Aluminum chloride catalyzed hydrosilylation of cyclopropanes with chlorodimethylsilane

Article abstract of DOI:10.1016/S0040-4039(01)00925-X

Aluminum chloride can be utilized as an active catalyst for the highly regioselective hydrosilylation of 1-alkyl, 1-aryl, 1,1-dialkyl, and cyclic cyclopropanes with chlorodimethylsilane in hexane at room temperature.

Full text of DOI:10.1016/S0040-4039(01)00925-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 5057–5060
Aluminum chloride catalyzed hydrosilylation of cyclopropanes
with chlorodimethylsilane
Shigeru Nagahara,a,* Takashi Yamakawaa and Hisashi Yamamotob
aDepartment of Chemistry and Biochemistry, Suzuka National College of Technology, Shiroko, Suzuka 510-0294, Japan
bGraduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
Received 11 May 2001; revised 28 May 2001; accepted 30 May 2001
Abstract—Aluminum chloride can be utilized as an active catalyst for the highly regioselective hydrosilylation of 1-alkyl, 1-aryl,
1,1-dialkyl, and cyclic cyclopropanes with chlorodimethylsilane in hexane at room temperature. © 2001 Elsevier Science Ltd. All
rights reserved.
Hydrosilylation of alkenes and alkynes is a highly
useful functional group manipulation in organic synthe-
sis.1 Despite the analogy between alkenes and cyclo-
propanes often drawn, surprisingly few studies have
been made on the catalytic hydrosilylation of cyclo-
propanes under ring cleavage. To the best of our
knowledge, only the hydrosilylation of vinylcyclo-
propanes and methylenecyclopropanes catalyzed by
Rh(I) complexes has been studied, resulting in the
addition of silanes to the cyclopropane rings to produce
silylated alkenes.2 The combination of cyclopropane
rings with multiple bonds and/or other functional
groups, which vinylcyclopropanes and methylenecyclo-
propanes include, is known to establish composite func-
tional groups,3 and hence, such cyclopropane rings are
activated by adjacent functional substituents. In this
context, we have been interested in the development of
the hydrosilylation of unactivated cyclopropanes hav-
ing only alkyl substituents. Here we wish to report the
realization of such a reaction under the influence of
AlCl3 catalyst.4
examined the catalytic activity of the Lewis acids FeCl3,
TiCl4, SnCl4, and AlCl3 in this reaction.6 Lewis acid
catalyst (20 mol%) was added to a mixture of equimo-
lar amounts of 1 and Me2ClSiH without solvent and
subsequent reaction at room temperature for 2 h was
carried out. In the use of TiCl4 and SnCl4 catalysts,
cyclopropane 1 was quantitatively recovered, respec-
tively, while FeCl3 catalyst provided a mixture of
nonane, 1-nonene, 2-nonenes, and unidentified com-
pounds without any hydrosilylation product formation.
In marked contrast, however, AlCl3 catalyst gave 1-
chlorodimethylsilylnonane
(2)
(45%)
and
1-
dichloromethylsilylnonane (3) (8%) without the
formation of other regioisomers after direct vacuum-
distillation,7,8 even though significant amounts of
unidentified by-products remained as residue. In this
AlCl3-catalyzed hydrosilylation, unfortunately, switch-
ing silanes from Me2ClSiH to other silanes, MeCl2SiH,
Cl3SiH and Et3SiH, gave unsuccessful results. The use
of MeCl2SiH and Cl3SiH resulted in high boiling by-
products with complete consumption of 1 for 0.2 h,
respectively. The reaction with Et3SiH was slower (59%
conversion for 2 h) and afforded complex mixtures of
products. Therefore, modifications of AlCl3-catalyzed
hydrosilylation conditions using Me2ClSiH were made
to prevent the formation of both high boiling by-prod-
ucts resulting from the apparent destruction of 1 and
dichloromethylsilyl compound 3. Interestingly, in the
reaction employing CH2Cl2 solvent (10 mL) the yield of
2 slightly increased (66%) by suppressing the formation
of 3, yet a significant proportion of high boiling by-
products arose. However, the reaction in polar solvents
such as diethyl ether and tetrahydrofuran resulted in
total recovery of the starting cyclopropane 1. Thus, the
In the reaction of 1-hexylcyclopropane (1)5 with
Me2ClSiH at room temperature without solvent, ordi-
nary hydrosilylation catalysts,1 Speier catalyst (0.5
mol% H2PtCl6·6H2O) and Wilkinson complex catalyst
(0.5 mol% Rh(PPh3)3Cl), respectively, indicated that the
starting cyclopropane 1 was recovered quantitatively
even after a prolonged reaction time (24 h). We then
Keywords: aluminum chloride; chlorodimethylsilane; cyclopropanes;
hydrosilylation; ring cleavage.
* Corresponding author. Tel.: +81-593-68-1825; fax: +81-593-87-0338;
e-mail: nagahara@chem.suzuka-ct.ac.jp
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00925-X

