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

Abstract

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