title: Study on the synthesis of the cyclopenta[f]indole core of raputindole A.
abstract: 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 SnCl4, 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.
authors.affiliation: Institute of Organic Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Marsch
authors.affiliation: Institute of Organic Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Kock
authors.affiliation: Institute of Organic Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lindel
keywords: gold-catalyzed reactions; heterocycles; indole alkaloids; natural products; synthesis