To a flame-dried 250-mL round-bottomed flask equipped with a magnetic stir bar was added THF (120 mL, 0.5 M) and diisopropylamine (10.1 mL, 72.0 mmol, 1.2 equiv). The reaction mixture was cooled to 0 °C by transferring the reaction apparatus to an ice-water bath. The reaction mixture was allowed to stir for 10 minutes at 0 °C before n-BuLi (28.8 mL, 72.0 mmol, 1.2 equiv, 2.5 M in hexanes) was added dropwise over 5 minutes to the stirred reaction mixture.