The general procedure for the synthesis of potassium (methoxymethyl)trifluoroborate from tributyl(methoxymethyl)stannane is as follows: n-butyllithium (1.5 M hexane solution, 0.77 ml, 1.2 mmol) was added dropwise to a mixed solution containing tributyl(methoxymethyl)stannane (360 mg, 1.1 mmol) and tetrahydrofuran (3 ml) at -78 °C (external temperature). The reaction mixture was stirred at the same temperature for 30 min. Subsequently, the above mixture was added dropwise to a mixed solution containing triisopropyl borate (0.3 ml, 1.3 mmol) and tetrahydrofuran (5 ml) via cannula at -78°C (external temperature). The reaction mixture was stirred at room temperature for 20 minutes. Next, potassium hydrogen fluoride (0.51 g, 6.5 mmol) was added to the mixture at 0°C (external temperature). Then, water (60 ml) was added slowly and dropwise to the reaction mixture. After warming the reaction mixture to room temperature, the solvent was removed by distillation under reduced pressure. The obtained residue was washed with ether. Acetone was added to the washed residue which was subsequently filtered. After distillation of the solvent from the filtrate under reduced pressure, the resulting residue was recrystallized using acetone to give the final potassium (methoxymethyl)trifluoroborate (30 mg, 0.20 mmol, 18% yield). The product was characterized by 1H-NMR (DMSO-d6) with chemical shifts δ (ppm) of 2.39-2.43 (2H, m), 3.05 (3H, s).
