Relay Catalysis of Rh (II) and Cobaloxime: Stereoselective Synthesis of Spiroindanones from N-Sulfonyl-1,2,3-triazoles.

A novel relay Rh (II)/cobaloxime (III) dual catalysis strategy has been developed for the stereoselective synthesis of indolyl spiroindanones from readily accessible N-sulfonyl-1,2,3-triazoles. This binary-catalyst system enables an aza-vinyl carbene initiated Pictet-Spengler-type cyclization and sequential cobaloxime promoted intramolecular Mannich-type reaction cascade. The easily accessible reagents, high diastereoselectivity, and operational simplicity make this reaction a method of choice for the preparation of functionalized spiroindanones, which are difficult to access by other classic reactions in one step.