Chemoselective Synthesis of Naphthyridines and Pyrano[3,2-c]pyridines

Significance

Reported here is the chemoselective synthesis of pyrano[3,2-c]pyridines 3 and 1,6-naphthyridines 4 from chalcones 1 and malononitrile (2) under microwave heating conditions. The chemoselectivity is dependent on the choice of solvent. While products 3 were formed in DMF in excellent yield, compounds 4 were obtained in AcOH. The reaction tolerates both electron-rich and electron-poor aryl R^¹ groups to give the desired products with equal efficiency. One example of a heterocyclic chalcone (R^¹ = thiophen-2-yl) was also demonstrated.