The Correlation of Lewis Acidities of Silyl Triflates with Reaction Rates of Catalyzed Diels–Alder Reactions

The Lewis acidity of various silyl triflates was quantified by utilizing [D 5 ]pyridine as a 2 H NMR spectroscopy probe. The chemical shifts of the 2 H NMR signals for pyridine–silyl adducts are reported. The rate constants of silyl triflate catalyzed Diels–Alder reactions were determined by using UV/Vis spectroscopy. A correlation of the magnitude of the 2 H NMR chemical shifts with the rate constants for most silyl triflates investigated was observed, but Me 3 SiOTf exhibits a surprisingly large deviation. Control experiments indicate that proton catalysis of the Diels–Alder reaction can be excluded.