Carbon-Carbon Bond Formation: An Investigation of [2+2] Cycloadditions by Visible Light Photoredox Catalysis

Photochemical transformations have sparked great interest among synthetic chemists for their effective carbon-carbon bond formation abilities. Photochemical reactions follow a mechanistic pathway that allows them to access high-energy intermediates that would be forbidden under thermal conditions. For over a century, UV light has been commonly used in photoreactions and have proved very successful in C-C bond formation. However, UV light catalyzed reactions have short-lived, highly reactive excited states and can decompose large molecules. In recent decades, scientists have focused their attention on using lower energy visible light for C-C bond formation reactions. Recent reports have shown the application of transition metal photocatalysts in various visible light irradiated systems to be effective in forming cyclobutane C-C bond via transition metal catalyzed [2+2] photocycloadditions. This research focuses on the energy transfer between ruthenium and iridium polypyridine complexes and oxazinone photosubstrates, which has been previously reported to undergo [2+2] cycloaddition of the alkenes in UV light. [2+2] cycloaddition was observed only in the presence of the iridium catalyst and not at all with the ruthenium catalyst. Further research into the triplet state energies of our photosubstrates will be conducted