Reductive homo-coupling of N-acyliminium ion by indium in water

Abstract

It is well known that indium (In) mediates pinacol-type reductive coupling reactions of carbonyl and imino compounds, while this method was not applicable to reductive homo-coupling reactions of N-acyliminium ion. Now, we found out that a combination of In and BrCF₂CO₂Et effectively mediated a reductive homo-coupling of N-acyl-β,γ-unsaturated- iminium ion generated from β,γ-unsaturated-a-methoxypiperidine derivatives in water to afford 2,2'-bipiperidine derivatives with high dl selectivity. Other solvents than water resulted in low yield of the coupling product.Active reducing species of this coupling reaction seems to be "In⁺" because commercially available InCl and InBr mediated this coupling reaction with low efficiency.