Rh^III‐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-pyridines and 2-aryl-sp(2) -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.

Advancements in the Synthesis and Applications of Cationic N‐Heterocycles through Transition Metal‐Catalyzed C−H Activation

“…[54,55] In Huang's approach, ac ationic Rh III -complex, {Cp*Rh(H 2 O) 3 (OTf) 2 }( 1mol %), was used as the catalyst along with one equivalento fH OTf in MeOH at 120 8Cf or 22 hours under an O 2 atmosphere. [54,55] In Huang's approach, ac ationic Rh III -complex, {Cp*Rh(H 2 O) 3 (OTf) 2 }( 1mol %), was used as the catalyst along with one equivalento fH OTf in MeOH at 120 8Cf or 22 hours under an O 2 atmosphere.…”

Synthesis of Phenalenyl‐Fused Pyrylium Cations: Divergent C−H Activation/Annulation Reaction Sequence of Naphthalene Aldehydes with Alkynes

“…[6,7] In this field, the synthesis of nitrogen-containing heterocycles,l ike pyrrole, [8] pyridine, [9] and pyridinium salts, [10] has been developed extensively, whereas there are only af ew reports on the synthesis of oxygen-doped heterocycles like furan [11] and pyran. [6,7] In this field, the synthesis of nitrogen-containing heterocycles,l ike pyrrole, [8] pyridine, [9] and pyridinium salts, [10] has been developed extensively, whereas there are only af ew reports on the synthesis of oxygen-doped heterocycles like furan [11] and pyran.…”

Modern Synthetic Avenues for the Preparation of Functional Fluorophores

“…For instance, Cheng and co‐workers described rhodium‐catalyzed annulations of 2‐aryl pyridines and alkynes under O 2 atmosphere to prepare fluorescent pyridinium salts with potential applications in organic electronic devices 34. Similarly, Wang and co‐workers prepared polycyclic quinolinium cations in double C−H activation/annulation processes (Figure 5 I) 35.…”