[OH:1][B:2]1[C:6]2[CH:7]=[C:8]([CH:11]=O)[CH:9]=[CH:10][C:5]=2[C:4]([CH3:14])([CH3:13])[O:3]1.[CH3:15][N+:16]([O-:18])=[O:17].CC(=O)OCC>CC(O)=O.O>[CH3:13][C:4]1([CH3:14])[O:3][B:2]([OH:1])[C:6]2[CH:7]=[C:8](/[CH:11]=[CH:15]/[N+:16]([O-:18])=[O:17])[CH:9]=[CH:10][C:5]1=2
To a solution of 1-hydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]oxaborole-6-carbaldehyde (1.14 g, 6 mmol) and NH4OAc (47 mg, 0.6 mmol) in AcOH (10 mL) at rt was added CH3NO2 (10 mL). The reaction mixture was stirred at 100° C. 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 column chromatography on silica gel by elution with PE:EA (2:1 to 1:1) to give (E)-3,3-dimethyl-6-(2-nitrovinyl)benzo[c][1,2]oxaborol-1(3H)-ol as a yellow solid (750 mg, yield 53%). 1F1 NMR (500 MHz, CDCl3) δ 9.18 (s, 1H), 8.18 (s, 2H), 8.01 (s, 1 H), 7.99 (d, J=8.0 Hz, 1 H), 7.57 (d, J=8.0 Hz, 1 H), 1.46 (s, 6H) ppm; MS: m/z=234.1 (M+1, ESI+).
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