Towards Catalytic, Asymmetric (4+3)-Cycloadditions

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

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.