Bismuth compounds in organic synthesis. A one-pot synthesis of homoallyl ethers and homoallyl acetates from aldehydes catalyzed by bismuth triflate

Article abstract of DOI:10.1021/jo048475m

(Chemical Equation Presented) Three one-pot methods for the conversion of aldehydes to homoallyl ethers catalyzed by Bi(OTf)₃? xH ₂O (1 < x < 4) have been developed. The one-pot synthesis of homoallyl ethers can be achieved either by

Full text of DOI:10.1021/jo048475m

Bismuth Compounds in Organic Synthesis. A One-Pot Synthesis of
Homoallyl Ethers and Homoallyl Acetates from Aldehydes
Catalyzed by Bismuth Triflate
Peter W. Anzalone, Ashvin R. Baru, Eric M. Danielson, Patrick D. Hayes, Mai P. Nguyen,
Ambrose F. Panico, Russell C. Smith,† and Ram S. Mohan*
Laboratory for Environment Friendly Organic Synthesis, Department of Chemistry,
Illinois Wesleyan University, Bloomington, Illinois 61701
rmohan@iwu.edu
Received August 30, 2004
Three one-pot methods for the conversion of aldehydes to homoallyl ethers catalyzed by Bi(OTf)3‚
xH2O (1 < x < 4) have been developed. The one-pot synthesis of homoallyl ethers can be achieved
either by in situ generation of the acetal followed by its reaction with allyltrialkylsilane or by a
three-component synthesis in which the aldehyde, trimethylorthoformate or an alkoxytrimethyl-
silane and allyltrimethylsilane are mixed together in the presence of bismuth triflate (0.1-1.0 mol
%). In addition, a three-component synthesis of homoallyl acetates, which is achieved by reacting
the aldehyde, acetic anhydride, and allyltrimethylsilane in the presence of bismuth triflate (3.0-
5.0 mol %), has been developed. The use of a relatively nontoxic, easy to handle, and inexpensive
catalyst adds to the versatility of these methods.
Introduction
CF3COOH,10 BiBr3,11 trimethylsilyl bis(trifluoromethane-
sulfonyl)amide [TMSNTf2],12 Sc(OTf)3,13 indium metal,14
and Bi(OTf)3‚xH2O.15 However, many acetals are not
Homoallyl ethers and homoallyl acetates are versatile
functional groups amenable to further synthetic manipu-
lation, and hence, their synthesis has attracted consider-
able attention. The allylation of acetals using organosil-
icon reagents is a useful method to generate homoallyl
ethers, and hence, several catalysts have been used to
effect this transformation. These include TiCl4,1 AlCl3,2
BF3‚Et2O,2 trityl perchlorate,3 diphenylboryl triflate,3
montmorillonite,4 Pb/Al,5 trimethylsilyl bis(fluorosulfo-
nyl)imide,6 (CH3)3SiI,7 TMSOTf,8 TiCp2(CF3SO3)2,9
(6) Trehan, A.; Vij, A.; Walia, M.; Kaur, G.; Verma, R. D.; Trehan,
S. Tetrahedron Lett. 1993, 34, 7335.
(7) Sakurai, H.; Sasaki, K.; Hosomi, A. Tetrahedron Lett. 1981, 22,
745.
(8) (a) Tsunoda, T.; Suzuki, M.; Noyori, R. Tetrahedron Lett. 1980,
21, 71. (b) For allylation of acetals using TMSOTf in ionic liquids, see:
Zerth, H. M.; Leonard, N. M.; Mohan, R. S. Org. Lett. 2003, 5, 55.
(9) Hollis, T. K.; Robinson, N. P.; Whelan, J.; Bosnich, B. Tetrahe-
dron Lett. 1993, 34, 4309.
(10) McCluskey, A.; Mayer, D. M.; Young, D. J. Tetrahedron Lett.
1997, 38, 5217.
(11) Komatsu, N.; Uda, M.; Suzuki, H.; Takahashi, T.; Domae, T.;
Wada, M. Tetrahedron Lett. 1997, 38, 7215.
