Glycosylated cardenolides. VI. Ribosides of strophanthidin and digitoxigenin
Partial syntheses of ribosides of strophanthidin (I) and digitoxigenin (II) have been carried out by the orthoester method [i] by analogy with previous work [2]. 3,4-Di-O-acetyl~-D-ribopyranose 1,2-(methyl orthoacetate) (III) was obtained by the method of Mazurek and Perlin [3]. The orthoester (III), Cz2H~,Os, had mp 82-84°C (from diethyl ether--petroleum ether), [~]~4 --7.7 _+ 2 ° (c 1.78; chloroform). NMR spectrum (CDCI3), ppm: 1.75 (3 H at CH3, s), 2.10 (6 H at 2 Ac, s), 3.28 (3 H at OCH~, s). The NMR spectrum shows the exo position of the OCH3 group in compound (III) [3, 4].
SYNTHESIS OF β-D-MANNOSE 1,2-ORTHOACETATES
Synthesis of 3,4,6-tri-O-acetyl-β-D-mannopyranose 1,2-orthoacetates (I) from 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide (II) and various alcohols in the presence of pyridine and substituted pyridines is described. 2,6-Lutidine is a particularly effective acid acceptor in these condensations, and the use of chloroform as a diluent is advantageous. The lutidine-buffered system has afforded a good yield of orthoacetate (I) with several alcohols that barely react with II in the presence of silver ion; this difference is attributed to the dominance of side reactions under the latter conditions. The N-bases also promote a more highly stereoselective orthoester synthesis than does the silver-catalyzed reaction, leading to formation of the OR-exo-diastereoisomer almost exclusively.
Women writers of traditional china :an anthology of poetry and criticism
Editorial conventions Abbreviations Maps Introduction: genealogy and titles of the female poet Part I. Poetry: 1. From ancient times to the six dynasties (222-589) 2. Tang (618-907) and five dynasties (907-60) 3. Song dynasty (960-1279 4. Yuan dynasty (1264-1368) 5. Ming dynasty (1368-1644 6. Qing dynasty (1644-1911) Part II. Criticism: 7. Female critics and poets 8. Male critics and poets Appendixes Notes Bibliography Index of names.