Azulene‐Substituted Pyridines and Pyridinium Salts. Synthesis and Structure. Part 1. Azulene‐Substituted Pyridines.

Abstract

Pyridine derivatives R 0380Azulene-Substituted Pyridines and Pyridinium Salts. Synthesis and Structure. Part 1. Azulene-Substituted Pyridines. -The classical route from pyranylium salts (I) to pyridines (II) consists in the replacement of the heterocyclic oxygenatom by nitrogen using ammonium acetate as the nitrogen source. An alternative procedure utilizes the nucleophilic substitution of chlorine in pyranylium salt (III) by azulenes, followed by in situ replacement of oxygen by nitrogen. The classical route can be used both for 2,6-diphenyl-or 2,6-dimethylpyridines whereas the alternative method only works for 2,6-diphenyl derivatives. However, the last route is preferable for the preparation of 2,6-diphenyl derivatives, especially with a substituent at the 3-position, e.g.V). -(RAZUS*, A. C.; BIRZAN, L.; PAVEL, C.; LEHADUS, O.; CORBU, A.; CHIRALEU, F.; ENACHE, C.; J. Heterocycl. Chem. 44 (2007) 1, 245-250; Inst. Org. Chem., Rom. Acad., RO-060023 Bucharest, Rom.; Eng.) -H. Hoennerscheid 25-133