Dimethyl sulfoxide methylthiomethyl ether

The methylthiomethyl (MTM) group is a related alcohol-protecting group. There are several methods for introducing the MTM group. Alkylation of an alcoholate by methylthiomethyl chloride is efficient if catalyzed by iodide ion.9 Alcohols are also converted to MTM ethers by reaction with dimethyl sulfoxide in the presence of acetic acid and acetic anhydride10 or with benzoyl peroxide and dimethyl sulfide.11 The latter two methods involve the generation of the methylthiomethylium ion by ionization of an acyloxysulfonium ion (Pummerer reaction). 

Methylthiomethyl (MTM) ethers. These ethers (h, 109-lltY) ear he prepared by reaction of alcohols with dimethyl sulfide (8 equiv.) and dibenzoyl peroxide (4 equiv.) in CH3CN at 0° (75-90% yield). Excess dimethyl sulfide is required since some of the sulfide is oxidized to dimethyl sulfoxide. 

The new oxidation process has one important limitation. Allylic or benzylic alcohols are not oxidized but instead replacement of hydroxyl by chlorine is observed. Still another reaction may occur in polar media thus, methylthiomethyl ether formation becomes pronounced when methylene chloride-dimethyl sulfoxide is used as solvent. 

The reaction of thiols with alkyl halides produces sulfides, which are converted into sulfonium halides in the presence of excess alkyl halides.2680 Dimethyl sulfoxide (42) and acetic anhydride (41) react with starch365 to cause oxidation at the C-3 and C-6 positions, and methylthiomethyl ethers are formed at 0-6, according to the following reaction (43-46) ... 

Formation of methylthiomethyl ethers is often observed in oxidation of alcohols by dimethyl sulfoxide-acetic anhydride. Suggest a mechanism that would account for the formation of these by-products. 

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