† Currently a first-year graduate student at the University of Illinois
Urbana-Champaign.
(1) Hosomi, A.; Masahiko, E.; Sakurai, H. Chem. Lett. 1976, 941.
(2) Hosomi, A.; Endo, M.; Sakurai, H. Chem. Lett. 1978, 499.
(3) Mukaiyama, T.; Nagaoka, H.; Murakami, M,; Ohshima, M.
Chem. Lett. 1985, 980.
(4) Kawai, M.; Onaka, M.; Izumi, Y. Chem. Lett. 1986, 381.
(5) Tanaka, H.; Yamashita, S.; Ikemoto, Y.; Torii, S. Tetrahedron
Lett. 1988, 14, 1721.
(12) Ishii, A.; Kotera, O.; Saeki, T.; Mikami, K. Synlett 1997, 1145.
(13) Yadav, J. S.; Subba Reddy, V. B.; Srihari, P. Synlett 2001, 673.
(14) (a) Yadav, J. S.; Subba Reddy, B. V.; Reddy, G. S. K. K.
Tetrahedron Lett. 2000, 41, 2695. (b) Kwon, J. S.; Pae, A. N.; Choi, K.;
Koh, H. Y.; Kim, Y.; Cho, Y. S. Tetrahedron Lett. 2001, 42, 1957.
(15) Wieland, L. C.; Zerth, H. M.; Mohan, R. S. Tetrahedron Lett.
2002, 43, 4597.
10.1021/jo048475m CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/10/2005
J. Org. Chem. 2005, 70, 2091-2096
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Anzalone et al.
TABLE 1. Bismuth Triflate Catalyzed One-Pot Method for the Synthesis of Homoallyl Ethers Using
Trialkylorthoformates
a t1 refers to the time for the acetal formation step, and t2 refers to time for the allylation step. b Refers to yield of isolated, purified
product. Yields are not optimized. The purity of all products was determined to be 96-99% by 1H and 13C NMR spectroscopy and GC
analysis. Superscript against yield refers to literature reference for the product. c Only 0.1 mol % Bi(OTf)3‚xH2O was used. The allylation
proceeded without the need for additional catalyst. d Ethanol and HC(OEt)3 were used in place of CH3OH and HC(OMe)3.
commercially available and must be synthesized from the
corresponding aldehydes.16 In addition, most of these
methods only report allylation of dimethyl or diethyl
acetals which results in the formation of homoallyl
methyl or ethyl ethers, respectively. Although the alkene
moiety of homoallyl alkyl ethers can be easily trans-
formed into other groups, alkyl ethers are somewhat inert
and not amenable to easy synthetic manipulation. An-
other disadvantage of this approach is that many acetals
have poor shelf lives. However, there are very few reports
of one-pot syntheses of homoallyl ethers and homoallyl
acetates from aldehydes.17 Further, many of these meth-
ods require the use of corrosive catalysts such as TMS
triflate or expensive, highly moisture-sensitive and toxic
catalysts such as Sc(OTf)3. Recently, an environment-
friendly approach to the synthesis of homoallyl benzyl
ethers, in which the acetal is generated in situ from the
corresponding aldehyde using FeCl3 as the catalyst, has
been reported.18 With increasing environmental concerns,
the need for environmentally benign synthetic chemistry
has assumed significant importance. According to the
principles of green chemistry, synthetic methods should
be designed to use substances that exhibit little or no
toxicity to human health and the environment.19 In this
regard, bismuth compounds have recently attracted
considerable attention. Bismuth compounds are remark-
ably nontoxic,20 and many bismuth reagents have proven
to be versatile catalysts for a variety of organic trans-
formations.21 The low toxicity of bismuth has earned it
the status of a green element. Our continued interest in
bismuth compounds, due largely to their remarkably low
toxicity, low cost, and ease of handling, prompted us to
investigate a bismuth(III) triflate catalyzed one-pot ap-
proach to the synthesis of homoallyl ethers and homoallyl
acetates.22 A one-pot synthesis saves steps by eliminating
the need to isolate the intermediate and thus minimizes
waste. Herein we report the results of our studies leading
(18) Watahiki, T.; Akabane, Y.; Mori, S.; Oriyama, T. Org. Lett. 2003,
5, 3045.
