Complexity via Gold-Catalyzed Molecular Gymnastics

Reactions of 1,6-enynes catalyzed by gold(I) complexes usually proceed stereospecifically through highly distorted cyclopropyl gold carbenes. Substrates with an alkoxy substituent at the propargylic position undergo stereoselective transformations through intermediates in which the OR group and the gold carbene are anti-oriented. Intramolecular attack of carbonyl groups to the cyclopropyl gold carbene is faster than the 1,5-migration of the OR groups, which itself is faster than the intramolecular cyclopropanation by a pendant alkenyl group. The intramolecular attack of carbonyl groups is the key transformation in the [2+2+2] gold-catalyzed cycloaddition, which has been applied in the total synthesis of (+)-orientalol F.