Thiocyanation Of Unsaturated Carboxylic Acid Through Electrochemical Decarboxylation

Alkenyl/alkynyl thiocyanate compounds are key intermediates for the synthesis of other sulfur-containing and heterocyclic compounds,and they also have important pharmaceutical properties and biological activities,such as antifungal,antibacterial,and antiparasitic.Therefore,the synthesis of alkenyl/alkynyl thiocyanate structural units is an important class of reactions.The traditional methods to synthesize thiocyanate compounds are mainly coupling reactions of activated olefins and alkynes with thiocyanate sources catalyzed by transition metals.However,most of these methods require high temperature,metal reagents or strong chemical redox and produce chemical wastes.Therefore,it is necessary to explore new methods to synthesize alkenyl/alkynyl thiocyanate compounds,which is simple,direct and mild.Electrochemical organic synthesis,which replaces the external chemical redox with electrons,could effectively reduce or even avoid the generation of chemical waste,and reduces environmental pollution.This is in line with the contemporary "green synthesis" and "sustainable development" concepts.In recent years,chemists have gradually paid more attention to the electrochemical organic synthesis.This article summarizes the research progress in the synthesis of alkenyl/alkynyl thiocyanate compounds in the past two decades.Based on the previous research results and the disadvantages,we try to synthesize alkenyl/alkynyl thiocyanate compounds in one step by decarboxylative cross-coupling of unsaturated carboxylic acid compounds(such as cinnamic acid and phenyl-propynic acid)with thiocyanate sources under electrochemical conditions.In this paper,the optimal reaction conditions were finally determined by screening of the solvents,bases,electrode materials,currents,and electrolytes.We also explored a series of cinnamic acid substrates,and the reactions can afford the target products in moderate to good yields.In addition,this paper studied the mechanism in detail and proposed a feasible free radical mechanism: thiocyanate losed an electron at the anode to generate a thiocyanate radical,and after attacking cinnamic acid,it was further oxidized and decarboxylated at the anode to produce the final product.In addition,this article also introduces an electrochemical method of decarboxylation of phenyl-propynoic acid to synthesize alkynyl thiocyanate,We will continue to conduct in-depth research on the scope of substrates and the reaction mechanism.