3-Bromo-1,1,1-trifluoro-2-propanone → 5-[1-[4-(methylsulfonyl)phenyl]-4-hydroxy-4-(trifluoromethyl)-4,5-dihydro-1H-imidazol-2-yl)-1,3-benzodioxole

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To a mixture of 3,4-methylenedioxy-N-[4-(methylsulfonyl)phenyl]benzenecarboximidamide from Step 1 (2.32 g, 7.3 mmol) and sodium bicarbonate (1.23 g, 14.6 mmol) in isopropanol (100 mL), 3-bromo-1,1,1-trifluoroacetone (5.4 mL, 52 mmol) was added. After heating the reaction mixture to reflux for 24 hours, the solvent was removed. The residue was redissolved in methylene chloride and washed with water. The organic fractions were combined, dried over sodium sulfate, filtered and concentrated in vacuo. The crude mixture (7.1 g) was purified by chromatography (silica gel, toluene/ethyl acetate, 1/1) to give 5-[1-[4-(methylsulfonyl)phenyl]-4-hydroxy-4-(trifluoromethyl)-4,5-dihydro-1H-imidazol-2-yl)-1,3-benzodioxole (1.46 g, 47%) as a white solid: mp 200–202° C. Anal. Calc'd. for C18H15N2SO5F3.0.25 PhCH3: C, 52.55; H, 3.80; N, 6.21. Found: C, 52.73; H, 3.78; N, 6.01.

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