Oxidation bipyridinium chlorochromates

In this type of cleavage reaction, it appears that the axial benzoate is the preferred product. If water is excluded from the reaction, a bromo benzoate is obtained.The highly oxidizing medium of 2,2 -bipyridinium chlorochromate and MCPBA in CH2CI2 at rt for 36 h effects a similar conversion of benzylidene acetals to hydroxy benzoates in 25-72% yield. ... 

Dicarboxypyridinium chlorochromate (2,6-DCPCC)392 possesses an acidic character that allows the in situ deprotection and oxidation of alcohols, protected as tetrahydropyranyl and trimethylsilyl ethers. 2,2 -Bipyridinium chlorochromate (BPCC)393 contains a ligand that complexes efficiently with the reduced chromium species, generated during the oxidation of alcohols, allowing for a substantial simplification of the work-ups. For this reason, it enjoys a popularity among chlorochromates surpassed by only PCC. 

From the temperature dependence of the substantial kinetic isotope effect (KIE) observed in the oxidation of diols to hydroxycarbonyl compounds by 2,2/-bipyridinium chlorochromate (BPCC), it is proposed that hydride transfer occurs in a chromate ester intermediate, involving a six-electron Hiickel-type transition state.9 A similar conclusion is drawn for the oxidation of substituted benzyl alcohols by quinolinium chlorochromate.10... 

The kinetics of oxidative deoximation of aldo- and keto-oximes by 2,2/-bipyridinium chlorochromate (back to the parent carbonyl compounds) have been studied in DMSO, where the reaction is found to be first order in both oxime and oxidant.89 The aldoximes proved more reactive, and rates correlated well with the Pavelich-Taft dual substituent equation. Following extension of the study to hindered cases, and to 18 other solvents (analysed by Taft and Swain multi-parametrics), a cyclic intermediate is proposed for the rate-determining step. The same reaction order behaviour is found using the pyridinium version, and again electronic, steric, and solvent effects were examined.90... 

Bipyridinium chlorochromate (4) is a mild, air stable nonhygroscopic oxidant. It is weaker than PCC, and thus 2-4 equiv. are required to obtain good yields of carbonyl compounds. The bipyridyl system acts as an internal buffer, permitting the ready oxitktion of alcohols in sul trates with acid labile groups. Bipyridinium chlorochromate will also oxidize sulfides to sulfoxides and sulfones." ... 

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. ... 

Oxidative Cleavage of Cyclic Acetals. Benzylidene acetals are cleaved to hydroxyesters upon treatment with a mixture of 2,2 -bipyridinium chlorochromate and m-CPBA (eq 48). ... 

Benzylic oxidation of A(-substituted phthalimidines by treatment with 2,2 -bipyridinium chlorochromate/m-CPBA affords phthalimides in good yields. ... 

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