Ethynyl ketene-S,S-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.