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  • Title: Studies on the Enantioselective Synthesis of E-Ethylidene-bearing Spiro[indolizidine-1,3'-oxindole] Alkaloids.
    Author: Yayik N, Pérez M, Molins E, Bosch J, Amat M.
    Journal: Molecules; 2021 Jan 15; 26(2):. PubMed ID: 33467493.
    Abstract:
    A synthetic route for the enantioselective construction of the tetracyclic spiro[indolizidine-1,3'-oxindole] framework present in a large number of oxindole alkaloids, with a cis H-3/H-15 stereochemistry, a functionalized two-carbon substituent at C-15, and an E-ethylidene substituent at C-20, is reported. The key steps of the synthesis are the generation of the tetracyclic spirooxindole ring system by stereoselective spirocyclization from a tryptophanol-derived oxazolopiperidone lactam, the removal of the hydroxymethyl group, and the stereoselective introduction of the E-ethylidene substituent by acetylation at the α-position of the lactam carbonyl, followed by hydride reduction and elimination. Following this route, the 21-oxo derivative of the enantiomer of the alkaloid 7(S)-geissoschizol oxindole has been prepared.
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