A. (S)-Phenylalanol. A dry, 3-L, three-necked flask is equipped with a mechanical stirrer and a reflux condenser connected to a mineral oil bubbler. The flask is loaded with 165 g (1.00 mol) of (S)-phenylalanine (Note 1), then equipped with a 250-mL pressure-equalized addition funnel capped with a rubber septum through which is inserted a nitrogen inlet needle. The flask is swept with nitrogen and filled with 500 mL of anhydrous tetrahydrofuran, and the addition funnel is charged with 123 mL (1.00 mol) of freshly distilled boron trifluoride etherate via cannula (Note 2). The boron trifluoride etherate is added dropwise to the phenylalanine slurry over a 30-min period with stirring, and the mixture is heated at reflux for 2 hr, resulting in a colorless, homogeneous solution. The addition funnel is then charged via cannula with 88 g (110 mL, 1.15 mol) of 20 M borane–dimethyl sulfide complex (Note 3), which is added carefully to the vigorously refluxing solution over a 100-min period. During the course of the addition there is continuous evolution of dimethyl sulfide and hydrogen gas, and the solution turns from orange to light brown. A vigorous exotherm occurs approximately half way through the addition period. (Caution! See (Note 4)) The solution is heated at reflux for an additional 6 hr after the addition is complete (Note 5) and (Note 6), then allowed to cool to ambient temperature. The excess borane is quenched by the slow addition of 125 mL of a 1:1 tetrahydrofuran–water solution followed by 750 mL of 5 M aqueous sodium hydroxide. The resulting two-phase mixture is heated at reflux for 12 hr, cooled to room temperature, and filtered through a coarse fritted funnel. The residual solids are washed with two 25-mL portions of tetrahydrofuran, and the filtrate is concentrated on a rotary evaporator to remove the bulk of the tetrahydrofuran. The resulting slurry is extracted with one 400-mL and three 200-mL portions of dichloromethane. The combined organic extracts are dried over anhydrous sodium sulfate, filtered, and concentrated by rotary evaporation, yielding 141–158 g (93–104%) of a white crystalline solid that is recrystallized from ca. 600 mL of ethyl acetate to give 111–113 g (73–75%) of the desired product as white needles in two crops, mp 88.5–91°C (Note 7).

B. (S)-4-(Phenylmethyl)-2-oxazolidinone. A dry, 1-L, three-necked flask is equipped with a mechanical stirrer and a 12-in. Vigreux column fitted with a distillation head and a 200-mL receiver flask connected to a nitrogen source and a bubbler. The flask is charged with 151 g (1.00 mol) of (S)-phenylalanol, 13.8 g (0.100 mol) of anhydrous potassium carbonate, and 250 mL (2.06 mol) of diethyl carbonate (Note 8). The mixture is lowered into an oil bath, preheated to 135°C, and is stirred until dissolution is achieved (ca. 5 min). The distillation receiver is cooled in an ice bath, and ca. 120 mL of ethanol is collected from the reaction over a 2.5-hr period. The oil bath is removed on cessation of the ethanol distillation. After the light-yellow solution is cooled to ambient temperature, it is diluted with 750 mL of dichloromethane, transferred to a separatory funnel, and washed with 750 mL of water. The organic phase is dried over anhydrous magnesium sulfate, filtered, and concentrated on the rotary evaporator affording 200 g (113%) of a white crystalline solid. This material is taken up into 600 mL of a hot 2:1 ethyl acetate–hexane solution, filtered while hot, then allowed to crystallize to afford 136–138 g (78–79%) of large white plates, mp 84.5–86.5°C (Note 9) and (Note 10).