An Effective Method for the Synthesis of Carboxystyryl Derivatives of 1,10-Phenanthroline, 2,2′-Bipyridine, and Pyridine

An effective, eco-friendly method was developed for the synthesis of carboxystyryl derivatives of 1,10-phenanthroline, 2,2′-bipyridine, and pyridine via a catalyst- and solvent-free condensation reaction of 4-carboxybenzaldehyde with 2,9-dimethyl-1,10-phenanthroline, 6-methyl-2,2′-bipyridine, 6,6′-dimethyl-2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, or 2-methylpyridine. For dimethylbipyridines, monosubstituted products were primarily formed, whereas for dimethylphenanthroline, a bis-product was obtained. The formation of a hydrogen bond between the nitrogen atom of the heterocycle and the carboxylic proton of 4-carboxybenzaldehyde enhances the reactivity of the methyl group in the heterocycle.