An efficient bismuth(III) chloride-catalyzed synthesis of 1,1-di-arylalkenes via Friedel-Crafts reaction of acyl chloride or vinyl chloride with arenes

Article abstract of DOI:10.1002/adsc.200606157

In the presence of catalytic amount of bismuth(III) chloride, the reactions of acyl chlorides or vinyl chlorides with arenes afforded 1,1-diarylalkenes in 25-82% isolated yield. In the case of the reaction of acyl chlorides with arenes, the procedure includes an initial Friedel-Crafts acylation, subsequent formation of vinyl chlorides and final Friedel-Crafts-type vinylation of another arene molecule with vinyl chloride. This paper reports the first Lewis acid-catalyzed cleavage of the C-Cl bond of vinyl chloride and its application in the synthesis of multiply subtituted alkenes.

Full text of DOI:10.1002/adsc.200606157

FULL PAPERS
DOI: 10.1002/adsc.200606157
An Efficient Bismuth(III) Chloride-Catalyzed Synthesis of 1,1-Di-
N
arylalkenes via Friedel–Crafts Reaction of Acyl Chloride or Vinyl
Chloride with Arenes
Hongbin Sun,a,b Ruimao Hua,a,* Songjie Chen,a and Yingwu Yinb
a
Department of Chemistry, Tsinghua University, Key Laboratory of Organic Optoelectronics & Molecular Engineering of
Ministry of Education, Beijing 100084, People’s Republic of China
Fax: (+86)-10-6279-2596; e-mail: ruimao@mail.tsinghua.edu.cn
Key Laboratory of Bioorganic Phosphorus Chemistry of Ministry of Education, Beijing 100084, People’s Republic of
b
China
Received: April 1, 2006; Accepted: June 19, 2006
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: In the presence of catalytic amount of with vinyl chloride. This paper reports the first Lewis
À
bismuth
G
or vinyl chlorides with arenes afforded 1,1-diarylal- chloride and its application in the synthesis of multi-
kenes in 25–82% isolated yield. In the case of the re- ply subtituted alkenes.
action of acyl chlorides with arenes, the procedure
includes an initial Friedel–Crafts acylation, subse- Keywords: acyl chlorides; arenes; bismuth(III) chlo-
quent formation of vinyl chlorides and final Friedel– ride; 1,1-diarylalkenes; Friedel–Crafts reaction; vinyl
Crafts-type vinylation of another arene molecule chlorides
Introduction
cleaved by Lewis acids (BiCl3). To the best of our
knowledge, there has been no report on a Lewis acid-
À
1,1-Diarylalkenes are an important class of organic catalyzed cleavage of the C Cl bond of vinyl chloride
compounds, which are useful intermediates in organic for Friedel–Crafts-type vinylation, although the transi-
À
synthesis, particularly in the preparation of fluores- tion metal-catalyzed cleavage of the C Cl bond and
cent materials.[1] Some of 1,1-diarylalkene moiety-con- its application in C C bond formation have been well
À
taining compounds have physiological and biological documented.[7]
activities.[2] 1,1-Diarylalkenes are usually synthesized
through multistep reactions, thus the development of
simple, efficient methods is still an interesting and sig- Results and Discussion
nificant subject of organic synthesis.
Because bismuth
A
Bi
A
(NO3)3 are stable in air, relatively the preparation of aryl ketones. In the course of our
non-toxic and inexpensive when compared with tran- study on the development of the BiCl3-catalyzed Frie-
sition metal complexes, in recent years the diverse ap- del–Crafts acylation of mesitylene (1a) with cyclohex-
plications of bismuth(III) salts as catalysts in organic anecarbonyl chloride (2a) (Scheme 1), we have found
G
synthesis have been reported. In this work, with the that when a mixture of 1a (4.0 mmol), 2a (2.0 mmol)
purpose of developing new synthetic methods for 1,1- and BiCl3 (0.2 mmol) was heated at 1208C with stir-
diarylalkenes from simple and easily available starting ring for 16 h, the reaction produced an unidentified
materials, we investigated the reactions of acyl chlor- compound 3a as major product, along with the forma-
ides with arenes in the presence of catalytic amounts tion of a small amount of [chloro-(2,4,6-trimethylphe-
of BiCl3, in which 1,1-diarylalkenes were obtained in- nyl)-methylene]-cyclohexane (4a) (<5%), a trace
stead of normal Friedel–Crafts acylation products. amount of the expected cyclohexylmesitylmethanone
The results reported in this paper disclose an unprece- (5), and a considerable amount of cyclohexanecarbox-
dented Friedel–Crafts-type vinylation of arenes in ylic acid as confirmed by GC and GC-MS analyses.
which the C Cl bond of vinyl chlorides is catalytically Compound 3a was isolated in 42% yield,[8] and
À
Adv. Synth. Catal. 2006, 348, 1919 – 1925
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Hongbin Sun et al.
