Reactions of pyrylium salts with nucleophiles—V : Reaction of 2,4,6-trimethylpyrylium perchlorate with primary amines

Abstract

N-Aryl-2,4,6-trimethylpyrydinium salts were prepared from 2,4,6-trimethylpyrylium perchlorate and ArNH 2, the aryl group being p-chloro-, bromo, iodo, methyl-, hydroxy- or amino-phenyl. The reaction of 2,4,6-trimethylpyrylium perchlorate with primary aliphatic amines (methyl, ethyl n-propyl, n-butyl, isopentyl, benzyl, cyclohexyl, n-heptyl and n-octadecyl) was found to afford along with N-alkylpyridinium salts, N-alkyl-3,5-xylidines. Such cyclizations to an aniline derivative were known only in the reactions of pyrylium salts with secondary amines. A third kind of product is formed in very small yield with aromatic amines, in larger yield with higher aliphatic amines and as the only product with t-butyl amine; it is possibly an imino-enol. IR and NMR spectra are discussed and assignments of bands are made on the basis of deuteration of amino and methyl groups. In N-aryl-2,4,6-trimethylpyridinium salts the upfield shift of the α-methyl NMR signal implies non-coplanarity of the pyridinium and phenyl rings.