Comparative study of catalytic activity/efficiency of synthesized Lewis acid catalysts in 2,4,5-trisubstituted arylimidazole derivative synthesis (4a)^a.

Entry	Catalyst sample	Timeb (min)	Yieldc (%)
1	La(OCOCF3)3·nH2O	45	71
2	La(OCOCCl3)3·nH2O	48	68
3	La(OCOCF 3 ) 3 ·nH 2 O/SiO 2	14	96
4	La(OCOCCl 3 ) 3 ·nH 2 O/SiO 2	17	94
5	Kieselgel K100 (silica gel)	220	41

^aReaction conditions: benzaldehyde (1 mmol), benzil (1 mmol), ammonium acetate (3 mmol) and synthesized Lewis acid catalysts.

^bReaction progress monitored by TLC.

^cIsolated yields.