Benzyl alcohol, hydroxycarbonylation

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... 

Hydroxycarbonylation and alkoxycarbonylation of alkenes catalyzed by metal catalyst have been studied for the synthesis of acids, esters, and related derivatives. Palladium systems in particular have been popular and their use in hydroxycarbonylation and alkoxycarbonylation reactions has been reviewed.625,626 The catalysts were mainly designed for the carbonylation of alkenes in the presence of alcohols in order to prepare carboxylic esters, but they also work well for synthesizing carboxylic acids or anhydrides.137 627 They have also been used as catalysts in many other carbonyl-based processes that are of interest to industry. The hydroxycarbonylation of butadiene, the dicarboxylation of alkenes, the carbonylation of alkenes, the carbonylation of benzyl- and aryl-halide compounds, and oxidative carbonylations have been reviewed.6 8 The Pd-catalyzed hydroxycarbonylation of alkenes has attracted considerable interest in recent years as a way of obtaining carboxylic acids. In general, in acidic media, palladium salts in the presence of mono- or bidentate phosphines afford a mixture of linear and branched acids (see Scheme 9). 

Toste s vanadium oxidation system currently has more limited scope, although it seems to be orthogonal to the Pd(II) system. Whereas the Pd-sparteine system was unable to effectively resolve a-hydroxycarbonyl compounds, these alcohols were resolved with high selectivity using vanadium(V) (Table 2) [11]. Benzylic and allylic a-hydroxycarbonyls performed well in the reactions (entries 1-3,6). Alkyl hydroxy esters were oxidized more slowly, but with high selectivity (entry 5). Activated alcohols not a to a carbonyl led to poor selectivity or low reactivity. 

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