Conformational Studies by Dynamic NMR. 37. Monitoring the Stereomutations of Symmetric Amines by Means of a Chiral Auxiliary Agent

Article abstract of DOI:10.1021/jo00280a031

The chiral auxiliary agent (R)-l-2,2,2-trifluoro-1-(9-anthryl)ethanol was used to monitor the exchange between the enantiotopomers of symmetric amines lacking diastereotopic probes.The free energies of activation for stereomutations involving both C-N rotation and N-inversion processes were measured by line-shape simulation of the low-temperature NMR spectra.The effect of the chiral alcohol upon the barriers has also been evaluated, thus allowing one to compare these data with those of other amines where the stereomutations had been detected in achiral environment.The existence of steric deceleration for the exchange between enantiotopomers related by torsion and of steric acceleration for enantiotopomers related by N-inversion has been also verified.The highest N-inversion barrier observed in a simple noncyclic trialkyl amine (8.6 kcal mol^-1 for Me2NEt) could thus be measured.