Study on the synthesis of the cyclopenta[ f ]indole core of raputindole A

• Published in: Beilstein journal of organic chemistry Vol. 12; no. 1; pp. 334 - 342
• Main Authors: Marsch, Nils, Kock, Mario, Lindel, Thomas
• Format: Journal Article
• Language: English
• Published: Germany Beilstein-Institut zur Föerderung der Chemischen Wissenschaften 23.02.2016; Beilstein-Institut
• Subjects: Chemistry; Full Research Paper; gold-catalyzed reactions; heterocycles; indole alkaloids; natural products; synthesis; synthesis; indole alkaloids; natural products; heterocycles; gold-catalyzed reactions
• ISSN: 1860-5397; 2195-951X; 1860-5397
• DOI: 10.3762/bjoc.12.36

The raputindoles from the rutaceous tree Raputia simulans share a cyclopenta[ f ]indole partial structure the synthesis of which is subject of this investigation. An efficient route to a series of 1,5-di(indol-6-yl)pentenones was developed via Mo/Au-catalyzed Meyer–Schuster rearrangement of tertiary propargylic alcohol precursors. However, none of the enones underwent the desired Nazarov cyclization to a cyclopenta[ f ]indole. More suitable were 6-hydroxyallylated indolines which gave good yields of cyclopenta[ f ]indolines after treatment with SnCl 4 , as soon as sterically demanding β-cyclocitral adducts were reacted. Most successful were Pt(II) and Au(I)-catalyzed cyclizations of N- TIPS-protected indolin-6-yl-substituted propargylacetates which provided the hydrogenated tricyclic cyclopenta[ f ]indole core system in high yield.