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Abstract
Over the past decade, photoredox catalysis has emerged as a powerful technique in synthetic organic chemistry for its ability to perform difficult transformations under mild reaction conditions. Complexes of ruthenium or iridium, under activation of visible light, have garnered significant attention for their ability to execute single-electron processes. Using complexes of light-activated earth-abundant metals, such as chromium, our group has developed a sustainable approach to the field of photocatalysis. To find new chromium complexes as potential photocatalysts, a series of novel ligands and chromium photocatalysts were synthesized. The photophysical properties of the unique Cr complexes were investigated, as well as the use of these complexes as the photocatalysts in different reactions. Remarkably, we found a Cr photocatalyst that increases reactivity in cycloaddition reactions. Recent research has uncovered a dearomative Cr-photocatalyzed radical-cation [3+2] cycloaddition reaction using indoles and vinyl diazo species. Nucleophilic interception of indole radical-cation species, generated by Cr photocatalysis, by vinyl diazo compounds yields new indoline structural motifs. This is the first example of a photocatalyzed [3+2] cycloaddition reaction using indoles. Furthermore, progress toward the synthesis of the Cripowellin alkaloids using Cr photocatalysis has developed an intramolecular Baeyer-Villiger transformation to synthesize a key intermediate along the synthetic pathway. Overall, new Cr photocatalysts has made tremendous strides to overtake traditional Ru/Ir catalysts.