Asymmetric induction in intramolecular [5 + 2] cycloaddition of 2-(4-alkenyl)-5-benzoyloxy(or 5-silyloxy)-4-pyrones involving migration of the pyrone O-5 group to O-4

Article abstract of DOI:10.3987/com-97-7941

Heating of the title compounds (1a,b) at 130°C in o-dichlorobenzene afforded [5+2] annulation products (2a,b) in 70% yield; 27-33% d.e. via 3-oxidopyrylium ylide. Reaction of the title compounds (1b,c) in the presence of ZnCl₂ at 40°C furnished