Papaverine dimerization

The aromatic dibenzopyrrocoline dimer 33 was obtained by Hess etal. (22) by electrochemical oxidation of papaverine at a platinum anode in methanolic so-... 

The initial attack in the anodic oxidation of papaverine [75] probably involves a similar attack further oxidation and dimerization leads to the isolated product, 12,12 -bis-(2,3,9,10-tetramethoxyindolo[2,l-fl]isoquinolyl). An analogous reaction is the electrooxidation of a tetramethoxy-substituted 2-methyl-l-phenethyl-l,2,3,4-tetrahydroisoquinoline to a dibenzoquinolizinium derivative [76] and the oxidation of A,A -triphenyl-( -phenyle-nediamine to 9,10-diphenylphenazine [77]. Intramolecular Michel addition of nitrogen in a tetrahydroquinoline derivative to an o-quinone moity have resulted in the formation of a 5,6-dihydrodibenz[6,d]indolizine derivative [78]. A similar ring closure occurs during the oxidation of various catecholamines [79] and similar compounds [79] to indoles. Cyclic a-carbonylazo compounds, generated by anodic oxidation of the hydrazines, may be trapped by reaction with dienes to the expected heterocycles [80]. 

Papaverine can be dimerized by oxidation with vanadium oxytrifluoride in trifluoroacetic acid. Such condensation does not usually occur with tetra-hydrobenzylisoquinolines which instead tend to undergo intramolecular... 

Isoquinoline alkaloid biosynthesis is one of the well-characterized pathways in the secondary metabolism of plant cells which comprises some of the most important drugs for therapy and euphoria (e.g., morphine and its chemical derivatives, papaverine, berberine, dimeric bisbenzylisoquinolines). 

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