Prevost reaction

The first step of the Provost reaction is the reaction of the alkene with iodine to form the cyclic iodonium ion. Next, the iodonium ion is stereospecifically opened by the silver carboxylate to form the corresponding frans-1,2-iodo carboxylate. The iodine is displaced intramolecularly by the carbonyl group of the carboxylate (anchimeric assistance) to form a cyclic cationic intermediate. In the absence of water, this cation is opened with the inversion of configuration by the second equivalent of silver carboxylate to afford the frans-1,2-dicarboxylate. However, in the presence of water Woodward-Brutcher modification) the common intermediate is converted to a c/s-orthocarboxylate which is hydrolyzed to the corresponding c/s-1,2-diol. 

In the laboratory of S. Kumar, the synthesis of phenolic derivatives of frans-7,8-dihydroxy -7,8-dihydrobenzo[a]pyrene, a highly tumorigenic compound, was accomplished. The frans-vicinal diol functionality was introduced by using the dry Prevost conditions. The alkene was subjected to a mixture of iodine and silver benzoate in dry refluxing benzene to give a good yield of the corresponding frans-7,8-dibenzoate derivative. 

The total synthesis of (-)-SS20846A, a 2-alkyl-4-hydroxypiperidine natural product exhibiting antibacterial and anticonvulsant properties, was achieved by C.R. Johnson and co-workers. The key transformations included an alkene metathesis for the preparation of the piperidine ring and the Prevost reaction for the installation of the 4-hydroxy substituent. 

The key steps in the first total synthesis of (+)-momilactone A by P. Deslongchamps et al. were a highly diastereoselective transannular DIels-Alder cycloadditlon and the Prdvost reaction The 3-ketolactone moiety was installed by first treating the tricyclic alkene with A/-bromo acetamide and silver acetate to obtain the trans bromoacetate with excellent diastereoselectivlty. The cIs stereochemistry of the lactone was achieved a few steps later by the intramolecular nucleophilic displacement of the bromide with the carboxylate ion on the adjacent six-membered ring. 

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. 

An alternative route to 1,2-diols reacts alkenes with a mixture of silver carboxylate and iodine rather than with peroxides. Prevost found that silver benzoate and iodide converted styrene to 1,2-dibenzoate 272, which could be saponified to the l,2-diol. 358 xhe transformation is called the Prevost reaction.3 6 This 

It is noted that an alternative. route to trans diols is available by hydrolysis of epoxides. Reaction of cyclohexene with MCPBA gives cyclohexene oxide and hydrolysis (acid or base) gives trans-1,2-cyclohexanediol. 

The functional group transforms for all of the hydroxylation reactions in this section are 

The synthesis of nitrogen-containing natural products is also possible via diols such as these. Hudlicky and co-workers prepared the bicyclic alkaloid (+)-kifunensine, for example, from 284. 0 More complex molecules can also be prepared, as illustrated by the conversion of 285 into (+)-pancratistatin (291), via synthetic intermediate 290. Banwell et al. reported an asymmetric synthesis of (-)-patchoulenone from 287 

The use of 284-287 as well as other diol derivatives derived from functionalized aromatic compounds is clearly an important method for the preparation of molecules that can be used in asymmetric synthesis. This process provides an important source of diol starting materials that can be manipulated to form a variety of important natural products. This interesting oxidation leads to the functional group transform  

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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. ... 

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. ... 

Atta-ur-Rahman et al. reported the oxidation of catharanthine by a modified Prevost reaction to result in formation of the 20-a-acetoxy derivative. Coupling of its A-oxide (77) to vindoline, using trichloroacetic anhydride (rather than the usual trifluoro compound), and subsequent re-... 

Polyhalo ketones, reductive dehalogenation of, 29, 2 Pomeranz-Fritsch reaction, 6, 4 Prevost reaction, 9, 5 Pschorr synthesis, 2, 6 9, 7 Pnmmerer reaction, 40, 3 Pyrazolines, intermediates in diazoacetic ester reactions, 18, 3 Pyridininm chlorochromate, 53, 1 Pyrolysis ... 

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... 

This Woodwardr-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. 

The acyl hypohalit reaction with iodine ob a halogen component is the well-known Prevost reaction,18i0 whioh has found some application during recent years in the field of natural prodwtB.. u. . w. In thiB ease the acyl hypoholite is acetyl hypoiodite, generated by reaction of iodine with silver nitrate in glacial acetic arid (Eq. 130). 

The syn- and anfi-diol epoxides of benz[a] anthracene and benzo[a] pyrene have been prepared from dihydroarenes by sequential Prevost reaction with silver benzoate-iodine, dehydrogenation, methanolysis, and epoxidation, e.g.,... 

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. 

Similar to the Prevost Reaction, initial addition of iodine leads o a cyclic iodonium ion, that is opened through nucleophilic substitution by acetate anion ... 

In contrast to the course of the Prevost Reaction, water appears to add readily as a nucleophile to the partially positive carbon atom of the intermediate. The cyclic orthoacetate is then cleaved to a monoacylated diol ... 

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. 

Most of the transformations carried out on catharanthine have naturally been concerned with the preparation of potential precursors of dimeric bases related to vinblastine. For example, 15-acetoxydihydrocatharanthine (configuration at C-15 unknown) is also obtained, together with the recently reported221 20-acetoxydi-hydrocatharanthine, when catharanthine is subjected to the modified Prevost reaction.139 The conversion of catharanthine (236) into the potentially useful epoxides (237a), (237b), and (239), the lactone (238), and the diol (240) (stereochemistry at C-15 and C-20 not rigorously proved) has also been described (Scheme 25).140,141... 

Aromatic ketones of the a-tetralone type 11/74 can be converted by a Wittig reaction to compounds of type 11/75, Scheme 11/11. Under Prevost reaction conditions (AgN03,I2,CH30H) two ring enlargement products are formed, 11/77 and 11/78 (both together in 67 % yield), which by hydrolysis are converted to the a-cyano ketone 11/79 [56], This procedure has been applied successfully to... 

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. 

Silver-mediated C—X bond formation was known for many years as the Hunsdiecker reaction, in which substrates bearing carboxylic acids are oxidatively decarboxylated to give alkyl halides in the presence of halogens (142). If olefins are used with silver benzoate and I2, the Prevost reaction occurs to yield diols (143). 

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