Bisbenzylisoquinoline alkaloids and related compounds. V. A total synthesis of diastereoisomeric mixture of liensinine.

Diastereoisomeric mixture of O, O-dibenzyl-liensinine (II) was successfully obtained by the modified Ullmann reaction of dl-1-(4-benzyloxybenzyl)-2-methyl-6-methoxy-7-hydrozy-1, 2, 3, 4-tetrahydroisoquinoline (XVII) with dl-1-(3-bromo-4-benzyloxybenzyl)-2-methyl-6, 7-dimethoxy-1, 2, 3, 4-tetrahydroisoquinoline (X) which has a large substituent such as benzyloxy-group at the ortho position of bromobenzene nucleus, without any detectable side reaction on the thin-layer chromatography. Removal of benzyl group by treating II with hydrochloric acid gave diastereoisomeric mixture of liensinine (I'), whose infrared and ultraviolet spectra were identical with those of natural product.