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 1H NMR signals and thus absolute conformations. The solvation models proposed also explained the strong temperature dependence of the 1H 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.

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