Hydroxylation Woodward-Prevost

Vicinal iodo carboxylates may also be prepared from the reaction of olefins either with iodine and potassium iodate in acetic acid/ or with N-iodosuccinimide and a carboxylic acid in chloroform. " A number of new procedures for effecting the hydroxylation or acyloxylation of olefins in a manner similar to the Prevost or Woodward-Prevost reactions include the following iodo acetoxylation with iodine and potassium chlorate in acetic acid followed by acetolysis with potassium acetate reaction with iV-bromoacetamide and silver acetate in acetic acid reaction with thallium(III) acetate in acetic acid and reaction with iodine tris(trifluoroacetate) in pentane. ... 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

Only much later was the hydroxylation of pure trans-307 and cis-307 performed, and the corresponding ci.s-diols were obtained in 22-26% yield. The compound obtained from t ran 4-307 was converted199 into ert/fhro-pentopyranos-4-ulose hydrate by successive alkaline de-benzoylation, and hydrolysis of the acetal in the presence of Dowex W-50 resin. An attempt at direct tran.s--hydroxylation of trans-307 by Woodward s or Prevost s method failed, as have attempts at its epoxi-dation with peroxy acids.200 Nevertheless, a number of 3,4-epoxides... 

The Woodward Reaction (or Woodward c/s-Hydroxylation) allows the synthesis of syn-diols from alkenes by the addition of iodine followed by nucleophilic displacement with acetate in the presence of water. Hydrolysis of the intermediate ester gives the desired diol. The Prevost Reaction gives crn/z -diols. 

The desired diol can be isolated after hydrolysis. Woodward noted, that his modification of the Prevost reaction offers the opposite facial selectivity as compared to oxidations with 0s04 in the hydroxylation of synthetic steroid intermediates. Here, the steric approach factors first direct the stereochemistry of the iodination, which is followed by hydroxylation from the opposite face, whereas 0s04 leads to the isomeric cw-diol by direct attack from the most accessible face. 

Hydrolysis of the ester does not change the configuration. The Woodward modification of the Prevost reaction is similar, but results in overall syn hydroxylation. The alkene is treated with iodine and silver acetate in a 1 1 molar ratio in acetic acid containing water. Here again, the initial product is a (3-halo ester the addition is anti and a nucleophilic replacement of the iodine occurs. However, in the presence of water, neighboring-group participation is prevented or greatly decreased by solvation of the ester function, and the mechanism is the normal Sn2 process, ... 

Prevost method The overall //7//-hydroxylation of an alkene achieved by treating the alkene with a 1 2 molar ratio of iodine and silver benzoate, followed by hydrolysis. Overall. syw-hy droxy 1 ation may be achieved by the method of Woodward. 

Woodward method The syn-hydroxylation of an alkene the first step involves treating the alkene with iodine and silver acetate in a 1 1 molar ratio in wet acetic acid. The hydrolysis of the intermediate c/////-P-halogenoester is via a normal SN2 reaction in which there is no neighbouring group effect because the ester function is solvated by the water. Overall //-addition may be achieved by the method of Prevost. 

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