The first total synthesis of (±)-melinonine-E and (±)-strychnoxanthine is described. The key common step for the synthesis of both alkaloids is the elaboration of the 2-azabicyclo[3.3.1]nonane nucleus (D and E rings) by a radical carbocyclization, using an α-carbamoyldichloromethyl radical as a donor. The closure of the C ring by a Bischler−Napieralski cyclization, followed by an epimerization process to gain the axial nitrile 20, and appropriate reduction transformations afforded pentacyclic alcohol 23. This alcohol was converted into either (±)-melinonine-E (1) or (±)-strychnoxanthine (2) by means of a palladium black dehydrogenation of the C ring or a SeO2 oxidation of the corresponding acetate 25, respectively.

First Total Synthesis of (±)-Melinonine-E and (±)-Strychnoxanthine Using a Radical Cyclization Process as the Core Ring-FormingStep.-The synthesis of both title alkaloids (VI) and (VII) starts from tryptamine (I) and, in the key steps, makes use of a radical cyclization process to generate the bicyclononane DE ring system present in compound (III) and a Bischler-Napieralski cyclization to achieve the pentacyclic skeleton of (IV). The final steps require the adjustment of the stereochemistry at C-20 by epimerization of nitrile (V), the derivatization of the nitrile group and the oxidation of the C ring. -(QUIRANTE, J.; ESCOLANO, C.; MERINO, A.; BONJOCH, J.; J.