Episode II in the series of organic reactions that I never really learned belongs to the Knoevenagel condensation. It’s big brother, the aldol condensation, involves nucleophilic attack of a carbonyl compound by an enolate. The K.C. is similar, but involves nucleophilic attack by a deprotonated carbon followed by a loss of water (hence the “condensation”…duh).
The reaction was actually employed in the discovery of tear gas:The base used is typically weak, as the reactive site of the nucleophile should have a pretty acidic proton already. The base used in the above reaction is typically piperidine or pyridine.