Asymmetric Synthesis of 4,4‐(Difluoro)glutamic Acid via Chiral Ni(II)‐Complexes of Dehydroalanine Schiff Bases. Effect of the Chiral Ligands Structure on the Stereochemical Outcome
Dr. Yoshinori Tokairin,
Yuhei Shigeno,
Dr. Jianlin Han,
Prof. Dr. Gerd‐Volker Röschenthaler,
Dr. Hiroyuki Konno,
Dr. Hiroki Moriwaki,
Vadim A. Soloshonok
Affiliations
Dr. Yoshinori Tokairin
Department of Life Sciences and Chemistry Jacobs University Bremen GmbH Campus Ring 1 28759 Bremen Germany
Yuhei Shigeno
Department of Biochemical Engineering, Graduate School of Science and Technology Yamagata University, Yonezawa Yamagata 992-8510 Japan
Dr. Jianlin Han
College of Chemical Engineering Nanjing Forestry University Nanjing 210037 China
Prof. Dr. Gerd‐Volker Röschenthaler
Department of Life Sciences and Chemistry Jacobs University Bremen GmbH Campus Ring 1 28759 Bremen Germany
Dr. Hiroyuki Konno
Department of Biochemical Engineering, Graduate School of Science and Technology Yamagata University, Yonezawa Yamagata 992-8510 Japan
Dr. Hiroki Moriwaki
Hamari Chemicals Ltd. 1-4-29 Kunijima, Higashi-Yodogawa-ku Osaka 533-0024 Japan
Vadim A. Soloshonok
Department of Organic Chemistry I, Faculty of Chemistry University of the Basque Country UPV/EHU Paseo Manuel Lardizábal 3 20018 San Sebastián Spain
Abstract Four differently substituted chiral Ni(II)‐complexes of dehydroalanine Schiff base were prepared and reacted with BrCF2COOEt/Cu under the standard reaction conditions. The observed diastereoselectivity was found to depend on the degree and pattern of chlorine substitution for hydrogen in the structure of the dehydroalanine complexes. The unsubstituted complex gave the ratio of diastereomers (S)(2S)/(S)(2R) of 66/34. On the other hand, introduction of chlorine atoms in the strategic positions on the chiral ligands allowed to achieve a practically attractive diastereoselectivity of (∼98.5/1.5). Diastereomerically pure major product was disassembled to prepare 9‐fluorenylmethyloxycarbonyl (Fmoc) derivative of (S)‐4,4‐difluoroglutamic acid.
