Pendant Alkoxy Groups on N-Aryl Substitutions Drive the Efficiency of Imidazolylidene Catalysts for Homoenolate Annulation from Enal and Aldehyde

R. Kyan, K. Sato, N. Mase and T. Narumi*

Angew. Chem. Int. Ed. 2020, 59, 19031–19036.

The formation of conjugated Breslow intermediate is a turnover-limiting step in the NHC-catalyzed γ-butyrolactone formation via homoenolate addition. Structural and mechanistic studies including deuterium exchange experiments revealed that the formation of conjugated Breslow intermediate is facilitated by the proximity effects of pendant alkoxy groups on ortho-N-aryl groups of imidazolylidene catalyst.