Total synthesis of the spirocyclic imine marine toxin (-)-gymnodimine and an unnatural C4-epimer |
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Authors: | Kong Ke Moussa Ziad Lee Changsuk Romo Daniel |
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Institution: | Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, USA. |
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Abstract: | The first total synthesis of the marine toxin (-)-gymnodimine (1) has been accomplished in a convergent manner. A highly diastereo- and enantioselective exo-Diels-Alder reaction catalyzed by a bis-oxazoline Cu(II) catalyst enabled rapid assembly of the spirocyclic core of gymnodimine. The preparation of the tetrahydrofuran fragment utilized a chiral auxiliary based anti-aldol reaction. Two major fragments, spirolactam 56 and tetrahydrofuran 55, were then coupled through an efficient Nozaki-Hiyama-Kishi reaction. An unconventional, ambient temperature t-BuLi-initiated intramolecular Barbier reaction of alkyl iodide 64 was employed to form the macrocycle. A late stage vinylogous Mukaiyama aldol addition of a silyloxyfuran to a complex cyclohexanone 83 appended the butenolide, and a few additional steps provided (-)-gymnodimine (1). A diastereomer of the natural product was also synthesized, C4-epi-gymnodimine (90), derived from the vinylogous Mukaiyama aldol addition. |
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