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

Experimental procedure⁵⁾: To a solution of 1 (3.52 g, 10.8 mmol) in toluene (85 mL) is added (R)-CBS-Me catalyst (1 mol/L in toluene, 4.30 mL, 4.30 mmol) and the solution is cooled to -78 °C. A solution of catecholborane (3.44 mL, 32.3 mmol) in toluene (20 mL) is added dropwise over 30 minutes. After stirring for 6 hours at -78 °C, water (40 mL) is added and the reaction is allowed to warm to rt. The reaction mixture is poured on water (150 mL) and extracted with Et₂O (3 x 125 mL). The combined organic layers are washed with 1 mol/L NaOH (2 x 100 mL), saturated NaCl (100 mL), dried over MgSO₄, and concentrated under vacuum. The crude product is purified by flash chromatography (hexanes:EtOAc = 4:1) to provide 3.00 g (85% yield, 98% ee) of 2 as a clear oil.