p‐Toluenesulfonic Acid Promoted Annulation of 2‐Alkynylanilines with Activated Ketones: Efficient Synthesis of 4‐Alkyl‐2,3‐Disubstituted Quinolines

Reactions between readily available 2‐alkynylanilines and activated ketones such as β‐keto esters promoted by p‐toluenesulfonic acid afford 4‐alkyl‐2,3‐disubstituted quinolines in good to excellent yields. The generality of substituents at the other end of the triple bond of 2‐alkynylanilines makes the method a valuable approach to diversified 4‐alkylquinolines, which are difficult to obtain by classical methods such as the Friedländer reaction. Quinoline dimers can be prepared efficiently with alkyl or aryl linkers at C‐4.