Aerobic Oxidative Synthesis Of Imines Catalyzed By ABNO Or ABNO/KOH

Imines containing the reactive C=N bond are capable of involving various transformations such as reduction,addition,cyclization and aziridination reactions.Furthermore,they are also versatile intermediates and are widely used in field of pharmeceuticals,agrochemicals and materials science.The typical process for the preparation of the imines involves the condensation of primary amines with carbonyl compounds,especially odorous and unstable aldehydes,whereas this protocol requires acid,alkali,dehydrating agent promotes in many situations.During the past decade,new methodologies allowing the synthesis of imines have been developed,such as the oxidative coupling of amines with the greener and more available alcohols,the self-coupling of primary amines and the oxidative dehydrogenation of secondary amines.A wide variety of catalysts have been extensively explored and bring significant developments to these three new approaches.However,some drawbacks still remained to be solved satisfactorily in these reported methods.Thus,we are trying to develop an environmentally friendly,simple and efficient methods for the synthesis of imines.Part 1.The 9-aza-bicyclo[3.3.1]nonane N-oxyl(ABNO)/KOH catalytic system was developed in the preparation of imines from alcohols and amines.With benzyl alcohol and aniline were used as the model substrate,We initiated this study by screening for the nitroxyl radical and base,the effect of solvents,the reaction temperature,the amount of ABNO and KOH on the catalytic system.On the basis of these experimental data,we concluded that 3 mol% ABNO and 30 mol% KOH in toluene at 80 oC was suitable for oxidative coupling of alcohols with amines under atmospheric pressure of air.The reactions of various aromatic,heteroaromatic alcohols reacted smoothly with different aromatic,aliphatic amines,and afforded the corresponding substituted imine in 80-96% yields.Part 2.The ABNO catalytic system was developed in the preparation of imines from primary and secondary amines.With benzylamine were used as the model substrate,We initiated this study by screening for the effect of solvents,the reaction temperature,the amount of ABNO on the catalytic system.On the basis of these experimental data,we concluded that 5 mol% ABNO in toluene at 100 ?C was suitable for self-coupling of primary amines under atmospheric pressure of air.Both electron-withdrawing and electron-donating amines,heterocyclic methylamine could be smoothly converted to corresponding imine.10 mol% ABNO and 50 mol% KOH are required in the oxidation of secondary amines.cyclic secondary amines such as 1,2,3,4-tetrahydroisquinoline and 1,2,3,4-tetrahydroquinoline could be readily oxidized to 3,4-dihydroinisoquinoline and aromatized quinolone in moderate yield.When indoline and 2-methylindoline were subjected to the reaction,1H-indole and 2-methyl-1H-indole could be obtained.Unfortunately,only a low yield(20%)of the product was obtained when dibenzylamine was employed.