D‐Ribose, D‐xylose and some of their glycosylamine derivatives. A 300‐MHz ¹H‐NMR study

The 1 H‐n.m.r. parameters of the major tautomers of D‐xylose and D‐ribose have been determined, and the conformational features are discussed. α‐ And β‐D‐ribopyranose dissolve in D 2 O to give a conformational mixture of 4 C 1 and 1 C 4 forms; the 4 C 1 form accounts for 40% of the former and for 70% of the latter. β‐D‐Ribo‐, and β‐D‐xylopyranosylamines have been synthesized and their 1 H‐n.m.r. parameters suggest 4 C 1 to be the unique conformation in D 2 O. Some N‐aryl‐D‐glycopyranopyramines derived from these pentoses were also prepared and, at variance with literature proposals, the chair form having an equatorial anomeric substituent is the preferred conformer throughout the series.