Cationic Rh(I) complex [Rh(binap)(MeOH)(2)]ClO4 catalyzes reductive dimerization of dialkyl acetylenedicarboxylates 1 to give 1,2,3,4-tetrakis(alkoxycarbonyl)-1,3-butadienes 2 in methanol selectively. (C) 1998 Elsevier Science S.A. All rights reserved.