Oxidative [3+2]-annulation of nitroalkenes and azolium ylides in the presence of Cu(II): efficient synthesis of [5,5]-annulated N-fused heterocycles

A facile synthesis of [5,5]-annulated N-fused heterocycles – pyrrolo[2,1-b]thiazoles and pyrrolo[1,2-b]indazoles via Cu(II)-mediated oxidative [3+2]-annulation between nitroalkenes and azolium ylides was developed. The reaction proceeds in mild conditions with copper (II) trifluoroacetate/2,6-lutidine system as a promoter. The method is applicable to a broad range of nitroalkenes and azolium salts, providing target N-fused heterocycles in moderate to good yields. In the case of α-fluoronitroalkenes unique fluorinated derivatives were accessed via this methodology.