Synthesis of various poly-substituted piperidine derivatives^a.

Entry	R1	R2	R3	Product	Time (h)	Yieldb (%)	m.p./°C	Lit. m.p./°C [ref.]
1	H	H	Et	4a	2	92	173–174	174–175 [ref. 35]
2	H	H	Me	4b	2	94	169–170	169–171 [ref. 35]
3	H	4-Br	Et	4c	3	87	198–199	196–198 [ref. 36b]
4	H	4-Cl	Et	4d	3	83	201–202	202 [ref. 36c]
5	4-OMe	4-Cl	Me	4e	2.5	85	195–196	193–195 [ref. 36e]
6	4-OMe	4-Br	Me	4f	2.5	78	177–178	177–179 [ref. 20]
7	2-NO2	H	Me	4g	2	70	217–218	217–219 [ref. 35]
8	4-NO2	H	Me	4h	3	82	240	239–241 [ref. 36d]
9	4-NO2	H	Et	4i	3	87	249–250	247–250 [ref. 36d]
10	4-Br	H	Me	4j	4	84	245–246	245–247 [ref. 36c]
11	4-Br	4-Cl	Me	4k	4	82	160–161	160–163 [ref. 36c]
12	4-Cl	H	Me	4l	4	82	227	225–227 [ref. 36e]

^aReaction conditions: benzaldehyde (2 mmol), aniline (2 mmol), β-ketoester (1 mmol), and catalyst (1.5 mol%) in 5 mL of EtOH at 50 °C.

^bIsolated yield.