Copper on charcoal: Cu0 nanoparticle catalysed aerobic oxidation of α-diazo esters

By using a charcoal supported nano Cu-0 catalyst (Cu/C), a highly efficient oxidation of alpha-diazo esters to alpha-ketoesters with molecular oxygen as the sole oxidant has been developed. In the presence of the Cu/C catalyst, 2-aryl-alpha-diazo esters with both electron-donating and electron-withdrawing groups can be oxidized to the corresponding alpha-ketoesters efficiently. Furthermore, this Cu/C catalyst can catalyse the reaction of aryl alpha-diazo ester with water to form aryl ketoester, 2-aryl-2-hydroxyl acetate ester and 2-aryl acetate ester. In this case, water is split by alpha-diazo ester, and the diazo group is displaced by the oxygen or hydrogen atom in water. Mechanistic investigation showed that the reaction of alpha-diazo ester with oxygen proceeds through a radical pathway. In the presence of 2,2,6,6-tetramethyl piperidine nitrogen oxide, the reaction of alpha-diazo ester with oxygen is dramatically inhibited. Furthermore, the reaction of alpha-diazo ester with water is investigated by an isotopic tracer method, and GCMS detection showed that a disproportionation reaction occurred between alpha-diazo ester and water.

Automated summary

A highly efficient oxidation method of alpha-diazo esters to alpha-ketoesters using a Cu/C catalyst has been developed, with the mechanism proceeding through a radical pathway. The reaction can be inhibited by the presence of 2,2,6,6-tetramethyl piperidine nitrogen oxide, and a disproportionation reaction can occur between alpha-diazo ester and water.