Iodine with silver acetate

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. ... 

Hydrolysis of the ester does not change the configuration. Woodward s method is similar, but results in overall syn hydroxylation. The olefin 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-... 

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). 

Chlorination by sulfuryl chloride occurs at position 3 for l-oxa-6,6aA4-dithiapentalenes (71AHC(13)161, p. 181). Bromination of l,6-dioxa-6aA4-thiapentalene occurs readily and leads to the 3,4-dibromo derivative. With the same compound, iodine and silver acetate give the 3-iodo and the 3,4-diiodo derivatives (72CC1283). 

The Leukart reaction has also been used in the conversion of dehydroepiandro-sterone into 17/3-formylamino-3/3-formyloxyandrost-5-ene, which on reduction with lithium aluminium hydride afforded 3/3-hydroxy-17/3-me thylaminoandrost-5-ene. Acylation with isocaproyl chloride then furnished the N-methyl-N-isocaproyl steroid (197), after selective ester hydrolysis of the initially formed ON-diacyl derivative. The amide (197) was further converted into its 3,5-cyclo-6-ketone via the 3,5-cyclo-6/3-alcohol and thence by reaction with hydrogen bromide into the corresponding 3/3-bromo-5a-6-ketone which upon dehydrobromination furnished a A2-5a-6-ketone and ultimately the 2-monoacetate of the 2/3,3/3-diol (198) after reaction with silver acetate and iodine. Hydrolysis to the 2/3,3/3-diol (198) gave a separable mixture of the 2/3,3/8-dihydroxy-5a- and -5/3-ketones.88... 

Several related procedures for syn hydroxylation of alkenes involve a halohydrin ester (32) as the key intermediate. In Woodward s procedure an alkene in glacial acetic acid is treated with iodine and silver acetate. Acetyl hypoiodite, MeCOjI, formed by reaction of the latter two reagents attacks the alkene, R R 0=CR R in an electrophilic manner, from the less hindered side to give, by overall anti addition. 

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. 

We may also note that acetonium or benzonium bridged ions are intermediates in the hydroxylation of olefinic bonds with iodine and silver acetate or benzoate (see p. 99). 

The Markownikov addition of the elements of water to a cleavamine derivative may also have important application in the synthesis of bisindole alkaloids. Although this appears not to have been achieved, a route to the corresponding derivative of catharanthine has been developed, by use of a modified Prevost reaction. Thus, treatment of catharanthine with iodine and silver acetate in glacial acetic acid afforded an intermediate, which was reduced to the acetate (223) by NaBH4. Although formulated otherwise this acetate must be the 20a -acetate, by reason of its later conversion into vinblastine (q.v.). 

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. 

Woodward cis-hydroxylation. The hydrox-ylation of an olefin with iodine and silver acetate in acetic acid to give cw-glycols. The method involves the trans addition of iodine and silver acetate to give a trans-iodo-acetoxy derivative. The latter is hydrolyzed to a cw-mono-glycol acetate with acetic acid and water. Alkaline hydrolysis results in the final cis-glycol. 

An (iodovinyl)cyclopropane has also been converted to an alkynylcyclopropane by dehydro-iodination. Thus, an EjZ mixture of (l-iodoprop-l-enyl)cyclopropane (5) reacted with potassium /ert-butoxide in dimethyl sulfoxide at room temperature to give a 77% yield of (prop-1-ynyl)cyclopropane (6). The individual isomers were also converted to 6 by treatment with silver acetate in acetic acid, with or without added sodium acetate, but a mixture of products was obtained in which the propynylcyclopropane made up only 16 to 21% of the mixture at > 95% conversion. 

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. 

In contrast to bromination of thebaine (137), which gave 14-bromocodeinone (138 R1 + R2 = O), iodination in methanol-chloroform solution produced the 7-iodo-derivative (141 R1 = H, R2 = I).156 The latter was transformed into the indolinocodeine (147 X = OAc) by treatment with silver acetate in acetic acid, thus offering an alternative route to those derivatives which had been previously prepared by solvolysis of 14-bromocodeine (138 R1 = OH, R2 = H). Similarly, treatment of (141 R = H, R2 = I) with silver cyanide and sodium azide afforded compounds (147 X = NC) and (147 X = N3) respectively. This report should stimulate further investigation of the factors involved in yielding predominantly C(14)- or C(7)-substituted products in electrophilic reactions on thebaine.156... 

Glacial acetic acid is a suitable solvent for use with silver acetate and CC14 or, up to 150°, nitrobenzene for use with silver trifluoroacetate. The Hunsdiecker reaction (see p. 1005) may intervene as competing reaction 377 trifluoroiodo-methane, for example, may be formed when iodine, silver trifluoroacetate, and nitrobenzene are heated in the absence of a substance that can be iodinated CF3COOAg + I2 ------------------------ CF3I + Agl + C02... 

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). ... 

There are limited examples of S Ar displacements of haloindoles. The simplest example is the ipso-displacement of iodine from 3-iodoindole (53) when the latter is treated with silver acetate in acetic acid. 3-Acetoxyindole (54), a valuable intermediate in the synthesis of indoxyl (55), is produced in 28% yield [29]. 

The alkene 11 reacts with electrophiles on the less-hindered (exo) face of the double bond. Thus, catalytic osmium tetroxide andNMO (seeScheme 5.80) or KMn04 provide the exo-cis-diol resulting from approach of the osmium from the more accessible face of the molecule. To prepare the isomeric endo-cis-diol, the Woodward-Prdvost reaction may be used (iodine and silver acetate in the presence of water). In this case, iodine should approach the exo face, but subsequent attack on the exo-iodonium ion by acetate anion would occur from the opposite (endo) face (see Scheme 5.93). Formation and hydrolysis of the cyclic intermediate cation gives the endo-cis-d o. ... 

It is believed that acetyl hyperbromite or hyperiodite is formed as an intermediate when bromine or iodine reacts with silver acetate, giving bromine or iodine cation. Positive iodine has been stabilized via coordination with pyridine. Therefore, a tentative mechanism is illustrated here. 

A particularly interesting approach to the l,6 3,4-dianhydro-D-talopyranose was reported by Matsumoto and coworkers (63). The reaction sequence starts from the allylic alcohol (reduced levoglucosenone), which upon treatment with iodine and silver acetate in acetic acid, followed by heating with water and neutralization with methanolic ammonia, forms two compounds (Scheme 13). 

The hydroxylation of an olefin with iodine and silver acetate in wet acetic acid to give cis-glycols ... 

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