Radical Reactions Based on the Thione Function

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Abstract
The advantages of radical reactions for Organic Synthesis are summarised. Based on the idea of the disciplined radical, it is now possible to design radical reactions which afford a good yield of a single desired product. The system needs to contain a disciplinary group. In the case of radical reactions involving tin hydrides, it is the weak tin-hydrogen bond that is the disciplinary group. For the esters of thiohydroxamic acids, the disciplinary group is the thione function. Examples are given. Recent work has involved the design of stereospecific radical reactions. The hindrance around one chiral center is used to control the formation of the second. The ketal of (+)-(2R,3R) tartaric acid gives excellent stereospecificity (≃ 24:1) with retention of configuration. Furthermore, radicals, generated from isopropylidene uronic esters of N-hydroxy-2-thiopyridone, add readily to electron-poor alkenes in a stereospecific fashion, leading to functionalised chain-elongated furanosides and D-ribo-nucleosides through carbon-4. The directive effect of the ketal group in controlling the newly created chirality is noteworthy.