Iodohydrin

The ready reduction of iodohydrins is utilized in the Cornforth reaction for preparing olefins from epoxides. Here the opening and reduction are carried out in one step by treatment of the epoxide, in an acetic acid-sodium acetate buffer, with sodium iodide and zinc. A less common use of iodohy-drin reduction is illustrated in the synthesis of the diene (127) ... 

A considerable extension of the synthetic utility of the hypoiodite reaction is achieved if the steroid hypoiodite (2) is generated from the alcohol and acetyl hypoiodite and then decomposed in a nonpolar solvent. In this case ionic hydrogen iodide elimination in the 1,5-iodohydrin intermediate (3) is slow, thereby allowing (3) to be converted into an iodo hypoiodite (5). 

No systematic study of the minimal required amount of lead tetraacetate has been made. In cases where the product of the hypoiodite reaction is an iodo ether (20-hydroxy steroids) the reaction can be interrupted at the iodohydrin stage by reducing the amount of iodine to about 0.5 mole. For the oxidation of iodo ethers to lactones, chromium trioxide-sulfuric acid in acetone has been used. Silver chromate is often added to the reaction mixture but comparable yields are obtained without the addition of silver salt. 

Iodine isocyanate, 22 1,5-Iodohydrin formation, 252 21-Iodo-3 -Hydroxypregn-5-en-20-one acetate, 208 W-iodosuccinimide, 209 Isohexylmagnesium bromide, 68... 

The reaction can be applied to simple epoxides if polyhydrogen fluoride-pyridine is the reagent. The epoxide-to-fluorohydrin conversion has also been carried out with Sip4 and a tertiary amine.Chloro-, bromo-, and iodohydrins can also be... 

Magnesium iodide reacts with a,p-epoxy esters to form p-iodo-a-hydroxy esters selectively (200 1). The regioselectivity is attributed to favorable chelation of the iodohydrin. These products are reduced by Bu,SnH to hydroxy esters in 75-95% overall yields with retention of the original configuration at the a-position. 

This reaction also converts 1,2-epoxides into secondary alcohols, possibly via an iodohydrin.2 Examples ... 

Chlorine and bromine can be replaced by iodine by means of alkali iodide, and this is of importance in cases where direct treatment of alcohols with hydriodic acid gives a bad yield or none at all, e.g. in the preparation of ethylene iodohydrin ... 

Iodine was found to be an efficient catalyst for the aziridination of alkenes (Scheme 6) utilizing chloramine-T (A-chloro-A-sodio-p-toluenesulfonamide) as the nitrogen source. For example, when 2 equiv. of styrene (45a) were added to chloramine-T in the presence of a catalytic amount of iodine (10mol%) in a 1 1 solvent mixture of acetonitrile and neutral buffer, the corresponding aziridine (46) was obtained in 91% yield. The reaction proved to work with other acyclic and cyclic alkenes, such as oct-l-ene and cyclohexene. The aziridination of para-substituted styrene derivatives (45b-e) demonstrated that, as expected for an electrophilic addition, electron-rich alkenes reacted faster than electron-poor alkenes. However, with 1 equiv. of I2, mainly iodohydrin (47) was formed. A catalytic cycle has been proposed to account for the fact that only a catalytic amount of iodine is required (Scheme 1) ... 

Another procedure which is useful for the preparation of both bromohydrins and iodohydrins involves in situ generation of the hypohalous acid from NaBr03 and NaI04.39... 

An unusual incorporation of iodine derived from the Na(lO ) used in RuClj/aq. Na(10 )/CCl -CH3CN was noted in the oxidation of the terminal alkene 2-allyl-2,5-dichloro-4-morpholino-cyclopent-4-ene-l,3-dione giving the iodohydrin 5 3,7-dichloro-l-P-hydroxy-3 3-iodomethyl-8-morpholino-2-oxabicyclo[3.3.0]-oct-7-en-6-one and its 3a-epimer. The iodine apparently derives from the formation of or T from the lOj" to which IO is reduced after the RuClj/IO " reaction (Fig. 3.21) [236]. 

Similarly, the oxidation of iodocyclohexane by DMD under a nitrogen-gas atmosphere leads to the iodohydrin and diol as unexpected products (equation 24). The iodohydrin, formed as the major product, clearly reveals that hypoiodous acid (HOI) is generated in situ, which adds to the liberated cyclohexene. Indeed, when methyl iodide (Mel) is oxidized by DMD at subambient temperature in the presence of cyclohexene, the corresponding iodohydrin is obtained in very good yield The latter method may be utilized for the preparation of allylic alcohols with a vinylic iodo functional group from allenes (equation 25) . ... 

Electrophilic addition to 9-vinylcarbazole occurs in the Markovnikov sense, thus hydrogen chloride,hydrogen bromide,chlorine, and bromine in carbon tetrachloride, and iodine chloride in pyridine are recorded as adding with initial electrophilic attack at the methylene. Mercuric acetate in methanol gave 9-(2-acetoxymercuri-l-methoxyethyl)carbazole. Although 9-vinylcarbazole gave an iodohydrin, comparable reaction with methanolic sodium hypochlorite led to 9-(2-chlorovinyl)carbazole. Catalytic reduction of the latter produced 9-(2-chloroethyl)carbazole. Tri-phenyltin hydride gave 96. ... 

An interesting example exists of variation of diastereoselectivity, due both to the nature and sense of chirality of the electrophile, and to the configuration of the 2-pyrrolidinemethanol auxiliary6. Thus, the use of epoxide 16 as electrophile leads to an unexpected reversal of the diastereoselectivity relative to that observed when the corresponding O-protected iodohydrin 10 is employed. Both of the electrophiles are chiral and therefore reaction of each with the enantiomers of 1-(l-oxopropyl)-2-pyrrolidinemethanol leads to different diastereoselectivities due to the fact that there is a matched and a mismatched pair of reactions. 

Fe(CO)5,29B TiCI3-LiA H4,2W FeCI -BuLi,300 the tungsten reagents mentioned in 7-21,265 and Nal-NaOAc-Zn-AcOH.301 The last-mentioned method is actually a variation of 7-31, since iodohydrins are intermediates. Some of these methods give syn elimination. 

The conversion can be formulated as occurring through substitution at Ci by the lla-alkoxy radical to give the iodohydrin (27), which undergoes a /3-elimination to furnish 28. 

Deoxygenation of epoxidesEpoxides are converted to alkenes with retention of configuration by treatment with this combination in hexane at 0 -> 25°. The reaction involves anti-opening of the epoxide to an iodohydrin, which undergoes trans-elimination to an alkcnc. 

Since the reaction of I2 + H20 with alkenes is an equilibrium process, the use of oxidizing agents allows one to shift the equilibrium by oxidizing the I-formed.148 149 Substituted cyclohexenes can be converted to iodohydrins in regio-selective and stereoselective maimer with I2 and pyridinium dichromate.149 High yields of iodohydrins may be achieved by reacting alkenes with iodine in the presence of moist tetramethylene sulfone—CHCI3.150... 

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