ORGANOFLUORINE COMPOUNDS AND FLUORINATING AGENTS .14. THERMOTROPIC LIQUID-CRYSTALLINE GLYCOSYL FLUORIDES

The liquid crystalline 6-O-alkyl-alpha-D-galactopyranosyl fluorides (3 a-f) and the mesogenic 6-O-dodecyl-alpha-D-glucopyranosyl fluoride (7) were prepared from the homologous ,4-di-O-isopropylidene-alpha-D-gala cto-pyranosides (1a-f) and from the methyl 2,3,4-tri-O-benzyl-glucopyr anoside (4), respectively, in two and three steps. The fluorinations o f 1a-f to the alpha-fluorides 2a-f and of 5 to the alpha-fluoride 6 we re carried out with the reagent system HF/nitromethane/acetic anhydrid e, which simultaneously effects the complete exchange of the isopropyl idene groups (1a-f) and of the benzyl groups (5) for acetyl functions in the non-glycosidic positions. Moreover, the dodecyl-2,3,4-tri-O-ace tyl-beta-D-galactopyranosyl fluoride (11) was prepared in three steps from the 6-O-dodecyl-galactopyranose (8). The stereoselective introduc tion of the fluoride into the beta-anomeric position (10 --> 11) was a chieved by bromide-fluoride exchange with the two-phase system triethy lamine-trishydrofluoride/petroleum ether. Dodecyl 6-deoxy-6-fluoro-alp ha-D-glucopyranoside (13), prepared from the glucoside 12 with the flu orinating agent DAST, shows a narrow monotropic SA-phase and lyotropic liquid crystalline behaviour in contact with water. Dodecyl 6-deoxy-6 -fluoro-beta-D-galactopyranoside (17), prepared in three steps from th e acetal 14, does not form mesophases. The liquid crystalline behaviou r of the amphiphilic glycosyl fluorides 3a-f, 7, and of the 6-deoxy-6- fluoro derivative 13 is described.