Diastereoselective Total Synthesis of Raputindole A.

The first diastereoselective total synthesis of the bisindole alkaloid raputindole A is reported. After Au(I)-catalyzed assembly of the cyclopenta[ f]indole tricycle, it was possible to hydrogenate the indene double bond regio- and diastereoselectively through iridium catalysis, guided by a preinstalled hydroxy function. Attempted HWE reaction led to formal elimination of formaldehyde from an α-quaternary cyclopentane carbaldehyde, which was circumvented by Takai olefination. After Suzuki-Miyaura cross coupling and deprotection/oxidation, (±)-raputindole A was obtained in 13 linear steps in 18% overall yield.