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Synlett 2004(11): 1980-1984  
DOI: 10.1055/s-2004-830879
LETTER
© Georg Thieme Verlag Stuttgart · New York

Enamination of β-Dicarbonyl Compounds Catalyzed by CeCl3·7H2O at ­Ambient Conditions: Ionic Liquid and Solvent-Free Media

Mohammad Mehdi Khodaei*, Ahmad Reza Khosropour*, Mehdi Kookhazadeh
Department Of Chemistry, Razi University, Kermanshah 67149, Iran
Fax: +98(831)4274559; e-Mail: mmkhoda@razi.ac.ir; e-Mail: arkhosropour@razi.ac.ir;
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Publication History

Received 10 March 2004
Publication Date:
04 August 2004 (online)

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Abstract

Enamination of a wide various primary amines was successfully carried out in the presence of catalytic amounts of cerium chloride heptahydrate in ionic liquid and solvent-free conditions as ‘green’ media under mild reaction conditions.

Keywords

ionic liquid - solvent-free - TBAB - CeCl3·7H2O - chemoselectivity - primary amine - catalyst

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Typical Experimental Procedure (Method A): To a mixture of ethyl acetoacetate (1.0 mmol) and aniline (1.0 mmol) under solvent-free conditions, CeCl3·7H2O (0.1 mmol) was added and the reaction mixture stirred at r.t. for the appropriate time according to Table [2] . After completion of the reaction as indicated by TLC, the mixture was washed with EtOAc. The crude products were separated by preparative chromatography on silica gel using n-heptane-EtOAc (10:1) as eluent. The pure b-enaminones were prepared in 50-87% yields.

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Typical Experimental Procedure (Method B): To the molten of TBAB (0.5 mmol), CeCl3·7H2O (0.1 mmol) was added and the mixture cooled to r.t., then ethyl acetoacetate (1.0 mmol) and aniline (1.0 mmol) were added to it. The reaction mixture stirred magnetically at r.t. for the appropriate time as shown in Table [2] . The reaction was followed by TLC. When the reaction was completed, the mixture washed with EtOAc. The crude products were separated by preparative chromatography on silica gel using n-heptane/EtOAc (10:1) as eluent. The pure b-enaminones were prepared in 74-99% yields. Selected characterization data of compounds 8, 11, 13 and 20 are shown below.
Compound 8: mp 110-111 °C. IR (KBr): nmax = 3240, 2923, 1668, 1584, 1250, 1012, 955, 763 cm-1. 1H NMR (200 MHz, CDCl3): dH = 8.32 (br, 1 H, NH), 4.28 (t, J = 8.7 Hz, 2 H), 3.75 (t, J = 5.8, 2 H), 3.41 (q, J = 5.1, 2 H), 3.18 (br, 1 H, OH), 2.75 (t, J = 7.3 Hz, 2 H), 2.1 (s, 3 H, CH3). 13C NMR (50 MHz, CDCl3): dc = 174.8, 158.4, 156.9, 85.2, 65.8, 62.1 45.7, 26.9. Anal. Calcd for C8H13NO3: C, 56.13; H, 7.65; N, 8.18. Found: C, 56.00; H, 7.70; N, 8.30.
Compound 11: mp 92-94 °C IR (KBr): nmax = 3182, 3072, 2900, 1666, 1637, 1245, 1019, 955 cm-1. 1H NMR (200 MHz, CDCl3): dH = 9.9 (br, 1 H, NH), 7.25-7.00 (m, 4 H, Ar), 4.42 (t, J = 8 Hz, 2 H, OCH2), 3.03 (t, J = 8.1 Hz, 2 H, =C-CH2-), 2.45 (s, 3 H, CH3), 2.08 (s, 3 H, CH3). 13C NMR (50 MHz, CDCl3): dc = 174.4, 154.5, 147.8, 136.8, 135.2, 130.1, 124.9, 88.9, 65.8, 26.9, 21.3. Anal. Calcd for C13H15NO2: C, 71.86; H, 6.95; N, 6.45. Found: C, 71.60; H, 7.00; N, 6.70.
Compound 13: mp 105-107 °C; IR (KBr): nmax = 3288, 2895, 1679, 1618, 1440, 1017, 760, 740, 696 cm-1. 1H NMR (200 MHz, CDCl3): dH = 8.72 (s, 1 H, NH), 7.42-7.20 (m, 5 H, Ph), 4.46 (d, J = 3.9 Hz, 2 H, CH2N), 4.32 (t, J = 4.7 Hz, 2 H, OCH2), 2.85 (t, J = 4.8 Hz, 2 H, CH2C=), 1.95 (s, 3 H, CH3). 13C NMR (50 MHz, CDCl3): dc = 174.6, 168.0, 157.4, 139.3, 129.2, 127.8, 127.0, 86.5, 65.6, 53.6, 47.1, 26.9, 16.8. Anal. Calcd for C13H15NO2: C, 71.90; H, 7.00; N, 6.50. Found: C, 71.60; H, 7.00; N, 6.70.
Compound 20: mp 177-179 °C. IR (KBr): nmax = 3360, 3120, 1525, 1512, 1080, 800, 748, 705 cm-1. 1H NMR (200 MHz, CDCl3): dH = 11.6 (s, 2 H, NH), 8.17-7.1 (m, 10 H, Ph), 5.70 (s, 2 H, =CH-), 3.82-3.30 (m, 4 H, -CH2), 2.10 (s, 6 H, CH3). 13C NMR (50 MHz, CDCl3): dc = 188.7, 165.4, 140.5, 131.1, 128.7, 127.4, 93.4, 44.2, 19.7. Anal. Calcd for C22H24N2O2: C, 75.83; H, 6.94; N, 9.16. Found: C, 75.44; H, 6.80; N, 8.40.