Study On Asymmetric Electrochemical Reduction Of Chiral Multifaren

A supramolecular chiral electrode was constructed by layer-by-layer assembly of gold nanoparticles(Au NPs)and an S-chiral multifarene[3,2,1](S-CMF)on the surface of a glassy carbon electrode,which was applied for the electroreduction of acetophenone.The host-guest encapsulation of the substrate within the chiral cavity was confirmed by ~1H NMR,fluorescence titration,and molecular simulation.The composite on the electrode surface was characterized by electrochemical impedance spectroscopy(EIS)and transmission electron microscopy(TEM).Optimization of the electrolysis process was performed to give a high yield of 70.9%and high enantioselectivity of 63.9%ee,which exhibited superior reactivity to the previously reported materials.The repeatability of the experiment was tested via five separate experiments and indicated consistent stability,recyclability,and reusability of the novel chiral electrode.The proposed mechanism involved supramolecular encapsulation,two single-electron transfer steps,and proton addition.The chiral electroorganic reduction was extended to more substrates to provide successful yields and enantioselectivity.The supramolecular strategy was subjected to the asymmetric hydrogenation of 4-methylumbelliferone in electrochemical reduction,with the host-guest interaction between a chiral macrocyclic multifarane[3,3]and the coumarin guest.The electroorganic synthesis performed an enantioselective reduction to offer L-7-hydroxy-4-methylchroman-2-one product with high chemical yield of 65%and enantioselectivity up to>99%ee.The control conditions of the chiral electroreduction system were optimized,and a reasonable mechanism with establishment of chiral supramolecular microenvironment and performance of electrochemical process was proposed.The high stability of the developed chiral supramolecular electrode guaranteed the recyclability and repeatability in the electrolysis,and therefore,the application was extended to different coumarin derivatives to provide successful results in chemical yields and enantioselectivities.