Table 1.

Reaction of indole with piperidine using different approaches^a.

Entry	Time (min)	Reaction conditions	Yields (%)c
			2	3	4
1	20	USb (50°C)	21	24	–
2	40	US (50°C)	30	39	–
3	80	US (50°C)	39	44	–
4	120	US (50°C)	40	51	–
5	180	US (50°C)	40	37	12
6	120	T = 25°C	31	16	2
7	120	T = 80°C	52	34	6
8	10	μW (100°C)	26	39	10

^aReaction conditions: 1.0 mmol of indole, 1.5 mmol of piperidine, 2.0 mmol of base, 4 mL of DCM, 1 mL of DMF.

^bUltrasound irradiation.

^cYields were calculated with standardized HPLC method.