ChemInform Abstract: CONFORMATION OF SOME ANOMERIC O‐BENZYLATED D‐GLUCO‐, L‐IDO‐, AND HEX‐4‐ENOPYRANOSIDE DERIVATIVES

Abstract

By use of 1H-NMR. spectroscopy it is shown that in the anomeric tri-O-benzyl derivatives of D-gluco- and L-idopyranosides the C(5) (aliphatic) substituent has a strong tendency to assume an equatorial position. The conformer (4C1 or 1C4) with C(6) in equatorial position is favoured, even if other bulky substituents are forced to occupy an axial position; the same effect is observed in some anomeric O-benzylated 6-deoxy-L-idopyranoside derivatives. If, however, the tetragonal configuration of the saturated C(5) is changed into a trigonal (sp2) configuration, e.g. in the anomers of 1,2,3-tri-O-benzylated L-threo-hex-4-enopyranosiduronates, the C(5)–C(6) bond no longer determines the equilibrium of (distorted) pyranoid conformations; the anomeric (‘Eduard-Lemieux’) effect then becomes important in the stabilization of the corresponding half-chair (1H2 or 2H1) conformations.