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In order to elucidate the route of the formation of
3a, under the same reaction conditions, the reaction
of 1a with 5 was examined, and 3a was not formed at
all, both 1a and 5 were recovered completely. Further-
more, we also carried out the reaction of 1a with 2a
in a sealed tube with an HCl saturated solution at
1208C for 10 h, the formation of 3a could not be de-
tected by GC and GC-MS.
Therefore, the present one-pot formation of 3a
from the reaction of 1a with 2a indicates the genera-
tion of the vinyl chloride in the reaction mixture, and
the proposed reaction route is shown in Scheme 2. It
involves the initial Friedel–Crafts acylation of arene
with acyl chloride to produce aryl ketone (5), and
then HCl or acyl chloride converts this to the vinyl
chloride (4), and the final Friedel–Crafts-type vinyla-
Scheme 1.
showed a molecular ion peak at m/z=332. Both tion of 4 with another arene molecule to afford 3.
13C NMR and IR spectra indicate that 3a does not This new catalytic procedure disclosed two interesting
contain a ketone group. The structure of 3a was final- transformations: (1) the formation of vinyl chloride
ly determined by X-ray crystallography and shown in from a ketone; (2) the Friedel–Crafts-type vinylation
Figure 1.[9] A noteworthy feature in the conformation of an arene in the presence of BiCl3.
of 3a is that the two aryl groups are not coplanar.
It had been reported that aryl ketones could be
converted into vinyl chlorides by the reactions of aryl
ketones with acetyl chloride in the presence of silica
gel-supported ZnCl2.[10] In order to get the substantial
evidence to confirm the formation of vinyl chlorides
in the present BiCl3-catalyzed reaction, we have also
examined the reaction of aryl ketones with acyl chlor-
ides, and disclosed that BiCl3 is an efficient catalyst
for the transformation of aryl ketones into vinyl chlor-
ides. For example, when 2,3,5,6-tetramethyl-isobutyro-
phenone and propionyl chloride in CCl4 were heated
at 1208C for 6 h in the presence of BiCl3, the corre-
sponding vinyl chloride was obtained in good yield
(Scheme 3).
Figure 1. Crystal structure of 3a.
Scheme 3.
Scheme 2. Proposed mechanism for the formation of 3.
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Bismuth(III) Chloride-Catalyzed Synthesis of 1,1-Diarylalkenes
A
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In order to determine the scope and limitation of
In addition, we have performed the reactions of 1a
this new catalytic reaction, the reactions of 1a with with acetyl chloride, chloroacetyl chloride, and diphe-
several acyl chlorides 2 were examined. The reaction nylacetyl chloride. However, acetyl chloride and
progress was monitored by GC, and the time indicat- chloroacetyl chloride proceeded by the normal Frie-
ed in Table 1 was the optimal reaction time. As del–Crafts acylation to give the corresponding acyl
ketones in 60% and 62% isolated yields, respectively,
and the reaction of diphenylacetyl chloride produced
the vinyl chloride-type compound as major product
(31% isolated yield). Only trace amounts of 3-type
compounds were found in the reaction mixtures
(Scheme 4).
Table 1. BiCl3-catalyzed reaction of mesitylene with acyl
chlorides.[a]
Scheme 4.
Pentamethylbenzene (1b) is a more nucleophilic
substrate than 1a, but unexpectedly, the reaction of
1b with 2b in the presence of BiBr3 at 1208C for 20 h
gave the product 3e in only 27% yield (Scheme 5).
[a]
Reactions were carried out using 4 mmol of 1a, 2 mmol
of 2 and 0.2 mmol of catalyst.
Based on the amount of 2 used. Values in parentheses
[b]
Scheme 5.
are GC yields.
BiBr3 was used as catalyst.
