The Knoevenagel Condensation Reaction is a classic organic synthesis, described by Emil Knoevenagel in the 1890s. The Knoevenagel reaction is a modified Aldol Condensation with a nucleophilic addition between an aldehyde or ketone, and an active hydrogen compound in the presence of a basic catalyst, resulting in C–C bond formation. The active hydrogen compound contains a C–H bond which can be deprotonated by the basic catalyst. The reaction is usually followed by spontaneous dehydration resulting in an unsaturated product.1
Figure 1.Knoevenagel Condensation Reaction
Z, Z' (electron withdrawing groups) = CO2R, COR, CHO, CN, NO2, etc.
Knoevenagel’s use of primary and secondary amines, and their salts as catalysts provided an early foundation for the study of aminocatalysts.2 Research continues into synthetic methods using the Knoevenagel condensation with novel new catalysts and reaction activation being reported:
Microwave and ultrasound irradiated reactions3–6
Solvent free conditions7,8
Photochemical condensation with fruit extracts as catalysts10,11
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