Diastereomeric excess upon cleavage and reformation of diastereomeric alkoxyamines.
The thermal reactions of several TEMPO and DEPN (N-(2-methylpropan-2-yl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-aminoxyl) based alkoxyamines were studied by means of (1)H and (31)P NMR spectroscopy aiming to distinguish the contributions of diastereoselective homolysis and coupling to the total equilibrium diastereomeric distribution. The TEMPO-based compounds reveal no diastereomeric excess while DEPN based compounds show a moderate excess both upon homolysis and coupling. The diastereomeric preference of homolysis for DEPN-(propionate-like) adducts does not depend on the ester group and it is mainly affected by the size of beta-substituents. The diastereoselective coupling is sensitive to the total recombination rate constant k(c) and diastereoselectivity increases with the decrease of k(c). Small diastereoselective coupling is found in the recombination of DEPN with sec-butyl isobutyrate radical, where no prochiral centers are formed upon cleavage of corresponding alkoxyamine.
Ananchenko
Gennady
G
Physikalisch-Chemisches Institut, Universitat Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Marque
Sylvain
S
Gigmes
Didier
D
Bertin
Denis
D
Tordo
Paul
P
D000588:Amines / Q000138:chemical synthesis*; D005609:Free Radicals / Q000737:chemistry; D008968:Molecular Conformation; D015394:Molecular Structure; D013237:Stereoisomerism; D013997:Time Factors
D000588:Amines; D005609:Free Radicals