[CH2:1]([O:3][C:4](=[O:19])[CH2:5][CH:6]1[O:10][B:9]([OH:11])[C:8]2[CH:12]=[C:13]([OH:18])[CH:14]=[C:15]([CH2:16]Br)[C:7]1=2)[CH3:2].[N-:20]=[N+:21]=[N-:22].[Na+]>CC#N.O>[CH2:1]([O:3][C:4](=[O:19])[CH2:5][CH:6]1[O:10][B:9]([OH:11])[C:8]2[CH:12]=[C:13]([OH:18])[CH:14]=[C:15]([CH2:16][N:20]=[N+:21]=[N-:22])[C:7]1=2)[CH3:2]To a crude (4-bromomethyl-1,6-dihydroxy-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl)-acetic acid ethyl ester in CH3CN/H2O (10/2 mL) was added sodium azide (3.1 g, 48 mmol). The solution was stirred overnight at r.t. The crude solution was purified by HPLC, yielded 450 mg of the title compound. 1H NMR (300 MHz, CD3CN) δ 7.21 (s, 1H), 6.99 (s, 1H), 5.61 (dd, 1H), 4.31-4.56 (dd, 2H), 4.10 (q, 2H), 3.02-3.14 (dd, 1H), 2.37-2.43 (m, 1H), 1.21 (t, 3H).
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