Towards the core structure of Strychnos alkaloids using samarium diiodide-induced reactions of indole derivatives
Christine Beemelmanns1, Steffen Gross, Hans-Ulrich Reissig
1Institut 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).
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.
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