Asymmetric cyclopropanation catalysed by cationic bis(oxazoline)-Cu-II complexes exchanged into clays

Several clays, exchanged with cationic bis(oxazoline)-Cu-II complexes, have been tested as catalysts in the benchmark cyclopropanation reaction of styrene with ethyl diazoacetate. Either the catalytic activity or the enantioselectivity are improved with regard to the same complexes when used in homogenous phase. The solvent used to carry out the cationic exchange has a decisive influence on the enantioselectivity and the same is true with regard to the solvent used in the homogeneous reaction. The clay-catalysed reactions lead to an increase in the amount of cis-cyclopropanes. These catalysts are recoverable and retain most of their catalytic activity. (C) 1997 Elsevier Science Ltd.