Bisoxazoline ligands with an axial-unfixed biaryl backbone: the effects of the biaryl backbone and the substituent at oxazoline ring on Cu-catalyzed asymmetric cyclopropanation

• Published in: Tetrahedron: asymmetry Vol. 17; no. 5; pp. 767 - 777
• Main Authors: Zhang, Wanbin, Xie, Fang, Matsuo, Shigeaki, Imahori, Yuji, Kida, Toshiyuki, Nakatsuji, Yohji, Ikeda, Isao
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 06.03.2006
• ISSN: 0957-4166; 1362-511X
• DOI: 10.1016/j.tetasy.2006.02.014

The synthesis of novel C 2-symmetric bisoxazoline ligands with an axial-unfixed biaryl backbone and different substituents at the oxazoline ring is reported. The diastereomer equilibrium of these ligands in solution and their complexation behavior with the copper(I) ion were studied. Their application in Cu-catalyzed cyclopropanation of styrene, with diazoacetate, was carried out and the effects of the biaryl backbone and the substituent on the oxazoline ring in the catalysis were examined. The best result was obtained with the ligand having a 1,1′-binaphthyl backbone and a t-butyl group on the oxazoline ring, which afforded 89% de and 96% de for the trans- and cis-products of the above asymmetric cyclopropanation reaction, respectively.