4-Chloro-3-nitrocoumarin as a precursor for synthesis of 2-arylchromeno[3,4-b]pyrrol-4(3H)-ones: a case of nitro group directed reductive coupling

Abstract

A series of 2-aryl substituted chromeno[3,4-b]pyrrol-4(3H)-ones were prepared in two steps by employing 4-chloro-3-nitrocoumarin as a precursor. The reaction involved the base-mediated reductive coupling of 4-chloro-3-nitrocoumarin with α-bromoacetophenone, followed by reductive intramolecular cyclization to afford the pyrrolocoumarin ring. When α-bromoacetophenone was replaced with α-cyanoacetophenone, (E)-4-(nitromethylene)-4H-chromen-2-amine was isolated as the major product. The molecular structures of the prepared compounds were characterized by X-ray crystallography and the mechanisms for their formation were proposed.