Phosphoric Acid Catalyzed Desymmetrization of Bicyclic Bislactones Bearing an All-Carbon Stereogenic Center: Total Syntheses of (−)-Rhazinilam and (−)-Leucomidine B
the presence of a catalytic amount of an imidodiphosphoric acid, enantioselective desymmetrization of bicyclicbislactones by reaction with alcohols took place smoothly to afford enantiomerically enriched monoacids having an all‐carbon stereogeniccenter. Concise catalytic enantioselective syntheses of both (−)‐rhazinilam and (−)‐leucomidine B were subsequently developed using (S)‐methyl 4‐ethyl‐4‐formylpimelate
leading to the total synthesis of 18,19-dehydrotabersonine, described in the following paper, some older work on the synthesis of (±)-3-oxo-20-desethyl-20-allylvincadifformine, its C-20 epimer, and (±)-3-oxo-19-vinylvincadifformine is reported. Attempts to convert these compounds,by appropriate manipulation of the isolated double bond, into a wide range of anilinoacrylate alkaloids, minovincine, tuboxenine