Synthesis of the bis-spiroacetal moiety of the shellfish toxins spirolides B and D using an iterative oxidative radical cyclization strategy |
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Authors: | Meilert Kai Brimble Margaret A |
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Institution: | Department of Chemistry, University of Auckland, 23 Symonds St., Auckland, New Zealand. |
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Abstract: | The enantioselective synthesis of the bis-spiroacetal fragment of the shellfish toxins, spirolides B 1 and D 2, is reported. The carbon framework was constructed via a Barbier reaction of dihydropyran 10 with aldehyde 11, followed by two oxidative radical cyclizations to construct the bis-spiroacetal ring system. A silyl-modified Prins cyclization and enantioselective crotylation successfully installed the stereocenters in the cyclization precursor 21. The initial unsaturated bis-spiroacetals 9a-d underwent equilibration during epoxidation to trans-epoxide 24 that was converted to tertiary alcohol 7. |
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