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the same conditions, and the 1,4-dienes 6m–q were obtained in
good yields with the complete retention of the configuration of
double bond (entries 13–17).
Table 3 (continued)
According to the proposed reaction mechanism (Scheme 2),
it is reasonable to assume that the cross-coupling proceeds
using only a catalytic amount of copper(I) iodide. Indeed, the
reaction of 8 with allylic chlorides 2 using 15 mol% of copper(I)
iodide produced the coupling products 6 in comparable yields
(entries 1–3, 10 and 11). The catalytic allylation also proceeded
when the E- and Z-alkenylsilanes 8g and 8h were employed,
albeit with lower yields (entries 14 and 16). It was confirmed
that formation of coupling product was not observed when 8a
was treated with 2b in the absence of copper(I) iodide. The
result might deny the possible pathways for cross-coupling via
the cyclic lithium silicates similar to 12 or the organolithium
species which were suggested by Hudrlik and co-workers for the
reaction of allyl- or benzyl group substituted (3-hydroxypropyl)-
dimethylsilanes with electrophiles.5
Entry
8
2
6
Yieldb (%)
14
15
8g
8g
2a
2b
6n
6o
61
70 (42)c
16
8h
8h
2a
2b
6p
6q
60
17
60 (30)c
a
In conclusion, we have developed a new fluoride free cross-
coupling of aryl- and alkenylsilanes with organic halides. The
starting materials are readily available and easy to handle in air.
The coupling consists of multiple steps, but the operation is
extremely straightforward; just mixing the four reagents, two of
which are stable powders, affords the coupling products. Further
extension of the present cross-coupling method and exploration
of detailed reaction mechanism are currently underway.
This work was supported by JSPS KAKENHI Grant Number
26410037.
All reactions were performed using 8 (0.3 mmol), 2 (0.6 mmol), pre-
prepared powdered 10 (0.6 mmol), copper(I) iodide (0.3 mmol) and
b
DMF (1.5 mL) at 50 1C for 16 h, unless otherwise noted. Isolated yield
based on 8 used. Carried out using a catalytic amount of copper(I)
iodide (15 mol%) and 10 (0.6 mmol) in DMF (1.5 mL). A mixture of 2c,
E-2d and Z-2d (2c : E-2d : Z-2d = 71 : 28 : 1). A mixture of E-2d, Z-2d and
c
d
e
f
2c (E-2d : Z-2d : 2c = 86 : 13 : 1). Contaminated with biphenyl. The yield
was determined by 1H NMR spectroscopy. Carried out at 70 1C for 6 h.
g
h
Carried out at 60 1C for 16 h.
methoxide did not act as a promoter supports our assumption
that the formation of cyclic silicates 12 is indispensable for the
cross-coupling (entry 1). The lithium alkoxides of secondary diols
partly mediated the coupling (entries 3 and 4) and the reaction
carried out in the presence of lithium alkoxide of sterically
demanding pinacol (entry 5) produced the coupling product 6b
only in 18% yield. These results indicate that the facile formation
of cyclic silicate is crucial to obtain the cross-coupling products in
satisfactory yields. The coupling product 6b was produced in the
same yield by the reaction using pre-prepared powdered lithium
2-hydroxyethoxide (10), which made it possible to simplify the
experimental procedure (entry 2).
Table 3 summarizes the results of reactions of various
aryl- and alkenylsilanes 8 with organic halides 2 under the
optimized conditions. As shown in the reactions of 8a with
3-chloro-1-butene (2c) and its isomer, 1-chloro-2-butene (2d),
the regioselectivity of allylic coupling seems to be controlled by
steric factors (entries 3 and 4). The reaction of 8a with the
benzylic chloride 2e also proceeded to give the coupling pro-
duct 6e (entry 5). Although the reaction of 8a with methyl iodide
(2f) produced 4-methylbiphenyl (6f) in a moderate yield (entry 6),
Notes and references
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Sons, Chicheter, 2004, p. 338; S. E. Denmark and R. F. Sweis, in Metal-
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Wiley-VCH, Weinheim, 2004, p. 163; T. Hiyama and E. Shirakawa, Top.
Curr. Chem., 2002, 219, 61–85; W.-T. T. Chang, R. C. Smith, C. S.
Regens, A. D. Bailey, N. S. Werner and S. E. Denmark, Org. React., 2011,
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2 H. Taguchi, K. Ghoroku, M. Tadaki, A. Tsubouchi and T. Takeda, Org. Lett.,
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A. Tsubouchi and T. Takeda, Chem. Commun., 2002, 2218–2219;
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Tetrahedron Lett., 2004, 45, 429–432; A. Tsubouchi, M. Itoh, K. Onishi
and T. Takeda, Synthesis, 2004, 1504–1508; A. Tsubouchi, K. Onishi
and T. Takeda, J. Am. Chem. Soc., 2006, 128, 14268–14269; A. Tsubouchi,
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no formation of the cross-coupling product was observed when 4 For the dehydrogenative alkoxylation of trialkylsilanes catalyzed
by copper(I) complexes, see: H. Ito, A. Watanabe and M. Sawamura,
Org. Lett., 2005, 7, 1869–1871, and references cited therein.
5 P. F. Hudrlik, Y. M. Abdallah and A. M. Hudrlik, Tetrahedron Lett.,
ethyl iodide was employed. Halogen, amino, and ester functional
groups were compatible with the present reaction (entries 7–9).
The allylation of alkenyldimethylsilanes was performed under
1992, 33, 6747–6750.
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