Total Synthesis of (+)-Alstonlarsine A

An enantioselective total synthesis of (+)-alstonlarsine A (1), a monoterpenoid indole alkaloid possessing a unique pentacyclic skeleton as well as a rare biological activity, is achieved. The key step is an efficient domino sequence, comprising enamine formation followed by an inverse-electron-demand intramolecular dearomative Diels-Alder cycloaddition for the construction of 9-azatricyclo[4.3.1.0^3,8 ]decane core. The key intermediate for this domino sequence was synthesized by a newly developed methodology, relying on indole C₍₂₎ -H bond functionalization, combined with intramolecular Horner-Wadsworth-Emmons reaction. This tactical combination offers a new general entry into other (privileged) tricyclic frameworks possessing indole ring fused to 6-, 7- or 8-membered rings.