Stereoselective Introduction of Oxygen Functionalities at the 11.BETA.-Position of Erythrinan Skeleton: Total Syntheses of (.+-.)-Erythristemine and (+)-Erythrartine.
Oxidation of an erythrinan alkaloid erysotramidine (4) with CAN in AcOH-MeCN gave, in moderate yield, the 11-beta-acetoxy derivative (5b), which was transformed into erythrartine (8). Its O-acetate (O-acetylerythrartine) was not identical with erythrascine in the H-1-nmr spectra, presenting an ambiguity on the reported structure of erythrascine.