To a solution of 5-[4-chloro-2-(trifluoromethyl)phenyl]-4-methyl-N-[4-(methylsulfonyl)phenyl]-1H-pyrrole-3-carboxamide (21 g, 47 mmol) in anhydrous DMA (234 ml) was added sodium tert-butoxide (10 g, 0.11 mol) and stirred at room temperature for 30 min under N2. (4S,5S)-4,5-dimethyl-1,3,2-dioxathiolane 2,2-dioxide (11 g, 70 mmol) in anhydrous DMA (50 ml) was added to the solution and stirred at 70° C. for 2.0 h. The reaction mixture was cooled to 0° C. and added 2N HCl (100 ml) and concentrated on a rotary evaporator. To this residue was added anhydrous THF (120 ml) and 5N HCl (120 ml) and stirred at 60° C. for 90 min. The mixture was diluted with ethyl acetate and washed with water, satd NaHCO3 and brine, then dried over sodium sulfate and concentrated on a rotary evaporator. The resulting residue was purified by silica-gel column chromatography (1:1 to 1:9 hexane:ethyl acetate) to give an atropisomeric mixture of the title compound (10.9 g, 44%) as a white solid.
