Nano TiO2@SiO2 as an efficient and reusable catalyst for the synthesis of multi-substituted imidazoles

Nano TiO2 supported on SiO2 (Nano TiO2@SiO2) as a solid Lewis acid, was described to be an effective and reusable catalyst for one-pot three-component reaction of benzil, aryl aldehydes and ammonium acetate for the synthesis 2-aryl-4,5-diphenyl-1H-imdazoles synthesis. To explore the high efficacy of the catalytic system the four-component cyclization of benzil, aryl aldehydes, ammonium acetate and anilines has also been accomplished successfully to obtain their 1,2-diaryl-4,5-diphenyl-1H-imidazole adducts. A plausible mechanism has also been expressed. The catalyst has been recovered and its reusability confirmed in 4 runs. High yields, simple operation, easy-work procedure, mild reaction conditions in addition with the reusability are some advantages of this protocol.