Divergent Mechanisms for the Skeletal Rearrangement and [2+2] Cycloaddition of Enynes Catalyzed by Gold

摘要

Transition-metal-catalyzed reactions of 1,6-enynes proceed via two general pathways (Scheme 1).If the metal coordinates selectively to the alkyne 1,cyclopropyl-metal carbenes 2 are initially formed,which can react with alcohols or water to give products of alkoxy- or hydroxycyclization,whereas in the absence of nucleophiles,skeletal rearrangement forms dienes 3 (single cleavage) and/or 4 (double cleavage).Alternatively,coordination of MX_n to the alkyne and the alkene (as in 5) is followed by oxidative cyclometalation to form 6,which usually evolves by beta-hydrogen elimination to give Alder-ene-type products.