Stereoelectronic Effects in the Activation of Oxygens by Lewis Acids

这个项目属于有机动力学项目，由内华达大学里诺分校的年轻研究员罗伯特·c·科科伦负责，他将研究提高某些含氧有机化合物化学反应活性的方法。所得到的信息有望帮助设计催化剂，以允许在这些官能团上更快速和/或立体选择性的反应。研究了缩醛和羰基中氧在路易斯酸活化中的立体电子效应。在路易斯酸介导的缩醛裂解中，酸可以与与相邻的C-O键反周面或与间扭式键的氧孤对络合；对反周面孤对激活的动力学偏好应该是可以观察到的。羰基氧的Lewis酸活化有两种模式；在羰基的平面上，或者垂直于这个平面。虽然平面内络合通常被认为是主要的激活方式，但垂直络合也可能起作用。这些系统中氧活化中存在的立体电子偏好将通过检查包含路易斯碱附属物的构象刚性系统来研究，该附属物可以与螯合环中的氧合作。螯合定向络合将允许路易斯酸相对于目标氧的选择性定位。在几何意义上被不同激活的其他类似底物之间的速率差异将是立体电子偏好的指示。这种立体电子偏好的测定将有助于缩醛和羰基化合物反应中的非对映选择性。

This project, within the Organic Dynamics Program,is by a young investigator, Robert C. Corcoran of the University of Nevada-Reno, who will study methods for increasing the chemical reactivity of certain oxygen containing organic compounds. The resulting information is expected to aid in the design of catalysts to allow more rapid and/or stereoselective reactions at these functional groups. Stereoelectronic effects in the Lewis acid activation of the oxygen in acetals and carbonyls are to be investigated. In the Lewis acid mediated cleavage of acetals the acid may complex with an oxygen lone pair which is antiperiplanar to the adjacent C-O bond, or to one which is gauche; a kinetic preference for activation of the antiperiplanar lone pair should be observable. Two modes of Lewis acid activation of carbonyl oxygens are possible; in the plane of the carbonyl, or perpendicular to that plane. Though in-plane complexation is generally assumed to be the dominant mode of activation, perpendicular complexation may also play a role. The existence of stereoelectronic preferences in the activation of oxygens in these systems will be investigated by examining conformationally rigid systems which incorporate a Lewis base appendage that can cooperate with the oxygen in question in a chelate ring. The chelation-directed complexation will allow the selective positioning of a Lewis acid with respect to the target oxygen. Rate differences between otherwise similar substrates which are differentially activated in a geometric sense will be an indication of steroelectronic preferences. The determination of such stereoelectronic preferences will aid diastereoselectivity in the reactions of acetals and carbonyl compounds.