Lewis acidic ionic liquids for the synthesis of electrophilic alkenes via the Knoevenagel condensation

1-Butyl-3-methylimidazolium chloroaluminate. [bmim](ClAlCl3)-Al-., N=0.67 and 1-butylpyridinium chloroaluminate, [bpy](ClAlCl3)-Al-., N=0.67 ionic liquids were found to work well as the Lewis acid catalyst an solvent in the Knoevenagel condensations of benzaldehyde and substituted benzaldehydes with diethyl malonate to give benzylidene malonates. The benzylidene malonates subsequently underwent Michael additions with diethyl malonate. The extent of Michael product formed during the reaction was found to vary with the Lewis acidity and the molar proportion of ionic liquid. The influence of Lewis acidity of the ionic liquid on the Knoevenagel and Michael products is demonstrated. In the case of 2-hydroxyarylaldehydes, the reactions led to the formation of 3-ethoxycarbonyl coumarins under ambient conditions. (C) 2002 Elsevier Science Ltd. All rights reserved.