Barrier to enantiomerization of unstabilized, chelated, and dipole-stabilized 2-lithiopyrrolidines
by Ashweek, Neil J.; Brandt, Peter; Coldham, Iain; Dufour, Samuel; Gawley, Robert E.; Haeffner, Fredrik; Klein, Rosalyn; Sanchez-Jimenez, Graciela
Kinetics experiments have been used to establish the free energy, enthalpy, and entropy of activation for the enantiomerization of three structural classes of 2-lithiopyrrolidines. We find that alpha-aminoorganolithiums chelated by a N-methoxyethyl or N-Boc group have a barrier to enantiomerization (DeltaG(double dagger)) 2-3 kcal/mol lower than that of unstabilized alpha-aminoorganolithiums at 273 K. Density functional calculations were performed to clarify possible ground state and transition structures and to identify possible pathways for inversion of these chiral organolithium species.
- Journal of the American Chemical Society
- Start Page
- 1520-5126; 0002-7863