Sodium borohydride sulfonates

Ueno and coworkers49 have developed a procedure for the synthesis of chiral sulfinic acids. Treatment of (R)-( + )-23 with disulfide 24 and tributylphosphine in THF gave (S)-( — )-25. Compound 25 was oxidized with potassium permanganate to the sulfone, which was then reduced to the sulfinic acid, (S)-( — )-26, by treatment with sodium borohydride. Conversion of 26 or an analog to an ester would lead to diastereomers. If these epimers could be separated, then they would offer a path to homochiral sulfoxides with stereogenic carbon and sulfur atoms. 

SRP [Sulfonation-Reduction-Peroxide] A pulp-bleaching process which combines reduction with sodium borohydride and oxidation with hydrogen peroxide. Developed by Atochem in 1991 and licensed to Morton International, Chicago. 

Japanese workers have also displaced a methyl sulfone group with a variety of nucleophiles. Thus they were able to introduce, ethoxy, thiophenyl, aniline, and malonic acid groups in to the pyridine A -oxide derivative (105). Acid hydrolysis produced the 2-one compound, while reduction with sodium borohydride cleaved off the methylsulfone group <87CPB1030>. 

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... 

Potassium triethylborohydride, 260 Sodium borohydride, 21 Ring-forming reactions 2,2 -Dihydroxy-1,1 -binaphthyl, 113 Other asymmetric reactions Camphor-10-sulfonic acid, 62 Di-jjL-chlorobis(l,5-cyclooctadiene)di-rhodium-2,3-0-Isopropylidene-2,3-dihydroxy-1,4-bis(diphenyl-phosphine)butane, 153... 

Reduction of halides and sulfonates.2 Sodium borohydride effects this reaction under phase-transfer conditions (aqueous C6H5CH3 or CH2C12). The more lipophilic salts hexadecyltributylphosphonium bromide or tetraoctylammonium bromide are the most effective catalysts. 

Desulfonylation homoallylic alcohols.24 Allyl sulfones (2), prepared as shown, undergo desulfonylation by sodium borohydride in the presence of catalytic amounts of Pd(0). This reaction was used to prepare homoallylic alcohols (3) from allylic p-tolyl sulfones (1). 

Hydroxylamine-O-sulfonic acid Pyridinium bromide perbromide Sodium borohydride Butyl lithium... 

Treatment of halides or sulfonates with hydride donors such as tetrabutylammonium borohydride,38 lithium aluminium hydride,39 lithium triethylborohydride46 or sodium borohydride generate deoxy sugar derivatives (Scheme 3.8c).41 When sodium borohydride is employed, a transition metal catalyst (PdCk or NiC-b) may be added. 

Next step of this synthesis consisted in the conversion of alcohol (17) to pisiferic acid (1) and this has been described in Fig. (3). The alcohol (17) in hexane was treated with Pb(OAc)4 in presence of iodine at room temperature to obtain the epoxy triene (19) (51%) whose structure was confirmed by spectroscopy. Treatment of (19) with acetyl p-toluene-sulfonic in dichloromethane yielded an olefinic acetate (20) and this was hydrogenated to obtain (21). The compound (22) could be isolated from (21) on subjection to reduction, oxidation and esterification respectively. The conversion of (22) to (23) was accomplished in three steps (reduction with sodium borohydride, immediate dehydration in dichloromethane and catalytic hydrogenation). Demethylation of (23) with anhydrous aluminium bromide and ethanethiol at room temperature produced pisiferic acid (1). Similar treatment of (23) with aluminium chloride and ethanethiol in dichloromethane yielded methylpisiferate (3). 

Several replacement reactions at C-4 in sydnones may be carried out but aqueous bases must be avoided. Butyllithium can be used to displace bromine from a 3-phenylsydnone the resulting organolithium salt can be carbonylated, will add to ketones, and forms a silyl derivative (80CB1830). A sydnone Grignard derivative can also be made and will add ketones in the normal way (80JCS(Pl)20). Sodium borohydride will reduce a sydnone sulfone, formed by oxidation of a thioether (Table 5) with hydrogen peroxide, back to the unsubstituted sydnone (74T409). 

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. 

Epoxidadon of (Z)-vinyl sulfone, which is available from the Peterson olefination of (S)-O-pentylideneglyceraldehyde and phenyl trimethylsilylmethyl sulfone in three steps (40% overall yield), with f-BuOOH/t-BuOK in THE gives epoxy sulfone (eq 2). Deprotection of the ketal group and recrystallization affords an optically pure epoxy diol, which is then treated with sodium periodate followed by sodium borohydride to give an alcohol. Protection of the resulting alcohol as its silyl ether yields l/ ,25)-l-phenylsulfonyl-2- [ fcrf-butyldiphenyl)silyl]oxymethyl oxirane ). Its enantiomer is available in the same manner starting from / )-isopropylideneglyceraldehyde. ... 

Reduction of tertiary kaiides. Tertiary halides are reduced to hydrocarbons by. sodium borohydride in tetramethyicne sulfone (sulfolane, 1, 1144-1145 2, 402 -403). The reaction proceeds by way of elimination, hydroboration, and protonolysis. Halides... 

Sodium borohydride reduction offers a significant advantage in synthetic applications. The method allows the reductive removal of halides selectively without affecting other functional groups, such as ester, carboxylic acid, nitrile and sulfone. A typical chemoselective dehalogenation is illustrated in Scheme 19. ... 

Raney nickel is a stronger desulfurizing agent than nickel boride. On the other hand nickel boride, prepared from nickel(II) chloride and sodium borohydride, is more selective since it does not desulfurize aromatic sulfones. An example of such selectivity is desulfurization of p-phenylsulfonylphenyl p-tolyl sulfide (33), which affords diphenyl sulfone in 91% yield and toluene in 84% yield. In contrast. Raney nickel desulfurizes both the sulfide and the sulfone giving a mixture of benzene and toluene (equation 82). 5... 

Qy chemical transfonnation. 3-Thletanol 14-dtoxide, whidb Gontaine an hydroxyl group, can be converted to 8-chlorothietane Ll-dioxide by thionyl chloride in the presence of pyridine or, better, of 2,4,B-ooUidine. On treatment with triedi ainine in benzene at 40 c. dua derivative loses hydroohlcrio add to form thiete sulfone, whi< in turn b reduced by sodium borohydride into tiuetane 1,1-... 

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