Alkenes anti hydroxylation

A complementary method one that gives anti hydroxylation of alkenes by way of the hydrolysis of epoxides will be described m Section 16 13... 

A method for achieving net anti hydroxylation of alkenes combines two stereo specific processes epoxidation of the double bond and hydrolysis of the derived epoxide... 

Attack has been shown on only one of the two possible carbon atoms in (49) and (50), though on different ones in the two cases. Attack on the other carbon, in each case, will lead to the same product, the meso 1,2-diol (51). By comparing the configuration of (51) with that of the original alkene (48b), it will be seen that—in overall terms— stereoselective ANTI hydroxylation has been effected. 

Anti-hydroxylation of alkenes preparation of ontr-diols... 

Like alkenes, the double bonds of ,/3-unsaturated acids can be brominated, hydroxylated, hydrated, and hydrobrominated, although the reactions often are relatively slow. In the addition of unsymmetrical reagents the direction of addition is opposite to that observed for alkenes (anti-Markownikoff). Thus propenoic (acrylic) acid adds hydrogen bromide and water to form 3-bromo-and 3-hydroxypropanoic acids ... 

Acid-catalyzed hydrolysis of the epoxide yields a diol its stereochemistry corresponds to net anti hydroxylation of the double bond of the original alkene. 

Direct anti hydroxylation of an alkene (without isolation of the epoxide intermediate) is possible by using an acidic aqueous solution of a peroxyacid. As soon as the epoxide is formed, it hydrolyzes to the glycol. Peroxyacetic acid (CH3CO3H) and peroxyformic acid (HCO3H) are often used for the anti hydroxylation of alkenes. 

Anti hydroxylation of an alkene is readily achieved with peroxycarboxylic adds. Add-catalyzed ring opening of the irutial produd, an oxirane (epoxide), forms the monoester of a 1,2-diol, hydrolysis of which affords the parent diol. Alternative reagents whi ate often used for anti hydroxylation of alkenes are hydrogen peroxide with oxides of tungsten > 4.2i gj. selenium, 444i and iodine-silver benzoate (Pr6vost reaction).. ... 

Transition metal catalysts not only increase the reaction rate but may also affect the outcome of the oxidation, especially the stereochemistry of the products. Whereas hydrogen peroxide alone in acetonitrile oxidizes alkenes to epoxides [729], osmic acid catalyzes syn hydroxylation [736], and tungstic acid catalyzes anti hydroxylation [737]. The most frequently used catalysts are titanium trichloride [732], vanadium pentoxide [733,134], sodium vanadate [735], selenium dioxide [725], chromium trioxide [134], ammonium molybdate [736], tungsten trioxide [737], tungstic acid [737],... 

Peroxytrifluoroacetic acid is used for the epoxidation [283, 287] and anti hydroxylation [285, 288] of alkenes the Baeye Villiger oxidation of... 

Hydroxylation, the addition of two hydroxyl groups across double bonds, converts alkenes and cycloalkenes into vicinal dials. Stereochem-ically. the addition may occur in the syn or the anti mode. In open-chain alkenes (with the exception of terminal alkenes for which stereochemistry is irrelevant), syn hydroxylation transforms cis alkenes into erythro (or meso) diols and trans alkenes into threo (or dl) diols. anti Hydroxylation of cis alkenes gives threo (or dl) diols, whereas anti hydroxylation of trans alkenes yields erythro (or meso) diols. syn Hydroxylation of cycloalkenes gives cis diols, whereas anti hydroxylation furnishes trans diols (Table I). 

Another kind of anti hydroxylation is the reaction of alkenes with hydrogen peroxide in the presence of vanadium pentoxide, molybdenum trioxide, selenium dioxide, and especially tungsten trioxide (tungstic acid) [131, 144]. Cyclohexene is thus converted into DL-/rarts-l,2-cyclohex-anediol [131],... 

Hydroxylation at double bonds of unsaturated carboxylic acids is accomplished stereoselectively by the same reagents as those used to hy-droxylate alkenes. syn Hydroxylation is carried out with potassium permanganate [101] or osmium tetroxide with hydrogen peroxide [130], sodium chlorate [310, 715], potassium chlorate [715], or silver chlorate [310] as reoxidant, anti Hydroxylation is achieved with peroxyacids, such as peroxybenzoic acid [310] or peroxyformic acid, prepared in situ from hydrogen peroxide and formic acid [101] (equation 472). 

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