Optimization of the four-component reaction of benzil, benzaldehyde, benzylamine and ammonium acetate under various conditions^a.

Entry	Solvent	Catalyst (mol%)	Temp.	Time (min)	Yieldb (%)
1	Ethanol	0.36	Reflux	55	69
2	Acetonitrile	0.36	Reflux	55	61
3	Water	0.36	Reflux	80	78
4	Dichloromethane	0.36	Reflux	70	45
5	Chloroform	0.36	Reflux	70	49
6	Tetrahydrofuran	0.36	Reflux	70	43
7	Solvent-free	0.36	80 °C	35	95
8	Solvent-free	0.24	80 °C	55	79
9	Solvent-free	0.48	80 °C	35	92
10	Solvent-free	0.36	25 °C	120	35
11	Solvent-free	0.36	60 °C	65	69
12	Solvent-free	0.36	70 °C	45	75
13	Solvent-free	0.36	90 °C	35	93
14	Solvent-free	0.36	100 °C	35	91
15w	Solvent-free	BF3–SiO2/0.36	80 °C	150	68
16	Solvent-free	MgCl2/0.36	80 °C	80	56
17	Solvent-free	SbCl5–SiO2/0.36	80 °C	150	65

^aReaction conditions: benzil (1 mmol), benzaldehyde (1 mmol), benzylamine (1 mmol), ammonium acetate (4 mmol), and the required amount of catalyst.

^bThe yields refer to the separated product.