Jm. Fraile et al., ASYMMETRIC CYCLOPROPANATION CATALYZED BY CATIONIC BIS(OXAZOLINE)-CU-II COMPLEXES EXCHANGED INTO CLAYS, Tetrahedron : asymmetry, 8(13), 1997, pp. 2089-2092
Several clays, exchanged with cationic bis(oxazoline)-Cu-II complexes,
have been tested as catalysts in the benchmark cyclopropanation react
ion of styrene with ethyl diazoacetate. Either the catalytic activity
or the enantioselectivity are improved with regard to the same complex
es when used in homogenous phase. The solvent used to carry out the ca
tionic exchange has a decisive influence on the enantioselectivity and
the same is true with regard to the solvent used in the homogeneous r
eaction. The clay-catalysed reactions lead to an increase in the amoun
t of cis-cyclopropanes. These catalysts are recoverable and retain mos
t of their catalytic activity. (C) 1997 Elsevier Science Ltd.