Reduction of imines using NADH models

Abstract

Reduction of substituted N-arylideneanilines (3) and NN′-bisarylidene-ethylenediamines (10) in glacial acetic acid takes place smoothly with 3,5-bis(ethoxycarbonyl)-2,6-dimethyl-1,4-dihydropyridine (Hantzsch ester)(2) at room temperature in the dark. One-pot reductive amination of aromatic aldehydes in glacial acetic acid using (2) was equally efficient. Enamines (6)–(8) underwent reduction on protonation with trifluoroacetic acid in dichloromethane, but not in acetic acid. These reductions are analogous to NADH-mediated biochemical reductive aminations of carbonyl compounds. Imines (3) are also reduced to the corresponding amines (4) when irradiated with Pyrex-filtered light in the presence of (2) in benzene under nitrogen. This photoreduction also proceeds in the solid state and a two-phase system was successfully tested for recycling an NADH model for photoreduction of (3) using sunlight.