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 beta-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 Friedlander reaction. Quinoline dimers can be prepared efficiently with alkyl or aryl linkers at C-4.