An assessment of late transition metals as hydroamination catalysts in the cyclization of C-propargyl vinylogous amides into pyrroles

It has been shown that common and inexpensive salts of the late transition metals serve as effective hydroamination catalysts in the conversion of C-propargyl vinylogous amides into pyrroles. The oxide, acetate, nitrate and chloride derivatives of Cu(II), Ag(I), Zn(II), Cd(II) and Hg(II) were utilized as hydroamination catalysts in the oxidation states shown. Although the Zn(II) catalysts with the exception of ZnO afforded the highest yields of product under mild conditions, all of the group 12 metal catalysts provided excellent yields of product under more forcing conditions. The nature of the counterion plays an important role in the efficiency of hydroamination reactions, as well as the Lewis acidity of the metal centre. (C) 2007 Elsevier Ltd. All rights reserved.