Application of vicinal carbon-proton coupling constants to the conformational analysis of benzylidene-type acetals of 1,6-anhydro-β-d-hexopyranoses

Three 1,6-anhydro-β-D-glycopyranose derivatives

“…These differences can be explained by the dissimilar participation of the O atoms in the hydrogen bonding and by the conformation of the O4R group in (I) and (II), trans to C3 versus gauche, respectively [H41/ C7ÐO4ÐC4ÐC3 = 167 (3) in (I) and 87.1 (3) in (II)]. Furthermore, the greatest differences between (I) and the previously reported analogue 4-O-acetyl-1,6-anhydro-2,3-O-(S)-benzylidene--d-mannopyranose [Cano et al, 1986;Cambridge Structural Database (CSD;Allen & Kennard, 1993) reference FOJMEW] are for the bond distances and angles around O4, where the hydroxyl group is protected with an acetyl one. Similar features are found between (III) and 2-O-acetyl-1,6-anhydro-3,4-O-(S)-benzylidene--d-galactopyranose (Cano et al, 1986;CSD reference FOJLUL).…”