Branched-chain sugars. Part 9. Characterisation of the stereoisomeric methyl 3-deoxy-3-C-methyl-3-nitropentopyranosides resulting from the condensation of nitroethane with L′-methoxydiglycolaldehyde and the X-ray crystal structure of methyl 2,4-di-O-acetyl-3-deoxy-3-C-methyl-3-nitro-β-D-xylopyranoside

Abstract

Base-catalysed cyclisation of the ‘dialdehyde’(7)(obtained on periodate oxidation of methyl β-D-xylopyranoside) with nitroethane gave, after acetylation, a mixture containing five of the eight possible methyl 2,4-di-O-acetyl-3-deoxy-3-C-methyl-3-nitropentopyranosides. The solvolytic behaviour of the corresponding methyl 3-acetamido-3-deoxy-2,4-di-O-methanesulphonyl-3-C-methylpentopyranosides [e.g. (17) and (22)] and interconversions between the stereoisomers, by way of the monosulphonates (24) and (25), revealed that four of the stereoisomers formed in the nitroethane condensation possess α-L-lyxo, α-L-xylo, β-D-xylo, and α-L-arabino configurations. The crystal structure of methyl 2,4-di-O-acetyl-3-deoxy-3-C-methyl-3-nitro-β-D-xylopyranoside (8) is reported.