Oxidation MoOPH enolate oxygenation

Oxidative desulfonation is achieved by reaction of a sulfonyl carbanion with a source of electrophilic oxygen. One useful reagent is MoOPH, a well-known oxidant for enolates which will convert a sulfone (183), as the sulfonyl carbanion, directly to the ketone (184) (Scheme 74). 

Group 6 metal-promoted oxidations enolate oxygenation with MoOPH... 

The diastereoselectivity in these oxidations can generally be predicted assuming that the MoOPH reagent approaches the enolate from the less hindered direction. In one example, the diastereoselectivity was improved from 26% to 66% by addition of 18-crown-648. Where a comparison was made, MoOPH gave higher diastereomcric excesses than did molecular oxygen, 38% versus 0%, respectively (see Table 1, entry 7 and I able 3, entry 6). A limitation of MoOPH is that it can apparently not be used for the oxygenation of stabilized enolates derived from /3-dicarbonyl compounds. 

MoOPH is less effective than the boron method for oxidation of aromatic enolates too. In a similar comparison the pyridine 269 was lithiated and treated with oxygen, MoOPH, or the boro-nate sequence to give the hydroxypyridine 271. The results are very clear.45... 

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