Synthesis of Novel Heterocycles: Oxazolo(4,5-b)pyridines and Oxazolo-(4,5-d)pyrimidines.

Abstract Novel purine isosters (title compounds) have been prepared by condensation of the appropriate o-hydroxyaminoazine with ethyl orthoformate ; extension to other orthoesters and to benzyl thioacetimidate afford 2-alkyl substituted derivatives of these new fused heterocycles.