An Effective Approach to the Strychnos Alkaloids: Total Synthesis of Tubifolidine

A facile total synthesis of tubifolidine has been developed, which is accomplished in an 11-step synthesis of the ABCDE pentacyclic of the strychnos alkaloids with an overall yield of 10%. The key steps are the cyclization reaction for starting tetrahydrocarbazoles bearing a nitrilealkyl side chain at the C-2 position, mediated by tetrachloro-1,4-benzoquinone (TCB) and the intramolecular addition of the amide as the nucleophile. This cyclization reaction was obtained with the relevant architecture, including strychnos skeletal-type alkaloids.