An Efficient Route to Acyclic C-Nucleosides and Fused-Ring Analogues of Uridine from exo-Glycals

beta-Amino esters prepared from activated exo-glycals are transformed into acyclic C-nucleoside with a C-4-substituted uracil derivative that can be cyclized under Mitsututed conditions to provide it new Family of fused-ring analogues of uridine nucleoside in which the N-1 nitrogen atom is embedded in an amino sugar ring. An analogue of uridine of D-1 ibo configuration is prepared.