RhIII-catalyzed C-H activation: A versatile route towards various polycyclic pyridinium salts

Abstract

An efficient and convenient method for the synthesis of highly substituted polycyclic pyridinium salts from the reaction of various 2-aryl-pyr-idines and 2-aryl-sp2-nitrogen-atom-containing heterocycles with alkynes through rhodium(III)-catalyzed C-H activation and annulation under an O2 atmosphere is described. A possible mechanism that involves the chelation-assisted C-H activation of the 2-arylpyridine substrate, insertion of the alkyne, and reductive elimination is proposed. This mechanism was supported by the isolation of a five-mem-bered rhodacycle (I'). In addition, kinetic isotope studies were performed to understand the intimate reaction mechanism. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA.