Inverse Electron Demand Diels-Alder Reactions of Heterodienes Catalyzed by Potassium Hydrogen Sulfate: Diastereoselective, One-Pot Synthesis of Pyranobenzopyrans, Furanobenzopyrans and Tetrahydroquinolines Derivatives

Abstract

Potassium hydrogen sulfate catalyzes the one-pot three components coupling of aldehydes, anilines, and electron rich dienophiles such as dihydropyran, dihydrofuran, ethyl vinylether, and cyclopentadiene. With o-hydroxybenzaldehyde, the reaction probably proceeds through the formation of o-quinonemethide intermediate, which subsequently undergoes cycloaddition with cyclic and acyclic enol ethers leading to the formation of respective chromanes. However, in case of benzaldehydes with no o-hydroxy group, the imine formed acts as the heterodiene and leads to the formation of tetrahydroquinolines.