(Trifluoromethyl)sulfonyl (Triflyl) Migration. Synthesis of 6,3’-Anhydro-3-benzyl-l-(5-chloro-5-deoxy-β-D-xylofuranosyl)barbituric Acid from the 2’-Trifluoromethanesulfonate (Triflate) of 6,5’-Anhydro-3-benzyl-1-β-D-ribofuranosylbarbituric Acid

The first evidence of (trifluoromethyl)sulfonyl (triflyl) migration is presented. The 2’,3’-0-stannylene derivative of 6,5’ acid (1) afforded a 9:1 mixture of isomeric 2’- and 3’-triflates 2 and 3 upon treatment with triflyl chloride in N,N-dimethylformamide. On acetylation, 2 and 3 afforded their corresponding acetyl derivatives 4 and 5. Compound 4 was converted into 6,2’-anhydro-3-benzyl-l-(3-O-acetyl-5-chloro-5-deoxy-β-D-arabinofuranosyl)barbituric acid (6) by treatment with LiCl in hexamethylphosphoric triamide (HMPA), whereas 5 afforded the 6,3’-anhydro-xylo isomer 7. Compounds 6 and 7 were reduced to the 5’-deoxy nucleosides 8 and 9, respectively. Treatment of both 2’- and 3’-triflates 2 and 3 with LiCl in HMPA afforded, exclusively, the same 6,3’-anhydro-xylo derivative 10, which was acetylated to 7. The triflyl group on C-2’ in 2 migrated to C-3’ prior to the formation of the 6,3’-anhydro linkage during the conversion to 10. A plausible mechanism is discussed.