Iodine and silver oxide

A different cychzation reaction of 460, by treatment with iodine and silver oxide, gave l,6-dioxaspiro[3.4]octanes 469 (Scheme 130). This heterocychc core present in a series of sesquiterpenic lactones has interesting biological activity and is isolated as secondary metabolites from species of the Compositae family . 

Iodine and silver oxide oxidize alkenes to epoxides [751], whereas iodine and silver ebromate convert alkenes into a-iodoketones [610]. 

Other oxidants used for epoxidation are dimethyldioxirane [210], ozone [107], thallium triacetate [412], chromic oxide [564], chromyl compounds [679], sodium hypochlorite [112, 689], calcium hypochlorite [704], N-bromosuccinimide in water [746], iodine and silver oxide [751], iodine triacetate [785], electrolysis [119], and microorganisms [1055, 1063]. 

Other epoxidizing reagents which have been proposed but have not been extensively employed with olefinic acids include r-butyl hydroperoxide and transition metal salts, hydrogen peroxide and isocyanate, sodium chlorate and osmium tetroxide, iodine and silver oxide and hydrogen peroxide and ortho esters. 

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. ... 

Aromatic cation-radicals can also react with NOj", giving nitro compounds. Such reactions proceed either with a preliminary prepared cation-radical or starting from nncharged componnd if iodine and silver nitrite are added. As for mechanisms, two of them seem feasible—first, single electron transfer from the nitrite ion to a cation-radical and second, nitration of ArH with the NOj radical. This radical is quantitatively formed when iodine oxidizes silver nitrite in carbon tetrachloride (Neelmeyer 1904). 

The interaction of diaryl tellurides and the esters of halogenated fatty acids, e.g. methyl bromacetate, gives diarvl-telluretin halide alkyl esters, e.g. (C6H5)2Te(Br).CH2.COOCH3. The halogen present may be chlorine, bromine or iodine, moist silver oxide replacing the bromine by the hydroxyl group. 

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. 

Alicyclic, aromatic, aliphatic, steroidal and triterpenoid 1,2-diols are cleaved by iodine triacetate and iodine(I) acetate to generate carbonyl compounds. Aldehydic products are not further oxidized. Iodine triacetate is prepared firom iodine trichloride and silver(l) acetate, whereas iodine(I) acetate is prepared from iodine and silver(I) acetate. Reactions occur in acetic acid at room temperature under nitrogen, and a radical pathway involving a hypoiodite is suggested. The cost and the availability of these reagents are probable reasons for their unpopularity. 

The preferred procedure for iodination of veratrole employs silver trifluoroacetate. An aqueous solution of the salt is prepared from the acid and silver oxide, filtered, and evaporated to dryness the salt is purified by Soxhlet extraction with ether. A solution of iodine in chloroform is added with stirring under reflux to a mixture of... 

Some BS-analogues with additional double bond in the A-cycle were synthesized using the a-cis-hydroxylation method developed by us earlier (13-16). As shown in Figure 4, the oxidation of 2 with osmium tetroxide followed by bromination and dehydrobromination led to dienoketone 13 which was subjected to hydroxylation under the action of iodine and silver acetate in aqueous acetic acid to give the unsaturated BS analogue 14. 

Molecular models suggested to us that the proper conformational features might well be adopted if the oxirane ring were positioned instead on the more sterically congested inner surface of this unsaturated center. Indeed, the desired diastereofacial outcome was realized upon treatment of 181 with iodine and silver(I) oxide in aqueous dioxane [97,98]. The conclusion that 183 had indeed been formed was corroborated by NOE measurements and by the fact that the synthetic material was identical to an authentic sample produced by the saponifi-... 

C-17, gave 3 -melhanesulphonyloxyandrost-5-en-17 -ol acetate (403). Diborane addition to the A -double bond and oxidation afforded the 6-keto-derivative (404). Elimination of the 3-mesylate, followed by iodine and silver acetate treatment furnished the 2-acetoxy-3-alcohol (405), which was successively acetylated at C-3, brominated at C-7, and dehydrobrominated to the triacetoxy-A -6-ketone (406). Enol acetylation of the conjugated carbonyl furnished the tetra-acetate (407), which was treated with peracid and then hydrolysed and isomerized at C-5 to yield the desired tetraol (408). ... 

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. 

Oxidation of iodide to iodine is undoubtely involved in these reactions, but the details of the mechanism have not been explored. lodination of moderately reactive aromatics can be effected by mixtures of iodine and silver or mercuric salts. Hypoiodites are presumably the active iodinating species. Some examples of iodina-tion procedures are included in Scheme 11.2. 

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