Reaction with basic condensing agents

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

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) ... 

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. ... 

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... 

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>. 

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