N-Amino pyridinium salts in organic synthesis

Abstract

This review summarizes the synthesis and reactivity of N-aminopyridinium salts, discusses applications in organic synthesis, and highlights the potential for these reagents to enable novel synthetic disconnections and innovations.

Photoredox Catalysis for the Synthesis of N‐CF2H Compounds Using 1‐((N‐(difluoromethyl)‐4‐methylphenyl)‐sulfonamido)pyridin‐1‐ium Trifluoromethanesulfonate

“…Studies in N‐ aminopyridinium salts coupled with the growing field of photoredox catalysis have produced efficient and impressive amino‐transformations in recent years (Scheme 1c) [16–20] . Since Studer's seminal work on direct arene amination, [21] the field has grown to include difunctionalization of alkenes with various nucleophiles, [22–25] yielding highly functionalized aminated products.…”

“…Studies in N-aminopyridinium salts coupled with the growing field of photoredox catalysis have produced efficient and impressive amino-transformations in recent years (Scheme 1c). [16][17][18][19][20] Since Studer's seminal work on direct arene amination, [21] the field has grown to include difunctionalization of alkenes with various nucleophiles, [22][23][24][25] yielding highly functionalized aminated products. The rapid fragmentation event upon reductive SET, modular scaffold design, and divergent reactivity inspired us to explore the synthetic versatility of N-aminopyridinium reagents for the diversification of NCF 2 H compounds.…”

Dearomatization of Pyridines: Photochemical Skeletal Enlargement for the Synthesis of 1,2-Diazepines

“…38−41 However, tedious synthesis and isolation of the starting materials remain a significant drawback. Despite the indisputable interest of 1-aminopyridinium salts in organic synthesis, 42 this reaction remained a scientific curiosity and was never applied to any synthesis. To tackle these hurdles, a unified and standardized protocol is required to facilitate access to 1,2-diazepines and ensure reproducibility.…”

“…An important milestone was reached in the 70s with the photochemical rearrangement of 1-aminopyridinium ylides into 1,2-diazepines by Streith and Cassal (Figure C). , Several research groups slightly extended the scope of accessible 1,2-diazepines. − However, tedious synthesis and isolation of the starting materials remain a significant drawback. Despite the indisputable interest of 1-aminopyridinium salts in organic synthesis, this reaction remained a scientific curiosity and was never applied to any synthesis. To tackle these hurdles, a unified and standardized protocol is required to facilitate access to 1,2-diazepines and ensure reproducibility.…”

Photo-induced cyclization of olefinic amides towards sulfonamidylated iminoisobenzofurans and benzoxazines

“…12 Moreover, the utilization of the in situ generated sulfonamidyl radical for the C–H sulfonamidation/difunctionalization of alkenes was also developed for the synthesis of sulfonamide derivatives. 13,15,16 Among them, N -sulfonylaminopyridinium salts 14 have been proven to be convenient sulfonamidyl radical precursors towards sulfonamide 15 and sulfonamidylated cyclic compounds 16 via the sulfonylamidation of alkenes. We also describe the radical sulfonamidation/cyclization of unactivated alkenes to construct polycyclic quinazolinones, benzosultams and oxazolines.…”