Preorganized Hydrogen Bond Donor Catalysts: Acidities and Reactivities.

摘要: Measured DMSO pKa values for a series of rigid tricyclic adamantane-like triols containing 0–3 trifluoromethyl groups (i.e., 3(0)–3(3)) are reported. The three compounds with CF3 substituents similar or more acidic than acetic acid (pKa = 13.5 (3(1)), 9.5 (3(2)), 7.3 (3(3)) vs 12.6 (HOAc)), and the resulting hydrogen bond network enables remote γ-trifluoromethyl group to enhance acidity as well one located at α-position. Catalytic abilities 3(0)–3(3) were also examined. In nonpolar environment rate enhancement up 100-fold over flexible acyclic analogs was observed presumably due an entropic advantage locked-in structure. Gas-phase acidities found correlate catalytic activity better appear be measure in low dielectric constant media. These trends reduced reversed polar solvents highlighting importance reaction environment.