Optimization of the solvent for the synthesis of piperidine in the model reaction^a.

Entry	Solvent	Catalyst (mol%)	Temp. (°C)	Time (h)	Yieldb (%)
1	H2O	1.5	40	12	40
2	EtOH	1.5	40	2	94
3	MeOH	1.5	40	5	88
4	EtOAc	1.5	40	5	50
5	CH3CN	1.5	40	8	85
6	Solvent free	1.5	40	12	43
7	DMF	1.5	40	6	55
8	THF	1.5	40	12	70
9	EtOH	—	40	24	Trace
10	EtOH	0.5	40	8	58
11	EtOH	1	40	2	77
12	EtOH	2	40	2	95
13	EtOH	1.5	RT	12	70
14	EtOH	1.5	50	2	94
15	EtOH	1.5	60	1 : 45	90
16	EtOH	1.5	70	1 : 30	85
17	EtOH	1.5c	40	24	0
18	EtOH	1.5d	40	24	Trace
19	EtOH	1.5e	40	12	75

^aExperimental conditions: benzaldehyde (2 mmol), aniline (2 mmol), methyl acetoacetate (1 mmol), and catalyst (1.5 mol%) in 5 mL of solvent at 40 °C.

^bIsolated yields.

^cReaction was performed in the presence of MNPs as the catalyst.

^dReaction was performed in the presence of MNPs@CNF as the catalyst.

^eReaction was performed in the presence of MNPs@CNF@ATS–Co(ii) as the catalyst.