[c]
Furthermore, under the reaction conditions as indi-
shown in Table 1, a-monosubstituted acyl chlorides cated in Table 1, the reactions of a variety of other
showed higher reactivity than a,a-disubstituted ones. arenes such as 2-bromomesitylene, 1,2,4,5-tetrame-
Thus the reaction of 1a with 2b afforded 3b in 62% thylbenzene, m-xylene and toluene could not produce
yield (Table 1, entry 2). Repeating the same reaction the corresponding 1,1-diarylalkenes 3 at all.
using BiBr3 as catalyst resulted in the similar result,
Although many attempts including changing the
indicating that both BiCl3 and BiBr3 displayed the ratio of reactants, performing the reactions at differ-
similar catalytic activity (Table 1, entry 3). In the case ent temperatures and using different bismuth salts as
of isobutyryl chloride (2c), the corresponding tetra- catalysts have been made with the purpose to im-
substituted alkene 3c was obtained in only 25% prove the yield of 3 in the reactions included in
(34% GC yield, Table 1, entry 4). As expected, 2d Table 1, little improvement was achieved. Therefore,
showed reactivity similar to that of 2b to produce 3d we next turned our attention to the reaction of vinyl
in 63% yield (Table 1, entry 5). The formation of 3b chloride 4 with arenes to develop the Friedel–Crafts-
and 3d in higher yields was considered to be due to type vinylation and the general synthetic method to
the lower steric hindrance of their structures.
make 1,1-diarylalkenes 3 in the presence of BiCl3.
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Hongbin Sun et al.
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We initiated our studies on the synthesis of vinyl
chloride 4 with the same reaction as described above
by changing the reaction conditions. Fortunately,
when the reaction of 1a with 2a was carried out at a
lower temperature (at 808C) and a shorten reaction
time (2 h), 4a was formed as a major product and
could be isolated from the reaction mixture in 61%
yield (Scheme 6). Next, we investigated the reactions
Scheme 6.
of 4a with a variety of arenes (4.0 equivs.) in the pres- action shown in Scheme 5. The reaction of 4a with 1c
ence of BiCl3. As shown in Table 2, the reaction of 4a produced a mixture of 3g and 3g’ in a ratio of 84:16
with 1a in the presence of BiCl3 at 1208C for 16 h af- (Table 2, entry 3).[11] Notably, in the cases of 1d–g
forded 3a in a good isolated yield (62%, Table 2, used, the reactions proceeded with high selectivity to
entry 1). However, the reaction of 4a with 1b gave 3f generate the 1,1-diaryl alkenes 3h–k in good yields
also in a low yield (Table 2, entry 2), similar to the re- (Table 2, entries 4–7). In the reaction of 4a with 1h,
Table 2. BiCl3-catalyzed Friedel–Crafts-type vinylation of arenes.[a]
[a]
Reactions were carried out using 4 mmol of 1a, 2 mmol of 2 and 0.2 mmol of catalyst.
Based on the amount of 4a used. Values in parentheses are GC yields. Selectivity is the ratio of the major product to the
[b]
other product(s) in the reaction mixture.
At 1508C in a sealed glass tube using 0.5 mL of benzene.
[c]
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Bismuth(III) Chloride-Catalyzed Synthesis of 1,1-Diarylalkenes
A
FULL PAPERS
Table 3. BiCl3-catalyzed Friedel–Crafts-type vinylation of arenes.[a]
[a]
Reactions were carried out using 4 mmol of 1a, 2 mmol of 2 and 0.2 mmol of catalyst.
Based on the amount of 4 used. Selectivity is the ratio of the major product to the other product(s) in the reaction mix-
[b]
ture.
[c]
At 1508C in a sealed glass tube using 0.5 mL of 1i.
two isomers were formed in a ratio of 79:21 (Table 2, products 3p and 3p’ in a ratio of 79:21 in 77% total
entry 8), the structure of 3l’ was tentatively assigned yield (Table 3, entry 2), while the latter gave 3q in a
by compared with the results of the reaction of a- high selectivity (Table 3, entry 3). These results indi-
chloro-2,3,4,5,6-pentamethylstyrene (4c) with 1e (vide cated that in the case of the trisubstituted vinyl chlo-
Table 3, entry 2). In addition, the reactions of 4a with ride (e.g., 4d) used, the formation of 3p’-type com-
the electron-neutral arenes also occurred smoothly. pound was unfavorable due to the steric hindrance.
