.
Angewandte
Communications
Gold Catalysis
Gold(I)-Catalyzed Addition of Silylacetylenes to Acylsilanes: Synthesis
À
of Indanones by C H Functionalization through a Gold(I) Carbenoid
Jairo Gonzµlez, Javier Santamaría, and Alfredo Ballesteros*
Dedicated to Professor JosØ Barluenga on the occasion of his 75th birthday
Abstract: A gold(I)-catalyzed synthesis of indanones from
trimethylsilylacetylenes and acylsilanes is presented. The
reaction is initiated through a synergistic acylsilane activa-
tion–gold acetylide formation and involves consecutive alkyne
s-gold(I) addition, p-activation, and 1,2-migration of a silyl
group. Studies performed on the reaction mechanism allowed
to establish the nature of the silyl migrating group and invoke
the participation of a gold(I) carbenoid intermediate. The
tion[5] possibly leading to a gold carbenoid intermediate. In
this context, the search for alternative routes involving gold
carbenoids as intermediates,[6] thus avoiding the use of
hazardous and potentially explosive diazo compounds as
precursors,[7] is highly pursued. General methodologies
involve intramolecular procedures as 1,2-acyloxy migra-
tions,[8] cycloisomerization of enynes,[9] ring cleavage of
cyclopropenes,[10] retro-Buchner reactions,[11] and alkyne
oxidations with sulfoxides[12] or N-oxide oxidants.[13] However,
intermolecular procedures beyond the methodology involv-
ing intermolecular oxygen incorporation to alkynes by
pyridine N-oxide derivatives are lacking.[13]
Here we present an efficient synthesis of indene deriva-
tives as the result of an intermolecular formal [3+2] gold(I)-
catalyzed cycloaddition between trimethylsilylacetylenes and
acylsilanes (Figure 1b).
First, we selected benzoylsilane 1 and trimethylsilylalkyne
2 as model compounds to test the activity of different gold(I)
complexes. The reaction was performed at 708C in the
presence of 5 mol% of the corresponding gold(I) catalyst,
leading, after a period of 30 min, to the formation of indene
derivatives 3 (Scheme 1).[14] As the result of these preliminary
assays, we selected phosphite P(ArO)3 as the appropriate
ligand in terms of conversion and yield of indene 3. As the
À
reaction is completed by a gold(I) C H functionalization step.
D
uring the last decade homogeneous gold catalysis has
emerged as one of the most powerful tools in organic
synthesis and a huge number of transformations of increasing
molecular complexity have been achieved.[1] While processes
involving p-carbophilic gold activation of alkynes have been
extensively studied, s-gold alkyne activation has received less
attention.[2] Our group has recently reported a synergistic
trimethylsilyl activation/double gold(I) catalytic alkynylation
of aldehydes (Figure 1a).[3] As a continuation of this work, we
explored a special class of carbonyl groups: the acylsilanes, as
they can act as aldehyde equivalents.[4]
As a working hypothesis, a synergistic acylsilane activa-
tion/gold acetylide addition could trigger a 1,2-silyl migra-
Figure 1. Gold(I)-catalyzed addition of trimethylsilylalkynes to carbonyl
derivatives.
Scheme 1. Gold(I)-catalyzed formation of indene 3.[a] Yields and con-
versions were determined by NMR spectroscopy with 1,3,5-trimethoxy-
benzene as the internal standard.
[*] J. Gonzµlez, Dr. J. Santamaría, Prof. Dr. A. Ballesteros
Instituto Universitario de Química Organometµlica “Enrique Moles”
and Departamento de Química Orgµnica e Inorgµnica
Universidad de Oviedo
counterion we selected bis(trifluoromethanesulfonyl)imidate
on a routine basis, thus avoiding the use of silver salts to
generate the corresponding gold catalyst.[15]
c/Juliµn Clavería 8, 33007 Oviedo (Spain)
E-mail: abg@uniovi.es
Due to the low stability of enol ether 3[16] we decided to
incorporate to the experimental procedure a quenching step
Supporting information for this article is available on the WWW
13678
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 13678 –13681