Electrochemical oxidation of aromatic ethers. Part 6. Oxidation of 4-(3,4-dimethoxybenzyl)-6,7-dimethoxy-2-methyl-1,2,3,4-tetrahydroisoquinoline and attempted synthesis of 4-(3,4-dimethoxybenzyl)6,7-dimethoxy-2-methyl-1,4-dihydro-3(2H)-isoquinolone

Abstract

The cyclisation of 3-(3,4-dimethoxyphenyl)-2-(2-hydroxymethyl-4,5-dimethoxyphenyl)-N-methylpropionamide (5) and related compounds does not yield 4-(3,4-dimethoxyphenyl)-6,7-dimethoxy-2-methyl-1,4-dihydro-3(2H)isoquinolone, but gives instead dibenzo[b,f]cycloheptane derivatives. Anodic oxidation of 4-(3,4-dimethoxyphenyl)-6,7-dimethoxy-2-methyl-1,2,3,4-tetrahydroisoquinoline affords the corresponding 3,4-dihydroisoquinolinium and 4-(3,4-dimethoxybenzylidene)-6,7-dimethoxy-2-methyl-1,4-dihydroisoquinolinium salts. No intramolecularly aryl-aryl coupled products are isolated and the implication of this result on the design of substrates for the synthesis of biphenyl derivatives is discussed.