“…8,16 Many reactions of cycloaddition are known in organic chemistry, for instance -[2 + 3] cyloaddition, 47 [3 + 4] cycloaddition, 48 [4 + 2] cycloaddition. Many examples of pre-organized dimeric pairs are described in the literature via the coordination of the initial ethylene systems with metal cations 11,30,32,34,38,40,43,50 or the formation of hydrogen bonds between the components, 7,9,10,12,14,15,17,20,21,[23][24][25]29,30,40,41,46,50 as well as entering two structural units in cavitand cavitycyclodextrins, calixarenes, cucurbit [8]uril, nanocages. Whereas, PCA represents a temperature independent process.…”