Angewandte
Communications
Chemie
Alkenes
Reductive Cross-Coupling of Conjugated Arylalkenes and Aryl
Bromides with Hydrosilanes by Cooperative Palladium/Copper
Catalysis
Kazuhiko Semba,* Kenta Ariyama, Hong Zheng, Ryohei Kameyama, Shigeyoshi Sakaki,* and
Yoshiaki Nakao*
Abstract: A method for the reductive cross-coupling of
conjugated arylalkenes and aryl bromides with hydrosilanes
by cooperative palladium/copper catalysis was developed, thus
resulting in the highly regioselective formation of various 1,1-
diarylalkanes, including a biologically active molecule. Under
the applied reaction conditions, high levels of functional-group
tolerance were observed, and the reductive cross-coupling of
internal alkynes with aryl bromides afforded trisubstituted
alkenes.
Cross-coupling reactions of aryl halides with 1-arylalkyl
metal species represent a convenient method to prepare 1,1-
diarylalkanes,[4] which are often found in biologically active
compounds.[5] 1-Arylalkylmetal reagents such as organoboron
and organosilicon compounds are conventionally prepared by
the transition metal catalyzed hydrometallation of styrenes.[6]
The resulting 1-arylalkylmetal reagents are subsequently
purified and used for the cross-coupling with aryl halides.
Sigman and co-workers then developed reductive cross-
coupling reactions of styrenes with arylstannanes[7a] or
arylboronic esters[7b] in the presence of iPrOH as a hydrogen
source to afford 1,1-diarylethanes via an alkylpalladium
species [Eq. (3)]. However, in these reactions, the scope
with respect to the alkenes is limited to vinylarenes, and in
many cases the main-group aryl nucleophiles have to be
prepared from the corresponding aryl halides. Herein, we
report the reductive cross-coupling of conjugated arylalkenes
and aryl bromides with hydrosilanes by cooperative palla-
dium/copper catalysis [Eq. (4)].[8,9] This reaction furnishes
a variety of 1,1-diarylalkanes in a highly regioselective
manner from the palladium-catalyzed coupling of the 1-
arylalk-1-ylcopper species generated in situ by catalytic
hydrocupration[10] of arylalkenes with aryl halides.[11]
T
ransition metal catalyzed cross-coupling reactions of alkyl
and alkenyl organometallic reagents represent a powerful
method for the alkylation and alkenylation, respectively, of
organic electrophiles.[1] The hydrometallation of alkenes and
alkynes is an atom-efficient and practical way to prepare alkyl
and alkenyl metal reagents, respectively, because a variety of
main-group metal hydrides, alkenes, and alkynes are readily
available.[2] However, these organometallic nucleophiles are
usually presynthesized and often purified prior to subsequent
cross-coupling reactions [Eq. (1)], and such processes gen-
erally involve multistep operations. In contrast, cross-cou-
pling reactions based on organometallic nucleophiles gener-
ated by hydrometallation of alkenes and alkynes with
a catalytic amount of transition-metal hydrides in situ can
be more step-economical, because this process requires just
a single operation, and isolation of the organometallic
reagents is not necessary [Eq. (2)].[3]
To evaluate the validity of Equation (4), we carried out
cross-coupling reaction of the alkylcopper 1a, which is
prepared from hydrocupration of styrene (2a), with p-
bromoanisole (3a) in the presence of Pd(OAc)2/tricyclopen-
tylphosphane (PCyp3) [Equation (5); see Equation (S1) in the
Supporting Information].[12] As a result, 4a was obtained in
98% yield. This result encouraged us to develop a catalytic
reaction.
[*] Dr. K. Semba, K. Ariyama, R. Kameyama, Prof. Dr. Y. Nakao
Department of Material Chemistry, Graduate School of Engineering
Kyoto University
Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)
E-mail: semba.kazuhiko.5n@kyoto-u.ac.jp
Dr. H. Zheng, Prof. Dr. S. Sakaki
Fukui Institute for Fundamental Chemistry, Kyoto University
Sakyo-ku, Kyoto 606-8103 (Japan)
After optimization of various reaction parameters,[12] we
found that in the presence of Pd(OAc)2 (1.0 mol%), PCyp3
(2.0 mol%), (SIPr)CuCl (10 mol%), and LiOtBu (1.2 mmol),
the reductive cross-coupling of 2a with 3a and HSi(OEt)3
afforded 1,1-diarylalkane 4a in 94% yield with concomitant
E-mail: sakaki.shigeyoshi.47e@st.kyoto-u.ac.jp
Supporting information for this article can be found under:
Angew. Chem. Int. Ed. 2016, 55, 6275 –6279
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6275