Chiral Bis(oxazolinyl)phenyl Ru^II Catalysts for Highly Enantioselective Cyclopropanation

Abstract

Good to excellent enantioselectivities (up to 99 % ee) of trans-cyclopropane derivatives were achieved in the cyclopropanation of alkenes with tert-butyl α-diazoacetate by using 0.5 mol % of a mononuclear chiral ruthenium aqua complex containing the chiral bis(oxazolinyl)phenyl ligand, which was obtained via CH activation by RuCl3⋅3 H2O in the presence of Mg and cyclooctadiene (cod). Intramolecular cyclopropanation reactions using the new Ru complex also proceed with high yields and excellent enantioselectivities.