Side Reactions in Baylis-Hillman Reaction in Ionic Liquids

In an attempt to speed up some sluggish Baylis-Hillman reactions, the group of Aggarwal at Bristol (Aggarwal VK et al, Chem Comm, 2002, 1612) tried the ionic liquid solvents. Yields were low, partly because benzaldehyde reacted with the imidazolium chloride ionic liquid to give a by-product.

Caution is recommended in the use of ionic liquids in the presence of mild bases (i.e. pKa as low as 8-9), since if the ionic liquid reacts, yields will be low and the ionic liquid is contaminated and cannot be reused. The work of Rosa (Tetrahedron 2001, 57, 4189) on reactions in ionic liquids may now need reinterpretation.