Visible light-mediated copper catalyzed regioselective diamination of terminal alkynes at room temperature: a facile synthesis of substituted imidazo[1,2-]pyridines

We have developed a visible-light mediated copper(i) chloride catalyzed regioselective oxidative diamination reaction of 2-aminopyridines with terminal alkynes to form substituted imidazo[1,2-alpha]pyridine products at room temperature using molecular oxygen as a green oxidant. This is the first photochemical report on the synthesis of 3-alkyl/aryl-2-(aryl/alkylethynyl)imidazo[1,2-alpha]pyridines and involves the formation of two C-N and one C-C bond at RT. Compared to a literature reported 3-step thermal method, the current photochemical process requires a single step to synthesize the substituted imidazo[1,2-alpha]pyridine product. Moreover, the green chemistry metrics (E-factor is 5.5) and Eco-Scale (value is 53.65) evaluations reveal that this process is an acceptable green organic synthesis process. Thus, this photochemical oxidative diamination reaction is simple, green, environmentally-friendly, cost-effective, and energy-efficient. We have developed a protocol for the regioselective synthesis of substituted imidazo[1,2-alpha]pyridines at room temperature using low-energy visible light, inexpensive CuCl as a catalyst, readily available starting materials, mild reaction conditions, and O2 as a green oxidant.