Sulfuric Acid → 1-(4-Bromophenyl)-3,3,3-trifluoropropane-1,2-dione

온도

45 °C

3-(4-bromophenyl)-3-(2,2-dimethylhydrazono)-1,1,1-trifluoropropan-2-one (2.0 g, 6.2 mmol) was suspended in 5N sulfuric acid (60 mL) and heated at 45° C. for 6 h. The temperature was raised to 85° C. for 2 h, and upon cooling a precipitate formed. This material which was isolated by filtration to give 1-(4-bromophenyl)-3,3,3-trifluoropropane-1,2-dione 1.6 g (92%) as a yellow solid. The dione (1.6 g, 5.7 mmol) was taken up in methanol (30 mL), N-(tert-butoxycarbonyl)-L-prolinal (1 g, 5.0 mmol) was added, followed by addition of 28% ammonium hydroxide solution (10 mL). The reaction was stirred at room temperature for 18 h, poured onto dichloromethane (200 mL), washed with water and dried with MgSO4. Filtration, concentration and application to a 40 M Biotage cartridge, gradient elution with 5%-30% ethyl acetate/Hexanes, gave J32.a 1.3 g (50%). 1H NMR (300 MHz, DMSO-d6) δ 12.88 (br.s, 1H), 7.72 (d, J=8.4 Hz, 2H), 7.39 (d, J=8.0 Hz, 2H), 4.84-4.70 (m, 1H), 3.57-3.49 (m, 1H), 3.39-3.29 (m, 1H), 2.31-2.20 (m, 1H), 1.98-1.78 (m, 3H), 1.39/1.13 (m, 9H). LRMS: Anal. Calcd. for C19H20BrF3N3O2 458.07. found: 458.06 and 460.06 (M−H)−. HRMS: Anal. Calcd. for C19H22BrF3N3O2 460.0847. found: 460.0866 and 462.0840 (M+H)+.