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Hydrogen Atom Transfer (HAT): A Versatile Strategy for Substrate Activation in Photocatalyzed Organic Synthesis
No full textThe adoption of hydrogen atom transfer (HAT) in a photocatalytic approach, in which an excited catalyst is responsible for substrate activation, offers unique opportunities in organic synthesis, enabling the straightforward activation of R–H (R = C, Si, S) bonds in desired reagents. Either a direct strategy, based on the intrinsic reactivity of a limited number of photocatalysts in the excited state, or an indirect one, in which a photocatalytic cycle is used for the generation of a thermal hydrogen abstractor, can be exploited. This microreview summarizes the most recent advances (mainly from the last two years) in this rapidly developing area of research, collecting the selected examples according to the nature of the species promoting the HAT process. From the synthetic point of view, this area has led to the development of a plethora of strategies for C–C, C–Si, C–N, C–S, and C–halogen (particularly, fluorine) bond formation, as well as for oxidation reactions
Photoorganocatalyzed Direct Hydrogen Atom Transfer (HAT): A Tool for Transition Metal-Free C-C Bond Formation
No full textPhotocatalytic hydrogen atom transfer (HAT) is a valid tool for the functionalization of aliphatic C-H bonds in a mild way, offering a straightforward path to ameliorate the step and atom economy of synthetic processes. Thus, carbon-centered radicals are smoothly generated via a homolytic C-H cleavage and they are mainly used to forge valuable C-C bonds. Among the photocatalysts available, both metal-containing derivatives and organic compounds are viable options in some respect. However, the adoption of the latter class of photocatalysts is appreciated from an environmental point of view, since the desired products are free from metal contaminants. In this frame, the aim of this article is to collect the processes (mainly the most recent ones) making use of a photoorganocatalyst (POC_HAT) for the generation via HAT of carbon-centered radicals, in turn, used for diverse synthetic purposes. These include hydroalkylation and hydroacylation of olefins, along with the preparation of alkenes, alkynes, and substituted heteroaromatics
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