In oxidation of diols

Ester formation is especially easy in oxidations of diols (with at least one primary hydroxyl group) that can cyclize to five- or six-membered lactones after partial oxidation [355, 1035] see equations 292-295). 

The formation of side product ester 10 in oxidation of diol 5 (Table 3.1, entry 4) can be explained with the intermediacy of aldehyde as well. Upon generation of aldehyde 11 from 5, intermolecular nucleophilic attack of the carbonyl group by the free hydroxyl group produced hemiacetal 12, oxidation of which led to carboxylic ester 10 (Scheme 3.2). Formation of similar by-products during oxidation of primary hydroxyl groups in carbohydrates has been observed previously. ... 

Alkah manganate(VI) salts are used as oxidants in synthetic organic reactions (100) and their reactions have been observed to be similar to permanganate, except that manganate(VI) exhibits lower reactivity. Additionally, sohd BaVInO in methylene chloride has been reported to achieve high yields for the oxidation of diols to dialdehydes (101). 

Mechanisms involving glycol bond fission have been proposed for the oxidation of vicinal diols, and hydride transfer for other diols in the oxidation of diols by bromine in acid solution.The kinetics of oxidation of some five-ring heterocyclic aldehydes by acidic bromate have been studied. The reaction of phenothiazin-5-ium 3-amino-7-dimethylamino-2-methyl chloride (toluidine blue) with acidic bromate has been studied. Kinetic studies revealed an initial induction period before the rapid consumption of substrate and this is accounted for by a mechanism in which bromide ion is converted into the active bromate and hyperbromous acid during induction and the substrate is converted into the demethylated sulfoxide. 

Abstract This is one of the most important classes of oxidation effected by Ru complexes, particnlarly by RnO, [RuO ] , [RnO ] and RuCljCPPhj), though in fact most Ru oxidants effect these transformations. The chapter covers oxidation of primary alcohols to aldehydes (section 2.1), and to carboxylic acids (2.2), and of secondary alcohols to ketones (2.3). Oxidation of primary and secondary alcohol functionalities in carbohydrates (sugars) is dealt with in section 2.4, then oxidation of diols and polyols to lactones and acids (2.5). Finally there is a short section on miscellaneous alcohol oxidations in section 2.6. 

In 1976, Ueno and Okawara highlighted the fact that no oxidation of primary saturated alcohols to aldehydes via tin alkoxides had been reported in the literature and published a procedure for the selective oxidation of secondary alcohols.25 Interestingly, rather than performing the oxidation on pre-formed tin alkoxides, these researchers subjected a mixture of the diol and (Bu3Sn)20 in CH2C12 to the action of Br2. Regardless of the fact that no complete formation of tin alkoxides is secured and no HBr quencher is added, this method may provide useful yields of hydroxyketones during the selective oxidation of diols.26... 

Subsequent researchers introduced substantial improvements on the Ueno and Okawara s protocol of selective oxidations via tin alkoxides and broadened considerably the scope of its application.223 24b,c Thus, it was established that good yields in the selective oxidation of diols—and even triols and tetrols can be achieved in two steps i) pre-formation of a tin alkoxide, by reaction with either (Bu3Sn)20 or Bu2SnO with elimination of water by molecular sieves or azeotropic distillation of water ii) treatment of the tin alkoxide with Br2 or NBS in the presence of a HBr quencher. 

The oxidation of diols by quinolinium dichromate (QDC) shows a first-order dependence on QDC and acid.5 The oxidation of phenols to quinones by quinolinium dichromate in aqueous acetic acid is acid catalysed rate-determining formation of a cationic intermediate is indicated by a p value of —3.79 and further analysis shows the rates to be influenced equally by both inductive and resonance effects of the substituents.6... 

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... 

From the kinetics of oxidation of diols by Fc(CN) in aqueous alkali catalysed by R11CI3, it is concluded that oxidation proceeds not by hydride ion transfer from alcohol to Ru(III) but via hydrogen atom transfer, to generate Ru(II) species and an intermediate radical which is further oxidized by more Ru(III).86 Similar conclusions were made from a related study of die oxidation of propan-l-ol under comparable conditions.87... 

The oxidation of glutamic acid to cyanopropionic acid with CAB in acid solution showed an inverse fractional dependence on acidity. Similarly in alkaline medium, the order in alkali is fractional inverse.143 Kinetics of ruthenium(III)-catalysed oxidation of diols with CAB have been obtained. The products arise due to a fission of the glycol bond.144 The oxidation of isatins with CAB, in alkaline solutions, showed a first-order dependence on CAB and isatin and fractional order in alkali. The rates correlate with the Hammett relationship, the reaction constant p being —0.31. The observed results have been explained by a plausible mechanism and the related rate law has been deduced.145 The oxidation of cysteine with CAB in sulfuric acid medium is first order in CAB and cysteine and the rate is decreased with an increase in the hydrogen ion concentration.146... 

Oxidation of diols.1,2 Both 1 and 2 can serve as effective catalysts for oxidation of diols by NaOCl in aqueous CH2CI2. This method is useful for selective oxidation... 

The Wittig reaction of dialdehyde 175, prepared by chromic anhydride-pyridine oxidation of diol 94 (53), with 176 in dilute methylene chloride solution produced cyclophane 177 in 86% yield. Epoxidation of 177 with m-chloroperbenzoic acid followed by hydrogenolysis over Pd/C, acetylation, and PtOz-Raney Ni-catalyzed hydrogenation afforded the cis-substituted piperidine derivative (178). 

The Dess-Martin periodinane oxidation of diol 150 and subsequent thermal equilibration at 45 °C gives the dihydrooxocine 151 in 92% yield (Scheme 39) <20020L3891>. 

The selective oxidation of diols in which one or both hydroxy groups are allylic has been reported on a number of occasions. Reagents which have proved use for this include silver carbonate on Celite, barium manganate/ and manganese dioxide, as illustrated in equations (29)-(31). 

---