Photochemical Functionalization of Helicenes

Jakubec, Martin; Ghosh, Indrajit; Storch, Jan; König, Burkhard

doi:10.1002/chem.201904169

Cited by 14 publications

(8 citation statements)

References 56 publications

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“…The photochemical reaction protocols permits the regiospecific and classic late‐stage functionalization of helicenes that can be effortlessly brought about either through the activation of C(sp 2 )−Br bonds in helicenes utilizing K 2 CO 3 as inorganic base or direct C(sp 2 )−H helicene bond functionalization by means of oxidative photoredox conditions (Scheme 171). [189] …”

Section: Photochemical Methods Of C−h Functionalizationmentioning

confidence: 99%

Recent Advances in Functionalization of Pyrroles and their Translational Potential

Hunjan

Panday

Gupta

et al. 2021

The Chemical Record

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Among the known aromatic nitrogen heterocycles, pyrrole represents a privileged aromatic heterocycle ranging its occurrence in the key component of “pigments of life” to biologically active natural products to active pharmaceuticals. Pyrrole being an electron‐rich heteroaromatic compound, its predominant functionalization is legendary to aromatic electrophilic substitution reactions. Although a few excellent reviews on the functionalization of pyrroles including the reports by Baltazzi in 1963, Casiraghi and Rassu in 1995, and Banwell in 2006 are available, they are fragmentary and over fifteen years old, and do not cover the modern aspects of catalysis. A review covering a comprehensive package of direct functionalization on pyrroles via catalytic and non‐catalytic methods including their translational potential is described. Subsequent to statutory yet concise introduction, the classical functionalization on pyrroles using Lewis acids largely following an ionic mechanism is discussed. The subsequent discussion follows the various metal‐catalyzed C−H functionalization on pyrroles, which are otherwise difficult to implement by Lewis acids. A major emphasize is given on the radical based pyrrole functionalization under metal‐free oxidative conditions, which is otherwise poorly highlighted in the literature. Towards the end, the current development of pyrrole functionalization under photocatalyzed and electrochemical conditions is appended. Only a selected examples of substrates and important mechanisms are discussed for different methods highlighting their scopes and limitations. The aromatic nucleophillic substitution on pyrroles (being an electron‐rich heterocycle) happened to be the subject of recent investigations, which has also been covered accentuating their underlying conceptual development. Despite great achievements over the past several years in these areas, many challenges and problems are yet to be solved, which are all discussed in summary and outlook.

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Section: Photochemical Methods Of C−h Functionalizationmentioning

confidence: 99%

Recent Advances in Functionalization of Pyrroles and their Translational Potential

Hunjan

Panday

Gupta

et al. 2021

The Chemical Record

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“…Storch and König studied both reductive and oxidative light-induced transformations of helicene derivatives . They showed that bromohelicenes can generate helicenyl radicals upon irradiation with blue light in the presence of potassium carbonate in DMSO (Scheme A, transformations of 9-bromo[7]helicene ( 55 ) are shown as representative examples).…”

Section: Transformation Of Reactive Functional Groupsmentioning

confidence: 99%

“…Storch and Konig studied both reductive and oxidative lightinduced transformations of helicene derivatives. 44 They showed that bromohelicenes can generate helicenyl radicals upon irradiation with blue light in the presence of potassium carbonate in DMSO (Scheme 11A, transformations of 9bromo [7]helicene (55) are shown as representative examples). This species can be subsequently reacted with a suitable trapping agent, ranging from various heterocycles (pyrrole, thiophene, furan, indole) to heteroatomic compounds, such as triethyl phosphite, dimethyldisulfide, or bis(pinacolato)diboron.…”

Section: Transformation Of Reactive Functionalmentioning

confidence: 99%

Recent Advances in Functionalizations of Helicene Backbone

Jakubec

Storch

2020

J. Org. Chem.

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of twisted arylamines into their respective o-diketones by aerial oxygen (Scheme 4D). 16 The reaction is self-catalytic; the arylamine sensitizes formation of singlet oxygen, which then oxidizes the amine-substituted double bond via [2 + 2]cycloaddition. This method was used for preparation of 5 different derivatives, including very densely functionalized tetraketones 19d and 19e.1.3. C−H Activation. Reactions proceeding via the activation of the C−H bond represent a very valuable approach to the preparation of new molecules since they require little to no presubstitution and can provide valuable helicene derivatives with high regioselectivity. An example of C−H borylation was published by Necǎs and co-workers (Scheme 5A). 30,31 They used an iridium catalyst for the introduction of a pinacolboronate group with certain regioselectivity toward positions 2 and 3 of the helicene. The [4]helicene 20a showed 65% isolated yield of both regioisomers in 2.8:1 ratio. Longer [5]helicene 20b showed increased yield (89%) and regioselectivity (8:1) after the authors opted for a different catalytic system than in the first example. Both isomers were separated using HPLC, and the authors further explored their reactivity in several Suzuki coupling reactions. The same transformation was accomplished on carbazole-based helicene 22, although with low yield (Scheme 5B).

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“…78 Non-C-H photocatalyzed phosphinylation systems that involve a carbon radical species have also been reported in the literature, such as the phosphonylation of aryl halides/triflates, 79 arylazosulfones, 80 benzotriazoles 81 or bromo [6]helicenes. 82 In pioneering work, Barton, in 1993, used a photogenerated carbon radical to attack directly white phosphorus and obtained phosphonic acids in good yields after oxidative work-up. 83…”

Section: Review Synthesismentioning

confidence: 99%

Shining Light on the Light-Bearing Element: A Brief Review of Photomediated C–H Phosphorylation Reactions

Ung¹,

Mechrouk²,

Li³

2020

Synthesis

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Organophosphorus compounds have numerous useful applications, from versatile ligands and nucleophiles in the case of trivalent organophosphorus species to therapeutics, agrochemicals and material additives for pentavalent species. Although phosphorus chemistry is a fairly mature field, the construction of C–P(V) bonds relies heavily on either prefunctionalized substrates such as alkyl or aryl halides, or requires previously oxidized bonds such as C=N or C=O, leading to potential sustainability issues when looking at the overall synthetic route. In light of the recent advances in photochemistry, using photons as a reagent can provide better alternatives for phosphorylations by unlocking radical mechanisms and providing interesting redox pathways. This review will showcase the different photomediated phosphorylation procedures available for converting C–H bonds into C–P(V) bonds.1 Introduction1.1 Organophosphorus Compounds1.2 Phosphorylation: Construction of C–P(V) Bonds1.3 Photochemistry as an Alternative to Classical Phosphorylations2 Ionic Mechanisms Involving Nucleophilic Additions3 Mechanisms Involving Radical Intermediates3.1 Mechanisms Involving Reactive Carbon Radicals3.2 Mechanisms Involving Phosphorus Radicals3.2.1 Photoredox: Direct Creation of Phosphorus Radicals3.2.2 Photoredox: Indirect Creation of Phosphorus Radicals3.2.3 Dual Catalysis3.3 Photolytic Cleavage4 Conclusion and Outlook

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Photochemical Functionalization of Helicenes

Cited by 14 publications

References 56 publications

Recent Advances in Functionalization of Pyrroles and their Translational Potential

Recent Advances in Functionalization of Pyrroles and their Translational Potential

Recent Advances in Functionalizations of Helicene Backbone

Shining Light on the Light-Bearing Element: A Brief Review of Photomediated C–H Phosphorylation Reactions

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