Metal-catalyzed di-tert-butylsilylene transfer: Synthesis and reactivity of silacyclopropanes

Article abstract of DOI:10.1021/jo0355505

Metal-catalyzed di-tert-butylsilylene transfer was developed as a mild, operationally simple, functional-group-tolerant method for silacyclopropane formation. Di-tert-butylsilylene was transferred from cyclohexene silacyclopropane 1 to an alkene through the use of a metal salt. Silacyclopropanation occurred at temperatures as low as -27°C when AgOTf or AgOC(O)CF₃ were used as catalysts. Complex silacyclopropanes were formed stereospecifically and diastereoselectively from functionalized alkenes. Silacyclopropanes reacted with various carbonyl compounds, including aldehydes, ketones, formate esters, and formamides, in an overall process that efficiently converts alkenes into oxasilacyclopentanes with defined stereochemistry.

Full text of DOI:10.1021/jo0355505

VOLUME 69, NUMBER 12
J UNE 11, 2004
© Copyright 2004 by the American Chemical Society
Meta l-Ca ta lyzed Di-ter t-bu tylsilylen e Tr a n sfer : Syn th esis a n d
Rea ctivity of Sila cyclop r op a n es
J elena CÄ irakovic´, Tom G. Driver, and K. A. Woerpel*
Department of Chemistry, University of California, Irvine, California 92697-2025
kwoerpel@uci.edu
Received October 20, 2003
Metal-catalyzed di-tert-butylsilylene transfer was developed as a mild, operationally simple,
functional-group-tolerant method for silacyclopropane formation. Di-tert-butylsilylene was trans-
ferred from cyclohexene silacyclopropane 1 to an alkene through the use of a metal salt.
Silacyclopropanation occurred at temperatures as low as -27 °C when AgOTf or AgOC(O)CF3 were
used as catalysts. Complex silacyclopropanes were formed stereospecifically and diastereoselectively
from functionalized alkenes. Silacyclopropanes reacted with various carbonyl compounds, including
aldehydes, ketones, formate esters, and formamides, in an overall process that efficiently converts
alkenes into oxasilacyclopentanes with defined stereochemistry.
SCHEME 1
In tr od u ction
Silacyclopropanes are strained1 silanes that undergo
carbon-carbon bond-forming reactions with various car-
bonyl compounds.2,3 Carbonyl insertions proceed with
high stereo-, regio-, and chemoselectivity to afford oxasi-
lacyclopentane adducts under mild, metal-catalyzed con-
ditions.2 Upon oxidation of the carbon-silicon bond,
oxasilacyclopentanes give 1,3-diols with up to three
contiguous sterocenters, thus making silacyclopropanes
useful intermediates for the synthesis of polyoxygenated
organic compounds (Scheme 1).4,5
strate compatibility.6-8 Thermal methods for silacyclo-
propane formation involve thermolysis of cyclic silanes
such as hexamethylsilacyclopropane,11 cyclotrisilanes,8,9,14,15
or cyclohexene silacyclopropane (1, eq 1)6,7,16 in the
Silacyclopropanes are typically prepared by reaction
of an alkene with a silylene or a silenoid species. Methods
for generating silylenes, however, require forcing condi-
tions, including photolysis, strongly reducing conditions,
or elevated temperatures, which limit the alkene sub-
(6) Boudjouk, P.; Black, E.; Kumarathasan, R. Organometallics
1991, 10, 2095-2096.
(1) (a) Naruse, Y.; Ma, J .; Inagaki, S. J . Phys. Chem. A 2003, 107,
2860-2864. (b) Sella, A.; Basch, H.; Hoz, S. J . Am. Chem. Soc. 1996,
118, 416-420. (c) Sella, A.; Basch, H.; Hoz, S. Tetrahedron Lett. 1996,
37, 5573-5576. (d) Gordon, M. S.; Boatz, J . A.; Walsh, R. J . Phys.
Chem. 1989, 93, 1584-1585.
(7) Boudjouk, P.; Samaraweera, U.; Sooriyakumaran, R.; Chrusciel,
J .; Anderson, K. R. Angew. Chem., Int. Ed. Engl. 1988, 27, 1355-1356.
