Conformational Studies of Acetonated α-<scp>l</scp>-Sorbo- and β-<scp>d</scp>-Fructopyranoses by Means of Proton Magnetic Resonance Spectroscopy

Abstract

Abstract The favored conformations of the pyranose rings of several acetonated α-l-sorbo- and β-d-fructopyranoses have been revealed by proton magnetic resonance spectroscopy. The conformations of the rings of the pyranoses are unchanged by the introduction of 1,2-O- or 1,3-O-isopropylidene groups in α-orientation of l-sorbose, but they are affected by the introduction of the 2,3-O-isopropylidene group. These findings support the fact that 2,3-O-isopropylidene-α-l-sorbopyranose was not obtained by the acetonation of l-sorbose. The rings of diacetonated d-fructopyranoses with a cis-fused acetal ring adopt a distorted conformation; however, those of diacetonated l-sorbopyranoses with a trans-fused acetal ring are only slightly distorted from the stable 1C conformation. Angyal’s anticipation of the difficult acetalation of the trans-glycol of a pyranose has been further experimentally supported.