Preorganized Hydrogen Bond Donor Catalysts: Acidities and Reactivities

Masoud Samet, Steven R Kass

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

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 are 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 a remote γ-trifluoromethyl group to enhance the acidity as well as one located at the α-position. Catalytic abilities of 3(0)-3(3) were also examined. In a nonpolar environment a rate enhancement of up to 100-fold over flexible acyclic analogs was observed presumably due to an entropic advantage of the locked-in structure. Gas-phase acidities are found to correlate with the catalytic activity better than DMSO pKa values and appear to be a better measure of acidities in low dielectric constant media. These trends are reduced or reversed in polar solvents highlighting the importance of the reaction environment.

Original languageEnglish (US)
Pages (from-to)7727-7731
Number of pages5
JournalJournal of Organic Chemistry
Volume80
Issue number15
DOIs
StatePublished - Aug 7 2015

Bibliographical note

Publisher Copyright:
© 2015 American Chemical Society.

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