Both 'H-and 13C-n.m.r. spectroscopy have been employed in structural studies of the 4,6-O-benzylidene-D-aldohexopyranosides and derivatives, including some deoxy sugars .
I4 We now report i3C-n.m.r. data (Table I) for the 4,6-O-benzylidene derivatives of methyl 2-deoxy-( 2) 2-deoxy-3-O-methyl-(3), 3-deoxy-(4) and 3-deoxy-2-O-methyl-/I-o-ar&ino-hexopyranoside (!I), methyl 3-deoxy-(9) and 3-deoxy-2-O-methyl-c-oarabino-hexopyranoside (lo), methyl 2-deoxy-(6) and 2-deoxy-3-O-methyl-B-o++&hexopyranoside (7), and methyl 3-deoxy-2-O-methyl-(8) and 2-deoxy-3-O-methyl-a-Dribo-hexopyranoside (11). The signals for C-1 in l-l 1 appear downfield of all other ring-carbon signals. The equatorial MeO-1 groups resonated at -57 p.p.m., and axial MeO-1 at -55 p.p.m., as expected4. Furthermore, the C-2 resonances in l-3,6,7, and 11 and the C-3 resonances in 4,5, and 8-10 were at substantially higher field than those of the other ring carbons. Selective 'H-spin-decoupling and off-resonance experiments were used for some compounds. For example, the '3C-n.m.r. spectrum of the 2-deoxy-/?-D-urabino-hexopyranoside (2) contained four signals at lowest field due to the phenyl group [137.2 (quaternary), 129%@), 128.9 and 126.8 p.p.m. (o and m)] with little or no change in the positions of these signals throughout the series. Selective irradiation of H-7 confirmed that the signal at 101.9 p.p.m. was due to C-7. The signal at 101.3 p.p.m. was assigned to C-l following selective irradiation of H-l. Likewise, the signals at 38.6,68.1,83.2, and 66.3 p.p_m. were assigned to C-2, C-3, C-4, and C-5, respectively. Finally, the offresonance spectrum showed that the signal at 56.9 p.p.m_ was due to Me0 and that at 68.8 p.p.m. to C-6. Methyl 3,4,6-tri-O-acetyl-2-deoxy-B_D-arabino-hexopyranoside (1) and methyl 4,6-O-benzylidene-3-deoxy-&-D-~~~~~~~-hexopyranoside (9) were subjected to X-ray crystallography. Perspective views of the molecules and the numbering are given in Figs. 1 and 2. As expected', the pyranose ring in 1 and the dioxane and pyranose rings in 9 are in chair conformations.