Direct Photocatalyzed Hydrogen Atom Transfer (HAT) for Aliphatic C–H Bonds Elaboration

Chemical Reviews, Год журнала: 2021, Номер 122(2), С. 1875 - 1924

Опубликована: Авг. 6, 2021

Direct photocatalyzed hydrogen atom transfer (d-HAT) can be considered a method of choice for the elaboration aliphatic C–H bonds. In this manifold, photocatalyst (PCHAT) exploits energy photon to trigger homolytic cleavage such bonds in organic compounds. Selective bond may achieved by judicious abstractor (key parameters are electronic character and molecular structure), as well reaction additives. Different classes PCsHAT available, including aromatic ketones, xanthene dyes (Eosin Y), polyoxometalates, uranyl salts, metal-oxo porphyrin tris(amino)cyclopropenium radical dication. The processes (mainly C–C formation) most cases carried out under mild conditions with help visible light. aim review is offer comprehensive survey synthetic applications d-HAT.

Язык: Английский

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Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

Chemical Reviews, Год журнала: 2021, Номер 122(2), С. 2487 - 2649

Опубликована: Ноя. 9, 2021

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do and catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) enable bond formations not constrained by rules ionic 2 electron (e) mechanisms. Instead, they 1e mechanisms capable bypassing electronic steric limitations protecting group requirements, thus enabling chemists disconnect molecules in new different ways. However, while providing similar intermediates, differ several physical chemistry principles. Understanding those differences can be key designing transformations forging disconnections. This review aims highlight these similarities between comparing their underlying principles describing impact electrochemical photochemical methods.

Язык: Английский

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Photocatalysis in the Life Science Industry

Chemical Reviews, Год журнала: 2021, Номер 122(2), С. 2907 - 2980

Опубликована: Сен. 24, 2021

In the pursuit of new pharmaceuticals and agrochemicals, chemists in life science industry require access to mild robust synthetic methodologies systematically modify chemical structures, explore novel space, enable efficient synthesis. this context, photocatalysis has emerged as a powerful technology for synthesis complex often highly functionalized molecules. This Review aims summarize published contributions field from industry, including research industrial-academic partnerships. An overview developed strategic applications synthesis, peptide functionalization, isotope labeling, both DNA-encoded traditional library is provided, along with summary state-of-the-art photoreactor effective upscaling photocatalytic reactions.

Язык: Английский

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Electroreductive Carbofunctionalization of Alkenes with Alkyl Bromides via a Radical-Polar Crossover Mechanism

Journal of the American Chemical Society, Год журнала: 2020, Номер 142(49), С. 20661 - 20670

Опубликована: Ноя. 24, 2020

Electrochemistry grants direct access to reactive intermediates (radicals and ions) in a controlled fashion toward selective organic transformations. This feature has been demonstrated variety of alkene functionalization reactions, most which proceed via an anodic oxidation pathway. In this report, we further expand the scope electrochemistry reductive alkenes. particular, strategic choice reagents reaction conditions enabled radical-polar crossover pathway wherein two distinct electrophiles can be added across highly chemo- regioselective fashion. Specifically, used strategy intermolecular carboformylation, anti-Markovnikov hydroalkylation, carbocarboxylation alkenes—reactions with rare precedents literature—by means electroreductive generation alkyl radical carbanion intermediates. These reactions employ readily available starting materials (alkyl halides, alkenes, etc.) simple, transition-metal-free display broad substrate good tolerance functional groups. A uniform protocol achieve all three transformations by simply altering medium. development provides new avenue for constructing Csp3–Csp3 bonds.

Язык: Английский

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Nickel-Catalyzed Reductive Cross-Couplings: New Opportunities for Carbon–Carbon Bond Formations through Photochemistry and Electrochemistry

