Lead tetraacetate diols, cleavage

Kavirayani R. Prassad s elegant brevicomin synthesis starts also from tartaric add, although actually from its Weinreb amide, which is converted into the desired intermediate hy a double Grignard reaction. Other key steps in the synthesis are the lead tetraacetate-mediated cleavage of the diol and the Wacker oxidation of the terminal alkene. [204]... 

The oxidative cleavage of the central carbon-carbon bond in a vicinal diol 1, by reaction with lead tetraacetate or periodic acid, yields two carbonyl compounds 2 and 3 as products. 

Lead tetraacetate and periodic acid complement one another in their applicability as reagents for glycol cleavage. The water sensitive lead tetraacetate is used in organic solvents, while periodic acid can be used for cleavage of water-soluble diols in aqueous medium. 

Alcohols (diols, polyols, sugan) Lead(IV) acetate -dichloro fluorescein Diol cleavage of vicinal diols, e. g. sugars, sugar alcohols. The lead tetraacetate consumed is no longer available to decompose the fluorescent dichlorofluorescein. [3, 8]... 

This reaction pathway is suitable for cis as well as tram diols. In principle, the oxidative cleavage is achieved by lead tetraacetate as well. However, these reagents are complementary, since periodic acid compounds are best used in water and lead tetraacetate in organic solvents. The last step is the reduction of the aldehyde with three equivalents of sodium borohydride to provide alcohol 5. 

Mechanism The cleavage of diols with lead tetraacetate [Pb(OAc)4] proposed by Criegee is shown in Scheme 7.29. 

The two reagents (periodic acid and lead tetraacetate) are complementary, since periodic acid is best used in water and lead tetraacetate in organic solvents. Chiral lead carboxylates have been prepared for the oxidative cleavage of l,2-diols. ° When three or more OH groups are located on adjacent carbons, the middle one (or ones) is converted to formic acid. 

Two oxidants essentially dominate these oxidations lead tetraacetate in organic solvents and periodic acid in aqueous media. On occasion, other oxidation reagents cause the cleavage of vicinal diols ceric ammonium nitrate [424], sodium bismuthate [482, 483], chromium trioxide [482, 555], potassium dichromate with perchloric acid [949], manganese dioxide [817], and trivalent [779, 789] or pentavalent [798] iodine compounds. 

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