Indium-mediated nucleophilic substitution reaction of β,γ-unsaturated α-methoxypiperidine derivative in water

Water as a solvent was found to accelerate the indium-mediated Barbier type allylation and benzylation of β,γ-unsaturated piperidinium ion which was generated from β,γ-unsaturated α-methoxy-N-methoxycarbonylpiperidine, while ring-opened allylated product was obtained in a case using β,γ-saturated α-methoxy-N-methoxycarbonylpiperidine. Other solvents than water resulted in low yield of the allylated and benzylated products, suggesting that water is essential to generate the piperidinium ion intermediate from β,γ-unsaturated α-methoxy-N-methoxycarbonylpiperidine.