<i>N</i>-Oxides of Adenosine-Type Nucleosides Undergo Pyrimidine Ring Opening and Closure To Give 5-Amino-4-(1,2,4-oxadiazol-3-yl)imidazole Derivatives^†

Treatment of acylated adenosine N-oxides with carboxylic anhydrides and thiophenol resulted in pyrimidine ring opening followed by exocyclic ring closure. Ammonolysis gave 5-amino-4-(5-substituted-1,2,4-oxadiazol-3-yl)-1-(β-d-ribofuranosyl)imidazole derivatives, whereas iodine in methanol selectively unmasked the 5-amino group. Related flexible nucleoside analogues can be prepared from adenine-type precursors.