Reaction Knoevenagel condensation

The cyanoacryhc esters are prepared via the Knoevenagel condensation reaction (5), in which the corresponding alkyl cyanoacetate reacts with formaldehyde in the presence of a basic catalyst to form a low molecular weight polymer. The polymer slurry is acidified and the water is removed. Subsequendy, the polymer is cracked and redistilled at a high temperature onto a suitable stabilizer combination to prevent premature repolymerization. Strong protonic or Lewis acids are normally used in combination with small amounts of a free-radical stabilizer. 

The initial step of the Hantzsch synthesis is likely to be a Knoevenagel condensation reaction of aldehyde 2 and /3-ketoester 1 to give the a ,/3-unsaturated ketoester 6 ... 

Scheme 2.13 gives some examples of Knoevenagel condensation reactions. 

These alkoxo complexes are also capable of cleavage of the C—Si bond of TMSCF3. The gold(III) fluoroalkoxides m-[AuMe2(OR)(PPh3)] (R = CH2CF3, CF1(CF3)2) can act as catalysts for the Knoevenagel condensation reaction.1775... 

A wide variety of M W-assisted aldol [59, 60] and Knoevenagel condensation reactions have been accomplished using relatively benign reagents such as ammonium acetate [61], including the Gabriel synthesis of phthalides with potassium acetate [62],... 

Knoevenagel condensation reaction of creatinine with aldehydes occurs rapidly under solvent-free reaction conditions at 160-170 °C using focused microwave irradiation (Scheme 6.18) [66],... 

Scheme 6.18 Knoevenagel condensation reaction of creatinine with aldehydes.

In this stndy 5-(Quinoline-2-ylidene)-l,3-diethyl-2-thiobaibituric acid have been synthesized via Knoevenagel condensation reaction, the prodnct solntions were prepared 10 -10 M in CHCIj, THF, MeOH, DMF and DMSO. UVAfiS spectra recorded and then compared at each other. Absorbance of the solntions were measured at 200-300 nm. The maximum absorbance valne increased and a new absorption appeared at 400-500 nm. The samples were excited at 337 nm in order to measure fluorescence. The maximum emission was observed in MeOH at 398 nm. These values increased by time therefore, the samples were not stable in solution state. 

Figure 19. Reaction scheme for solid-base catalysed Knoevenagel condensation reaction [36],...

Zhang, X. and Man Lai, E.S. and Martin-Aranda, R. and Yeimg, K.L. (2004). An investigation of Knoevenagel condensation reaction in microreactors using zeolite catalyst. Applied Catalysis A General, 261,109-118. 

On nitrided aluminophosphates, AlPON, Massinon et al. [206] observed on a series of six samples with increasing nitrogen contents a good correlation between the catalytic activity in the Knoevenagel condensation reaction and the amount of surface NH, species (1 < x < 4) quantified by the Kjeldahl method. The authors suggest that those species are not the only active species and evoke an additional role of the nitride ions in the reaction [206] on the other hand, Benitez et al. [207] suggest hydroxyls linked to aluminum cations in the vicinity of terminal P-NH2 groups as basic centers. 

The AlGaPON samples were used as catalysts of the Knoevenagel condensation reaction and the authors [211] found that the -NH2 groups present at the surface of the samples were the basic sites responsible for the condensation properties of the catalysts. The catalytic performances of the studied samples increased with their basic character observed by SO2 adsorption microcalorimetry. 

Amongst other systems reported for the Knoevenagel condensation reaction have been, nitrogen incorporated ZSM-5 and high surface area silicon oxynitride." The ZSM-5 based -system potentially combines tuneable acid/ base properties with shape selectivity leading to the potential of selective conversion and/or unusual reaction pathways. 

The thiepin (234) has been synthesized from phthalaldehyde by the double Knoevenagel condensation reaction shown in equation (72) (53JA6332). 

