The general procedure for the synthesis of 2-(chloromethyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane from pinacol was as follows: to a mixed solution containing triisopropylborate (15 mL, 65 mmol), chloroiodomethane (13 g, 72 mmol), and tetrahydrofuran (78 mL) was added slowly and dropwise at -78 °C (external temperature) n-butyllithium ( 1.6 M hexane solution, 41 mL, 65 mmol) at -78 °C (external temperature), and the dropwise addition lasted for 20 min. After the dropwise addition, the reaction mixture was warmed to room temperature and stirred for 2.5 hours. Subsequently, the reaction mixture was cooled to 0 °C (external temperature) and a 4N hydrochloric acid-ethyl acetate solution was slowly added dropwise at this temperature until the reaction mixture reached neutrality. Pinacol (7.7 g, 65 mmol) was added to the reaction mixture while maintaining 0 °C, then the mixture was warmed to room temperature and stirred for 40 min. Upon completion of the reaction, the solvent was removed by evaporation under reduced pressure and the resulting residue was distilled under reduced pressure conditions (63-70 °C, 11 mmHg) to afford finally 2-(chloromethyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (9.2 g, 52 mmol, 81% yield). The product was characterized by 1H-NMR (CDCl3) with chemical shift δ (ppm) of 1.30 (12H, s), 2.97 (2H, s).
