3-Aryl-2H-azirines as annulation reagents in the Ni(II)-catalyzed synthesis of 1H-benzo[4,5]thieno[3,2-b]pyrroles

A high-yielding method for the synthesis of 3-arylbenzo[4,5]thieno[3,2- b ]pyrroles has been developed via pyrrole ring annulation to the aromatic benzo[ b ]thiophene system, using 3-arylazirines as a N‒C=C synthon. The reaction is catalyzed by Ni(hfacac) 2 and proceeds through the azirine ring opening across the N=C3 bond. Azirines with both electron-donating and electron-withdrawing C3-aryl substituents tolerate the reaction conditions. The reaction of the N -methylindole analog also provides the annulation product but in moderate yield. The described synthesis is the first example of a dealkoxycarbonylative annulation reaction, in which 2 H -azirines act as the annulation reagent.