Electrochemical Decarboxylative Sulfonylation Of Cinnamic Acids With Aromatic Sulfonylhydrazides

Vinyl sulfones are particularly valuable units in organic synthesis and biological chemistry.As a consequence,formation of vinyl sulfones building units is significant in synthetic organic chemistry.The conventional method for synthesis of vinyl sulfones mainly involves the direct coupling reaction of alkenes,alkynes,vinyl halides or alkenyl boronic acids with sulfone resources.In recent years,the decarboxylative cross-coupling methods of acrylic acids or propiolic acids with sulfone resources to synthesize vinyl sulfones have been developed.However,these existing methods suffer from one or more disadvantages,such as high-temperature,transition-metal catalysis and strong oxidants,hence efficient methods for preparation of vinyl sulfones under mild conditions are still in demand.Electrosynthesis has been found to be very useful in organic synthesis and has demonstrated efficient and environmentally friendly characteristics.Therefore,it is of practical importance for the development of electrochemical method for the synthesis of organic compounds.A brief review of sulfonylation reactions to construct C-S bond was presented in this paper,and the research progress of vinyl sulfones was also introduced.In connection with the previous work of formation of vinyl sulfones and our interests in electrochemistry,we envisioned that the sulfonylation to construct C-S bond could be achieved via an electrochemical oxidation process.This paper focused on the optimization of reaction conditions such as electrode,electrolyte,current and solvent by the controlled variable method.The results showed that in an undivided cell,using platinum foils as anode and cathode,dimethyl sulfoxide as solvent and tetrabutylammonium borofluoride(0.1 M)as electrolyte,lithium tert-butoxide as base,the reactions of cinnamic acids and benzenesulfonohydrazides proceeded in good yields in the constant current.This protocol refrains from using transition-metal catalysts,strong oxidants and halogens.A range of cinnanic acids and benzenesulfonohydrazides with both the electron-deficient groups and electron-donating groups on the aromatic rings can give corresponding products.Heterocyclic acrylic acids and sulfonohydrazides can also afford the desired products.In this paper,the mechanism of the reaction has been studied in detail.It is speculated that sulfonoylhydrazide was oxidized to produce sulfonoyl radical and then the radical reacted with cinnamic acids by decarboxylative coupling to give the desired product.