Regioselective Synthesis of Fused Imidazo[1,2-a]pyrimidines via Intramolecular C—N Bond Formation/6-Endo-Dig Cycloisomerization.

An efficient regioselective cascade synthesis of N-fused imidazo heterocycles has been developed. This cascade transformation proceeds via a transition-metal (copper/silver) catalyzed coupling reaction between 2-aminobenzimidazole, aldehydes, and alkynes leading to the formation of propargylamine intermediate, which regioselectively undergoes 6-endo-dig cyclization through intramolecular N–H bond activation interceded C–N bond formation leading to highly functionalized imidazo[1,2-a]pyrimidines in good to excellent yields.