Recent Advances in Aerobic Oxidation of Alcohols and Amines to Imines

Imines as valuable intermediates are widely applied in pharmaceutical syntheses and organic transformation. However, the traditional imine synthesis involves unstable aldehydes, dehydrating agents, and Lewis acid catalysts. The topic of this review is focused on three new approaches, namely, the cross-coupling of alcohols with amines, the self-coupling of primarily amines, and the oxidative dehydrogenation of secondary amines, utilizing much more readily available starting materials and green oxidant (O-2/air) to furnish the imine products. The related catalysts are classified into metal, metal-free, photo-, and bioinspired catalysts. Particular emphasis is placed on the high-active, low-cost, and versatile catalysts; key factors that affect the catalytic activity and reaction mechanisms are also highlighted.