Diols selective oxidation

The reactions of olefins with peracids to form epoxides allows for the selective oxidation of carbon-carbon double bonds in the presence of other functional groups which may be subject to oxidation (for example, hydroxyl groups). The epoxides that result are easily cleaved by strong acids to diols or half-esters of diols and are therefore useful intermediates in the synthesis of polyfunctional compounds. 

A 1,3-diol sometimes represents a more convenient precursor to cyanohydrin acetonides. For these instances, an alternate procedure has been developed. Selective oxidation of a 1,3-diol with TEMPO/NaOCl generates a sensitive -hydroxy aldehyde (see also Sect. 3.2). The neat -hydroxy aldehyde is prone to dimerization, but can be handled in solution without significant dimerization. Conversion to the cyanohydrin acetonide is accomplished in a manner similar... 

Dehydration of cortisone (198) affords the diene 199. This is then converted to ketal 200. The selectivity is due to hindrance about both the 11- and 20-carbonyl groups. The shift of the double bond to the 5,6-position is characteristic of that particular enone. Treatment of protected diene 200 with osmium tetroxide results in selective oxidation of the conjugated double bond at C-16,17 to afford the cis-diol (201). Reduction of the ketone at C-ll (202) followed by hydrolysis of the ketal function gives the intermediate 203. Selenium dioxide has been... 

The nickel hydroxide electrode resembles in its applications and selectivity the chemical oxidant nickel peroxide. The nickel hydroxide electrode is, however, cheaper, easy to use and in scale-up, and produces no second streams/ waste- and by-products [196], Nickelhydroxide electrode has been applied to the oxidation of primary alcohols to acids or aldehydes, of secondary alcohols to ketones, as well as in the selective oxidation of steroid alcohols, cleavage of vicinal diols, in the oxidation of y-ketocarboxylic acids, of primary amines to nitriles, of 2,6-di-tert-butylphenol to 2,2, 6,6 -tetra-rert-butyldiphenoquinone, of 2-(benzylideneamino)-phenols to 2-phenyloxazols, of 1,1-dialkylhydrazines to tetraalkyltetrazenes. For details the reader is referred to Ref. [195]. 

Bu2Sn=0 Selective oxidation of 1,2-diols to a-hydroxy ketones was electro-chemically achieved in a double mediatory system consisting of dialkyl tin oxide and the bromide ion (Fig. 3) [34]. 

For example, 1,2-diol (14) was selectively oxidized to give a-hydroxy ketone (15) in 84% yield at a current consumption of 2 F mol , even though the electrolysis was carried out in the presence of... 

Incubation of the (1R,2R) diol 25 over a shorter time period of 4 days gave a mixture of the meso cis diol 26 (26%) and the trans diol 25 RR/SS 76 26) showing conversion over to the (1S,2S) diol. As with the previous examples, no conversion was observed when using the S,S diol 25 as a substrate. Although no intermediate a-hydroxyketone was observed for this substrate we proposed the operation of at least two dehydrogenase enzymes, DH-1 and DH-2, catalysing the (i )-selective oxidation and (S)-selective reduction respectively (Scheme 12). Incubation of cis cycloheptan-l,2-diol afforded only the (S)-2-... 

However, oxidation with H2O2 in acetone resulted in a high diol selectivity with an equilibrium mixture of the cis- and trans-diols, illustrating the role of the residual acidity of the support The reaction is suggested to occur via heterolyhc cleavage of the vanadium peroxo species. Less than 0.5% leaching of the bipy complex was observed over 50 h of operation. 

It is noteworthy that allylic alcohols are oxidized to products with retained configuration of the olefinic bond. Geraniol and nerol were oxidized to the corresponding ( )-and (Z)-a-enals, respectively. As expected, primary alcohols were oxidized faster than secondary ones with the RuCl2(PPh3)3/BTSP system with relative rates from 20-40 1. The new system was applicable for the selective oxidation of primary-secondary diols... 

Oxidation and Reduction.—A number of selective oxidation procedures have been reported. Trichloroacetaldehyde on dehydrated chromatographic alumina converts the diol (15) into the 3/3-hydroxy-17-ketone (68%)." Primary alcohols are reported to be less readily oxidized than secondary alcohols by this reagent. Similarly, bromine or chlorine with HMPA oxidizes secondary alcohols more readily than primary alcohols. Thus the diol (16) was converted into the ketol (17)... 

Simple side-chain reactions of 1,2-dithiin diols have been conducted. Besides the formation of esters, ethers (R = Me, Et, 7-Pr, cyclopropyl, Ph, pyridyl, cyclopentyl), and thioethers (R = H, TBDMS R = 4 -(4-hydroxyphenyl)-l//-tetrazole-5-thiol), selective oxidation of the primary alcohol groups in the presence of the 1,2-dithiin heterocycle could be readily achieved (Scheme 36) <1995JME2628, 1994SL201>. Additionally, amides, ureas, and carbamates of the dithiin diol were synthesized <1995JME2628>. 

To complete the synthesis, the ketone of 2 was homologated to the alkene 12. Selective oxidative cleavage of the two vinyl groups followed by reduction provided the diol, the less encumbered alcohol of which was protected to deliver the fully-differentiated ester 13. Oxidation followed by ester cleavage then gave 3. 

Selective oxidation ef primary diols. 2,2-Diphcnyl-1.4-butancdiol (1) is oxidized... 

If used under mild, alkaline conditions to prevent further oxidation of the 1,2-diol formed, KMnC>4 can be a selective oxidizing agent434,435 However, proper experimental conditions (extensive stirring in dilute solution,436 phase-transfer catalysis437 140), or other permanganate salts441 [Eq. (9.93)] are required to achieve high yields ... 

Alkali periodates (in aqueous solution)646 and ammonium periodate (in anhydrous aprotic solvent),647 when applied in the presence of a catalytic amount of 0s04, are selective oxidizing agents used to form carbonyl compounds. Os04 apparently transforms the alkene to an 1,2-diol that is subsequently cleaved by the periodate to the carbonyl compound end products. The periodate also serves to regenerate Os04. 

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