Absolute configuration assignment of 3-oxindolylacetyl-4-phenyloxazolidinone derivatives

The straightforward determination of the absolute configuration of 2-oxo-3-indolylacetic acid derivatives 5a?e, based on analysis of the 1H NMR spectra of their oxindolylacetyl-phenyloxazolidinones 6a?e, is described. The conformational preferences for two diastereomeric amides were calculated by DFT, which matched well with the experimental results, while X-ray diffraction analysis allowed us to validate the methodology. Independent absolute configuration evidence was also obtained by vibrational circular dichroism.