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DOI: 10.1055/sos-SD-035-00487

Härtinger, S.; Härtinger, M.Science of Synthesis, (200735569.

Thermolysis of N-(acyloxy)pyridine-2(1H)-thiones 10, derived from aliphatic carboxylic acids and N-hydroxypyridine-2(1H)-thione 9 (Y=H) in the presence of an iodine donor, undergo a radical chain reaction, which results in the overall loss of carbon dioxide and the formation of an iodoalkane 11 (Scheme 3).[‌6‌,‌7‌,‌34‌‌37‌] The analogous thiohydroxamic ester, derived from 4-methylthiazole-2(3H)-thione is an equally suitable starting material for iododecarboxylation.[‌38‌] The N-(acyloxy)pyridine-2(1H)-thiones (Barton esters, 10) are obtained by reacting an acid chloride with the sodium salt of N-hydroxypyridine-2(1H)-thione (9, Y=Na) and a catalytic amount of 4-(dimethylamino)pyridine.[‌6‌,‌35‌,‌36‌,‌39‌‌42‌] Alternatively, the free acid may be condensed with N-hydroxypyridine-2(1H)-thione (9, Y=H) and dicyclohexylcarbodiimide in dichloromethane.[‌34‌,‌36‌,‌43‌,‌44‌] The iododecarboxylation reaction is conveniently performed without isolation of intermediate 10. As well as triiodomethane[‌41‌,‌42‌,‌45‌,‌46‌] and molecular iodine[‌6‌] as the initial radical source, iodoacetonitrile[‌47‌] or 1,1,1-trifluoro-2-iodoethane[‌6‌,‌34‌‌36‌,‌40‌,‌43‌,‌44‌] may also be used as efficient iodine atom donors. A slight excess of the iodine source, which in certain cases may also serve as the solvent, is required to compensate for radical chain side reactions. Visible-light-induced radical decomposition of 10 at ambient temperature in the presence of triiodomethane, represents a mild alternative to thermal treatment.[‌45‌] Ultrasonic irradiation of 10 in carbon tetrachloride also affords the iododecarboxylation product.[‌42‌]

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