Phosphine-Catalyzed Cascade Michael Addition/[4+2] Cycloaddition Reaction of Allenoates and 2-Arylidene-1,3-indanediones.

The phosphine-catalyzed cascade Michael addition/[4+2] cycloaddition reaction of tetrahydrobenzofuranone-derived allenoates and 2-arylidene-1,3-indanediones has been reported, affording spirocyclic 1,3-indanedione derivatives in moderate to high yields with moderate to good diastereoselectivities. A scaled-up reaction worked well under mild conditions, and a plausible mechanism is proposed.