PROTOBERBERINES FROM REISSERT COMPOUNDS .2. A NEW SYNTHESIS OF 8-METHYLDIBENZO[A,G]QUINOLIZIDINES

The Reissert compounds 16 are benzylated by 2-bromomethylacetophenone dioxolane 14 to give the dihydroisoquinolines 5. Treatment of 5 with KOH yields the 1-benzylisoquinolines 6 which spontaneously form the deoxygenated coralynes 4 in acidic solution. 4a and 18 are reduced by NaBH4 to give the 8-methyl-trans-dibenzoquinolizidines 19. The sequence 5 --> 6 --> 4 --> 19 is a new efficient access to coralyne analogues and 8-substituted tetrahydroprotoberberines.- Bromination of 2-methylacetophenone does not lead to 2-bromomethylacetophenone but to the benzalbromide 9 or to the phenacylbromide 11.