pubs.acs.org/joc
involving C-H bond activation are highly desirable, not
C-C Bond Formation via C-H Bond Activation
Under Protic Conditions: On the Role of Phosphane
Ligand and Cosolvent
only because they allow the functionalization of more easily
available starting materials (atom economy concept1) but
also because they produce clean reactions (reduced amounts
of salts).2 In the field of C-C bond formation via C-H
activation,2 several catalytic reactions have been recently
developed,3 and hydroarylation reactions, allowing the func-
tionalization of alkenes with a total atom economy, appear
quite promising.2,4
Another point of concern in the development of green
processes is the reaction solvent. Even if solvent-free reac-
tions are highly desirable, the use of less hazardous and less
toxic solvents is also an attractive alternative.5 Hydroaryl-
ation reactions, involving low-valent active transition metal
complexes (except electrophilic Pd(II)) are generally con-
ducted in inert toxic hydrocarbon solvents like toluene or
benzene.2,4
ꢀ
Marc-Olivier Simon, Remi Martinez, Jean-Pierre Genet, and
Sylvain Darses*
Laboratoire Charles Friedel (UMR 7223, CNRS), Ecole
ꢀ
Nationale Superieure de Chimie de Paris, 11 rue Pierre et
Marie Curie, 75231 Paris Cedex 05, France
Received October 22, 2009
We report here, for the first time, that hydroarylation
reactions involving C(sp2)-H activation can be conducted in
isopropanol, a protic solvent,6 with higher efficiency and at
moderate temperature (Scheme 1).
We recently reported an effective catalytic system, gener-
ated from an easily available ruthenium(II) source, allowing
either the hydroarylation of alkenes (Murai type reaction)7-9
or the formation of functionalized allysilanes via C-H bond
activation.10 The catalytically active ruthenium species was
generated in situ from the reaction of inexpensive [RuCl2-
(p-cym)]2 (p-cym = p-cymene) and sodium formate, in asso-
ciation with a phosphane ligand, but the reaction has to be
Effective conditions for the hydroarylation of vinyl-
silanes, allowing functionalization of various aromatic
ketones in good yields at low temperature, using isopro-
panol, a protic solvent, are reported. Moreover, conduct-
ing this C-C bond-forming reaction under conditions
similar to those used for hydride transfer reduction, the
reduction of the ketone could be suppressed, simply by
using acetone cosolvent as hydride acceptor. This reac-
tion, conducted with an inexpensive and nontoxic sol-
vent, constitutes the first C(sp2)-H activation under
protic conditions with low-valent ruthenium complexes.
(4) For some recent hydroalkylation reactions see: (a) Grutters, M. M. P.;
€
Muller, C.; Vogt, D. J. Am. Chem. Soc. 2006, 128, 7414. (b) Tsai, A. S.;
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208 J. Org. Chem. 2010, 75, 208–210
Published on Web 12/03/2009
DOI: 10.1021/jo902264u
r
2009 American Chemical Society