Knoevenagel condensation modified

The domino process probably involves the chiral enamine intermediate 2-817 formed by reaction of ketone 2-813 with 2-815. With regard to the subsequent cy-doaddition step of 2-817 with the Knoevenagel condensation product 2-816, it is interesting to note that only a normal Diels-Alder process operates with the 1,3-bu-tadiene moiety in 2-817 and not a hetero-Diels-Alder reaction with the 1-oxa-l,3-butadiene moiety in 2-816. The formed spirocydic ketones 2-818/2-819 can be used in natural products synthesis and in medidnal chemistry [410]. They have also been used in the preparation of exotic amino adds these were used to modify the physical properties and biological activities of peptides, peptidomimetics, and proteins... 

As part of a search for environmentally friendly solid acid-base catalysts, a modified Mg-Al hydrotalcite has been used as a base catalyst for aldol and Knoevenagel condensations. Yields are often quantitative, reaction times are about Ih, the catalyst can be recovered by filtration, and only moderate temperatures are required (60 °C for the aldol, ambient for the Knoevenagel). 

The presence of substituents in the vinyl group of vinylthiophenes modifies reactivity. The vinylthiophene 70, obtained via a Knoevenagel condensation from 2-thienylacetonitrile and acetaldehyde as an 87 13 E-Z mixture, reacted with DMAD (11 days at reflux in acetonitrile) to give the adducts 71, 72, and 73 (87T991). The surprising compound 73 could be formed through the ene intermediate 74. 

Lakshmi Kantam, M., Choudary, B. M., Reddy, C. V., Koteswara Rao, K. and Figueras, F. Aldol and Knoevenagel condensations catalyzed by modified Mg-Al hydrotalcite a solid base as catalyst useful in synthetic organic chemistry, Chem. Commun., 1998, 1033-1034. 

Major modifications to the Friedlander reaction frequently involve different starting materials that deviate from the conventional examples. A one-pot combination of a modified Friedlander annulation and a Knoevenagel condensation have provided 2-styrilquinolines 152 in the presence of 1-methylimidazolium trifluoroacetate ([HmimJTFA) (Scheme 28) (08TL5366). 

Preparation of new aiuminophosphate oxynitride (AlPON) and nickel modified AlPON are presented. Such basic and polyfunctional catalysts are tested in Knoevenagel condensation and one step synthesis of methylisobutylketone (MIBK) from acetone. It is evidenced that the nitrogen content of the AlPON, which controls the rate of benzaldehyde-ethylcyanoacetate condensation depends on the activation procedure. 90% selectivity in the MIBK synthesis is obtained on Ni formate impregnating AlPON activated at 400 °C for 4 hours. TPD of CO2 and NH3, DRIFT analysis and quantum mechanical calculation evidence that the 0/N substitution creates strong basic sites. 

MCM-41 and silica gel as efficient and reusable heterogeneous catalyst for the Knoevenagel Condensation reactions. Burwell and Leal (1974) first reported selective chemisorption of sulfur dioxide on amine-modified silica gel. Leal et al. (1995) studied carbon dioxide adsorption on amine surface-bonded silica gel, although their CO2 adsorption amount (0.3 mmol/g-sorbent at 1 atm CO2) was low. Further work by Huang et al. (2003) produced high-capacity and selective sorbents for both CO2 and H2S. 

The use of a heterogeneous catalyst not only iaciUtates its reutihzation but also provides certain heat and mass transfer limitations, which are known to modify selectivity and yield. As MSRs offer high spedfic siulaces, the influence of transfer phenomena on the overall reaction can be reduced partially or completely improving the catalytic performance. Some examples reported in the hterature are the Simiki coupling reactions, the Knoevenagel condensation reaction, enzymatic hydrolysis [10], and the esterification reaction [5]. 

Hydrogen chloride silica Modified Knoevenagel condensation... 

Knoevenagel condensation between carbonyl compounds and methylene malo-nic esters on a CsNaX zeolitic coating in a microreactor demonstrated an order of magnitude higher productivity as compared with a traditional packed-bed reactor while the selectivity remained the same in both reactors [107,108]. A nearly fourfold increase in reaction conversion was obtained for the microreactor when NH2 modified CsNaX zeolitic coatings were apphed [109]. The conversion was further improved when zeolitic coatings were grown onto a stainless steel membrane (0.2 pm pores) inserted in a microreactor [110]. 

Initial reports from Knoevenagel used secondary amines such as piperidine or diethylamine as the catalyst, usually in an alcohol as solvent, and at temperatures between 0 °C and room temperature. The range of possible promoters of the Knoevenagel condensation was soon expanded by Harm and Lapworth to include tertiary amines, and soon thereafter, many, many modified reaction conditions were discovered, some of which had clear advantages over the standard conditions, while the benefits of others are less clear. This section will focus on those modifications that have shown some advantage over the standard conditions. 

Subsequent to Hantzsch s communication for the construction of pyridine derivatives, a number of other groups have reported their efforts towards the synthesis of the pyridine heterocyclic framework. Initially, the protocol was modified by Beyer and later by Knoevenagel to allow preparation of unsymmetrical 1,4-dihydropyridines by condensation of an alkylidene or arylidene P-dicarbonyl compound with a P-amino-a,P-unsaturated carbonyl compound. Following these initial reports, additional modifications were communicated and since these other methods fall under the condensation approach, they will be presented as variations, although each of them has attained the status of named reaction . 

Typically, in the Knoevenagel polycondensation, a terephthalic aldehyde is condensed with a bis-(cyanomethyl)-benzene compound. Since two monomers are used, PPVs with a strictly alternating structure can be synthesized. The Knoevenagel polycondensation allows the convenient synthesis of compounds in that the backbone double bond is substituted. PPV modified with cyano groups show a high EL activity. The synthesis is shown in Figure 3.8. In a quite similar way, PPV can be formed by the Wittig... 

Purpose. trans-Cinnamic acid is prepared as the first intermediate in the Sequence D set of reactions that ultimately lead to 2 -bromostyrene. You will review the chemistry associated with an important variety of aldol-type condensation, the modified Knoevenagel reaction. 

Keywords Aromatic carbraiyl compounds, malononitrile, ethyl cyanoacetate, modified and activated Mg-Al hydrotalcite (MHT), toluene or DMF, room temperature, condensation, Knoevenagel reaction, substituted alkenes... 

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