BF 3 ·OEt 2 mediated metal-free one-pot sequential multiple annulation cascade (SMAC) synthesis of complex and diverse tetrahydroisoquinoline fused hybrid molecules

A highly efficient and distinct BF3·OEt2 mediated metal-free SMAC protocol for the synthesis of complex and diverse hybrid molecules viz. indazole fused tetrahydroisoquinolinoquinoxalines, and tetrahydroisoquinolinodiazepine has been developed. The transformation is based on sequential cascade processes involving 2H-indazole formation and deprotection Pictet-Spengler cyclization steps in one-pot fashion. The protocol demonstrates the utility of sequential multiple annulations in a cascade fashion. The present one-pot protocol uses the Solid State Melt Reaction (SSMR) strategy for the synthesis of the intermediate 2H-indazole. The method is operationally simple and represents a new approach for C-C, three C-N and N-N bond formation with a wide substrate scope.