Oxidation of Sulfur Atoms the MacDonald-Fischer Degradation

Oxidation of Sulfur Atoms The MacDonald-Fischer Degradation 

174 and 175, and they prepared three, isomeric disulfoxides from D-galactose dibenzyl dithioacetal. In contrast with the parent dithio-acetals, the monosulfoxides are weakly basic, and the latter undergo rapid disproportionation in the presence of dilute mineral acid to liberate the aldose plus a disulfide the disulfoxides derived from D-galactose are acid-stable, but undergo a base-catalyzed, retroaldol type of reaction to afford bis(benzylsulfinyl)methane and D-lyxose.321 

MacDonald and H. O. L. Fischer372 oxidized D-glucose diethyl dithioacetal pentaacetate (24) and its D-manno isomer with mono-peroxyphthalic acid in ether, isolating not the epimeric disulfones but a common product, to which they assigned the structure 3,4,5,6-tetra- O - acetyl -1,2- dideoxy-1,1 -bis (ethylsulfonyl)-D-arabtno-hex-1-enitol (176). Ammonolysis of 176 and reacetylation afforded 177, which was also prepared by oxidation of 2-acetamido-3,4,5,6-tetra-0-acetyl-2-deoxy-D-glucose diethyl dithioacetal, whereas the action of hydrazine in methanol on 176 produced a retroaldol reaction (and saponification) affording D-arabinose (179, 40% yield) and bis(ethyl-sulfonyl)methane (178). The latter reaction accords with earlier ob- 

Hough and Richardson390 proposed that the loss of 178 from the 2,6-anhydro disulfone 189 occurs by dissociation of the C-l-C-2 bond to give the oxonium ion 190, which would be expected to adopt a conformation approximating the half-chair form illustrated, plus the bis(alkylsulfonyl)methyl anion, which subsequently react with solvent to yield D-lyxose and 178, respectively. In accord391 with this rationalization, (a) the C-methyl homologue (191) of 189 is not de- 

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