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Journal ArticleDOI: 10.1002/TCR.202100010

Recent Advances in Functionalization of Pyrroles and their Translational Potential.

02 Mar 2021-Chemical Record (John Wiley & Sons, Ltd)-Vol. 21, Iss: 4, pp 715-780
Abstract: 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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8 results found

Journal ArticleDOI: 10.1039/D1OB01455B
Saumitra Sengupta1, Parthasarathi Das1Institutions (1)
Abstract: Ring substitution reactions of nitroarenes remain an under-developed area of organic synthesis, confined to the narrow domains of SNAr and SNArH reactions. While searching for alternative methodologies, we took stock of the C–H activation reactions of nitroarenes which unearthed a variety of examples of nitro directed regioselective C–H functionalization reactions such as ortho-arylation, -benzylation/alkylation, and -allylation, oxidative Heck and C–H arylation reactions on (hetero)aromatic rings. A collective account of these reactions is presented in this review to showcase the existing landscape of C–H activation reactions of nitroarenes, to create interest in this field for further development and propagate this strategy as a superior alternative for ring substitution reactions of nitroarenes. The prospect of merging the C–H activation of nitroarenes with C–NO2 activation, thereby harnessing NO2 as a transformable multitasking directing group, is also illustrated.

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Topics: Substitution reaction (50%)

1 Citations

Open accessJournal ArticleDOI: 10.1007/S42823-021-00252-3
Samuel Ghomsi Wabo1, Olaf Klepel1Institutions (1)
03 May 2021-Carbon letters
Abstract: The simultaneous use of KOH and nitrogen to manufacture carbon materials provides these materials with properties that the presence of only one of these additives would not give them, such as high porosity and reactivity. However, it is difficult to obtain nitrogen-doped carbon materials with both high porosity and high nitrogen content, as the KOH significantly reduces the nitrogen content. In this review the complex relationships between nitrogen content and nitrogen precursor amount, KOH amount and the activation temperature are discussed, with a focus on the different N-functional groups and the porosity of the fabricated carbons. Generally, increasing activation temperature and increasing KOH amount decrease the nitrogen content due to reactions with the N-containing substructures of carbon, resulting in the release of nitrogen as N2, HCN and other N gases. Increasing these parameters can also result in the reduction of pyridine-N while the amount of quaternary-N increases simultaneously. Besides this, an increase in the amount of nitrogen precursor leads to an increase in the porosity of N-doped materials. However, too high amounts of the nitrogen precursor generate an excess of nitrogen which blocks the pore system and consequently reduces the porosity of the doped carbons.

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Topics: Nitrogen (55%), Porosity (53%), Carbon (52%)

1 Citations

Journal ArticleDOI: 10.1142/S1088424621500619
Abstract: The synthesis of dipyrromethanes from pyrrole and arylglyoxylic acids in the presence of K2S2O8at 90 ∘C is reported affording dipyrromethanes in very good yields. Unlike an excess pyrrole tradition...

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Topics: Porphyrin (53%), Pyrrole (52%)


192 results found

Abstract: The asymmetric conjugate addition of various carbon and heteroatom nucleophiles to nitroalkenes as a tool for the construction of highly functionalized synthetic building blocks is presented. Diastereoselective, substrate-controlled 1,4-additions are also included. Besides auxiliary controlled asymmetric Michael additions, external asymmetric versions employing enantiopure additives, addition-elimination processes with enantiopure leaving groups, and catalytic asymmetric syntheses are described. The use of the highly reactive nitroalkenes as Michael acceptors opens the way to synthetically very useful C−C and C−X bond-forming reactions and subsequent transformations as is demonstrated by various applications. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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Topics: Enantioselective synthesis (57%), Heteroatom (54%)

738 Citations

Journal ArticleDOI: 10.1021/JA212099R
Abstract: Visible light along with 1 mol % eosin Y catalyzes the direct C–H bond arylation of heteroarenes with aryl diazonium salts by a photoredox process. We have investigated the scope of the reaction for several aryl diazonium salts and heteroarenes. The general and easy procedure provides a transition-metal-free alternative for the formation of aryl–heteroaryl bonds.

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Topics: Meerwein arylation (61%), Aryl (54%)

541 Citations

Journal ArticleDOI: 10.1126/SCIENCE.1258232
07 Nov 2014-Science
Abstract: Biological photosynthesis uses the energy of several visible light photons for the challenging oxidation of water, whereas chemical photocatalysis typically involves only single-photon excitation. Perylene bisimide is reduced by visible light photoinduced electron transfer (PET) to its stable and colored radical anion. We report here that subsequent excitation of the radical anion accumulates sufficient energy for the reduction of stable aryl chlorides giving aryl radicals, which were trapped by hydrogen atom donors or used in carbon-carbon bond formation. This consecutive PET (conPET) overcomes the current energetic limitation of visible light photoredox catalysis and allows the photocatalytic conversion of less reactive chemical bonds in organic synthesis.

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Topics: Photoredox catalysis (59%), Photoinduced electron transfer (57%), Electron transfer (54%) ... show more

539 Citations

Journal ArticleDOI: 10.1021/JA511011M
Abstract: The first cobalt-catalyzed cyanation, halogenation, and allylation via C–H activation have been realized. These formal SN-type reactions generate valuable (hetero)aryl/alkenyl nitriles, iodides, and bromides as well as allylated indoles using a bench-stable Co(III) catalyst. High regio- and mono-selectivity were achieved for these reactions. Additionally, allylation proceeded efficiently with a turnover number of 2200 at room temperature, which is unprecedented for this Co(III) catalyst. Alkenyl substrates and amides have been successfully utilized in Cp*Co(III)-catalyzed C–H activation for the first time.

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Topics: Cyanation (65%), Halogenation (59%), Catalysis (51%) ... show more

411 Citations

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