Condensing agents, basic

This reaction involves the condensation of an aldehyde or ketone with an a-halo ester in the presence of a basic condensing agent (sodium ethoxlde, sodamide, finely divided sodium or potassium iert.-butoxide) to give a glycldio (or ap-epoxy) ester. Thus acetophenone and ethyl chloroacetate yield phenyl-methylglycidic ester (I) ... 

This compound may be produced by reacting o-chlorobenzophenone with acetonitrile in the presence of sodium amide or another strongly basic condensing agent, to form the nitrile of /3-phenyl-/3-o-chlorophenyl-hydracrylic acid, which is then hydrogenated to yield Tphenyl-l-o-chlorophenyl-S-aminopropanol-l. The latter intermediate compound is subsequently dimethylated with an agent such as methyl sulfate to provide the desired end product l-o-chlorophenyl-Tphenyl-S-dimethylaminopropanol. 

A further unusual feature of the matrix-dependent polycondensation lies in the character of the nucleobases themselves. Purine mononucleotides undergo polycondensation, in good yields, at complementary matrices consisting of pyrimidine polymers. However, the synthesis of pyrimidine oligonucleotides from their mononucleotides at purine matrices is not effective. This important fact means that a pyrimidine-rich matrix leads to a purine-rich nucleic acid, which is itself not suitable to act as a matrix. This phenomenon also occurs when matrices are used which contain both basic species, i.e., purines and pyrimidines. An increase in the amount of purine in a matrix leads to a clear decrease in its effectiveness (Inoue and Orgel, 1983). However, the authors note self-critically that the condensation agent used cannot be considered to be prebiotic in nature. 

It appears that treatment of phenacyl bromides 1239 with methylhydrazine in refluxing acetic acid leads also to 1,4-disubstituted triazoles 1244. Fivefold excess of methylhydrazine is used in these reactions. According to the proposed mechanism, structures 1240-1243, methylhydrazine has a double role, as a condensing agent and an oxidant. In the final account, three molecules of methylhydrazine have to be used to produce one molecule of triazole 1244, two molecules of methylamine and one molecule of ammonia. The basic triazole 1244 (X = Y = H) is separated in 59% yield. The reactions go well with electron-donating substituents (for X = OH, the yield is 81%), but electron-withdrawing substituents can lower the yield dramatically (11% for X = N02) (Scheme 206) <2003JCM96>. 

Esters, such as those of malonic, acetoacetic or cyanoacetic acids, in which the methylene group is doubly activated, will condense even with ketones. By varying the proportion of aldehyde or ketone to ester, 2 mols. of the former can be made to condense with 1 of the latter, using the basic condensing agents only (4, below). The following will illustrate these points — ... 

Phenoxazine resists alkylation with alkyl halides, because the nitrogen atom of the phenoxazine nucleus is not sufficiently basic for direct action. N-Alkylation can be achieved, however, in the presence of basic condensing agents like sodamide. 

The favorable influence of a hexamethylphosphotriamide (hexa-metapol) medium upon a variety of reactions with ionic mechanism is shown by the iV-methylation of phenothiazine with CH3I in the presence of basic condensing agents. Very good yields of 10-methyl-phenothiazine have thus been obtained. ... 

DCC as condensation agent. Such amides are stable under basic conditions, but converted to A-acylindoles readily. 

Potassium hydride, being more basic and more active than sodium hydride, is suggested for use as a condensing agent in acetoacetic ester, Claisen, Stobbe, and related condensations which proceed with difiSculty. 

On treatment of compounds containing active C-H bonds with 1,3,5-triazine (1), enamines 11 and 12 are usually the first isolable products. In order to isolate such compounds, the reactions are preferably conducted in the absence of a basic condensing agent.18... 

Reaction with basic condensing agents a. C-C linkage between two halides... 

Condensing agents are basic catalysts such as alkali carbonates, hydrogen carbonates, hydroxides, or alkoxides, or primary aliphatic amines or calcium hydroxide zinc chloride may also be used with aromatic aldehydes. Ethylene-diamine was introduced by Lerner972 for use in the synthesis of unsaturated nitriles in the aromatic series and he gave a large number of examples in which yields were around 95%. 

Morpholine, bp 128°C, is a colourless, hygroscopic liquid, miscible with water, and as a result of the inductive influence of the oxygen atom, it possesses lower basicity pKa = 8.4) than piperidine (11.2) and piperazine (9.8). Morpholine is synthesized either by acid-catalysed cyclodehydration of bis(2-hydroxyethyl)amine or from bis(2-chloroethyl) ether and NH3. Morpholine, like piperidine, is used as a basic condensing agent and as a solvent. In industry, it is employed as an additive to the feed-water inhibiting corrosion in steam boilers. 

Two basic synthetic routes have been reported for the preparation of propiomazine hydrochloride. Farbenfabriken Bayer prepared propiomazine by reacting 2-dimethyland.no-propyl chloride with 2-propionylphenothiazine in the presence of sodium amide as the condensing agent, and subsequently converting the base form to the hydrochloride (See Figure 6). 

When a quinaldinium salt and 2-unsubstituted thiazolium are condensed together in the presence of a basic agent, the resulting bis-(methylquinoline-2)trimethine cyanine is issued from the cleavage of the thiazolium ring of the anhydrobase (25). It is induced by the -CHj attack of quinaldinium according to a process already described (Scheme 28). 

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