Synthesis of the bis-spiroacetal moiety of the shellfish toxins spirolides B and D using an iterative oxidative radical cyclization strategy.
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.
Meilert
Kai
K
Department of Chemistry, University of Auckland, 23 Symonds St., Auckland, New Zealand.
Brimble
Margaret A
MA
D000818:Animals; D003500:Cyclization; D005609:Free Radicals / Q000737:chemistry; D008387:Marine Toxins / Q000138:chemical synthesis / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D012758:Shellfish; D013141:Spiro Compounds / Q000138:chemical synthesis* / Q000737:chemistry
D005609:Free Radicals; D008387:Marine Toxins; D013141:Spiro Compounds; C467770:spirolide B; C467769:spirolide D