Formation of 3,6-anhydro-4,5-O-isopropylidene-D-allose dimethyl acetal in the methanolysis of 1,2: 5,6-di-O-isopropylidene-3-O-p-tolylsulphonyl-α-D-glucofuranose. Synthesis of 3,6-anhydro-D-allose
The acid-catalysed methanolysis of 1,2:5,6-di-O-isopropylidene-3-O-p-tolylsulphonyl-α-D-glucofuranose yields principally methyl 3-O-p-tolylsulphonyl-α- and -β-D-glucopyranosides, together with a minor amount of 3,6-anhydro-4,5-O-isopropylidene-D-allose dimethyl acetal (VI). Under the same conditions, 1,2-O-isopropyl-idene-5-O-methyl-3-O-p-tolylsulphonyl-α-D-glucofuranose yields 3,6-anhydro-5-O-methyl-D-allose dimethyl acetal in good yield.
3,6-Anhydro-D-allose (IV) and 3,6-anhydro-5-O-methyl-D-allose (V) have been prepared by hydrolysis of the above derivatives and have been found to exist in aqueous solution in aldehydo, aldehydrol (i.e. hydrated aldehyde), and dimeric forms.