Indium-Mediated 2-Oxonia Cope Rearrangement of 1,4-Dienols to 1,3-Dienols.

An indium-mediated isomerization of 1,4-dienols to 1,3-dienols is described. This procedure consists of the addition of pentadienylindium, in a protic solvent, to aldehydes giving the kinetic γ-allylation product in high yields. The subsequent conversion of this γ-allylation product to its thermodynamic 1,3-dienol α-isomer can be achieved by its exposure to indium triflate in the presence of a substoichiometric amount of aldehyde at room temperature. This transformation exhibited moderate to good substrate scope and has been shown to proceed by a 2-oxonia Cope rearrangement.