Preparation of Carboxylic Esters
3213
0 ꢁC under an argon atmosphere. The mixture was stirred for 5 min at
the same temperature, and solvent was evaporated. The obtained white
solid was cooled down to 0 ꢁC and suspended in dry THF (3.0 mL).
(S)-(–)-1-Phenylethyl alcohol (151.2 mg, 1.24 mmol), triethylamine
(346.7 mL, 2.49 mmol), and 2,4-dinitorobenzoic acid (176.1 mg,
0.83 mmol) were added sequentially. After the reaction mixture was stir-
red for 16 h at room temperature, it was quenched with water. The mix-
ture was extracted with AcOEt. The organic layer was washed with
brine, dried over anhydrous Na2SO4, filter, and concentrated. The
crude
product
was
purified
by
column
chromatography
(hexane=EtOAc ¼ 3=1) to afford the desired product 3f (250.8 mg,
96%, 95% ee) as a coloress solid. 1H NMR (270 MHz, CDCl3) d
8.77 (d, J ¼ 2.1 Hz, 1H), 8.50 (dd, J ¼ 8.4 Hz, 2.1 Hz, 1H), 7.90 (d,
J ¼ 8.4 Hz, 1H), 7.41–7.29 (m, 5H), 6.16 (q, J ¼ 6.6 Hz, 1H), 1.69 (d,
J ¼ 6.6 Hz, 1H). The enantiomeric purity was determined by HPLC
analysis using DAICEL Chiralpak AD-H, hexane=2-propanol ¼ 20=1,
k ¼ 254 nm, flow rate ¼ 1.0 mL=min, retention times ¼ 19.1 min (R)
and 24.6 min (S).
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¨
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