Chemoselective reactions of (E)-1,3-dienes: Cobalt-mediated isomerization to (z)-1,3-dienes and reactions with ethylene

Abstract

In the asymmetric hydrovinylation (HV) of an E/Z-mixture of a prototypical 1,3-diene with (S,S)-(DIOP)CoCl2 or (S,S)-(BDPP)CoCl2 catalyst in the presence of Me3Al, 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 [η4-(diene)(LCo-H)]+ complex, followed by p-s-p isomerization of the intermediate Co(allyl) species, is proposed for this reaction. © 2014 American Chemical Society.