Acetophenone → 1-Phenylethanol, (S)-

Participants

Reaction Steps

Under a nitrogen atmosphere, with stirring, acetophenone (3.05 mL, 26 mmol) was added to a solution of diisopinocampheylchloroborane (9.0 g, 28 mmol) in THF (20 mL) at -25° C. A yellow color developed immediately. The reaction was complete after 7 h at -25° C. (followed by 11B NMR after methanolysis of an aliquot). The volatiles were pumped off at aspirator pressure and the α-pinene was removed under reduced pressure (0.1 mm Hg, 8 h). The residue was dissolved in ethyl ether (100 mL) and diethanolamine (2.2 equiv) was added. The separated solid was filtered off after 2 h and washed twice with pentane (~30 mL). The combined ether and pentane filtrates were concentrated. The residue, upon distillation (bp 118° C., 22 mm Hg) provided [S]-1-phenylethanol (2.3 g, 72% yield) [α]20D-42.6° (neat) after purification by preparative gas liquid chromatography on Carbowax 20M; 98% ee based on -43.5° for maximum reported rotation. Gas chromatography analysis of its α-methoxy-α-(trifluoromethyl)phenylacetate (made from (+)-MTPA chloride, Aldrich) on Supelcowax glass capillary column (15 m) showed a composition of 98.7% S+1.3% R (i.e., 97.4% ee), in good agreement with the optical rotation measurement.

Provenance & Evidence