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F.-Y. Zhang, A. S. C. Chan / Tetrahedron: Asymmetry 9 (1998) 1179–1182
mmol), and toluene (5 mL) at −60°C. The reaction mixture was stirred for 2 hours, warmed to room
temperature, and then filtered. The filtrate was cooled to −40°C and was treated with a 2.0 M solution of
lithium diisopropyl amide (1.5 mL, 3 mmol) for 3 hours. The reaction mixture was warmed to ambient
temperature and was filtered, concentrated, and purified by recrystallization to give the pure product
(S)-2 in 95% yield. The analytical data for (S)-2 are as follows: m.p.: 123–125°C; [α]D=+178.6 (c=1.0,
CHCl3); 1H-NMR (400 MHz, CD3OD) δ: 7.06–6.88 (m, 4H); 3.29–3.27 (m, 2H); 2.85–2.2.74 (m, 4H);
2.70–2.58 (m, 2H); 2.36–2.20 (m, 2H); 1.81–1.71 (m, 6H); 1.59–1.52 (m, 2H); 13C-NMR (101 MHz,
CD3OD) δ: 149.9, 149.1, 149.0, 138.2, 137.5, 134.1, 132.7, 129.8, 129.7, 129.6, 129.4, 128.9, 128.6,
128.2, 127.9, 126.2, 125.9, 125.6, 119.3, 119.0, 44.8, 44.7, 29.5, 29.4, 28.1, 28.0, 26.0, 24.9, 23.2, 23.1,
22.9; 31P-NMR (162 MHz, toluene) δ: 149.36 ppm; HRMS calculated for C26H34O2NP M+: 423.233,
found: 423.237.
3.2. A typical procedure for the catalytic conjugate addition of diethylzinc to 2-cyclohexen-1-one
A solution of Cu(OTf)2 (3.6 mg, 0.01 mmol) and (S)-2 (9.0 mg, 0.021 mmol) in 2 mL dichloromethane
was stirred for 1.0 hour. The solution was cooled to −20°C and 2-cyclohexen-1-one (32 µL, 0.33 mmol)
and a 1.0 M toluene solution of diethylzinc (0.5 mL, 0.5 mmol) were added. After stirring for 3.0 hours at
−15°C, the solution was mixed with 2.0 mL water and 0.2 mL 1.0 M hydrochloric acid solution, and the
product was extracted with 5.0 mL ethyl acetate. The conversion and enantioselectivity were determined
by GLC with a Chiraldex G-PN capillary column.
Acknowledgements
We thank the Hong Kong Research Grant Council for financial support of this study.
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