Knoevenagel condensation polymerization

Horhold et al. and Lenz et al. [94,95]. The polycondensation provides the cyano-PPVs as insoluble, intractable powders. Holmes et al. [96], and later on Rikken et al. [97], described a new family of soluble, well-characterized 2,5-dialkyl- and 2,5-dialkoxy-substituted poly(pflrfl-phenylene-cyanovinylene)s (74b) synthesized by Knoevenagel condensation-polymerization of the corresponding alkyl-or alkoxy-substituted aromatic monomers. Careful control of the reaction conditions (tetra-n-butyl ammonium hydroxide as base) is required to avoid Michael-type addition. 

Synthesis. The most facile synthetic scheme found for making the accordion polymers involves a Knoevenagel condensation polymerization of two precursors. One is a bis-aldehyde precursor which will form the electron-donating ends of a pair of linked chromophores, e.g. ... 

Accordion polymers—Continued orientational and chemical stability, 139 synthesis by Knoevenagel condensation polymerization, 135-136 waveguide construction, 139-140 Aluminum metal electrode, deposition on polymer in LED, 411,412/ Aromatic amine-containing polymers dye-dispersed poly(N-vinylcarbazole), 387, 390-393... 

Knoevenagel condensation of the corresponding 3-methylfuran-2-carbaldehyde 379 and 3-methybenzo[4]furan-2-carbaldehyde 382 with diethyl malonate followed by bromination with iV-bromosuccinimide (NBS) in the presence of dibenzoyl peroxide afforded bromides 380 and 383, respectively. Treatment of 380 and 383 with benzylamine, isopropylamine, /-butylamine 3-hydroxypropylamine, aniline and -toluidine in ethanol yielded furo[2,3-c]pyrroles 381 and benzo[4,5]furo[2,3-c]pyrroles 384, respectively (Scheme 41). The yields of furopyrroles 381 are only moderate (16-46%), because these compounds are highly sensitive to acid, and partially polymerized upon silica... 

Monomer 33 was made to undergo transesterification polymerization using Ti(OC4H9)4, while monomer 34 was appropriate for a Knoevenagel polycondensation. The transesterification polymerization resulted in the formation of an intractable material of unknown structure. Homopolymerization of 34 by the Knoevenagel technique afforded polymer 35 with a low molecular weight (M 6800). A major byproduct in this polymerization was a macrocyclic lactone, formed via an intramolecular Knoevenagel condensation (Scheme 10-14). 

The catalytic effectiveness of polymeric reagents has been demonstrated in nucleophilic substitution reactions (91), O- and N-alkylation [92] and Knoevenagel condensation [91,93]. The preparation procedure of catalyst 1 during the reaction of halogen substitution in alkyl or aryl halogenides by an anion of a potassium salt is shown in Table 7 ... 

Alkyl-2-cyanoacrylates can be prepared by several synthetic procedures. The only method of importance involves the Knoevenagel condensation of an alkylcyanoacetate with formaldehyde. As this is a base-catalysed reaction, the monomer is rapidly polymerized to give a low-molecular-weight poly(alkyl-2-cyanoacrylate). The resulting polymer is retropolymer-ized by heating under controlled conditions to yield monomeric cyanoacrylate (Scheme 1). 

Z.-J. Zheng, L.-X. Liu, G. Gao, H. Dong, J.-X. Jiang, G.-Q. Lai, L.-W. Xu, RSC Adv. 2012, 2, 2895-2901. Amine-fiinctional polysUoxanes (AFPs) as efficient polymeric organocatalyst for amino catalysis efficient multicomponent Gewald reaction, a-allyhc alkylation of aldehydes, and Knoevenagel condensation. 

A microfluidic reaction system has also been used for the production of prodrugs. A multichannel membrane microreactor was fabricated and tested for Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate to produce a-cyanocinnamic acid ethyl ester, a known intermediate for the production of an antihypertensive drug [9]. Knoevenagel condensations of carbonylic coiiqtounds and malonic esters yield several important key products such as nitriles used in anionic polymerization, and the a,p-unsaturated ester intermediates employed in the synthesis of several therapeutic drugs that include niphendip-ine and nitrendipine. Unlike most condensation reactions. 

