Synthesis of imidazo[1,2-a] pyridinium salts from 2-alkylaminopyridines. A reexamination

1-Alkyl-2-hydroxy-2,3-dihydroimidazo [1,2-a] pyridinium salts (III) have been identified as isolatable intermediates in the synthesis of 1-alkylimidazo[1,2-a] pyridinium salts (II) from 2-alkylaminopyridines and α-haloketones. Spectral data suggest that these intermediates exist exclusively as the cyclic ring tautomers III rather than chain tautomers VI.