Flavin Catalysts in Organic Synthesis.

Flavin cofactors are nature's all-rounders with several essential roles in the active site of flavin-dependent enzymes. These flavoenzymes display an astonishingly broad activity spectrum, which also translates to the organic laboratory. In synthetic chemistry, flavin catalysis is now an integral part of several organocatalytic and photochemical methods with applications ranging from total synthesis to biocompatible photoproximity labeling. Flavins take a unique position in the field: they are easily accessible through synthesis or biochemical methods, while additionally exhibiting orthogonal reactivity compared to other (organo-)catalysts. Several flavin-mediated organic reactions were developed in a biomimetic fashion guided by extensive literature on enzymatic mechanisms. Additionally, flavin modification to tailored catalysts enabled desired non-natural transformations. This minireview gives an overview of and highlights the different key chemical transformations achieved with flavin catalysis in synthetic organic chemistry with a focus on photochemical oxidation and reduction, sensitization, oxygenation, and the activation of substrates by reversible covalent bond formation. The individual requirements for achieving specific flavin reactivity are illustrated based on example reactions. Finally, remaining challenges in the field of flavin catalysis are identified.