REACTION OF AMINES WITH 1-PHENACYL-2-BROMOPYRIDINIUM SALTS . A NEW ROUTE TO IMIDAZO[1,2-A]PYRIDINIUM, OXAZOLO[3,2-A]PYRIDINIUM, AND DIHYDROPYRIDO[2,1-C]-AS-TRIAZINIUM SALTS

The reaction of 2-bromo-1-phenacylpyridinium bromide (1) with arylamines, acethydrazide, or butylamine leads to 1-substituted imidazo[1,2-a]pyridinium salts (10). If the reaction with butylamine was interrupted, two intermediates, 1-butyl-2-hydroxy-2-phenyl-2,3-dihydroimidazo[1,2-a]pyridinium (7, R = Bu) bromide and a 2-phenyloxazolo[3,2-a]pyridinium salt (9) were isolated. With tertiary amines the latter (9) became the major product. With hydrazine or methylhydrazine, 3-phenyl-1,4-dihydropyrido[2,1-c]as-triazinium ion (13) or its 1-methyl homolog (15) were obtained, while with 1,2-dimethylhydrazine the product was the 1,2-dimethyl-3-phenyl-1,2-dihydropyrido[2,1-c]triazinium ion (19). In boiling acid 19 loses a methyl group from the nitrogen at the 2 position affording 15. In boiling acid 3-phenyl-1,4-dihydro[2,1-c]-as-triazinium ion (13) undergoes ring contraction to 1-amino-2-phenylimidazo[1,2-a]pyridinium ion (22). © 1969, American Chemical Society. All rights reserved.