Synthesis of DL-chalcose from acrolein dimer

Abstract

1,6:2,3-Dianhydro-4-deoxy-β-DL-ribo-hexopyranose (1), a product obtained from acrolein dimer (3,4-dihydro-2H-pyran-2-carboxaldehyde), has been converted to 1,6-anhydro-4-deoxy-3-O-methyl-β-DL-xylo-hexopyranose (2) by reaction with acidic methanol or sodium methoxide in methanol. The structure and conformation of 2 have been confirmed by nuclear magnetic resonance spectroscopy. The reaction of 2 with methanol in the presence of Amberlite IR-120 (H+) gave a 2:1 mixture of the α and β isomers of methyl 4-deoxy-3-O-methyl-DL-xylo-hexopyranoside (3) from which the individual α and β isomers of the di-p-nitrobenzoates could be obtained as crystalline solids. Conversion of 3 to the corresponding di-O-p-toluenesulfonates 4, followed by selective reduction of these diesters with LiAlH4 gave a mixture of the α and β isomers of methyl 4,6-dideoxy-3-O-methyl-2-O-p-toluenesulfonyl-DL-xylo-hexopyranoside (5). Reaction of 5 with sodium methoxide in methanol gave a 2:1 mixture of the α and β isomers of methyl 4,6-dideoxy-3-O-methyl-DL-xylo-hexopyranoside (6) (methyl DL-chalcoside) from which only the α isomer could be separated in pure form by column chromatography or gas–liquid chromatography. The α isomer, 6-α, upon acid-catalyzed hydrolysis in aqueous dioxane, gave a mixture of the α and β isomers of 4,6-dideoxy-3-O-methyl-DL-xylo-hexopy-ranose (DL-chalcose) which gave the same nuclear magnetic resonance spectrum in D2O as did authentic D-chalcose. Yields are good to excellent in the various steps from 1 on.