Thus, benzene (1i) reacted with 4a to give 3m in 64% Compound 3p and 3p’ could be separated by careful
yield (Table 2, entry 9), and naphthalene (1j) afforded two-fold preparative TLC separation, and the struc-
the corresponding vinylated products, 3n and 3n’, in ture of 3p’ obtained from the vinylation of the meta-
1
80% yield in a ratio of 55:45 (Table 2, entry 10). Be- position of 1e with 4c was confirmed by its H NMR
cause attempts to separate 3n and 3n’ failed, again, spectroscopic data (see Supporting Information). In
we tentatively assigned the b-substituted naphthalene addition, in a sealed tube, 4d reacted with 1i at an ele-
3n as the major product on the basis of the higher re- vated temperature (1508C) in the presence of BiBr3
activity of the b-position of naphthalene in Friedel– resulting in the formation of 3r in 82% yield (Table 3,
Crafts alkylation.
entry 4).
It should be noted that, under the present reaction
conditions, the electron-deficient arenes could not un-
dergo a similar vinylation reaction.
Conclusions
Furthermore, three other vinyl chlorides were pre-
pared and their reactivity with arenes were also exam- In conclusion, we investigated the reactions of arenes
ined. As demonstrated in Table 3, the reaction of a- with acid chlorides or with vinyl chlorides in the pres-
chloro-2,4,6-trimethylstyrene (4b) with 1a afforded 3o ence of BiCl3. The present catalytic procedure pro-
in 80% isolated yield (Table 3, entry 1). The forma- vides a one-pot synthetic method for the synthesis of
tion of 3o in a higher yield (80%) than 3a (62%) by various 1,1-diarylalkenes. The reaction includes both
the reaction of 4a with 1a might be due to the lower the unusual formation of vinyl chlorides and the Frie-
steric hindrance of 3o (Table 3, entry 1 vs. Table 2, del–Crafts-type vinylation of arenes catalyzed by
entry 1). The reaction of 4c or 1-chloro-1-mesityl-2- BiCl3. Further studies to develop another new catalyt-
À
methylpropene (4d) with 1e displayed significantly ic C C bond formation using bismuth(III) salts as cat-
G
different selectivity. The former afforded a mixture of alysts are now in progress.
Adv. Synth. Catal. 2006, 348, 1919 – 1925
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Hongbin Sun et al.
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Cushman, J. Med. Chem. 2001, 44, 4092–4113; c) M. A.
Silvestri, M. Nagarajam, E. De Clercq, C. Pannecou-
que, M. Cushman, J. Med. Chem. 2004, 47, 3149–3162;
d) T. Kamei, K. Itami, J. Yoshida, Adv. Synth. Catal.
2004, 346, 1824–1835, and references cited therein.
[3] Recent reports, see: a) T. Ohe, S. Uemura, Tetrahedron
Lett. 2002, 43, 1269–1271; b) G. Sabitha, E. V. Reddy,
C. Maruthi, J. S. Yadav, Tetrahedron Lett. 2002, 43,
1573–1575; c) N. R. Swamy, Y. Venkateswarlu, Tetrahe-
dron Lett. 2002, 43, 7549–7552; d) T. Ollevier, G.
Lavie-Compin, Tetrahedron Lett. 2002, 43, 7891–7893;
e) S. Repichet, C. Le Roux, N. Roques, J. Dubac, Tetra-
hedron Lett. 2003, 44, 2037–2040; f) G. Sabitha, E. V.
Reddy, R. Swapna, N. M. Reddy, J. S. Yadav, Synlett
2004, 1276–1278; g) S. K. De, R. A. Gibbs, Tetrahedron
Lett. 2004, 45, 7407–7408; h) J. A. R. Salvador, S. M.
Silvestre, Tetrahedron Lett. 2005, 46, 2581–2584;
i) S. K. De, R. A. Gibbs Tetrahedron Lett. 2005, 46,
8345–8350.