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S. Nagahara et al. / Tetrahedron Letters 42 (2001) 5057–5060
use of hexane solvent in this hydrosilylation process is
essential for achieving high product selectivity and
chemical yield, affording only the regioselective
hydrosilylation product 2 in 92% yield as depicted in
Table 1 (entry 1). 1-Methyl-1-pentylcyclopropane (4),
bicyclo[4.1.0]heptane (6), spiro[2.5]octane (8), in addi-
tion to 1-phenylcyclopropane (10) were also regioselec-
tively hydrosilylated in this process,5 being converted to
the almost pure chlorodimethylsilyl compounds, 5, 7, 9,
and 11, in good to high yields (entries 2–5).8 These
products involved silicon addition to the least-substi-
tuted cyclopropane ring carbon and hydrogen to the
most substituted, respectively.
formed by the reaction of AlCl3 with Me2ClSiH to give
a more stable, g-silylated secondary or tertiary carbo-
cation intermediate. Similarly, the formation of di-
chloromethylsilyl products such as 3 in the reaction
without solvent can be ascribed to the addition of a
dichloromethylsilyl complex, Cl2MeSi+HMeAlCl2 ,
−
generated by the redistribution of the chlorodimethyl-
silyl complex.
In the reaction of unsymmetrical 1,2-disubstituted
cyclopropane, 1-methyl-2-pentylcyclopropane (12),5
hydrosilylated regioisomers, 13–15 and 17, will proba-
bly be obtained, because these regioisomers can be
attributed to the reaction proceeding via the corre-
sponding g-silyl secondary carbocation intermediate,
respectively (Scheme 1). The formation of regioisomers,
16 and 18, might have to proceed through primary
carbocation intermediates. The reaction of 12 actually
afforded a mixture of the expected regioisomers, 13–15
and 17, though a small amount of other regioisomers, 5
and 19, were also formed (entry 6).9 The regioisomer 15
On the basis of the regiochemistry of the products and
the mechanism proposed for both the reaction of cyclo-
propanes with electrophiles6 and the AlCl3-catalyzed
hydrosilylation of alkenes with Me2ClSiH,7c,d we inter-
preted that the reaction proceeds through the elec-
trophilic ring opening of the cyclopropane with a cata-
lytic chlorodimethylsilyl complex, ClMe2Si+HAlCl3−,7d
Table 1. Aluminum chloride catalyzed hydrosilylation of cyclopropanes with Me2ClSiHa

S. Nagahara et al. / Tetrahedron Letters 42 (2001) 5057–5060
5059
Scheme 1.
was a major product in this reaction. Therefore, we have
performed semiempirical calculations10 in order to esti-
mate the stability difference among secondary carboca-
tion compounds, 13%–15% and 17%, as model compounds
corresponding to the proposed g-silyl carbocation inter-
mediates, by comparing the heat of formation (DHf). The
parameters for the semiempirical calculations and the
stability order of the secondary carbocation compounds
estimated from the calculated DHf values (298 K) are as
follows: 15%>13%>14%$17% (AM1); 13%$14%$15%>17%
(PM3). The calculation results (AM1) agreed well with
the experimental results, demonstrating that the most
stable carbocation compound is 15%.
References
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5. The starting cyclopropanes, except 1-phenylcyclopropane
(10), were prepared from the corresponding alkenes using
the trialkylaluminum–alkylidene iodide system, see:
Maruoka, K.; Fukutani, Y.; Yamamoto, H. J. Org.
Chem. 1985, 50, 4412. For literature procedures of the
cyclopropanes 6, 8, and 20, see: Rickborn, B.; Chan, J. H.
J. Org. Chem. 1967, 32, 3576. The cyclopropanes 1, 4, and
12 were identified by the following data. 1: 1H NMR (400
MHz, CDCl3): l −0.04 (2H, m), 0.36 (2H, m), 0.63 (1H,
m), 0.86 (3H, t, J=7.0 Hz), 1.16 (2H, q, J=7.2 Hz),
1.2–1.4 (8H, m). 13C NMR (100 MHz, CDCl3): l 4.33,
10.91, 14.11, 22.70, 29.24, 29.65, 31.97, 34.81. 4: 1H
NMR: l 0.15–0.22 (4H, m), 0.87 (3H, t, J=7.1 Hz), 0.98
(3H, s), 1.1–1.4 (8H, m). 13C NMR: l 12.87, 14.07, 15.28,
22.71, 22.73, 26.61, 32.13, 39.36. (E)-12: 1H NMR l
As the AlCl3-catalyzed hydrosilylation of alkenes7d,f and
alkynes7e has been reported to proceed stereoselectively
in a trans-addition manner, the stereochemical aspect of
this process was also examined with 1-methylbicyclo-
[4.1.0]heptane (20).5 Although the reaction of 20 was
quite regioselective, unfortunately, it was nonstereoselec-
tive, yielding a mixture of stereoisomers of 218 in a ratio
of 35:65 in hexane and 43:57 without solvent (entry 7).
The experimental procedure is illustrated here for the
synthesis of 2. To a solution of 1 (379 mg, 3.0 mmol) and
Me2ClSiH (333 mL, 3.0 mmol) in hexane (10 mL) was
added a powder anhydrous AlCl3 (80 mg, 0.6 mmol) at
0°C under argon atmosphere. The resulting suspension
was allowed to warm to room temperature where it was
stirred for 2 h. After evaporation of hexane solvent, the
residue was directly vacuum-distilled by Kugelrohr
apparatus to afford 2 (610 mg, 92% yield) as a colorless
oil.
Acknowledgements
This work was supported by the OKASAN-KATO
Foundation.