(8) Schafer, A.; Weidenbruch, M.; Peters, K.; von Schnering, H.
Angew. Chem., Int. Ed. Engl. 1984, 23, 302-303.
(9) Belzner, J .; Ihmels, H.; Kneisel, B. O.; Gould, R. O.; Herbst-
Irmer, R. Organometallics 1995, 14, 305-311.
(10) (a) Pae, D. H.; Xiao, M.; Chiang, M. Y.; Gaspar, P. P. J . Am.
Chem. Soc. 1991, 113, 1281-1288. (b) J iang, P.; Trieber, D., II; Gaspar,
P. P. Organometallics 2003, 22, 2233-2239.
(2) Franz, A. K.; Woerpel, K. A. Acc. Chem. Res. 2000, 33, 813-
820.
(3) (a) Seyferth, D.; Duncan, D. P.; Shannon, M. L. Organometallics
1984, 3, 579-583. (b) Saso, H.; Ando, W.; Ueno, K. Tetrahedron 1989,
45, 1929-1940. (c) Saso, H.; Ando, W. Chem. Lett. 1988, 1567-1570.
(d) Boudjouk, P.; Samaraweera, U. Organometallics 1990, 9, 2205-
2206. (e) Kroke, E.; Willms, S.; Weidenbruch, M.; Saak, W.; Pohl, S.;
Marsmann, H. Tetrahedron Lett. 1996, 37, 3675-3678. (f) Bobbitt, K.
L.; Gaspar, P. P. J . Organomet. Chem. 1995, 499, 17-26.
(4) Smitrovich, J . H.; Woerpel, K. A. J . Org. Chem. 1996, 61, 6044-
6046.
(5) For reviews on oxidation of carbon-silicon bonds, refer to: (a)
J ones, G. R.; Landais, Y. Tetrahedron 1996, 52, 7599-7662. (b)
Fleming, I. Chemtracts-Org. Chem. 1996, 9, 1-64. (c) Tamao, K.
Advances in Silicon Chemistry; Larson, G. L., Ed.; J AI: Greenwich,
CT, 1996; Vol. 3, pp 1-62.
(11) Seyferth, D.; Annarelli, D. C. J . Am. Chem. Soc. 1975, 97, 7162-
7163.
(12) Seyferth, D.; Annarelli, D. C.; Vick, S. C.; Duncan, D. P. J .
Organomet. Chem. 1980, 201, 179-195.
(13) Seyferth, D.; Annarelli, D. C.; Duncan, D. P. Organometallics
1982, 1, 1288-1294.
(14) Belzner, J .; Dehnert, U.; Ihmels, H. Tetrahedron 2001, 57, 511-
517.
(15) Weidenbruch, M. Chem. Rev. 1995, 95, 1479-1493.
(16) Driver, T. G.; Franz, A. K.; Woerpel, K. A. J . Am. Chem. Soc.
2002, 124, 6524-6525.
10.1021/jo0355505 CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/10/2004
J . Org. Chem. 2004, 69, 4007-4012
4007

CÄ irakovic´ et al.
TABLE 1. Ca ta lyst Scr een in g for th e Silylen e Tr a n sfer
(Eq 1)
1). Catalytic amounts (10 mol %) of Zn(OTf)2 reduced the
temperature for the transfer to 55 °C (entry 2). Room
temperature (25 °C) silylene transfer was possible with
use of substoichiometric amounts of CeCl3 (entry 3), CuF2
(entry 4), and AgI (entry 5). Catalytic amounts of CuOTf‚
PhH and Cu(OTf)2 further decreased the reaction tem-
perature to 0 °C (entries 7 and 8), though with increased
reaction times (compare entries 6 and 7).23 The most
efficient catalysts, AgOTf and AgOC(O)CF3, reduced the
transfer temperature to -27 °C (entries 9 and 10).23
Control experiments suggest that the silylene transfer
is not reversible. Exposing the in situ formed n-butyl
silacyclopropane to allylbenzene and AgOTf did not
furnish any benzyl-substituted silacyclopropane (eq 2).
