Copper-Catalyzed Oxidative [3+2] Cycloaddition of N-Alkyl Pyridinium Salts to Imidazo[1,2-a]pyridines

A copper-catalyzedreaction of pyridinium salts and trimethylsilylcyanide (TMSCN) in the presence of diethyl phosphite is developed.This reaction, which allows the single-step construction of biologicallyimportant 2-cyanoimidazo[1,2-a]pyridine from readilyavailable starting materials, is realized for the first time and isfeasible at the gram scale. The scope of the protocol is demonstratedwith 27 examples. A consecutive double cyanation and cyclization canbe achieved in this one-pot process. TMSCN plays a dual role not onlyas the "CN" source but also as the coupling partnerfor the cyclization of imidazo[1,2-a]pyridines.