Aziridine strategy for stereospecific synthesis of 1′-alkyl/aryl-5′-aryl-2′,5′-dihydropyrrolofullerene-2′-carboxylates and NMR study of hindered 5′-aryl group rotation

Abstract

A reaction of aziridines with fullerene C60 is shown to provide a stereospecific route to fulleropyrrolidines for a diverse range of substituents. The important limitation of the approach is shown to be the synthesis of N-unsubstituted fulleropyrrolidines, where the imine route described elsewhere suits better. For 2-arylsubstituted fulleropyrrolidines the activation free Gibbs energy, enthalpy and entropy of a hindered aryl group rotation are determined based on the line-shape analysis of temperature dependent NMR spectra. ortho-Fluorophenyl substituted pyrrolofullerenes are shown to have the activation barrier of ca. 16 kcal/mol, which poses these compounds as possible hindered rotors in molecular machines application.