Benzyltetrahydroisoquinolines, oxidative cyclization

The solvent may influence the course of such coupling reactions. Thus N-trifluoracetyl-l-benzyltetrahydroisoquinolines (82) cyclize on anodic oxidation in acetonitrile to neospirodienones (83), whereas morphinandienones (84) are formed in methanol-acetonitrile [Eq. (70)].147... 

Additional examples of intramolecular oxidative coupling of phenolic ethers include the oxidative biaryl coupling of various N-substituted 1-benzyltetrahydroisoquinolines 313 to the corresponding aporphines 314 [374], the oxidative cyclization of 3,4-dimethoxyphenyl 3,4-dimethoxyphenylacetate (315) leading to the seven-membered lactone 316 [375] and the conversion of phenol ether derivatives 317 into the products of... 

An interesting variation on the above theme for the biosynthesis of the pavines and isopavines has been proposed by Dyke (169). This proceeds via a quinone methine intermediate. The precursor, a l-benzyltetrahydroisoquinoline-3-car-boxylic acid 165 oxidizes to a quinone methide 166, which then decarboxylates to afford a reactive enamine 167. Cyclization then readily furnishes a pavine. Alternatively, hydration of the enamine 167 at C-4 would ultimately result in formation of an isopavine (Scheme 36). 

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