The potassium permanganate (5.58 g, 35.3 mmol) and Montmorillonite K-10 clay (10 g) were mixed and finely grounded. The mixture was slowly (about 15 minutes) added into the mixed solution of dichloromethane (50 mL), acetonitrile (150 mL) and 1-(1,3-diisopropyldibenzo[b,d]furan-4-yl)-2-phenyl-4,5-dihydro-1H-imidazole (7 g, 17.6 mmol), which was cooled by ice bath. Then the reaction was stirred for another hour and quenched by adding 20 mL of ethanol. Filtered through a Celite plug. The crude product was purified by silica gel column (up to 30% EtOAc in hexanes) and recrystallization from hexane. 1-(1,3-diisopropyldibenzo[b,d]furan-4-yl)-2-phenyl-1H-imidazole (2.6 g, 6.57 mmol, 37.2% yield) was obtained as white solid (99.8% HPLC).
