Investigation of Oxidopyrylium-Alkene [5+2] Cycloaddition Conjugate Addition Cascades and Extension to Chiral Auxiliary-Based Variants

Oxidopyrylium-based [5+2] cycloadditions have been extensively utilized to construct oxabridged seven-membered ring systems that often serve as the core structures in numerous biologically active natural products. By investigating these processes, we hope to reveal the highest potentials of [5+2] cycloaddition as a synthetic tool. A novel oxidopyrylium-alkene [5+2] cycloaddition conjugate addition cascade (C3) sequence, which allows rapid build-up of molecular complexity with excellent diastereocontrol, was investigated. The scope and limitation of this process were explored as mixed results were shown for various acetoxypyranone-alkene substrates. In addition, oxidopyrylium [5+2] cycloadditions of ï?¢-silyloxy-ï?§-pyrones were investigated which revealed the accelerating role of carbonyl substituents at the trans-terminal position of alkenes. Finally, we have demonstrated the utility of sulfinimine chiral auxiliary in the asymmetric [5+2] cycloaddition of ï?¢-silyloxy-ï?§-pyrones