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Total Synthesis of the Quinone Epoxide Dimer (+)-Torreyanic Acid: Application of a Biomimetic Oxidation/Electrocyclization/Diels−Alder Dimerization Cascade1
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posted on 2003-04-03, 00:00 authored by Chaomin Li, Richard P. Johnson, John A. PorcoAn asymmetric synthesis of the quinone epoxide dimer (+)-torreyanic acid (48) has been
accomplished employing [4 + 2] dimerization of diastereomeric 2H-pyran monomers. Synthesis of the related
monomeric natural product (+)-ambuic acid (2) has also been achieved which establishes the biosynthetic
relationship between these two natural products. A tartrate-mediated nucleophilic epoxidation involving
hydroxyl group direction facilitated the asymmetric synthesis of a key chiral quinone monoepoxide
intermediate. Thermolysis experiments have also been conducted on a model dimer based on the torreyanic
acid core structure and facile retro Diels−Alder reaction processes and equilibration of diastereomeric
2H-pyrans have been observed. Theoretical calculations of Diels−Alder transition states have been
performed to evaluate alternative transition states for Diels−Alder dimerization of 2H-pyran quinone epoxide
monomers and provide insight into the stereocontrol elements for these reactions.
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pyran quinone epoxide monomersstereocontrol elementsThermolysis experimentsdiastereomeric 2 Hchiral quinone monoepoxidebiosynthetic relationshipTheoretical calculationsDielmodel dimersynthesisdimerizationhydroxyl group directiontorreyanic acid core structureTotal Synthesisalternative transition statespyran monomers2 H
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