Synthesis and Characterization of Binary-Complex Models of Ureas and 1,3-Dicarbonyl Compounds: Deeper Insights into Reaction Mechanisms Using Snap-Shot Structural Analysis
作者:Takumi Azuma、Yusuke Kobayashi、Ken Sakata、Takahiro Sasamori、Norihiro Tokitoh、Yoshiji Takemoto
DOI:10.1021/jo4028775
日期:2014.2.21
The mechanism of the enantioselective Mannich reaction catalyzed by a hydrogen-bond (HB)-donor bifunctional organocatalyst has been fully investigated using experimental evidence and computational analysis. Several binary complexes have been designed as models of a catalyst and a nucleophile, where the urea moieties were linked to a 1,3-dicarbonyl compound through the diphenylacetylene motif. X-ray
使用实验证据和计算分析已充分研究了氢键(HB)-供体双官能有机催化剂催化的对映选择性曼尼希反应的机理。已经设计了几种二元配合物作为催化剂和亲核试剂的模型,其中尿素部分通过二苯基乙炔基团与1,3-二羰基化合物连接。对模型9和10的X射线分析表明,脲的两个N–H质子通过HB双重相互作用与相同的羰基相互作用。进一步研究11的晶体结构可以直接观察到双官能氨基尿素和1,3-二酮之间形成的不稳定的烯醇铵中间体。β-酮酯-氨基脲配合物12与几种亲电试剂以非常快的速度反应,从而提供相应的加合物15和17作为单一非对映异构体,分别具有优异的收率。密度泛函理论计算揭示了对映选择性曼尼希反应的去质子化和CC键形成步骤的细节。1,3-二羰基部分的去质子化主要通过烯醇形式发生,从而得到铵-烯醇盐中间体。这些结果应提供对催化剂的HB-供体和布朗斯台德碱部分功能作用的更深入,更准确的理解。