Reductive Amination and Enantioselective Amine Synthesis by Photoredox Catalysis

Photochemistry usually functions on a one-photon-one-electron basis, leading to unstable radical intermediates that must be intercepted rapidly to allow efficient product formation. This can render multi-electron reductions and enantioselective reactions particularly challenging. In this minireview, we discuss recent advances in the area of photo-driven multi-electron transfer with a particular focus on our own work on reductive amination and the enantioselective synthesis of amines by combined photoredox and enzyme catalysis. Polarity-matched hydrogen atom transfer (HAT) between photochemically-generated α-amino alkyl radicals and thiols is a key step in these reactions. A cyclic reaction network comprised of light-driven imine reduction by an Ir-photocatalyst and enantioselective amine oxidation by the enzyme monoamine oxidase (MAO-N-9) was used to obtain enantioenriched amines from imines.