N-Oxide Route to the Marine Natural Product Cyanogramide D

The first synthesis of the marine natural product cyano­gramide D is reported. The key step is the acetylation of a β-carboline N-oxide, followed by acetyl migration. Since in this particular case it was not possible to incorporate the styryl side chain by Buchwald coupling, a phenylethanolamine side chain was attached, which was dehydrated with Martin’s sulfurane after assembly of the tetracycle. Pentacyclic products were obtained under Appel conditions. The synthesis will facilitate the exploration of the biomimetic oxidative spirocyclization of cyanogramide D to the spirooxindole cyanogramide.