A new mechanistic proposal for the origin of α-homoallylic alcohols in indium-mediated allylation reactions in water

A new mechanism is proposed for the α-regioselective indium-mediated allylation reaction in water. Based on the results and observations obtained from an NMR study, a cross-over experiment and the complete inversion of the stereochemistry of 22β γ-adduct homoallylic sterols to the 22α α-adduct homoallylic sterols, it is suggested that the initially formed γ-adduct undergoes a bond cleavage to generate the parent aldehyde in situ followed by a concerted rearrangement, perhaps a retro-ene reaction followed by a 2-oxonia [3,3]-sigmatropic rearrangement to furnish the α-adduct.