O-mesitylene sulfonyl hydroxylamine (MSH) (3) was used to prepare the N-amino salt as an aminating agent as described by Tamura et al., (1972) Tetrahedron Letter. 40: 4133, incorporated herein by reference in its entirety. An ice cooled solution of 7-hydroxyisoquinoline (2.0 g, 13.78 mmol) in 30 mL of dry methylene chloride, and 15 ml of dry methanol was added drop wise to O-mesitylenesulfonylhydroxylamine (2.97 g, 13.78 mmol) in 10 mL of dry methylene chloride over 5 min with stirring. The reaction stirred at 0° C. for 6 h. 70 mL of ether was added and the suspension filtered. The precipitate was recrystallized from ethyl acetate to give 2-amino-7-hydroxyisoquinolinium 2,4,6-trimethylbenzenesulfonate (6) in 60.5% yield.
