ABSTRACT
The selective replacement of hydroxyl groups by hydrogen is an important functional group transformation in organic synthesis. In the pioneering work of Barton and coworkers on radical chain reductions of thiocarbonyl compounds, easily prepared from the parent alcohols, it has been demonstrated that radical processes can be carried out more effectively than the relatively more drastic ionic reactions, which are also more susceptible to steric retardation and rearrangements (reviews: [1-4]). In the initial work by Barton and McCombie, tributyltin hydride was used as the hydrogen source.5,6 A broad range of compound classes with great functional group tolerance have been deoxygenated in generally good yields using this tin hydride. Examples of this very ef¥cient deoxygenation in the sugar area were presented as procedures in Org. Syntheses.7 However, the toxic nature and the need to remove relatively large amounts of tin compounds prompted the search for improvement. Thus, a catalytic variant8,9 or the use of polymer-bound tin hydrides were proposed.9,10 Alternatively, a number of less toxic silicon compounds such as tris(trimethylsilyl)silane,11 phenylsilane,12 diphenylsilane,13-16 triphenylsilane,17 or even triethylsilane18 were suggested as reducing agents. Other sources of hydrogen were the formate ion19 or magnesium in methanol.20 Irradiation of thiocarbonyl compounds in the sugar series also led to deoxygenation in good yields.21
