cis- and Enantio-selective Cyclopropanation with Chiral (ON+)Ru–Salen Complex as a Catalyst

Cyclopropanation of styrene with α-diazoacetate in the presence of (R,R)-(salen)ruthenium complex 4 in THF which dissolves the complex exhibits remarkable cis- and enantio-selectivity [cis:trans=97:3, >97% ee (1S,2R)], while the same reaction in hexane which does not dissolve it shows good but opposite sense of enantioselectivity [−83% ee (1R,2S)] together with moderate cis-selectivity (cis:trans=68:32). In homogeneous and heterogeneous conditions, (salen)ruthenium complexes are considered to have different ligand-conformation which, in turn, causes the opposite sense of enantioface selectivity in the cyclopropanation.