Abstract The preparation of a variety of N-substituted 3-azaisatoic anhydrides 3 and 8 is described. These anhydrides reacted with thiopseudoureas to give interesting bicyclic, tricyclic, and tetracyclic heterocycles many of which are new ring systems. One such heterocycle, the imidazo [1, 2-a] pyrido [2, 3-d] pyrimidine ring system, was studied further with respect to alkylation and reduction reactions. Alkylation of 12h occurred on the ...