Further projects dealt with the fabrication of heterogeneous, basic or acidic solid-state catalysts or adsorbents carrying, for instance, amino or sulfonic acid groups. Amino-functionalized silicas were prepared and analyzed for the catalytic activity in Knoevenagel condensation reactions of aldehydes or ketones with ethyl cyanoace-tate ions by Macquarrie et al.154 155 Recently, Zhang et al.156,157 reported on the successful preparation of amino-functionalized silica thin films by means of the EISA approach. 

Lewis base sites in PCPs have the potential to show different catalytic properties from Lewis acid sites.52 165 166 The three-dimensional PCP, [Cd(NC>3)2(4-btapa)2] 6H20 2DMF (4-btapa = 1,3,5-benzenetricarboxylic acid tris[/V-(4-pyridyl)-amide]), has amide groups that act as guest interaction sites on the surfaces of channels with dimensions of 4.7 x 7.3 A2165 A Knoevenagel condensation reaction catalyzed by this PCP demonstrates its selective heterogeneous base catalytic properties, which depend on the size of the reactants. This solid catalyst maintains its crystalline framework after the reaction and is easily recycled. 

In practise a Knoevenagel condensation reaction yields coumarin 9.16 directly, without isolation of diester 9.17. The mechanism is shown below. ... 

Among the most important reactions in organic synthesis are those that form carbon-carbon bonds. Classically this was accomplished using base-catalyzed reactions such as the aldol, Claisen, and Knoevenagel condensation reactions. Modem versions of these reactoins often display remarkable stereoselectivity.1 Unfortunately, many types of carbon atoms cannot be joined together by these reactions, for example, an aryl carbon to another aryl carbon. It took the development of transition metal-catalyzed reactions before new types of carbon-carbon and carbon-heteroatom bonds could be created. Of particular note in this regard are the reactions catalyzed by palladium, usually in its 0 or +2 oxidation state.2,3,4,5... 

Similarly, Perozo-Rondon et al. [22] gave the microwave enhanced synthesis of N-propargyl derivatives of imidazole (xxii, xxiii, xxiv) involving the Knoevenagel condensation reaction. The synthesized derivatives proved to be good fungicidal compounds. 

Lai SM, Ng CP, Martin-Aranda R, and Yeung KL. Knoevenagel condensation reaction in zeohte membrane microreactor. Micropor Mesopor Mater 2003 66(2-3) 239-252. 

Rodriguez, I., Sastre, G., Corma, A., Iborra, S. Catalytic Activity of Proton Sponge Application to Knoevenagel Condensation Reactions. J. Catai. 1999, 183, 14-23. 

In the Knoevenagel condensation reaction, the anion is derived from a compound of the general formula CH2X2, where X is a -M group, such as an ester. The resultant anion then reacts with a... 

Primary amines anchored to silica have been utilized as catalysts for Knoevenagel condensation reactions. For example, silica gel functionalized with a propylamino moiety [SiO2-(CH2)3-NH2] was employed in the reaction of different methylene active compounds with aldehydes and ketones for the production of electron-poor olefins 73 (Scheme 3.21). ... 

The primary amino groups bound on sihca was previously reported to be an efficient catalyst for the Knoevenagel condensation reaction in mild conditions... 

The Knoevenagel condensation reaction of equimolar solution of BA and EGA in DMSO was carried out on the various catalysts 1-4 in batch conditions. During all the experiments, the selectivities observed in the Knoevenagel condensation product are nearly 100% (>95%). 

In connection with a synthesis of the hydroazulenic sesquiterpene kessanol (304), Knoevenagel condensation of photocitral-A (302) with ethyl cyanoacetate was found to give (303) as a single isomer. The following sequence includes an intramolecular Prins reaction initiated with SnCU.310 In Isobe s synthesis of vemolepin (307) the two carbons of the y-lactone are introduced by a Knoevenagel condensation. Reaction of ketone (305) with di-r-butyl malonate followed by treatment with DBU affords (306), which is transformed to the a,a -dihydroxy compound (308). Hydrolysis of the esters followed by decarboxylation, formation of the 7-lactone, Mannich reaction and elimination yields vemolepin (307 Scheme 58).311... 

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