title: Au- and pt-catalyzed cycloisomerizations of 1,5-enynes to cyclohexadienes with a broad alkyne scope.
abstract: We describe the development of gold- and platinum-catalyzed cycloisomerizations of 1,5-enynes. This catalytic process displays a wide alkyne scope and furnishes a range of highly functionalized 1,4- and 1,3-cyclohexadienes. In the case of 1-siloxy-1-yne-5-enes, the reactions are efficiently catalyzed by AuCl (1 mol %) at ambient temperature to afford siloxy cyclohexadienes or the corresponding 1,2- and 1,3-cyclohexenones upon subsequent protodesilylation. We propose that the reaction proceeds via a novel mechanism involving a series of 1,2-alkyl shifts. Elucidation of this unusual reaction mechanism enabled us, in turn, to significantly expand the scope of the cycloisomerization by incorporation of a quaternary center at the C(3) position of the enyne. Indeed, we established that PtCl(2) (5 mol %) efficiently catalyzed the cycloisomerizations of 1,5-enynes containing terminal, internal, and arene-conjugated alkynes. Since a variety of 1,5-enynes are readily accessible, the cycloisomerization provides a rapid approach to a wide range of highy substituted cyclohexadienes for many subsequent synthetic applications.
authors.affiliation: University of Chicago, Department of Chemistry, 5735 South Ellis Avenue, Chicago, Illinois 60637, USA.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Sun
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Conley
authors.forename: Liming
authors.initials: L
authors.lastname: Zhang
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Kozmin