cis- and enantio-selective cyclopropanation with chiral (ON+)Ru-salen complex as a catalyst

Cyclopropanation of styrene with alpha-diazoacetate in the presence of (R,R )-(salen)ruthenium complex 4 in THF which dissolves the complex exhibits re markable cis- and enantio-selectivity [cis:trans=97:3, >97% ee (1S,2R)], wh ile the same reaction in hexane which does not dissolve it shows good but o pposite sense of enantioselectivity [-83% ee (1R,2S)] together with moderat e cis-selectivity (cis:trans=68:32). In homogeneous and heterogeneous condi tions, (salen)ruthenium complexes are considered to have different ligand-c onformation which, in turn, causes the opposite sense of enantioface select ivity in the cyclopropanation. (C) 2000 Elsevier Science Ltd. All rights re served.