Total Synthesis and Absolute Configuration of Raputindole A.

The first total synthesis of the bisindole alkaloid raputindole A from the rutaceous plant Raputia simulans is reported. The key step is a Au(I)-catalyzed cyclization that assembles the cyclopenta[f]indole tricycle from a 6-alkynylated indoline precursor. The isobutenyl side chain was installed by Suzuki-Miyaura cross-coupling, followed by a regioselective reduction employing LiDBB. Starting from 6-iodoindole, the sequence needs nine steps and provided (±)-raputindole A in 6.6% overall yield. The absolute configuration of the natural product (+)-raputindole A was determined by quantum chemical calculation of the ECD spectrum.