Diastereomeric excess upon cleavage and reformation of diastereomeric alkoxyamines
Authors:
- 1 January 2004
- journal article
- Published by Royal Society of Chemistry (RSC) in Organic & Biomolecular Chemistry
- Vol. 2 (5) , 709-715
Abstract
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 1H and 31P 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 β-substituents. The diastereoselective coupling is sensitive to the total recombination rate constant kc and diastereoselectivity increases with the decrease of kc. 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.Keywords
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