Prevost reagent

The Prevost reagent unexpectedly converts isophyllodadene (1) into the allylic benzoate (2) in good yield (1.1 g.—>0.7 g.). The same product is obtained... 

The Prevost reagent converts A -cholestene into both possible trans-diol dibenzoates. The diaxial 2/3,3a-isomer predominates over the diequatorial 2a,3/3-isomer in the ratio of 2 1, but difficulty in the separation limits the total yield to 31%. 

Hydroxylation by iodine-silver benzoate (Prevost reagent)... 

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. ... 

With dry reagents, anti addition takes place to form diesters, which yield diols on hydrolysis (Prevost reaction). 

The formation of 1,2-diol products from alkenes can be achieved using Prevost s reagent - a solution of iodine in carbon tetrachloride together with an equivalent of silver(l) acetate or silver(I) benzoate. " Under anhydrous conditions, this oxidant yields directly the diacyl derivative of the anh-diol (Prdvost conditions), while in the presence of water the monoester of the syn-diol is obtained (Woodward conditions). Thus, treatment of a cw-alkene with iodine and silver benzoate in boiling carbon tetrachloride under anhydrous conditions gives the tra 5-dibenzoate (5.92). With iodine and silver(I) acetate in moist acetic acid, however, the monoacetate of the cw-1,2-dihydroxy compound is formed. 

An interesting example with a switchover of the stereochemical course was observed during the enantioselective diacetoxylation of alkenes using chiral iodine (III) reagents (Scheme 13) [56]. Enantioselective Prevost and Woodward reaction products were formed through the optically active l,3-dioxolan-2-yl cation intermediates 30. 

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