Design and Synthesis of Novel Chiral Dirhodium(II) Carboxylate Complexes for Asymmetric Cyclopropanation Reactions

A novel approach to the design of dirhodium(II) tetracarboxylates derived from ( S )‐amino acid ligands is reported. The approach is founded on tailoring the steric influences of the overall catalyst structure by reducing the local symmetry of the ligand's N‐heterocyclic tether. The application of the new approach has led to the uncovering of [Rh 2 ( S ‐ tert PTTL) 4 ] as a new member of the dirhodium(II) family with extraordinary selectivity in cyclopropanation reactions. The stereoselectivity of [Rh 2 ( S ‐ tert PTTL) 4 ] was found to be comparable to that of [Rh 2 ( S ‐PTAD) 4 ] (up to >99 % ee ), with the extra benefit of being more synthetically accessible. Correlations based on X‐ray structures to justify the observed enantioinduction are also discussed.