Organofluorine compounds and fluorinating agents. 14. Thermotropic Liquid-Crystalline Glycosyl Fluorides
作者:Ralf Miethchen、Cornelia Zur
DOI:10.1002/prac.19953370142
日期:——
The liquid crystalline 6-O-alkyl-alpha-D-galactopyranosyl fluorides (3a-f) and the mesogenic 6-O-dodecyl-alpha-D-glucopyranosyl fluoride (7) were prepared from the homologous 6-O-alkyl-1,2:3,4-di-O-isopropylidene-alpha-D-galacto-pyranosides (1a-f) and from the methyl 2,3,4-tri-O-benzyl-glucopyranoside (4), respectively, in two and three steps. The fluorinations of 1a-f to the alpha-fluorides 2a-f and of 5 to the alpha-fluoride 6 were carried out with the reagent system HF/nitromethane/acetic anhydride, which simultaneously effects the complete exchange of the isopropylidene groups (1a-f) and of the benzyl groups (5) for acetyl functions in the non-glycosidic positions. Moreover, the 6-O-dodecyl-2,3,4-tri-O-acetyl-beta-D-galactopyranosyl fluoride (11) was prepared in three steps from the 6-O-dodecyl-galactopyranose (8). The stereoselective introduction of the fluoride into the beta-anomeric position (10 --> 11) was achieved by bromide-fluoride exchange with the two-phase system triethylamine-trishydrofluoride/petroleum ether. Dodecyl 6-deoxy-6-fluoro-alpha-D-glucopyranoside (13), prepared from the glucoside 12 with the fluorinating 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 the acetal 14, does not form mesophases. The liquid crystalline behaviour of the amphiphilic glycosyl fluorides 3a-f, 7, and of the 6-deoxy-6-fluoro derivative 13 is described.