Cai C, Soloshonok V A, Hruby V J
Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA.
J Org Chem. 2001 Feb 23;66(4):1339-50. doi: 10.1021/jo0014865.
This study has demonstrated that the readily available and inexpensive 3-(trans-3'-alkyl/arylpropenoyl)oxazolidin-2-ones, featuring high electrophilicity and conformational homogeneity, are synthetically superior Michael acceptors over the conventionally used alkyl enoylates, allowing for a remarkable improvement in reactivity and, in most cases, diastereoselectivity of the addition reactions with a Ni(II) complex of the chiral Schiff base of glycine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone. Kinetically controlled diastereoselectivity in the corresponding Michael addition reactions between the Ni(II) complex of glycine and the oxazolidin-2-ones was systematically studied as a function of steric, electronic, and position effects of the substituents on the starting Michael acceptor. In both aliphatic and aromatic series the simple diastereoselectivity was found to be virtually complete, affording the products via the corresponding TSs with the approach geometry like. The face diastereoselectivity of the reactions between the Ni(II) complex of glycine and the 3-(trans-3'-alkylpropenoyl)oxazolidin-2-ones was found to depend exclusively on the steric bulk of the alkyl group on the starting Michael acceptor. In contrast, the face diastereoselectivity in the reactions of aromatic oxazolidin-2-ones with the Ni(II) complex of glycine was shown to be controlled predominantly by the electronic properties of the aryl ring. In particular, the additions of the Ni(II) complex of glycine with 3-(trans-3'-arylpropenoyl)oxazolidin-2-ones, bearing electron-withdrawing substituents on the phenyl ring, afforded the (2S,3R)-configured products with synthetically useful diastereoselectivity and in quantitative chemical yields, thus allowing for an efficient access to the sterically constrained beta-aryl-substituted pyroglutamic and glutamic acids.
本研究表明，易于获得且价格低廉的3-(反式-3'-烷基/芳基丙烯酰基)恶唑烷-2-酮具有高亲电性和构象均匀性，是比传统使用的烯酰基烷基酯更具合成优势的迈克尔受体，这使得与甘氨酸手性席夫碱与(S)-o-[N-(N-苄基脯氨酰基)氨基]二苯甲酮的镍(II)配合物的加成反应的反应性以及在大多数情况下的非对映选择性有显著提高。系统地研究了甘氨酸镍(II)配合物与恶唑烷-2-酮之间相应迈克尔加成反应中的动力学控制非对映选择性，该选择性是起始迈克尔受体上取代基的空间、电子和位置效应的函数。在脂肪族和芳香族系列中，发现简单的非对映选择性几乎是完全的，通过具有类似接近几何形状的相应过渡态得到产物。发现甘氨酸镍(II)配合物与3-(反式-3'-烷基丙烯酰基)恶唑烷-2-酮之间反应的面非对映选择性仅取决于起始迈克尔受体上烷基的空间体积。相反，芳香族恶唑烷-2-酮与甘氨酸镍(II)配合物反应中的面非对映选择性主要受芳环电子性质的控制。特别地，甘氨酸镍(II)配合物与在苯环上带有吸电子取代基的3-(反式-3'-芳基丙烯酰基)恶唑烷-2-酮的加成反应，以合成上有用的非对映选择性和定量化学产率得到(2S,3R)构型的产物，从而能够有效合成空间受限的β-芳基取代焦谷氨酸和谷氨酸。
