Direct coupling of alcohols with alkenylsilanes catalyzed by indium trichloride or bismuth tribromide

Article abstract of DOI:10.1039/b816072d

Indium halides or bismuth halides catalyzed the coupling of various alcohols with alkenylsilanes to give the corresponding alkenes stereospecifically without any other activators. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b816072d

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Direct coupling of alcohols with alkenylsilanes catalyzed by indium
trichloride or bismuth tribromidew
Yoshihiro Nishimoto, Masayuki Kajioka, Takahiro Saito, Makoto Yasuda and Akio Baba*
Received (in College Park, MD, USA) 15th September 2008, Accepted 6th October 2008
First published as an Advance Article on the web 4th November 2008
DOI: 10.1039/b816072d
Indium halides or bismuth halides catalyzed the coupling of
various alcohols with alkenylsilanes to give the corresponding
alkenes stereospecifically without any other activators.
products (Entries 1–8). Reactions of benzhydrols bearing elec-
tron-donating substituents 1f and 1g proceeded in excellent
yields, whereas p-chlorobenzhydrol 1h gave a moderate yield
(Entries 9–14). Although benzyl alcohol gave no product, the
p-methoxy-substituted one 1i successfully afforded the corres-
ponding product 3ia (Entries 15 and 16). In the case of propargyl
alcohol 1j, both InCl3 and BiBr3 gave satisfactory results (Entries
17 and 18). Allylic hydroxy groups were also substituted to give
the products 3ka and 3la in high yields (Entries 19–22). A simple
aliphatic alcohol was not applicable.10 Adamantanol 1m, how-
ever, produced the alkenyl adamantane 3ma (Entries 23–24).
Next, Table 3 shows the scope and limitation of alkenyl-
silanes for this system. Electron-rich alkenylsilanes 2b
(Ar = 4-MeOC6H4) and 2c (Ar = 4-MeC6H4) gave only
moderate yields (Entries 1, 2, 4 and 5), perhaps because obtained
styrene compounds were easily polymerized under the conditions.
In contrast, the electron-deficient alkenylsilane 2d (Ar =
4-ClC6H4) afforded satisfactory results (Entries 3 and 6). Un-
expectedly, the coupling of Z-isomer of alkenylsilane 2e did not
proceed at all, and the starting material 2e was recovered
(Entries 7 and 8). Alkyl-substituted alkenylsilanes were also
applicable although yields were somewhat low (Entries 9–14).
2,2-Dimethylalkenylsilane 2f afforded the trisubstituted olefin in
32% yields along with 22% of isomerized olefin (Entry 9).11
Interestingly, stereospecific reactions were observed in both
of E- and Z-isomers of 1-trimethylsilyl-1-hexene (2g and 2h),
furnishing the corresponding E- and Z-geometries of coupling
products (3ag and 3ah), respectively (Entries 11–14).
Although a carbon–carbon bond formation using an alcohol as a
coupling partner might be fascinating in organic chemistry, the
system is much more difficult than that using other partners such
as organic halides because of the poor leaving ability of the
hydroxy group. The use of alcohols, which are plentiful and
inexpensive compounds, can have advantages over the use of the
corresponding organic halides, and the establishment of this
reaction system has been a long-cherished dream of organic
chemists. Many groups, including our’s, have recently reported
the coupling of alcohols with various metallic nucleophiles such
as allyl, alkynyl, aryl, allenyl and propargyl ones.1,2 However, the
catalytic coupling with alkenyl nucleophiles has been limited to
the transition metal-catalyzed reaction of allylic alcohols based
on a p-allylic species as a key intermediate.3,4 Although Kabalka
reported the coupling of non-allylic alcohols with vinylboron
dihalides in terms of intramolecular rearrangement,5 an equi-
molar amount of strong base (BuLi) was required. Here, we report
the first practical example of direct catalytic coupling of alcohols
including alkyl, benzylic and allylic ones with alkenylsilanes.
Coupling reaction of benzhydrol 1a with (E)-2-phenyl-1-
trimethylsilylethylene 2a was carried out as a model reaction in
the presence of 5 mol% of various Lewis acids (Table 1). No
reaction took place when a catalyst was not loaded (Entry 1).
We have recently developed the indium-catalyzed reactions of
alcohols with various nucleophiles such as silyl compounds
and 1,3-dicarbonyls,1,6,7 and thus InCl3 was examined to give
the alkenyl product 3aa in an excellent yield with complete
E-selectivity (Entry 2). InBr3 gave a lower yield of 85% (Entry 3).
