[OH:1][B:2]1[C:6]2[CH:7]=[CH:8][C:9]([CH:11]=O)=[CH:10][C:5]=2[C:4]([CH3:14])([CH3:13])[O:3]1.[NH2:15][OH:16].Cl.CC([O-])=O.[Na+]>C1COCC1.O>[OH:1][B:2]1[C:6]2[CH:7]=[CH:8][C:9]([CH:11]=[N:15][OH:16])=[CH:10][C:5]=2[C:4]([CH3:14])([CH3:13])[O:3]1To a solution of 1-hydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]oxaborole-5-carbaldehyde (10 mg, 0.053 mmol) and NH2OH.HCl (4.4 mg, 0.063 mmol) in THF (4 mL) and H2O (1 mL) at rt was added NaOAc (6 mg, 0.074 mmol). The reaction mixture was stirred for 3 h and diluted with H2O. The mixture was extracted with EA and the organic layer was separated. The organic solution was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by prep-TLC to provide 1-hydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]oxaborole-5-carbaldehyde oxime (8 mg; yield 74%) as a colorless oil. 1H NMR (400 MHz, CDCl3): δ 8.23 (s, 1 H), 7.76 (d, J=7.6 Hz, 1 H), 7.55 (m, 2 H), 2.81 (s, 1 H), 1.61 (s, 6 H) ppm.
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