Woodward-Prevost reaction

The mechanisms of these reactions are presumably analogous to those of the Pr6vost and Woodward-Prevost reactions. In the first step of the reaction of iodine and thallium(I) acetate with cyclohexene in both parts A and B of this procedure, trans-2-iodocyclohexyl acetate is formed. The second equivalent of thal-lium(I) acetate scavenges iodide ion during formation of the 1,3-... 

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. ... 

Myint, Y. Y., Pasha, M. A. Preparation of a-iodoacetates from alkenes by Co(OAc>2 catalysed Woodward-Prevost reaction. Indian J, Chem, Sect. B 2004, 43B, 590-592. 

This Woodward-Prevost reaction provides cis diols at the more hindered face. This is due to the first step, the addition of iodine from the less-hindered face. 

Recently, Vidari et al. synthesized 9-deoxygelsemide (75), which was isolated earlier from Gelsemium elegans by Takayama et al. [104, 105]. The key synthetic steps were the variant Woodward-Prevost reaction for installation of characteristic cis-a-l,2-dioxygenated system at C-6 and C-7, and construction of the dihydropyran ring via formylation of y-lactone. The total synthesis of the iridoid was achieved in 11 steps and 6.6% overall yield from enantiomerically pure lactone (76) (Scheme 97.5). 

The present procedure offers a convenient alternative to the Prevost reaction and the Woodward modification of the Prevost reaction in which silver carboxylates are used instead of thal-lium(I) carboxylates. Thallium(I) salts have the advantages of being generally stable crystalline solids that can be readily prepared in high yield by neutralization of the appropriate carboxylic acid with thallium(I) ethoxide. Silver salts, on the other hand, are frequently unstable and difficult to dry. Thallium and its compounds are, however, extremely toxic, and great care must therefore be taken in the use and disposal of thallium salts. ... 

Stereoselective cis-dihydroxylation. Details have been published for preparation of cither treats- or cis-1,2-cyclohexenediol by the thallium-based version of the Woodward version of the Prevost reaction (equation I).3... 

Methyla-arylacetates. These esters have been obtained by oxidative rearrangement of alkyl aryl ketones with thallium(III) nitrate in acidic methanol or trimethyl orthoformate (4,496 5, 656 7, 362). A new method, which avoids the toxic TTN, is based on the Woodward version of the Prevost reaction. Thus, treatment of the ketone with iodine (or bromine) and silver nitrate (2 equiv.) in refluxing methanol containing trimethyl orthoformate results in methyl a-arylacetates in 90% yield from simple substrates. Yields are lowered by electron-withdrawing substituents on the aromatic group and by a-branching in the alkyl group.2... 

The Prevost Reaction allows the synthesis of anti-diols from alkenes by the addition of iodine followed by nucleophilic displacement with benzoate in the absence of water. Hydrolysis of the intermediate diester gives the desired diol.The Woodward Modification of the Prevost Reaction gives syn-diols. 

The use of expensive silver salts, the requirement for a stoichiometric amount of molecular halogen, and the formation of a relatively large amount of organic and inorganic wastes are definite drawbacks to this reaction. Sudalai recently reported on catalytic versions of both the Prevost Reaction and the Woodward-Modification. 

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. 

Alkenes can be oxidized to diols by the Prevost method, which involves the reaction of an alkene with iodine and silver acetate. The frans-1,2-diacetate formed first on hydrolysis gives frans- 1,2-diols (Scheme 7.26). In the Woodward variation of the Prevost reaction, the monoester is formed under aqueous conditions, which on hydrolysis gives ds-diol. 

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, ... 

The Woodward-Brutcher modification of the Prevost reaction was used by P.T. Lansbury to install the cis vicinal diol moiety of (+)-2,3-dihydrofastigilin The cis vicinal diacetate was formed in high yield and with good diastereoselectivity (5 1) when the reaction was conducted in wet acetic acid. 

Despite the dominance of dihydroxylation reactions employing Os(VlIl) for the production of vicinal diols, alternatives have been utilized in asymmetric syntheses. The best known of these is perhaps Woodward s modification [205] of the Prevost reaction [206]. This classic oxidation is known to generally yield anti-1,2-diacetates from olefinic substrates [207]. Woodward s key modification involves the inclusion of water in the reaction mixture. The intermediate iodo-acetate 303 undergoes hydrolytic cleavage... 

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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