Experimental Section
General Methods
1H and 13C NMR spectra were recorded on a JEOL JNM-
ECA 300 spectrometer at 300 MHz and 75 MHz, respective-
ly. The chemical shifts (d) were referenced to TMS or inter-
nal solvent resonance. GC-MS was obtained on a Hewlett
Packard Series II 5890 GC/MS spectrometer. High-resolu-
tion mass spectra were obtained with a ZAB-HS mass spec-
trometer in the Department of Chemistry of Beijing Univer-
sity. GC analyses were performed on an Agilent Technolo-
gies 1790 GC instrument. All reactions were carried out
under air. Solvents and all reagents were used as received.
Typical Procedure for the Synthesis of 1,1-
Diarylalkenes from the Reaction of Arenes with Acyl
Chlorides: Formation of 3a (Table 1, entry1)
A mixture of mesitylene (1a) (480.0 mg, 4.0 mmol), cyclo-
hexanecarbonyl chloride (2a) (293.0 mg, 2.0 mmol) and
BiCl3 (63.0 mg, 0.2 mmol) was heated with stirring at 1208C
for 16 h. After cooling to room temperature, cyclohexane
(15 mL) was added and the insoluble materials were filtered
out. Removal of the solvent and volatiles under reduced
pressure afforded a viscous residue, which was dissolved in
CH2Cl2 (3.0 mL), and the resulting solution was subjected to
preparative TLC (silica) separation using a mixture of dieth-
yl ether and cyclohexane (2:100 v/v) to afford 3a as a white
solid; yield: 269.0 mg (0.84 mmol, 42.0%). Recrystallization
of 3a from hot ethanol gave crystals suitable for X-ray dif-
fraction analysis.
[4] a) El M. Keramane, B. Boyer, J. P. Roque, Tetrahedron
2001, 57, 1917–1921; b) J. N. Arnold, P. D. Hayes, R. L.
Kohaus, R. S. Mohan, Tetrahedron Lett. 2003, 44, 9173–
9175; c) P. A. Evans, J. Cui, S. J. Gharpure, R. J. Hinkle,
J. Am. Chem. Soc. 2003, 125, 11456–11457.
[5] Recent reports, see: a) M. D. Carrigan, D. Sarapa, R. C.
Smith, L. C. Wieland, R. S. Mohan, J. Org. Chem. 2002,
67, 1027–1030; b) N. M. Leonard, M. C. Oswald, D. A.
Freiberg, B. A. Nattier, R. C. Smith, R. S. Mohan, J.
Org. Chem. 2002, 67, 5202–5207; c) L. C Wieland,
H. M. Zerth, R. S. Mohan, Tetrahedron Lett. 2002, 43,
4597–4600; d) J. R. Stephens, P. L. Butler, C. H. Clow,
M. C. Oswald, R. C. Smith, R. S. Mohan, Eur. J. Org.
Chem. 2003, 3827–3831; e) J. S. Yadav, B. V. S. Reddy,
T. Swamy, Tetrahedron Lett. 2003, 44, 4861–4864;
f) J. S. Yadav, B. V. S. Reddy, G. Satheesh, Tetrahedron
Lett. 2003, 44, 6501–6504; g) A. V. Reddy, K. Ravinder,
T. V. Goud, P. Krishnaiah, T. V. Raju, Y. Venkateswar-
lu, Tetrahedron Lett. 2003, 44, 6257–6260; h) T. Ollevi-
er, T. Ba, Tetrahedron Lett. 2003, 44, 9003–9005; i) J. S.
Yadav, B. V. S. Reddy, T. Swamy, Tetrahedron Lett.
2003, 44, 9121–9124; j) T. Ollevier, V. Desyroy, M.
Asim, M.-C. Brochu, Synlett 2004, 2794–2796; k) T. Ol-
levier, G. Lavie-Compin, Tetrahedron Lett. 2004, 45,
49–52; l) H. Gaspard-Iloughmane, C. Le Roux, Eur. J.
Org. Chem. 2004, 2517–2532; m) T. Ollevier, E.
Nadeau, J. Org. chem. 2004, 69, 9292–9295; n) J. S.
Yadav, B. V. S. Reddy, G. Parimala, A. K. Raju, Tetra-
hedron Lett. 2004, 45, 1543–1546; o) M. P. Nguyen,
J. N. Arnold, K. E. Peterson, R. S. Mohan, Tetrahedron
Lett. 2004, 45, 9369–9371; p) J. S. Yadav, B. V. S.
