Towards Catalytic, Asymmetric (4+3)-Cycloadditions

有了这个奖项，化学部的化学合成计划正在支持密苏里-哥伦比亚大学Michael Harmata教授的研究，以开发（4+3）-环加成化学。 在这样的环加成反应中，两个分子片段，一个四碳片段（二烯）和一个三碳片段（烯丙基阳离子）在一个反应中结合。 关键特征是生成烯丙基阳离子，其具有正电荷，并且与也是手性的伴侣（带负电荷）阴离子配对。 手征性是任何物体不能叠加在其镜像上的条件。 例如，左手和右手是镜像，但不能重叠。 这个想法是，这种手性可以用来诱导手性的（4+3）-环加成反应的产物的形成。 这是重要的，因为生命分子以及许多药物是手性的，并且不是作为右手和左手分子的混合物出现，而是作为右手或左手分子出现。 这通常被称为不对称。 不对称反应的发展，只产生右手或左手的产品，是整个科学和化学工业的巨大兴趣。 Harmata教授将把这个项目的研究和教育部分整合到一个面向中学生的新的外展计划中。通过一系列旨在突出日常经验和化学进步之间联系的研讨会，该计划为中学生提供了一个基于发现的体验，通过实验捕捉STEM领域的创造力。Harmata教授与当地学区和特许学校建立了合作伙伴关系，以覆盖在科学领域代表性不足的贫困社区。该计划通过为中学生提供一个在与大学生互动的同时讨论科学观察的机会，促进在STEM领域追求高等教育。这一概念将通过染色过程来证明，在染色过程中，带电荷的染料将选择性地染色带相反电荷的织物。 程序将由中学教师开发，他们将在夏季测试和完善4 H成员的想法，然后在学年期间将教学技术转移回教室。 目标教室特别是那些农村或在接触STEM项目的背景下服务不足的教室。该科学计划将包括使用手性磷酸从烯丙醇生成烯丙基阳离子，该磷酸被设计为与烯丙基阳离子离子配对。 预期这些物质以非对映选择性方式与二烯反应，导致环加合物中的净对映选择性。这将为七元碳环的不对称合成提供新的方法学依据。 作为反应开发过程的一部分，还将进行一些筛选。 将检查分子间和分子内反应。 优化协议将追求在努力最大限度地提高对映体选择性。

With this award, the Chemical Synthesis Program in the Chemistry Division is supporting the research of Professor Michael Harmata at the University of Missouri-Columbia to develop (4+3)-cycloaddition chemistry. In such cycloadditions, two molecular fragments, a four-carbon piece (the diene) and a three-carbon piece (the allylic cation)are joined in a single reaction. The key feature is the generation of the allylic cation, which possesses a positive charge, and is paired with a partner (negatively-charged) anion that is also chiral. Chirality is the condition of any object that cannot be superimposed on its mirror image. For example, left and right hands are mirror images, but cannot be superimposed. The idea is that this chirality can be used to induce chirality in the formation of the products of the (4+3)-cycloaddition reaction. This is significant because the molecules of life, as well as many drugs are chiral and occur not as mixtures of right and left handed molecules, but as either right or left. This is generally known as asymmetry. The development of reactions that are asymmetric, producing only right or left handed products, is of great current interest across science and the chemical industry. Professor Harmata will integrate the research and educational components of this project within a new outreach program for middle school students. Through a series of workshops aimed at highlighting the connections between everyday experience and chemistry advances, this program provides middle school students with a discovery-based experience that captures the creativity of the STEM fields through experiments. Professor Harmata has established partnerships with local school districts and charter schools to reach an underprivileged community, which is underrepresented in the sciences. The program promotes the pursuit of higher education in the STEM fields by providing an opportunity for middle-school students to discuss scientific observations while interacting with college students. This concept will be demonstrated through the process of dyeing, in which charged dyes will selectively dye oppositely charge fabrics. Procedures will be developed by middle school teachers who will test and refine the ideas on 4H members during the summers and then transfer the teaching technology back to their classrooms during academic years. Targets classrooms are particularly those that are rural or otherwise underserved in the context of exposure to STEM programs.The scientific program will consist of the generation of allylic cations from allylic alcohols using chiral phosphoric acids that have been designed to ion pair with allylic cations. These species are anticipated to react with dienes in a diastereoselective fashion, resulting in a net enantioselectivity in the cycloadducts. This will provide new methodology for the enantioselective synthesis of seven-membered carbocyclic rings. Some screening will also be conducted as part of the reaction development process. Both inter- and intramolecular reactions will be examined. Optimization protocols will be pursued in an effort to maximize enantioselectivity.