Dimethyl disulfide, reaction with lithium enolate

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). ... 

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]. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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