2,4-Bis(trifluoromethyl)phenylboronic Acid (contains varying amounts of Anhydride)

• Benzoic Acid [B2635]
• Benzylamine [B0406]
• 2,4-Bis(trifluoromethyl)phenylboronic Acid [B3022]
• Fluorobenzene [F0034]

To a solution of benzoic acid (122 mg, 1.0 mmol) and benzylamine (107 mg, 1.0 mmol) in fluorobenzene (5 mL, 0.2 mol/L) was added molecular sieves 3A (2 g) at room temperature. After that 2,4-bis(trifluoromethyl)phenylboronic acid (13 mg, 0.05 mmol) was added to the reaction mixture and stirred at reflux temperature for 24 hours. The reaction mixture was filtered on celite pad and washed with EtOAc. The filtrate was washed with 2 mol/L HCl aq. (30 mL), saturated NaHCO₃ aq. (30 mL), and brine (30 mL), dried over sodium sulfate and filtered. The solvent was removed under reduced pressure to give N-benzylbenzamide as a white solid (135 mg, 64%).

The reaction mixture was monitored by LC.

N-benzylbenzamide

¹H NMR (270 MHz, DMSO-d6); δ 9.05 (brt, 1H, J = 5.4 Hz), 7.90 (dd, 1H, J = 7.3, 1.6 Hz), 7.56-7.44 (m, 3H), 7.36-7.32 (m, 4H), 7.25 (q, 1H, J = 7.3 Hz).

• The ortho-substituent on 2,4-bis(trifluoromethyl)phenylboronic acid catalyzed dehydrative condensation between carboxylic acids and amines
• K. Wang, Y. Lu, K. Ishihara, Chem. Commun. 2018, 54, 5410.