Reagents Cleaving Glycols

The favored oxidative cleavage of a primary-secondary over a primary-tertiary vicinal diol grouping has been utilized in the synthesis of branched-chain sugar derivatives.482,483 

Periodic acid in dimethyl sulfoxide has been reported to show 

In contrast to the oxidation of acyclic polyhydric alcohols in benzene,508 treatment of 1,2-O-isopropylidene-a-D-glucofuranose with silver carbonate-on-Celite in boiling methanol led to selective oxidation of the primary hydroxyl group, with the formation of the al-duronic acid derivative in 68% yield.517 

A study518 of the mechanism of oxidation of alcohols by the reagent suggested that a reversible, oriented adsorption of the alcohol onto the surface of the oxidant occurs, with the oxygen atom of the alcohol forming a coordinate bond to a silver ion, followed by a concerted, irreversible, homolytic shift of electrons to generate silver atoms, carbon dioxide, water, and the carbonyl compound. The reactivity of a polyhydroxy compound may not, it appears, be deduced from the relative reactivity of its component functions, as the geometry of the adsorbed state, itself affected by solvent polarity, exerts an important influence on the selectivity observed.519 

Chromium trioxide in pyridine selectively oxidizes the hydroxymethyl groups in thymidine, 2 -deoxyadenosine, 2 -deoxyguano-sine, and 2 -deoxycytidine to carboxyl groups,525 but the partial liberation of the free, heterocyclic bases in the reactions suggested that oxidation at C-3 also occurs to some extent. 

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Among the very selective oxidants are the glycol-cleaving reagents, periodic acid and lead tetraacetate. These have been briefly mentioned... 

The high selectivity of periodate and lead tetraacetate as glycol-cleaving oxidants is attributed mainly to the ability of the central atom of the reagent to complex with a 1,2-diol and effect a two-electron transfer. That an intermediate complex is formed has been shown for periodate by pH " and ultraviolet spectral changes, and, for both oxidants, less directly by consideration of the reaction kinetics. ... 

The 17,20-glycol grouping (with or without an additional C-21 alcohol) can be cleaved to the 17-ketone by any of the four reagents. However, the presence of a 20-ketone has a marked influence on reactivity. Thus, 17a-hydroxy-20-ketones lacking additional oxygenation at C-21 are readily cleaved only by chromium trioxide. A recent report,however, claims that 17a-hydroxypregnenolone 3-acetate can be quantitatively cleaved to dehydroepiandrosterone acetate using lead tetraacetate in an aprotic solvent... 

The mechanism of oxidation probably involves in most cases the initial formation of a glycol (15-35) or cyclic ester,and then further oxidation as in 19-7. In line with the electrophilic attack on the alkene, triple-bonds are more resistant to oxidation than double bonds. Terminal triple-bond compounds can be cleaved to carboxylic acids (RC=CHRCOOH) with thallium(III) nitrate or with [bis(trifluoroacetoxy)iodo]pentafluorobenzene, that is, C6F5l(OCOCF3)2, among other reagents. 

Fission of carbon-carbon double bonds with the combined use of an osmium catalyst and periodate as a comsumable reagent is an alternative to ozonolysis. In diis process a catalytic amount of osmium is oxidised to osmium(viii) by preiodate and converts the alkene to a glycol which is then cleaved by the periodate. In the electrochemical modification of this process, which uses a divided cell and aque-... 

HBTU/HOBt in NMP (1.4 equiv) was used to couple the protected N-terminal fragment (1.2 equiv) to Glull of the resin-bound C-terminal fragment over 24 h. To then cleave the fully assembled protected peptide from the Rink amide resin, reagent K (TFA/PhOH/H20/PhSH/ethylene glycol 82.5 5.5 5 2.5) was used. 

The chemical researches were directed towards three main aims. The first dealt with periodic acid oxidation. In 1928, L. Malaprade, at the University of Nancy, hoping to specify the effect of D-mannitol upon the acidity of periodic acid, observed that the carbon-carbon linkages of the polyol were cleaved, and showed that this was a general feature of the specific reaction of periodic acid with a-glycols. Then, P. Fleury had the premonition that this acid should be an invaluable reagent for analytical purposes. He described the utilization and determination of this remarkably selective oxidant, working under mild conditions of pH and temperature. 

The method is based on the fact that periodic acid or the reagent more commonly used, sodium metaperiodate, will oxidize a-glycols and cleave the carbon-carbon bond, with the formation of dialdehydes.166166 A pentofuranosylpyrimidine (XVIII, R = a pyrimidyl group) would be expected to consume one mole of metaperiodate per mole of nucleoside. The dialdehyde (XIX) resulting from this oxidation would... 

The reaction of alkenes with osmium tetroxide (0s04) is an example of an oxidation reaction (Following fig.). In this case the alkene is not split, but, a 1,2-diol is obtained which is also called a glycol. The reaction involves the formation of a cyclic intermediate where the osmium reagent is attached to one face of the alkene. On treatment with sodium bisulphite, the intermediate is cleaved such that the two oxygen atoms linking the osmium remain... 

Jones reagent (CrO -H ) in acetone (1, 142). Jones reagent can oxidatively cleave sec-ferf-1,2-glycols in high yield.1 An a-hydroxy ketone may be an intermediate (equation I). Note that an epoxide can also be cleaved to a keto acid.1... 

Pentavalent derivatives of triphenylbismuth such as p,-oxobis(chlorotriplienylbismudi) (1) and triphe-nylbismuth carbonate (2) have been developed recently as oxidizing agents which cleave a-glycols into the corresponding carbonyl derivatives (equation 1). Aldehydic products do not undergo further oxidation. Reagent (1) also oxidizes saturated ilcohols as well as allylic and benzylic alcohols, whereas (2) selectively oxidizes allylic alcohols in the presence of saturated alcohols. ... 

A catalytic bismuth system (Ph3Bi-NBS-K2C03-MeCN with 1% water) has been repotted to cleave a range of 1,2-glycols efficiently and is shown to have a different mechanism from the cyclic process observed with the stoichiometric bismuth reagent (2). The catalytic system cleaves cis- and rra/t -decalin-... 

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