Pyrazolines special

Azomethines add with great ease and stereospecificity to carbon-carbon double bonds affording pyrazolidines. They also add to carbon-carbon triple bonds with the formation of pyrazolines. Benzimidazolium iV-imines, e.g. (622), are a special case of azomethines. Its reaction with DMAD yields l-(2-methylaminophenyl)pyrazole (624), which is formed by cleavage of the initial adduct (623) (75JHC225). 

Acrylic fibres can also be brightened during manufacture by gel application during the wet spinning process. Special FBAs have not been developed for this purpose. Products such as the pyrazoline sulphone 11.50 and the benzofuranyl-benzimidazole 11.55 are suitable for this application. 

The stable products of the reaction are the cyclopropanes and isomeric olefins. The decomposition of cis- and tra j-3,5-dimethyl-1-pyrazolines are of special interest in that they exhibit a stereochemical reversal in the dimethyl cyclopropane product. The cw-pyrazoline forms predominantly trans, and the franj-pyrazoline predominantly cw-dimethyl cyclopropane. This is a consequence of the orbital symmetry of the intermediate trimethylene species which requires a conrotatory motion as the preferred mode of ring closure, and as such lends experimental support to the validity of Hoffman s mo calculations. 

Functional group substituents on N-l of 2-pyrazolin-5-ones (Table XXXVII) are acyl, sulfonyl and various carboxyl derivatives, such as carbalkoxy, amides, thioamides, hydrazides, thiohydrazides and amidines. The usual synthesis of these compounds is by the classical 2-pyrazolin-5-one synthesis, reaction of a /J-ketoester with a hydrazine. In these cases the hydrazines are special types such as hydrazide,... 

Pyrazoline heterocycles and specially dihydropyrazolones are widely used as dyes for various applications in food, textile, photography and cosmetics industries. Some of these heterocycles exhibit useful biological properties, and for example, phenazone was one of the first synthetic drugs. The corresponding saturated pyrazolidin-3-ones exhibit similar properties, as exemplified with the anti-inflammatory drug phenylbutazone. Moreover, this heterogeneous copper(I)-modified zeolite catalyst can be reused six times without significant loss of activity. 

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