-C1-C5 106.47(9), Si1-C1-P1 121.21(8).
2
exhibited a lower-field chemical shift (d = À7.1 ppm, JPSi
=
Scheme 3. Synthesis of 3 by the thermolysis of 2.
23.9 Hz) relative to that observed for 2 (d = À69.1 ppm), close
to the region for silene–Lewis base adducts (d = À18 to
À39 ppm).[23] In the 13C NMR spectrum, the signal for the Si
=
C atom appeared as a doublet at d = 48.3 ppm (2JPC
=
127.8 Hz), in the chemical-shift range typical for carbon
atoms in base-stabilized silenes (d = 40–52 ppm).[23] The
1H NMR spectrum revealed a singlet for the SiCH atom
Scheme 4. Relative energies of the silacyclopropan-1-one 2 and its
isomers.
À
(d = 3.82 ppm), in agreement with C C bond cleavage of the
three-membered ring. The structure of 3 was confirmed by X-
ray diffraction analysis (Figure 3),[14] which showed a rela-
À
tively short Si C1 bond (1.794 ꢀ), intermediate between
the silacyclopropan-1-one 2 is more stable than its silenol
tautomer 2enol (DE =+ 22.4 kcalmolÀ1). Moreover, the iso-
merization of silacyclopropanone 2 to form the five-mem-
bered-ring cyclic silenol 3 is strongly exothermic (DE =
À34.0 kcalmolÀ1).
typical single and double Si C bonds.[24] The elongation of the
À
=
Si C bond is probably due to Lewis base coordination of the
silicon center as well as p-electron delocalization to the
adjacent phosphonio fragment. On the other hand, the Si1 O
À
À
bond length (1.644 ꢀ) is typical for a single bond. To the best
of our knowledge, 3 is the first stable 1-silenol derivative to be
reported. There have only been a few studies on 1-silenols and
their derivatives, and only one stable 1-silenol ether has been
reported.[25] Nevertheless, several related compounds, such as
2-silenolates[26] and Brook-type silenes,[27] have been synthe-
sized and fully characterized.[24,28]
Calculations demonstrated that the silenol 3 is consider-
ably more stable than the corresponding keto tautomer,
silanone 3keto, by 23 kcalmolÀ1, probably as a result of the
efficient stabilization of the silene moiety by the adjacent
phosphonio center (Scheme 4). Indeed, in marked contrast,
The rearrangement reaction of 2 probably starts with C C
bond cleavage to form the silaoxyallyl isomer 4 (Scheme 3).
Intermediate 4 then undergoes cyclization through an intra-
molecular Friedel–Crafts reaction between the oxyallyl frag-
ment and one of the phenyl substituents to give a transient
a,b-unsaturated silanone 5.[29] Finally, the rearomatization of
5 by a 1,4-proton migration affords the isolated silenol
derivative 3.
In spite of the efficient stabilization of 2 by complexation
of the imine fragment, the silanone functionality remains
highly reactive. Indeed, the silacyclopropan-1-one 2 reacted
readily with dimethylphenylsilane at room temperature
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spectra of the two isomers 7/7’ and 7’’ (7/7’:7’’ = 80:20 in C6D6
and 0:100 in CDCl3).
In conclusion, we have successfully synthesized the first
stable and isolable sila analogue of ketones, the Lewis base
stabilized silacyclopropan-1-one 2, which presents a novel
silacyclopropanone–oxyallyl hybrid structure. This feature is
mainly due to negative hyperconjugation involving the strong
Lewis acidity of the silanone functionality, in spite of the
coordination of the imine fragment. Indeed, the silacyclopro-
pan-1-one 2 remains highly reactive, and its unique reactivity
also enabled the first synthesis of an isolable base-stabilized 1-
silenol, 3. Further investigations on the reactivity of these new
species are under way.
Scheme 5. Reactions of 2 with an alcohol and a silane.
=
À
Received: December 14, 2012
Published online: March 12, 2013
through Si O insertion into the Si H s bond to afford the
siloxane with seven-membered heterocyclic ring
6
a
(Scheme 5). A similar ring-opening reaction of the three-
membered silacyclopropane fragment was observed in the
reaction of the silacycloprop-1-ylidene 1 with ethyl vinyl
ketone.[13] Similarly, 2 reacted with ethanol to give the
silaester derivative 7’’, which was isolated in the solid state
and characterized by X-ray diffraction analysis (Figure 4).[14]
The bonding situation around the silicon center in 7’’ is very
Keywords: reactive intermediates · silanones · silicon ·
silylenes · small ring systems
.
[1] a) M. H. J. Cordes, J. A. Berson, J. Am. Chem. Soc. 1992, 114,
11010; b) T. Ichino, S. M. Villano, A. J. Gianola, D. J. Goebbert,
L. Velarde, A. Sanov, S. J. Blanksby, X. Zhou, D. A. Hrovat,
W. T. Borden, W. C. Lineberger, Angew. Chem. 2009, 121, 8661;
Angew. Chem. Int. Ed. 2009, 48, 8509.
