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 Friedlander-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 AlCl3 catalysis. The fluorescence spectroscopic data of compounds 1–4, 6–8, 11, 12, 14 and 15 measured and significant results were observed.