Knoevenagel reaction: alum-mediated efficient green condensation of active methylene compounds with arylaldehydes

Abstract

A solvent-free stirred mixture of active methylene compounds, arylaldehyde and 10 mol% alum at 80°C afforded Knoevenagel products in excellent yields. The use of a green catalyst, the solvent-free conditions, and shorter reaction times are the main features of this efficient protocol.     

Reaction of semiquinoid compounds derived fromN-arylsulfonyl-p-quinonemono- and diimines with tosylhydrazine

Reaction of 4-arylsulfonylimino-2,3,5,6,6-pentachloro-2-cyclohexen-l-ones with tosylhydrazine gives rise toN-arylsulfonyl-N-p-tolylsulfonyl-2,5,6,-tetrachloroaminophenols. With 4-arylsulfonylimino-2,2,3-trichloro-1,2,3,4-tetrahydronaphthalen-1-ones and 4-arylsulfonylimino-2-dihalo-1,2,3,4-tetrahydronaphthalen-1-ones reaction products are 4-arylsulfonylamido-2,3-dichloro-4-p-tolylsulfonylhydrazido-l,4-dihydronaphthalen-1-ones and 2-p-toIylsulfonyl-l,4-naphthoquinone-4-diazide respectively. First stage of the processes consists in dehydrohalogenation yielding the correspondingN-arylsulfonyl-p-quinonimines.     

Reaction ofN-arylsulfonyl-p-quinonimines and semiquinoid compounds derived therefrom with arylsulfinic acids

N-Arylsulfonyl-2,3,5,6-tetrachloro-l,4-benzoquinonimines and 4-arylsulfonylimino-2,3,5,6,6-pentachloro-2-cyclohexen-l-ones react with arylsulfinic acids regioselectively along 6,1-addition. With 4-arylsulfonylimino-2,3,5,6,6-pentachloro-2-cyclohexen-l-ones the 6,1 addition is preceded by nucleophilic substitution of chlorine in position 2. WithN-arylsulfonyl-2,3-dichloro-l,4-naphthoquinonimines, 4-arylsulfonyl-2,2,3-trichloro-l,2,3,4-tetrahydronaphthalen-l-ones and 4-arylsulfonyl-2,2,3,3-tetrachloro-1,2,3.4-tetrahydronaphthalen-l-ones occurred nucleophilic substitution of chlorine in position 2 followed by 6,1-addition of arylsulfinic acid molecule.     

Knoevenagel condensation reaction in a membrane microreactor

A multi-channel membrane microreactor was fabricated and tested for Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate using Cs-exchanged faujasite NaX as the catalyst; the membrane microreactor achieves supra-eqiulibrium conversion at higher product purity.     

Synthesis, optical, and thermal properties of conjugated, bispyridyl and tetrapyridyl compounds by Knoevenagel reaction

A series of conjugated, bispyridyl and tetrapyridyl compounds were synthesized from either terephthalaldehyde or isophthalaldehyde and activated pyridyl compounds by Knoevenagel reaction on heating in acetic anhydride in presence of acetic acid and their optical and thermal properties were examined. All of them exhibited photoluminescence in chloroform, tetrahydrofuran, and dimethyl sulfoxide as well as in solid state. In solid state, their emission spectra exhibited bathochromic shifts when compared with those in less or more polar solvents. Some compounds emitted UV light both in polar solvents and in the solid state; other compounds emitted UV light in polar solvents, but emitted visible light in the solid state.     

Synthesis of photocrosslinkable polyesters by the Knoevenagel reaction

A new group of photocrosslinkable polyesters formed by the Knoevenagel reaction is described. The approach permits preparation of photoesensitive polymers, where physical properties can be potentially varied through choice of the polyol and the dicarboxylic acid. The following compounds were prepared and studied: (1) products from a Knoevenagel reaction of poly(trimethylopropane azelate cyanoacetate) with benzaldehyde, furaldehyde, and 2-ethylbutyraldehyde and (2) products from a Knoevenagel reaction of poly(1,3-propyl malonate) with benzaldehyde, p-methoxybenzaldehyde, and 2-ethylbutyraldehyde. Conventional unsaturated polyesters such as poly(1,3-propyl fumarate) and poly(1,3-propyl maleate) were prepared and used for comparison.     

Chirality of exo-heterosubstituted semiquinoid systems

Conclusions The observation of diastereotopism of the methoxy groups (at a distance of eight bonds from the asymmetric center) in the PMR spectra of 4,4-disubstituted l-(dimethylphosphorylmethylidene)-2,5-cyclohexadienes has been used to demonstrate the chirality of para-semiquinoid systems containing a heteroatom in the unsaturated exo-fragment of the molecule and two substituents distinguishable from each other in the geminal position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2296–2299, October, 1986.     

Use of a water solution of surfactant in Knoevenagel reaction

In reaction of vanillin with active methylene compounds in the presence of detergent Oksipav AP the corresponding substituted alkenes were formed in high yields.     

