Pyrylium-mediated transformations of natural products. Part 3. Synthesis of water-soluble pyrylium salts and their preparative reactions with amines

Abstract

A series of water-soluble pyrylium salts and zwitterions has been prepared containing two or three carboxylic or sulphonic acid groups. These pyrylium salts react in aqueous solution with ammonia to give the corresponding pyridines and with n-butylamine, benzylamine, and the ω-amino groups of lysine to give the corresponding pyridinium systems, usually as betaines. The pyridinium betaines (m.p. > 300 °C) show characteristic ¹³C n.m.r. spectra which have been nearly fully assigned.