It was found that bismuth trihalide, which has been recently
used as a Lewis acid,8,9 also worked well (Entries 4 and 5) and
that BiBr3 showed a higher catalytic activity than BiCl3. Other
Lewis acids such as BF3ÁOEt2, AlCl3, TiCl4, Sc(OTf)3 and
Yb(OTf)3 afforded low yields (Entries 6–10).
A plausible mechanism is shown in Scheme 1. The oxygen
atom of the alcohol 1 coordinates to MtX3 and the R–O bond
Table 1 Effect of catalysts in the coupling reaction of benzhydrol 1a
with (E)-2-phenyl-1-trimethylsilylethylene 2aa
Entry
Catalyst
Yield (%)
In the presence of either InCl3 or BiBr3, various alcohols 1
were treated with (E)-2-phenyl-1-trimethylsilylethylene 2a, and
the results are summarized in Table 2. InCl3 gave higher yields
than BiBr3 in most cases. 1-Phenylethanol 1b and its para-
substituted derivatives 1c–1e effectively afforded the desired
1
2
3
4
5
6
7
8
9
10
None
InCl3
InBr3
BiCl3
0
91
85
56
82
7
BiBr3
BF3ÁOEt2
AlCl3
TiCl4
5
Department of Applied Chemistry, Center for Atomic and Molecular
Technologies (CAMT), Graduate School of Engineering, Osaka
University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
E-mail: baba@chem.eng.osaka-u.ac.jp; Fax: +81-6-6879-7387;
Tel: +81-6-6879-7386
20
33
8
Sc(OTf)3
Yb(OTf)3
a
Alcohol:
ClCH2CH2Cl: 1 mL.
1
mmol, alkenylsilane: 2 mmol, catalyst: 5 mol%:
w Electronic supplementary information (ESI) available: Experimental
section. See DOI: 10.1039/b816072d
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Table 2 Coupling reactions of various alcohols with (E)-2-phenyl-1-
trimethylsilylethylene 2aa
Table 3 Coupling reactions of benzhydrol 1a with various alkenyl-
silanesa
Yield
t/h Product (%)
Entry Alkenylsilane
Cat. t/h Product
Yield (%)
3ab 39b
3ac 58
3ad 85
3ab 36b
3ac 59
3ad 82
Entry R–OH
X
H
Cat.
1
2
3
4
5
6
2b lnCl3
4
2
2
2
2
2
1
2
3
4
5
6
7
8
1b lnCl3
2
2
2
2
2
2
2
2
3ba
3ca
3da
3ea
3ba
3ca
3da
3ea
51
68
79
52
43
63
69
49
2c lnCl3
2d lnCl3
2b BiBr3
2c BiBr3
2d BiBr3
OMe 1c lnCl3
Me
Cl
H
1d lnCl3
1e lnCl3
1b BiBr3
OMe 1c BiBr3
Me
Cl
1d BiBr3
1e BiBr3
7
8
InCl3
BiBr3
2
2
0
0
2e
3ae
9d
OMe 1f lnCl3
1
2
2
1
2
3fa
3ga
3ha
3fa
3ga
87
97
57
78
87
59
10d
11d
12d
13d
14b,d
Me
Cl
1g lnCl3
1h lnCl3
9
10
lnCl3 1
BiBr3 1.5
35 (27)c,d
29 (11)c
OMe 1f BiBr3
Me
Cl
1g BiBr3
1h BiBr3 2.5 3ha
2f
3af
15
16c
lnCl3
BiBr3
2
4
66
53
11
12
lnCl3
BiBr3
2
2
35e
17e
1i
3ia
3ja
3ka
2g
2h
3ag
3ah
17
18
lnCl3
BiBr3
2
2
63
79
13
14
InCl3
BiBr3
2
2
26
4
1j
19
20
lnCl3
BiBr3
2
2
46
42
a
Alcohol:
ClCH2CH2Cl: 1 mL. CH2Cl2: 1 mL, rt. The value in the paren-
1
mmol, alkenylsilane:
b
2
mmol, catalyst:
c
5
mol%:
1k
d
thesis indicates the yield of the isomerization product. At 50 1C.
Alkenylsilane: 3 mmol.
e
21d
22d
lnCl3
BiBr3
2
2
57
60
1l
3la
hyperconjugation of the Si–C bond. Immediately, the silyl group
leaves and the olefin is stereoselectively given.15 A large steric
interaction in the rotation disturbs the coupling, and the reaction
of benzhydrol 1a with (Z)-2-phenyl-1-trimethylsilylethylene 2e
gives no product (Table 3, Entries 7 and 8).
