Highly reductive photocatalytic systems in organic synthesis

The recent development of highly reductive photocatalytic systems for the reduction of challenging substrates (substrates with very negative reduction potentials) with super electron donors for C–C and C–X (X = H, B, P, S, Sn) bond formations via single- or multiphoton excitation is highlighted. Several elegant strategies, including consecutive photo-induced electron transfer (conPET), electrochemically mediated photoredox catalysis (e-PRC), or tandem photoredox strategy, play a significant role in highly reductive photocatalytic systems. These highly reductive photocatalytic systems provide a new strategy for the reduction of inert substrates under mild conditions with adjustable photosensitizers, showing an advantage to the direct UVC photolysis, electrolysis, and classical transition-metal catalysis via two-electron activation. Reductive organic transformations, which are important in both academia and industry to generate valuable chemicals, have been widely investigated. However, the reductive transformations of inert substrates still face many challenges, such as high cost and potential safety issues arising from strong reductants in excess, UVC light irradiation, or strong current density for electrolysis. In this context, visible-light photocatalysis has emerged as an ideal approach to provide highly reductive systems for the activation of inert substrates via single-electron reduction under mild conditions. In this review, we highlight some recent contributions to this field, classify them as single- or multiphoton excitation systems, elucidate the mechanisms with different super electron donors, and analyze their structural features on reducibility. Furthermore, the limitations and potential applications of this field will be discussed. Reductive organic transformations, which are important in both academia and industry to generate valuable chemicals, have been widely investigated. However, the reductive transformations of inert substrates still face many challenges, such as high cost and potential safety issues arising from strong reductants in excess, UVC light irradiation, or strong current density for electrolysis. In this context, visible-light photocatalysis has emerged as an ideal approach to provide highly reductive systems for the activation of inert substrates via single-electron reduction under mild conditions. In this review, we highlight some recent contributions to this field, classify them as single- or multiphoton excitation systems, elucidate the mechanisms with different super electron donors, and analyze their structural features on reducibility. Furthermore, the limitations and potential applications of this field will be discussed. proton-transfer reactions play critical roles in biology and chemistry, in which a proton is transferred from one atom to another atom. substrates with very negative reduction potentials, Ered < –2.0 V. reductants that are needed and consumed in stoichiometric amounts for the reduction of catalyst in the reaction. a reductive reaction of a substrate that proceeds by transferring one electron. highly aggressive species that can force chemical transformations of otherwise unreactive molecules. an activation mode for a substrate being reduced or oxidized while gaining or losing two electrons.