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0 °C

A solution of (1,6-dihydroxy-4-methyl-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl)-acetic acid ethyl ester (0.835 g, 3.34 mmol) in THF (10 mL) was treated with lithium hydroxide (0.383 g, 16.70 mmol) in water (10 mL) at 0° C. The solution was stirred at 0° C. for 1 hour then quenched with 2N HCl to pH 2. The mixture was concentrated to approximately half of the entire volume. The solid that precipitated was collected by vacuum filtration, then rinsed with cold water and dried to give (1,6-dihydroxy-4-methyl-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl)-acetic acid as a light yellow solid (0.65 g, 88%). mp 165-166° C. 1H NMR (400 MHz, DMSO-d6) δ 12.31 (s, 1H), 9.30 (s, 1H), 9.08 (s, 1H), 6.88 (s, 1H), 6.66 (s, 1H), 5.38 (d, J=9.38 Hz, 1H), 3.00 (d, J=15.24 Hz, 1H), 2.20 (s, 3H), 2.00 (dd, J=15.24, 10.16 Hz, 1H). MS (ESI) m/z: 221 [M−1].

1. customthen quenched with 2N HCl to pH 2
2. concentrationThe mixture was concentrated to approximately half of the entire volume
3. customThe solid that precipitated
4. filtrationwas collected by vacuum filtration
5. washrinsed with cold water
6. customdried