超声辐射下的无溶剂Knoevenagel缩合反应

在无溶剂,无催化剂,超声辐射下芳香醛与丙二腈发生knoevenagel缩合反应,合成了一系列苄叉基化合物,通过熔点的测定,红外光谱、核磁共振及元素分析对产物的结构进行了表征。结果表明,该方法不但化学选择性好,而且产物易处理,对环境污染小,符合绿色化学的要求。     

New synthesis of 2-benzimidazoleacetates and study of their Knoevenagel reaction

To obtain 2-benzimidazolyl acrylate 2, a new efficient synthesis of 2-benzimidazoleacetate, involving esterification of 2-benzimidazole acetic acid at low temperature as the crucial step, was developed. The generality and efficiency of the process was illustrated by the high-yield synthesis of methyl, ethyl, i-propyl, and n-butyl 2-benzimidazoleacetate. The Knoevenagel reaction of 2-benzimidazoleacetate with aromatic aldehydes was studied. It was found that only in the presence of a catalytic amount of morpholine could the Knoevenagel reaction proceed to give the expected 3-aryl-2-benzimidazolyl acrylate. A mechanism for the morpholine-catalyzed reaction is suggested.     

Applications of Knoevenagel condensation reaction in the total synthesis of natural products

Monatshefte für Chemie - Chemical Monthly - The Knoevenagel condensation reaction is a prominent organic reaction commonly being utilized in the total synthesis of natural and biologically...     

The Knoevenagel reaction: analysis and recycling of the ionic liquid medium

A study involving the scope of substrate in the Knoevenagel reaction in an IL medium has been conducted. Reactivity trends favor formation of the condensation product using electron deficient aryl aldehydes. Use of electron rich aldehydes and ketones lead to lower levels of conversion and no measurable amounts of condensation products, respectively. A recycling study confirmed that the reaction medium could be used multiple times affording, with each run, the desired condensation product 1a in excess of 90% conversion. Post-run analyses of the IL documented that the IL medium was unaltered upon reuse.     

酸碱双功能MgO/HMCM-22催化剂上Knoevenagel缩合反应

采用浸渍法制备了一系列MgO改性催化剂MgO/HMCM-22, 利用X射线衍射、N₂物理吸附-脱附、扫描电镜、傅里叶变换红外光谱、NH₃及CO₂程序升温脱附等技术对所制催化剂进行了表征. 结果表明, MgO改性后MCM-22分子筛仍保持原有的结构; 随着MgO负载量的增加, 催化剂的碱强度和碱含量显著增加, 而强酸含量明显减少, 弱酸酸位有所增加. 以Knoevenagel缩合为探针反应, 考察了所制催化剂的性能. 在优化的反应条件下, MgO/HMCM-22上苯甲醛转化率高达92.6%. 催化剂 MgO/HMCM-22和MgO/NaMCM-22的催化性能明显优于HMCM-22和MgO. 酸中心和碱中心均对该缩合反应起着重要的促进作用. MgO/HMCM-22对Knoevenagel缩合反应显示出较高的催化活性, 体现出明显的酸碱协同催化作用.     

Dialkylimidazolium dimethyl phosphates as solvents and catalysts for the Knoevenagel condensation reaction

The reaction between benzaldehyde and ethyl cyanoacetate is investigated in 1,3-dialkylimidazolium salts as solvents. The impact of both ions in these ionic liquids on the yield of the condensation reaction product is examined. Potentiometric titrations are employed for quantitative analyses of the best ionic liquids, revealing these to be 1,3-dialkylimidazolium dimethyl phosphates.     

New magnetic nanocatalyst containing a bis-dicationic ionic liquid framework for Knoevenagel condensation reaction

Research on Chemical Intermediates - Bis[(3-aminopropyl)triethoxysilane]dichloride immobilized on magnetic nano-γ-Fe2O3@SiO2 has been prepared. After characterization, the reagent was used for...     

Knoevenagel condensation reactions catalyzed by nitrogen-containing mesoporous carbon materials under mild reaction conditions

Research on Chemical Intermediates - A series of nitrogen-containing ordered mesoporous carbon (NOMC) materials have been prepared by a convenient soft-templating method. The physicochemical...     

Polycarbosilane‐supported titanium(IV) catalyst for Knoevenagel condensation reaction

Polycarbosilane (PCS) was synthesized by the polycondensation of trichloromethylsilane and trimethoxyvinylsilane in the presence of sodium metal. PCS has a highly crosslinked structure, high ceramic yield and high surface area. Titanium metal ion was attached to the polycarbosilane and its catalytic activity was investigated. The Knoevenagel condensation reaction catalysed by titanium‐incorporated polycarbosilane is reported. The titanium‐incorporated PCS catalysed the reaction well and with a diverse set of substrates the reaction proceeded with good yield. PCS‐supported transition metal catalysts have been prepared for the first time and used successfully in the Knoevenagel condensation reaction. Copyright © 2012 John Wiley & Sons, Ltd.     

Combinatorial Knoevenagel reactions

Chlorotrimethylsilane (TMSCl) has been utilized as an efficient promoter and water scavenger in the Knoevenagel condensations of aromatic aldehydes with various methylene active compounds. High yields and a simple workup of target compounds enables the facile generation of combinatorial libraries comprising 11,000 compounds of high structural and functional diversity.