A,-Hydroxypyridine-2-thione

The acyl derivatives of A-hydroxypyridine-2-thione are a synthetically versatile source of free radicals. These eompounds are readily prepared from reactive acylating agents, sueh as acyl chlorides, and a salt of A-hydroxypyridine-2-thione ... 

Aminyl radicals are produced by the sequence outlined in equation 114. The action of phosgene on the sodium salt of A-hydroxypyridine-2-thione yields the salt 326, which reacts with amines to give 327. The latter decompose to the radicals 328 on heating or irradiation380. 

The esters of A-hydroxypyridine-2-thione are another versatile source of radicals.195 The radical is formed by decarboxylation of an adduct formed by attack at sulfur by the... 

A very efficient methodology for generating carbon radicals utilizes esters of A-hydroxypyridine-2-thione as radical precursors, and these have been used by Blood-... 

Decarboxylation of the aliphatic esters of A-hydroxypyridine-2-thione by tributyltin hydride leads to reduction of the radical and the formation of the alkane lacking the carboxyl carbon, as in the Barton-McCombie reaction (Scheme 3.61). 

Barton has devised such a pathway for converting carboxylic acids to hydroperoxides via A -hydroxypyridine-2-thione esters [16a,b] (Scheme 5). The yields of hydroperoxides are 45-89% [16]. Reduction of the crude products with trimethyl phosphite (rt) or dimethyl sulfide (80 °C) readily provides the corresponding alcohols. On the other hand, tosylation and ensuing Kornblum-De La Mare type fragmentation [17] leads to carbonyl compounds [16b] (Scheme 5). 

Related Reagents. A -Hydroxypyridine-2-thione 4-Methyl-3-hydroxythiazole-2-thione 5-(/ Methoxyphenyl)-4-methyl-3-hydroxythiazole-2-thione (Diacetoxyiodo)benzene AAHydroxy-phthalimide. 

This method works also for electron-rich aromatic and a,/8-unsaturated carboxylic acids and requires neither heavy metals nor strong oxidants. Among the various thiohy-droxamic esters investigated, A-hydroxypyridine-2-thione derivatives are exceptionally efficient. They are conveniently available by reaction of the respective acyl chloride with the sodium salt of A-hydroxypyridine-2-thione or by DCC-mediated coupling of the free acid. The Barton reaction gives the best yields of bromo derivatives the corresponding iodo derivatives are produced in much lower yields. Chlorine donors do... 

Related Reagents. Carbon Disulfide A(-Hydroxypyridine-2-thione l,l -Thiocarbonyldiimidazole p-Tolyl Chlorothionocar-bonate Phenyl Chlorothionocarbonate. 

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