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Sequential one-pot cyclizations: concise access to the ABCE tetracyclic framework of strychnos alkaloids.

A sequential one-pot biscyclization route to the ABCE tetracyclic framework of Strychnos alkaloids has been developed. Specifically, the AgOTf-mediated spirocyclization of an appropriately functionalized indole 3-carbinamide afforded a stable spiroindolenine intermediate; subsequent addition of DBU to the reaction mixture effected an unprecedented intramolecular aza-Baylis-Hillman reaction, delivering a tetracyclic product in 70% isolated yield.