Determination of the absolute stereochemistry and the activation barriers of thermally interconvertible heterocyclic compounds bearing a naphthyl substituent

The enantiotopic methyl signals of the compounds studied were resolved in the presence of the optically active chiral auxiliary (S)-(+)-2,2,2-trifluoroanthryl ethanol, [(S)-TFAE] via complex formation between (S)-TFAE and the respective compounds. Two different solvation models were proposed for both M and P conformations leading to the assignments of the H-1 NMR signals and thus absolute conformations. The solvation models proposed also explained the strong temperature dependence of the H-1 NMR signals upon cooling. The activation barriers for interconversion between the enantiomers of the compounds studied have been determined by either temperature dependent NMR or enantioresolution on a chiral sorbent via HPLC. (c) 2005 Elsevier Ltd. All rights reserved.