A facile synthesis of highly fluorescent pyrido[2,3- d ]pyrimidines and 1,8-naphthyridines via oxazine transformation and enaminic addition reactions

Abstract The synthesis and fluorescence properties of highly substituted bicyclic pryridine derivatives are described. 2-Substituted-4-oxo-pyrido[2,3- d ]pyrimidines 2–8 resulted from the acylation reaction of α-aminonicotinonitrile 1 with aroyl chlorides, diethyl malonate, morpholine-4-carboxylate, acetic anhydride or formic acid under solvent-free conditions. [4 + 2] Cyclocondensation and cycloaddition reactions of compound type 1 with formamide and ammonium thiocyanate tolerated the fused pyrimidines 9 and 11 , respectively. Finally, the Friedländer-like reaction was applied for the synthesis of 1,8-naphthyridines 12–15 via reaction of compound 1 with cyclohexanone, dimedone, acetyl acetone and benzyl methyl ketone, respectively, under AlCl 3 catalysis. The fluorescence spectroscopic data of compounds 1–4, 6–8, 11, 12, 14 and 15 measured and significant results were observed. Graphical abstract