Regioselective Synthesis of Fused Imidazo[1,2-a]pyrimidines via Intramolecular C–N Bond Formation/6-Endo-DigCycloisomerization

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.