syn/anti Switching by Specific Heteroatom-Titanium Coordination in the Mannich-Like Synthesis of 2,3-Diaryl-β-amino Acid Derivatives
syn/anti Switching by Specific Heteroatom-Titanium Coordination in the Mannich-Like Synthesis of 2,3-Diaryl-β-amino Acid Derivatives
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DOI：
10.1002/ejoc.201400142
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发表时间：
2014-05-01
影响因子：
2.8
通讯作者：
Gelmi, Maria Luisa
中科院分区：
文献类型：
--
作者：
Bonetti, Andrea;Clerici, Francesca;Gelmi, Maria Luisa
一种非常有效的合成2，3-二芳基-β-氨基酸衍生物是通过TiCl_4/三乙胺催化的芳基乙酸酯或芳基硫代乙酸酯与芳基亚胺的类Mannich反应实现的。能够与钛中心配位的邻位杂原子基团在芳基乙酸部分上的存在对于反应的结果和调节顺/反非对映选择性是非常重要的。特别是，与o-F-，o-Cl-和o-Br-芳基乙酸酯，顺式加合物被分离为主要流行的异构体。当使用（-）-8-苯基（2-氟苯基）乙酸薄荷酯时，与亚胺的缩合导致高的非对映体和对映体选择性。与立体化学结果和核磁共振研究相一致，提出了一个可能的反应机理。
A very efficient synthesis of 2,3-diaryl--amino acid derivatives is realized by a TiCl4/triethylamine-catalyzed Mannich-like reaction of arylacetic or arylthioacetic esters with arylimines. The presence on the arylacetic moiety of an ortho-heteroatom group able to coordinate to the titanium center is of dramatic importance for the outcome of the reaction and to tune the syn/anti diastereoselection. In particular, with o-F-, o-Cl-, and o-Br-arylacetates, the syn adduct was isolated as the largely prevalent isomer. When (-)-8-phenylmenthyl (2-fluorophenyl)acetate was used, the condensation with imines resulted in high diastereo- and enantioselectivity. In agreement with the stereochemical results and NMR studies, a conceivable reaction mechanism was proposed.