Sequential Strecker–Ugi, Pictet–Spengler, and Ring-Expansion Reactions for the Synthesis of the Imidazopyridine-Fused Azocinoindole Scaffold

Abstract

A method involving sequential Strecker–Ugi, Pictet–Spengler, and ring-expansion reactions is developed for the synthesis of an imidazopyridine-fused azocinoindole scaffold. It is highly efficient for the regioselective preparation of a novel polycyclic scaffold. The three-component Strecker–Ugi reaction assembles five-membered imidazole; the regioselective Pictet–Spengler reaction at C-4 of indole affords seven-membered azepinoindole, and ipso ring expansion of azepinoindole at C-4 of indole results in eight-membered azocinoindole.