Asymmetric reactions disulfides synthesis

Although bis(disubstitutedthiocarbamoyl) disulfides (thiuram disulfides) have been known for some time, the synthesis of the titled disulfides have never been reported. In 1977 D Amico and Morlta (60) reported that the reaction of thiocarbamoylsulfenamides (61-62) with carbon disulfide in methyl alcohol afforded either the symmetrical or previously unknown asymmetrical thiuram disulfides in 87 to 98% yield. The thiocarbamoylsulfenamides (61-62) were prepared by the oxidative condensation of a salt of a dlsubstituteddithiocarbamic acid and a secondary amine or by the reaction of the above salt with a N-chloro secondary amine. 

Considerably less is known about the chemistry of palladium and platinum 1,1-dithio complexes. Of late, there has been only one report that dealt with the synthesis of a large number of palladium dithiocar-bamates 392). Twenty-five yellow palladium dithiocarbamate complexes were obtained by reaction of PdCla with NaR2dtc in methanol solution. Several other reports have appeared in which a few dithiocarbamate complexes of palladium were synthesized. Thus, the novel [Pd (OH)2dtc 2], which is soluble in water, was isolated 393). The synthesis of optically active palladium(II) complexes of AT-alkyl-a-phen-ethyldithiocarbamates, similar to (XXIV), via the reaction between the optically active amine, CS2, and PdCl2, has been described. From ORD and CD spectra, it has been established that the vicinal contribution of a remote, asymmetric carbon center could give rise to optical activity of the d—d transitions of palladium 394). Carbon disulfide has been shown to insert into the Pt-F bond of [PtF(PPh3)3]HF2, and X-ray studies indicated the structure (XXIX). 

In 2001, Braga et al. reported the synthesis of new chiral C2-symmetric oxazolidine disulfide ligands from (R)-cysteine and successfully applied them as catalysts in the asymmetric addition of ZnEt2 to various aldehydes (Scheme 3.23). In the presence of 2mol% of ligand, excellent enantioselectivities of up to >99% ee were obtained even with aliphatic aldehydes such as n-decanal or n-hexanal. These authors proposed that the active catalyst did not maintain its C2-symmetry during the reaction. The disulfide bond was probably cleaved in situ by ZnEt2. 

Oxaziridines. Davis has developed the use of chiral 2-sulfonyloxaziridines derived from camphorsulfonic acid as chiral auxiliaries in the asymmetric oxidation reactions. Although other oxaziridines may be preferable, the camphor-derived oxaziridines can be used for the oxidation of sulfides and disulfides to sulfoxides and thiosulfinates as well as for the epoxidation of alkenes. On the other hand, the camphoryloxaziridines are the preferred reagents for hydroxylation of lithium enolates of esters, amides, and ketones, as utilized in the synthesis of kjellmanianone (eq 17). ... 

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