1,3-Dichloro-5-(3,3,3-trifluoroprop-1-en-2-yl)benzene → 5-(5-(3,5-dichlorophenyl)-5-(trifluoromethyl)-4,5-dihydro-isoxazol-3-yl)-6-fluoro-3,3-dimethylbenzo[c][1,2]oxaborol-1(3H)-ol

To a solution of the crude compound 6-fluoro-N,1-dihydroxy-3,3-dimethyl-1,3-dihydro benzo[c][1,2]oxaborole-5-carbimidoyl chloride (300 mg, 0.92 mmol) and 1,3-dichloro-5-(3,3,3-trifluoroprop-1-en-2-yl)benzene (222 mg, 0.92 mmol) in DMF (5 mL) at rt was added TEA (152 μL, 1.1 mmol). The reaction mixture was stirred for 12 h, poured into ice-water and extracted with DCM (60 mL×3). The organic layer was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by prep-TLC eluted with PE-EA (3:2) and then purified by combiflash to give the title compound 5-(5-(3,5-dichlorophenyl)-5-(trifluoromethyl)-4,5-dihydro-isoxazol-3-yl)-6-fluoro-3,3-dimethylbenzo[c][1,2]oxaborol-1(3H)-ol (108 mg; yield 29% over 3 steps) as a white solid. 1H NMR (400 MHz, DMSO-d6): δ 9.379 (s, 1H), 7.815-7.848 (m, 2H), 7.660 (s, 2H), 7.513 (d, J=10.0 Hz, 1H), 4.401 (d, J=18.4 Hz, 1H), 4.254 (d, J=18.8 Hz, 1H), 1.485 (s, 6H) ppm; HPLC purity: 100% at 220 nm and 100% at 254 nm; MS: m/z=462.0 (M+1, ESI+).