Studies on the syntheses of heterocyclic compounds. Part CDXXI. General synthesis of 7,8-dioxygenated 1-benzyl-1,2,3,4-tetrahydroisoquinolines and elucidation of the structure of caseadine

Abstract

Bischler–Napieralski reactions of the phenolic bromo-amides (11c and d)[prepared by condensation of 5-benzyloxy-2-bromo-4-methoxyphenethylamine (9) with 3,4-dimethoxy-(10a) and 3,4-methylenedioxy-phenacetyl chloride (10b) followed by debenzylation] and reduction of the resultant benzyldihydroisoquinolines (12a and b) gave the 1-benzyl-5-bromo-1,2,3,4-tetrahydro-8-hydroxy-7-methoxyisoquinolines (13a and b). The former (13a) was converted into 1-hydroxy-2,10,11-trimethoxyberbine (3), which was different from caseadine.