Angewandte
Chemie
DOI: 10.1002/anie.201306882
Cross-Coupling
Copper(I)-Catalyzed Alkylation of Aryl- and Alkenylsilanes Activated
by Intramolecular Coordination of an Alkoxide**
Akira Tsubouchi,* Daisuke Muramatsu, and Takeshi Takeda*
Dedicated to Professor Teruaki Mukaiyama
Organosilicon-based cross-coupling has attracted much atten-
tion as a useful tool for carbon–carbon bond formation
because of the low toxicity, high availability, and high
chemical stability of organosilicon compounds.[1] Activation
À
of the unreactive Si C bond, however, has been imperative
and hence heteroatom-functionalized organosilanes such as
halo- and alkoxysilanes have practically been employed in
conjunction with a fluoride-ion activator for palladium-
catalyzed cross-couplings.[2] In recent advances, organosila-
nols and silanolates,[3] as well as silacyclobutanes[4] have been
introduced as silane coupling partners in the Hiyama
coupling. The intramolecular coordination of heteroatoms
À
to the silicon atom also activates the Si C bond in the silicon-
based coupling reactions.[5] In this regard, the transition-
metal-catalyzed cross-couplings of aryl- and alkenyldi-
Scheme 1. Formation of organocopper species via cyclic silicates.
TMS=trimethylsilyl.
methyl[(2-hydroxymethyl)phenyl]silanes were extensively
2
studied.[6] In the Hiyama coupling, C(sp ) X electrophiles
À
such as aryl and alkenyl (pseudo)halides have been success-
fully employed, but little is known about the coupling with
species 4 are also reactive toward alkenyl and aryl halides in
the presence of a catalytic amount of [Pd(PPh3)4].
3
[7,8]
À
unreactive C(sp ) X electrophiles.
In this context, we
The five-membered silicate intermediates similar to those
in our copper(I)-promoted silyl migration have been assumed
to be key intermediates in the palladium-catalyzed Hiyama
cross-coupling of organo[2-(hydroxymethyl)phenyl]silanes.
The palladium-catalyzed cross-coupling of organolithiums
and aryl and alkenyl halides in the presence of 1-oxa-2-
silacyclopentene as a silicon-based transfer agent was also
categorized into the same type of reaction[11] because of the
similarity of their cyclic silicate intermediates.[12] Stoichio-
metric allylation, benzylation, and silylation of electrophiles
such as aldehydes, ketones, and enones via similar cyclic
silicates generated from lithium alkoxides of [2-(hydroxy-
methyl)phenyl]silanes[13] and (3-hydroxypropyl)silanes[14]
were also classified in this category.
aimed at the development of a catalytic cross-coupling of
3
À
alkenyl- (1) and arylsilanes (2) with C(sp ) X electrophiles
[Scheme 1, Eq. (1)].
We have developed new methods for the generation of the
alkenyl and arylcopper species by the copper(I) tert-butoxide-
promoted Brook-like silyl migration from an sp2-carbon atom
to an oxygen atom.[9,10] The 1,4-silyl migration proceeds by
formation of the five-membered cyclic silicates 3, which
undergo the transmetallation to copper(I) to form the
À
organocopper species 4 by the “endo”cyclic Si C bond
cleavage in association with the silyl migration [Scheme 1,
Eq. (2)].[9a–d] The organocopper species 4 reacts with alkyl,
3
À
allylic, and benzylic halides [C(sp ) X electrophiles] to give
the alkylation products 5 in good yields. The organocopper
Based on our results on the formation of organocopper
À
species by the “endo”cyclic Si C bond cleavage of the cyclic
silicates, we conceived that the silanes 1 and 2 bearing
a hydroxy group should undergo copper(I)-catalyzed cross-
[*] Dr. A. Tsubouchi, D. Muramatsu, Prof. Dr. T. Takeda
Department of Applied Chemistry, Graduate School of Engineering
Tokyo University of Agriculture and Technology
Koganei, Tokyo 184-8588 (Japan)
3
À
coupling with organic halides [6; C(sp ) X electrophiles] to
2
3
À
give the C(sp ) C(sp ) coupling products 7 through the
À
“exo”cyclic Si C bond cleavage of the cyclic silicates 3
[Eq. (1)]. Herein we describe fluoride-free copper(I)-cata-
E-mail: tubouchi@cc.tuat.ac.jp
2
3
À
lyzed C(sp ) C(sp ) cross-couplings of alkenyl- and arylsi-
lanes with organic halides effected by intramolecular activa-
tion through the formation of cyclic silicate intermediates.
In initial experiments, we examined the cross-coupling of
the alkenylsilanes 1a,b, bearing a hydroxypropyl group as an
intramolecular activator, using 2 equivalents of copper(I) tert-
butoxide (Table 1). Thus, the reaction of the (Z)-stylylsilane
[**] This work was supported by Grant-in-Aid for Scientific Research (C)
(No. 23550118) from the Ministry of Education, Culture, Sports,
Science, and Technology (Japan). Dedicated to Professor Teruaki
Mukaiyama in celebration of the 40th anniversary of the Mukaiyama
aldol reaction.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2013, 52, 12719 –12722
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
12719