Direct Electrochemical Transformation Of Fine Chemicals Based On Aldehydes And Their Derivatives

Organic Electrochemical Synthesis is a technique for organic synthesis that the old bond is broken and the new bond is formed by the charge transfer of organic molecules or catalysts at the"electrode/solution"interface and the mutual conversion of electrical energy and chemical energy.In such a method,electrons act as clean redox agents to relieve environmental pollution,and the overall energy consumption is also reduced,and the electrochemical reactions are usually performed at room temperature under mild and simple operational conditions.Therefore,organic electrochemical synthesis strategy that complies with the concept of“green chemistry”,has attracted extensive attention of many synthetic chemists in industry and academia.Aldehydes and their derivatives,which are widely used in medicine,natural products and functional materials,can serve as important intermediates in organic synthesis.Currently,these high value-added products are mainly prepared by traditional methods that use expensive Lewis acid catalysts,metal salts and excessive oxidative reagents,which is contrary to viewpoints of green chemistry in terms of atomic economy and environmental protection.Therefore,it is still a challenging task to develop a simple,efficient,and environmentally friendly synthetic method to achieve the transformation of aldehydes and their derivatives.On the basis of the above-mentioned issues,we would like to apply direct electrochemical synthesis to construct of carbon-carbon and carbon-heteroatom bonds from aldehydes and their derivatives.The concrete research contents are as follows:(1)Direct electrochemical anodic oxidation of aldehydes with alcohol/thiol was developed to synthesize(thio)acetals,avoiding the use of Lewis acid catalyst and mediators and energy consumption was reduced.Various aliphatic/aromatic substituted(thio)acetals with isolated yield up to 98%were obtained by electrolysis using graphite electrode as cathode and anode,and Ag/Ag Cl electrode as reference electrode.This strategy was compatible with a wide range of substrates and shows excellent functional group tolerance as well as chemo-selectivity.The reaction was successfully amplified at gram-scale with isolated yield up to 94%.DFT calculation and mechanistic experiments revealed that direct electron transfer between substrates and anode played an important role to activate carbonyl group.(2)A variety of bis/tri(heterocyclic)aryl methane derivatives were obtained by direct electrochemical oxidation of aldehydes and heterocyclic aromatics.The alkylation of heterocyclic aromatics was completed by used graphite electrodes as anode and cathode and tetrabbutylammonium perchlorate as electrolyte in H-type electrolytic cell with simple optimization.In comparison to traditional methods,the electrochemical process was carried out under milder conditions and did no require extra acid catalysts and excessive chemical oxidants.Based on the different electric excitation and controlling experiments,we found that the reaction underwent an autocatalytic process promoted by some in-situ generated reactive cation species from the interaction between anode and aldehydes.The continuous electrical pulses were beneficial to the accumulation of reactive cations in the reaction solution and thus promoted the reaction towards complete transformation.(3)The direct anodic oxidation of 1,3-dithiane and heterocyclic aromatics was performed to produce bis/tri(heteroaryl)substituted alkanes with isolated yield up to95%.The alkylation of heterocyclic aromatics was carried out in a two-electrode system with graphite as anode and copper as cathode with constant current mode.This electrochemical process allowed the preparation of desired products in high yields with broad substrate scope and high functional group compatibility.Various substituted 1,3-dithiane,such as electron-deficient/electron-rich,heterocyclic and aliphatic substituents,were well tolerated without excessive chemical oxidants.Additionally,the products with single heterocyclic aromatic were observed.The mechanism study showed that disulfide intermediates may be generated at the anode,which reacted with electron-rich heteroaromatics to give alkylation products.(4)Difunctional reaction of gem-difluoroalkenes was achieved by direct anodic oxidation,and a variety of methoxylated/chlorinated difunctionalized products were obtained.Various aryl-substituted gem-difluoroalkenes with alcohols and concentrated hydrochloric acid had been studied in undivided cell with graphite as cathode and nickel foam as anode,and acquired various bifunctional products containing CF₂with high isolated yields.This method had a wide range of substrates and functional group compatibility.This method allowed the preparation of bifunctionalized florine-containing products with good yields and chemoselectivity,and a fluorinated cholesterol derivative was obtained.The mechanism study revealed that the bifunctional reaction may undergo a single electron transfer process.In conclusion,direct electrochemical synthesis had successfully achieved multifunctional and high value-added conversion of aldehydes and their derivatives in the absence of additional catalysts and mediators.And this strategy is substantially reflected as a transformation in the electrochemical process with low energy consumption,environmental friendly and high atomic efficiency.