Base-catalyzed condensation

Synthesis and Properties. Polyquinolines are formed by the step-growth polymerization of o-aminophenyl (aryl) ketone monomers and ketone monomers with alpha hydrogens (mosdy acetophenone derivatives). Both AA—BB and AB-type polyquinolines are known as well as a number of copolymers. Polyquinolines have often been prepared by the Friedlander reaction (88), which involves either an acid- or a base-catalyzed condensation of an (9-amino aromatic aldehyde or ketone with a ketomethylene compound, producing quinoline. Surveys of monomers and their syntheses and properties have beenpubhshed (89—91). 

The Madelung Synthesis and Related Base-Catalyzed Condensations. The Madelung cyclization involves an intramolecular condensation of an o-aLkylanilide. A classic example of the Madelung synthesis is the high temperature condensation of o-methylacetanihde [120-66-1] to 2-methylindole [95-20-5] by sodium amide. 

Such copolymers of oxygen have been prepared from styrene, a-methylstyrene, indene, ketenes, butadiene, isoprene, l,l-diphen5iethylene, methyl methacrjiate, methyl acrylate, acrylonitrile, and vinyl chloride (44,66,109). 1,3-Dienes, such as butadiene, yield randomly distributed 1,2- and 1,4-copolymers. Oxygen pressure and olefin stmcture are important factors in these reactions for example, other products, eg, carbonyl compounds, epoxides, etc, can form at low oxygen pressures. Polymers possessing dialkyl peroxide moieties in the polymer backbone have also been prepared by base-catalyzed condensations of di(hydroxy-/ f2 -alkyl) peroxides with dibasic acid chlorides or bis(chloroformates) (110). 

Viaylpyrroles and 3-vinylpyrroles can be prepared by the base-catalyzed condensation of the corresponding formyl pyrroles with activated... 

Synthesis of stilbenes by base catalyzed condensation of reactive toluenes with benzalanillnes. 

Experimental studies of this base-catalyzed condensation have revealed that it is third-order, indicating that either the second or the fourth step must be rate-determining. Studies on the intermediate I obtained by an alternative synthesis have shown that is about four times as large as k - so that about 80% of the intermediate goes on to product. These reactions are faster than the overall reaction under the same conditions, so the second step must be rate-controlling. ... 

Chapters 1 and 2. Most C—H bonds are very weakly acidic and have no tendency to ionize spontaneously to form carbanions. Reactions that involve carbanion intermediates are therefore usually carried out in the presence of a base which can generate the reactive carbanion intermediate. Base-catalyzed condensation reactions of carbonyl compounds provide many examples of this type of reaction. The reaction between acetophenone and benzaldehyde, which was considered in Section 4.2, for example, requires a basic catalyst to proceed, and the kinetics of the reaction show that the rate is proportional to the catalyst concentration. This is because the neutral acetophenone molecule is not nucleophihc and does not react with benzaldehyde. The much more nucleophilic enolate (carbanion) formed by deprotonation is the reactive nucleophile. 

The Reissert procedure involves base-catalyzed condensation of an o-nitrotoluene derivative 1 with an ethyl oxalate (2) which is followed by reductive cyclization to an indole-2-carboxylic acid derivative 4, as illustrated below . ... 

Base catalyzed condensation of 2-azidobenzaldehyde 796 with cyano-carbanions in piperidine or NaOEt in ethanol afforded tetrazoloquinolines... 

The double bond is then reduced by catalytic hydrogenation (59). Base-catalyzed condensation... 

The utility of base catalyzed condensations of esters to give jS-ketoesters is well known. A straightforward example of this reaction is the intermolecular cyclization of diethyl succinate giving 2,5-dicarbethoxy-l,4-cyclohexanedione, which can in turn be easily decarboxylated to give 1,4-cyclohexanedione. 

The Darzens reaction involves a two-step, base-catalyzed condensation of ethyl chloroacetate with a ketone to yield an epoxy ester. The first step is a carbonyl condensation reaction, and the second step is an SK2 reaction. Write both steps, and show their mechanisms. 

By Base-Catalyzed Condensation (Including Wittig Reaction)... 

Base-catalyzed condensation of 2-iminoindane-2-carbonitrile (62) with phthalaldehyde affords indeno[2,l-c]-2-benzazepine-5-carbonitrile (63) in excellent yield (95%),97 which is identical to an uncharacterizcd byproduct obtained earlier98 by condensing benzene-1,2-diacetonitrile with phthalaldehyde in the presence of sodium methoxide. The naphthalene analog 64 is prepared by condensing naphthalene-2,3-dicarbaldehyde with the indanecarbonitrile 62 under similar conditions. 

In the base-catalyzed condensation of diethyl ethylsulfonylmethylphosphate with aldehydes or ketones, the corresponding a, /1-unsaturated sulfones were obtained in good yields297,364,365. 

Reactions 16-38-16-49 are base-catalyzed condensations (though some of them are also catalyzed to acids). In 16-38-16-47, a base removes a C—H proton to give a carbanion, which then adds to a C=0. The oxygen acquires a proton, and the resulting alcohol may or may not be dehydrated, depending on whether an a hydrogen is present and on whether the new double bond would be in conjugation with double bonds already present ... 

TABLE 16.1 Base Catalyzed Condensations Showing the Active Components and the Carbonyl Compounds... 

This result is similar to that obtained in the Reformatsky reaction (16-31), but this is more general since no ester or other group is required to be a to the halogen. Another important advantage of the Wittig reaction is that the position of the new double bond is always certain, in contrast to the result in the Reformatsky reaction and in most of the base-catalyzed condensations (16-38-16-46). Examples of this are given below. 