catalyst
(10 mol %)
entry
temp, °C
time
36 h
12 h
15 h
18 h
30 min
17 min
2 h
% transfera,b
1
2
3
4
5
6
7
8
9
none
Zn(OTf)2
CeCl3
CuF2
AgI
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2‚PhH
AgOTf
130
55
25
25
25
25
0
0
-27
-27
100
95
69
70
80
100
100
100
100
100
2 h
2 h
2 h
10
AgOC(O)CF3
a
As determined by 1H MMR spectroscopic analysis of the
b
reaction mixture. Reaction took place in a sealed NMR tube with
C6D6 as a solvent.
presence of an alkene.6-15 The catalytic silacyclopropa-
nation of alkenes would be a mild alternative to the more
stringent conditions normally required to form silacyclo-
propanes. While metal-catalyzed reactions are commonly
employed in three-membered-ring syntheses from
alkenes,17-20 catalytic alkene silacyclopropanation was
unknown.
We recently reported metal-catalyzed silylene transfer
as a mild method for silacyclopropane synthesis,21 and
we report here our improvements in this methodology.
By using silver salts as catalysts, alkene silacyclopropa-
nation proceeds stereospecifically, and with high diaste-
reoselectivity. The mild reaction conditions allow for a
broad alkene substrate scope. By using low silver catalyst
loading, in situ formed silacyclopropanes undergo inser-
tions with a wide variety of carbonyl compounds, afford-
ing oxasilacyclopentane products with diverse structures
and high regioselectivities.
The generality of the metal-catalyzed silylene transfer
methodology was explored utilizing AgOTf and AgOC-
(O)CF3, the most efficient catalysts. A variety of mono-
subtituted alkenes undergo metal-catalyzed silacyclopro-
panation in high yield (eq 3, Table 2). Increasing the
steric bulk of the vinyl substituent did not affect the yield
of the reaction (entries 1-3). The mild reaction conditions
allowed for a broad substrate scope, including aryl,
benzyl, and silyl ethers (entries 4-6 and 8-10), as well
as primary and aryl pivaloate esters (entries 7 and 10).
Resu lts a n d Discu ssion
Since di-tert-butylsilylene can be generated thermally
from cyclohexene silacyclopropane 1 (eq 1, Table 1, entry
1), we initiated a search for conditions that would allow
the silylene transfer process at reduced temperatures.
We investigated various metal salts to catalyze the trans-
fer of di-tert-butylsilylene to 1-hexene (eq 1).22 Of the
large number of metal salts screened, several were shown
to reduce the temperature of the silylene transfer (Table
Disubstituted alkenes underwent silacyclopropanation
stereospecifically and diastereoselectively. Transforma-
tions of cis- and trans-2-butene yielded the corresponding
products 37 and 47 with complete transfer of stereochem-
ical information (Table 3, entries 1 and 2).24 Metal-
catalyzed silylene transfer was also diastereoselective
(Table 3, entries 3-5): cyclopentene derivative 5 and
â-pinene 725 (entries 3 and 4) afforded single isomers of
the silacyclopropane products 6 and 8, respectively.24
Norbornene 9 afforded only the exo isomer of the corre-
sponding silacyclopropane (entry 5).26 Acyclic alkene 11
provided the corresponding silacyclopropane 12 as an 89:
11 ratio of isomers.24,27 The diastereoselectivity observed
(17) For recent examples of metal-catalyzed cyclopropanation, refer
to: (a) Miki, K.; Nishino, F.; Ohe, K.; Uemura, S. J . Am. Chem. Soc.
2002, 124, 5260-5261. (b) Wurz, R. P.; Charette, A. B. Org. Lett. 2002,
4, 4531-4533. (c) Li, Y.; Huang, J .-S.; Zhong, Z.-Y.; Che, C.-M. J . Am.
