New Chiral Br??nsted Acids for Asymmetric Synthesis

描述(由申请人提供)：拱形联芳基配体VANOL和VAPOL形成了一种独特的以硼酸盐为核心的多硼阴离子，并开始被认为是一种非常独特和多功能的不对称催化平台。作为质子化亚胺的离子对，这种手性阴离子将以非常高的产率、非对映选择性和重氮化选择性影响亚胺与重氮化合物的偶氮化反应。将进行机理研究，包括自然丰度动力学同位素研究，以了解硼酸盐催化剂是如何形成的，以及它如何在包括氮杂环化反应在内的各种反应中发挥作用。硼酸盐核是阴离子的，有七个氧基团，它们都带有一些负电荷，它可能作为模板，其中多个底物可以同时与硼氧酸盐核形成氢键，这有助于确定过渡态。为了了解底物如何在氮杂环化和其他反应的过渡态与硼酸盐核相互作用，将进行计算。除了这种硼酸盐催化剂的独特结构外，它的实用性也大大增强，因为它可以由配体、一个硼源、两个当量的醇或苯酚和三个当量的水的底物组装而成。因此，这一过程可以产生的各种催化剂几乎是无限的。还将进行研究，以确定这种硼酸盐催化剂在其他反应中的有效性，包括Darzens反应、[3 2]环加成反应、醛的氨烯丙基化反应和Ugi反应。

DESCRIPTION (provided by applicant): The vaulted biaryl ligands VANOL and VAPOL form a unique polyborate anion with a boroxinate core and is beginning to be recognized as a very unique and versatile platform for asymmetric catalysis. As an ion-pair with a protonated imine, this chiral anion will effect the aziridination of imines with diazo compounds with very high yields, diastereoselectivity and enanatioselectivity. Mechanistic investigations including natural abundance kinetic isotope studies will be undertaken to understand how the boroxinate catalyst is formed and how it functions in a variety of reactions including aziridination reactions. The boroxinate core is anionic and has seven oxygens which all bear some of the negative charge and it is possible that it serves as a template in which more than one substrate can H-bond with the boroxinate core at the same time and this helps to determine the transition state. Computations will be persued in an effort to understand how the substrates interact with the boroxinate core in the transition state of the aziridination and other reactions. In addition to the unique structure of this boroxinate catalyst, its utility is greatly enhanced by the fact that it can be assembled by the substrate from the ligand, a boron source, two equivalents of an alcohol or phenol and three equivalents of water. The diverse array of catalysts that can be generated by this process is thus virtually limitless. Investigations will also be carried out to determine the effectiveness of this boroxinate catalyst in other reactions including the Darzens reaction, [3+2] cycloadditions, aminoallylation of aldehydes, and the Ugi reaction.