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Cyclopentenones are synthetically versatile structures, and their straightforward construction from alkynone substrates by employing synthetically streamlining C--H insertion is conceptually appealing and of high synthetic potential. But, its implementation is very limited. Herein we report a Au-catalyzed version, which affords 2- bromocyclopent-2-en-l-ones with a broad scope and synthetically desirable diastereoselectivities. The proposed key intermediate capable of the observed insertion into unactivated C--H bonds is a fully functionalized gold vinylidene, which is generated via a novel intermolecular strategy. This flexible access of likely gold vinylidenes opens various opportunities to explore their versatile reactivities. [ABSTRACT FROM AUTHOR]

Generation of reactive α-oxo gold carbene intermediates via gold-catalyzed oxidation of alkynes has become an increasing versatile strategy of replacing hazardous diazo carbonyl compounds with benign and readily available alkynes in the development of efficient synthetic methods. However, one of the hallmarks of metal carbene/carbenoid chemistry, i.e., insertion into an unactivated C(sp³)-H bond, has not be realized. This study reveals for the first time that this highly valuable transformation can be readily realized intramolecularly by oxidatively generated β-diketone-α-gold carbenes using ynones as substrates. Substrate conformation control via the Thorpe-Ingold effect is the key design feature that enables generally good to excellent efficiencies, and synthetically versatile cyclopentanones including spiro-, bridged, and fused bicyclic ones can be readily accessed. [ABSTRACT FROM AUTHOR]