[CH3:1][O:2][C:3](=[O:31])[CH2:4][CH2:5][C:6]([C:8]1[C:13]([B:14]2[O:18]C(C)(C)C(C)(C)[O:15]2)=[CH:12][C:11]([O:23]C2CCCCO2)=[CH:10][C:9]=1[CH3:30])=O.[BH4-].[Na+]>CO>[CH3:1][O:2][C:3](=[O:31])[CH2:4][CH2:5][CH:6]1[O:18][B:14]([OH:15])[C:13]2[CH:12]=[C:11]([OH:23])[CH:10]=[C:9]([CH3:30])[C:8]1=2To a solution of 4-[2-Methyl-4-(tetrahydro-pyran-2-yloxy)-6-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-phenyl]-4-oxo-butyric acid methyl ester (1.15 g, 2.57 mmol) in MeOH (50 mL) was added NaBH4 (0.244 g, 6.42 mmol) at 0° C. The reaction mixture was stirred at 0° C. for 30 minutes, quenched with 6 N HCl and concentrated in vacuo. The residue was purified by silica gel flash column chromatography followed by lyophilization to give 3-(1,6-dihydroxy-4-methyl-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl)-propionic acid methyl ester (0.19 g, 30%). 1H NMR (400 MHz, Actone-d6) δ 8.20 (s, 1H), 7.96 (s, 1H), 7.00 (s, 1H), 6.80 (s, 1H), 5.20 (m, 1H), 3.60 (s, 3H), 2.40 (m, 2H), 2.30 (m, 3H), 1.65 (m, 1H).
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