Homologation of Aryl Aldehydes Using Nitromethane as a C1 Source Enabled by Nitrogen-Doped Carbon-Supported Palladium Catalysts

Homologation of aryl aldehydes provides useful synthetic intermediates, but it requires multistep reactions and generates significant amounts of waste. We considered such reactions using nitromethane as a C1 source through nitroolefin formation, partial hydrogenation to oximes, and hydration of oximes; however, the control of selectivity in the second reaction is challenging. To achieve this pathway, nitrogen-doped carbon-incarcerated palladium nanoparticle catalysts were developed for selective hydrogenation. We found that the presence of nitrogen dopants effectively tuned the catalytic activity to show almost perfect selectivity, high activity, and reusability under ambient pressure. We then performed a three-step homologation reaction in both batch and flow systems with only one purification step. The sequential continuous-flow system worked efficiently for more than 2 days to afford the product in a high yield.