Cleavage of a-hydroxy ketone

Thiamine pyrophosphate promotes the decarboxylation of a-keto acids and the cleavage of a-hydroxy ketones. 

Fig. 31 Oxidative cleavage of a-hydroxy ketones catalyzed by EtOVOCl2...

Samarium(ll) iodide-induced reductive cleavage of a-hydroxy ketones provides a useful entry to unsubstituted ketones (eq 5). ... 

A short review describes a new transition-metal-free aerobic oxidative C-C cleavage of a-hydroxy ketones a dimeric intermediate is implicated, with 0-labelling being used to probe the mechanism. °... 

Isotopic-labeling experiments and evidence of a dimeric intermediate in the transition-metal-free aerobic oxidative C-C bond cleavage of a-hydroxy ketones and their esterification, on reaction with O2 as the ideal oxidant in the presence of K2CO3, have disclosed the reaction mechanism. ... 

El Aakel, L., Launay, R, Atlamsani, A., et al. (2001). Efficient and Selective Catalytic Oxidative Cleavage of a-Hydroxy Ketones Using Vanadium-Based HPA and Dioxygen, Chem. Commun.,... 

The reagent is effective for oxidative cleavage of a-glycols to aldehydes, of a-hydroxy ketones to an aldehyde and a carboxylic acid, and of a-diketones and a-keto iicids to acids.3... 

Cleavage of a-hydroxy ketoximes. a-Hydroxy ketoximes when treated with phosphonitrilic chloride (1) and pyridine undergo fragmentation to aldehydes or ketones and nitriles in high yield ... 

Reductive cleavage of a-substituted ketones, such as a-halo-, a-hydroxy- and a-acyloxy-ketones to the unsubstituted ketone can be carried out with zinc and acetic acid or dilute mineral acid. The reaction is thought to proceed by transfer of two electrons to the carbonyl group, followed by departure of the leaving group as the anion (7.39). This generates an enolate, which is converted into the ketone by acid. For a-halo-ketones, a different mechanism, with ahack by zinc on the halogen, is possible. 

Another common type of C—C cleavage is a-cleavage of an a-hydroxy-ketone ... 

A carbocation stabilized on a to a hydroxy group—that is a protonated ketone—is generated by cleavage of a carbon-carbon bond. This also leads to the formation of an aldehyde, which is oxidized in situ to a carboxylic acid. 

Aside from oxidative dimerizations [175-186] vanadium catalysts are able to induce C-C and C-0 bond cleavages. Momose and coworkers developed a catalytic system to fragment a-hydroxy ketones 101 to diesters or ketoesters 102 (Fig. 31) [190]. Using 1 mol% of EtOVOCl2 as a catalyst and oxygen as the terminal oxidant, 55-87% of 102 was obtained. The reaction mechanism is not known, but the reaction is inhibited by 2,6-di-tert-butylcresol (BHT) pointing to the involvement of a radical process. 

Cleavage of a,[i-epoxy ketones.1 The reagent (1), possibly (CH3)2SC1, formed from DMSO and ClSi(CH3)3, cleaves a,(3-epoxy ketones to 2-chloro-3-hydroxy ketones with high regioselectivity (equation I). If the epoxide has a phenyl substituent, 3-chloro-2-hydroxy ketones are formed (equation II). 

Alumina (activity m) may also be used to create an even milder oxidant. Diol (6 equation 11) unde went cleavage to die aldehyde when treated with bipyridinium chlorochromate alone, but bipyridinium chlorochromate/alumina (1 1) gave a good yield of the a-hydroxy ketone. ... 

Cyclobutanols oxidize with ring cleavage to 4-hydroxy ketones, 4-hydroxy acids, or 1,4-diones under the influence of chromium(Vl) reagents (Scheme 11). The first formed product is a 4-hydroxycarbonyl compound (31) which exists as the five-membered ring hemiacetal (32). This form will persist in the absence of excess reagent under nonforcing conditions otherwise further oxidation takes place to give a... 

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