Modular ligands in asymmetric synthesis. Copper-mediated cyclopropanation

The chiral imidazoline/copper catalyst system efficiently mediates asymmetric intermolecular cyclopropanations. Complexes derived from (R,R)- or (S,S)-1,1-diphenylethylenediamine, cyclic ketones, and Cu(I) or Cu(II) triflates were compared. The reaction between (−)-menthyl diazoacetate and 1,1-diphenylethylene affords cyclopropane carboxylates in up to 80% yield and with up to 78% de.