1-Phenethylisoquinoline alkaloids. Part IV. Isolation, structural elucidation, and synthesis of c-homoaporphines

Abstract

Extraction of Kreysigia multiflora has yielded six alkaloids, three not having previously been found. (RS)-Kreysigine, (–)-floramultine, and (–)-multifloramine are shown to have the novel C-homoaporphine structures (11)–(13) by spectroscopic study and by synthesis. The (R)-configuration is established for (–)-multifloramine by carrying out the synthesis with resolved materials. Kreysiginone, a trace alkaloid, is shown in a similar way to be the benzo[de]quinoline-7-spirocyclohexadienone (21). Comment is made on the surprising stereochemical relationships among the various alkaloids.