NHC-Catalyzed Umpolung Driven Intramolecular Cyclizations for the Generation of 3,4-Cycloheptanone Annulated Tetracyclic Indole Derivatives.

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

Carbene-Catalyzed Tandem Imine Umpolung-Intramolecular Aza-Conjugate Addition-Oxidation to Access -Substituted Isoindolinones.

Herein, we have described a novel N-heterocyclic carbene (NHC)-catalyzed synthesis of -substituted isoindolinone acetates. The presented transformation proceeds through NHC-catalyzed tandem imine umpolung-intramolecular aza-Michael addition followed by oxidation, while molecular oxygen in air acts as a sole oxidant. Atom efficiency, operational simplicity, large-scale syntheses, and mild reaction conditions are the salient features of this method.