Syntheses of Oxazolo [4,5-b]pyridines and [4,5-d]pyrimidines

Oxazolo [4, 5-b] pyridines and [4, 5-d] pyrimidines and their 2-substituted compounds have been prepared respectively by condensation of orthoesters or thioimidates derivatives with 2-amino-3-hydroxypyridine and 4-amino-5-hydroxypyrimidine.