(19) Anastas, P.; Warner, J. C. In Green Chemistry: Theory and
Practice; Oxford University Press: Oxford, 1998.
(16) For bismuth triflate catalyzed synthesis of acetals, see:
Leonard, N. M.; Oswald, M. C.; Freiberg, D. A.; Nattier, B. A.; Smith,
R. C.; Mohan, R. S. J. Org. Chem. 2002, 67, 5202.
(17) (a) Sakurai, H.; Sasaki, K.; Hayashi, J.; Hosomi, A. J. Org.
Chem. 1984, 49, 2808. (b) Mekhalfia, A.; Marko´, I. E. Tetrahedron Lett.
1991, 32, 4779 (c) Wang, M. W.; Chen, Y. J.; Wang, D. Synlett 2000,
385.
(20) (a) Reglinski, J. In Chemistry of Arsenic, Antimony and
Bismuth; Norman, N. C., Ed.; Blackie Academic and Professional: New
York, 1998; pp 403-440. (b) Organobismuth Chemistry; Suzuki, H.,
Matano, Y., Ed.; Elsevier: Amsterdam, 2001.
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Bismuth Compounds in Organic Synthesis
TABLE 2. Bismuth Triflate Catalyzed
Three-Component Synthesis of Homoallyl Ethers Using
Trialkylorthoformatesa
to the development of three one-pot methods for the
conversion of aldehydes to a variety of homoallyl ethers
(Tables 1-3) catalyzed by bismuth(III) triflate. In the
first approach (Table 1), the acetal was generated in situ
and then converted to the corresponding homoallyl ether.
The use of a nonaqueous workup eliminates an aqueous
waste stream. The acetal was generated in situ by
reaction of the aldehyde with trialkylorthoformate and
the corresponding alcohol in the presence of 0.1 mol %
Bi(OTf)3‚xH2O. The reaction progress was monitored by
GC. After the aldehyde was consumed, the alcohol was
removed under reduced pressure, and then acetonitrile,
the corresponding allylsilane, and 1.0 mol % of the
catalyst were added. It was found that this was more
effective than having 1.0 mol % Bi(OTf)3‚xH2O in the
beginning of the reaction. If the methanol was not
removed prior to addition of the allyltrimethylsilane, no
allylation was observed and the acetal intermediate was
isolated. With a more nucleophilic silane such as meth-
allyltrimethylsilane (Table 1, entry 2), the reaction
proceeded without the addition of the second portion of
the catalyst. To the best of our knowledge, this is the first
example of such a highly catalytic one-pot method for the
generation of homoallyl ethers. This procedure works well
with a variety of aldehydes. Both dimethyl and diethyl
acetals (entry 6) could be generated easily and converted
to the corresponding homoallyl ethers.
The allylation reaction proceeded rapidly and smoothly
at room temperature in all cases. In contrast, the use of
harsher Lewis acid catalysts such as TiCl4 requires
inconveniently low temperatures (-78 °C) for the ally-
lation reaction.1 Acetals derived from ketones reacted
sluggishly with allyltrimethylsilane. In a few trial runs
with cyclohexanone and acetophenone, the expected
homoallyl ether did form, but significant amounts of
unreacted ketone remained (>30%). Although with time
(24 h) the ketone was slowly converted to the homoallyl
ether, indicating that an equilibrium exists between the
ketone and acetal, the allylation reaction never reached
completion.
a Reaction conditions: 2 equiv of trialkylorthoformate and 2
equiv of allyltrimethylsilane were used. b Refers to yield of isolated,
purified product. Yields are not optimized. The purity of all
products was determined to be 96-99% by 1H and 13C NMR
spectroscopy and GC analysis unless otherwise mentioned. Su-
perscript against yield refers to literature reference for the product.
c Reaction was carried out with 5.0 mol % of Bi(OTf)3‚xH2O.
d Reaction was carried out with 2.0 mol % of Bi(OTf)3‚xH2O.
e Product was determined to be 94% pure by GC and NMR
spectroscopy. Remainder was starting material.
