Azulene‐substituted pyridines and pyridinium salts. Synthesis and structure. 1. Azulene‐substituted pyridines

Abstract

4-Azulen-1-yl substituted 2,6-dimethyl-and 2,6-diphenyl-pyridines are obtained in good yields from the reaction of corresponding 4-azulen-1-yl-pyranylium salts and ammonium acetate in ethanol or starting from 4-chloro-2,6-diphenyl-pyranylium salts in two steps: reaction with azulenes followed by in situ treatment with ammonium acetate. The effect of substitution at the 3-position of the heterocycle was taken into account. The structure assignment was accomplished with NMR and uv-vis spectra.

2‐(Azulen‐1‐yl)‐4,6‐diphenyl substituted six‐membered heteroaromatics

“…The synthesis of 2-(azulen-1-yl) substituted pyranylium salts was carried out following a similar route to that used for the generation of corresponding 4substituted isomers (Scheme 1) [1]. The synthesis of 2-(azulen-1-yl) substituted pyranylium salts was carried out following a similar route to that used for the generation of corresponding 4substituted isomers (Scheme 1) [1].…”

“…Our recent works has emphasized the stabilizing influence of the azulen-1-yl group on pyranylium [1] and pyridinium [2a] salts as well as on pyridine [2b] when it is attached in the 4-position of these heterocycles. Our recent works has emphasized the stabilizing influence of the azulen-1-yl group on pyranylium [1] and pyridinium [2a] salts as well as on pyridine [2b] when it is attached in the 4-position of these heterocycles.…”

“…Our recent works has emphasized the stabilizing influence of the azulen-1-yl group on pyranylium [1] and pyridinium [2a] salts as well as on pyridine [2b] when it is attached in the 4-position of these heterocycles. There are several pathways for the synthesis of azulenyl-substituted heterocycles either by coupling of suitable substituted azulenes and heterocycles [4] or starting from pyranones [1,2]. Thus, for 4-(azulen-1yl)-2,6-dimethyl-pyridinium salts when the nitrogen was quaternized by isopropyl we have observed a difference between chemical shift of the methyl protons at C-2 and C-6 positions.…”

Azulene Moiety as Electron Reservoir in Positively Charged Systems; A Short Survey

“…The pyranylium salts were then used as valuable synthons for obtaining a series of pyridines and pyridinium salts [34]. The general pathway for the synthesis of pyridinium salts in two steps [39] was applied to the generation of salts substituted with azulen-1-yl moieties (Scheme 13) [38,40,41]. In the first step the pyranylium ring is opened by amine in the presence of triethylamine followed by the ring closure of the intermediate enamine.…”

“…Without going into details, a remark must be made regarding the influence of the heteroaromatic magnetic field, which exerts influence mainly on the neighboring azulene protons 2, 7 and 8, which are more deshielded [40,41].…”