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 (H ads ) 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 H 2 gas. This study demonstrates the potential of PEM reactors as reliable, robust, and green systems for the electrochemical production of fine chemicals.