Determination of the Conformation of the Key Intermediate in an Enantioselective Palladium-Catalyzed Allylic Substitution from Residual Dipolar Couplings
Determination of the Conformation of the Key Intermediate in an Enantioselective Palladium-Catalyzed Allylic Substitution from Residual Dipolar Couplings
复制标题
DOI：
10.1002/anie.200903649
复制
发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Thiele, Christina M.
中科院分区：
文献类型：
--
作者：
Boettcher, Benjamin;Schmidts, Volker;Thiele, Christina M.
过渡金属催化的不对称C±C键形成反应，如烯丙基取代反应，在学术研究和工业过程中具有重要意义。[1]在研究这种反应立体选择性的起源时，了解配体(S)、过渡金属和底物之间的空间关系是至关重要的一步。[2]如果能够分离出中间体，原则上可以通过X射线结晶学或核磁共振光谱获得中间体的空间结构。然而，这里应该指出的是，中间体的平衡构象不一定导致对反应性和选择性的确凿见解，因为这取决于产物的形成涉及早过渡态还是晚过渡态。[3，4]已有广泛的研究致力于探索具有双齿配体的烯丙基取代中立体选择的起源，这里只提到很少。[5-14]对于具有单齿配体的体系，如本研究(见1)中的情况，存在几种催化剂-底物络合物的X射线结构，但据我们所知，在溶液中还没有进行详细的核磁共振波谱研究。中间体络合物在溶液中的构象不一定与结晶学测定的相似。此外，溶液的构象，特别是中间物种的动力学对于了解立体选择性步骤可能很重要。
Transition-metal-catalyzed enantioselective CÀC bond-forming reactions such as allylic substitution are of great importance in academic research and industrial processes.[1] In investigating the origin of the stereoselection of such a reaction knowledge about the spatial relationships between the ligand (s), the transition metal, and the substrate is a crucial step.[2] If an intermediate can be isolated, the spatial structure of the intermediate can in principle be obtained either by X-ray crystallography or NMR spectroscopy. However, it should be pointed out here that the equilibrium conformation of the intermediate does not necessarily lead to conclusive insights on reactivity and selectivity, since that depends on whether an early or late transition state is involved in the formation of the product.[3, 4] Extensive studies have been devoted to probing the origin of stereoselection in allylic substitutions with bidentate ligands, of which only few can be mentioned here.[5–14] For systems with monodentate ligands,[15–21] as is the case in the present study (see 1), several X-ray structures of catalyst–substrate complexes exist, but to our knowledge no detailed NMR spectroscopic study in solution has yet been performed. The conformation of an intermediate complex in solution might not necessarily resemble that determined crystallographically. Furthermore, the solution conformation and in particular the dynamics of the intermediate species might be important for insight into the stereoselective step.