Ethynyl Ketene-<i>S</i>,<i>S</i>-acetals: The Highly Reactive Electron-Rich Dienophiles and Applications in the Synthesis of 4-Functionalized Quinolines via a One-Pot Three-Component Reaction

An efficient synthetic method for 4-functionalized quinoline derivatives, 4-((1,3-dithian-2-ylidene)methyl)quinolines, has been developed. Mediated by trifluoromethanesulfonic acid, ethynyl ketene-S,S-acetals can react in a one-pot procedure with various arylamines and aldehydes under mild conditions to give the corresponding quinoline derivatives in good to high yields via a consecutive arylimine formation, regiospecific aza-Diels−Alder (Povarov) reaction, and reductive amination.