Chem. Soc. 2001, 123, 4843-4844. (d) For a review on metal-catalyzed
cyclopropanation see: Lebel, H.; Marcoux, J .-F.; Molinaro, C.; Charette,
A. B. Chem. Rev. 2003, 103, 977-1050.
(18) For recent examples of metal-catalyzed aziridination, refer to:
(a) Chanda, B. M.; Vyas, R.; Bedekar, A. V. J . Org. Chem. 2001, 66,
30-34. (b) Dauban, P.; Saniere, L.; Tarrade, A.; Dodd, R. H. J . Am.
Chem. Soc. 2001, 123, 7707-7708. (c) Evans, D. A.; Bilodeau, M. T.;
Faul, M. M. J . Am. Chem. Soc. 1994, 116, 2742-2753.
(19) For recent examples of metal-catalyzed epoxidation, refer to:
(a) Daly, A. M.; Renehan, M. F.; Gilheany, D. G. Org. Lett. 2001, 3,
663-666. (b) Adam, W.; Stegmann, V. R.; Saha-Moller, C. R. J . Am.
Chem. Soc. 1999, 121, 1879-1882.
(20) For metal-catalyzed silacyclopropene synthesis, refer to: (a)
Palmer, W. S.; Woerpel, K. A. Organometallics 1997, 16, 4824-4827.
(b) Ishikawa has reported tungsten-catalyzed silylene transfer for
silacyclopropene synthesis: Ohshita, J .; Ishikawa, M. J . Organomet.
Chem. 1991, 407, 157-165.
(21) CÄ irakovic´, J .; Driver, T. G.; Woerpel, K. A. J . Am. Chem. Soc.
2002, 124, 9370-9371.
(22) For recent examples of metal-silylene complexes, refer to: (a)
Mork, B. V.; Tilley, T. D. Angew. Chem., Int. Ed. 2003, 42, 357-360.
(b) Evans, W. J .; Perotti, J . M.; Ziller, J . W.; Moser, D. F.; West, R.
Organometallics 2003, 22, 1160-1163. (c) Okazaki, M.; Tobita, H.;
Ogino, H. Dalton Trans. 2003, 493-506. (d) Cai, X.; Gehrhus, B.;
Hitchcock, P. B.; Lappert, M. F.; Slootweg, J . C. J . Organomet. Chem.
2002, 643-644, 272-277. (e) Papkov, V. S.; Gerasimov, M. V.; Dubovik,
I. I.; Sharma, S.; Dementiev, V. V.; Pannell, K. H. Macromolecules
2000, 33, 7107-7115.
(23) To examine reactions performed below room temperature,
TMEDA was added to quench the metal catalyst so that 1H NMR
spectroscopic analysis could be performed at room temperature.
(24) Based on 1H and 29Si NMR spectroscopic analysis of the
unpurified product mixture.
4008 J . Org. Chem., Vol. 69, No. 12, 2004

Silacyclopropane Synthesis and Reactivity
TABLE 2. Sila cyclop r op a n a tion of Mon osu bstitu ted
Alk en es (Eq 3)
TABLE 3. Sila cyclop r op a n a tion of Disu bstitu ted
Alk en es
a
b
1.3 equiv of alkene was used. As determined by 1H NMR
spectroscopic analysis of the product mixture relative to an
internal PhSi(CH3)3 standard. c An excess of alkene was used (ca.
10 equiv).
a
b
1.3 equiv of alkene were used. As determined by 1H NMR
spectroscopic analysis of the product mixture relative to an
internal PhSi(CH3)3 or 1,3-dimethoxybenzene standard. c An ex-
in these reactions represents an improvement over that
obtained with thermal silylene transfer from 1 or sila-
cyclopropanation by reduction of t-Bu2SiCl2 with lithium.16
By using the catalyst loadings initially developed (10
mol %), attempts to isolate silacyclopropanes resulted
only in decomposition products.28 While stable in solution,
silacyclopropanes generated in the presence of metal salts
decomposed upon concentration. We propose that the
decomposition of silacyclopropanes is likely catalyzed by
silver salts, so upon removal of the solvent, the concen-
tration of both the silacyclopropane and the silver salt
increase, leading to faster decomposition.
d
cess of alkene was used (ca. 10 equiv). One diastereomer was
1
visible by H NMR and 29Si NMR spectroscopy (dr g 95:5). e dr )
89:11, as determined by 29Si NMR spectroscopy.
