A library of fused pyridine-4-carboxylic acids (including pyrazolo [3, 4-b] pyridines, isoxazolo [5, 4-b] pyridines, furo [2, 3-b] pyridines, thieno [2, 3-b] pyridines, and pyrido [2, 3-d] pyrimidines) was generated by Combes-type reaction of acyl pyruvates and electron-rich amino heterocycles followed by hydrolysis of the ester. The library members were also demonstrated to undergo the standard combinatorial transformations including amide ...