No abstract

Enantioselective Copper-Catalyzed Cyclopropanation of Silyl EnolEthers.-Silyl enol ethers can be converted to optically active silyloxycyclopropanes with good enantioselectivities by copper-catalyzed cyclopropanation in the presence of chiral azasemicorrin or related bisoxazoline ligands. Due to the instability of the trimethylsilyl group, large scale reactions are performed using triisopropylsilyl protected enol ethers and tetramethylpiperidine as an additive. A cyclopropanation-ring opening sequence allows the enantioselective introduction of an acetic acid side chain at the α-position of cycloalkanones. -(EBINGER, A.; HEINZ, T.; UMBRICHT, G.; PFALTZ, A.; Tetrahedron 54 (1998) 35, 10469-10480; MPI Kohlenforsch., D-45470 Muelheim/Ruhr, Germany; EN)