Visible light-induced electron and energy transfer: Applications in strong bond activation and transiently strainable cycloalkenes and their use in cycloaddition chemistry

Light has a remarkable ability to inject substantial amounts of energy into chemical reactions. However, many reactions are unable to utilize this light due to their transparent nature. Using a dye can resolve this issue by absorbing the light. Herein, we investigate two distinct mechanisms- electron transfer and energy transfer, that serve to drive otherwise very challenging reactions. Ir-dyes are among the most potent reducing photocatalysts available, making them exceptionally suited for reducing organic molecules with very extremely negative reduction potential. Previous research in our lab demonstrated that combining a catalytic amount of Ir-dye along with a perfluoroarene and a tertiary amine along with blue light led to the mesolytic fragmentation of Csp²–F bonds to accomplish hydrodefluorination. We explore how to leverage the reduction capabilities of Ir-dyes, in conjunction with additional factors, to expand the range of Csp²–F that could be activated, thereby expanding the range of products that can be obtained starting from just a few commercially available highly fluorinated starting materials. Mild reaction conditions and excellent regioselectivity make the approach ideal for synthesis. Additionally, we have developed expedited synthetic routes for a wide range of pharmaceutically significant molecules. Next, we investigate the ability of the Ir-dye to mediate energy transfer to cycloalkenes. This process generates an excited-state alkene, which can then undergo rotation around the former double bond, leading to the formation of a highly strained trans-cycloalkene. Previous work has provided evidence for this phenomenon through the observation of conjugated products and their relative stereochemistry. Our research builds upon this foundation by aiming to enhance the practicality of this chemistry and address existing limitations. Ultimately, by gaining a deeper understanding of the underlying reaction mechanisms, we were able to design a cycloalkene that obviates the need for the Ir-dye altogether, further broadening its applicability and utility. Additionally, we developed a light-driven skeletal editing strategy exploiting strain energy to drive cycloreversion of the aryldihyropyrans, producing reactive dienes which further enabled the synthesis of diverse arylcyclohexenes in a one-pot process, expanding synthetic capabilities through precise structural modifications.