During the course of developing the sequential one-
pot allylation method with aldehydes, we found that even
if acetal formation was not complete (ca. 70% complete
as determined by GC analysis), high yields of the ho-
moallyl ether were obtained upon addition of the allyl-
trimethylsilane. This observation suggested that the
reaction of the acetal with allyltrimethylsilane shifts the
aldehyde-acetal equilibrium toward acetal formation,
which subsequently undergoes rapid allylation. This
observation prompted us to investigate a three-compo-
nent, one-pot method for the conversion of aldehydes to
homoallyl ethers.23 These results are summarized in
Table 2. This method involves stirring the aldehyde,
trialkylorthoformate, and allyltrimethylsilane in the
presence of Bi(OTf)3‚xH2O in CH3CN. The reaction is
rapid and gives moderate to good yields of the homoallyl
ether (Table 2). A control experiment revealed that the
reaction of allyltrimethylsilane with aldehydes under the
reaction conditions is very slow. Although allyltrimeth-
ylsilane does react with trialkylorthoformates, the suc-
cess of the three-component method indicates that the
conversion of the aldehyde to the acetal is the fastest
reaction in the pot and the acetal in turn undergoes rapid
allylation. Although the method worked with the aro-
matic conjugated aldehyde, cinnamaldehyde (entry 5), the
attempted conversion of trans-2-hexenal (entry 6) to the
corresponding homoallyl ethyl ether gave poor yields.
(21) For recent reviews on use of bismuth(III) compounds in organic
synthesis, see: (a) Leonard, N. M.; Wieland, L. C.; Mohan, R. S.
Tetrahedron 2002, 58, 8373. (b) Gaspard-Iloughmane, H.; Le Roux, C.
Eur. J. Org. Chem. 2004, 2517. For some recent applications of
Bi(OTf)3 as a catalyst in organic synthesis, see: (c) Yadav, J. S.; Reddy,
B. V. Subba; Swamy, T.; Rao, Raghavender, K. Tetrahedron Lett. 2004,
45, 6037. (d) Yadav, J. S.; Reddy, B. V. S.; Premalatha, K. Synlett 2004,
963. (e) Matsushita, Y.; Sugamoto, K.; Matsui, T. Tetrahedron Lett.
2004, 45, 4723. (f) Ollevier, T.; Lavie-Compin, G. Tetrahedron Lett.
2004, 45, 49. (g) Arnold, J. N.; Hayes, P. D.; Kohaus, R. L.; Mohan, R.
S. Tetrahedron Lett. 2003, 44, 9173.
(22) Bismuth triflate was purchased from Lancaster Chemical Co.
It can also be synthesized in the laboratory from triphenylbismuth and
triflic acid. See: Labrouille`re, M.; Le Roux, C.; Gaspard, H.; Laporterie,
A.; Dubac, J.; Desmurs, J. R. Tetrahedron Lett. 1999, 40, 285. Recently,
a synthesis of bismuth triflate from bismuth oxide and triflic acid in
aqueous ethanol has been reported. Re´pichet, S.; Zwick, A.; Vendier,
L.; Le Roux, C.; Dubac, J. Tetrahedron Lett. 2002, 43, 993. A more
convenient procedure for the synthesis of bismuth triflate uses
chlorobenzene as the solvent. See: Peyronneau, S. M.; Arrondo, C.;
Vendier, L.; Roques, N.; Le Roux, C. J. Mol. Catal. A 2004, 211, 89.
(23) A one-pot method for the conversion of aldehydes to homoallyl
ethers catalyzed by 10 mol % of Sc(OTf)3 has been reported (ref 13).
J. Org. Chem, Vol. 70, No. 6, 2005 2093

Anzalone et al.
