Undivided Parallel Paired Electrolysed Chemoselective Cathodic Reduction of α-Keto Amides and Anodic Oxidative Esterification of Aldehydes

A sustainable parallel paired electrolysis (PPE) methodology has been developed to synthesise αhydroxy amides via chemoselective hydride-free cathodic ketone reduction over amide in α-keto amides at a Pt cathode, and the formation of esters via anodic oxidative esterification of aldehydes at a Pt anode in alcohol. In this PPE, any substitution on α-keto amide not only affects the yield of the reduction process, but also influences the oxidation process as well. Similarly, if a substitution on the aldehyde increases the yield of the oxidation product, it also increases the yield of the reduction product due to potential alignment. In this PPE, aldehydes are necessary for the reduction of α-keto amide by suppressing the formation of hemiketal intermediate at the cathode to form the reduced product, while the oxidation process occurs independently in the absence of α-keto amides at the anode. EPR, CV, controlled experiments, and radical-quenching experiments suggest a radical reaction pathway with an alkoxy radical intermediate generated at the anode and a radical anion intermediate at the cathode. The formation of an acyl radical is crucial in this reaction to suppress the formation of the hemiketal intermediate. The deuterium labelled study reveals that the source of hydrogen is alcohols.