Reduction sulfonate esters

An aiyl methane- or toluenesulfonate ester is stable to reduction with lithium aluminum hydride, to the acidic conditions used for nitration of an aromatic ring (HNO3/HOAC), and to the high temperatures (200-250°) of an Ullman reaction. Aiyl sulfonate esters, formed by reaction of a phenol with a sulfonyl chloride in pyridine or aqueous sodium hydroxide, are cleaved by warming in aqueous sodium hydroxide. ... 

Reduction of iodates by ene-diols. . 100 Reduction of unsaturated acetates. 153 Replacement of a sulfonate ester... 

The importance of reactions with complex, metal hydrides in carbohydrate chemistry is well documented by a vast number of publications that deal mainly with reduction of carbonyl groups, N- and O-acyl functions, lactones, azides, and epoxides, as well as with reactions of sulfonic esters. With rare exceptions, lithium aluminum hydride and lithium, sodium, or potassium borohydride are the... 

Nucleophilic displacement using [ F] fluoride works well in aUphatic systems where reactive haUdes or sulfonates esters can undergo substitution at unhindered sites. In order to introduce a F fluorine atom in a secondary or tertiary position, a two steps strategy was developed. It involves a F-bromofluorination of alkenes, followed by reductive debromination (n-BujSnH, AIBN). [ F]BrF is usually generated in situ from [ F]potassium fluoride and l,3-dibromo-5,5-dimethylhydantoin (DBH) in sulfuric acid. This methodology was successfully applied to label steroids at the 11 and 6a positions [245] (Scheme 60) and to prepare [ F]fluorocyclohexanes [246]. 

Another example of solvolysis of a sulfonate has been described by Buchanan and coworkers 90 it occurs without acid, but utilizes a highly polarizable sulfonic ester group. Solvolysis of methyl 2-0-(p-nitrophenylsulfonyl)-a-D-glucopyranoside (84) in water in the presence of sodium acetate for 6 hours at 100° leads, after reduction of the reaction mixture by means of sodium borohydride, to a fraction identified as 2,5-anhydro-D-mannitol (85). This reaction, which... 

The selectivity of the reduction of methyl a-DL-ald-2-enopyranosid-4-ulose 326 and, consequently, the low availability of the 2,3-unsatu-rated pyranosides of the a-threo (329) configuration, required the inversion of the configuration of C-4 (C-5 in the glyeulopyranosides) for completion of several syntheses. The benzoic acid-diethyl azodicar-boxylate-triphenylphosphine reagent was reported to effect the esterification specifically, with inversion of the configuration the yields were significantly higher than those obtained in the two-step, sulfonic-ester, displacement procedure.229... 

In case (a), labelled secondary alkyl benzenesulfonates (alkyl = 2-adamantyl, 2-propyl, cyclopentyl, etc.) with 18-28% of lsO in the sulfonyl group were partially solvolysed in a range of solvents (SOH), and recovered unreacted alkyl benzenesulfonates were then subject to reductive cleavage of the O—S bond of the sulfonate ester [39]. For water as solvent, the... 

At an early date it was already recognized that the ketone (IX) derived from an oxidation of the C-18 carbinol function of methyl reserpate could be of considerable utility for further transformation of the reserpine pentacyclic ring system, but early attempts at the preparation of the desired compound by conventional oxidation, e.g., by Oppenauer s method, AAchlorosuceinimide, sodium dichromate, or chromic oxide in pyridine, were unsuccessful with both methyl reserpate and methyl 18-epireserpate. The ketone was finally obtained by heating methyl reserpate p-bromobenzene sulfonate with dimethyl sulfoxide in the presence of triethylamine (162), a method successfully used for simpler compounds (163). Subsequently, it was found that this oxidation could also be realized with other benzene sulfonate esters of methyl reserpate and 18-epireserpate. That the stereochemistry of the molecule was unaffected was proved by sodium borohydride reduction of the ketone, which gave equal amounts of methyl reserpate and its 18-epimer. This and other simple reactions of the ketone are sketched in Chart III, and additional observations will be given. 

However, reduction of primary sulfonic esters of D-galactopyrano-sides with lithium aluminum hydride in tetrahydrofmran can also result in formation of deoxy sugars. Heyns and coworkers reduced methyl 3-0-methyl-6-0-p-tolylsulfonyl- 8-D-galactopyranoside in this... 

Lithium aluminum hydride, effect of solvents on reduction of carbohydrate sulfonic esters, 269 Lutease, 380 Luteic acid, fungal, 378 Lyxitol, 1-acetamido-l-deoxy-L-, 170 Lyxofuranose, 5 - acetamido - 5 - deoxy-D-, 171... 

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