The fabrication of colloidal silica and optical glasses by the sol-gel process has attracted a great deal of attention (8). The process relies on the hydrolytic polycondensation reactions of alkoxysilanes, usually (EtO)4Si, in which the reactive silanols (EtO)4 Si(OH)n (n = 1-4) are formed. These then undergo acid- or base-catalyzed condensation with both water and alcohol formation, as shown in Scheme 2. 

Base-catalyzed condensation between phenylacetic acid and phthalic acid produces enol lactone 78, which is reduced to benzoate 79 with HI and phosphorous. Friedel-Crafts cyclization by polyphosphoric acid followed by reduction produces alcohol 80. This alcohol forms ethers exceedingly easily, probably via the carbonium ion. Treatment with N-methyl-4— piperidinol in the presence 6f acid leads to the antidepressant hepzidine (81). 

It is of interest that antibacterial activity can be retained even when the imine carbon-nitrogen bond is replaced by a carbon to carbon double bond. Base-catalyzed condensation of 5-nitrofurfuraldehyde (24) with 2,6-dimethylpyridine (38) affords olefin 39. Treatment of this compound with hydrogen peroxide gives the corresponding N-oxide (40). Heating of... 

Lounasmaa and Johansson have developed a synthetic route useful for the preparation of 4-benzyltropane alkaloids (97). The base-catalyzed condensation of tropinone (124) with benzaldehyde under carefully controlled... 

Boiadjiev and Lightner synthesized fluorescent tricyclic-bridged pyrrinones such as 31 by base-catalyzed condensation-cyclization of pyrrolin-2-one 112 with pyrrole aldehyde 113 (Equation 24) <2005M553, 2005JOC689>. 

The Friedlander reaction is the acid- or base-catalyzed condensation of an ortho-acylaniline with an enolizable aldehyde or ketone. Henichart and coworkers have described microwave-assisted Friedlander reactions for the synthesis of indoli-zino[l,2-b]quinolincs, which constitute the heterocyclic core of camptothecin-type antitumor agents (Scheme 6.238) [421], The process involved the condensation of ortho-aminobenzaldehydcs (or imines) with tetrahydroindolizinediones to form the quinoline structures. Employing 1.25 equivalents of the aldehyde or imine component in acetic acid as solvent provided the desired target compounds in 57-91% yield within 15 min. These transformations were carried out under open-vessel conditions at the reflux temperature of the acetic acid solvent. 

Organometallic compounds or carbanions undergo a number of reactions in which the carbanion or carbanion-like moiety of the organometallic compound acts as a nucleophilic displacing agent. Examples are the formation of hydrocarbons from alkyl halides, alkyl halides from halogens, and ketones from acid chlorides or esters. The latter two reactions are closely related to the base-catalyzed condensations and are perhaps additions as well as displacement reactions. Related addition reactions are the carbonation of organometallic compounds and the addition to ketones or aldehydes. 

Base catalyzed condensation reactions of esters and ketones have an additional factor of importance in determining the product, and this is the fact that the overall reaction, as well as the intermediate steps, is highly reversible. The final product may be rate or equilibrium determined, and in the latter case the result may depend on the relative acidity of the various possible products. In a highly basic medium the product will be partly in the form of a salt and the stability of the salt is then a product-determining factor. Failure of a condensation to take place may be due either to an insufficiently high concentration of carbanions or to the instability of the product. The reactions of ethyl isobutyrate will illustrate both points.419... 

Several total syntheses of antirhine (11) and 18,19-dihydroantirhine (14) have been developed during the last decade. Wenkert et al. (136) employed a facile route to ( )-18,19-dihydroantirhine, using lactone 196 as a key building block. Base-catalyzed condensation of methyl 4-methylnicotinate (193) with methyl oxalate, followed by hydrolysis, oxidative decarboxylation with alkaline hydrogen peroxide, and final esterification, resulted in methyl 4-(methoxycar-bonylmethyl)nicotinate (194). Condensation of 194 with acetaldehyde and subsequent reduction afforded nicotinic ester derivative 195, which was reduced with lithium aluminum hydride, and the diol product obtained was oxidized with manganese dioxide to yield the desired lactone 196. Alkylation of 196 with tryptophyl bromide (197) resulted in a pyridinium salt whose catalytic reduction... 

Scheme 33 Base catalyzed condensation of aldehydes by electrogenerated bases (EGB s) R alkyl, yields 72-77%, very high current efficiency.

Thorpe reaction org chem The reaction by which, in presence of lithium amides, a,(rt-dinitriles undergo base-catalyzed condensation to cyclic iminonitriles, which can be hydrolyzed and decarboxylated to cyclic ketones. thorp re,ak-shan TMPC See tetrakis(hydroxymethyl)phosphonium chloride, thulia See thulium oxide. thu-le-a ... 

Base-catalyzed condensation of esters to afford (3-keto esters. 

The base-catalyzed condensation of azides with activated methylene compounds is a well-established route to IJT-triazoles. In particular, it is the best route to triazoles bearing a 5-amino or hydroxy substituent and an aryl or carbonyl-containing function in the 4-position. The addition is regiospecific. The reaction is a stepwise one, since anomerism of glycosyl azides has been observed in their reaction with activated methylene compounds, indicating the presence of an intermediate. The mechanism can be envisaged as a nucleophilic attack by the car-banion on the terminal nitrogen of the azide, followed by cyclization to a... 

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