Heterocycles. III. Syntheses of berbans from 6,7-dimethoxy-3,4-dihydroisoquinoline.

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Twice annulations of 6, 7-dimethoxy-3, 4-dihydroisoquinoline hydrochloride (7) stereoselectively give the pseudoberbenone (12), the catalytic reduction of which preferentially affords the alloberbanone (15). On a series of reactions (oxidation, O-methylation, sodium borohydride reduction, ether cleavage and catalytic reduction) 12 is converted into the berbanone (25) via the berbadienone (21). Oxidations of 15 and 25 with mercuric acetate smoothly afford the 1, 11-didehydro compounds (17) and (26), respectively. Two isomeric metho salts (18) and (19) obtained from 17, and the one (31) from 21 are found to give the starting materials by demethylation under conditions of the Hofmann degradation. Stereostructures of the compounds obtained here are examined on the basis of the infrared and nuclear magnetic resonance spectra. Their formation pathways are also discussed.

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