Ethyl ester 3 (4.00 g, 17.2 mmol) was added to diethyl ether (70 mL) and cooled to -78 °C. DIBAL-H (1M in hexane, 20 mmol, 20 mL) was added cautiously dropwise over 1 h. The solution was stirred for a further 4 h at -78 °C before being quenched with MeOH (40 mL) and warmed to room temperature. Saturated potassium sodium tartrate solution (60 mL) was added and the mixture was left to stir for 12 h before being extracted with diethyl ether (3 x 15 mL). The organic extracts were dried with MgSO4, filtered, and concentrated under reduced pressure to give the crude (S)-2-(tert-Butyldimethylsilyloxy)propanal (3.22 g, 99%) as a clear oil.
