Diisopropylamine → 2-Fluoro-5-(thiomorpholinomethyl)pyridin-3-ylboronic acid

Participants

Reaction Conditions

Reaction Steps

A solution of diisopropylamine (0.767 mL, 5.43 mmol) in 2 mL of THF at −40° C. was treated with n-butyllithium (3.4 ml of 1.6 M solution in hexanes, 5.43 mmol) and stirred at this temperature for 30 min. The solution was cooled to −78° C. and treated dropwise via cannula with a solution of 4-((6-fluoropyridin-3-yl)methyl)thiomorpholine (922 mg, 4.34 mmol) in THF (2+2 mL) over 10 min. The brown mixture was stirred at −78° C. for 90 min and then treated dropwise via syringe with a solution of triisopropyl borate (1.49 mL, 6.51 mmol) in THF (1 mL). The mixture was stirred at −78° C. for 30 min. The cooling bath was removed, and the reaction mixture was allowed to warm up to RT. The mixture was quenched with 1.0 N NaOH (5 mL) and stirred for an additional 30 min. The mixture was transferred to a separatory funnel and extracted with 5 mL of ether. The ether layer was discarded, and the aqueous layer was carefully acidified with 2.5 N aqueous HCl until acidic (pH 4about5) and the resulting cloudy mixture was diluted with EtOAc (50 mL). The separated aqueous layer was extracted with EtOAc (2×15 mL) and the combined organic extracts were washed with brine, dried (Na2SO4), filtered, and concentrated to give 2-fluoro-5-(thiomorpholinomethyl)pyridin-3-ylboronic acid (790 mg, 3.08 mmol, 71.0% yield) as an off-white crystalline solid. 1H NMR (400 MHz, d4-MeOH) δ 8.11 (1H, d, J=2.5 Hz); 8.00 (1H, dd, J=8.0, 2.5 Hz); 3.75 (2H, s.); 2.91 (4H, m); 2.73 (4H, br. s.). m/z (ESI, +ve ion) 257 (M+H)+.

Provenance & Evidence