New Chiral Br??nsted Acids for Asymmetric Synthesis

描述（由申请人提供）：双芳基配体VANOL和VAPOL形成独特的多硼酸盐阴离子，其核心为硼氧酸盐，并开始被认为是一种非常独特和通用的不对称催化平台。作为质子化亚胺的离子对，该手性阴离子可影响亚胺与重氮化合物的叠氮化反应，具有很高的产率、非对映选择性和对映选择性。将进行包括自然丰度动力学同位素研究在内的机理研究，以了解硼氧酸盐催化剂是如何形成的，以及它如何在包括叠氮化反应在内的各种反应中起作用。硼氧酸盐核心是阴离子的，有7个氧原子，它们都带有一些负电荷，它可能作为一个模板，在这个模板中，多个底物可以同时与硼氧酸盐核心形成氢键，这有助于确定过渡态。计算将用于理解底物如何在叠氮化和其他反应的过渡态中与硼氧酸盐核相互作用。除了这种硼酸盐催化剂的独特结构外，它的实用性大大增强了，因为它可以由配体、硼源、两个等价物的醇或苯酚和三个等价物的水组成的底物来组装。因此，通过这一过程可以产生的各种催化剂实际上是无限的。研究还将确定这种硼氧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、醛的氨基化和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.