We synthesized a two-dimensional (2D) crystalline covalent organic framework (sp2c-COF) that was designed to be fully π-conjugated and constructed from all sp2 carbons by C=C condensation reactions of tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile. The C=C linkages topologically connect pyrene knots at regular intervals into a 2D lattice with π conjugations extended along both x and y directions and develop an eclipsed layer framework rather than the more conventionally obtained disordered structures. The sp2c-COF is a semiconductor with a discrete band gap of 1.9 electron volts and can be chemically oxidized to enhance conductivity by 12 orders of magnitude. The generated radicals are confined on the pyrene knots, enabling the formation of a paramagnetic carbon structure with high spin density. The sp2 carbon framework induces ferromagnetic phase transition to develop spin-spin coherence and align spins unidirectionally across the material.

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Two-dimensional sp2 carbon–conjugated covalent organic frameworks

In 1894 Knoevenagel published a paper in the journal Chemisehe Berichte on the reaction of formaldehyde and diethyl malonate in the presence of diethylamine as catalyst.1 He obtained the bis adduct (1). Two years later he was able to show that the reaction of benzaldehyde and ethyl acetoacetate in the presence of piperidine gives the bis adduct (2) at room temperature and at 0 °C the benzylidene-1,3-di- carbonyl (3; Scheme 1).2

1.11 – The Knoevenagel Reaction

Knoevenagel's first papers in this field were concerned with the condensation of formaldehyde with diethyl malonate and with ethyl benzoylacetate. The catalyst was ethylamine. A number of other aldehydes were reported to condense similarly with diethyl malonate, ethyl benzoylacetate, ethyl benzoylpyruvate, and acetylacetone under the influence of various primary and secondary amines. In 1896, Knoevenagel reported benzaldehyde with ethyl aceoacetate condensed at room temperature in the presence of piperdine to give a bis compound, but that when the reaction was run in a freezing mixture, the product was acetoacetate. For the purposes of this chapter, the Knoevenagel condensation is defined as the reaction between an aldehyde or ketone or any compound having an active methylene group, brought about by an organic base or ammonia and their salts.


Keywords:

Knoevenagel condensations;
decarboxylation;
malonic acid;
active methylene component;
stereochemical aspects;
cyanoacetic acid;
ketones;
derivatives. caatalysts;
experimental conditions

The Knoevenagel Condensation

Electrochemically induced multicomponent transformation of salicylaldehydes and two different C-H acids in alcohols in an undivided cell in the presence of sodium bromide as an electrolyte results in the efficient and selective formation of diversely functionalized, medicinally privileged 2-amino-4H-chromene scaffolds in 65-86% yields. The developed electrocatalytic system affords the distinction between two C-H acids according to their reactivity, and offers an efficient approach to the 2-amino-4H-chromene scaffold with a predefined arrangement of desired substituents. The electrocatalytic multicomponent reaction smoothly proceeds with salicylaldehydes bearing both electron-donating and electron-withdrawing groups. Thus, fifteen previously inaccessible, close structural analogues of the tumor antagonists HA14-1 and MX58151 have been synthesized. The electrocatalytic process was found to be advantageous in terms of selectivity and yields compared to classic chemical base catalysis, and includes a remarkable mechanistic feature that is promising for the further development of 2-amino-4H-chromene chemistry. The application of this convenient electrocatalytic multicomponent method to the formation of medicinally relevant 2-amino-4H-chromenes is also beneficial from the viewpoint of diversity-oriented large-scale processes and represents a novel, facile and environmentally benign synthetic concept for multicomponent reaction strategy.

Catalysis of Salicylaldehydes and Two Different C ? H Acids with Electricity: First Example of an Efficient Multicomponent Approach to the Design of Functionalized Medicinally Privileged 2‐Amino‐4H‐Chromene Scaffold

Solvent-free cascade reaction: direct multicomponent assembling of 2-amino-4H-chromene scaffold from salicylaldehyde, malononitrile or cyanoacetate and nitroalkanes

https://pubs.rsc.org/en/content/articlepdf/1960/jr/jr9600002020

411. The kinetics and mechanisms of carbonyl–methylene condensations. Part VII. The reaction of malononitrile with aromatic aldehydes in ethanol

413. The kinetics and mechanisms of carbonyl–methylene condensations. Part IX. The reaction of cyanoacetamide with aromatic aldehydes in ethanol and in water

Yigal Israeli

Papers

411. The kinetics and mechanisms of carbonyl–methylene condensations. Part VII. The reaction of malononitrile with aromatic aldehydes in ethanol

413. The kinetics and mechanisms of carbonyl–methylene condensations. Part IX. The reaction of cyanoacetamide with aromatic aldehydes in ethanol and in water