Nucleosides and nucleotides. 191 : Ring expansion reaction of 1-[2,3,5-tri-o-TBS-4α-formyl-β-D-ribo-pentofuranosyl]uracil by treating with (methylene)triphenylphosphorane to give a new nucleoside containing dihydrooxepine ring at the sugar moiety

When 1-2,3,5-tri-O-TBS-4α-formyl-β-D-ribo-pentofuranosyl]uracil (5) was treated with (methylene)triphenylphosphorane in THF, an unusual ring-expansion reaction occurred to give a nucleoside (7) containing dihydrooxepine ring at the sugar moiety. A deuterium-label experiment showed that one carbon unit derived from the ylide was incorporated into the 5'-position of 7. A ring cleavage between the C-3' and C-4' of 5 during the reaction was suggested.