Total synthesis of an elusive indole alkaloid isolated from Halichondria melanodocia

The total synthesis of an elusive indole alkaloid isolated from the marine sponge Halichondria melanodocia, is reported. Since previous synthetic efforts to prepare 1a failed (1b obtained, instead), probably because there are few methods for selective installation of exo/endo double bonds at C3 position of piperidines, the recent development of a β-C−H alkenylation of N-heterocycles followed by double-bond isomerization enabled the stereoselective and transition-metal-free total synthesis of the indole title alkaloid (1a).