Construction of Multiring Frameworks by Metal-Free Cascade Reactions of Stable Isochromenylium Tetrafluoroborate

Efficient methodologies for constructing several multiring frameworks have been developed utilizing the cascade reactions of air-stable isochromenylium tetrafluoroborates with olefins. Successive additions of two equivalents of styrene-type olefins to isochromenylium tetrafluoroborate (ICTB) 1 have been observed and their mechanisms were proposed and discussed. Intramolecular capture of the early stage cationic intermediates by predevised heteroatoms or Friedel−Crafts donors provided two different types of bridged-ring systems.