CCS Chemistry, Год журнала: 2021, Номер 4(1), С. 9 - 30

Опубликована: Окт. 15, 2021

Open AccessCCS ChemistryMINI REVIEW1 Jan 2022Nickel-Catalyzed Reductive Cross-Couplings: New Opportunities for Carbon–Carbon Bond Formations through Photochemistry and Electrochemistry Liang Yi†, Tengfei Ji†, Kun-Quan Chen, Xiang-Yu Chen Magnus Rueping Yi† Institute of Organic Chemistry, RWTH Aachen University, 52074 †L. Yi T. Ji contributed equally to this work.Google Scholar More articles by author , Ji† School Chemical Sciences, University the Chinese Academy Beijing 100049 Google *Corresponding authors: E-mail Address: [email protected] King Abdullah Science Technology (KAUST), Thuwal 23955 https://doi.org/10.31635/ccschem.021.202101196 SectionsAboutAbstractPDF ToolsAdd favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Metal-catalyzed cross-electrophile couplings have become a valuable tool carbon–carbon bond formation. This minireview provides comprehensive overview recent developments in topical field couplings, explanations current state-of-the-art, highlights new opportunities arising emerging fields photoredox catalysis electrochemistry. Download figure PowerPoint Introduction Carbon–carbon formations always been one most useful reactions both industry academia gained considerable attention from many synthetic chemists who developed novel strategies achieve improved sustainable transformations. Transition metal has continually provided activation modes C–C formations1–5 fascinated long time. Many named associated with transition powerful method cross-couplings electrophiles organometallic nucleophiles (Scheme 1a). Despite progress, use reagents can cause undesired side chemical wastes. Alternatively, cross-nucleophile coupling as an efficient synthesis synthetically biologically important compounds 1b).6–8 However, lower availability carbon represents limitation. Recently, metal-catalyzed cross-coupling between two bench stable under reductive conditions emerged construction bonds. In particular, nickel (Ni) catalysts, characterized low reduction potential electronegativity, undergo rapid oxidative addition.9 As such, it is not surprising that nickel-catalyzed flourishing area organic chemistry characteristic advantages over classical synthesis, such widely available avoiding unstable time-consuming costly prefunctional processes. Scheme 1 | (a–c) cross-coupling. Thus, there significant progress development constructing The first example was published about 100 years ago Wurtz10 Tollens Fittig11 using sodium reductant mediator aryl halides alkyl halides. Stoichiometric high temperatures are needed. Therefore, functional group tolerance application limited. Another strategy electrosynthesis. Early explorations electroreductive include cross/homo-coupling halides, acyl, carboxylation cross-couplings.12 be difficult specialized laboratory equipment required. These limitations restricted further formation bonds several years. electrosynthesis recently seen renaissance cross-couplings. popular combination metallic reducing agents number Mn or Zn reductants.13–20 its success, addition scalability efficiency problems, utility powders inevitably produces excess waste. photochemical alternatives developed. impressive achievements made merging photo- electrochemistry create avoid powders. Considering construction, provide conceptual understanding 1c). Against background, we attempt give state-of-the-art highlight pathways. Alkyl–Aryl Cross-Coupling Nickel/metallic agent system viability alkyl-aryl via initially demonstrated research groups Durandetti,21 Lipshutz,22 Wangelin23 2). Specifically, Durandetti co-workers21 described α-chloroesters, well Refortmatsky reaction presence manganese metal. Lipshutz co-workers22 investigated participation zinc palladium-catalyzed halide bromide, Wangelin co-workers23 reported cobalt-catalyzed early examples combined metal/reducing systems construct milder conditions. 2 reporting catalysis. recently, more recognized general concept actively researched exciting 2010, Weix co-workers24 Ni/Mn selective equimolar quantities halide. High cross-selectivities were achieved bipyridyl phosphine ligand 3a). 3 Overview alkyl–aryl protocol, stoichiometric required, broad range tolerated. drawback, secondary bromides resulted mixed isomer products. Nevertheless, direct without intermediate organomanganese species protocol. Regarding mechanism 3b), postulated key step valent Ni(0) generates Ar–Ni(II) I. Subsequent radical affords Ar–Ni(III)–R II. Finally, elimination II desired product Ni(I) III, which could produce single-electron transfer (SET) halogen-atom abstraction. Reduction III finishes catalytic cycle. Concurrently, similar results cobalt/phosphine disclosed Amatore Gosmini25 electron-deficient bromides. After these studies, great efforts focused on different 3c).26–38 Notably, Molander co-workers39,40 successfully expanded installation fragments onto pharmaceutically relevant heterocyclic motifs. A variety aliphatic tosylates underwent moderate good yields, furnishing substituted heteroaromatic compounds. achievements, alkylamines, abundant natural feedstocks, had realized until recently. 2017, Watson co-workers41 Suzuki–Miyaura boronic acids, employing Katritzky salts C-centered-radical precursors. Very Rueping,42 Watson,43 Martin,44 Han45 independently applied cases, employed optimal reductants elevated usually Han’s Ni/Zn enabled wider substrate scope including bromoalkynes Although primary developed, tertiary easy due dominant β-hydride reaction. 2015, Gong co-workers46 resolved issue pyridine (Py) 4-(N,N-dimethylamino)pyridine (DMAP) carbene salt additives suppress enhance 4). tolerated various better obtained electron-withdrawing substituents. 