Oxidative Esterification of Aldehydes Using Mesoionic 1,2,3-Triazolyl Carbene Organocatalysts

The
synthesis and catalytic activity of a new class of 1,2,3-triazolyl
N-heterocyclic carbene organocatalysts is described. These new catalysts
chemoselectively facilitate the oxidative esterification of aldehydes.
NMR acidity studies show an inverse correlation between triazolium
acidity and reactivity. Kinetic studies show that the resting state
of the catalyst involves a NHC–aldehyde adduct. A catalytically
active intermediate was synthesized and characterized by X-ray diffraction
as the initial carbene–aldehyde adduct.