Oxazolinylferrocene Ligands for the Addition of Diethylzinc to Benzaldehyde: Effects of the Symmetry and the Substituent on the Oxazoline Ring of the Ligands on Asymmetric Catalysis

Wanbin Zhang; Hidefumi Yoshinaga; Yoshitane Imai; Toshiyuki Kida; Yohji Nakatsuji; Isao Ikeda

doi:10.1055/s-2000-7659

Synlett 2000; 2000(10): 1512-1514
DOI: 10.1055/s-2000-7659

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Oxazolinylferrocene Ligands for the Addition of Diethylzinc to Benzaldehyde: Effects of the Symmetry and the Substituent on the Oxazoline Ring of the Ligands on Asymmetric Catalysis

Wanbin Zhang^* , Hidefumi Yoshinaga, Yoshitane Imai, Toshiyuki Kida, Yohji Nakatsuji, Isao Ikeda

^*Department of Applied Chemistry, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan; Fax + 81-6-6879-7359; E-mail: ikeda@ap.chem.eng.osaka-u.ac.jp

Abstract

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Several tetrasubstituted oxazolinylferrocene ligands were prepared, and with these ligands, up to 97% chemical yield and 93% ee were afforded in asymmetric alkylation of benzaldehyde with diethylzinc. It was found that the C ₂-symmetric ligands afforded almost the same enantioselectivity but different catalytic activity with their diastereomer, C ₁-symmetric ligands, in this test reaction. The bulkiness of the substituent on the oxazoline ring has significant effect on the enantioselectivity and particularly on catalytic activity. These effects of the symmetry and the bulkiness of the substituent on the oxazoline ring of the ligands on asymmetric catalysis have been rarely reported. A plausible mechanism is proposed.

chiral ligand - oxazoline - ferrocene - asymmetric reaction - diethylzinc

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