ИСТИНА

Azide-alkyne Huisgen cycloaddition is the well-recognized example of the click-reaction concept. In its original version this reaction requires no catalyst but leads to mixtures of isomeric 1,4- and 1,5-disubstituted 1,2,3-triazoles (when terminal alkynes reacted). The selectivity of the cycloaddition can be shifted completely towards the 1,4-disubstituted 1,2,3-triazoles by the addition of a Cu(I)-catalyst. This has created the valuable synthetic methodology in modern organic chemistry abbreviated as CuAAC (Cu(I)-catalyzed azide-alkyne cycloaddition). Selective preparation of 1,5-disubstituted 1,2,3-triazoles is also possible by using the Ru(II)-catalysts (RuAAC), but these reactions are less explored due to higher cost of the catalysts and lesser tolerance of the process towards functional groups and reaction conditions. In this research a selective intramolecular formation of solely 1,5-triazoles at narrow rims of calix[4]arenes under Huisgen conditions was found. A series of calix[4]arenes containing azidoalkyl- and propargyl groups in distal positions of the narrow rims was prepared by propargylation of the respective azidoalkylated calix[4]arenes. First, these compounds were tried in CuAAC reactions either with azides, alkynes or with no additives. But in all cases mixtures of polymeric/oligomeric products were obtained. Quite unexpectedly, heating of the toluene solutions of the 2-azidoethylated, 3-azidopropylated or 4-azidobutylated calix[4]arenes containing propargyl groups at the narrow rims led to the formation of a single cycloaddition product in each case. NMR correlations and HRMS ESI-mass spectra showed that the products were calixarenes having 1,5-disubstituted 1,2,3-triazole bridges formed selectively by the non-catalytic intramolecular azide-alkyne cycloaddition. Structures of the products were further confirmed by X-ray crystallography.