23b,d
24b,d
lnCl3
BiBr3
2
6
57
71
1m
3ma
Intramolecular cyclization reactions are important for the
synthesis of ring skeletons that constitute a part of biological
compounds.16 We demonstrated that our reaction system is
a
Alcohol:
1
mmol, alkenylsilane:
b
3
mmol, catalyst:
5
mol%:
ClCH2CH2Cl: 1 mL. PhCl instead of ClCH2CH2Cl: 1 mL, 130 1C.
c
d
CH3CN instead of ClCH2CH2Cl: 1 mL, 80 1C. Alkenylsilane: 2 mmol.
is activated to increase the positive charge on the R group.
Then, the carbocation R+ is produced,12 and the a-carbon of
alkenylsilane 2 attacks R+ to generate a cation on the
b-carbon, which is stabilized by the silyl group.13,14 The sub-
stituents that can stabilize the cation also effect the formation
of 3, as shown in Table 3. The leaving of the silyl group affords
the product 3 along with the regeneration of MtX3. The
characteristic features of InCl3 and BiBr3, such as the stability
toward active protons, moderate Lewis acidity and low
oxophilicity, synergistically complete the catalytic cycles.
Fig. 1 explains the stereospecificity in the coupling of E- and
Z-isomers of alkenylsilanes. Simultaneously with the addition of
carbocation R+ to the double bond, rotation occurs about the
developing carbon–carbon single bond in the direction to permit
the silyl group to continuously stabilize the incipient b-cation by
Scheme 1 Plausible mechanism.
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Notes and references
1 (a) T. Saito, Y. Nishimoto, M. Yasuda and A. Baba, J. Org.
Chem., 2006, 71, 8516; (b) T. Saito, M. Yasuda and A. Baba,
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A. Baba, Angew. Chem., Int. Ed., 2004, 43, 1414.
2 (a) G. W. Kabalka, M.-L. Yao and S. Borella, Org. Lett., 2006, 8,
879; (b) M. Georgy, V. Boucard and J.-M. Campagne, J. Am.
Chem. Soc., 2005, 127, 14180; (c) S. K. De and R. A. Gibbs,
Tetrahedron Lett., 2005, 46, 8345; (d) Y. Kayaki, T. Koda and
T. Ikariya, Eur. J. Org. Chem., 2004, 4989; (e) S. H. Kim, C. Shin,
A. N. Pae, H. Y. Koh, M. H. Chang, B. Y. Chung and Y. S. Cho,
Synthesis, 2004, 1581; (f) G. W. Kabalka, G. Dong and
B. Venkataiah, Org. Lett., 2003, 5, 893; (g) M. R. Luzung and
F. D. Toste, J. Am. Chem. Soc., 2003, 125, 15760; (h) M. Rubin
and V. Gevorgyan, Org. Lett., 2001, 3, 2705; (i) G. Kaur,
M. Kaushik and S. Trehan, Tetrahedron Lett., 1997, 38, 2521.
3 (a) Y. Kayaki, T. Koda and T. Ikariya, Eur. J. Org. Chem., 2004,
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Commun., 2004, 1200; (c) G. W. Kabalka, G. Dong and
B. Venkataiah, Org. Lett., 2003, 5, 893; (d) K. -G. Chung,
Y. Miyake and S. Uemura, J. Chem. Soc., Perkin Trans. 1, 2000,
15; (e) B. M. Trost and M. D. Spagnol, J. Chem. Soc., Perkin
Trans. 1, 1995, 2083.
4 (a) There are some reports for the coupling of alkyl halides with
alkenyl nucleophiles: X. Dai, N. A. Strotman and G. C. Fu, J. Am.
Chem. Soc., 2008, 130, 3302; (b) D. A. Powell, T. Maki and G. C. Fu,
J. Am. Chem. Soc., 2005, 127, 510; (c) S. L. Wiskur, A. Korte and
G. C. Fu, J. Am. Chem. Soc., 2004, 126, 82; (d) J. Zhou and G. C. Fu,
J. Am. Chem. Soc., 2003, 125, 12527; (e) H. Tang, K. Menzel and
G. C. Fu, Angew. Chem., Int. Ed., 2003, 42, 5079.
Fig. 1 Stereoselectivity and stereospecificity.
5 G. W. Kabalka, M.-L. Yao, S. Borella and Z.-Z. Wu, Org. Lett.,
2005, 7, 2865.
6 M. Yasuda, T. Somyo and A. Baba, Angew. Chem., Int. Ed., 2006,
45, 793.
