MoOPh reaction with ketones

Oxygenation of the dianion of a ketoxime - by MoOPH (c/. Section 2.3.2.1.2) provides a-l droxy ketones after hydrolysis, albeit in relatively low yield. The equivalent process for hydrazcmes was unsuc-essful, although it appears that this was a problem associated with manipulation of the products rather than an intrinsic failure of reaction. Indeed subsequent work with hydrazone anions has shown that the process is viable. 

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). 

It is also possible to oxygenate an enolate to give the corresponding acyloin (an a-hydroxy ketone) or alkoxy derivative. Reaction of an enolate anion with oxygen and trimethylphosphite [(MeO)3P], for example, gives an a-hydroxy derivative. 3 Reaction of an enol ether such as 105 with 3,3-dimethyldioxirane leads to the protected a-hydroxy ketone (106), in an example taken from Danishefsky s synthesis of myrocin An effective oxygenation reagent for enolate anions is MoOPh, and a typical use is taken from work by Vedejs to... 

Note that nitro enolates have other synthetic uses. When nitrobutane was treated with sodium hydroxide, nitro-enolate 205 was formed. Rather than addition of an aldehyde or a ketone, 205 was treated with concentrated sulfuric acid to form butanal, with loss of N2O, in what is known as the Nef reaction. 28 Modern versions of this reaction use bases such as LDA and less vigorous oxidizing agents such as MoOPh. 29 The Knoevenagel disconnection is ... 

Enolate hydroxylation is a problem of long standing. Direct oxygenation succeeds with the fully substituted enolates of certain o,a-disubstituted ketones and a variety of carboxylic acid derivatives (ester anions, acid dianions, amide anions), but the reaction of enolates, RCH = C(0")R or CH2 = C(0")R, with oxygen results in complex products of overoxidation. The stable molybdenum peroxide reagent MoOj Py-HMPA (MoOPH), first prepared by Mimoun, allows the conversion of RCH = C(0Li)R into RCH(0H)C0R in generally good yields (Table I). In some cases, the a-diketone is formed as a byproduct. 

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