Synthesis
General procedure for the synthesis of 3-amino-4-fluorophenylboronic acid from 4-fluoro-3-nitrophenylboronic acid: 4-fluoro-3-nitrophenylboronic acid (63 g) was placed in a 500 mL single-necked flask, methanol (100 mL) and palladium-carbon catalyst (6.3 g, 10% loading) were added, followed by sealing the flask with a stopper. After evacuating the system, hydrogen was introduced. The reaction flask was placed in an oil bath at 55 °C with continuous stirring. The hydrogen pressure in the reaction system was maintained by replacing the hydrogen balloon until hydrogen was no longer absorbed. Upon completion of the reaction, the reaction mixture was filtered through a Brinell funnel to remove the palladium-carbon catalyst, and the filtrate was subsequently concentrated to dryness. The concentrate was pulped with n-heptane followed by vacuum drying. The resulting solid was dissolved in methanol (30 mL) and water (150 mL) was added to precipitate out the bulk solid. After removing the methanol and some of the water by distillation, the mixture was cooled to 5 °C. The light gray solid was collected by filtration through a Brinell funnel and dried under vacuum to give 42.6 g of 3-amino-4-fluorophenylboronic acid in 80.7% yield. The structure of the product was confirmed by 1H NMR and the purity was 99.1% as determined by HPLC.
