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 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.

Synthesis of N-vinyl isothiocyanates and carbamates by the cleavage of NH-1,2,3-triazoles with one-carbon electrophiles

“…6 In comparison to N -sulfonyl and N -fluoroalkyl triazoles, which require multiple synthetic steps, NH-1,2,3-triazoles are easily accessible in one step from simple azide sources (NaN 3 or TMSN 3 ) and commercial alkynes, 7 or aldehydes and nitroalkanes. 8 It is known that the ring cleavage of 1,2,3-triazole is synthetically useful in the presence of an electron-withdrawing group at N1, 2 fused triazole derivatives 9 and specific substrates with more reactive centres. 10 Thus, for a long time NH-1,2,3-triazoles were not considered as building blocks in ring cleavage chemistry.…”