Synthesis of 1,6-diamino-4-aryl-2-oxo-1,2-dihydropyridine-3,5-dicarbonitrile 4a–l^a.

Entry	Aromatic aldehyde	Product	Time (h)	Yield (%)	M.p. (°C)
1			12	93	340 (dec.)41
2			12	88	355 (dec.)
3			12	91	360 (dec.)41
4			16	83	321–323 (ref. 41)
5			15	85	265–267
6			12	90	332–334 (ref. 41)
7			11	87	305–307 (ref. 41)
8			12	85	292–294
9			13	80	365 (dec.)
10			17	75	290–292 (ref. 41)
11			11	83	338–340
12			13	78	324–326

^aAll reactions were carried out with cyanoacetohydrazide 1 (1 mmol), malononitrile 2a (1 mmol), aromatic aldehydes 3 (1 mmol) and piperidine (0.02 mmol) in water (10 ml).