Enantioselective,Protecting‐Group‐Free Total Synthesis of Sarpagine Alkaloids—A Generalized Approach |
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Authors: | M?Sc Sebastian Krüger Dr Tanja Gaich |
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Institution: | Institute of Organic Chemistry, Leibniz University of Hannover, Schneiderberg 1b, 30167 Hannover (Germany) |
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Abstract: | A generalized synthetic access to sarpagine alkaloids through a joint synthetic sequence has been accomplished. Its applicability is showcased by the enantioselective total syntheses of vellosimine ( 1 ), N‐methylvellosimine ( 3 ), and 10‐methoxyvellosimine ( 8 ). The synthetic sequence is concise (eight steps) from known compound 13 , and requires no protecting groups. The indole heterocycle was introduced in the last step. This strategy allows access to sarpagine alkaloids through a shared synthetic route leading to precursor 10 , which we term “privileged intermediate”. Starting from this intermediate, all sarpagine alkaloids can be synthesized using phenylhydrazines with different substitution patterns ( 15 – 17 ). Our approach brings about the advantage, that synthesis optimization only needs to be performed once for many natural products. The key features of the synthesis are a 5+2]‐cycloaddition and a ring enlargement. |
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Keywords: | cycloaddition oxidopyridinium ion ring enlargement sarpagine alkaloid total synthesis |
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