[2] a) N. J. Turro, S. S. Edelson, J. R. Williams, T. R. Darling, W. B.
Hammond, J. Am. Chem. Soc. 1969, 91, 2283; b) “Recent
Aspects of Cyclopropanone Chemistry”: H. H. Wasserman,
G. M. Clark, P. C. Turley, Stereochemistry I, Topics in Current
Chemistry, Vol. 47, Springer, Berlin, 1974, p. 73; c) N. J. Turro,
Acc. Chem. Res. 1969, 2, 25.
[3] a) R. Noyori, Acc. Chem. Res. 1979, 12, 61; b) H. Takaya, S.
Makino, Y. Hayakawa, R. Noyori, J. Am. Chem. Soc. 1978, 100,
1765; c) Y. Hayakawa, K. Yokoyama, R. Noyori, J. Am. Chem.
Soc. 1978, 100, 1791; d) Y. Hayakawa, Y. Baba, S. Makino, R.
Noyori, J. Am. Chem. Soc. 1978, 100, 1786; e) K. Lee, J. K. Cha,
Org. Lett. 1999, 1, 523.
[4] For the detection of oxyallyl intermediates by UV/Vis spectros-
copy, see: T. Hirano, T. Kumaggi, T. Miyashi, K. Akiyama, Y.
Ikegama, J. Org. Chem. 1991, 56, 1907.
[5] S. Bhargava, J. Hou, M. Parvez, T. S. Sorensen, J. Am. Chem.
Soc. 2005, 127, 3704.
[6] R. C. West, CRC Handbook of Chemistry and Physics, 62nd ed.,
CRC, Boca Raton, FL, 1981, C-301, E-61.
[7] C. A. Arrington, R. C. West, J. Michl, J. Am. Chem. Soc. 1983,
105, 6176.
Figure 4. Molecular structure of 7’’. Thermal ellipsoids represent 30%
probability. Only hydrogen atoms on the C1 and C2 atoms are shown
for clarity. Selected bond lengths [ꢂ] and angles [8]: Si1–O1 1.5422(16),
Si1–O2 1.6312(16), Si1–N1 1.8062(16), Si1–C2 1.8915(18), C1–C2
1.560(3), C1–P1 1.8235(18), P1–C3 1.7357(18), C3–C4 1.393(3), N1–
C4 1.347(2); O1-Si1-O2 119.81(9), O1-Si2-N1 114.54(9), O1-Si1-C2
111.57(9), O2-Si1-C2 106.20(8), O2-Si1-N1 98.28(8).
[8] G. Raabe, J. Michl, Chem. Rev. 1985, 85, 419.
[9] a) Y. Xiong, S. Yao, R. Mꢁller, M. Kaupp, M. Driess, Nat. Chem.
2010, 2, 577; b) Y. Xiong, S. Yao, R. Mꢁller, M. Kaupp, M. Driess,
J. Am. Chem. Soc. 2010, 132, 6912; c) Y. Xiong, S. Yao, M. Driess,
J. Am. Chem. Soc. 2009, 131, 7562.
[10] S. Yao, Y. Xiong, M. Brym, M. Driess, J. Am. Chem. Soc. 2007,
129, 7268.
similar to that observed in related silacarbamates VI;[10] in
À
À
particular, the two Si O bonds have different lengths (Si1
[11] a) S. Yao, M. Brym, C. van Wꢁllen, M. Driess, Angew. Chem.
2007, 119, 4237; Angew. Chem. Int. Ed. 2007, 46, 4159; b) Y.
Xiong, S. Yao, M. Driess, Dalton Trans. 2010, 39, 9282; c) R. S.
Ghadwal, R. Azhakar, H. W. Roesky, K. Prçpper, B. Dittrich, S.
Klein, G. Frenking, J. Am. Chem. Soc. 2011, 133, 17552; d) Y.
Xiong, S. Yao, M. Driess, Angew. Chem. 2010, 122, 6792; Angew.
Chem. Int. Ed. 2010, 49, 6642; e) R. S. Ghadwal, R. Azhakar,
H. W. Roesky, K. Prçpper, B. Dittrich, C. Goedecke, G.
Frenking, Chem. Commun. 2012, 48, 8186.
À
O1: 1.542 ꢀ, Si1 O2: 1.631 ꢀ). In solution, the silaester 7’’
exists in equilibrium with a silanol tautomer. The intercon-
version of the two compounds involves a 1,4-proton migra-
tion. This silanol isomer could be either the sila-hemiacetal 7
or its ring-opened derivative 7’. However, owing to its highly
fluxional character, the complete characterization of 7/7’ is
quite difficult. The equilibrium is strongly solvent-dependent,
1
as indicated by the signals observed in the H and 13C NMR
[12] T. Muraoka, K. Abe, Y. Haga, T. Nakamura, K. Ueno, J. Am.
Chem. Soc. 2011, 133, 15365.
Angew. Chem. Int. Ed. 2013, 52, 4426 –4430
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www.angewandte.org 4429

.
Angewandte
Communications
[13] R. Rodriguez, T. Troadec, T. Kato, N. Saffon-Merceron, J.-M.
