Studies on Wallach's imidazole synthesis

Abstract

The reaction of the N-benzylamides of N-heterocyclic carboxylic acids 3 and 6–9 with phosphorus pentachloride affords heterocondensed imidazoles 4 and 10–14 by a scheme reminiscent of Wallach's imidazole synthesis starting from N.N′-dialkyloxamides. Kinetic and labelling experiments are described which support a mechanism involving nitrite ylide species and allow a better understanding of the Wallach reaction. The limiting parameter for the formation of heteroanellated imidazoles is the electron availability of the heterocyclic ring.