Stereoselective synthesis and conformational study of novel 2′,3′-didehydro-2′,3′-dideoxy-4′-selenonucleosides

(Chemical Equation Presented) Stereoselective synthesis of novel 2′,3′-didehydro-2′,3′-dideoxy-4′- selenonucleosides (4′-seleno-d4Ns) 4a-c was accomplished via 4′-selenoribofuranosyl pyrimidines 11a-c, as key intermediates. 4′-Selenoribofuranosyl pyrimidines 11a-c were efficiently synthesized from D-ribose or D-gulonic γ-lactone using a Pummerer-type condensation as a key step. Introduction of 2′,3′-double bond was achieved by treating cyclic 2′,3′-thiocarbonate with 1,3-dimethyl-2-phenyl-1,3,2- diazaphospholidine.