CONFORMATIONAL STUDIES ON PYRANOID SUGAR DERIVATIVES . CONFORMATIONAL EQUILIBRIA OF BETA-D-RIBOPYRANOSE TETRAACETATE AND BETA-D-XYLOPYRANOSE TETRAACETATE

β-d-Ribopyranose tetraacetate (1) has been shown to exist, in acetone-d6 at room temperature, as a 9:11 mixture of the 1C (d) and C1 (d) conformers in rapid equilibrium. The rate of chair-chair interconversion at -60° is 130 times per second. At -84°, a temperature at which n.m.r. spectral signals of the two separate conformers can be observed, the ratio of the 1C (d) to C1 (d) conformers is 2:1. For β-d-xylopyranose tetraacetate (2), in acetone-d6 at room temperature, the all-axial, 1C (d) conformer exists in equilibrium with the all-equatorial, C1 (d) conformer to the extent of 1 part in 5. At -84°, the 1C (d) conformer was not detected. © 1969.