Copper‐Catalyzed Aerobic Oxidation of Amines to Imines under Neat Conditions with Low Catalyst Loading

Abstract

Abstract:The copper (I)-catalyzed direct synthesis of imines from amines under mild aerobic conditions is described. The method is applicable for the synthesis of various imines from corresponding amines such as benzylic, aliphatic, cyclic secondary, heteroaromatic species and the oxidative condensation of benzylamines with anilines extends the scope of the CuCl catalytic system. Noteworthy, solvent-free procedure, air as a benign oxidant, and the cheap and easy availability of the catalyst are the vital advantages of the method.

Recent Advances in Aerobic Oxidation of Alcohols and Amines to Imines

“…In 2012, Kerton et al first reported a CuBr 2 /2,2,6,6-tetramethyl piperidinyl-N-oxyl (TEMPO)-mediated imine formation from primary amines. 13 Unlike the simple CuCl system, 8 the reaction here can be performed at room temperature, and no residual aldehydes was detected during the reaction. Besides, the electronic properties of the substrates have no effect on the efficiency of the catalyst.…”

Aerobic Copper-Catalyzed Organic Reactions

“…1113 The benzylic, aliphatic, cyclic, heteroaromatic amines proceed well with catalytic and stoichiometric amounts of copper (Scheme 569). …”

Heterogeneous copper-catalyzed coupling of amines: a possible way for the preparation of imines

“…Under aerobic conditions or in the presence of oxidizing agents, the formation of aldehydes has been expected from the amines, and this aldehyde would condensate with the amines [9,29]. Another proposition was the oxidation of the amine first to hydroxylamine, and its transformation into aldehyde [29].…”

“…Several methods with different catalysts have been published, among others CuCl [9], CuI [10] or CuBr 2 [11] and TEMPO, Ru-complex [12,13], Au powder [14,15], gold supported on alumina [15], magnetic gold nanoparticles [16], Au-Pd nanoparticles [17], Fe/CCl 4 [18], Co-porphyrin complex [19], the heteropolyacid NPV 6 Mo 6 [20], VO(Hhpic) 2 [21] under aerobic conditions, V 2 O 5 /H 2 O 2 [22], AIBN and oxygen [23], TiO 2 as photocatalyst [24][25][26], or TBHBQ [27] have been described. Several other metals were also used in photocatalytic reactions [28].…”