Substrate-Controlled Regioselective Cobalt(I)-Catalysed 1,4-Hydrovinylation Reactions

The substrate-directed regiochemistry of the cobalt-catalysed 1,4-hydrovinylation reaction is described. A variety of symmetrical and unsymmetrical 2,3-disubstituted 1,3-dienes are synthesised by ruthenium-catalysed enyne metathesis, and then reacted with a terminal alkene catalysed by cobalt(II) bromide-[1,2-bis(diphenylphosphino)ethane] [CoBr2(dppe)] under reductive conditions. The regiochemistry of the branched 1,4-diene products is influenced by the nature of the substituents on the unsymmetrical 2,3-disubstituted 1,3-dienes. The influence of steric and electronic effects is also discussed.