FeCl3-Catalyzed Allylation Reactions onto 3-Hydroxy 2-Oxindoles: Formal Total Syntheses of Bis-Cyclotryptamine Alkaloids, (±)-Chimonanthine and (±)-Folicanthine.

An FeCl3-catalyzed efficient strategy for the allylation reactions of 3-hydroxy-2-oxindoles with allyltrimethylsilane has been developed. The reaction affords a variety of 2-oxindoles having quaternary center at the pseudobenzylic position in an operationally simple and inexpensive procedure. Control experiments using enantioenriched 3-hydroxy-2-oxindole show that the reaction proceeds through in situ generated 2H-indol-2-one (8). The methodology presents an efficient and concise access to the pyrroloindoline alkaloids (+/-)-deoxyeseroline (la), (+/-)-esermethole (1b), (+/-)-physostigmine (1c), (+/-)-phenserine (1d), and (+/-)-physovenine (1e). Eventually, we extrapolated the scope of this methodology to the formal total syntheses of dimeric cyclotyrptamine alkaloids (+/-)-chimonanthine (3a), (+/-)-folicanthine (3c), and (+/-)-calycanthine (4).