Dimethyl Sulfoxide-promoted Direct Epoxidation Of Alkyl Halides And Alcohols

Epoxide and its derivatives are an important class of oxygen-containing three-membered ring compounds.Epoxy functional groups are widely present in natural products and bioactive molecules and they could be transformed into many other groups,such as dihydroxy,amine hydroxyl,carbonyl,etc.,through ring opening reactions.It is of great significance to carry out efficient epoxidation studies.The epoxidation of olefins is currently the most widely used method for synthesizing epoxy compounds,but the preparation of olefins requires multiple steps and the preparation of olefin compounds with more complex structures is difficult.The Corey–Chaykovsky epoxidation of carbonyl groups has also been developed as a complementary method for the preparation of epoxy compounds.Alkyl halides and alcohols are the most basic chemical raw materials.In this dissertation,we have developed the direct conversion of the readily available alkyl bromides and alcohols to value-added epoxides with in situ generation of dimethyl sulfonium ylide in DMSO oxidations.This thesis is divided into the following two parts:In the first part,the direct epoxidation of benzyl bromides was achieved by a tandem reaction.Using DMSO as the oxidant and solvent,and Na OH as the base,the epoxidation of benzyl bromide compounds was achieved under mild room temperature conditions,and a series of symmetrical and cross-linked diaryl epoxy compounds were obtained with a yield of up to 85%.Based on the studies on the reaction process,we propose a DMSO–promoted tandem Kornblum–Corey–Chaykovsky reaction mechanism.DMSO first oxidizes benzyl bromide to benzaldehyde,and the resulting dimethyl sulfide quickly converts unreacted benzyl bromide to sulfonium salt and sulfonium ylide,which subsequently transforms benzaldehyde to the epoxy compound.The method has the advantages of simple operation,mild conditions,cheap and easily available starting materials.Dimethyl sulfoxide is a safe,low toxicity,and environmental reagent.The method uses the side product dimethyl sulfide to in situ generate the sulfonium ylide intermediate.It is a new and green reaction with extremely high step-economy.Based on the proposed reaction mechanism,the second part of this dissertation described the extension of the method using alkyl halides and alcohols as substrates for synthesis of the cross-coupled epoxidation products.Swern oxidation is a reaction of oxidizing alcohol to carbonyl compounds with DMSO as oxidant.Based on this reaction,we directly added one equivalent of alkyl halides to the reaction system after the completion of the Swern oxidation,so that it could react with the side product dimethyl sulfide to produce the sulfonium ylide under base conditions.The sulfonium ylide finally transformed aldehyde to the epoxides via one-pot Swern–Corey–Chaykovsky reaction.This method has a wider range of substrate scope,and benzyl alcohols and alphatic alcohols are all good substrates with a yield of 79–98%.Compared with the epoxidation of olefins and carbonyl compounds,this paper has achieved the direct epoxidation of alkyl halides and alcohols using dimethyl sulfoxide as the oxidant under mild reaction conditions.This study provides a more direct and efficient method for the synthesis of epoxy compounds.