Base-Catalyzed Sequential Knoevenagel/Intramolecular Hetero-Diels–Alder Strategy with Late-Stage Ring Contraction: Access to Cyclopentadiene-Fused Pyrroloquinolinones

We report a novel base-catalyzed one-pot protocol for the efficient synthesis of cyclopentadiene-fused pyrroloquinolinones via a sequential Knoevenagel condensation, intramolecular hetero-Diels-Alder (IMHDA) reaction, and distinctive late-stage ring contraction. The method displays broad functional group tolerance and delivers a range of cyclopentadiene-fused pyrroloquinolinones in good to high yields. Additionally, the use of cyclic nucleophiles enables access to pyran-fused pyrroloquinolinone scaffolds. The synthetic utility of the resulting fused products is further demonstrated through diverse postsynthetic derivatizations, establishing this strategy as a valuable platform for the construction of structurally complex heteroaromatic frameworks.