Barrier to enantiomerization of unstabilized, chelated, and dipole-stabilized 2-lithiopyrrolidines.
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++) 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.
Ashweek
Neil J
NJ
Department of Chemistry, University of Exeter, UK.
Brandt
Peter
P
Coldham
Iain
I
Dufour
Samuel
S
Gawley
Robert E
RE
Haeffner
Fredrik
F
Klein
Rosalyn
R
Sanchez-Jimenez
Graciela
G
D007700:Kinetics; D008094:Lithium / Q000737:chemistry*; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D011759:Pyrrolidines / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics
D009942:Organometallic Compounds; D011759:Pyrrolidines; D008094:Lithium