Selective Synthesis of Enantiomeric η6‐Arene Chromium Tricarbonyl Complexes with Epimeric Pyrroloimidazolones

A pair of epimeric l‐proline derived chiral auxiliaries have been developed for the diastereoselective lithiation–substitution of η6‐arene chromium tricarbonyl complexes. Lithiation of the anti epimer affords planar chiral imidazolones in >95:5 dr upon electrophile quench. Application of the same reaction sequence to the syn epimer provides products with opposite planar chirality in equally high levels of diastereomeric purity. The ortho‐substituted epimeric imidazolones give rise to planar chiral enantiomers upon acid‐induced elimination, thus precluding the need to prepare a d‐proline‐derived starting material. magnified image