Cyclic Dimerization of lmidazole Carboxylic Acids and Cleavage Reaction of the Dimer

Abstract

Imidazole-4-carboxylic acid [1] and imidazole-4, 5-dicarboxylic acid [2] reacted with phosphorus pentachloride or thionyl chloride to give diimidazo[1, 5-a, 1', 5'-d]pyrazine-4, 9-dione [3] and 4, 9-dioxo-4, 9-dihydrodiimidazo[1, 5-a, 1', 5'-d]pyrazine-1, 6-dicarbonyl dichloride [4], respectively. The dioxopyrazine rings of the resulting dimers [3] and [4] were cleaved in their reactions with methanol or amines, giving the corresponding esters or amides of imidazole4-carboxylic acid and imidazole-4, 5-dicarboxylic acid.