Diastereoselective Electrocatalytic Hydrogenation of Cyclic Ketones Using a Proton-Exchange Membrane Reactor: A Step toward the Electrification of Fine-Chemical Production

We report the diastereoselective electrocatalytic hydrogenation of cyclic ketones using a proton-exchange membrane (PEM) reactor. The adsorbed monatomic hydrogen species (Hads) generated from protons at the triple-phase boundary of the cathode were found to reduce cyclic ketones with high diastereoselectivity. As high as 94% cis-selectivity was realized under optimal conditions upon using a Rh catalyst. Operando infrared spectroscopy enabled the direct observation of the adsorbed ketone involved in the reaction. We also demonstrate 5 g scale electrolysis of 4-tert-butylcyclohexanone by coupling the hydrogenation process with water oxidation as an anodic reaction. This reaction successfully produced cis-4-tert-butylcyclohexanol, which is 52 times more expensive than the starting material, according to commercial prices, uses only electrical energy and water as the reagent, and, remarkably, does not require H2 gas. This study demonstrates the potential of PEM reactors as reliable, robust, and green systems for the electrochemical production of fine chemicals.