Chemoselective Reactions of (E)-1,3-Dienes: Cobalt-Mediated Isomerization to (Z)-1,3-Dienes and Reactions with Ethylene

[Image: see text] In the asymmetric hydrovinylation (HV) of an E/Z-mixture of a prototypical 1,3-diene with (S,S)-(DIOP)CoCl(2) or (S,S)-(BDPP)CoCl(2) catalyst in the presence of Me(3)Al, the (E)-isomer reacts significantly faster, leaving behind the Z-isomer intact at the end of the reaction. The presumed [LCo–H](+)-intermediate, especially when L is a large-bite angle ligand, similar to DIOP and BDPP, promote an unusual isomerization of (E/Z)-mixtures of 1,3-dienes to isomerically pure Z-isomers. A mechanism that involves an intramolecular hydride addition via an [η(4)-(diene)(LCo–H)](+) complex, followed by π–σ–π isomerization of the intermediate Co(allyl) species, is proposed for this reaction.