RhIII-Catalyzed CH Activation: A Versatile Route towards Various Polycyclic Pyridinium Salts

An efficient and convenient method for the synthesis of highly substituted polycyclic pyridinium salts from the reaction of various 2‐aryl‐pyridines 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‐aryl‐pyridine substrate, insertion of the alkyne, and reductive elimination is proposed. This mechanism was supported by the isolation of a five‐membered rhodacycle (I′). In addition, kinetic isotope studies were performed to understand the intimate reaction mechanism. RhIII and easy: A convenient synthesis of polycyclic pyridinium salts in excellent yields through RhIII‐catalyzed CH activation under an O2/CuII atmosphere at ambient temperature is described (see scheme). These salts showed strong fluorescence in CH2Cl2 (DME=1,2‐dimethoxyethane).