Tetrahedron, 67(47), P. 9104-9111 (2011); doi:10.1016/j.tet.2011.09.083
Starting from Evans’ imidazolidin-2-one (1) two compounds were obtained by trans-N-acylation: the expected one 3 with S,R configuration and a second compound 5, that is, related to 3 by the loss of a CH(CH3)Cdouble bond; length as m-dashO fragment. The stereochemistry of 3 was established by NMR spectroscopy, mainly NOE experiments, as expected, the new center has an S configuration, the compound being thus S,R. The structure of compound 5 was determined by X-ray crystallography. A mechanism of formation of 5 was proposed.