Asymmetric cyclopropanation of styrene with ethyl diazoacetate using a N2P2-ligand ruthenium(II) catalyst: axial ligand controlled enantioselectivity

The N2P2–Ru(II) complex 1, activated by silver triflate, exhibited good catalytic activity but low enantioselectivity in the asymmetric cyclopropanation of styrene with ethyl diazoacetate. N-Donor additives were introduced into the activated system as axial ligands to improve the eeʹs for this reaction. Up to 90% ee for cis-isomers was achieved by using 2,4,6-collidine as an additive.