4-Oxa(thia)-9-oxa-2-azabicyclo[4.2.1]nonane-3-on(thion) derivatives

The synthesis of 7,8‐dihydroxy‐2‐(2‐methoxycarbonylethyl)‐4,9‐dioxa‐2‐azabicyclo[4.2.1]nonane‐ 3‐thione (16) and of its parents 9‐oxa‐4‐thia‐3‐thione 17, and 9‐oxa‐4‐thia‐3‐one 18 is described. The conversion of 5′‐deoxy‐5′‐iodo‐2′,3′‐O, O‐isopropylidene‐5,6‐dihydrouridin (1) into the 2‐O‐methyl‐5,6‐dihydrouridine 5, the 5′‐O‐acetyl‐5,6‐dihydrouridine 4, and into the N‐(5‐O‐acetyl‐2,3‐O, O‐isopropylidene‐β‐D‐ribofuranosyl)‐N‐(2‐methoxycarbonyl thyl)‐urea (6) invoked 2′,3′‐O, O‐isopropylidene‐2,5′‐anhydro‐5,6‐dihydrouridine (2) as the common intermediate.