Hydrochloric Acid → 5-(1-Propynyl)pyridine-3-boronic Acid (contains varying amounts of Anhydride)

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3-Bromo-5-(prop-1-ynyl)pyridine (Intermediate 14, 25 g, 117 mmol), 2-methyl-tetrahydrofuran (60 mL), toluene (200 mL) and triisopropyl borate (33.2 mL, 140.78 mmol) were mixed. The mixture was cooled to −50° C. To the cold mixture was added n-BuLi (59.8 mL, 149.5 mmol) dropwise during 30 min. The mixture was stirred for 60 min. at −50° C. 2M HCl aq. (100 mL) was added. The mixture was then allowed to reach r.t. and stirred for 20 min. The organic and water phase were separated. The organic phase was extracted with Noah (2M aq.) (2×100 mL). The water phases were combined and the pH was adjusted to pH 5. The product was extracted with 2-methyl-THF (2×100 mL). The organic phase was dried with Na2SO4, filtered and concentrated to give the title compound (16.47 g, 87% yield): 1H NMR (500 MHz, CD3OD) δ ppm 2.11 (s, 3 H) 8.21 (br. s., 1 H) 8.53 (m, 2 H); MS (APCI+) m/z 162.2 [M+H]+.

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