TABLE 3. Bismuth Triflate Catalyzed Three-Component Synthesis of Homoallyl Ethers Using Alkoxytrimethylsilanes
a Reactions were carried out using 1.2 equiv of allyltrimethylsilane unless otherwise mentioned. b Refers to yield of isolated, purified
product. Yields are not optimized. The purity of all products was determined to be 96-99% by 1H and 13C NMR spectroscopy and GC
analysis. Superscript numbers refer to the literature reference for the product. c Reaction was carried out using 2.0 equiv of
allyltrimethylsilane. d Reaction was carried out neat. e Reaction was carried out using 1.7 equiv of allyltrimethylsilane.
Even after 2.5 h, the crude product contained significant
amounts of unreacted starting material (20%) in addition
to several unidentifiable products that contained olefinic
protons as indicated by NMR analysis. The desired
homoallyl ether product was obtained in low yield after
flash chromatography. Similar results have been reported
with the use of AlCl3 or BF3‚Et2O as a catalyst.2 The low
yields were attributed to the formation of polymeric
material. Again, it was not possible to achieve high con-
version with ketones. With cyclohexanone, after 18 h, the
corresponding homoallyl ether was obtained in a 40%
yield after chromatographic purification. With acetophe-
none, less than 40% product formed after 24 h.
One drawback of the method outlined in Table 2 is that
only a few trialkylorthoformates are commercially avail-
able, thus limiting the type of homoallyl ether that can
be synthesized by this method. Hence, we investigated
the utility of alkoxytrimethylsilanes to achieve similar
transformations. This approach to generating homoallyl
ethers presents several advantages. A wide range of
alkoxytrimethylsilanes is commercially available. Also,
we were able to carry out the reaction with 0.1-1.0 mol
% bismuth triflate instead of 2.0-5.0 mol % required in
the procedure using trialkylorthoformates (Table 2). The
versatility of this method can be seen from the results
presented in Table 3. A wide variety of homoallyl ethers
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Bismuth Compounds in Organic Synthesis
TABLE 4. Three-Component Method for the Conversion
of Aldehydes to Homoallyl Acetates Using Bi(OTf)3‚xH2O
as a Catalysta
an approach using Sc(OTf)3 as the catalyst has been
reported by Aggarwal and co-workers.26 The success of
this method again relies on the fact that the allylation
of aldehydes under the reaction conditions is slow. Thus,
the aldehyde is first converted to the acylal which then
leads to the homoallyl acetate. Confirming this, we
detected the intermediacy of an acylal in these reactions
by NMR spectroscopy.27 The low yields are a consequence
of diallylation that occurs as a side reaction. In fact, with
aldehydes containing a strongly electron-donating group
such as p-MeO (entry 5, Table 4), the major product was
one resulting from diallylation. With a conjugated alde-
hyde such as cinnamaldehyde, the reaction gave a
complex mixture consisting of unreacted starting mate-
rial, acylal, as well as mono- and diallylation product.
With aliphatic aldehydes, the reaction did not proceed
to any significant extent at all. Although we have
previously reported that acylals can be generated easily
from aliphatic aldehydes under solvent-free conditions,
the attempted one-pot synthesis of homoallyl acetates
from aldehydes under solvent free conditions did not
work. When the acylal generated from heptanal was
reacted with allyltrimethylsilane, even after 24 h, very
little homoallyl acetate formed (<10% as indicated by
NMR analysis). The remainder was a mixture of unre-
acted acylal and aldehyde. The aldehyde is presumably
obtained by deprotection of the acylal catalyzed by
bismuth triflate during the prolonged reaction time.
a Reaction conditions: 3 equiv of acetic anhydride and 2 equiv
of allyltrimethylsilane were used. b Refers to yield of isolated,
purified product. Superscript numbers refer to the literature
reference for the product.
including allyl, benzyl, ethyl, and methyl ethers could be
synthesized. Homoallyl benzyl ethers allow functional
group manipulation at the alkene as well as at the benzyl
group, whereas homoallyl alkyl ethers are somewhat
inert at the ether functionality. The formation of homo-
allyl benzyl ethers from aliphatic aldehydes (Table 3,
entry 3d) did not give high yields. Although the alde-
hyde was consumed in <1 h, purification of the crude
product by flash chromatography gave only 30-45% yield
of the desired product. Similar results were obtained with
heptanal and decanal.
