Knoevenagel condensation

Summary

In organic chemistry, the Knoevenagel condensation (ˈknøːvənaːɡl̩) reaction is a type of chemical reaction named after German chemist Emil Knoevenagel. It is a modification of the aldol condensation. A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated (hence condensation). The product is often an α,β-unsaturated ketone (a conjugated enone). In this reaction the carbonyl group is an aldehyde or a ketone. The catalyst is usually a weakly basic amine. The active hydrogen component has the form

or for instance diethyl malonate, Meldrum's acid, ethyl acetoacetate or malonic acid, or cyanoacetic acid.
, for instance nitromethane.

where Z is an electron withdrawing group. Z must be powerful enough to facilitate deprotonation to the enolate ion even with a mild base. Using a strong base in this reaction would induce self-condensation of the aldehyde o

Official source

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications

Related people

Related units

Related concepts

Related courses

Related lectures

Multicomponent Assembly of Boronic Acid-Based Macrocycles, Cages, and Polymers

Burçak Içli

This work describes the synthesis and characterization of boronic acid-based supramolecular structures. Different reversible interactions such as boronate ester formation, imine condensation and dative B–N bond formation are used to assemble macrocycles, cages and polymers. Multicomponent condensation reactions of different diamines with tetraols and formylphenylboronic acids give macrocycles via formation of imine bonds and boronate esters. The [4+2+2] condensation products are generally preferred but larger macrocycles are observed for some combinations of staring materials. The larger macrocycles are in dynamic equilibrium with the smaller [4+2+2] products. Utilization of a triamine instead of the diamine results in the formation of molecular cages. The syntheses of these cages require the formation of 18 covalent bonds between 11 building blocks, and, interestingly, can be performed in a ball mill. Multicomponent reactions of diboronic acids, catechol derivatives, and different pyridyl ligands are described. The condensation of diboronic acids with catechols gives dioxaboroles. Upon crystallization, the ester aggregates with the N-donor ligands via dative B−N bonds. Depending on the nature of the pyridyl ligand, molecularly defined macrocycles, cages or polymeric structures are obtained. One-dimensional polymers are formed with 4,4-bipyridine and 1,2-di(4-pyridyl)ethylene, whereas a two-dimensional network is obtained with the tetradentate ligand tetra(4-pyridylphenyl)ethylene. A tripyridyl linker results in the formation trigonal prismatic cages. The size of the cages can be varied by changing the diboronic acid building block. The cages are able to encapsulate polyaromatic molecules such as triphenylene or coronene. The results highlight the potential of dative B−N bonds in structural supramolecular chemistry and crystal engineering.

EPFL2012

Synthesis of Molecular Nanostructures by Multicomponent Condensation Reactions in a Ball Mill

Nicolas Christinat, Burçak Içli, Christian Schüttler, Rosario Scopelliti, Kay Severin, Justus Tönnemann

The condensation of multiple building blocks in a ball mill allows molecular cages with a size up to 3.1 nm to be built.

2009

Aliphatic polyesters receive increasing attention over the last years driven by their application as biodegradable substitutes for conventional commodity thermoplastics and applications in the biomedical field, where amongst the family of biodegradable polymers, aliphatic polyesters possess the leading position as a consequence of the ready metabolization of the degradation products in most cases. This has led to a wide spread use of polyester homo- and copolymers in drug delivery, surgical implants, and functional materials in tissue engineering. In general, polyesters have a high level of commercial importance, and a variety of well known processing technologies are available. To tune the properties of these materials, e.g. their degradation behavior and to add further functionality, there is significant interest in synthetic strategies which can be used to prepare side-chain functionalized polyesters with variable architectures. This Thesis explores the feasibility of a novel approach towards functional polyesters that is based on the Baylis-Hillman reaction, which involves the base catalyzed condensation of an aldehyde and an acrylate building block to produce an α-methylene-β-hydroxycarbonyl compound. As the Baylis-Hillman polymerization does not require the use of side chain protected monomers, this route may represent an interesting alternative strategy for the preparation of functional polyesters. An attractive feature of the Baylis-Hillman polymerization is that it generate polymer with reactive hydroxyl and vinyl groups, which can be used in a subsequent step for post-modification or prepare functional crosslinked scaffolds. This Thesis consists of four chapters. The different synthetic strategies that have been used for the preparation of multi-functional polyesters and the Baylis-Hillman reaction are reviewed in Chapter 1. Chapter 2 investigates the feasibility of the Baylis-Hillman polymerization of diacrylates and dialdehydes to prepare side-chain functional polyesters and explores the subsequent post-polymerization modification of these polymers to further enhance their functionality. Using 1,3-butanediol acrylate and 2,6-pyridinecarboxaldehyde as monomers and DABCO as catalyst, polymers with a degree of polymerization of up to 25 were prepared. These polymers are attractive as they contain chemically orthogonal side-chain hydroxyl and vinyl groups that can be further modified. In first experiments, it was demonstrated that the side-chain hydroxyl and vinyl groups can be quantitatively post-modified with phenyl isocyanate, respectively, methyl-3-mercaptopropionate. Chapter 3 explores the feasibility of the Baylis-Hillman reaction for the synthesis of hyperbranched polyesters. This Chapter describes an efficient and novel approach to functional hyperbranched polyesters via an A2 + B3 approach based on the Baylis-Hillman reaction. Using trimethylolpropane triacrylate and 2,6-pyridinedicarboxaldehyde as monomers and 3-quinuclidinol as the catalyst, polymer swith a degree of branching between 0.36 and 0.8, and a molecular weight of up to 28,100 were prepared. The effects of monomer ratio and addition mode on the final molecular weight, polydispersity index and degree of branching were studied. In order to demonstrate the potential of this polyester as a reactive polymer, the hydroxyl, vinyl groups and pyridine residues were post-modified with phenyl isocyanate, methyl-3-mercaptopropionate and methyl iodide. Chapter 4 aims to further explore the scope and versatility of the Baylis-Hillman polymerization and studies the preparation of side-chain functional polyesters by polymerization of 1,3-butanediol diacrylate with meta- and para-phthalaldehyde, which are two commercially available dialdehyde building blocks.

EPFL2011