Sotiropoulos, A. Baceiredo, Angew. Chem. 2012, 124, 7270;
Angew. Chem. Int. Ed. 2012, 51, 7158.
[14] CCDC 913900 (1), 914627 (2, structure analysis), 912563 (2,
electron-density-distribution analysis), 913790 (3), and 922352
(7’’) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
[15] M. H. J. Cordes, S. de Gala, J. A. Berson, J. Am. Chem. Soc.
1994, 116, 11161.
[16] a) K. K. Baldridge, Y. Kasahara, K. Ogawa, J. S. Siegel, K.
Tanaka, F. Toda, J. Am. Chem. Soc. 1998, 120, 6167; b) H. Kawai,
T. Takeda, K. Fujiwara, M. Wakeshima, Y. Hinatsu, T. Suzuki,
Chem. Eur. J. 2008, 14, 5780.
[17] International Tables for Crystallography, Vol. C (Ed.: A. J. C.
Wilson), Kluwer Academic Publishers, Dordrecht, 1996,
pp. 627 – 645.
[18] For some other reports on electron-density analysis on the basis
of diffraction data, see: a) E. Espinosa, C. Lecomte, E. Molins, S.
Veintemillas, A. Cousson, W. Paulus, Acta Crystallogr. Sect. B
1996, 52, 519; b) K. Akiba, Y. Moriyama, M. Mizozoe, H.
Inohara, T. Nishii, Y. Yamamoto, M. Minoura, D. Hashizume, F.
Iwasaki, N. Takagi, K. Ishimura, S. Nagase, J. Am. Chem. Soc.
2005, 127, 5893.
[22] Selected bond lengths [ꢀ] and angles [8] calculated at M06/6-
31G** for 2: Si1–O 1.542, Si1–C1 1.940, Si1–C2 1.839, C1–C2
1.638, Si1–N1 1.793; C1-Si1-C2 51.29, Si1-C1-C2 61.14, Si1-C2-
C1 67.57.
[23] a) D. Gau, T. Kato, N. Saffon-Merceron, F. P. Cossꢃo, A.
Baceiredo, J. Am. Chem. Soc. 2009, 131, 8762; b) N. Wiberg, G.
Wagner, G. Reber, J. Riede, G. Mꢁller, Organometallics 1987, 6,
35; c) M. Mickoleit, K. Schmohl, R. Kempe, H. Oehme, Angew.
Chem. 2000, 112, 1679; Angew. Chem. Int. Ed. 2000, 39, 1610.
[24] H. Ottosson, A. M. Eklçf, Coord. Chem. Rev. 2008, 252, 1287.
[25] S. Inoue, M. Ichinohe, A. Sekiguchi, Angew. Chem. 2007, 119,
3410; Angew. Chem. Int. Ed. 2007, 46, 3346.
[26] R. Dobrovetsky, L. Zborovsky, D. Sheberla, M. Botoshansky, D.
Bravo-Zhivotovskii, Y. Apeloig, Angew. Chem. 2010, 122, 4178;
Angew. Chem. Int. Ed. 2010, 49, 4084; T. Guliashvili, I. El-Sayed,
A. Fischer, H. Ottosson, Angew. Chem. 2003, 115, 1678; Angew.
Chem. Int. Ed. 2003, 42, 1640.
[27] a) A. G. Brook, F. Abdesaken, B. Gutekunst, G. Gutekunst,
R. K. Kallury, J. Chem. Soc. Chem. Commun. 1981, 191; b) K. M.
Baines, A. G. Brook, R. R. Ford, P. D. Lickiss, A. K. Saxena,
W. J. Chatterton, J. F. Sawyer, B. A. Behnam, Organometallics
1989, 8, 693; c) A. G. Brook, A. Baumegger, A. J. Lough,
Organometallics 1992, 11, 3088; d) I. Bejan, D. Gꢁclꢁ, S. Inoue,
M. Ichinohe, A. Sekiguchi, D. Scheschkewitz, Angew. Chem.
2007, 119, 3413; Angew. Chem. Int. Ed. 2007, 46, 3349.
[19] V. G. Avakyan, V. F. Sidorkin, E. F. Belogolova, S. L. Guselni-
kov, L. E. Guselꢂnikov, Organometallics 2006, 25, 6007.
[20] G. D. Ruggiero, I. H. Williams, J. Chem. Soc. Perkin Trans. 2
2001, 733.
[28] a) Y. Apeloig, M. Karni, J. Am. Chem. Soc. 1984, 106, 6676; b) H.
Ottosson, Chem. Eur. J. 2003, 9, 4144; c) A. M. Eklçf, T.
Guliashvili, H. Ottosson, Organometallics 2008, 27, 5203.
[29] A similar cyclization reaction was reported previously for
cyclopropanones: A. G. Moiseev, M. Abe, E. O. Danilov, D. C.
Neckers, J. Org. Chem. 2007, 72, 2777.
À
[21] The comparatively lower density of the Si1 C1 bond is due to
further extended electron delocalization towards the adjacent
phosphonio fragment.
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