Background. Compounds of 1,2,3-triazole row display high biological activity and other practically useful characteristics. The most important way to build Natural Sciences. Chemistry 47 a 1,2,3-triazole system is based on 1,3-dipolar cycloaddition of alkyl- and arylazides to acetylenes activated by electron-withdrawing group. In the case of disubstituted acetylenes the formation of two regioisomeric products is possible. To make progress in comprehending the factors influencing regiochemical result, it is necessary to expand the range of both reagents and substrates. The purpose of the study was to examine the regiosectivity of phenylazide addition to insufficiently explored sulfonyl-substituted acetylenes.
Materials and methods. We used methyl-, n-tolyland n-chlorophenyl (phenylethynyl)sulfones, which are different in steric volume of sulfonyl substituent, as substrates. The reactions were carried out in dry diethyl ether at 20 °С for 18–20 days using a triple excess of the reagent, which was added to the mixture by two equal portions at interval of 10 days. The reaction was controlled by TLC and 1Н and 13С NMR.
Results. In each reaction the one of two potential cycloaddition products, namely, 4-sulfonyl-substituted 1H-1,2,3-triazole, was obtained (51–54 % yield). The products were isolated by crystallization. Their structure is confirmed by the methods of IR, 1Н and 13С NMR spectroscopy and mass spectrometry. One of the products was also obtained by the counter synthesis based on the reaction of the corresponding -ketosulfone with phenylazide (the Dimroth condensation). The regioselectivity of the addition obtained in the experiment differs from the results of the reactions between the same and related sulfonyl-substituted acetylenes with other organic azides, in which the formation of double-component mixtures of isomeric 1,2,3-triazoles was observed.
Conclusions. The formation of the single product in the reactions of phenylazide with the studied sulfonyl-substituted acetylenes can be explained by the influence of electronic effect of the phenyl group in the azide. It indicates considerable influence of a reagent nature on regioselectivity of 1,3-dipolar cycloaddition. This conclusion adds new details to the well-known fact about the significant role of electronic and steric effects of substituents in activated acetylenes responsible for the regiochemical result of the reaction.
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