Triisopropyl borate → (R)-5-(1-(4-(tert-butoxycarbonyl)piperazin-1-yl)ethyl)-2-fluoropyridin-3-ylboronic acid

Participants

Reaction Conditions

Reaction Steps

n-Butyllithium (2.5 M in hexanes, Aldrich; 20.0 mL, 50.0 mmol) was added (dropwise over 20 min) to a solution of (R)-tert-butyl 4-(1-(6-fluoropyridin-3-yl)ethyl)piperazine-1-carboxylate (10.0 g, 32.3 mmol) in THF (150 mL) at −78° C., and the resulting mixture was stirred at −78° C. for 20 min. Triisopropyl borate (15.0 mL, 65.2 mmol) was then added (dropwise over 10 min), followed by additional THF (20 mL) to rinse solidified triisopropyl borate from the side of the flask. The resulting mixture was stirred at −78° C. for 15 min, and the cooling bath was then removed. The reaction mixture was stirred for 1 h, and 1 N aq. NaOH (100 mL) and water (40 mL) were then sequentially added. The resulting mixture was stirred for 10 min, and the organic layer was separated. The organic layer was extracted with 1 N aq. NaOH (40 mL), and the aqueous layers were then combined and pH-adjusted with 5 N aqueous HCl to a final pH of about 5. The resulting mixture was extracted with EtOAc (3×200 mL), and the combined organic extracts were dried over sodium sulfate, filtered, and concentrated in vacuo to provide (R)-5-(1-(4-(tert-butoxycarbonyl)piperazin-1-yl)ethyl)-2-fluoropyridin-3-ylboronic acid (9.27 g, 81% yield) as a white solid. 1H NMR (400 MHz, d4-MeOH) δ 8.39 (br. s., 1H), 8.26 (d, J=6.5 Hz, 1H), 4.54-4.63 (m, 1H), 3.31 (br. s., 4H; masked by MeOH), 3.13 (br. s., 4H), 1.80 (d, J=6.8 Hz, 3H), 1.45 (s, 9H). 19F NMR (377 MHz, d4-MeOH) δ −60.93 (br. s., 1 F). m/z (ESI, +ve) 354.2 (M+H)+.

Provenance & Evidence