CC(OC([N:8]1[CH2:14][C:13]2[CH:15]=[C:16]([B:19]([OH:21])[OH:20])[CH:17]=[CH:18][C:12]=2[O:11][CH2:10][CH2:9]1)=O)(C)C.[ClH:22]>O1CCOCC1.C(OCC)C>[ClH:22].[O:11]1[C:12]2[CH:18]=[CH:17][C:16]([B:19]([OH:21])[OH:20])=[CH:15][C:13]=2[CH2:14][NH:8][CH2:9][CH2:10]1(4-{[(1,1-dimethylethyl)oxycarbonyl}-2,3,4,5-tetrahydro-1,4-benzoxazepin-7-yl)boronic acid (Example 1, step 2) (1.07 g, 3.64 mmol) was dissolved into 4M hydrogen chloride in dioxane and the resulting solution was allowed to stir at room temperature for 1.3 h. The heterogeneous mixture was then diluted with ethyl ether (100 mL) and the solid collected by filtration to give 2,3,4,5-tetrahydro-1,4-benzoxazepin-7-ylboronic acid hydrochloride salt (791 mg, 95%). 1H NMR (400 MHz, D2O): 7.79 (dd, 1H), 7.74 (d, 1H), 7.21 (d, 1H), 4.47 (s, 2H), 4.36 (m, 2H), 3.69 (m, 2H).
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