[75-18-3] · C2H6S · Dimethyl Sulfide · (MW 62.13)
(reducing reagent; methylation; sulfide complex; ylide formation)
Alternate Names: DMS; methyl sulfide.
Physical Data: mp -98 °C; bp 38 °C; d 0.85 g cm-3.
Solubility: insol water; sol ethanol, diethyl ether.
Handling, Storage, and Precautions: disagreeable odor; use in a fume hood.
Diacetals are obtained in high yields when the ozonolysis products of alkenes are treated with dimethyl sulfide and trimethyl orthoformate (see Triethyl Orthoformate) (eq 1).1 Hydrolysis to the diacetals is performed by heating in water containing tartaric acid. Ozonolysis (see Ozone) of maleic acid followed by reduction with dimethyl sulfide gives Glyoxylic Acid (eq 2).2
Methyl phenyl sulfoxide is quantitatively reduced to the corresponding sulfide by treatment with dimethyl sulfide (2 equiv) and Trifluoroacetic Anhydride at 0 °C in CH2Cl2 (eq 3).3 Trifluoroacetic anhydride can be replaced by acetyl trifluoroacetate or Thionyl Chloride.
Aromatic and heteroaromatic amines are methylated at the o-position via N-chloro derivatives. Aniline is treated with t-Butyl Hypochlorite or N-Chlorosuccinimide (1 equiv) in CH2Cl2 at -65 °C, and dimethyl sulfide (3 equiv) is added, followed by sodium methoxide (1.2 equiv) in methanol. 2-(Methylthiomethyl)aniline is obtained in 90% yield; its desulfurization by Raney Nickel gives o-toluidine (eq 4).4 2-Amino-3-methylpyridine is obtained in 50% overall yield by a similar sequence of reactions starting from 2-aminopyridine (eq 5).5
The above o-methylation can be successfully extended to o-alkylation4 and also to the synthesis of indoles and hetero analogs. Use of methylthio-2-propanone (1), methylthioethanal (2), or methylthioethanal dimethyl acetal (3) instead of dimethyl sulfide, in similar processes using aniline and 2-aminopyridine, provides an elegant entry to indoles and hetero analogs (4)-(7).6
Dimethyl sulfide rapidly reacts with Chlorine (1 equiv) in carbon tetrachloride at 0 °C to give the complex (8) as an insoluble solid. This complex (Dimethyl Sulfide-Chlorine; Corey-Kim reagent) is useful for oxidation of primary and secondary alcohols. Treatment of 4-t-butylcyclohexanol with (8) at -25 °C and then with Triethylamine gives 4-t-butylcyclohexanone (eq 6).7 For the oxidation of primary alcohols, e.g. cyclohexanemethanol, N-Chlorosuccinimide-Dimethyl Sulfide (9)8 is superior.
Allylic and benzylic alcohols are not oxidized with the complex (8), but instead are converted into the corresponding chlorides. Of particular interest is the chemoselective chlorination of (Z)-3-methyl-2-pentene-1,5-diol, which bears allylic and homoallylic alcohol moieties in the same molecule (eq 7).9 The allylic chloride is the only product obtained.
The Borane-Dimethyl Sulfide complex is a useful substitute for diborane and has been widely used for hydroborations and reductions, although it is a little less reactive than diborane itself.10
Heating of a-bromo esters with dimethyl sulfide leads to methyl sulfides. Subsequent S-methylation with Trimethyloxonium Tetrafluoroborate followed by a-deprotonation provides dimethylsulfonium ylides (eq 8).11 These ylides undergo smooth reactions with electron-deficient alkenes, producing cyclopropanes. In the case shown in eq 8, a better yield (90%) of cyclopropane formation results when the ylide is generated in situ by treatment with Sodium Hydride rather than when the isolated ylide is used.
Boron Trifluoride-Dimethyl Sulfide;
Kyushu University, Kasuga, Japan