Departamento de Química Orgánica, Instituto de Ciencia de Materiales de Aragón and Instituto Universitario de Catálisis Homogénea, Facultad de Ciencias, Universidad de Zaragoza-CSIC, E-50009, Zaragoza, Spain.
Dalton Trans. 2010 Feb 28;39(8):2098-107. doi: 10.1039/b919274c. Epub 2010 Jan 14.
Aza-pyridinoxazoline ligands, a new class of C(1)-symmetric ligands, are described and tested in the heterogeneous enantioselective catalysis of a cyclopropanation reaction, with the aim of improving surface confinement effects by the clay support on the reaction stereoselectivity. In the case of trans/cis diastereoselectivity, these surface effects lead to a systematic reversal of selectivity, cis-cyclopropanes being favored. Regarding the enantioselectivities, support confinement has a positive effect in the case of major cis-cyclopropane products, leading to moderate enantioselectivity values (60% ee). A theoretical (DFT) mechanistic study is carried out to explain the origin of the enantioselectivity in the homogeneous phase at a molecular level, and to get insights on the geometries of the key intermediates and transition structures.
氮杂吡啶恶唑啉配体，一类新型的 C(1)对称配体，在非均相的环丙烷化反应的对映选择性催化中被描述和测试，目的是通过粘土载体提高反应的立体选择性的表面限制效应。在反式/顺式非对映选择性的情况下，这些表面效应导致选择性的系统反转，有利于顺式环丙烷。关于对映选择性，在主要的顺式环丙烷产物的情况下，载体限制具有积极的影响，导致中等的对映选择性值（60%ee）。进行了理论（DFT）的机理研究，以在分子水平上解释均相相中对映选择性的起源，并深入了解关键中间体和过渡态的几何形状。
