Effect of Substitution, Ring Size, and Counterion on the Intermediates Generated in the Gold-Catalyzed Intramolecular Hydroalkoxylation of Allenes

The reaction of 2,2-diphenylhepta-4,5-dien-1-ol (4) with (L)­AuOTs [L = P­(t-Bu)2o-biphenyl] and the reactions of 2,2-diphenylhepta-5,6-dien-1-ol (10) with either (L)­AuOTs or (L)­AuCl/AgSbF6 have been investigated. For both substrates, the mono­(gold) vinyl complexes generated via C–O bond formation have been independently synthesized, and the protodeauration behavior has been investigated. Analysis of the reaction of 4 with (L)­AuOTs supported a mechanism involving rapid and reversible C–O bond formation followed by rate-limiting and stereochemically determining protodeauration. Analysis of the reaction of 10 with (L)­AuOTs was in accord with irreversible C–O bond formation followed by rapid auration of the resulting mono­(gold) vinyl complex. In comparison, analysis of the reaction of 10 with (L)­AuCl/AgSbF6 pointed to a mechanism involving rate-limiting C–O bond formation followed by rapid protodeauration of the resulting mono­(gold) vinyl complex without competitive auration.