Electrochemical Synthesis Studies Of Sulfinic Esters

Organic electrochemical synthesis is an important and useful synthesis strategy in organic synthesis,which through electrochemical oxidation or electrochemical reduction reaction.Compared with traditional metal catalyzed?such as copper,nickel,palladium,etc.?and photocatalytic organic synthesis,organic electrochemical synthesis has unique advantages:no additional oxidizing agent or reducing agent is required,the reaction conditions are mild,can be conducted under normal temperature and pressure,with low requirements on the reaction equipment,clean and efficient,and the reaction rate can be controlled by adjusting the current conveniently.Organic electrochemical synthesis can reduce the occurrence of side reactions effectively,which is very consistent with the principles of atomic economy and green chemistry.At present,organic electrochemical synthesis involves many types of reactions.According to the gain or loss of the target product electron,it can be divided into electrochemical oxidation reaction and electrochemical reduction reaction;According to the process of electron transfer between reactants and electrodes,it can be divided into direct electrochemical reaction and indirect electrochemical reaction;Or according to the different catalytic systems,it can be divided into simple electrochemical reaction,co-catalytic reaction of metals and electrochemical and co-catalytic reaction of light and electrochemical.Our current research direction is mainly to develop some new oxidative coupling reactions through organic electrochemical synthesis.Sulfinic esters are not only exist widely in drug molecules,but also are important intermediates in the synthesis of sulfur-containing compounds.In this case,we have developed organic electrochemical synthesis to form sulfinate esters through the oxidative esterification of thiols and alcohols.4-chlorothiophenol and methanol were selected as the model substrates for optimization studies and the reaction was performed in an undivided cell employing carbon plate as the anode,carbon plate as the cathode and n Bu₄NBF₄as electrolyte in air atmosphere,the reaction worked smoothly in methanol under a constant current of 20 m A for 6 h,providing the desired product in91%isolated yield.Then we investigated the scope of this reaction in the electrochemical oxidative couplings with different thiophenols,thiols and alcohols.It was found that various substrates could be smoothly converted to the corresponding sulfinic esters in moderate to good yields where various para-,meta-,or ortho-substituents were well tolerated.At the same time,the scale-up reaction can be easily performed with good efficiency.Finally,mechanism studies indicate that persulfide is an important intermediate in this reaction.In summary,our reaction provides a clean,efficient and convenient method for the synthesis of sulfinic esters.Compared to stoichiometric oxidants or metal-catalyzed oxidation,the electrochemical oxidation we used is an environmentally friendly and powerful synthesis strategy and the prodcedure has certain practical application value.