1,721,040 research outputs found
The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle
No full textPhotocatalytic strategies have recently revolutionized the field of organic synthesis. However, while the progress has been impressive in terms of reported methodologies, less attention has been devoted to mechanistic aspects. In this regard, key to the development of efficient strategies is the recovery of the exhausted photocatalyst formed upon quenching of the excited state. This review summarizes the different ways available to turn over the photocatalyst and classifies them according to the species responsible for this step, being a reaction intermediate, a co-catalyst, a reaction partner or an electrode. Finally, an analysis of the common aspects of the described alternatives is offered, also showcasing how the tuning of the photocatalyst turn-over step can completely divert the reaction outcome
Direct Photocatalyzed Hydrogen Atom Transfer (HAT) for Aliphatic C–H Bonds Elaboration
Full text linkDirect photocatalyzed hydrogen atom transfer (d-HAT) can be considered a method of choice for the elaboration of aliphatic C–H bonds. In this manifold, a photocatalyst (PCHAT) exploits the energy of a photon to trigger the homolytic cleavage of such bonds in organic compounds. Selective C–H bond elaboration may be achieved by a judicious choice of the hydrogen abstractor (key parameters are the electronic character and the molecular structure), as well as reaction additives. Different are the classes of PCsHAT available, including aromatic ketones, xanthene dyes (Eosin Y), polyoxometalates, uranyl salts, a metal-oxo porphyrin and a tris(amino)cyclopropenium radical dication. The processes (mainly C–C bond formation) are in most cases carried out under mild conditions with the help of visible light. The aim of this review is to offer a comprehensive survey of the synthetic applications of photocatalyzed d-HAT
Photocatalytic hydrogen atom transfer: the philosopher's stone for late-stage functionalization?
No full textAn overview about the potentialities of photocatalytic Hydrogen Atom Transfer (HAT) for the Late-Stage Functionalization (LSF) of complex molecules is offered. The examined approach allows the smooth homolytic cleavage of the C-H bonds embedded in the substrate, offering a straightforward access to valuabe C-centred radical intermediates to be exploited for the desired transformations. The examples have been classified according to the species responsible for the activation of the substrate, also showcasing the opportunities in terms of selectivity offered by the different alternatives
Synthetic Applications of Photocatalyzed Halogen-Radical Mediated Hydrogen Atom Transfer for C−H Bond Functionalization
No full textThe opportunity to activate C(sp3)-H bonds via homolytic cleavage by means of halogen radicals has long been disregarded in synthetic endeavors due to the unpredictable selectivity. Nowadays, photocatalysis has established itself as a method of choice for the generation of such reactive intermediates under mild conditions. This Minireview collects recent examples showcasing how photocatalytic manifolds have been used to tame aggressive halogen radicals to activate C(sp3)-H bonds via Hydrogen Atom Transfer (HAT) for synthetic purposes. In the last section of this work, we address site selectivity issues posed by this methodology and show how it can be guided through the judicious choice of reaction
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Decatungstate as Direct Hydrogen Atom Transfer Photocatalyst for SOMOphilic Alkynylation
Full text linkA versatile approach for the alkynylation of a variety of aliphatic hydrogen donors, including alkanes, is reported. We used tetrabutylammonium decatungstate as photocatalyst to generate organoradicals from C–H/Si–H bonds via hydrogen atom transfer. The latter intermediates underwent SOMOphilic alkynylation by methanesulfonyl alkynes to afford internal alkynes upon loss of a sulfonyl radical. The effect of different radicofugal groups on the reaction outcome was evaluated and rationalized via a combined experimental and computational approach
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