Lewis Acid‐Catalyzed C(sp3)–C(sp3) Bond Forming Cyclization Reactions for the Synthesis of Tetrahydroprotoberberine Derivatives

An efficient Lewis acid‐catalyzed C(sp3)–C(sp3) bond forming annulation reaction has been developed. This strategy serves as a new method for the facile synthesis of tetrahydro‐5H‐isoquinolino[2,1‐g][1,6]naphthyridine derivatives. A wide range of 2‐methylquinoline‐3‐carbaldehydes and 1,2,3,4‐tetrahydroisoquinolines can be applied for this process to afford structurally diverse tetrahydroprotoberberine derivatives in excellent yields.