Table 3. Use of Different Lewis Acids and Lewis Bases by Ultrasonic Irradiation (US) for the Reaction 4a^b.

entry	catalyst (mol %)	conditionsb	yield (%)a
1	no catalyst	water, 1 day	trace
	no US
2	no catalyst	water, 1 h	49
3	AlCl3 (10)	water, 15 min	42
4	MgCl2 (10)	water, 15 min	52
5	FeCl3·6H2O (10)	water, 15 min	43
6	I2 (10)	water, 15 min	51
7	ZnBr2 (10)	water, 15 min	54
8	CuCl2 (10)	water, 15 min	57
9	CuO (10)	water, 15 min	54
10	Pd(OAc)2 (10)	water, 15 min	73
11	TiCl4 (10)	water, 15 min	49
12	PTSA (10)	water, 15 min	44
13	Et3N (10)	water, 15 min	67
14	TBABrc (10)	water, 15 min	64
15	MATYCu (10)	water, 15 min	84
16	MATYFe (10)	water, 15 min	89
17	MATYpd (10)	water, 15 min	97
18	MATYpd (10)	water, 15 min	88
	no US

^aIsolated yields based on 4a.

^bReaction conditions: 1a (1 mmol), 2 (1 mmol), 3 (1 mmol), and catalyst (0.1 mmol) in water were heated at 80 °C under ultrasonic irradiation condition for 15 min.

^cTetrabutylammonium bromide.