Ketene Dithioacetals in the Aza-Diels−Alder Reaction with <i>N</i>-Arylimines:  A Versatile Approach to Tetrahydroquinolines, 2,3-Dihydro-4-quinolones, and 4-Quinolones

[reaction: see text] The first successful use of ketene dithioacetals as dienophiles in the aza-Diels-Alder reaction with N-arylimines is described. Among the ketene dithioacetals tested, 1,4-benzodithiafulvenes are most effective in assembling the tetrahydroquinoline core. Subsequent chemical manipulations provide a concise and divergent approach to the synthesis of 2,3-tetrahydroquinolines, 2,3-dihydro-4-quinolones, and 4-quinolones.