Nucleosides CIII. Anhydropyrimidine‐ C ‐nueleosides. Synthesis of 4,2′‐anhydro‐5‐(β‐ D ‐arabinofuranosyl)‐ and 5‐(β‐ D ‐arabinofuranosyl)pyrimidine C‐nucleosides

4,2′‐Anhydro‐5‐(β‐ D ‐arabinofuranosyl)isocytosine and 4,2′‐anhydro‐5‐(β‐ D ‐arabinofuranosyl)‐uracil were synthesized. Treatment of Ψ‐isocytidine with either α‐acetoxyisobutyryl chloride or salicyloyl chloride in acetonitrile afforded the acylated anhydronucleoside. Deacylation of the product with methanol‐hydrogen chloride afforded 4,2′‐anhydro‐5‐(β‐ D ‐arabinofuranosyl)isocylosine hydrochloride in crystalline form. Analogous reaction of Ψ‐uridine with the acyl chloride reagents, however, always gave a mixture of the acylated anhydronucleoside and 2′‐chloro‐2′‐deoxy‐Ψ‐uridine. Treatment of these products either singly or as a mixture with sodium methoxide in methanol afforded 4,2′‐anhydro‐5‐(β‐ D ‐arabinofuranosyl)uracil in crystalline form in good yield. 5‐(β‐ D ‐Arabinofuranosyl)isocytosine was obtained upon treatment of the corresponding 4,2′‐anhydronucleoside with 10% sodium hydroxide under reflux for 30 minutes. Treatment of the anhydro uracil nucleoside with a small amount of Dowex 50(H + ) in water at 50° gave 5‐(β‐ D ‐arabinofuranosyl)uracil.