Benzologs of the thiazolo[3,2-a]pyridinium system

By use of concentrated sulfuric acid rather than hydrobromic acid as the cyclizing medium, good yields of the thiazolo3,2-a]quinolinium ion and its derivatives may be obtained from α-(2-quinolylthio) ketones or acetals. In the same way, α-(1-isoquinolylthio) and α-(6-phenanthridylthio) ketones afford thiazolo2,3-a]isoquinolinium and thiazolo-3,2-f]phenanthridinium salts.