Ring-Opening Reconstruction of Indoles Enabled by C-N Bond Cleavage: Synthesis of Benzo[c]pyrazolo[3,4-h][2,6]naphthyridine Derivatives.

Here we report the iodine-mediated tandem process of indole-ring-opening reconstruction, which accomplishes scaffold hopping from indoles to polycyclic heteroaromatics (PHAs), offering the advantages of simple operation and easily accessible substrates. The proposal is compatible with a wide range of active molecules and natural products, affording derivatives endowed with both thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) properties. Importantly, the reaction mechanism was further investigated by density functional theory (DFT) calculations, confirming that the reaction involves chemoselective formation of a diene and a stereoselective [4 + 2] cycloaddition. The analyses further clarify that a hindering group at the 2-position of the indole is critical for driving the C-N bond ring-opening and recombination process. This work highlights the versatility of the approach as a strategic extension to advancing indole chemistry and skeletal reconstruction.