Dimethyl disulfide, reaction with lithium

Interestingly, if the tribromo compound is treated with five equivalents of n-BuLi, then tetralithiation occurs, as was shown by the isolation of an a-butyl-2,4,5-trimethylthio derivative after reaction with excess dimethyl-disulfide [87JCS(P1)1453]. The a-butyl group in the product is derived from reaction of the a-benzyl carbanion with the n-butyl bromide produced by the initial bromine-lithium exchange reaction (Scheme 59). However,... 

A solution of 150 mL of 1.6 M butyl-lithium in hexane under N2 was vigorously stirred and diluted with 150 mL petroleum ether (30-60 °C) and then cooled with an external ice bath to 0 °C. The addition of 26.7 g of veratrole produced a flocculant white precipitate. Next, there was added a solution of 23.2 g of N,N,N ,N -tetramethylethylenediamine in 100 mL anhydrous Et20 and the stirred reaction mixture was allowed to come to room temperature. The subsequent addition of 20.7 g of dimethyl disulfide over the course of several min produced an exothermic response, and this was allowed to stir for an additional 30 min. There was then added 10 mL EtOH followed by 25 0 mL of 5 % NaOH. The organic phase was washed first with 150 mL 5% NaOH, followed by 2x100 mL portions of 5% dilute HC1. The removal of solvent and bulb-to-bulb distillation of the residue provided 2,3-... 

Diethyl (trimethylsilyl) phosphine has been prepared by the reaction of lithium diethylphosphide with chlorotrimethyl-silane in ether solution.4 The lithium diethylphosphide may be prepared by the reaction of an ether solution of phenyllithium with diethylphosphine.6 However, the dialkylphosphines are most conveniently prepared by the reduction of the corresponding tetraalkyldiphosphine disulfides with lithium tetrahydro-aluminate in ether.6 7 An alternative method for the preparation of dimethyl(trimethylsilyl)phosphine which eliminates the handling of the volatile dimethylphosphine involves the preparation of lithium dimethylphosphide from tetramethyldiphosphine. The latter is prepared by the reduction of tetramethyldiphosphine disulfide8 with tributylphosphine.9 The reaction of chlorotrimethylsilane with lithium dimethylphosphide is most conveniently carried out in a vacuum system without solvent at -78°. 

Gem-dibromocyclopropanes can be converted into synthetically useful cyclopropanone equivalents by a process consisting of lithium-halogen exchange followed by reaction of lithiocyclopropane (113) with dimethyl disulfide (Scheme 43) . The resulting bromo-methylthio derivative (114) undergoes a variety of substitution reactions. Methanolysis gives S,0-dimethylketal (115) which can be converted into l,l bis(methyl-thio)cyclopropane (116) with methyl mercaptan in trifluoroacetic acid. Reaction of 114 with other nucleophiles provides the derivatives shown in Scheme 44 . The sulfur-... 

The chemistry of zirconium and hafnium amides has been investigated further 101) using the general reactions of (1) metal amide with excess protic compound, (2) metal amide with a stoichiometric amount of protic compound, and (3) the reaction of a metal chloride with lithium dimethyl amide. The comyiounds jirepared are listed in Table V. They are all monomeric. Hafnium amides have not been described before, although there is a reference by Bradley (7fl) to the reaction of hafnium amide with carbon disulfide and metal carbonyls. 

Jones and colleagues have prepared 1,4-dicarbonyl compounds by conjugate additions of enolate and related anions to a,P-unsaturated sulfoxides [80,81]. For example, the lithium enolate of acetone dimethylhydrazone (83), in the presence of dimethyl sulfide-copper(I) bromide complex, underwent conjugate addition to 2-phenylsulfinyloct-l-ene (82). Quenching the reaction mixture with dimethyl disulfide gave the doubly protected 1,4-diketone derivative (84), which, on sequential hydrolysis with copper(II) acetate and trifluoroacetic acid gave the dodecane-2,5-dione (85) as the product in 54% yield from (82) (Scheme 5.27). Other examples of the addition of enolate-type species to a,p-unsaturated sulfoxides have also been reported [82.83]. 

Dimethyl disulfide traps organometallic species very effectively. For example, it converts the poorly soluble lithium 3-lithio-2-naphthoate into 3-methylthio-2-naphthol in 83% yield. Treated with the same reagent, iV,0-dilithiated ter/-butyl- -phenyl-carbamate furnishes the methyl sulfide in 89% yield. The smelly workup can be avoided if dimethyl disulfide is replaced by diphenyl disulfide, sulfur di-chloride, or di(benzenesulfonyl)sulfide. Particularly clean reactions are achieved with thio-A,A -diimidazole (83, Scheme 1-58). ... 

The sulfenylation of esters,lactones, carboxylic acids,amides and lactams may be effected by reaction of the corresponding lithium enolates in THF at -78 to 0 C with dimethyl or diphenyl disulfides, or, less commonly, with methyl or phenyl sulfenyl halides. The enolates of ketones, however, are insufficiently nucleophilic to react wiA dialkyl sulfides unless HMPA is added to the reaction mixture, although they do react smoothly with diaryl sulfides. This difference allows the selective sulfenylation of esters in the presence of ketones (entry 5, Table 3). ... 

---