A Heterocyclic N-Oxide-Mediated Morita-Baylis-Hillman Reaction
Y. S. Lin, C. W. Liu, T. Y. R. Tsai*
National Dong Hwa University, Hualien, Taiwan
21 September 2005 (online)
This constitutes the first report of the use of a heterocyclic N-oxide, 1-methylimidazole 3-N-oxide (1) as an effective promoter for the Morita-Baylis-Hillman reaction. Aromatic aldehydes bearing EWG (NO2, CF3, Cl) or EDG (OMe, OH) undergo smooth condensation with α,β-unsaturated ketones and esters under solvent-less conditions in the presence of two equivalents of 1 to give products in low to excellent yields. As expected, aldehydes with EWGs (e.g. NO2) give better yields than those bearing EDGs (e.g. OMe). Substituted aryl, naphthalenyl, pyridyl, quinolinyl, furfuryl, and thiophenyl aldehydes were used. Replacement of the normally used strong Lewis base catalysts (such as DABCO) by 1 not only overcomes slow reaction rates but also reduces the formation of side products. Although two equivalents of 1 are required, it is regenerated.