TABLE 4. Isola tion of Sila cyclop r op a n es
The isolation procedure was optimized by reducing the
amount of silver catalyst from about 5 mol % to e1 mol
%. Schlenk filtration of the unpurified reaction mixture,
followed by bulb-to-bulb distillation, afforded pure sila-
cyclopropanes (Table 4). The decrease in the catalyst
loading had no effect on the yield of the silylene transfer.
The metal-catalyzed silacyclopropanation of alkenes
allows the reactive silacyclopropanes to be generated in
a
Isolated yield after bulb-to-bulb distillation.
(25) Silver-catalyzed silylene transfer to â-pinene provided the
opposite isomer of silacyclopropane product to the one that was
obtained by reduction of t-Bu2SiCl2 by lithium in the presence of
â-pinene.16 Studies to determine the origin of the reversal of selectivity
are underway.
situ and then carried on in subsequent reactions without
isolation (eq 4). Treatment of a monosubstituted alkene
(26) Norbornenes normally exhibit exo-selective reactions. See for
example: (a) Brown, H. C.; Kawakami, J . H.; Liu, K. T. J . Am. Chem.
Soc. 1973, 95, 2209-2216. (b) Houk, K. N.; Rondan, N. G.; Brown, F.
K.; J orgensen, W. L.; Madura, J . D.; Spellmayer, D. C. J . Am. Chem.
Soc. 1983, 105, 5980-5988.
(27) The configuration of the major product was assigned based on
1,3-allylic strain considerations: Hoffmann, R. W. Chem. Rev. 1989,
89, 1841-1860.
(28) Schlenk filtration of the unpurified product mixture through
Celite, silica, or alumina followed by concentration of the filtrate
resulted in the decomposition of the silacyclopropane product.
with cyclohexene silacyclopropane 1 and a catalytic
amount of silver triflate followed by ZnBr2-catalyzed
J . Org. Chem, Vol. 69, No. 12, 2004 4009

CÄ irakovic´ et al.
TABLE 5. On e-F la sk Silylen e Tr a n sfer a n d Meth yl
F or m a te In ser tion (Eq 4)
TABLE 6. On e-F la sk Silylen e Tr a n sfer , Ca r bon yl
In ser tion (Eq 5)a
a
b
20 mol % of MXn used. Isolated yield over two steps after
purification by flash chromatography.
Decreasing the silver catalyst loading from 5 mol % to
e1 mol % proved to be critical for the insertion of
saturated aldehydes. When 5 mol % of silver catalyst was
used, in situ formed silacyclopropanes did not react with
saturated aldehydes. With 0.5 mol % of AgOTf used in
the transfer step, the zinc bromide-catalyzed insertion
of butyraldehyde proceeded to give the corresponding
oxasilacyclopentane 16 in good yield over two steps (eq
6). Optimization of solvent, temperature, and use of
additives did not improve the diastereoselectivity of the
reaction.
a
As determined by 1H NMR spectroscopic analysis of the
b
unpurified product mixture. Isolated yield over two steps after
purification by flash chromatography.
insertion of methyl formate provided the oxasilacyclo-
pentane acetals 14a -g (Table 5, eq 4).21 The formate
insertion is regioselective, favoring the 1,3-regioisomer.29
n-Butyl-, isopropyl-, and benzyl-substituted ethenes gave
high yields of the corresponding five-membered-ring
products (entries 1, 2, and 4). The regioselectivity of the
formate insertion decreased with increased steric bulk
of the alkene substituent (entry 3). A high yield of the
oxasilacyclopentane product was also obtained for the
TIPS-protected eugenol (entry 7). Benzyl and silyl ethers
were also tolerated in this reaction sequence, albeit with
lower yield for the overall reaction (entries 5 and 6).
