Reaction for the Synthesis of Benzimidazol-2-ones, Imidazo[5,4-b]-, and Imidazo[4,5-c]pyridin-2-ones via the Rearrangement of Quinoxalin-2-ones and Their Aza Analogues When Exposed to Enamines

A synthetically useful protocol has been developed for the preparation of highly functionalized N-pyrrolylbenzimidazol-2-ones. The reaction of variously substituted 3-aroyl- and 3-alkanoylquinoxalin-2(1H)-ones with commercially available enamines in acetic acid results in a rapid rearrangement and formation of N-pyrrolylbenzimidazol-2-ones in modest to excellent yields. The key step of the rearrangement involves the novel ring contraction of 3-aroyl- and 3-alkanoylquinoxalin-2(1H)-ones with enamines. In this case, the atom of carbon which is displaced from the pyrazine ring of quinoxalin-2(1H)-one becomes the fourth carbon atom of the newly formed pyrrole ring. The method is applicable for the aza analogues of quinoxalin-2(1H)-ones.