Catalytic asymmetric transformation of nitrones and allenes to dihydropyridoindoles via chiral N , N '-dioxide/cobalt(II) catalysis.

A chiral N , N '-dioxide/cobalt(II) complex catalytic system is developed to promote the multistep cascade reaction of α , β -unsaturated- N -aryl nitrones with allenes, giving a variety of chiral dihydropyridoindoles in moderate to good yields with excellent dr and ee values. Mechanistic studies support a [3+2] cycloaddition/[3,3]-rearrangement/retro-Mannich process.