4 Until now, cases form at ipso-carbon where regioselectivity less explored 5a). An migratory Zhu co-workers47 2017 5b). proceeded smoothly Ni(ClO4)2(H2O)6/6,6′-dimethyl-2,2′-bipyridyl catalyst nonactivated affording 1,1-diarylalkane derivatives, widespread products active molecules, excellent yields regioselectivity. 5 Nickel-catalyzed proposed transformation 5c. Initially, inactivated bromide leads Ni(II) complex following insertion steps deliver thermodynamically benzylic-Ni(I) III. Then, Ni(III) IV. Ni(I)-X V. then reduced powder close class also Yin co-workers,48 NiI2/bathocuproine reductant. Interestingly, opposite proposed. step, rather than I′. chain process II′ generated SET Ni(I)−X ( IV′). Several control experiments trapping carried out support their mechanism. electrophiles, types cross-couplings, enable modes, still highly desirable. During last few years, metal/photoredox dual witnessed remarkable offered unconventional transformations.49–65 To date, strongly dominated redox neutral pathway, wherein nucleophile partner changes oxidation state nickel/photoredox offers alternative absence 6). 6 representation pathway Nickel-photoredox 2016, MacMillan co-workers66–68 catalyzed 7a). Ni/photoredox mechanism, Concomitantly, hydrogen-atom abstraction tris(trimethylsilyl)silane (TTMSS) bromine radicals forms stabilized silyl intermediate. mediated radical, binds I, leading photo Ir(II). case, photoexcited generate radical. 7 (a–d) Lei co-workers,69 studies MacMillan, Et3N terminal 7b. complex. At same time, low-valent resulting intercepted species. species, Ir(II) cycles. used Vannucci co-workers,70 triethanolamine Based previous developments, Jensen co-workers71 continuously stirred-tank reactor platform flow. gram-scale after 13 h, opened up applications system. related approach Brill co-workers72 assembly drug-like benzylic chlorides (hetero)aryl continuous flow highlighting industrial applicability. Furthermore, co-workers73 bathocuproine 7c). Compared iodides, simple abundant, inexpensive, readily methods. they electrophilic partners nucleophilic aromatic substitutions. chlorides. involving substrates, aminosilane reductant, NiCl2(bim) Ir-based photocatalyst, afforded C(sp2)−C(sp3) coupled generally 7d).74 context series salts, aziridines, epoxides. co-workers,75 identified C(sp3) 4CzIPN photocatalyst NiBr2(DME)/4,4′-di-tert-butylbipyridine (dtbbpy) catalyst, differently substrates 8a). 8 (a–f) Doyle co-workers32 nickel/Mn-catalyzed styrenyl aziridines iodides. drawback aziridine did work 8b). study co-workers76 constituted strategy. Their way newly showed scope. iodides NiBr2(DME)/dtbbpy catalyst. able cyclic classic methods, 8c). 8d. iodide β-iodoamine IV formed ring-opening aziridine. Subsequently, 4CzIPN−• Ni(I)−I III). I Then [4-CzIPN]−• nickel/Mn gave MnI2 instead β-iodoamine; thus, no obtained. Continued co-workers77 epoxides 8e). Ni/Ti/photoredox Various styrene oxides, epoxides, all reacted regioselectivities. Allylic carbonates proven suitable cross-couplings.78–80 nice Chu co-workers81 allylic vinyl triflates 8f). E- Z-configured 1,4-dienes choice photocatalysts. When Ir(ppy)2(dtbbpy)+ photoinduced contra-thermodynamic E→Z isomerization would occur (Z)-1,4-diene product.81 strategies, them rely potentials photocatalysts furnish addition, appealing when considering toxicity cost photoactive electron-donor-acceptor (EDA) allows generation mild based-photocatalysts dyes. strategy, co-workers82 EDA N-hydroxyphthalimide (NHPI) esters. proceeds NHPI ester Hantzsch (HE), upon radiation-induced (eq 1).82 Electrochemical may offer economical Recent ability bond-forming reactions. Within area, electrochemically induced integrating 9). seminal chloroesters electrochemical strategy.12 breakthrough very Hansen co-workers83 10a). sacrificial anode tuning found crucial cooperative circumvented need temperatures. exhibited generality. 9 10 aryl–alkyl Further Bio co-workers84 Hansen’s method, esters source amine divided cell 10b). Later, one-pot C(sp2)–C(sp3) Loren co-workers85 10c), redox-active situ carboxylates tetramethyluronium hexafluorophosphate. Sevov co-workers86 shuttles protect reduction, thus improving suppressing side-product 10d). across wide aryl, heteroaryl, Given importance concurrently, Rueping87 Mei88 11a). Both methods scope, giving rise corresponding derivatives yields. experimental density theory (DFT) co-workers87 plausible 11b). 11 (a b) cathode surface. gives Ar−Ni(I) occurs Ar−Ni(II)−Br cathodic will benzylic-Ni(II) release regenerate Ni(0). Aryl–Aryl Cross-Couplings comparison bonds, C(sp2)–C(sp2) challenging result subtle difference electrophiles. 2008, Gosmini89 unsymmetrical biaryl success reactivity profiles allowed extended 2-halopyridine group.90 co-workers91 selectivities controlled catalysts electronic properties reports 12a). Mechanistically, react exclusively Pd(0) Pd(II) transmetalation complex, Ar1–Pd(II)–Ar2 IV, asymmetrical biaryls. additive potassium fluoride (KF) achieving selectivity, presumably selectivity palladium triflate bromide. Olivares Weix92 other triflates, triflates,93 tosylates,94 ortho-fluoro-substituted amides,95 difluoromethyl 2-pyridyl sulfone,96 bromides, 2,2-difluorovinyl tosylate.97 12 aryl–aryl co-workers98 polyfluorinated arenes 12b). protocol opens entry multifluorinated starts generating [C5F5N]•− C5F5N, trapped II′. III′, Also, Ni(0)/Ni(I)/Ni(III)/Ni(I) cycle possible, involves Ni(I)–C5F4N IV′) Besides aryl-heteroarybond regard, Léonel co-workers99–102 heteroaryls, 3-chloro-6-methoxypyridazines, 3-amino-6-chloropyridazines, chloropyrimidines 12c). Alkyl–Alkyl discussed above,

