Metal-Free Regioselective Alkylation of Imidazo[1,2-a]pyridines with N-Hydroxyphthalimide Esters under Organic Photoredox Catalysis

A visible-light-induced direct C-H alkylation of imidazo[1,2-a]pyridines has been developed. It proceeds at room temperature by employing inexpensive Eosin Y as a photocatalyst and alkyl N-(NHP) esters as alkylation reagents. A variety of NHP esters derived from aliphatic carboxylic acids (primary, secondary, and tertiary) were tolerated in this protocol, giving the corresponding C-5-alkylated products in moderate to excellent yields. Mechanistic studies indicate that a radical decarboxylative coupling pathway was involved in this process.