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 [D5]pyridine as a 2H NMR spectroscopy probe. The chemical shifts of the 2H NMR signals for pyridinesilyl adducts are reported. The rate constants of silyl triflate catalyzed DielsAlder reactions were determined by using UV/Vis spectroscopy. A correlation of the magnitude of the 2H NMR chemical shifts with the rate constants for most silyl triflates investigated was observed, but Me3SiOTf exhibits a surprisingly large deviation. Control experiments indicate that proton catalysis of the DielsAlder reaction can be excluded.