ORGANIC
LETTERS
2
004
Vol. 6, No. 9
519-1521
Totally Chemo- and Regioselective
Cobalt(I)-Mediated Formal Intermolecular
Cyclotrimerization of Alkynes
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Ga e1 lle Chouraqui, Marc Petit, Corinne Aubert,* and Max Malacria*
UniVersit e´ Pierre et Marie Curie (Paris 6), Laboratoire de Chimie Organique associ e´
au CNRS, Tour 44-54, 2 e` me e´ tage, case 229, 4 place Jussieu, 75252,
Paris Cedex 05, France
aubert@ccr.jussieu.fr; malacria@ccr.jussieu.fr
Received March 18, 2004
ABSTRACT
The first examples of totally chemo- and regioselective formal intermolecular cobalt(I)-catalyzed [2 + 2 + 2] cyclizations of three different
alkynes are reported. The use of disposable silylated tethers in the sequence cyclization followed by the displacement of the silicon group led
to polysubstituted arenes as a unique cycloadduct in high yields.
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Transition metal mediated cyclotrimerizations of alkynes
have been recognized to be one of the most powerful and
general methods to synthesize substituted arenes. Despite
unnatural compounds. In addition, more recently, formal
[2 + 2 + 2] cyclizations of alkynes via a palladium homo-
and cross-coupling/[4 + 2] benzannulation were demon-
strated to occur also in a highly regioselective manner.4
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intensive research in this field, the intermolecular version
of this process suffers from poor chemo- and regioselectivity.
Various transition metal complexes have been used to
overcome this problem; however, the selectivity of catalytic
intermolecular reactions of two or three alkynes has remained
In this context, we turned our attention to the silylated
tethers that allow the transformation of intermolecular
reactions into intramolecular ones. Indeed, we thought that
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1,2
a crucial issue. Different alternative approaches have been
proposed to circumvent the lack of selectivity. Indeed,
intramolecular or partially intramolecular reactions of R,ω-
diynes with excess of monoynes have been successfully
employed to solve the selectivity problems and have been
elegantly used in the total synthesis of complex natural and
(
2) (a) Ozerov, O. V.; Patrick, B. O.; Ladipo, F. T. J. Am. Chem. Soc.
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2
Nakajima, K.; Kotora, M. J. Am. Chem. Soc. 1998, 120, 1672-1680. (c)
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(
1) For reviews, see: (a) Schore, N. E. In ComprehensiVe Organic
Synthesis; Trost, B. M., Fleming, I., Paquette, L. A., Eds.; Pergamon
Press: Oxford, 1991; Vol. 5, pp 1129-1162. (b) Grotjahn, D. B. In
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6, 49-92. (d) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J. Chem.
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00, 2901-2915. (f) Malacria, M.; Aubert, C.; Renaud, J. L. In Science of
Synthesis: Houben-Weyl Methods of Molecular Transformations; Lautens,
(4) (a) Gevorgyan, V.; Radhakrishnan, U.; Takeda, A.; Rubina, M.;
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4
39-530.
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0.1021/ol049484k CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/02/2004