7 For the selected review, see: G.-L. Chua and T.-P. Loh, in Acid
Catalysis in Modern Organic Synthesis, eds. H. Yamamoto and
K Ishihara, Wiley-VCH, Weinheim, 2008, vol. 1, ch. 8,
pp. 377–468.
8 For selected reviews, see: (a) H. Gaspard-Ilangovan, in Acid
Catalysis in Modern Organic Synthesis, eds. H. Yamamoto and
K. Ishihara, Wiley-VCH, Weinheim, 2008, vol. 2, ch. 11,
pp. 551–588; (b) N. Komatsu, in Organobismuth Chemistry, eds.
H. Suzuki and Y. Matano, Elsevier, Amsterdam, 2001, ch. 5,
pp. 371–440; Recently C–C bond formation reaction using bismuth
catalyst as a Lewis acid: (c) S. Tanaka, N. Tagashira, K. Chiba,
M. Yasuda and A. Baba, Angew. Chem., Int. Ed., 2008, 47, 6620;
(d) S. K. De and R. A. Gibbs, Tetrahedron Lett., 2005, 46, 8345;
(e) S. Kobayashi, T. Ogino, H. Shimizu, S. Ishikawa, T. Hamada
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S. J. Gharpure and R. J. Hinkle, J. Am. Chem. Soc., 2003, 125,
11456.
Scheme 2 Intramolecular cyclization reactions.
effective for the intramolecular coupling shown in Scheme 2.
Under dilution conditions, InCl3-catalyzed intramolecular
cyclization of alkenylsilanes 4 and 6 gave the five- and six-
membered ring compounds 5 and 7 in 38 and 85% yields,
respectively. Unfortunately, BiBr3 did not work under the
dilution conditions, and only a 43% yield of 7 was achieved.
These results indicate that InCl3 has catalytic activity that is
higher than that of BiBr3.
9 DFT analysis of Lewis acidity of BiX3: J. Sanderson and
C. A. Bayse, Tetrahedron, 2008, 64, 7685.
10 tert-Butyl alcohol gave no desired product.
In summary, we have accomplished stereospecific direct
coupling of alcohols with alkenylsilanes catalyzed by either
InCl3 or BiBr3. Various alcohols and alkenylsilanes including
aromatic- and alkyl-substituted ones were successfully em-
ployed in this reaction system, and its application to intra-
molecular coupling gave five- or six-membered ring compounds.
The details of the mechanism for this reaction are under further
investigation.
11 D. A. Evans and Y. Aye, J. Am. Chem. Soc., 2006, 128, 11034.
12 The coupling reaction of (R)-(+)-phenylethanol (R)-1b (Tokyo
Chemical Industry Co., Ltd.) with (E)-2-phenyl-1-trimethylsilyl-
ethylene 2a in the presence of either InCl3 or BiBr3 gave the racemic
product 3ba in o1% ee. See ESIw for experimental details.
13 The result of the reaction using 2e (Table 3, Entries 7 and 8) was
additionally explained that the intermediate cation was unstable
because the sp2 plane of the cation and the benzene ring are
noncoplanar and the cation dose not conjugate the phenyl group
due to the steric hindrance between the silyl and the phenyl group.
14 Hyperconjugation of the Si–C bond: T. G. Traylor, W. Hanstein,
H. J. Berwin, N. A. Clinton and R. S. Brown, J. Am. Chem. Soc.,
1971, 93, 5715.
15 Weber et al. illustrated the stereospecificity in the reaction of
deuterium chloride with (Z)- and (E)-2-phenyl-1-trimethylsilyl-
ethylene with this hyperconjugation: K. E. Koenig and
W. P. Weber, J. Am. Chem. Soc., 1973, 95, 3417.
16 (a) K. Miura and A. Hosomi, Synlett, 2003, 143; (b) E. Langkopf
and D. Schinzer, Chem. Rev., 1995, 95, 1375; (c) T. A. Blumenkopf
and L. E. Overman, Chem. Rev., 1986, 86, 857.
This work was supported by Grant-in-Aid for Scientific
Research on Priority Areas (No. 18065015, ‘‘Chemistry of
Concerto Catalysis’’ and No. 20036036, ‘‘Synergistic Effects
for Creation of Functional Molecules’’) and for Scientific
Research (No. 19550038) from Ministry of Education, Cul-
ture, Sports, Science and Technology, Japan. Y. N. thanks
The Global COE Program ‘‘Global Education and Research
Center for Bio-Environment Chemistry’’ of Osaka University.
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This journal is The Royal Society of Chemistry 2008
6398 | Chem. Commun., 2008, 6396–6398