Ligand Assisted Copper-Catalyzed N-arylation Reaction Of Bromamine Acid

N-arylation reaction of bromamine acid holds a very important role in dye industry and medical research. Though significant progress was achieved in recent years, the tolerance of catalyst in aqueous solution, the efficiency of catalysis, the catalyst loading, and the hydrolysis problem still need perfection.This study proposes a novel catalytic system composed of a divalent copper complex catalyst and a water-soluble reductant in order to achieve a stable aqueous solution of Cu+, enhance the catalytic activity of the catalyst, reduce the hydrolysis side reactions, and improve the yield of the N-arylation reaction.Five kinds of ligands with different structures were tested. It turned out that the catalyst system consisted of reducing ligands had a poor catalytic activity. When reducing agent was added, the system made up of L3exhibited a high catalytic effect (yield90.6%). However, it was no longer a homogeneous system. Five plane bidentate chelating ligands which were in common use in organic phase were tested, the catalyst systems turned out almost inactive apart from L6and L9which contains large steric effect and a phenolic hydroxyl group respectively. Inspired by L2, we synthesized five macrocyclic Schiff base ligands, and demonstrated that a moderate catalytic activity was achieved by the system composed by LI1and L14, and the size of the ring was very considerable to have catalytic effect. In order to introduce the phenolic hydroxyl group, we designed four salicylaldehyde Schiff base ligands, it indicated that this class of systems achieved the best catalytic effect. L20, which is resulting from the reduction reaction of L17, constitute the optimal system of all (yield93.0%).By means of UV-Vis, CV, IR analysis, we showed that ligands L6, L14, LI7, L20which formed the better-performing catalyts systems had strong coordination ability with Cu’Cu(CH3COO)2, NaHCO3(pH7.5-8.5), L20, and L-ascorbic acid were selected as the best candidates for catalyst, base, ligand, and reducing agent, respectively. Then, the scope of the substrates was tested. Various substituted aromatic amines were successfully condensed with bromamine acid at75℃(yield52%-87%). The catalyst system performed a high catalytic activity for substrates with an electron withdrawing group (more than52%of yield), but substrates with ortho-containing achieved poor activity(less than60%of yield).