NHC-Catalyzed\nUmpolung Driven Intramolecular Cyclizations\nfor the Generation of 3,4-Cycloheptanone Annulated Tetracyclic Indole\nDerivatives

In\nthis Letter, we disclose the development and exploitation of\numpolung reactivity of N-heterocyclic carbene (NHC) organocatalysts\nin generating tetracyclic indole derivatives with the introduction\nof a cycloheptane ring forming event. The NHC-catalyzed intramolecular\nvinylogous Stetter, Stetter, benzoin, and formal cross-dehydrogenative\ncoupling transformations have been executed, enabling the construction\nof 3,4-cycloheptannulated indole derivatives in good to excellent\nyields. The developed protocols utilize an inexpensive catalyst and\nfeature operational simplicity, atom economy, gram-scale syntheses,\nand postsynthetic availability.