Reductive desulphuration

Reaction of benzylideneaniline with optically active methyl p-tolyl sulphoxide 449 in the presence of lithium diethylamide produces the corresponding jS-anilinosulphoxide 450 with 100% asymmetric induction. Its reductive desulphurization with Raney nickel leads to the enantiomerically pure amine 451524 (equation 270). When the same optically active... 

The first study into the use of 6% sodium amalgam in refluxing ethanol for the reductive desulphurization of sulphones was reported116 in 1952. Methyl phenyl sulphone gave an... 

Starting from dihydrothiopyrans 2 and 3, the key intermediate 5 was prepared, from which the Cjg-JH (7) was synthesised by reductive desulphuration. 

Acid-catalysed cyclization of (246) (c/. Vol. 4, p. 5) yields cis- and trans lAl) together with some (248) cf. Vol. 6, p. 32) from which the more stable c/s-(247) may be readily obtained reductive desulphurization of cis-and trans-i Al) gives cis-and rran5-tetrahydroactinidiolide respectively, whereas thermal desulphurization gives (243). The structure of gentiocrucine (Vol. 6, p. 47) has been confirmed by synthesis. 

The products obtained by the action of peracids upon 3-alkoxy-3,5-dienes are dependent upon the reaction conditions. Aqueous organic solvents and the gradual addition of peracid favour the formation of 6 -hydroxy-4-en-3-one, but when an excess of peracid is added in one portion the product, obtainable in high yield, is the unsaturated aldehyde-ester (393) which has also been obtained (as ethyl ester) by photochemical oxidation of the oxathian (394) followed by a reductive desulphuration. In non-polar solvents a 1 1 adduct (395) is formed between m-chloroperbenzoic acid and 3-acetoxy-3,5-dienes which is sufficiently stable (in the presence of a 17-ketone function) to be isolated and acetylated to the 6 -acetate or oxidised by chromium trioxide in pyridine to the b-ketone. ... 

An extremely pleasing example of reductive desulphurization is the synthesis of [2]-staffane, wherein lithium in ethylamine is employed as the reducing agent (equation 32) . Finally, an example of the use of radical chemistry for the conversion of an alcohol to an alkane via a sulphide intermediate has been reported (equation 33). ... 

A popular two-step protocol for the deoxygenation of carbonyl compounds is the Mozingo reaction in which the aldehyde or ketone is transformed to a dithioacetal in the presence of a Lewis acid and then reductive desulphurization is carried out with Raney The reaction is mild, efficient and particularly convenient for small-scale... 

Dithioacetals can also be desulphurized under radical conditions using tributyltin hydride (TBTH) (equation 65) or by using metal-ammonia solutions (equation 66). Lithium aluminium hydride has also been used in some cases for reductive desulphurization. In a manner analogous to the preparation of dithioacetals, ketones can be transformed to diselenoacetals with aryl or alkyl selenol. These in turn have been reduced with Raney or Li-EtNH2 and under radical conditions with TBTH or... 

The synthesis of 2-acetamido-1,6-anhydro-2,3-dideoxy-B-D-rlbo-hexopyranose from a 3-thlo-sugar by reductive desulphurization is covered in Chapter 9. Reduction (NaBH ) of secondary mesylates with a vicinally related trans-dlallylamlno group proceeds to give deoxygenated products via aziridinium ion intermediates, sequence, sometimes the product is that of amino migration examples are detailed in Chapter 9. 

Dideoxy-sucrose has been synthesized reglospecifically from sucrose by synthesis (2,2 -dipyridyldisulphide-Ph P) and reductive desulphurization (Raney Ni) of 6,6 -dldeoxy-6,6 -bis(2-pyridylthlo)... 

As mentioned before [14c], the use of 3-pentanone as nucleophiles in the direct aldol reaction with aldehydes failed. As an alternative, tetrahydro-4/f-thiopyran-4-one (14) can be used to give mainly the expected products anti-15 (Scheme 4.5), giving after reductive desulphurization using Raney nickel (W-2), the corresponding 5-hydroxy-4-methylpentanone [27]. 

The use of //-(benzoylthiomethyl)piperidine hydrochloride (12) as a reagent for introducing a mercaptomethyl group into an active-methylene position has been demonstrated dimedone gives (13). A-Methylation of sulphonamides is the net result of mercaptomethylation in this way followed by reductive desulphurization using Raney nickel. ... 

Anion radicals of benzo-2,l,3-thia(and selena)diazole have been produced by metal reduction in several solvents at low temperatures, and their electron spin resonance has been studied. The reductive desulphurization of substituted benzo-2,l,3-thiadiazoles by stannous chloride in concentrated hydrochloric acid gives o-phenylenediamines in 80—90% yields. The stability of the heterocyclics against reduction increases with the number of chlorine substituents. ... 

The reductive desulphurization of a cyclic sulphonic ester plays a primary role in a stereospecific synthesis of /3-santalene (Scheme 164). 

TTie synthesis of 2 .3 -dldea7 ucleosides continues to attract attention. The synthon (44) has been used to give p-selective condensation with silylated bases reductive desulphurization then gave 2 ,3 -dideoxy systems.73 Deojqrgenation procedures have been used to prepare 2, 3 -dideoxy- and 2. 3 -dldeojqrdidehydro nucleosides of 2-substituted adeninesJ4.75 pyrrolol2.3-dl pyrimidines (42. R=H),56.71 and further pyrazolo(3.4-d]pyrimidlnes.59 Enzymic... 

An efficient method for the deoxygenation of protected keto-sugars to give deoxy-sugars involved treatment with phosphorus pentasulphide in pyridine and reductive desulphurization of the products, whose nature varied with the... 

A new, three-step synthesis of 1-deoxy-D-fructose (27% overall yield) is based on reductive desulphurization of 2-amino-2-deoxy-D-glucose diethyl dithioacetal to give 2-amino-l,2-dideoxy-D-glucitol, which was oxidatively deaminated using... 

L-3-(3-Deoxy-l,2 5,6-di-0-isopropylidene-a-D-allofuranos-3-yl)alanine (290) (R = R = H) has been synthesized by a route that involved the addition of the carbanion derived from methyl (methylthio)methyl sulphoxide to 3-C-cyano-methyl-3-deoxy-l,2 5,6-di-0-isopropylidene-a-D-allofuranose. Subsequent treatment of the resulting (glycosyl)enamino sulphoxide with acetic anhydride, base-catalysed ester-exchange, and reductive desulphurization afforded the A-acetyl-3-(glycos-3-yl)alanate (290) (R = Ac R = Me), which was hydrolysed to (290) (R = R = H) with base. 

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