C 2 ‐symmetric ligands demonstrate outstanding efficiency in coordinating iron, cobalt, and nickel salts to generate highly active catalysts for asymmetric transformations. Chiral complexes derived from these iron triad metals exhibit excellent performance in stereoselective reactions involving α,β‐unsaturated oxazolidinones, consistently affording high enantio‐ and diastereoselectivities. In the Diels–Alder reaction of cyclopentadiene and aliphatic dienes, enantiomeric and diastereomeric excesses of up to 99% are produced. 1,3‐Dipolar cycloadditions run with nitrones, azomethine imines, nitrile oxides, and diazo esters lead to high levels of selectivity mostly using Ni catalysts. The thia‐Michael addition of thiols to α,β‐unsaturated oxazolidinones successfully affords products with enantiomeric excesses of up to 97% ee . Chiral Ni complexes are efficient catalysts for other highly asymmetric transformations, such as Michael addition and α‐chlorination reactions. Fe catalysts provide excellent results of asymmetric conjugate radical addition reaching 98% ee . Coordinated iron triad metals are investigated through transition‐state analyses, which support the stereoselectivity observed with multidentate, sterically hindered catalysts. The bidentate BOX, tridentate PyBOX and DBFOX, tetradentate BINIM, and bipyridine diol ligands are particularly valuable in these stereoselective transformations.
David et al. (Fri,) studied this question.