Anti Hydroxylations

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... 

Anti hydroxylation can be achieved by treatment with H2O2 and formic acid. In this case, epoxidation (15-48) occurs first, followed by an Sn2 reaetion, which results in overall anti addition ... 

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. 

Epoxidation followed by acid-catalyzed hydrolysis constitutes a method for anti hydroxylation of a double bond. 

Figure 11.4 The overall result of epoxidation followed by acid-catalyzed hydrolysis is a stereospecific anti hydroxylation of the double bond. ds-2-Butene yields the enantiomeric 2,3-butanediols tra x-2-butene yields the meso compound.

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

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

Anti-hydroxylation of the double bond can also be achieved by forming an epoxide, then carrying out an acid-catalysed hydrolysis. 

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).. ... 

Thallium(in) sulfate in water brings about the anti hydroxylation of 3-r-butyl- and 4-r-butyl-cyck>-hexene. The reagent has been recommended for the one-step preparation of rranj-diols from ctmfor-mationally rigid cycloalkenes. 

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