Metal cyclopropyl carbenes in the reactions of alkynes with alkenes
and furans
A. M. Echavarren, M. M�ndez, M. P. Mu�oz, C. Nevado, B. Mart�n-Matute,
C. Nieto-Oberhuber, and D. J. C�rdenas
Departamento de Química Orgánica, Universidad
Autónoma de Madrid and Institut Catalá d’ Investigació
Química (ICIQ), Av. Països Catalans, 43007 Tarragona, Spain
Abstract: Electrophilic transition-metal complexes catalyze
the reaction of enynes in the presence of water or alcohols to give
hydroxy- or alkoxycyclization derivatives. The reaction proceeds by
the anti addition of the alkene and the metal to the alkyne. The key
intermediates in this reaction are cyclopropyl metal carbenes, which
are also probably involved in the metathesis-type rearrangement of enynes.
A general scheme is proposed for the cyclization of enynes initiated
by the coordination of the metal to the enyne by transition metals,
which included 5-exo -dig and 6-endo -dig pathways. The
intramolecular reaction of furans with alkynes also proceeds via cyclopropyl
metal carbenes.
*Plenary and invited lectures presented at the 12th
International Symposium on Organometallic Chemistry Directed Towards
Organic Synthesis (OMCOS-12), Toronto, Ontario, Canada, 6-10 July 2003.
Other lectures are published in this issue, pp.
453-695.
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