Phosphine-Catalyzed Sequential [3+3]/Aza-6π-Electrocyclization Reaction of Cross-Conjugated Azatrienes and δ-Sulfonamido-Allenoates

An unprecedented sequential [3+3]/aza-6π-electrocyclization between cross-conjugated azatrienes and δ-sulfonamido-allenoates, catalyzed by phosphine, has been developed, which provides efficient and facile access to highly functionalized tetrahydroisoquinoline derivatives. The products can be easily transformed into (dihydro)isoquinolines and their fused polycyclic compounds. The reactivity of both azatrienes and δ-sulfonamido-allenoates in this text, acting as a five-atom unit, is unique in the phosphine-catalyzed annulations of allenoates.