The Partial O‐Demethylation of Aromatic‐Substituted 3,4‐Dihydroisoquinolines

A detailed study has shown that all possible aromatic dimethoxy‐substituted 3,4‐dihydroisoquinolines can be partially O‐demethylated by controlled acid hydrolysis. Based on the structure elucidation of the monophenols thus obtained, it was established that preferential cleavage occurs at the 5‐methoxyl with the 5,6‐ and 5,8‐isomers 1 and 3, respectively, at the 6‐methoxyl with the 6,8‐isomer 4, at the 7‐methoxyl with the 5,7‐isomer 5, and at the 8‐methoxyl with the 7,8‐isomer 2.