(S)-5,5-Diphenyl-2-methyl-3,4-propano-1,3,2-oxazaborolidine

Typical Procedure:
A freshly prepared solution of 0.5 M dimethyl sulfide borane in toluene (48 µL, 0.024 mmol) is added to a solution of 1 (4.5 mg, 0.012 mmol) and 0.05 M (S)-Me-CBS catalyst in toluene (470 µL, 0.024 mmol) at -78 °C under N₂ atmosphere. After the mixture is stirred for 15 h at -30 ℃, methanol (100 µL) is added, followed by water (0.5 mL) and Et₂O (2 mL), and the mixture is warmed to 23 ℃. Water (10 mL) and Et₂O (10 mL) are added, and the aqueous portion is extracted with Et₂O (2 x 20 mL). The combined organic fractions are dried (MgSO₄) and concentrated in vacuo. Flash chromatography (SiO₂, Et₂O : hexane = 8 : 92) affords 2 (4.1 mg, 91% yield) as a clear oil.