Preparation and reactions of pyrylium salts containing α-pyridyl groups

Abstract

The preparation of unsymmetrical 2,4,6-trisubstituted pyrylium salts from αβ-unsaturated ketones and methyl ketones is complicated by retro-aldol reactions leading to corresponding symmetrical pyrylium salts.

4,6-Diphenyl-2-(1H-pyridinium-2-yl)pyrylium (5a) and (5b) is prepared successfully by oxidation of the 1,5-dione from chalcone and 2-acetylpyridine. The transformation of pyrylium into pyridinium occurs easily with primary amines to 2-(2-pyridyl)pyridiniums whose various reactions are studied.