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2004
Enantioselective syntheses
O 0031
Highly Efficient Chiral Copper Schiff-Base Catalyst for Asymmetric Cyclopropaof 2,5-Dimethyl-2,4-hexadiene. — The title reaction is studied for several cop51- 031 nation
per Schiff-base catalysts of type (I). They are synthesized as dimers and applied in the
reactions as monomers. Best enantioselectivities are achieved with complexes (Ia) and
(Ib) for the reaction of diene (II) with ethyl diazoacetate (IIIa). In general, the enantioselectivities increase if the reaction temperatures are decreased from 80 to 0 °C, but the
yields are lowered. This disadvantage is overcome by the presence of catalytic amounts
of Lewis acid Al(OEt)3 in addition to the copper complex, leading to significantly increased yields. — (ITAGAKI*, M.; HAGIYA, K.; KAMITAMARI, M.;
MASUMOTO, K.; SUENOBU, K.; YAMAMOTO, Y.; Tetrahedron 60 (2004) 36,
7835-7843; Org. Synth. Res. Lab., Sumitomo Chem. Co., Ltd., Konohana, Osaka 554,
Japan; Eng.) — Klein
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