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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][CoBr 2 (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.