Homoallyl allyl ethers can serve as useful precursors
to cyclic enol ethers via ring-closing metathesis reac-
tions.24 Hence, a simple method for their synthesis is
quite desirable. Entries 4a and 4b (Table 3) illustrate the
synthesis of two such compounds. The three-component
synthesis did not work well with ketones, and even after
extended reaction times (48 h), the product mixture was
found to be a mixture of unreacted ketone, acetal, and
the desired product. It was not possible to exceed 50%
conversion even with increased catalyst loading or in-
creased equivalents (2.0) of the allyltrimethylsilane and
the alkoxytrimethylsilane.
The conversion of acylals (1,1-diesters) to homoallyl
esters has been reported in the literature. At least three
approaches to the one-pot synthesis of homoallyl acetates
from aldehydes are possible. One approach consists of
converting the aldehyde to the homoallyl alcohol followed
by acylation.25 A second approach would be to convert
the aldehyde to the corresponding acylal (1,1-diester) and
then react it with allyltrimethylsilane. A third approach,
which we report here, consists of a three-component
synthesis of homoallyl acetates starting with aromatic
aldehydes and catalyzed by Bi(OTf)3‚xH2O (Table 4). Such
Conclusions
In summary, three highly catalytic, one-pot methods
for the conversion of aldehydes to homoallyl ethers have
been developed using bismuth triflate as a catalyst. A
one-pot method for the conversion of aldehydes to ho-
moallyl acetates has also been developed. The advantages
of these methods include the use of an easy to handle,
nontoxic catalyst and the generation of the homoallyl
ether or acetate in one step.
Experimental Section
Representative Procedure for the One-Pot Synthesis
of a Homoallyl Ether from an Aldehyde. A solution of
benzaldehyde (2.00 g, 18.85 mmol) and trimethylorthoformate
(3.00 g, 28.28 mmol, 1.5 equiv) in anhydrous CH3OH (6 mL)
was stirred at rt as Bi(OTf)3‚xH2O (12.3 mg, 0.1 mol %) was
added. The reaction mixture was heated at reflux under N2,
and the reaction progress was monitored by GC analysis.
When acetal formation was >95% (1 h), the reaction mixture
was cooled and methanol was removed on a rotary evaporator.
Anhydrous acetonitrile (20 mL) was added to the pot residue
followed by addition of allyltrimethylsilane (3.66 g, 32.05
mmol, 2 equiv) and Bi(OTf)3‚xH2O (0.1237 g, 1.0 mol %). The
reaction was stirred for 10 min at rt, and then solid Na2CO3
(0.5 g) was added and the mixture was stirred for 15 min. The
(26) Aggarwal, V. K.; Vennall, G. P. Synthesis 1998, 1822. Scandium
triflate is more difficult to handle than bismuth triflate due to its
hygroscopic nature and is considerably more expensive.
(27) The Bi(OTf)3‚xH2O-catalyzed conversion of aldehydes to acylals
has been reported. See: Carrigan, M. D.; Eash, K. J.; Oswald, M. C.;
Mohan, R. S. Tetrahedron Lett. 2001, 42, 8133.
(28) Sakurai, H.; Sasaki, K.; Hosomi, A. Tetrahedron Lett. 1981, 22,
745.
(29) Fujita, K.; Inoue, A.; Shinokubo, H.; Oshima, K. Org. Lett. 1999,
1, 917.
(30) Hixson, S. S.; Franke, L. A.; Gere, J. A.; Xing, Y. D. J. Am.
Chem. Soc. 1988, 110, 3601.
(24) Sutton, A. E.; Seigal, B. A.; Finnegan, D. F.; Snapper, M. L. J.
Am. Chem. Soc. 2002, 124, 13390.
(25) Chandrasekhar, S.; Mohanty, P. K.; Raza, A. Synth. Commun.
1999, 29, 257.
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Anzalone et al.
mixture was filtered, and the solids were rinsed with ether
(10 mL). The combined filtrates were concentrated on a rotary
evaporator to yield the crude product which was purified by
filtration through a short plug of silica gel (5% EtOAc/hexanes)
to afford the homoallyl ether as a colorless oil (2.29 g, 75%,
>99% pure by 1H and 13C NMR spectroscopy and GC analysis).
