title: Towards the core structure of Strychnos alkaloids using samarium diiodide-induced reactions of indole derivatives.
abstract: This report describes the development of a first and second generation approach towards the synthesis of the ABCEG pentacyclic core structure of Strychnos alkaloids. First, we discuss a sequential approach applying a series of functional group transformations to prepare suitable precursors for cyclization reactions. These include attempts of samarium diiodide-induced cyclizations or a Barbier-type reaction of a transient lithium organyl, which successfully led to a tetracyclic key building block earlier used for the synthesis of strychnine. Secondly, we account our first steps towards the development of an atom-economical samarium diiodide-induced cascade reaction using "dimeric" indolyl ketones as cyclization precursors. In this context, we discuss plausible mechanisms for the samarium diiodide-induced cascade reaction as well as transformations of the obtained tetracyclic dihydroindoline derivatives.
authors.affiliation: Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin (Germany); BCMP, Harvard Medical School, Harvard University, Longwood Avenue 240, 02115 Boston, MA (USA).
authors.forename: Christine
authors.initials: C
authors.lastname: Beemelmanns
authors.forename: Steffen
authors.initials: S
authors.lastname: Gross
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Reissig
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis / Q000737:chemistry*; D003500:Cyclization; D007211:Indoles / Q000737:chemistry*; D007454:Iodides / Q000737:chemistry*; D015394:Molecular Structure; D012493:Samarium / Q000737:chemistry*; D031451:Strychnos / Q000737:chemistry*
chemical_list: D000470:Alkaloids; D007211:Indoles; D007454:Iodides; D012493:Samarium; C030374:indole; C409809:samarium diiodide
keywords: Barbier reaction; alkaloids; cascade reaction; indole; samarium diiodide