In the presence of cesium carbonate, ynones bearing an ortho-amino group reacted with cyclic β-ketoesters through conjugated addition/carbon-carbon σ-bond cleavage/nucleophilic aromatic substitution tandem reaction to obtain 4-quinolones fused with medium-sized rings in good yields. This is the first example of synthesis of 4-quinolones through base-promoted insertion reactions of carbon-carbon triple bonds into carbon-carbon σ-bonds. Notable features of this program are mild and transition-metal-free reaction conditions.