Synthesis and Reactions of Dibenzopyrrocolines

Extension of oxidative coupling of laudanosoline by Harley-Mason (20), who investigated the oxidation of tetrahydropapaveroline (27) with potassium ferri-cyanide, afforded 2,3,9,10-tetrahydroxy-5,6-dihydrodibenzopyrrocoline (28) in 

64% yield, which was converted to the known tetraacetate 12. Subsequent air oxidation of the tetrahydroxy compound 28 afforded a product assigned structure 29 and acetylation gave a derivative believed to have structure 30. The tetraacetate 12 in contrast to the tetraphenol did not undergo air oxidation. 

Oxidation products from tetrahydropapaveroline with potassium ferricyanide were reinvestigated by Mak and Brossi 21), who confirmed structure 28 for the initial product. Air oxidation of 29 gave after acetylation a product with the same physical properties reported by Harley-Mason, but its mass spectrum showed a parent ion at m e 900 and molecular composition C48H40N2O16, suggesting it to be a dehydro dimer of 12. The H-NMR spectrum of the dimer showed that the double bonds at the 5,6 positions were intact. The point of dimerization was determined by comparing the multiplicities of carbons in the C-NMR spectra of the dimer and dibenzopyrrocoline models. For monomeric compounds the peak ascribed to C-12 in compound 11 was a triplet and a doublet in 12, but a singlet in the dimer. Thus, the products from oxidation of 28 had structures 31 and 32 rather than 29 and 30, respectively. 

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

Lead tetraacetate in acetic acid oxidizes phenolic 1-benzylisoquinolines to p-quinol acetates which usually rearrange to aporphines in trifluoroacetic acid (25). However, Blasko et al. (24) recently reported that lead tetraacetate oxidized ( )-A -norlaudanosine (34) to dibenzopyrrocoline 35 in 16% yield. 

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