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The thermal, catalytic, and acid-catalyzed transformation of 3,3,5-triphenylpyrazolenine-4-carboxylic acid esters was studied. The thermal and acid-catalyzed isomerization of the pyrazolenines leads not only to pyrazoles but also to isopyrazoles. A mechanism involving a 1,5-suprafacial sigmatropic shift is proposed for the isomerization. It is shown that the migration of substituents from the 4 position of the pyrazolenine ring, which has been previously proposed as a variant of the van Alphen rearrangement, does not occur.

The thermal isomerization of 5-methoxy-3-arylisoxazoles to methyl 3-aryl-2H-azirine-2-carboxylates was subjected to a kinetic study. A correlation between the isomerization rate constants and the σ+ constants of the substituents in the aromatic ring is observed. The enthalpies of formation of a number of isoxazoles and 2H-azirines were calculated. The effect of the nature of the substituents on the mutual isomerization of isoxazoles and azirines is discussed. The results make it possible to refute the approved and previously proposed diradical mechanism for the isomeric transformations and are in agreement with a nitrene mechanism for the formation of azirines.

The thermocatalytic isomerisation of ethyl 1-methyl-2-phenyl-1-cyclopropene-3-carboxylate, ethyl 1-methyl-2-n-butyl-1-cyclopropene-3-carboxylate and ethyl 1-methyl-2-t-butyl-1-cyclopropene-3-carboxylate to furan derivatives has been studied and a mechanism for this isomerisation has been proposed.

The thermal and thermocatalytic isomerisations of methyl 2,3,3-triphenylcyclopropene-1-carboxylate to methyl 2,3-diphenylindene-1-carboxylate have been studied. The rate constants of cyclopropene ring opening were determined and parameters of activation were calculated for the thermal process. The formation of cyclopropene and indene derivatives under the photochemical decomposition of methyl 3,3,5-triphenylpyrazolenine-4-carboxylate is discussed.

The authors use NMR and IR spectroscopy to ascertain the structure and composition of the cyclopentadienes resulting from the thermocatalytic isomerization of substituted 3-vinylcyclopropenes and the catalytic behavior of magnesium bromide and copper stearate in this process. They find that by varying the substituents at the carbon atoms of the three-membered ring and in the vinyl fragment of the substituted cyclopropenes it is possible to obtain a wide range of functionally substituted cyclopentadienes.

The thermal isomerization of 5-methoxy-3-arylisoxazoles to methyl 3-aryl-2H-azirine-2-carboxylates was subjected to a kinetic study. A correlation between the isomerization rate constants and the σ+ constants of the substituents in the aromatic ring is observed. The enthalpies of formation of a number of isoxazoles and 2H-azirines were calculated. The effect of the nature of the substituents on the mutual isomerization of isoxazoles and azirines is discussed. The results make it possible to refute the approved and previously proposed diradical mechanism for the isomeric transformations and are in agreement with a nitrene mechanism for the formation of azirines.

The treatment of 2,2,4,4-tetraalkyl-substituted 1,1,3,3-tetrachlorocyclobutanes with lithium in tert-butyl alcohol led to the production of 2,2,4,4-tetrasubstituted bicyclo(1.10)butanes. It was established that the reaction takes place through 1,3-dichlorobicyclo(1.1.0)butanes. The /sup 13/C NMR spectra were recorded on a CFT-20 instrument at 20 MHz for 40-50% solutions in deuterochloroform. Chromato-mass-spectrometric analysis was performed on a LKB-2091 instrument at 70 eV.