D-Ribopyranosyl fluoride

In the pentose series, attack has also been observed to occur mainly from the less-hindered side of the double bond, as in the addition of trifluoro(fluoroxy)methane to di-O-acetyl-D-arabinal. Trifluoromethyl 3,4-di-0-acetyl-2-deoxy-2-fluoro-/3-D-arabinopyranoside and 3,4-di-0-acetyl-2-deoxy-2-fluoro-/J-D-arabinopyranosyl fluoride were obtained,72,74 together with a very small proportion of 3,4-di-0-acetyl-2-deoxy-2-fluoro-a-D-ribopyranosyl fluoride.74 With di-O-acetyl-D-xylal, however, the lyxose derivatives were mainly obtained.72,73 The suggestion has been made73 that the greater conformational mobility of pentopyranoses results in a preponderance of the C d) conformer of the D-lyxose derivatives,72,73 such that F-l and CFsO-l are axially disposed. For further reactions of unsaturated carbohydrates with tri-fluoro(fluoroxy)methane, see Section 11,9. 

C. Pedersen and H. G. Fletcher Jr., The anomeric 2,3,4-tri-O-benzoyl-d-ribopyranosyl fluorides and 2,3,5-tri-O-benzoyl-d-ribofuranosyl fluorides. A novel transformation from the d-ribopyranose to the d-ribofuranose series, ]. Am. Chem. Soc., 82 (1960) 941-945. 

Tetra-0-benzoyl-/3-L-arabinopyranose (enantiomorph of 165b) is isomerized by hydrogen fluoride after 64 hours, to give 36% of 2,4-di-0-benzoyl-/3-L-ribopyranosyl fluoride (enantiomorph of 167). This reaction with D-arabinose derivatives has been examined by n.m.r. spectroscopy. Tetra-O-acetyl-a-D-arabinopyranose (165a)... 

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