The two-step, one-flask reaction sequence described
above was utilized for addition of other carbonyl electro-
philes into silacyclopropanes (eq 5, Table 6). Aromatic
Variation of the catalyst for the insertion step con-
trolled the regioselectivity of the oxasilacyclopentane
product.29,31 Treatment of the in situ formed butyl sila-
cyclopropane with cinnamaldehyde and CuI as the cata-
lyst resulted in formation of the 1,2-regioisomer, 17a (eq
7, Table 7, entry 1). ZnI2-catalyzed insertion of cinna-
maldehyde afforded the 1,3-product, 17b (Table 7, entry
2).
and R,â-unsaturated aldehydes inserted readily into the
carbon-silicon bond of the intermediate silacyclopropane
(entries 1-3). Both aliphatic and aromatic ketones
(entries 4 and 5) afforded five-membered-ring products
15d and 15e in 57% and 71% yield over two steps,
respectively. While the zinc-catalyzed insertion reaction
was completely regioselective, giving only the 1,3-regioi-
somer shown,30 the diastereoselectivity of the 1,3-product
formation was low. Both ZnBr2 and ZnI2 catalyzed the
carbonyl insertions with equal efficiency.
Low silver catalyst loading enabled the insertions of
formamides to disubstituted silacyclopropanes.32 cis-2-
Butene was converted to oxasilacyclopentane acetate 18
through the use of 0.5 mol % of AgOC(O)CF3 for silylene
transfer followed by CuI-catalyzed formamide inser-
(31) Franz, A. K.; Woerpel, K. A. J . Am. Chem. Soc. 1999, 121, 949-
957.
(29) Franz, A. K.; Woerpel. K. A. Angew. Chem., Int. Ed. 2000, 39,
4295-4299.
(30) Based on GC analysis of the unpurified product mixture.
(32) With high silver catalyst loading (5 mol %), 2,3-disubstituted
silacyclopropanes did not form oxasilacyclopentane products with any
carbonyl compounds. Instead, decomposition products were formed.
4010 J . Org. Chem., Vol. 69, No. 12, 2004

Silacyclopropane Synthesis and Reactivity
TABLE 7. On e-F la sk Silylen e Tr a n sfer a n d
Cin n a m a ld eh yd e In ser tion (Eq 7)a
SCHEME 2
entry
MXn
17a :17b
1,2 dr
82:18
1,3 dr
% yieldb
1
2
CuI
ZnI2
96:4
1:99
85
92
76:24
a
b
20 mol% of MXn used. Isolated yield over two steps after
purification by flash chromatography.
tion,31,33 and hydrolysis of the intermediate N,O-acetal.34
The hemiacetal product (not shown) was acetylated to
afford 18 in 90% yield over three steps (eq 8). trans-2-
Butene was elaborated in a similar fashion to provide
hemiacetal 19 in 91% yield over two steps (eq 9).34
(Table 2). Treatment of in situ formed 6 with N-benzyl-
N-methylformamide and CuI, followed by hydrolysis of
the intermediate N,O-acetal, afforded 22 as a mixture of
epimers at the hemiacetal position (eq 12). Hemiacetal
22 can be converted to triol 23 with five stereocenters in
three steps and in excellent yield (eq 13).16
The synthetic utility of the one-flask silacyclopropa-
nation/insertion methodology was demonstrated by the
functionalization of acetate 18 (eq 10). Under Lewis acidic
conditions, oxasilacyclopentane acetals undergo highly
stereoselective carbon-carbon bond-forming reactions with
various nucleophiles.2,35 Treatment of acetate 18 with the
silyl enol ether of diethyl ketone36 in the presence of
SnBr4 afforded ketone 20 in high yield and selectivity
(eq 10). Wittig methylenation followed by carbon-silicon
bond oxidation afforded diol 21 in high overall yield (eq
11).
A preliminary mechanism for silver-promoted silylene
transfer, involving silver silylenoid 2437 (Scheme 2), can
be proposed based on qualitative observations. Since
silver salts form complexes with alkenes,38 we propose
that the silver catalyst is complexed by one or more
alkene ligands. Because silylene transfer is dramatically
accelerated relative to thermal transfer,10b,39 silver must
be involved in the silylene extrusion step. This condition
can be satisfied by transmetalation with cyclohexene
silacyclopropane 1 to give 25.40 To obey the principle of
microscopic reversibility, the subsequent cyclization must
also be mediated by silver to afford product silacyclopro-
To demonstrate the level of complexity that can be
achieved utilizing silacyclopropane chemistry, cyclopen-
tene 5 was elaborated with use of the silacyclopropana-
tion/insertion protocol. Silacyclopropanation of cyclopen-
tene 5 afforded silacyclopropane 6 as a single diastereomer
(37) Lewis base stabilized metal silylenoids have been reported: (a)
Theil, M.; J utzi, P.; Neumann, B.; Stammler, A.; Stammler, H.-G. J .
