Axially chiral N-(o-aryl)-2-thioxo-oxazolidine-4-one and rhodanine derivatives: enantiomeric separation and determination of racemization barriers

Axially chiral 5,5-dimethyl-3-(o-aryl)rhodanine, 3-(o-aryl)rhodanine and 5,5-dimethyl-3-(o-aryl)-2-thioxo-4-oxazolidinone derivatives have been synthesized as racemates and the energy barriers to enantiomerization have been determined by dynamic 1H NMR or by following the thermal equilibration of the separated enantiomers using chiral HPLC. The barriers to rotation about the Nsp2–Caryl single bond were found to be 82–129 kJ/mol. The racemization barriers in these compounds are affected by the size of the ortho-substituent on the aryl ring. The magnitude of the barriers was found to change linearly with the van der Waals radii of the ortho-halogen substituents.

Thermally interconvertible enantiomers ΔG# = 82–129 kJ/mol.Figure optionsDownload as PowerPoint slide