Base-catalyzed enolization of 2,5-norbornanediones. Evidence for homoenolic assistance

The rate enhancements relative to the monoketones, for base-catalyzed exo and endo hydrogen isotope exchange in 2,5-norbornanedione (2), 3,3-dimethyl-2,5-norbornanedione (3), and 1,3,3-trimethyl-2,5-norbornanedione (4) have been determined at 25 ± 0.05 °C in 60% dioxane–40% D2O. After the increase in rate due to the inductive and strain effects of the second carbonyl group is taken into account, the homoenolic-assistance factors are extracted from the overall rate enhancements: for exo exchange in 2,3, and 4, the factors are 13, 39, and 32; for endo exchange in 2,3, and 4, the factors are 26, 64, and 71, respectively.

Base-catalyzed enolization of 2,5-norbornanediones. Evidence for homoenolic assistance Journal Articles