A novel ring closure leading to 3,9-dihydroxyaporphines (3,9-dihydroxy-4H-dibenzo[de,g]quinolines). Part 2

Abstract

3,9-Dihydroxyaporphines are formed by a novel and efficient ring closure when certain 1 -benzyl-1,2,3,4-tetrahydro-5,8-dimethoxyisoquinolines are demethylated in refluxing hydrobromic acid. In accordance with a mechanism proposed in Part 1, it has been shown that such a ring closure is facilitated by a labile 3-alkoxy group on the benzyl moiety but inhibited by the stable 3-phenoxy group. The general principle of the aporphine ring closure is further confirmed by an alternative, unambiguous, albeit less efficient, synthesis of 3,9-dihydroxyaporphine.