Representative Procedure for One-Pot Three-Com-
ponent Synthesis of a Homoallyl Ether from an Alde-
hyde Using a Trialkylorthoformate. A solution of piperonal
(0.502 g, 3.33 mmol) in CH3CN (5 mL) was stirred at rt as
HC(OMe)3 (0.707 g, 6.66 mmol), allyltrimethylsilane (0.761 g,
6.66 mmol), and Bi(OTf)3‚xH2O (0.044 g, 0.067 mmol) were
added. The solution turned red and, over time, became
colorless. After 75 min, solid Na2CO3 (1.0 g) was added, and
the mixture was stirred for 10 min. The reaction mixture was
filtered, and the solids were rinsed with ether (10 mL). The
combined filtrates were removed on a rotary evaporator to
yield 0.625 g of a colorless liquid. The crude product was
purified by flash chromatography on 30 g of silica gel (10%
EtOAc/hexanes) to yield the homoallyl ether product as a
colorless liquid (0.56 g, 82%, >98% by 1H and 13C NMR
spectroscopy and GC analysis).
Representative Procedure for One-Pot Three-Com-
ponent Synthesis of a Homoallyl Ether from an Alde-
hyde Using Alkoxytrimethylsilanes. A solution of benzal-
dehyde (0.5020 g, 4.72 mmol) in CH2Cl2 (10 mL) was stirred
at 0 °C as benzyloxytrimethylsilane (1.020 g, 1.1 mL, 5.66
mmol), allyltrimethylsilane (0.6470 g, 0.90 mL, 5.66 mmol),
and Bi(OTf)3‚xH2O (0.0310 g, 0.0472 mmol) were added. After
40 min, the reaction mixture was diluted with CH2Cl2 (20 mL),
and the organic layer was washed with 10% aqueous Na2CO3
(15 mL), saturated NaCl (15 mL) and dried (Na2SO4). The
solvent was removed on a rotary evaporator to yield 1.2746 g
of the crude product, which was purified by flash chromatog-
raphy on 70 g silica (5% EtOAc/hexane) to yield the homoallyl
benzyl ether as a clear colorless liquid (0.8976 g, 80% yield,
1
>98% by H and 13C NMR spectroscopy and GC analysis).
Representative Procedure for One-Pot Three-Com-
ponent Synthesis of a Homoallyl Acetate from an Alde-
hyde. A solution of benzaldehyde (0.5123 g, 4.828 mmol),
acetic anhydride (1.479 g, 14.493 mmol), and allyltrimethyl-
silane (1.099 g, 1.53 mL, 9.627 mmol) in anhydrous acetonitrile
(5.0 mL) was stirred under N2 as Bi(OTf)3‚xH2O (0.1605 g,
0.2446 mmol, 5.0 mol %) was added. After 1 h, aqueous 10%
Na2CO3 (15 mL) was added to the reaction and the mixture
was stirred for 15 min. The reaction mixture was extracted
with EtOAc (2 × 20 mL) and washed with water (3 × 15 mL).
The organic layer was washed with aqueous saturated NaCl
(15 mL) and dried (Na2SO4). The solvents were removed on a
rotary evaporator to yield an orange liquid that was purified
by flash chromatography on 10 g of silica gel (5% EtOAc/
hexanes) to yield the homoallyl acetate as a colorless oil (0.6065
g, 66%, >98% by 1H and 13C NMR spectroscopy and GC
analysis).
Acknowledgment. R.S.M. thanks The Camille
and Henry Dreyfus Foundation for a Henry Dreyfus
Teacher-Scholar Award. We also gratefully acknowl-
edge funding from the National Science Foundation
(RUI Grant No. 0350216).
Supporting Information Available: General Experi-
mental Section and spectral data (1H and 13C NMR spectra)
for all compounds whose spectral data has not been previously
reported in the literature. This material is available free of
charge via the Internet at http://pubs.acs.org.
JO048475M
2096 J. Org. Chem., Vol. 70, No. 6, 2005