Multiple pathways in rhodium-catalyzed reactions of 1-alkynes with 3-butenoic acid

Abstract

Rhodium(I) complexes have been shown to catalyze the reaction of 1-alkynes with 3-butenoic acid in alcoholic solvents at 85°C. Various pathways, involving rhodium-bonded vinylidene, α-vinyl, β-vinyl or alkynyl groups as intermediates, have been uncovered under slightly different conditions. The stereo- and regiochemisty of these reactions provide evidence for the intermediacy of vinylidenerhodium complexes when tertiary phosphine ligands are used. Subsequent protonation leads to β-vinylrhodium complexes. In contrast, α-vinylrhodium intermediates are involved in the case of di- or tri-alkyl or -aryl-phosphite ligands. The latter ligands also favour the formation of alkynylrhodium complexes at lower temperatures. Some mechanistic aspects are discussed.