Electrochemical Reductive Deoxidation Catalyzed By Lewis Acids

Organic electrochemical synthesis is a hot research field of organic synthesis.Electrochemical synthesis has a unique redox method,which uses electrons to replace the traditional redox reagent,and makes the substrate redox on the electrode under the action of current.Compared with traditional organic synthesis,electrochemical synthesis avoids the use of toxic redox agents,reduces the generation of by-products and improves atomic economy.At present,electrochemical organic synthesis strategy has been widely used in oxidation reaction,but it has not been fully developed and applied in reduction reaction,which is a field worthy of in-depth research.Deoxidation is a basic reaction in organic chemistry and biosynthesis.At present,the reported deoxidation conversion methods include transition metal catalysis,traditional reductant reduction and photochemical catalysis,which has developed rapidly in recent years.Most of these methods rely on different pre-activation steps to produce new reactive functional groups.However,there are relatively few one-step direct deoxidation methods,and the previously reported methods have more or less defects(harsh reaction conditions,many by-products,high toxicity,etc.).The electrochemical reduction strategy provides us with a new idea of direct deoxidation.We envisage using Lewis acid to activate carbon oxygen bond and realize the deoxidation and reduction of a series of oxygenated compounds through electrochemical reduction strategy.In this paper,a novel method for electrochemical sulfoxide reduction and deoxidation under mild conditions using cheap and readily available aluminum flakes as sacrificial anodes was developed.This method only needs to use sub-stoichiometric Lewis acid Al Cl₃,and the reaction proceeds well.Through the combination of chloride ion and Al³⁺produced by sacrificial anodic oxidation,Lewis acid can be regenerated to further participate in the reaction.The optimum conditions of the reaction were determined through a series of conditions:room temperature nitrogen atmosphere,aluminum flake as anode,graphite felt as cathode,tetrabutyl ammonium chloride as electrolyte,sub-equivalent aluminum trichloride as lewis acid additive,DCE as solvent,10 m A constant current electrolysis for 6 hours.Through substrate expansion and scale-up experiment(10g level),the applicability and industrial application potential of this method are fully demonstrated.Finally,the possible mechanism of sulfoxide reduction and deoxidation was proposed by potentiostatic electrolysis experiments,divided cell electrolysis experiments and cyclic voltammetry experiments.A green,efficient and sustainable electrochemical method for deoxidative reduction of alcohols under mild conditions were also developed.The optimum conditions of the reaction were determined through a series of conditions:room temperature nitrogen atmosphere,aluminum sheet as anode,metal copper sheet as cathode,lithium perchlorate as electrolyte,sub-equivalent aluminum chloride as Lewis acid additive,acetonitrile and ethyl acetate(3:1)as solvent,10 m A constant current electrolysis for 6 hours.Through this method,15 compounds(including various primary alcohols,secondary alcohols)have been successfully expanded.Finally,combined with the experimental results and related literature reports,a possible mechanism of alcohol deoxygenation reduction was proposed.The structures of all reduced products were characterized by ~1H NMR,¹³C NMR and HRMS.