The true configuration of the benzilosazone isomers

The 1H NMR-based argument previously used to assign configurations to the three stereoisomers of benzilosazone is briefly reviewed. The configuration of the stable isomer is shown to be Z,Z by single crystal X-ray diffraction analysis, instead of E,E as previously reported. This assignment, together with physical measurements and spectroscopic (NMR and UV) data, allows the establishment of the configuration of all isomers. Computational methods are employed to clarify the relation between the configuration of the isomers and their 1H NMR, thus explaining the origin of the previous erroneous assignment.