The reaction between isatin and some amines

Abstract

In acidic aqueous solution 2-(3,4-dimethoxyphenyl)ethylamine and isatin reacted to give 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline-1-spiro-3′-(2′-oxoindoline)(1a); 2-(3-hydroxy-4-methoxyphenyl)ethylamine gave a mixture of the analogous 6-hydroxy-7-methoxyspiran (1b) and the isomeric 8-hydroxy-7-methoxyspiran (1c). In neither case was a derivative of 1-benzyl-1,2,3,4-tetrahydroisoquinoline detected. A mixture of 2-(3-hydroxy-4-methoxyphenyl)ethylamine and benzylamine reacted with isatin to form, in addition to the spirans, some 6-hydroxy-7-methoxy-1-phenyl-1,2,3,4-tetrahydroisoquinoline (3b); but when a mixture of 2-(3,4-dimethoxyphenyl)-ethylamine and benzylamine was used, no 6,7-dimethoxy-1-phenyl-1,2,3,4-tetrahydroisoquinoline was detected.