General Zinc-Catalyzed Conia-Ene Reactions of 1,3-Dicarbonyl Compounds
COMMUNICATIONS
Scheme 4. Possible mechanism.
ene reaction with a catalytic amount of inexpensive References
ZnCl2 catalyst under neat conditions. Importantly, we
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provide the first example of the construction of four-
membered rings by the Conia-ene reaction. Work to
understand the mechanism and extend the scope of
both the reaction and products in the preparation of
biologically active compounds is currently underway.
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Experimental Section
Typical Experimental Procedure for Zn-Catalyzed
Conia-ene Reaction:
A mixture of substrate 1 (0.3 mmol) and ZnCl2 (10 mol%)
under neat or DCE (2 mL) conditions was added in turn
into a 25-mL glass sealed tube, the mixture was stirred
under an argon atmosphere at 1008C for the desired time
until complete consumption of the starting material as moni-
tored by TLC and GC-MS analysis. Then the mixture was
diluted with diethyl ether, washed with saturated NaCl, and
evaporated under vacuum. The residue was purified by flash
column chromatography (hexane/ethyl acetate) to afford the
pure product 2.
Dimethyl
2-methylenecyclopentane-1,1-dicarboxylate
(2a):[3a] Colorless oil; H NMR (500 MHz, CDCl3): d=5.30
(t, J=2.5 Hz, 1H), 5.27 (t, J=2.0 Hz, 1H), 3.75 (s, 3H),
2.48–2.44 (m, 2H), 2.35 (d, J=7.0 Hz, 2H), 1.78–1.70 (m,
2H); 13C NMR (125 MHz, CDCl3): d=171.2, 148.2, 112.0,
63.5, 52.7, 36.3, 33.7, 24.1; IR (KBr): n=1730 cmÀ1; LR-MS
(EI, 70 eV): m/z (%)=198 (M+, 4), 138 (M+ÀCOOMe,
100).
1
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Acknowledgements
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We thank the National Natural Science Foundation of China
(No. 20872112), Zhejiang Provincial Natural Science Foun-
dation of China (No. Y407116), and Program for New Cen-
tury Excellent Talents in University (No. NCET-06–0711) for
financial support.
Adv. Synth. Catal. 2009, 351, 3096 – 3100
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3099