Optimization of reaction conditions^a,b.

Entry	Catalyst (mol%)	Solventc	Time	Yieldd (%)
1	Catalyst free	None	12 h	NR
2	Catalyst free	CH2Cl2	8 h	NR
3	Catalyst free	CHCl3	8 h	NR
4	Catalyst free	1,4-Dioxane	6 h	10%
5	Catalyst free	Methanol	6 h	28%
6	Catalyst free	Ethanol	6 h	35%
7	Catalyst free	Water	6 h	23%
8	InCl3 (10 mol%)	Ethanol	3 h	53%
9	FeCl3 (10 mol%)	Ethanol	3 h	55%
10	ZnO NPs (10 mol%)	Ethanol	1 h	60%
11	ZrO NPs (10 mol%)	Ethanol	1 h	72%
12	TiO2 NPs (10 mol%)	Ethanol	1 h	78%
13	0.5% Er doped TiO2 NPs (25 mg)	Ethanol	20 min	82%
14	1% Er doped TiO2 NPs (25 mg)	Ethanol	20 min	86%
15	1.5% Er doped TiO2 NPs (25 mg)	Ethanol	20 min	91%
16	2% Er doped TiO 2 NPs (25 mg)	Ethanol	20 min	95%
17	5% Er doped TiO2 NPs (25 mg)	Ethanol	20 min	91%
18	7% Er doped TiO2 NPs (25 mg)	Ethanol	20 min	87%
19	10% Er doped TiO2 NPs (25 mg)	Ethanol	20 min	87%
20	2% Er doped TiO2 NPs (15 mg)	Ethanol	20 min	92%
21	2% Er doped TiO2 NPs (30 mg)	Ethanol	20 min	95%

^aBold row indicates the optimization condition for the reaction.

^b2-Hydroxynaphthalene-1,4-dione (1 mmol), benzene-1,2-diamine (1 mmol), N-methyl-4-piperidone (1 mmol) and 2-aminopyridine (1 mmol) were stirred with refluxing till completion of the reaction as indicated by TLC.

^cSolvents (2.0 ml).

^dIsolated yield after purification.