Vera L. Sigacheva

Electrosynthesis of cyclopropanes at the electrolysis of solutions of methyl esters of Di- and trichloroacetatic acids in aprotic media in the presence of acrylonitrile

The potentiostatic (galvanostatic) electrolysis of methyl esters of trichloroacetic acid on mercury (steel) cathodes in the cathodic compartment of a diaphragm cell in the presence of acrylonitrile affords a mixture of two stereoisomers of methyl ester of 1-chloro-2-cyanocyclopropanecarboxylic acid. The process involves a stage of dehalogenation of the original methyl ester followed by the reaction of the formed anion with acrylonitrile and proceeds more efficiently on a mercury cathode in the dimethylformamide medium with the current efficiency of 94% and the substance yield of 25%. In contrast to methyl trichloroacetate, the electrolysis of methyl dichloroacetate proceeds by an indirect mechanism involving its deprotonation on the steel cathode and by the cleavage of the C-Cl bond on the mercury cathode. In both cases, the acrylonitrile addition leads to formation of the corresponding cyclopropane structures. Moreover, the process is the most efficient on the steel cathode in the MeCN medium. In the latter case, the current efficiency of methyl ester of 1-chloro-2-cyanocyclopropanecarboxylic acid is 31% and substance yield is 41%. Peculiarities of these processes are discussed.

Reactions of 3-cyclopropyl-3-oxopropionitrile anion generated by electroreduction of 5-cyclopropylisoxazole

Abstract3-Cyclopropyl-3-oxopropionitrile anion obtained by cathodic reduction of 5-cyclopropylisoxazole in an aprotic medium was used as an example to demonstrate that cyano ketone anions show a dual reactivity. The reaction of acetyl chloride with the electrogenerated tetrabutylammonium salt of 3-cyclopropyl-3-oxopropionitrile gave O-acylation products, whereas the reaction with its sodium salt gives C-acylation products. The reactions of these salts with hydroxylamine hydrochloride follow a different route: in the case of the tetrabutylammonium salt, resinification takes place, while in the case of the sodium salt, 5-amino-3-cyclopropylisoxazole is formed. The condensation of this product with 4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione in glacial AcOH affords 3-cyclopropyl-6-(2-thienyl)-4-(trifluoromethyl)isoxazolo[5,4-b]pyridine in 85% yield.

Oxidative transformation of N-substituted 3-aminopyrazoles to azopyrazoles using electrogenerated bromine as a mediator

The one-pot process of anodic transformation of N-alkyl-3-aminopyrazoles into azopyrazoles under conditions of membraneless electrolysis in an aqueous solution of NaBr was studied for the first time. It was found that under these conditions the aminopyrazoles, which do not have a substituent at position 4, transform into the corresponding 4,4´-dibromoazopyrazoles. The corresponding yield was in the interval of 28—80%, depending on the structure of the products. The transformation of 4-substituted aminopyrazoles resulted in the formation of azopyrazoles in the yields lying within 62—86% when this process was implemented under conditions with the anodically generated Br2 acting as a mediator. A convenient method of anodic synthesis of azopyrazoles in an aqueous medium without the use of additives of chemical oxidants was proposed. The process is environmentally sound and is characterized by a high atom efficiency (>85%).

Cathodic deprotonation of 5-substituted isoxazoles

The regularities of electroreduction of 5-substituted isoxazoles are studied by examining their cyclopropyl and phenyl derivatives. It is found that this process proceeds on a steel electrode according to the mechanism of direct cathodic deprotonation and is accompanied by the removal of a proton from the 3rd position of the isoxazole ring with the formation of a corresponding carbanion, which is readily isomerized to enolate anion of an open type. The same mechanism is realized also in the electroreduction of 5-substituted isoxazoles on cathodes with a high overpotential of hydrogen evolution (C, Hg). An alternative process, namely, an indirect cathodic deprotonation of 5-substituted isoxazoles, can be realized with the use of MeOH or t-BuOH as the prebases.