Reported catalytic systems for the formation of spiro[indene-2,2′-naphthalene]-4′-carbonitriles^a.

Entry	Catalyst	Time (min)	Temp. (°C)	Yieldb (%)	Ref.
1	—	180	Reflux	21	This work
2	Fe3O4@SiO2 (20 mg)	300	Reflux	42	This work
3	l-Tryptophan (20 mg)	300	Reflux	68	This work
4	Nano Fe3O4@SiO2@l-tryp (20 mg)	80	rt	90	This work
5	Nano Fe 3 O 4 @SiO 2 @ l -tryp (20 mg)	30	Reflux	91	This work
6	Nano Fe3O4@SiO2@l-tryp (15 mg)	80	Reflux	90	This work
7	Nano Fe3O4@SiO2@l-tryp (30 mg)	30	Reflux	91	This work
8	l-Proline (15 mol%)	180	rt	89	18
9	Ethylene glycol (3.3 g)	150	100	84	19
10	DABCO (10 mol%)	90	rt	88	20

^aReaction conditions: malononitrile (1 mmol), cyclohexanone (1 mmol) p-nitro benzaldehyde (1 mmol), and 1,3-indandione (1 mmol) in the presence of Fe₃O₄@SiO₂-l-tryptophan in EtOH under reflux conditions.

^bIsolated yields.