Lewis Base-Catalyzed [4 + 3] Annulation of ortho-Quinone Methides and MBH Carbonates: Synthesis of Functionalized Benzo[ b]oxepines Bearing Oxindole Scaffolds.

A novel Lewis base-catalyzed [4 + 3] annulation process for the construction of benzo[ b]oxepine scaffolds has been developed. 1,4-Diazabicyclo[2.2.2]octane (DABCO) promotes the union of o-QMs and Morita-Baylis-Hillman carbonates in reasonable to excellent yields and good stereoselectivities (dr > 20:1). This straightforward, catalytic approach offers access to a variety of synthetically useful benzo[ b]oxepine derivatives bearing oxindole scaffolds containing all-carbon spiro-quaternary stereocenters.

Lewis Acid Catalyzed Tandem 1,4-Conjugate Addition/Cyclization of in Situ Generated Alkynyl o-Quinone Methides and Electron-Rich Phenols: Synthesis of Dioxabicyclo[3.3.1]nonane Skeletons.

A versatile Lewis acid catalyzed tandem cyclization of in situ generated alkynyl o-quinone methides ( o-AQMs) with electron-rich phenols has been developed on the basis of the mode involving an intermolecular 1,4-conjugate addition/6-endo cyclization/1,3-aryl shift/intramolecular 1,4-conjugate addition cascade. This reaction provides a new method for expeditious assembly of synthetically and biologically interesting tetracyclic bridged dioxabicyclo[3.3.1]nonane skeletons featuring a congested bridgehead oxa-quaternary stereocenter.