Organomet. Chem. 2002, 662, 34-42. (b) Mitchell, G. P.; Tilley, T. D.
J . Am. Chem. Soc. 1998, 120, 7635-7636. (c) Ueno, K.; Sakai, M.;
Ogino, H. Organometallics 1998, 17, 2138-2140.
(33) (a) Shaw, J . T.; Woerpel, K. A. Tetrahedron 1997, 53, 16597-
16606. (b) Shaw, J . T.; Woerpel, K. A. J . Org. Chem. 1997, 62, 442-
443.
(34) Higher yields of the overall reaction were observed when
silacyclopropanes were isolated after the first step.
(35) (a) Bear, T. J .; Shaw, J . T.; Woerpel, K. A. J . Org. Chem. 2002,
67, 2056-2064. (b) Shaw, J . T.; Woerpel, K. A. J . Org. Chem. 1997,
62, 6706-6707.
(36) Cazeau, P.; Duboudin, F.; Moulines, F.; Babot, O.; Dunogues,
J . Tetrahedron 1987, 43, 2075-2088.
(38) Kim, J . H.; Min, B. R.; Won, J .; Kang, Y. S. Chem. Eur. J . 2002,
8, 650-654.
(39) Driver, T. G.; Woerpel, K. A. J . Am. Chem. Soc. 2003, 125,
10659-10663.
(40) (a) Castillo, I.; Tilley, T. D. J . Am. Chem. Soc. 2001, 123, 10526-
10534. (b) Mintcheva, N.; Nishihara, Y.; Mori, A.; Osakada, K. J .
Organomet. Chem. 2001, 629, 61-67.
J . Org. Chem, Vol. 69, No. 12, 2004 4011

CÄ irakovic´ et al.
pane 2 and regenerate the active catalyst. If both
extrusion and cyclization require silver, the silylene is
probably shuttled between alkenes as silver silenoid 24.
oxasilacyclopentanes from alkenes and expands the util-
ity of silacyclopropanes as intermediates in organic
synthesis.
Ack n ow led gm en t. This research was supported by
the National Institute of General Medical Sciences of
the National Institutes of Health (GM54909). K.A.W.
thanks the Camille and Henry Dreyfus Foundation,
Merck Research Laboratories, J ohnson & J ohnson, and
the Sloan Foundation for awards to support research.
T.G.D. thanks Novartis Pharmaceuticals through the
ACS Division of Organic Chemistry and Eli Lilly and
Company for predoctoral fellowships. We thank Dr. Phil
Dennison for assistance with NMR spectrometry and
Dr. J ohn Greaves and Dr. J ohn Mudd for mass spec-
trometric data.
Con clu sion
Silver-catalyzed silylene transfer is a mild, efficient
method for silacyclopropane synthesis. The low temper-
ature of the transfer resulted in improved diastereose-
lectivity and substrate compatibility compared to other
methods for silacyclopropane formation. The silacyclo-
propanes formed react readily with a wide range of
carbonyl compounds in a process that efficiently converts
alkenes to oxasilacyclopentanes. Limiting the amount of
silver catalyst used proved to be important in the two-
step synthesis of oxasilacyclopentanes from alkenes.
Reducing the amount of silver catalyst also resulted in a
wider range of carbonyl compounds that underwent
insertion into the in situ formed silacyclopropanes,
without diminishing the efficiency of the silylene transfer
step. This methodology provides efficient access to diverse
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and spectroscopic and analytical data for the products.
This material is available free of charge via the Internet at
http://pubs.acs.org.
J O0355505
4012 J . Org. Chem., Vol. 69, No. 12, 2004