Uncatalysed Knoevenagel condensation in aqueous medium at room temperature

Knoevenagel condensation of various aromatic and heteroaromatic aldehydes with active methylene compounds like malononitrile, ethyl cyanoacetamide, ethyl cyanoacetate, barbituric acids, Meldrum’s acid, dimedone and pyrazolone proceeds smoothly with stirring in an aqueous medium. The reactions occur at room temperature giving excellent yields of the products. The work-up procedure is very simple and the products do not require further purification.     

Solvent-free Knoevenagel condensation over iridium and platinum hydroxyapatites

The Knoevenagel condensation between various aldehydes (benzaldehyde, p-methoxybenzaldehyde and 1-naphthaldehyde) and esters (ethylcyanoacetate, ethylacetoacetate and diethylmalonoester) was carried out under solvent-free condition in the presence of iridium or platinum hydroxyapatites as a catalyst.     

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.     

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.     

Cage-catalyzed Knoevenagel condensation under neutral conditions in water

A cationic coordination cage dramatically accelerates the Knoevenagel condensation of aromatic aldehydes in water under neutral conditions. The addition of a nucleophile to the aldehyde to generate anionic intermediates seems to be facilitated by the cationic environment of the cavity. The products are ejected from the cage as a result of the host-guest size discrepancy. As a result, the condensation is promoted by a catalytic amount of the cage.     

Knoevenagel condensation catalysed by aluminium oxide.

The Knoevenagel condensation of carbonyl compounds with active methylene compounds was readily carried out with aluminium oxide as catalyst.     

A novel light induced Knoevenagel condensation of Meldrum’s acid with aromatic aldehydes in aqueous ethanol

A highly efficient environment-friendly photochemical methodology has been developed for the condensation of Meldrum’s acid with aromatic aldehydes in water-ethanol solution sans any catalyst, support or promoter.     

水相中磷酸氢二铵催化Knoevenagel反应

醛与活泼亚甲基化合物的Knoevenagel反应是有机合成中广泛应用的形成碳碳键的重要方法,该反应一般是弱碱性催化剂存在下完成的,如各类胺、脲[1]等,Lerwis酸[2]、杂多酸[3]、氨基酸[4]等也可用于催化该反应。近年来,无溶剂条件下超声、微波辅射[5-6]也可以促进反应,但大部分是在     

Synthesis of substituted stilbenes via the Knoevenagel condensation

Knoevenagel condensations between aldehydes and substrates containing active methylene groups were carried out in ethanol at room temperature, in the presence of potassium phosphate, to afford unsymmetrical olefins. These condensations have been shown to afford only the E-isomers in greater than 80% yields. Salicylaldehyde first produces the Knoevenagel condensation products, which undergo a subsequent heterocyclization to give coumarin derivatives. The structures of the synthesized compounds were established on the basis of UV, IR, MS and NMR spectroscopy.     

酸性沸石分子筛催化Knoevenagel缩合反应

 在高硅／铝比的酸性沸石分子筛HY上实现了Knoevenagel缩合反应．Bronsted酸和Lewis酸均可催化Knoevenagel缩合反应．考察了羰基化合物和活泼亚甲基化合物的反应活性顺序．结果表明，羰基化合物的羰基极化程度越高，反应越容易进行；不同于碱催化时的Knoevenagel缩合反应，活泼亚甲基化合物的活泼氢的酸性并不是影响其反应活性的重要因素．     

Knoevenagel condensation catalyzed by novel Nmm-based ionic liquids in water

A series of novel N-methyl morpholine (Nmm) based ionic liquids with 1,2-propanediol group were synthesized and used as catalysts for Knoevenagel condensation at room temperature in water. Under the effect of the catalyst, various aldehydes or aliphatic ketones could react with a wide range of activated methylene compounds well, including malononitrile, alkyl cyanoacetate, cyanoacetamide, β-diketone, barbituric acid, 2-arylacetonitrile and thiazolidinedione. Furthermore, most of the products could be separated just by filtrating and washing with water. Additionally, the catalyst is recyclable and applicable for the large-scale synthesis.     

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。     

A DFT study of IRMOF-3 catalysed Knoevenagel condensation

It has been recently reported that IRMOF-3 [Gascon et al., J. Catal, 2009, 261, 75] may behave as a basic catalyst, active in the Knoevenagel condensation. In particular, it has been shown that the basicity of aniline-like amino moieties is enhanced, along with the catalytic activity, when incorporated into MOF structures. The computational study here was aimed at finding possible atomistic explanations of the increased basicity and catalytic activity of the IRMOF-3 embedded aniline groups, experimentally claimed. It was, moreover, aimed at guessing a reaction mechanism for the IRMOF-3 catalysed Knoevenagel condensation of benzaldehyde and ethyl-cyanoacetate. Within the DFT framework we have studied structure and basicity properties of IRMOF-3 and we have analysed the energetics of the catalytic cycle as well as of possible deactivation paths, including it. The increased basicity of IRMOF-3 over other amminic catalysts has been explained via the formation of protonated conjugate derivatives, involving hydrogen-bonds and originating quasi-planar 6-term rings. Several plausible reaction steps have been moreover taken into account and a mechanism for the Knoevenagel condensation, including catalyst deactivation, has been proposed for aniline molecules and embedded aniline moieties. This allowed us to suggest that the increased IRMOF-3 activity, as a basic catalyst, should be mostly related to its water adsorption ability, preserving the properties of the catalytically active amino moieties.     

Microwave-assisted aldol condensation of benzil with ketones

Under microwave irradiation,the corresponding hydroxycyciopentenones were prepared in high yields by the cross-aldol reactions of benzil with various ketones.When the reactions were performed in vailOUS solvents under classical heating for a long time,they produced the products in relatively low yields.     

Solvent-free Knoevenagel Condensations over TiO2

A study involving the scope of substrates in the Knoevenagel reaction under SFC has been conducted. Reactivity trends favored formation of the condensation product using both electron deficient and rich aryl aldehydes. A recycling study confirmed that the reaction medium could be used multiple times affording, with each run, the desired condensation product in excess of 95% conversion.     

Solvent-Free Knoevenagel Condensation over Cobalt Hydroxyapatite

The Knoevenagel condensation between various aldehydes (benzaldehyde, 1-naphthaldehyde, p-bromobenzaldehyde and p-methoxybenzaldehyde) and esters (ethylcyanoacetate, ethylacetoacetate and diethylmalonoester) was carried out under solvent free condition in the presence of cobalt hydroxyapatite (CoHAp), as a catalyst. Good to excellent yields (35–96%) were obtained. The catalyst is found to be superior over fluorapatite and several other heterogeneous catalysts. The catalyst can be recycled at least 3 times.     

Porous hierarchical magnesium oxide-based heterogeneous catalyst for the Knoevenagel condensation

Russian Journal of General Chemistry - Herein, an operationally facile and efficient Knoevenagel reaction catalyzed by porous hierarchical MgO/Mg(OH)2 is presented. Condensation of various...     

Simple and practical procedure for Knoevenagel condensation under solvent-free conditions

The Knoevenagel condensation reaction between araldehyde and active methylene using gallium chloride catalyst under solvent-free conditions has been described. The reaction takes place at room temperature by grind stone method and offers good purity of product in high yield. Work-up is very simple and the products do not need further purification. The reaction conditions are very mild and this protocol is applicable to various aldehydes such as araldehydes and heteroaromatic aldehydes as well as active methylene compounds, namely, malononitrile or ethyl cyanoacetate.

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