title: Gold(I)-catalyzed intramolecular [4+2] cycloadditions of arylalkynes or 1,3-enynes with alkenes: scope and mechanism.
abstract: The cyclizations of enynes substituted at the alkyne gives products of formal [4+2] cyclization with Au(I) catalysts. 1,8-Dien-3-ynes cyclize by a 5-exo-dig pathway to form hydrindanes. 1,6-Enynes with an aryl ring at the alkyne give 2,3,9,9a-tetrahydro-1H-cyclopenta[b]naphthalenes by a 5-exo-dig cyclization followed by a Friedel-Crafts-type ring expansion. A 6-endo-dig cyclization is also observed in some cases as a minor process, although in a few cases, this is the major cyclization pathway. In addition to cationic gold complexes bearing bulky biphenyl phosphines, a gold complex with tris(2,6-di-tert-butylphenyl)phosphite is exceptionally reactive as a catalyst for this reaction. This cyclization can also be carried out very efficiently with heating under microwave irradiation. DFT calculations support a stepwise mechanism for the cycloaddition by the initial formation of an anti-cyclopropyl gold(I)-carbene, followed by its opening to form a carbocation stabilized by a pi interaction with the aryl ring, which undergoes a Friedel-Crafts-type reaction.
authors: Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain.
authors: Cristina
authors: C
authors: Nieto-Oberhuber
authors: Patricia
authors: P
authors: Pérez-Galan
authors: Elena
authors: E
authors: Herrero-Gómez
authors: Thorsten
authors: T
authors: Lauterbach
authors: Cristina
authors: C
authors: Rodríguez
authors: Salomé
authors: S
authors: López
authors: Christophe
authors: C
authors: Bour
authors: Antonio
authors: A
authors: Rosellón
authors: Diego J
authors: DJ
authors: Cardenas
authors: Antonio M
authors: AM
authors: Echavarren