Methylthiol, formation

The reaction mechanism of the DNA (cytosine-5)-methyltransferase-catalyzed cytosine methylation was investigated at the MP2 and DFT levels [98JA12895]. This system has been modeled by 1-methylcytosine 117, methylthiolate, and trimethylsulfonium. The cytosine methylation is initiated by an attack of the anionic methylthiolate at Cg of the cytosine ring (Scheme 77). The formation of the methylthiolate adduct 118 of the neutral 117 was found to be endothermic in the gas phase and in solution. However, the MP2 and DFT results differ... 

Hitherto, thio ether formation has clearly been proved only in the case of the ji-donor substituted 4-nitrosophenetol and the electron-rich l-methyl-2-nitrosoimidazole. The low yields of this adduct (about 2% at 1 1- and about 10% at 1 5-stoichiometry for 4-nitrosophenetol reacting with GSH56) may be the reason for its rare discovery. However, other nitrosoarenes should yield this family, too. Semiempirical molecular orbital calculations (MNDO) indicate a similar positive charge at the exposition of the N-(methylthiol-S -yl)-aniline cation and -4-anisole cation as well (Scheme 6). Furthermore, formation of l-(glutathion-S -yl)-2-naphthylamine was reported to occur in mixtures of 2-nitrosonaphthalene and GSH12. 

Lower members of the series of salts formed between organic sulfoxides and perchloric acid are unstable and explosive when dry. That from dibenzyl sulfoxide explodes at 125°C [1], Dimethyl sulfoxide explodes on contact with 70% perchloric acid solution [2] one drop of acid added to 10 ml of sulfoxide at 20° C caused a violent explosion [3], and dibutyl sulfoxide behaves similarly [4]. A fatal explosion resulted from mistakenly connecting a DMSO reservoir to an autopipette previously used with perchloric acid [5], (The editor has met a procedure for methylthiolation of aromatics where DMSO was added to excess 70% perchloric acid he did not feel justified in trying to scale it up.) Explosions reported seem usually to result from addition to excess sulfoxide. Aryl sulfoxides condense uneventfully with phenols in 70% perchloric acid, but application of these conditions to the alkyl sulfoxide (without addition of the essential phosphoryl chloride) led to a violent explosion [4]. Subsequent investigation showed that mixtures of phenol and perchloric acid are thermally unstable (ester formation ) and may decompose violently, the temperature range depending on composition. DSC measurements showed that sulfoxides alone... 

One can open the epoxide, however, by treating it with sodium acetate in acetic acid at 85 °C for 48 hours and obtain the gylcol acetate, 12, in quantitative yield. Treatment of tridiphane with one equivalent of sodium methoxide in methanol at room temperature causes hydrogen chloride elimination and formation of the vinyl epoxide, 13, which has little herbicidal activity. In contrast to sodium methoxide, sodium methylthiolate readily opens the epoxide ring giving the / -thioalcohol, 14 in quantitative yield. 

Prop-2-ynyl)-5-(trifluoromethyl)-l, 3,4-thiadiazol-2(3//)-one (19) reacts with nucleophiles (ammonia, pyrrolidine, or potassium methylthiolate) with formation of 6-methylene-2-(trifluo-romethyl)-5,6-dihydro-4//-l,3,4-thiadiazine-4-carboxamides 20a, b or S-methyl 6-mcthylene-2-(trifluoromethyl)-5,6-dihydro-4//-l,3,4-thiadiazine-4-thiocarboxylate (20c).82 The action of aqueous sodium hydroxide on 19 gives rise to the 4//-1,3,4-thiadiazine 20d, which also bears an exocyclic methylene group.82... 

There has been a review of the use of transition-metal catalysts in the formation of C—S, C—Se, and C—Te bonds." Copper catalysis enables the formation of unsymmetrical diaryl thioethers from two differently substituted aryl iodides using ethylxanthogenate as the source of sulfur. Initial formation of an aryl xanthate, such as (17), is followed by hydrolysis to the arenethiolate, which couples with the second aryl iodide." Copper catalysis has also been used in the methylthiolation of aryl halides by DMSO. The method requires the presence of a source of fluoride ions, such as zinc fluoride." In the presence of a palladium catalyst, the reaction of aryl and heteroaryl bromides with AgSCp3 gives the corresponding trifluoromethylsulfldes." ... 

---