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S. Nagahara et al. / Tetrahedron Letters 42 (2001) 5057–5060
−0.37 (1H, m), 0.5–0.75 (3H, m), 0.87 (3H, t, J=6.8 Hz),
Chem. Abstr. 1983, 99, 53833z; (c) Oertle, K.; Wetter, H.
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lics 1999, 18, 3109.
0.99 (3H, d, J=6.1 Hz), 1.1–1.4 (8H, m). 13C NMR: l
9.27, 11.92, 13.18, 14.06, 15.66, 22.69, 28.39, 29.81, 31.85.
1
(Z)-12: H NMR: l 0.1 (1H, m), 0.35 (1H, m), 0.5–0.75
(2H, m), 0.87 (3H, t, J=6.6 Hz), 0.98 (3H, d, J=5.9 Hz),
1.1–1.4 (8H, m). 13C NMR: l 12.61, 12.84, 14.06, 19.02,
19.89, 22.69, 29.30, 31.70, 34.20.
8. All terminal silyl products were identified by comparison
of the spectral properties (NMR, GC/MS) and GLC
retention times with those of authentic samples prepared
by the hydrosilylation of the corresponding 1-alkenes
with Me2ClSiH or MeCl2SiH in the presence of 0.5 mol%
H2PtCl6·6H2O at room temperature without solvent.
9. Authentic samples of the products, 13, 14, and 19, were
prepared by the hydrosilylation of 2-nonene and 3-
nonene with Me2ClSiH in the presence of 20 mol% AlCl3
at room temperature without solvent. For example, the
hydrosilylation of 2-nonene resulted in a mixture of 14
and 19 (70:30), and the reaction of 3-nonene gave a
6. Transition metals and Lewis acids are known to promote
the cleavage of cyclopropane rings. For reviews on ring
cleavage of cyclopropanes, see: (a) DePuy, C. H. Top.
Curr. Chem. 1973, 40, 73; (b) Gibson, D. H.; DePuy, C.
H. Chem. Rev. 1974, 74, 605; (c) Crabtree, R. H. Chem.
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Group; Rappoport, Z., Ed.; John Wiley & Sons: London,
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induced ring cleavage of cyclopropanes, see: (e) Barrett,
A. G. M.; Tam, W. J. Org. Chem. 1997, 62, 4653; (f)
Barrett, A. G. M.; Tam, W. J. Org. Chem. 1997, 62, 7673
and references are cited therein. For examples of Lewis
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Grieco, P. A.; Finkelhor, R. S. Tetrahedron Lett. 1974,
527; (h) Ito, Y.; Sugaya, T.; Nakatsuka, M.; Saegusa, T.
J. Am. Chem. Soc. 1977, 99, 8366; (i) Pinnick, H. W.;
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1
mixture of 13 and 19 (53:47). 13: H NMR: l 0.37 (6H,
s), 0.7–0.9 (1H, m), 0.87 (3H, t, J=6.7 Hz), 0.88 (3H, t,
J=7.4 Hz), 1.2–1.6 (12H, m). 13C NMR: l 1.15, 14.09,
14.38, 22.00, 22.56, 27.73, 28.55, 28.81, 31.19, 32.19. 14:
1H NMR: l 0.35 (6H, s), 0.7–0.9 (1H, m), 0.87 (3H, t,
J=6.7 Hz), 0.99 (3H, d, J=7.3 Hz), 1.1–1.6 (12H, m).
13C NMR: l −0.05, 0.00, 13.15, 14.10, 21.86, 22.67, 28.28,
1
29.26, 29.59, 30.65, 31.91. 19: H NMR: l 0.38 (6H, s),
0.7–0.9 (1H, m), 0.87 (3H, t, J=6.7 Hz), 0.93 (3H, t,
J=7.4 Hz), 1.1–1.6 (12H, m). 13C NMR: l 1.25, 1.29,
13.33, 14.10, 21.52, 22.67, 28.17, 28.73, 29.62, 29.65,
31.77.
7. AlCl3-catalyzed hydrosilylation of alkenes and alkynes,
see: (a) Finke, U.; Moretto, H. Ger. Patent 2,804,204,
1979; Chem. Abstr. 1979, 91, 193413x; (b) Voronkov, M.
G.; Adamovich, S. N.; Sherstyannikova, L. V.;
Pukhnarevich, V. B. Zh. Obshch. Khim. 1983, 53, 806;
10. The semiempirical calculations were performed using
CAChe MOPAC ver. 94.10 on Macintosh G3. For the
parameters of the calculations, see: Stewart, J. J. P. J.
Comp. Chem. 1989, 10, 209.
.