Knoevenagel Condensation Reactions of Cyano Malononitrile-derivatives under Microwave Radiation

Knoevenagel condensation was discovered in the 20th century, and since then it has been present in a wide range of reactions in organic chemistry due to its potential for forming carbon-carbon bonds. This reaction is usually carried out between aldehydes or ketones and active methylene compounds in the presence of Lewis acids or basic catalysts. The great advantage of this reaction is that can be carried out in mild conditions, with easy handling and using solvents with low toxicity. In the last 15 years, this type of organic synthesis has been used for the formation of alpha,beta unsaturated carbonyl compounds according to the principles of Green Chemistry. The use of microwave radiation to perform Knoevenagel condensation reactions is today a reality due to their ability to reduce the reaction time from hours to minutes, absence of unwanted products and free-solvent reactions. In this article we will review and discuss a collection of these reactions under microwave radiation dividing it into two strands. The first presents the condensation of Knoevenagel between malononitrile and aldehydes and the second one, addresses the alternatives to use malononitrile-derivatives such as cyanoacetamides and cyanoacetates. The Knoevenagel adducts formed from aldehydes present excellent results in terms of reaction yield (above 90 %) in short reaction times (< 10 min). The authors left their contributions in order to corroborate with this complete analysis on the new trends of this subject with great potential on Green Chemistry.