Chiral Squaramide-Catalyzed Highly Enantioselective Michael Addition of 2-Hydroxy-1,4-naphthoquinones
References
naphthoquinone attacks the fixed nitroalkene from
the Si-face to afford the R-configured product, which
is consistent with the observed results.
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ACHTUNGTRENNUNGamides may represent a kind of good hydrogen-bond-
ing organocatalyst, and current studies are underway
in our group to broaden their application in asymmet-
ric catalysis.
Experimental Section
General Procedure for the Enantioselective Michael
Addition Reaction
Organocatalyst VIII (8.4 mg) was added to dichloromethane
to afford a solution of catalyst VIII (10.0 mL, 2.0 mmol/L).
To a solution of nitroalkenes 2 (0.20 mmol) in 0.25 mL of
the above catalyst VIII solution (0.0005 mmol) was added 2-
hydroxy-1,4-naphthoquinone 1 (0.20 mmol). The reaction
mixture was stirred at 308C for 6 h or 12 h. Then the mix-
ture was concentrated and purified by silica gel column
chromatography (CH2Cl2) to afford the desired products 3.
2-Hydroxy-3-(2-nitro-1-phenylethyl)naphthalene-1,4-dione
(3a): Compound 3a was obtained according to the general
procedure as an orange solid; yield: 61.9 mg (96%); mp
152–1538C. The enantiomeric excess was determined by
HPLC with a Daicel Chiralcel OJ-H column (n-hexane:2-
propanol 70:30 v/v, flow rate 1.0 mL·minÀ1, 254 nm): minor
enantiomer tr =17.3 min, major enantiomer tr =31.6 min,
98% ee; [a]2D5: À34.0 (c 1.46 g/100 mL, CH3COCH3);
1H NMR (500 MHz, CDCl3): d=8.11 (d, J=7.5 Hz, 1H),
8.06 (d, J=7.5 Hz, 1H), 8.00 (br s, 1H), 7.77 (dt, J1 =1.0 Hz,
J2 =7.5 Hz, 1H), 7.69 (dt, J1 =1.0 Hz, J2 =7.5 Hz, 1H), 7.47
(d, J=7.5 Hz, 2H), 7.32 (t, J=7.5 Hz, 2H), 7.28–7.25 (m,
1H), 5.48 (dd, J1 =9.0 Hz, J2 =13.5 Hz, 1H), 5.34–5.30 (m,
1H), 5.16 (dd, J1 =6.5 Hz, J2 =13.5 Hz, 1H).
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Acknowledgements
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We are grateful for financial support from the National Natu-
ral Science Foundation of China (Grant No. 21072020), the
Major Projects Cultivating Special Program in Technology
Innovation Program (Grant No. 2011CX01008) and the De-
velopment Program for Distinguished Young and Middle-
aged Teachers of Beijing Institute of Technology.
Adv. Synth. Catal. 2011, 353, 1241 – 1246
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1245