Base-Promoted Azinium- <i>N</i> -imines and Thioamide Dimeric Annulation for the Tunable Synthesis of 1,2,4-Triazole and Polycyclic Indolylhydroquinoline Skeletons

A base-promoted cycloaddition of azinium-<i>N</i>-imines with thioamides or indolin-2-thiones has been developed for the efficient construction of 1,2,4-triazole and polycyclic indolylhydroquinoline frameworks. This protocol features broad functional group tolerance, scalability, and significantly reduced reaction times. Notably, heteroaromatic <i>N</i>-imines derived from isoquinolinium and quinolinium salts serve as suitable substrates, delivering [1,2,4]triazolo[5,1-<i>a</i>]isoquinoline and [1,2,4]triazolo[1,5-<i>a</i>]quinoline derivatives, respectively, under mild reaction conditions. Furthermore, indole-annulated pentacyclic indolylhydroquinolines can also be accessed by the [3+3] annulation of <i>N</i>-imine quinolinium with indolin-2-thiones. These strategies provide a practical and modular entry to nitrogen- and sulfur-containing polycyclic scaffolds, structurally related to alkaloid natural products.