Condensations Knoevenagel-type

A similar Knoevenagel-type condensation takes place between methyl methyl-thiomethyl sulfone and aromatic aldehydes. In this reaction, use of K2C03 (2 mol equiv) as base and refluxing in isopropanol gave the best result178. 

Knoevenagel-type condensation of 1,4-xylylene dinitriles and aromatic dialdehydes gives access to cyano-containing poly(para-phenylene-cyanovinylene)s (74). The insoluble parent systems (74a R, R = H) have been reported by... 

The Knoevenagel condensation of a-lithiosulphoxides with hemiacetal 437 has been used to synthesize PGI2 analogues 438 (equation 261). The Knoevenagel-type condensation of dithioacetal monoxides with substituted benzaldehydes has been performed using Triton B as a base and gave the corresponding ketene dithioacetal monoxides 4395 2,513 (equation 262). 

The Knoevenagel-type condensation of salicylaldehydes with malonic acid [14, 27], malonic ester [28], cyanoacetic ester [29], or Meldrum s acid [30], is... 

Fig. 2 Representative traditional methods for coumarins synthesis, (a) Perkin synthesis (b) Pechmann-type condensation (c) Knoevenagel-type condensation...

Generally, MCRs based on aminoazoles and synthetic precursors of a,p-unsaturated carbonyl compounds proceed via a sequence of Knoevenagel-type condensation, which was already mentioned (see Scheme 3), Michael-like addition, cyclization, and water elimination. For example, the authors of [47] considered the following mechanism (Scheme 9). 

Di-tert-butyl methylenemalonate was originally prepared by phenyl-sulfenylation of di-tert-butyl methylmalonate and thermal elimination of the related sulfoxide.8 Because methylenemalonate esters are customarily prepared by Knoevenagel-type condensation of malonic esters with formaldehyde equivalents, the considerably more convenient procedure described herein was subsequently adapted from Bachman and Tanner s study using paraformaldehyde under metal ion catalysis.39 The approximately 6% di-tert-butyl malonate accompanying the product has presented no interference in the aforementioned reactions with nucleophilic alkenes under neutral or acidic conditions, but its presence should be taken into consideration in other applications. 

This three-component reaction as the key step of this synthesis is called a domino-Knoevenagel-hetero-Diels-Alder reaction. Domino reactions are defined as processes of two or more bond forming reactions in which a subsequent transformation takes place by virtue of the functionalities introduced in a former transformation.2,16 The tetrahydrocarbolinaldehyde 11 first reacts in a Knoevenagel type condensation with Meldrum s acid 14 and ethyleneammonium diacetate 41 as the catalyst to oxabutadiene 44 which then undergoes a Diels-Alder reaction with enol ether 13. 

Iminium catalysis directly utilizes the higher reactivity of the iminium ion in comparison to the carbonyl species and facilitates Knoevenagel-type condensations, cyclo- and nucleophilic additions, and cleavage of cr-bonds adjacent to the a-carbon. Enamine catalysis on the other hand involves catalytically generated enamine intermediates that are formed via deprotonation of an iminium ion, and react with various electrophiles or undergo pericyclic reactions. ... 

A new approach to a variety of a-branched alkynes 70 was achieved by a Knoevenagel type condensation of 4-unsubstituted isoxazolin-5-ones 66 with aldehydes or ketones 67, followed by conjugate addition of an organometallic species and nitrosative cleavage of the heterocyclic ring <02SL1257>. 

Hydroxy-2Q-ketosteroids.1 C17-Ketosteroids (1) undergo a Knoevenagel-type condensation with TosMIC to provide 17-(isocyanotosylmethylene)steroids (2). Phase-transfer catalyzed alkylation of 2 with formaldehyde gives an oxazoline, which is hydro-... 

Fused thiazolopyridazinones such as 96 and 97 were obtained from anilines which were converted to phenyl diazonium salts and reacted with ethyl acetoacetate to prepare phenyl hydrazones 98 (Scheme 23). These compounds participated in a Knoevenagel-type condensation with ethyl cyanoacetate to provide pyridazinones... 

Knoevenagel-type condensation of aldehydes with enantiomerically pure sulfoxides bearing electron-withdrawing substituents (R1 = CN, COO-r-Bu, S02C6H5) in the a-position, followed by isomerization and [2,3] sigmatropic rearrangement afforded enantiomerically enriched ( )-y-hydroxy-a,/ -unsaturated esters, nitriles or sulfones with enantiomeric excess in the range of 15-80% (Table 5)49-51-82 84. 

Preparation of Suliinyl Dienophiles. This sulfinyl ester was also used to prepare optically active sulfinyl dienophiles by a Knoevenagel-type condensation of Glyoxylic Acid (eq 7). ... 

Phenylaeetic acid derivatives. The reagent undergoes Knoevenagel-type condensation with benzaldehyde (Triton B) to give l-methylsulfinyl-l-methylthio-2-phenyl-ethylene (2). When (2) is treated with hydrochloric acid in ethanol at room temperature ethyl phcnylacetate (3) is obtained in 78% yield. 

Triafulvenes stabilized by electron-withdrawing groups at the e.vo-methylene carbon and alkyl or aryl groups in the three-membered ring can be prepared by Knoevenagel-type condensation of cyclopropenone derivatives with active methylene compounds under acidic conditions (heating in acetic anhydride). The procedure is simple, but the yields are generally poor. °... 

Abell et al. [288] reported the reaction of 5-formyl-lH-pyrrole-2-carboxylic amides bound to the polymeric support via their amide linkage (249) and dihydrocinna-moyl chloride. The acid chloride is believed to acylate the pyrrole nitrogen prior to an intramolecular Knoevenagel type condensation. The resulting bicycle (251) is deeply colored and was suggested by the authors to be used as a tag for combinatorial libraries. Upon treatment with NaOCHs, the bicycHc structure can be reverted to a 1-benzyl 3-pyrrolyl acrylic ester (Scheme 55). 

Disubstituted 4//-l,2,6-thiadiazine-3,5(2//,6//)-diones (140) in the presence of piperidine readily undergo Knoevenagel type condensation with a variety of aldehydes to yield the 4-arylidene derivatives (144) (Scheme 10) <92AP(325)509>. In contrast, however, the corresponding base-catalysed condensation with 3,5-diamino-4//-l,2,6-thiadiazine-l,1-dioxide (145) is successful only with 5-nitrofuran-2-carbaldehyde (145)->(146) (Equation (13)). 

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