Reduction of vicinal diol esters

Disulfonate esters of vicinal diols sometimes undergo reductive elimination on treatment with sodium iodide in acetone at elevated temperature and pressure (usually l(X)-200°). This reaction derived from sugar chemistry has been used occasionally with steroids, principally in the elimination of 2,3-dihy-droxysapogenin mesylates. The stereochemistry of the substituents and ring junction is important, as illustrated in the formation of the A -olefins (133) and (134). 

The acetates of vicinal diols undergo reductive elimination on treatment with metal-ammonia yields of olefin are only significant if one ester is tertiary and the arrangement is tran -diaxial. ... 

The di-O-tosylates (prepared by action of tosyl chloride in pyridine) are reduced with zinc (Nal/Zn route e Tipson-Cohen reaction) [13]. Cyclic ortho-esters (prepared by reaction of the diol with ethyl orthoformate) are transformed into olefins by simple heating in the presence of acids (Eastwood reaction, route b) [14]. Cyclic thiocarbonates (obtained by reaction of a diol with thiophosgene or (V,(V -thiocarbonyl-di-imidazole) are reduced to olefin with trimethyl phosphite (Corey-Winter method, route c) [15]. Finally, reduction of vicinal di-xanthates with tri- -butyltin hydride according to the Barton procedure [16] affords olefins via a reductive elimination process route a). The Corey-Winter, Garegg, and Tipson-Cohen methods are most commonly applied for deoxygenation of sugar diols. 

In Situ Generation of lodotrimethylsilane. Of the published methods used to form TMSI in situ, the most convenient involves the use of TMSCl with Nal in acetonitrile. This method has been used for a variety of synthetic transformations, including cleavage of phosphonate esters (eq 23), conversion of vicinal diols to alkenes (eq 2A), and reductive removal of epoxides (eq 25). ... 

The Corey-Winter reaction provides a useful method for the preparation of olefins that are not accessible by other routes. For instance it may be used for the synthesis of sterically crowded targets, since the initial attack of phosphorus at the sulfur takes place quite distantly from sterically demanding groups that might be present in the substrate molecule. Moreover the required vicinal diols are easily accessible, e.g. by the carbon-carbon bond forming acyloin ester condensation followed by a reductive step. By such a route the twistene 10 has been synthesized ... 

Acyloins were converted to mixtures of stereoisomeric vicinal diols by catalytic hydrogenation over copper chromite [972]. More frequently they were reduced to ketones by zinc (yield 77%) [913, 914], by zinc amalgam (yields 50-60%) [975], by tin (yields 86-92%) [173], or by hydriodic acid by refluxing with 47% hydriodic acid in glacial acetic acid (yields 70-90%) [916], or by treatment with red phosphorus and iodine in carbon disulfide at room temperature (yields 80-90%) [917] Procedure 41, p. 215). Since acyloins are readily accessible by reductive condensation of esters (p. 152) the above reductions provide a very good route to ketones and the best route to macro-cyclic ketones [973]. 

A MOM ether can be introduced onto the more sterically hindered alcohol of a vicinal diol via the regioselective reductive cleavage of the intermediate ortho-ester prepared in situ from the diol and trimethyl orthoformate [Scheme 4.258].477 478 Regioselectivities of >30 1 are typical. 

A novel dimethyl ester -lactone from Dammar resin has been shown to have the structure (210) by AT-ray analysis. A very probable biogenesis from asiatic acid [(211)— (212) (210)] has been suggested. Madasiatic acid (213), a close relative of asiatic and madecassic acids, has been isolated from Centella asiatica Protection of the vicinal diol system, followed by oxidation to the 6-ketone and Wolff-Kishner reduction yielded 2o,3)5-dihydroxyurs-12-en-28-oic acid. Rubitic... 

Oxyamination of olefins. This reagent reacts with a variety of olefins to give, after reductive cleavage of intermediate osmate esters, cis-vicinal amino alcohols in fair to high yield. The reaction is regiospecific in that the new C—N bond is formed at the least substituted carbon atom of the olefin. The reagent reacts more rapidly with monosubstituted olefins than with di- and trisubstituted olefins. Diols are obtained as the main products from hindered olefins. Methylene chloride or THF can be used as solvents, but pyridine is the solvent of choice. 

Chiral cyanohydrins serve as the alcohol moieties of several commercial pyre-throid insecticides (see below) [1527]. Hydrolysis or alcoholysis of the nitrile group affords chiral a-hydroxyacids or -esters and Grignard reactions provide acyloins [1528], which in turn can be reduced to give vicinal diols [1529], Alternatively, the cyanohydrins can be subjected to reductive amination to afford chiral ethanol-amines [1530]. a-Aminonitriles as well as aziridines are obtained via the corresponding a-sulfonyloxy nitriles [1531]. 

Methanesulfonates. The most common use of methanesulfonyl chloride is for the synthesis of sulfonate esters from alcohols. This can be readily accomplished by treatment of an alcohol with mesyl chloride in the presence of a base (usually Triethy-lamine or Pyridine). The methanesulfonates formed are functional equivalents of halides. As such they are frequently employed as intermediates for reactions such as displacements, eliminations, reductions, and rearrangements. Selective mesylation of a vicinal diol is a common method of preparation of epoxides." Alkynyl mesylates can be used for the synthesis of trimethylsilyl allenes. Oxime mesylates undergo a Beckmann rearrangement upon treatment with a Lewis acid. Aromatic mesylates have been used as substrates for nucleophilic aromatic substitution. Mesylates are more reactive than tosylates toward nucleophilic substitution, but less reactive toward solvolysis. 

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