N-Heterocyclic carbene catalyzed intramolecular nucleophilic addition of carbonyl anion equivalents to enol ethers

The intramolecular nucleophilic addition reaction of acyl anion equivalents to enol ethers is described, which was catalyzed by N-heterocyclic carbenes generated in situ from readily available thiazolium salt. In this transformation, benzofuranones were obtained in excellent yield. In combination with our previous work, the precise mechanistic elucidation for the formation of benzofuranones has been further investigated. A labeling experiment implied that the transformation proceeds through a nucleophilic addition mechanism.