Knoevenagel condensation reaction is a basic reaction of organic chemistry for its significant detergency in the formation of electrophilic alkenes. It has numerous applications in the ingenious synthesis of different heterocyclic systems and widely used in the total synthesis of a wide verity of biologically active natural products such as coumarins derivatives. Many traditional Knoevenagel reactions make use of huge amount of toxic and volatile organic solventsviz not in line with green chemistry. In this review we discuss recent synthetic developmentsin solvent-free or greener Knoevenagel condensation reactionsby the use of mechanochemical grinding over traditional conventions involving various solvents. Considering the enormous utility of Knoevenagel condensation reaction, number of greener protocols have been reported under solvent-free conditions like Microwave and ultrasonic irradiation, visible light irradiation, mechanochemical grinding, ionic liquids or green solvent like water, solid support and various heterogeneous base catalysts used whereby an excellent end was obtained. Certainly this review would put forward a great insight to research community to accelerate further research for the development of wide range of electrophilic alkenes, dienophiles for Diels-Alder reaction and various intermediates (coumarins) which are useful in cosmetics perfumes and biologically active compounds.
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