Electrochemical oxidation of aromatic ethers. Part 10. Regioselectivity in the aryl–aryl coupling reactions of some 4-benzylisochroman-3-ones and benzyl-1,2,3,4-tetrahydroisoquinolines.

Abstract

The anodic coupling reactions of 4-benzylisochroman-3-ones, 1- and 4-benzyl-1,2,3,4-tetrahydro-isoquinolines are compared and analysed. In neutral media 4-benryltetrahydroisoquinolines may afford products resulting from coupling to C-1 and/or to N-2 depending on the ring substituents. In acidic solution 4-benzyltetrahydroisoquinolines yield isoaporphines whereas their 1-benzyl analogues couple at C-8a to give morphindienones. This difference may be explained by considering the inductive effects inherent in the protonated forms of the bases. 4-Benzylisochroman-3-ones also couple at C-8a, but the intermediates thus produced are unstable and either rearrange or react with available nucleophiles.