The total synthesis of the alkaloid natural product ibophyllidine is described.  Utilizing the phosphine catalyzed (3+2) annulation of  sulfonyl imine 1  and electron deficient allene 2  to forge the substituted pyrroline 3.  T  he d-ring of ibophyllidine was established in good yield and with exquisite diastereoselectivity.  Hydrogenation of the resultant (3+2) adduct 3  yields an all syn, trisubstituted prrolidine ring bearing three of the four stereocenters of ibophyllidine in only two steps from imine 1  and allene 2  .  The E-ring is formed by an intramolecular alkylation at C-3 of the indole ring with the final C-ring resulting from an intramolecular aza-Baylis-Hillman reaction.  Future efforts include using a P-chiral phosphine catalyst in an effort towards an enantioselective total synthesis and synthesis of related alkaloids including deethylibophyllidine.

Application of the phosphine catalyzed (3+2) annulation: Total synthesis of ibophyllidine

243rd National Meeting (2012)

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