Studies on the syntheses of heterocyclic compounds. Part DCL. Total synthesis of corytenchirine

Abstract

(±)-Corytenchirine [rac-(8); 11-hydroxy-2,3,10-trimethoxy-8α-methyl-13aαH-berbine], isolated from Corydalis ochotensis, has been synthesised by two methods: (i) irradiation of the (Z)-1-benzylidenetetrahydroisoquinoline (3), derived from 1-(3-benzyloxy-4-methoxybenzyl)-3,4-dihydro-6,7-dimethoxyisoquioline (1), followed by reduction of the resulting dibenzoquinolizinylium salt (5) and debenzylation; and (ii) a Mannich reaction of 1,2,3,4-tetrahydro-1-(3-hydroxy-4-methoxybenzyl)-6,7-dimethoxyisoquinoline (18) with acetaldehyde. The 2,3,11-trimethoxy-isomer [rac-(10)] was also synthesised by the photochemical method. The stereochemistry of corytenchirine-type compounds is discussed.