Gold and Brّnsted acid catalyzed isomerization of [3]cumulenols and [3]cumulenones: efficient syntheses of 1,5-dien-3-ynes and furan derivatives

An attractive method for assembling π-conjugated dienynes with high stereoselectivity was achieved by dehydration reaction of TMS-substituted [3]cumulenols catalyzed by TsOH·H2O. On the other hand, cycloisomerizations of the corresponding [3]cumulenones catalyzed by gold(I) complexes afford vinyl furans through activation of the cumulenic double bond via a π-complex, and during the process, deprotonation from an alkyl group on cumulene terminus takes place to induce the isomerization.