Catalyst‐Free [3+2] Cycloaddition of Unactivated Imines with Cyclopropenones

Abstract We have developed a convenient and mild catalyst‐free synthesis of structurally diversified indolizinoindoles through [3+2] cycloaddition of dihydro‐β‐carbolines and diarylcyclopropenones. Dimethoxydihydroisoquinolines and 3,4‐dihydrobenzonaphthyridine can also be used in this process affording corresponding polycyclic N‐heterocycles with high molecular complexity.