Studies of specifically fluorinated carbohydrates. Part VI. Some pentofuranosyl fluorides

Detailed analyses of the 1H and 19F nuclear magnetic resonance spectra of seven pentofuranosyl fluoride derivatives are reported. With the help of 1H-{19F} heteronuclear decoupling experiments, some unexpectedly large 4J couplings have been detected between F and H-4; when these substituents are trans the coupling is 5.5–7.9 Hz while the cis relationship gives couplings of 1.0–1.8 Hz. The 4J couplings between F and H-3 are smaller when these groups are trans (< 0.7 Hz) than when they are cis oriented (1.7–2.4 Hz). These, and the other coupling constants are discussed in terms of the favored conformations of these derivatives. The ring conformations of the anomeric tri-O-benzoyl-D-ribo-furanosyl fluorides differ from each other.