ANODIC-OXIDATION OF 1,2,3,4-TETRAHYDRONAPHTHALENE AND ISOCHROMAN ANALOGS OF 1-BENZYLISOQUINOLINE AND 1-PHENETHYLISOQUINOLINE ALKALOIDS - PRODUCTS AND MECHANISM OF THE INTRA-MOLECULAR CYCLIZATION

The anodic oxidation of l-(3',4'-dimethoxybenzyl)-6,7-dimethoxy- (17a), l-(3',4'-dimethoxybenzyl)-l-methyl-6.7-dimethoxy- (17b), and l-(3',4'-dimethoxyphenethyl)-6,7-dimethoxy-1,2,3,4-tetrahydronaphthalene (17e), and l-(3',4'-dimethoxybenzyl)- (17c) and l-(3',4'-dimethoxybenzyl)-l-methylisochroman (17d) was studied by preparative electrolyses, cyclic voltammetry, and second harmonic ac measurements. With 17a,b, three different intramolecular coupling reactions were observed. The major reaction involved coupling between C-5a and C-14 leading, after demethylation, to a dienone of structure 18. The other cyclization reactions involved coupling between C-8a and C-14 with formation of an isomeric dienone (19) and coupling between C-4 and C-14 with formation of a 2,3: 6.7-bis(4',5'-dimethoxybenzo)bicyclo[3.2.2]nonane derivative (21). For 17e the only reaction was coupling between C-8a and C-14 leading to the dienone 19c. With 17c-d there was intramolecular coupling between C-5a and C-14 giving the dienones 18c,d and between the heteroatom and C-14 giving, after hydrolysis, the hydroxylated compounds 24a,b. Second harmonic ac measurements indicated that all coupling reactions involved a very fast initial ECE reaction leading to a relatively stable cationic intermediate. The products observed can be rationalized readily in terms of known rearrangements and substitution reactions of these cations. Copyright © 1979, American Chemical Society. All rights reserved.