Diisopropylamine → (5-((4-(tert-Butoxycarbonyl)piperazin-1-yl)methyl)-2-fluoropyridin-3-yl)boronic acid

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Reaction Conditions

Reaction Steps

n-Butyllithium (2.5 M in hexanes, 36.1 mL, 90 mmol) was added to a stirred solution of diisopropylamine (12.8 mL, 90 mmol) in tetrahydrofuran (150 mL, 75 mmol) at −40° C. and the slightly yellow solution was stirred at the same temperature for 1 h, and then cooled to −78° C. A solution of tert-butyl 4-((6-fluoropyridin-3-yl)methyl)piperazine-1-carboxylate (22.22 g, 75 mmol) in THF (100 mL) was cannulated slowly into the LDA solution over 30 min. The brown mixture was stirred at the same temperature for 1.5 h and then a solution of triisopropyl borate (25.9 mL, 113 mmol) in THF (50 mL) was added slowly. The resulting mixture was stirred at the same temperature for 30 min and then the cooling bath was removed. After the reaction mixture had warmed up to room temperature, the yellow heterogeneous mixture was quenched with 1.0 M NaOH(aq) (50 mL) and stirred for an additional 30 min. The separated aqueous layer was carefully acidified with 5N aqueous HCl until acidic (pH 4 to about 5) and the resulting cloudy mixture was diluted with EtOAc (150 mL). The separated aqueous layer was extracted with EtOAc (2×150 mL) and the combined organic phases were dried (Na2SO4), filtered, and concentrated to give 5-((4-(tert-butoxycarbonyl)piperazin-1-yl)methyl)-2-fluoropyridin-3-ylboronic acid (21.93 g, 64.7 mmol, 86% yield) as a pale yellow solid. LCMS (API-ES) m/z 340 (M+H)+.

Provenance & Evidence