Studies on tetrahydroisoquinoline. Part 13. Total syntheses of (±)-O-methylandrocymbine, (±)-androcymbine, (±)-kreysigine, (±)-multifloramine, and their related phenethylisoquinoline alkaloids

Abstract

Trifluoroacetic acid treatment of p-quinol acetates derived from phenethylisoquinolines has led to the formation of (±)-homoaporphines, (±)-homomorphinandienones, and (±)-homoproaporphines. Thus three new (±)-homoaporphines (10g–i) possessing a hydroxy group in ring D have been synthesized. The stereostructure of (±)-homoproaporphine (4b), formed as a single spiro-isomer, has been determined by means of X-ray crystallographic analysis, partly for the settlement of stereochemistry on isomeric natural kreysiginone. On the basis of the above result, the steric course for the formation of (4b) has been discussed. An efficient method, consisting of oxidation with lead tetra-acetate of phenethylisoquinolines in trifluoroacetic acid–acetic acid, for the predominant formation of (±)-homomorphinandienones, has been newly developed.