5 years ago

Threading of an Inherently Directional Calixarene Wheel with Oriented Ammonium Axles

Threading of an Inherently Directional Calixarene Wheel with Oriented Ammonium Axles
Placido Neri, Carmine Gaeta, Margherita De Rosa, Annunziata Soriente, Carmen Talotta, Pellegrino La Manna
The threading of monostoppered alkylbenzylammonium axles 7+ and 8+ with the calix[6]-wheel 3 can occur by both routes of entering the macrocycle 3 in the cone conformation: passage through the upper rim and the through the lower rim. Thus, under thermodynamic conditions, with both the axles 7+ and 8+, the two possible orientations of calix[2]pseudorotaxane, namely, endo-benzyl and endo-alkyl, are formed by a stereoselectivity controlled by the endo-alkyl rule. Interestingly, by 1H NMR monitoring of the threading process between 8+ and 3, we revealed two calix[2]pseudorotaxane isomers in which the calix-wheel adopts 1,2,3-alternate and cone conformations, which represent the kinetic and thermodynamic species, respectively. Finally, the synthesis of ammonium-based oriented calix[2]rotaxane is here described.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b01388

DOI: 10.1021/acs.joc.7b01388

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