Sulphur, thioether synthesis

Thiols and thioethers are the most commonly encountered sulphur derivatives which can be directly reduced to alkanes. For this purpose, Raney Ni has been traditionally used. An example of its use is the synthesis of let- and 7j5-eremophilanes from a tricyclic thiophene precursor (equation 29) However, more recently nickel complex reducing agents ( NiCRA ) have been profitably and effectively used for this purpose, as indicated by the reduction of dodecanethiol to dodecane (equation 30)". Similarly, nickelocene in the presence of LAH has been used to effect desulphurization of thiols . A combination of NaEtaBH and FeCl2 also achieves the thiol-to-alkane transformation quite satisfactorily The increasing utility of nickel boride has also been exploited for the transformation of sulphides to alkanes as indicated in equation 31. ... 

This can easily be explained by taking into account the weaker donor properties of thioether sulphur atoms as compared to thiol or thione sulphurs [62]. This mode of coordination of isothiosemicarbazones was later used for carrying out similar condensation reactions in the presence of other metal ions as templates. Thus by interaction of equimolar amounts of 2-hydroxybenzaldehyde 5-methyl-isothiosemicarbazone, anhydrous iron( III) chloride, and 2-hydroxybenzaldehyde in a mixture of absolute ethanol and DMF the template reaction became possible, giving rise to the formation of [Fe(L62)Cl] (Eq. 2.27) [63]. The synthesis of dimers [Fe(L62)]20 (R = CH3, C2H5, n-C3H7, n-C4H9) was performed by reaction of 2-hydroxybenzaldehyde 5-alkylisothiosemicarbazone and 2-hydroxybenzaldehyde with anhydrous FeCl3 in absolute ethanol or -butanol, followed by addition of triethylamine as base [64]. For these complexes the possibility was established of mutual transformations (Eq. 2.28). 

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