Synthesis of ethyl 1,6-diamino-4-aryl-3-cyano-2-oxo-1,2-dihydropyridine-5-carboxylate 5a–e^a.

Entry	Aromatic aldehyde	Product	Time (h)	Yield (%)	M.p. (°C)
1			20	87	245–247
2			20	85	280–282
3			22	80	322–324
4			24	75	218–220
5			24	75	237–239

^aAll reactions were carried out with cyanoacetohydrazide 1 (1 mmol), ethyl cyanoacetate 2b (1 mmol), aromatic aldehydes 3 (1 mmol) and piperidine (0.02 mmol) in water/EtOH (5 : 5 mL).