ИСТИНА

Copper-catalyzed azide-alkyne cycloaddition (CuAAC) has become useful synthetic tool in modern organic chemistry and related disciplines due to its high efficiency, selectivity, and tolerance to numerous functional groups when performed in mild conditions. In calixarene chemistry CuAAC is intensively applied, in particular, for grafting several aminoacid or sugar units onto macrocyclic platform and also for the preparation of efficient ionophores, sensors etc. In course of our research on trizole-containing peptidocalixarenes, an equimolar mixture of tetrakis(propargyloxy)calix[4]arene and azide was subjected to CuAAC which returned ~70 mol. % of starting calixarene, exhaustively reacted calix[4]arene, and only trace amount of expected partially modified calixarenes. Though established for oligoazides, the selectivity is unique for oligoalkynes, and was investigated more deeply using different azides, Cu-catalysts and reaction conditions with a series of bis- (distal and proximal), tris- and tetrakis(propargyloxy)calix[4]arenes in different conformations, and also with several calix[6]arenes. The influence of proximity of propargyl groups onto the selectivity of CuAAC was unambiguously concluded and discussed in terms of highly stable copper complex formation in course of the reaction.