Rapid cleavage of cyclic tertiary amides of Kempʹs triacid: effects of ring structure

The piperidyl and prolyl amides of Kempʹs triacid (7 and 8, respectively) have been prepared and their rates of intramolecular acylolysis measured as a function of pD. The piperidyl derivative 7 reacts approximately four-times faster (e.g., t1/2=3 min at 20 °C and pD 7.7) than the previously reported pyrrolidyl and methylphenethyl amide derivatives, while the prolyl derivative 8 reacts two-times more slowly (e.g., t1/2=30 min at 20 °C and pD 7.8). Molecular-mechanics calculations indicate that the nonbonded interactions in the piperidyl derivative 7 are distinct from those in the prolyl, pyrrolidyl, and methylphenethyl amide derivatives, a result that supports the suggestion that ground-state pseudoallylic strain contributes to the enormous reactivity of Kempʹs triacid tertiary amides. In sum, the results reported indicate that the Kempʹs triacid scaffolding provides a general means of activating tertiary amide derivatives.