Diastereoselectivity-Switchable Gold-Catalyzed Formal [3+2]-Cycloadditions of N-2,2,2-Trifluoroethylisatin Ketimines with Yne-Enones.

The unexpected gold-catalyzed formal [3+2]-cycloaddition of N-2,2,2-trifluoroethylisatin ketimines with 2-(1-Alkynyl)-2-alken-1-ones is reported. Both diastereomers of the corresponding cycloadducts were formed in moderate to excellent yields with excellent diastereoselectivities by switching the catalytic system from mono-gold to gold/silver bimetallic catalytic system. The practicality of this protocol is demonstrated by scale-up reaction and the transformations of the cycloadduct.