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

Abstract

Cationic N-heterocycles are an important class of organic compounds largely present in natural and bioactive molecules. They are widely used as fluorescent dyes for biological studies, as well as in spectroscopic and microscopic methods. These compounds are key intermediates in many natural and pharmaceutical syntheses. They are also a potential candidate for organic light-emitting diodes (OLEDs). Because of these useful applications, the development of new methods for the synthesis of cationic N-heterocycles has received a lot of attention. In particular, many C-H activation methodologies that realize high step- and atom-economies toward these compounds have been developed. In this review, recent advancements in the synthesis and applications of cationic N-heterocycles through C-H activation reactions are summarized. The new C-H activation reactions described in this review are preferred over their classical analogs.

Reaching Green: Heterocycle Synthesis by Transition Metal‐Catalyzed C−H Functionalization in Sustainable Medium

“…Quaternary ammoniums alts could be produced from nitrogen-directed metal-catalyzed CÀHa ctivation, predominantly in as ustainable reactionm edium. [47] In 2012, our group developed at hree-component coupling of aldehydes 44,a mines 45, and alkynest os ynthesize isoquinolinium salts 46 in the presence of Ru catalyst( Scheme 18). [48] Aw ide range of aldehydes and alkynes were transformed into desired salt products in good to excellent yields using ethanol solvent.…”

C–H Activation and Alkyne Annulation via Automatic or Intrinsic Directing Groups: Towards High Step Economy

“…DGs usually use heteroatoms for directing, which are suitable to coordinate with metals to form relatively stable metallocyclic intermediates. π ‐Bonds can also be used for direction, for example, alkynol can be transformed to alkene for directing in Liu's work (Scheme ). However, it is much more challenging for a linear alkyne group to direct on its ortho ‐site.…”

Recent Advances in the Synthesis of Quaternary Ammonium Salts via Transition‐Metal‐Catalyzed CH Bond Activation

“…developed the first Rh(III)‐ and Ru(II)‐catalyzed CH activation for the synthesis of isoquinolinium salts from aromatic aldehydes, amines, and alkynes . Later, several research groups also successfully developed metal‐catalyzed synthesis of quaternary ammonium salts such as cinnolinium, quinolizinium, pyridinium, imidazolinium, pyrazolocinnolinium, and benzoimidazoquinolizinium salts . So far, only a few reviews focusing on Rh(III)‐ and Ru(II)‐catalyzed CH bond activation for the synthesis of heterocyclic compounds and heterocyclic salts have appeared .…”

“…Later, several research groups also successfully developed metal‐catalyzed synthesis of quaternary ammonium salts such as cinnolinium, quinolizinium, pyridinium, imidazolinium, pyrazolocinnolinium, and benzoimidazoquinolizinium salts . So far, only a few reviews focusing on Rh(III)‐ and Ru(II)‐catalyzed CH bond activation for the synthesis of heterocyclic compounds and heterocyclic salts have appeared . In this mini‐review, we focus on the very recent reports for the synthesis of cationic N ‐heterocycles via transition‐metal‐catalyzed CH bond activation, including the catalytic mechanism, substrate scope, limitations, and applications.…”