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Synlett 2003(15): 2337-2340  
DOI: 10.1055/s-2003-43333
LETTER
© Georg Thieme Verlag Stuttgart · New York

Highly Efficient Aza-Michael Reactions of Enones with Carbamates Using a Combination of Quaternary Ammonium Salts and BF3·OEt2 as a Catalyst

Li-Wen Xu, Lyi Li, Chun-Gu Xia*, Shao-Lin Zhou, Jing-Wei Li, Xiao-Xue Hu
State Key Laboratory of Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, P. R. China
Fax: +86(931)8277088; e-Mail: cgxia@ns.lzb.ac.cn;
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Publication History

Received 13 October 2003
Publication Date:
07 November 2003 (online)

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Abstract

Aza-Michael reactions of enones with carbamates took efficiently in the presence of a catalytic amount of quaternary ammonium salts and BF3·OEt2 to afford the total products in high yields. The new catalytic system was also efficient in the aza-Michael reaction of chalcone, which was difficult to react with carbamates by transition metal salts catalysts.

Key words

quaternary ammonium salts - Lewis acids - Michael reaction - carbamate - enone

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Representative Experimental Procedure:
TBAB (0.1 mmol) and the enones (1 mmol) were dissolved in CH2Cl2 (3 mL). BF3·OEt2 (0.2 mmol) was added. Then carbamate (1.2 mmol) was added in one portion. The mixture solution was stirred at r.t. and conversion was monitored by TLC (for 24 h). After completion of the reaction, the mixture was quenched with sat. aq NaHCO3 (5 mL), and the aq layer was extracted with CH2Cl2. The combined organic layers were dried over Na2SO4, filtered, and evaporated. The crude product was purified by column chromatography (eluting solvent: EtOAc-petroleum ether). All the compounds were identified by GC-MS (Agilent 6890N GC/5973N MS, HP-5MS) and usual spectral methods. Selected spectral data of new compounds. 4a: IR(solid): 3366, 3029, 2965, 1721, 1681, 1526, 1291, 1241, 1221, 1022, 746, 699 cm-1. 1H NMR (400 MHz, CDCl3): δ = 7.88 (d, J = 7.2 Hz, 2 H), 7.54 (t, J = 7.2 Hz, 1 H), 7.44-7.22 (m, 12 H), 5.89 (br s, 1 H), 5.33 (d, J = 6.0 Hz, 1 H), 5.09 (s, 2 H), 3.68 (dd, J = 16.7 Hz, J = 4.2 Hz, 1 H), 3.45 (dd, J = 16.7 Hz, J = 4.8 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 197.8, 155.7, 141.2, 136.6, 136.3, 133.4, 128.6, 128.5, 128.1, 127.5, 126.3, 66.8, 51.8, 43.9. GC-MS: m/z = 359. 4f: 1H NMR: δ = 7.95 (d, J = 7.2 Hz, 2 H), 7.54 (t, J = 7.2 Hz, 1 H), 7.45-7.24 (m, 7 H), 5.36 (dd, J 1 = 6.0 Hz, J 2 = 8.6 Hz, 1 H), 4.22 (dd, J 1 = 1.6 Hz, J 2 = 8.8 Hz, 1 H), 3.57 (br s, 2 H), 3.43 (dd, J 1 = 8.0Hz, J 2 = 16.0 Hz, 1 H): 13C NMR: δ = 197.2, 157.9, 138.7, 136.6, 133.7, 129.1, 129.0, 128.4, 127.5, 62.2, 54.6, 43.4, 40.6. 4g: 1H NMR: δ = 7.88 (d, J = 7.2 Hz, 2 H), 7.57 (m, 1 H), 7.41 (m, 2 H),7.24 (m, 2 H), 6.81 (m, 2 H), 5.63 (br s, 1 H), 5.22 (dd, J 1 = 6.4 Hz, J 2 = 14.0 Hz, 1 H), 4.07 (dd, J 1 = 6.8 Hz, J 2 = 14.0 Hz, 2 H), 3.64-3.74 (m, 2 H), 3.37-3.43 (m, 1 H), 1.20 (t, J 1 = 6.4 Hz, J 2 = 15.2 Hz, 3 H). 13C NMR: δ = 198.2, 159.0, 156.1, 136.9, 133.7, 133.6, 128.9, 128.3, 127.8, 114.2, 61.1, 55.5, 51.5, 44.3, 14.8. 4h: 1H NMR: δ = 7.88 (d, J = 7.2 Hz, 2 H), 7.55-7.21 (m, 8 H), 5.72 (br s, 1 H), 5.28 (dd, J 1 = 6.4 Hz, J 2 = 14.0 Hz, 1 H), 3.67 (m, 2 H), 3.40-3.46 (m, 1 H), 1.21 (t, J 1 = 6.4 Hz, J 2 = 14.0 Hz, 3 H). 13C NMR: δ = 198.2, 159.8, 156.2, 141.6, 136.8, 133.6, 128.9, 128.3, 127.7, 61.2, 51.9, 44.2, 14.8. 4i: 1H NMR: δ = 7.85 (d, J = 7.2 Hz, 2 H), 7.57-7.20 (m, 12 H), 6.00 (br s, 1 H), 5.26 (dd, J 1 = 6.0 Hz, J 2 = 13.2 Hz, 1 H), 4.77 (br s, 2 H), 3.65 (m, 1 H), 3.40 (dd, J = 5.2 Hz, J = 16.8 Hz, 1 H). 13C NMR: δ = 197.9, 157.0, 156.0, 140.7, 136.6, 136.5, 133.9, 132.0, 129.0, 128.7, 128.5, 128.3, 127.9, 121.5, 67.1, 51.4, 43.8.