Synthesis of Luminescent Fused Imidazole Bicyclic Acetic Esters by a Multicomponent Palladium Iodide-Catalyzed Oxidative Alkoxycarbonylation Approach

A new multicomponent catalytic approach to important fused imidazole bicyclic acetic esters, whose core is present in many biologically active principles, is presented. It is based on the sequential cyclization-alkoxycarbonylation-isomerization of readily available N-heterocyclic propargylamine derivatives, carried out under oxidative conditions using a simple catalytic system consisting of PdI2 (1 mol%) in conjunction with KI (1 equiv.), in the presence of AcONa as additive (1 equiv.) at 100 °C under 20 bar of a 4 : 1 mixture CO-air. Under the optimized conditions, several N-(prop-2-yn-1-yl)pyridin-2-amines were smoothly converted into alkyl 2-(imidazo[1,2-a]pyridin-3-yl)acetates in fair yields (51–77 %). The method was also applied to the conversion of N-(prop-2-yn-1-yl)pyrimidin-2-amine into 2-(imidazo[1,2-a]pyrimidin-3-yl)acetate and of N-(prop-2-yn-1-yl)pyrazin-2-amine into 2-(imidazo[1,2-a]pyrazin-3-yl)acetate. Some of the newly synthesized bicyclic derivatives have shown promising luminescence properties.