Synthesis of Isoquinoline Derivatives through Rhodium(III)-Catalyzed Reactions of Benzylamines with Non-Terminal Alkynes

A new rhodium(III)-catalyzed N-annulation reaction of benzylamines with internal alkynes has been developed. Observations made during these efforts suggest that the mechanistic pathway followed in this process involves direct participation of benzylamines without their preliminary oxidative dehydrogenation. Moreover, N-annulation reactions of primary benzylamines result in the formation of mixtures of isoquinolines and 8-vinylisoquinolines. Finally, secondary and tertiary benzylamines undergo rhodium(III)-catalyzed N-annulation reactions to generate the respective isoquinolinium and hydroisoquinolinium salt products.