[CH3:1][C:2]1([CH3:13])[O:6][B:5]([OH:7])[C:4]2[CH:8]=[CH:9][C:10]([CH3:12])=[CH:11][C:3]1=2.C(OOC(=O)C1C=CC=CC=1)(=[O:21])C1C=CC=CC=1.C1C(=O)N(Br)C(=O)C1.C([O-])([O-])=O.[Na+].[Na+].Cl>C(Cl)(Cl)(Cl)Cl>[OH:7][B:5]1[C:4]2[CH:8]=[CH:9][C:10]([CH:12]=[O:21])=[CH:11][C:3]=2[C:2]([CH3:13])([CH3:1])[O:6]1To a solution of 3,3,5-trimethylbenzo[c][1,2]oxaborol-1(3H)-ol (27 mg, 0.153 mmol) in CCl4 (2 mL) at rt was added benzoyl peroxide (3.7 mg, 0.0153 mmol) followed by NBS (60 mg, 0.337 mmol). The reaction mixture was heated under reflux for 12 h, cooled to rt and treated with Na2CO3. The aqueous layer was acidified with 3 N HCl to pH of 3 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 prep-TLC to give 1-hydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]oxaborole-5-carbaldehyde (12 mg; yield 41%) as white solid. 1H NMR (400 MHz, CDCl3): δ 10.12 (s, 1 H), 7.88 (s, 2 H), 7.80 (s, 1 H), 1.62 (s, 6 H) ppm.
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