Lewis Acid Catalyzed Intramolecular [4+2] Cycloaddition of In Situ Generated Aza‐Quinone Methides for the Stereoselective Synthesis of Furo/pyrano[3,2‐c]tetrahydroquinolines

The TMSOTf catalyzed intramolecular [4+2] cycloaddition of in situ generated aza-o-quinone methide allows an expedient, stereoselective access to cis/trans-fused furo/pyrano[3,2-c]tetrahydroquinolines with excellent yields and diastereoselectivity. The geometry of the dienophile olefin was found to have a profound effect on the stereochemical outcome of these reactions.