Язык: Английский

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Switchable Divergent Synthesis Using Photocatalysis

ACS Catalysis, Год журнала: 2022, Номер 12(3), С. 1857 - 1878

Опубликована: Янв. 20, 2022

A highly selective and divergent synthesis enables access to various molecules has garnered broad interest from not only organic chemists but also medicinal biologists who work with chemical libraries. Since the 20th century, such transformations have been achieved using transition-metal-catalyzed reactions, in which choice of catalyst or ligand crucially affects selectivity. Over past several decades, photocatalysts attracted a considerable amount attention because they provide additional ways control reaction intermediates product selectivity via electron energy transfer. From this perspective, we highlight recent development switchable syntheses photocatalysts, are difficult achieve classical catalytic transformations.

Язык: Английский

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Halogen-bond-assisted radical activation of glycosyl donors enables mild and stereoconvergent 1,2-cis-glycosylation

Nature Chemistry, Год журнала: 2022, Номер 14(6), С. 686 - 694

Опубликована: Апрель 11, 2022

Язык: Английский

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A Triple Photoredox/Cobalt/Brønsted Acid Catalysis Enabling Markovnikov Hydroalkoxylation of Unactivated Alkenes

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(18), С. 7953 - 7959

Опубликована: Апрель 27, 2022

We demonstrate Markovnikov hydroalkoxylation of unactivated alkenes using alcohols through a triple catalysis consisting photoredox, cobalt, and Brønsted acid catalysts under visible light irradiation. The realizes three key elementary steps in single catalytic cycle: (1) Co(III) hydride generation by photochemical reduction Co(II) followed protonation, (2) metal hydrogen atom transfer (MHAT) hydride, (3) oxidation the alkyl complex to Co(IV). precise control protons electrons allows elimination strong acids external reductants/oxidants that are required conventional methods.

Язык: Английский

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Electrochemical radical-polar crossover: a radical approach to polar chemistry

Science China Chemistry, Год журнала: 2023, Номер 67(2), С. 450 - 470

Опубликована: Ноя. 3, 2023

Язык: Английский

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Photodriven Radical-Polar Crossover Cyclization Strategy: Synthesis of Pyrazolo[1,5-a]pyridines from Diazo Compounds

Organic Letters, Год журнала: 2024, Номер 26(12), С. 2511 - 2516

Опубликована: Март 20, 2024

This work demonstrates the synthesis of a variety perfluoroalkyl heterocycles via visible-light-driven radical-polar crossover cyclization strategy. In this process, single-electron reduction/SNV-type/cyclization sequences follow radical addition reaction diazoester, which differs from current role diazoesters as precursors/acceptors. transformation excellent functional group compatibility and allows for modification many bioactive molecules with diazoesters. Such could represent novel approach to photochemical diazo compounds.

Язык: Английский

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