Remote Electronic Control in Asymmetric Cyclopropanation with Chiral Ru-Pybox Catalysts

Article abstract of DOI:10.1016/0957-4166(95)00324-I

Electronic control by remote substituents far from a catalytically active center was found in an asymmetric cyclopropanation of olefins and diazoacetates with the ruthenium catalysts of chiral 4-substituted bis(4'-isopropyloxazolinyl)pyridine, 4-X-pybox.It was found that electron-withdrawing groups increase the catalytic activity, but electron-donating groups decrease it.The enantiomer ratios of the product cyclopropanes with the electron-withdrawing groups, X = Cl and COOMe, are higher than those with the electron-donating groups, X = OMe and NMe2.The enantiomer ratios of the ethyl and l-menthyl cyclopropanes were corelated toward Hammett's ?_para values to give positive ρ values, 0.365 for trans-ethyl ester, 0.486 for cis-ethyl ester, 0.517 for trans-l-menthyl ester, and 0.517 for cis-l-menthyl ester.However, the trans:cis ratios of the products were not affected by their substituents, ca. 90:10 for ethyl diazoacetate and ca. 96:4 for l-menthyl diazoacetate.Intramolecular cyclopropanation clearly gave a similar trend.