[F:1][C:2]1[C:3]([CH3:14])=[CH:4][C:5]2[C:9]([CH3:11])([CH3:10])[O:8][B:7]([OH:12])[C:6]=2[CH:13]=1.C(OOC(=O)C1C=CC=CC=1)(=[O:22])C1C=CC=CC=1.C1C(=O)N(Br)C(=O)C1.C([O-])([O-])=O.[Na+].[Na+].Cl>C(Cl)(Cl)(Cl)Cl>[F:1][C:2]1[C:3]([CH:14]=[O:22])=[CH:4][C:5]2[C:9]([CH3:10])([CH3:11])[O:8][B:7]([OH:12])[C:6]=2[CH:13]=1To a solution of 6-fluoro-3,3,5-trimethylbenzo[c][1,2]oxaborol-1(3H)-ol (388 mg, 2 mmol) in CCl4 (60 mL) at rt was added benzoyl peroxide (48.4 mg, 0.2 mmol) followed by NBS (783 mg, 4.4 mmol). The reaction mixture was heated under reflux for 16 h, cooled to rt and treated with Na2CO3. The aqueous layer was acidified with 3 N HCl to pH of 3 and extracted with DCM (60 mL×3). The organic layer was dried over Na2SO4, filtered and concentrated under reduced pressure to give 6-fluoro-1-hydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]oxaborole-5-carbaldehyde (378 mg, 91%) as a pale yellow solid. 1H NMR (500 MHz, CDCl3) δ 10.369 (s, 1H), 7.687 (d, J=5.5 Hz, 1H), 7.409 (d, J=8.0 Hz, 1H), 2.715 (s, 3H), 1.484 (s, 6H) ppm.
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