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.

中文翻译：

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脱氢丙氨酸席夫碱的手性Ni（II）络合物的不对称合成4,4-（二氟）谷氨酸 手性配体结构对立体化学结果的影响。

制备了脱氢丙氨酸席夫碱的四个不同取代的手性Ni（II）配合物，并在标准反应条件下与BrCF ₂ COOEt / Cu反应。发现观察到的非对映选择性取决于脱氢丙氨酸络合物结构中氯取代氢的程度和模式。未取代的复合物的非对映异构体（S）（2 S）/（S）（2 R）之比为66/34。另一方面，在手性配体的关键位置引入氯原子可以实现（〜98.5 / 1.5）的实用的非对映选择性。分解非对映体纯净的主要产物，以制备（）的9-芴基甲氧羰基（Fmoc）衍生物S）‐4,4-二氟谷氨酸。