Divergent Access to Imidazopyrazinones and Imidazodiazepinones by Regioswitchable Post-Ugi Heteroannulation

A metal-free expeditious strategy for the divergent synthesis of structurally diverse bicyclic imidazo[1,5-a]pyrazine and imidazo[1,5-a][1,4]diazepine scaffolds is disclosed by combining an Ugi four-component reaction of easily available building blocks and an exo/endo selectivity-switchable post-Ugi intramolecular heterocyclization. Using PPh3, the intramolecular umpolung aza-Michael addition is mediated to selectively generate imidazopyrazinones through a 6-exo-dig cyclization, while without PPh3 fused imidazodiazepinones are obtained through a thermal 7-endo-dig cyclization in moderate yields. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim