Studies toward the synthesis of torreyanic acid and related epoxyquinoid natural products

The first total synthesis of the dimeric epoxyquinone natural product (+/-)-torreyanic acid has been achieved by a biomimetic tandem oxidation/oxaelectrocyclization/Diels-Alder dimerization cascade. An additional stereoisomer has been identified in this tandem reaction resulting from dimerization of 2H-pyran enantiomers to produce a compound which may not be available from Nature. 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.; An efficient methodology involving tartrate-mediated asymmetric nucleophilic epoxidation of quinone monoketals has been developed. Employing this method, the first asymmetric syntheses of the epoxyquinoids (-)-cycloepoxydon and (+)-torreyanic acid have been accomplished. Absolute stereochemistries of both natural products were determined through asymmetric synthesis. Synthesis of the related monomeric natural product (+)-ambuic acid was also achieved which established the biosynthetic relationship between (+)-torreyanic acid and (+)-ambuic acid. Further understanding of the tartrate-mediated asymmetric nucleophilic epoxidation method has been gained by scope and limitation studies and mechanistic experiments.; The first total syntheses of the dimeric epoxyquinol natural products epoxyquinols A, B and RKB-3564 D have also been achieved. The relative and absolute stereochemistries of epoxyquinols B and RKB-3564 D were confirmed by single-crystal X-ray structural analysis of synthetic intermediates. In addition, extensive studies aimed at understanding the chemical reactivities of dimeric epoxyquinols and their 2H-pyran precursors have been carried out.