Enantiomerically Pure [2.2]Paracyclophane-4-thiol: A Planar Chiral Sulfur-Based Building Block Readily Available by Resolution with an Amino Acid Chiral Auxiliary

Acyl chloride of N-phthaloyl-(S)-isoleucine is an efficient
chiral auxiliary for the resolution
of (±)-[2.2]­paracyclophane-4-thiol. A preparative protocol, based
on the conversion into diastereoisomeric thiolesters and separation
by two fractional crystallizations and column chromatography, was
developed. Deprotection with LiAlH4 allowed isolation of
the individual thiol enantiomers in good yield (∼40%) and high
enantiomeric purity (ee >93%). The absolute configurations were
determined
by comparison of the optical rotation value of the products with literature
data and were confirmed by X-ray crystallography.