Synthesis of unsaturated secondary amines by direct reductive amination of aliphatic aldehydes with nitroarenes over Au/Al2O3 catalyst in continuous flow mode

Abstract

A series of unsaturated secondary amines was successfully synthesized by direct reductive amination of aliphatic aldehydes with nitroarenes over a 2.5% Au/Al₂O₃ catalyst in a continuous flow reactor using molecular hydrogen as a reducing agent. In most cases, the targeted secondary amines were obtained in good to excellent yields. Interestingly, the hydrogenation of CC group is practically absent in both initial aldehydes and secondary amines under the reaction conditions. It was found that the introduction of electron-donating substituents in the para- and meta-position of nitrobenzenes increased the yield of secondary amine, while in the case of nitrobenzenes with electron-withdrawing substituents or electron-donating substituents in the ortho-position a decrease in the yield of the target product was observed.