Kossmehl (1979) et at have described the polymerization of the benzothiazohum salts by the Knoevenagel condensation of 2,3,6-trimethylthiazolo[4,S- benzothiazohum perchlorate (117, X = CIO4-) and iodide (117, X = 1-) with dialdehydes such as p-phenylenedicarbaldehyde, 2,5-dimethoxy-p-phenylenedicarbaldehyde, thiophene-2,3 dicarbaldehyde (scheme-33) (Kossmehl et at 1979). In the same year Mukaiyama (1979) studied that the benzothiazolium compounds can be used to activate the carboxyhc adds or alcohols to give 2-acyloxy or 2-alkoxy intermediates, which can be converted into esters, thioesters, amides, lactones, add fluorides, isocyanates, etc (Mukaiyama 1979). 

Polymeric amines can be proton acceptors, acyl transfer agents, or ligands for metal ions. The 2- and 4-isomers of poly(vinylpyridine) (11) and (12) and the weakly basic ion exchange resins, p-dimethylaminomethylated PS (2) and poly(2-dimethylaminoethyl acrylate), are commercial. The ion exchange resins are catalysts for aldol condensations, Knoevenagel condensations, Perkin reactions, cyanohydrin formation and redistributions of chlorosilanes. " The poly(vinylpyridine)s have been used in stoichiometric amounts for preparation of esters from acid chlorides and alcohols, and for preparation of trimethylsilyl ethers and trimethylsilylamines from chlorotrimethylsilane and alcohols or amines. Polymer-suppored DBU (l,8-diazabicyclo[5.4.0]undec-7-ene) (52) in stoichiometric amounts promotes dehydrohalogenation of alkyl bromides and esterification of carboxylic acids with alkyl halides. The protonated tertiary amine resins are converted to free base form by treatment with aqueous sodium hydroxide. 

Polymeric l,3y4-Thiadiazoles. Knoevenagel condensation of 2,5-dimethyl-l,3,4-thiadiazole with mono- and di-aldehydes of the benzene and thiophen series has given a number of polymers of type (123), as well as their oligomers (122) their... 

The Knoevenagel reaction is a base-catalyzed condensation between a dialdehyde and an arene possessing two sites with relatively acidic protons. In this polymerization, shown schematically in Scheme 34, deprotonation affords a difunctional nucleophile that subsequently attacks the carbonyl functionalities present in the other monomers. Elimination is the final step in the Knoevenagel sequence, and the use of monomers with highly acidic protons drives the reaction to completion. A number of research groups have employed this method to obtain PPV and its substituted analogs 29 [126,140-146]. 

Introduction of these photocrosslinkable structures in macro-molecular chains can be performed by esterification of hydroxyla-ted polymers with cinnamoyl chloride. Cellulose Q).condensation products (4, ) and mainly poly(vinyl alcohol) have Been treated( by this method. Other chemical modifications have been studied as ester interchange of poly(vinyl acetate) 7) and Knoevenagel reaction on polyesters (8). Very few results on the synthesis of such photocrosslinkable polymers by polymerization have been reported. Therefore free radical polymerization of cinnamic acid vinyl derivatives did not lead to the expected polymers, but to insolubilization reactions. Howewer cationic procedure can be a good way in some cases since Kato et al. could polymerize by this way with high yields p-vinyl phenylcinnamate (9) and B-vinyloxyethyl cinnamate (10). 

The arylnitroalkenes may be produced by the condensation of aromatic aldehydes and nitroparaffins (Knoevenagel and Walter, Ber. vol. 37, p. 4502 (1904) Worrall, Jour. Am. Chem. Soc vol. 56, p. 1556 (1934) Alles, Jour. Am. Chem Soc. vol. 54, p. 271 (1932)). Compounds of this type are desirably reduced to form amino compounds and more or less successful reductions have been obtained in the case of compounds such as ome a-nitrostyrene, obtained by the condensation of nitromethane with an aromatic aldehyde. However, in the case of nitroalkenes of the type it has been found to be extremely difficult to effect satisfactory reduction. For example, Benzedrine (l-phenyl-2-aminopropane) may theoretically be obtained by the reduction of l-phenyl-2-nitropropene, but in practice it has been found to be almost impossible to effect the desired reaction. Relatively low yields of Benzedrine have been secured by electrolytic reduction of the nitropropene but catalytic hydrogenation appears to yield only high molecular weight polymerization products. 

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). 

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