E versus Z geometry in beta-D-arabino-hexopyranosidulose oximes.
Koenigs-Knorr-type glycosidations of peracylated 2Z-benzoyloxyimino-glycopyranosyl bromides invariably proceed with retention of the Z-geometry. Accordingly, the many beta-D-hexosidulose oximes in literature which were prepared in this way and for which the oxime geometry has not been addressed explicitly, are the Z-oximes throughout. By contrast, oximation of beta-D-hexopyranosid-2-uloses leads to mixtures of E and Z oximes readily separable and structurally verifiable by (1)H and (13)C NMR. Configurational assignments rested on comparative evaluation of NMR data of E and Z isomers, and, most notably on an X-ray structural analysis of the pivaloylated isopropyl 2E-benzoyloxyimino-2-deoxy-beta-D-arabino-hexopyranoside revealing the unusual (1)S(5)<==>(1,4)B conformation for the pyranoid ring.
Lergenmüller
Matthias
M
Clemes-Schöpf-Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, D-64287 Darmstadt, Germany.
Kläres
Ulrich
U
Lichtenthaler
Frieder W
FW
D009682:Magnetic Resonance Spectroscopy; D010091:Oximes / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
D010091:Oximes