Various synthetic methods have been elaborated to prepare pyrido [2, 3-d] pyrimidines and their 3-oxides from 0-aminocyanopyridine. Conversion of these 3-oxides into 1, 2, 4- oxadiazolylpyridines, s-triazolo [l, 5-a] pyridines, and pyrazolo [3, 4-b] pyridines as well as other transformations are described.