Investigations of novel reactions inside the resorcin[4]arene hexamer and of HCl as cocatalyst

Abstract

The readily accessible supramolecular host XII, based on the self-assembly of resorcin[4]arene \n60b, has been shown to facilitate a range of reactions. Its hexameric structure encloses an internal \nvolume of 1400 A³ and is capable of reversible guest encapsulation and release due to its highly \ndynamic nature. Its catalytic activity stems from the ability to stabilize intermediates and transition \nstates via cation-\uf070 interactions with the electron-rich aromatic walls of the cavity and to form \nH-bonds. \nInvestigations into the tail-to-head cyclization of monoterpenes revealed a dependence on the \npresence of HCl for catalytic activity to arise. This sparked a closer scrutiny of reactions known to \nbe catalyzed by host XII, which uncovered that the presence of HCl as cocatalyst is essential for \nreactions progressing through cationic intermediates. \nThe activation of tertiary alkyl fluorides and primary and secondary benzyl fluorides was \ninvestigated inside the supramolecular container XII. Kinetic measurements display a sigmoidal \nreaction progress, indicating synergistic catalysis by the host and HF released during the reaction. \nAn unprecedented transformation of electron-poor benzaldehydes and isocyanides to imines and \ncarbon monoxide catalyzed by hexamer XII was investigated. A mechanistic proposal put forth \nafter consulting kinetic measurements and quantum mechanical calculations, suggesting the \nreaction progresses via iminooxirane and aziridinone intermediates.