Reddy, T. Swamy, K. R. Rao, Tetrahedron Lett. 2004,
45, 6037–6039; q) T. Ollevier, V. Desyroy, B. Debail-
leul, S. Vaur, Eur. J. Org. Chem. 2005, 4971–4973;
r) E. D. Anderson, J. J. Ernat, M. P. Nguyen, A. C.
Palma, R. S. Mohan, Tetrahedron Lett. 2005, 46, 7747–
7750; s) P. W. Anzalone, A. R. Baru, E. M. Danielson,
P. D. Hayes, M. P. Nguyen, A. F. Panico, R. C. Smith,
R. S. Mohan, J. Org. Chem. 2005, 70, 2091–2096; t) Y.
Bonvin, E. Callens, I. Larrosa, D. A. Henderson, J.
Oldham, A. J. Burton, A. G. M. Barrett, Org. Lett.
2005, 7, 4549–4552.
Typical Procedure for Friedel–Crafts-Type
Vinylation: Reaction of 1a with 4a Affording 3a
(Table 2, entry 1)
A mixture of vinyl chloride (4a, 248.0 mg, 1.0 mmol), 1a
(480.0 mg, 4.0 mmol) and BiCl3 (32.0 mg, 0.1 mmol) was
heated with stirring at 1208C for 16 h. After treatment as
described above, 3a was obtained in 62% yield.
Characterization data of 3a–r and 4a–d are given in the
Supporting Information.
Acknowledgements
Project (20573061) was supported by National Natural Sci-
ence Foundation of China.
References
[1] a) M. Fischer; P. Wan, J. Am. Chem. Soc. 1999, 121,
4555–4562; b) K. Itami, K. Tonogaki, Y. Ohashi, J.
Yoshida, Org. Lett. 2004, 6, 4093–4096; c) K. Itami, Y.
Ohashi, J. Yoshida, J. Org. Chem. 2005, 70, 2778–2792.
[2] a) A. Casimiro-Garcia, M. Micklatcher, J. A. Turpin,
T. L. Stup, K. Watson, R. W. Buckheit, M. Cushman, J.
Med. Chem. 1999, 42, 4861–4874; b) G. Xu, M. Mick-
latcher, M. A. Silvestri, T. L. Hartman, J. Burrier, M. C.
Osterling, H. Wargo, J. A. Turpin, R. W. Buckheit, M.
1924
www.asc.wiley-vch.de
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A
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[6] a) B. A. Nattier, K. J. Eash, R. S. Mohan, Synthesis
2001, 1010–1012; b) N. Srivastava, S. K. Dasgupta,
B. K. Banik, Tetrahedron Lett. 2003, 44, 1191–1193;
c) N. Srivastava, B. K. Banik, J. Org. Chem. 2003, 68,
2109–2114; d) D. H. Aggen, J. N. Arnold, P. D. Hayes,
N. J. Smoter, R. S. Mohan, Tetrahedron 2004, 60, 3675–
3679; e) B. K. Banik, I. Banik, M. Renteria, S. K. Das-
gupta, Tetrahedron Lett. 2005, 46, 2643–2645.
[7] Recent reports, see: a) M. G. Organ, A. P. Murray, J.
Org. Chem. 1997, 62, 1523–1526; b) R. Hua, M.
Tanaka, New J. Chem. 2001, 25, 179–184; c) C. Dai,
G. C. Fu, J. Am. Chem. Soc. 2001, 123, 2719–2724;
d) G. Y. Li, J. Org. Chem. 2002, 67, 3643–3650; e) W.
Su, S. Urgaonkar, P. A. McLaughlin, J. G. Verkade, J.
Am. Chem. Soc. 2004, 126, 16433–16439.
[8] Compound 3a could also be obtained in 36% yield,
when the reaction was carried out using equimolar
amounts of 1a and 2a.
[9] Crystals for X-ray diffraction analysis were obtained by
recrystallization from ethanol. CCDC 603171 contains
supplementary crystallographic data for this paper.
These data can be obtained free of charge via
www.ccdc.cam.ac.uk.
[10] M. Kodomari, T. Nagaoka, Y, Furusawa, Tetrahedron
Lett. 2001, 42, 3105–3107, and references cited therein.
[11] Attempts to isolate 3g’ from the reaction mixture were
not successful.
Adv. Synth. Catal. 2006, 348, 1919 – 1925
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.asc.wiley-vch.de
1925