Reactions of isoquinolinium salts with hydroxylamine derivatives, 2nd communication N-(alkyl) and N-(aryl) substituted compounds

The N-alkyl- and N-aryl-isoquinolinium salts 7, 15-17 reacted with free hydroxylamine in pyridine to give the isoquinoline-2-oxide (9) as final product. The intermediate dioximes 8 were isolated and characterized by derivatisation with acetic anhydride to the oxime ester nitrile 10. From the reaction of 8 with trifluoroacetic anhydride/triethylamine 3-amino-isoquinoline-2-oxide (12) resulted after hydrolysis. Due to the electronic influence the 5-nitroisoquinolinium salts 1-3 react faster than the 5-hydroxy derivative 20, but with the same course of conversion via dioximes to amine oxides. An optimized method for preparation of the amine oxides was developed.