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48.1.5.4.3 Method 3: Synthesis from Acyl Derivatives of Thiohydroxamic Acids

DOI: 10.1055/sos-SD-048-00274

Margaretha, P.Science of Synthesis, (200948452.

Acyl derivatives of thiohydroxamic acids are a convenient source of carbon-centered radicals.[‌61‌,‌62‌] The most commonly used compound here is N-hydroxy-2-thiopyridone (45). Its easily available acyl derivatives, e.g. 46, lend themselves to the facile production of alkyl radicals either by heating to 80°C in the presence of tributyltin hydride and 2,2-azobisisobutyronitrile, or better, by irradiation with a tungsten lamp at room temperature in the presence of 2-methylpropane-2-thiol.[‌63‌] The overall reductive decarboxylation, which is also called the Barton reductive decarboxylation (Scheme 23) is a radical-induced chain reaction, in which a stannyl or thiyl radical adds to the sulfur atom of acyl compound 49 with concomitant cleavage of the NO bond. The newly formed acyloxy radical decarboxylates to an alkyl radical, which in turn is trapped by the stannane or thiol to afford the (decarboxylated) alkane compound.[‌64‌‌66‌] More recently, both tris(trimethylsilyl)silane in combination with triethylborane,[‌67‌] or tris(trimethylsilyl)methane in combination with 2,2-azobisisobutyronitrile,[‌68‌] have been proposed as tin-free reducing agents.

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