Total synthesis of (–)-discretine (2,10,11-trimethoxy-13aα-berbin-3-ol)

Abstract

(±)-Discretine (1) was obtained by a Mannich reaction of 1-(3,4-dimethoxybenzyl)-1,2,3,4-tetrahydro-6-hydroxy-7-methoxyisoquinoline with formalin. Optical resolution of (±)-discretine could not be achieved. (±)-O-Benzyldiscretine (3), which was synthesised by a Mannich reaction of 6-benzyloxy-1-(3,4-dimethoxybenzyl)-1,2,3,4-tetrahydro-7-methoxyisoquinoline (14) with formalin, was resolved to give (–)-O-benzyldiscretine through its di-p-toluoyltartrate; debenzylation then afforded (–)-discretine, which was identical with the natural base.