Metallaphotoredox catalysis with organic dyes
Andrea GualandiMichele AnselmiFrancesco CalogeroSimone PotentiElena BassanPaola CeroniPier Giorgio Cozzi
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Here…comes the fun…Combination of metals and organic photocatalysts allows the practical invention of new methodologies!Keywords:
Photoredox catalysis
Organic Synthesis
Organic reaction
ConspectusPhotoredox catalysis has emerged as a powerful tool for the utilization of visible light to drive chemical reactions between organic molecules that exhibit two rather ubiquitous properties: colorlessness and redox-activity. The photocatalyst, however, requires significant absorption in the visible spectrum and reversible redox activity. This very general framework has led to the development of several new modes of reactivity based on electron and energy transfer steps between photoexcited catalyst states and various organic molecules. In the past years, major effort has been devoted to photoredox-catalytic aromatic substitutions involving an initial reductive activation of various aryl electrophiles by the photocatalyst, which opens a new entry into selective arene functionalizations within organic synthesis endeavors. This, however, has led to a unilateral emphasis of synthetic developments including catalyst modifications, substrate scope studies, and combinations with other chemical processes.This Account summarizes recent reports of new protocols for the synthesis of aromatic esters, thioethers, boronates, sulfonates, heterobiaryls, deuteroarenes, and other functionalized arenes under mild photoredox conditions with organic dyes. On the other hand, mechanistic studies were largely neglected. This Account emphasizes the most relevant experiments and techniques, which can greatly assist in the exploration of the mechanistic foundation of aromatic photoredox substitutions and the design of new chemical reactivities. The nature and physicochemical properties of the employed organic dyes, the control of its acid–base chemistry, the choice of the irradiation sources, and the concentrations of substrates and dyes are demonstrated to decisively affect the activity of organic photocatalysts, the chemo- and regioselectivities of reactions, and the operating mechanisms. Several methods of distinction between photocatalytic and radical chain processes are being discussed such as the determination of quantum yields by conventional actinometric studies or modern photon counter devices. Careful analyses of key thermodynamic and kinetic data of the single electron transfer steps involved in aromatic photoredox substitutions by experimental and theoretical techniques are being exemplified with recent examples from the literature including the determination of redox potentials by DFT and CV, fluorescence quenching studies, and transient absorption/emission spectroscopy. This Account provides the uninitiated reader with an overview of the potential of organic photoredox catalysis for aromatic substitution reactions and encourages the practitioners to consult highly instructive synthetic, mechanistic, theoretical, and spectroscopic tools that are available in research laboratories.
Photoredox catalysis
Organic Synthesis
Reactivity
Organic reaction
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Preface / Part I: Microwave Assisted Organic Synthesis - Introduction / Microwave Assisted Organic Reactions in Water / Microwave Assisted Organic Reactions in Organic Solvents / Microwave Assisted Reactions in Solid State / Miscellaneous Reactions / Part II: Ultrasound Assisted Organic Synthesis - Introduction / Homogeneous Sonochemical Reactions / Heterogeneous Liquid - Liquid Reactions / Heterogeneous Solid - Liquid Reactions / Miscellaneous Applications / Part III: Solid State Solvent Free Organic Synthesis - Introduction / Solid State Organic Synthesis at Room Temperature / Solid State Organic Synthesis by Slight Warming of the Reactants / Miscellaneous Reactions / Part IV: Photoinduced Organic Synthesis / Introduction / Photochemical Reactions / Industrial Applications of Photochemistry / Miscellaneous Photochemical Reactions.
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Photochemical reactions have been attracting increasing attention owing to their efficiency and inherent sustainability. However, the photochemical reactions have provided few practical reactions for organic synthesis so far. This short review provides a recent development of organic reactions with photoredox catalysis which allows various transformations practically with visible light.
Photoredox catalysis
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Visible spectrum
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A fundamental challenge in the field of catalysis is the development of sustainable and efficient methods for the activation of molecules. One approach for the activation of organic molecules that has recently received much attention is photoredox catalysis with visible light. On the other hand, the application of aryl radicals in organic synthesis is challenging, but very useful. This thesis describes the generation of aryl radicals and their application in organic synthesis, such as the direct arylation of heteroarenes, the synthesis of benzothiophenes, phenanthrenes and the amino arylation of alkenes using visible light photoredox catalysis. In addition, the synthesis of substituted tetrahydroisoquinolines is described.
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Abstract Review: 53 refs.
Photoredox catalysis
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Site-selective peptide functionalization provides a straightforward and cost-effective access to diversify peptides for biological studies. Among many existing non-invasive peptide conjugations methodologies, photoredox catalysis has emerged as one of the powerful approaches for site-specific manipulation on native peptides. Herein, we report a highly N-termini-specific method to rapidly access itaconated peptides and their derivatives through a combination of transamination and photoredox conditions. This strategy exploits the facile reactivity of peptidyl-dihydropyridine in the complex peptide settings, complementing existing approaches for bioconjugations with excellent selectivity under mild conditions. Distinct from conventional methods, this method utilizes the highly reactive carbamoyl radical derived from a peptidyl-dihydropyridine. In addition, this itaconated peptide can be further functionalized as a Michael acceptor to access the corresponding peptide-protein conjugate.
Photoredox catalysis
Transamination
Conjugate
Posttranslational modification
Bioconjugation
Reactivity
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Abstract Site‐selective peptide functionalization provides a straightforward and cost‐effective access to diversify peptides for biological studies. Among many existing non‐invasive peptide conjugations methodologies, photoredox catalysis has emerged as one of the powerful approaches for site‐specific manipulation on native peptides. Herein, we report a highly N ‐termini‐specific method to rapidly access itaconated peptides and their derivatives through a combination of transamination and photoredox conditions. This strategy exploits the facile reactivity of peptidyl‐dihydropyridine in the complex peptide settings, complementing existing approaches for bioconjugations with excellent selectivity under mild conditions. Distinct from conventional methods, this method utilizes the highly reactive carbamoyl radical derived from a peptidyl‐dihydropyridine. In addition, this itaconated peptide can be further functionalized as a Michael acceptor to access the corresponding peptide‐protein conjugate.
Photoredox catalysis
Transamination
Conjugate
Bioconjugation
Posttranslational modification
Reactivity
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Here…comes the fun…Combination of metals and organic photocatalysts allows the practical invention of new methodologies!
Photoredox catalysis
Organic Synthesis
Organic reaction
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Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions, and redox reactions. In organic synthesis, organic reactions are used in the construction of new organic molecules. The production of many man-made chemicals such as the production of pharmaceuticals drugs, plastics, food additives, fabrics depends on organic reactions. Factors governing organic reactions are essentially the same as that of any chemical reaction. Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation, hyperconjugation, and aromaticity and the presence and stability of reactive intermediates such as free radicals, carbocations, and carbanions. An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity, and enantioselectivity is, therefore, an important criterion for many organic reactions. There is no limit to the number of possible organic reactions and mechanisms. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed description of steps is not always clear from a list of reactants alone. Organic reactions can be organized into several basic types. Some reactions fit into more than one category. For example, some substitution reactions follow an addition-elimination pathway. This overview isn't intended to include every single organic reaction. Rather, it is intended to cover the basic reactions.
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