Copper-Catalyzed Cross-Coupling Reactions Of Oxime Esters

The concept of green chemistry has been deeply rooted in the hearts of people,and the development of environmentally friendly and simple synthetic methods has become the pursuit of chemists.Oxime esters can generate corresponding metal complexes or free radical intermediates under the action of transition metal catalysts,and these two intermediates can be further translated to several heteroaromatic skeleton or nitrile compounds through the progress of imine radical rearranged to cyanoalkyl radical.Besides,the ester group of oxime esters can be used as internal oxidants in the reaction process,and additional oxidants are usually not required,thus the corresponding safety risks and environmental pollution problems are avoided.A variety of metal catalysts have been successfully developed and used in the coupling reactions involving oxime esters,among of them,palladium catalyst and copper catalyst are most widely used.Compared with palladium reagent,copper reagent has the advantages of low toxicity,stable property,easy to use and post-treatment,so the development of copper-catalyzed coupling reactions involving oxime esters is not only a simple and efficient synthetic method,but also in line with the concept of green chemistry.Based on the above viewpoints,we have developed two copper-catalyzed coupling reactions involving oxime esters,details are as follows:The first part studied copper-catalyzed cross-coupling/cyclization of oxime esters with 4-hydroxycoumarins to furnish furocoumarins.This redox-neutral reaction allows smooth and selective synthesis of 2-substituted,3-substituted,2,3-disubstituted and 2,3-fused polycyclic furo[3,2-c]coumarins.The reaction conditions are mild,need no oxidant,ligand or acid/base.It is worth mentioning that this method is the first example which build a furan blocks with oxime esters as substrates.Macrocyclic aromatic compounds with fully conjugated structures can also be synthesized by oxidative dehydrogenation of the corresponding products.The second part studied copper-catalyzed two different coupling reactions of cyclobutanone oxime esters with sulfur nucleophiles,a series of cyanoalkylarylsulfide compounds and N-arylmercapto cyclobutanone imines were synthesized.Initially,a copper-catalyzed iminyl radical-mediated electrophilic-ring-open/cross-coupling cascade reaction of cyclobutanone oxime estess with sulfur nucleophiles compound can be realized.Afterwards,a substitutional reaction can also be realized by altering the reaction conditions.