Synlett 2009(1): 75-78  
DOI: 10.1055/s-0028-1087389
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Efficient α-Methylenation of Carbonyl Compounds in Ionic Liquids at Room Temperature

Juliana A. Vale, Daniel F. Zanchetta, Paulo J. S. Moran, J. Augusto R. Rodrigues*
Institute of Chemistry, University of Campinas, UNICAMP, P.O. Box 6154, 13084-971 Campinas, SP, Brazil
e-Mail: jaugusto@iqm.unicamp.br;
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Publikationsverlauf

Received 19 August 2008
Publikationsdatum:
12. Dezember 2008 (online)

Abstract

The application of several 1-butyl-3-methylimidazolium (BMIM) salt ionic liquids as solvent in the α-methylenation of carbonyl compounds at room temperature is reported. The ionic liquid [BMIM][NTf2] gave a clean reaction in a short time and good yields of several α-methylene carbonyl compounds. This ionic liquid was reused without affecting the reaction rates or yields over seven runs.

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Spectroscopic Data for Ethyl 3-Methylene-2-oxo-4-phenylbutanoate (1)
¹H NMR (300 MHz, CDCl3): δ = 1.36 (t, 3 H, J = 9 Hz), 3.65 (s, 2 H), 4.35 (q, 2 H, J = 9 Hz), 5.98 (s, 1 H), 6.23 (s, 1 H), 7.25 (m, 5 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 14.0, 35.7, 62.2, 126.5, 128.6, 129.2, 133.1, 137.6, 144.4, 163.9, 188.1. MS: m/z (%) = 218 (5) [M+], 189 (4), 145 (43), 117 (100), 115 (76), 91 (40), 65 (18), 51 (19).
Spectroscopic Data for Ethyl 2-Methylene-3-oxo-3-phenylpropionate(2)
¹H NMR (300 MHz, CDCl3): δ = 1.10 (t, 3 H, J = 7.1 Hz), 4.19 (q, 2 H, J = 7.2 Hz), 6.2 (s, 1 H), 6.65 (s, 1 H), 7.44 (d, 2 H, J = 7.2 Hz), 7.52 (t, 1 H, J = 7.3 Hz), 7.84 (d, 2 H, J = 7.2 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 14.0, 61.5, 128.5, 129.4, 131.3, 133.5, 136.3, 141.5, 164.0, 193.0. MS: m/z (%) = 204 (11) [M+], 175 (13), 158 (12), 130 (11) 105 (100), 77 (99), 51 (62).
Spectroscopic Data for 2-Methylene-3-phenylpropan-aldehyde (6)
¹H NMR (300 MHz, CDCl3): δ = 3.6 (s, 2 H), 6.05 (s, 1 H), 6.1 (s, 1 H), 7.47 (m, 5 H), 9.61 (s, 1 H). ¹³C NMR (75.5 MHz, CDCl3): δ = 34.1, 126.4, 128.5, 129.1 135.1, 138.1, 149.7, 193.9. MS: m/z (%) = 146 (38) [M+], 145 (35), 128 (19), 117 (73), 116 (80), 115 (95), 103 (10), 91 (95), 78 (58), 65 (80), 50 (95), 40 (100).