Efficient Hydride-Assisted Isomerization of Alkenes via Rhodium Catalysis

We find that alkenes isomerize rapidly in the presence of catalytic amounts of a hydroborating reagent and a rhodium compound. The hydroborating reagent is apparently responsible for the in situ generation of a metal hydride species, which has been implicated to account for the stepwise migration of the double bond. Labeling studies reveal a high degree of reversibility in the catalytic cycle. A mechanism involving reversible alkene metal hydride insertion followed by β-hydride elimination is consistent with our data. Generally, the final product favors the thermodynamic equilibrium mixture of isomeric alkenes. The methodology provides for an efficient and economical route to alkene isomerization.