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.