Recent Advances in Pyridinium Salts as Radical Reservoirs in Organic Synthesis

Abstract

Pyridinium salts are valuable building blocks, which have been widely applied in various organic transformations during the past few decades. In particular, N-functionalized pyridinium salts have been explored as convenient radical precursors, which would go through reductive single-electron transfer. As a result, the chemistry of such pyridinium compounds for generating carbon-, nitrogen-, and oxygen-centered radicals has been witnessed, and a remarkable progress has been achieved, making it a hot topic over the last five years. This Review describes recent advances in the area of pyridinium salts as radical precursors, concerning the development of radical reactions involving pyridinium salts in organic synthesis.

Pyridinium Salts as Redox‐Active Functional Group Transfer Reagents

“…Recently,t he N-functionalized pyridinium core has emerged as apromising new scaffold for redox-active reagents,w hich enable the generation of aw ide range of synthetically important radicals. [7] Herein, we highlight these recent advances by providing as election of contemporary methods that demonstrate the quintessential features of this approach.…”

The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle

“…Recently, the use of Katritzky salts (pyridinium salts) under photocatalytic conditions has elicited increasing interest, due to the stability and ease of synthesis of these derivatives . In one instance, pyridinium salts were used as source of benzyl radicals for the dicarbofunctionalization of styrenes (Scheme ) …”

Salts in Organic Synthesis: An Overview and Their Diversified Use

“…Various papers are published by discussing the role of individual salts, their selective way of transformation, role in asymmetric synthesis and many more. Some of the recent influencing research on application of salts in organic synthesis are use of diaryliodonium salts for novel arylation [20], applications of ferrocenium salts [21], salt as linker source [22], pyridinium salts as radical reservoir [23], use of vinyliodonium salts for alkenylation of nitriles [24], use of sulfonium salts for synthesis of spirocyclopropanyl paradienones [25], use of phosphonium salts for selective functionalization of pyridines [26], tropylium salts as lewis acid to catalyze acetalization and transacetalization [27], use of Phenyltrimethylammonium salts in nickel-catalyzed methylation of C− H bonds [28], aryldiazonium salts for carbohydroxylation of styrenes [29], synthesis of bicyclic aziridines from pyridinium salts [30], nucleophilic arylation with tetraarylphosphonium salts [31], application of trimethylsilanolate alkali salts in organic synthesis [32], use of α, β-unsaturated acylammonium salts for asymmetric organocatalysis [33], review on cesium salts use in organic synthesis [34], iodonium salts as benzyne precursors [35], use of bunte salts as a sulfur source for synthesis of 3-thioindoles [36], and C− H functionalization of arenes by diaryliodonium salts [37] etc.…”