Aerobic Alcohol Oxidation Cayalyzed By Copper Catalyst

The selective alcohol oxidation to aldehydes or ketones with oxygen as the terminal oxidant is a pivotal protocol in organic synthesis. Aimed to reslove problems exsited in the field of alcohol oxidation, three highly efficient and novel methods have been developed for the copper-catalyzed aerobic alcohol oxidation, in which water, methanol or DMF was used as solvent, and the aromatic primary alcohos, secondary alcohols, allyl alcohols, heterocyclic aromatic alcohols were all oxidized to corresponding carbonyl compounds in high yield and selectivity.Firstly, an novel N,N-bidentate ligand containing a "2,2’-bipyridine analogue" fragment (pytl-β-CD) was designed and synthesized via a click reaction between2-ethynylpyridine and monoazido β-CD. The structure of the noval ligand was further characterized by FT-IR, UV-Vis, ICP-MS. The obtained pytl-β-CD has shown promising activity for copper-catalyzed aerobic oxidation of benzyl alcohols in the work. Under the optimized reaction conditions:1.0mmol alcohol,5mol%TEMPO,5mol%ligand,5mol%Cu(OAc)2·H2O,1.0mmol Na2CO3,4.0mL water, reflux under air, a range of primary alcohols were oxidized to the corresponding carbonyl compounds both efficiently and selectively with isolated yield up to95%. Meanwhile, the catalytic activity of the catalyst did not deteriorate even after it was recycled six times.Secondly, based on L-proline, glycine,8-hydroxyquinoline,2-picolinate and a series of N,O-bidentate ligand screening, L-proline was found to be served as an efficient N,O-bidenate ligand in copper-catalyzed aerobic alcohol oxidation. In the second part of our work, we have investgated the effects of the copper salts, solvent, base and etc. on the alcohol oxidation. By using L-proline as ligand, copper salt as catalyst, TEMPO as co-oxidant at room temperature, the aromatic primary alcohols, secondary alcohols, allyl alcohols and heterocyclic aromatic alcohols were all oxidized to corresponding aldehydes or ketones in high yield(up to95%) and high selectivity(>99%). Considering the promising results and related published research studies on catalytic reaction mechanism, a reasonable mechanism for the present Cu/L-proline/TEMPO-catalyzed alcohol oxidation was proposed.