The reaction of pyranoside 2-uloses with DAST revised. Synthesis of 1-fluoro-ketofuranosyl fluorides and their reactivity with alcohols

We have reinvestigated the reaction of α-pyranosides-2-uloses 13, 14, 19 and 24 with DAST and shown that the 1,2-difluorinated compounds 17, 18 and 25 are produced by a ring-contraction reaction. The reaction of 18 with benzyl alcohol gives the tri-benzyl derivative 26 or compound 27, depending on the reaction conditions. Treating 17 with 2-naphthol produced the spiranic compounds 29–31. The reaction of 17 with bis(trimethylsilyl)uracil produced the mononucleoside 28, which preserves the fluorine atom in the more substituted carbon.