N,1-dihydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]oxaborole-5-carbimidoyl chloride → 5-(5-(3,5-dichloro-2,4-difluorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)-3,3-dimethylbenzo[c][1,2]oxaborol-1(3H)-ol

To a solution of N,1-dihydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]-oxaborole-5-carbimidoyl chloride (3.0 g, 12.63 mmol) and 1,3-dichloro-2,4-difluoro-5-(3,3,3-trifluoroprop-1-en-2-yl)-benzene (3.93 g, 14.19 mmol) in DMF (20 mL) at rt was added TEA (2.7 mL, 18.95 mmol). The reaction mixture was stirred for 12 h, poured into ice-water and extracted with EA. The organic layer was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by column chromatography over silica gel eluted with PE-EA (1:1) to give the title compound 5-(5-(3,5-dichloro-2,4-difluorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)-3,3-dimethylbenzo[c][1,2]oxaborol-1(3H)-ol[1.3 g, yield: 21.4% (3 steps)] as a white solid. 1H NMR (500 MHz, DMSO-d6): δ 9.23 (s, 1 H), 7.87 (t, J=7.5 Hz, 1H), 7.83 (s, 1H), 7.75 (s, 2H), 4.59 (d, J=18.5 Hz, 1H), 4.37 (d, J=18.5 Hz, 1H), 1.50 (s, 3H), 1.48 (s, 3H) ppm; HPLC purity: 100.0% at 220 nm and 100.0% at 254 nm; MS: m/z=479.8 (M+1, ESI+).