Abstract
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.
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