A~bsfrtsc~ seconbp] +whols wem hansfamed inte various thiaxrbonyl derivatives. Rcdaetiee of t&e eempuuads using t&&~hy$deandsnnmaloratTatiedthccomspoldingdeexy.eempetmds.
Half-Rfeandeuapctitive meauaeme-etsshe~that mcttomwacfastaadcouldbenmtocomplctioh Deoxygenation of alcohols, especially secondary alcohols, using radical processes was a good synthetic challenge. Such mactions have many advantages over analogous ionic procedures in complex Natural Rroducts.
The original Barton-McCombie reaction3 has found many applications3. Radical deoxygenation of primary and tertiary alcohols is also possibld. Recently the tributylthr hydride normally used has been replaced by a variety of silane pmcedures3.
In our original pager3 we had examined the thiobenxoyl, the xanthate and the thioimidaxolide functions.
All of them gave efficient deoxygenation of secondary alcohols, but the rates of these reactions under competitive cimumstances were not detennhtai. The thiobenxoyl group was conveniently introduced by Vilsmeier chemistry, the xanthate by reaction of the corresponding anion with CS2 and then methyl iodide and the thioimidaxolide by use of freshly pmpared thiocarbonyl his-huidaxohde. The latter reagent was convenient for alcohols where anion formation was precluded by other base sensitive functional groups in the molecules. Normally xanthates pnpared using NaH or, better, and at lower temperature, butyl lithiuma, were the cheapest and most convenient procedure. lhiocarbonates, especially five-men&ted thiocarbonates also permit deoxygenation of one of the original alcohol tunctions7.
More recent studies by Robins and his colleagues* have shown that phenylthiocarbonyl chloride was also a convenient reagent to produce phenoxythiccarbonyl derivatives which were readily deoxygenated with tributyltin hydride. Further developments were the introduction of halogenated phenylthiocarbonyl reagents9 some of which am now available conunemiatlyl~