Total Synthesis and Absolute Configuration of Raputindole A
Mario Kock1, Peter G Jones1, Thomas Lindel1
1TU Braunschweig , Institute of Organic Chemistry, Hagenring 30, 38106 Braunschweig, Germany.
Abstract:
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.
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