Investigation On The Reactions Involving The Formation Of C–S Bonds Under The Electrochemical Conditions

Organic electrosynthesis is a green strategy.Using electrons as the redox reagents,it avoids the use of external chemical redox reagents and can prevent environmental pollution.In addition,the reaction conditions are very mild.It could usually be carried out at room temperature.Because of the advantage of the green and mild conditions,organic electrochemistry has recently attracted more and more attention from synthetic chemists.Sulfur/selenium-containing compounds are not only widely existed in pharmaceuticals, natural products and functional materials,but are also the significant synthetic intermediates.There is no doubt that oxidative cross-coupling with sulfur reagents(such as thiols,disulfides,sodium sulfinates and sulfonyl hydrazides)through C-H bonds activation is one of the most ideal methods for constructing C-S bonds.Although this strategy has shown the advantages of high efficiency and atomic economy,most of the conversion processes still require the use of expensive and toxic metal salts or excess chemical oxidants.Moreover,the standards for metal residues in drug synthesis are extremely stringent.Accordingly,developing the simple,efficient and environmentally friendly methods for building sulfur-containing compounds is still a highly challenging subject.The thesis reviewed the recent progress of the C–S bonds/C–Se bonds formation under electrochemical conditions.In addition,we explored on the electrosynthesis of alkenyl sulfides,alkenyl selenides and sulfonyl-containing heterocyclic compounds.The introductions of the chapters are as follows:Chapter two described the formation of the cyanomethyl radicals by C(sp~3)–H bonds activation of acetonitrile via an indirect anodic oxidation.And KI was the redox catalyst.The process could be carried out at room temperature under the atmosphere.The known methods of the activation of acetonitrile to form the cyanomethyl radical usually require the addition of excess chemical oxidation reagents or single electron transfer reagents under heating.The cyanomethyl radical added to another molecule of acetonitrile and then went through a 1,3-hydrogen transfer process to furnish theα-imine carbon center radical intermediate,which could react with the sulfur reagent.Two new C-C bonds and one new C-S/C-Se bond were formed in one pot,and a(Z)-configuration tetra-substituted olefin skeleton was constructed with the high stereoselectivity simultaneously.This process showed highly efficiency and highly atomic economy.Moreover,the process could be easily scaled up.Furthermor,4H-1,4-benzothiazine scaffolds which were widely used in pharmaceutical chemistry due to their activities of antimicrobial,anticancer could be obtained by a copper-catalyzed coupling reaction.The density functional theory calculation revealed that the phosphorous ligand had stabilized the highly active radical intermediate,and promoted its reaction with the sulfur/selenium reagent.In addition,the stereoselective synthesis of the(Z)-configuration tetra-substituted olefin had been shown to be a thermodynamic control.Chapter three described the radical cascade cyclizations of styrenyl amides with the sulfonyl radicals generated by direct anodic oxidation.Various sulfonated 4H-3,1-benzoxazines were obtained through this way.The products are a class of common structures which widely present in many pharmaceuticals and natural products,and are used as building blocks for remarkable bioactive molecules.One new C-O bond and one new C-S bond were formed in one pot.The reaction conditions were simple and mild.No external chemical reagent was added.Moreover,the by-products are only nitrogen and hydrogen gas,which is environmentally friendly.