Sulfones bearing vicinal hydroxyl groups

The radical species 129, generated under reductive conditions, can sometimes be a potential source of problems. For instance, during the course of the total syn- 

First Sml2-promoted reduction of hydroxy sulfones. 

From a mechanistic viewpoint, the reduction of vinyl sulfones and the reductive elimination of /f-acetoxy sulfones with Na(Hg) or Sml2 are the only procedures to have been investigated to any great extent. Recent work published by Keck et al. [105] has shown that different mechanisms are operative when Na(Hg)/MeOH or Sml2/HMPA are employed. They set out to study the reductive desulfonylation of several vinyl sulfones under two sets of reaction conditions, specifically 8 equiv. Sml2, N,N-dimethylpropyleneurea (DMPU), MeOD, 60 min. and 5% Na(Hg), Na2HP04, THF/MeOD (4 1), 0 °C, 60 min (Table 3.5). 

In all cases, excellent yields of alkenes, high degrees of deuterium incorporation, and virtually complete -selectivities were observed. These results suggest that a vinyl radical and PhS02 are formed rapidly after an initial electron transfer, and 

Entry Substrate Conditions Deut. incorp. (%j rield (%) 

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In his first contribution to the reaction that today bears his name, Julia already explored the reductive elimination of a wide range of functionalities [12]. Eliminations from vinyl sulfones as well as vicinal hydroxyl-, acetyl-, mesyl-, and tosyl sulfones to afford the corresponding alkenes were carried out using Na(Hg). He observed that the yields of the desired alkenes were invariably higher starting from any other group than a free ) -hydroxyl (Scheme 3.23). 

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See also in sourсe #XX -- [ ]

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