Glycols ketones, cleavage, oxidative

It is an important reagent for the oxidative cleavage of vicinal glycols which are oxidised at room temperatures to aldehydes, ketones or both depending on the nature of glycol. 

Another is the oxidation of a secondary alcohol to a ketone (9-3), where A and B are alkyl or aryl groups and Z is also CrOjH. In the lead tetraacetate oxidation of glycols (9-7) the mechanism also follows this pattern, but the positive leaving group is carbon instead of hydrogen. It should be noted that the cleavage shown is an example of an E2 elimination. 

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... 

Oxidation. The salt effects rapid cleavage of glycols in high yield. It can be used also for the oxidation of secondary nitro compounds to ketones (Nef reaction).- An excess of the guanidine base is used to form the nitronatc, which is then oxidized to the ketone by the salt. Yields are —80-95%, and are higher than those obtained with iodosylbenzene, C HjIO. Oxidation of primary nitro compounds by his method gives only low to moderate yields of aldehydes. 

The first total synthesis of the marine dolabellane diterpene (+)-deoxyneodolabelline was achieved in the laboratory of D.R. WilliamsJ In the final step of the synthetic sequence, the oxidation of a secondary alcohol functionality of a 1,2-diol to the corresponding a-hydroxy ketone was required. Such 1,2-diols are known to be unstable under most oxidation conditions, and often glycol cleavage is observed. Indeed, when Dess-Martin and Ley oxidations were tried, the substrate suffered carbon-carbon bond cleavage. However, under the Swern oxidation conditions, the desired a-hydroxy ketone was isolated in a 65% yield. Interestingly, the substrate was a mixture of four inseparable diastereomeric diols (obtained in a McMurry reaction), which gave two easily separable ketone products, one of which was the natural product. 

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