Recent Advances in Paired Electrosynthesis

The Chemical Record, Год журнала: 2021, Номер 21(9), С. 2585 - 2600

Опубликована: Апрель 8, 2021

Progress in electroorganic synthesis is linked to innovation of new synthetic reactions with impact on medicinal chemistry and drug discovery the desire minimise waste provide energy-efficient chemical transformations for future industrial processes. Paired electrosynthetic processes that combine use both anode cathode (convergent or divergent) minimal (or without) intentionally added electrolyte need additional reagents are growing interest. In this overview, recent progress developing paired electrolytic surveyed. The discussion focuses electrosynthesis technology proven value preparation small molecules. Reactor types contrasted concept translating light-energy driven photoredox into highlighted as a newly emerging trend.

Язык: Английский

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Electrooxidative palladium- and enantioselective rhodium-catalyzed [3 + 2] spiroannulations

Chemical Science, Год журнала: 2022, Номер 13(9), С. 2783 - 2788

Опубликована: Янв. 1, 2022

Despite indisputable progress in the development of electrochemical transformations, electrocatalytic annulations for synthesis biologically relevant three-dimensional spirocyclic compounds has as yet not been accomplished. In sharp contrast, herein, we describe palladaelectro-catalyzed C-H activation/[3 + 2] spiroannulation alkynes by 1-aryl-2-naphthols. Likewise, a cationic rhodium(iii) catalyst was shown to enable electrooxidative [3 spiroannulations via formal C(sp3)-H activations. The versatile featured broad substrate scope, employing electricity green oxidant lieu stoichiometric chemical oxidants under mild conditions. An array enones and diverse spiropyrazolones, bearing all-carbon quaternary stereogenic centers were thereby accessed user-friendly undivided cell setup, with molecular hydrogen sole byproduct.

Язык: Английский

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Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects

CCS Chemistry, Год журнала: 2021, Номер 4(5), С. 1796 - 1805

Опубликована: Июнь 29, 2021

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2022Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects Yangye Jiang, Kun Xu and Chengchu Zeng Jiang Faculty of Environment Life, Beijing University Technology, 100124 , *Corresponding authors: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.021.202101010 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Trialkylsilanes are important building blocks in organic synthesis; however, their widespread use redox chemistry is limited high oxidation potentials comparably bond dissociation energies (BDEs) α–Si–C–H bonds (>92 kcal mol−1). Herein, we report a new strategy for homolysis enabled the synergistic combination electrooxidation, photoinduced ligand-to-metal charge transfer (LMCT), radical-mediated hydrogen atom (HAT). polarity-matching effect, HAT electrophilic MeO· or [Cl-OHCH3]· from more hydridic instead C–H allows selective generation silyl radicals. This electrophotocatalytic protocol provides rapid access Si-functionalized benzimidazo-fused isoquinolinones with broad functional-group compatibility. Mechanistic studies have shown that n-Bu4NCl essential electrooxidation CeCl3 form Ce(IV) species. Download figure PowerPoint Introduction Organosilanes great interest fields medicinal chemistry,1,2 synthesis,3,4 electronics.5,6 Currently, most attractive approach Si-incorporation involves interception radicals alkenes heterocycles. In this regard, homolytic cleavage liable Si–X (X = Si,7,8 B,9 COOH,10 etc.11–13) has been identified as powerful tool obtain A practical economic alternative silicon hydrides. The classical activation relies on stoichiometric peroxide an initiator (Scheme 1a).14–18 However, limitations include harsh conditions functional group incompatibility driven identification strategies activation. Recently, photoredox catalysis19–28 emerged appealing radical formation substrates were invariably phenylsilanes (TMS)3SiH labile 1b).11,29–35 As pioneered Fagnoni et al.,36 decatungstate was found be effective (HAT) photocatalyst aromatic tertiary silanes 1c). Nevertheless, only poor selectivities observed trialkylsilanes owing mol−1).37 Wu colleagues38,39 recently developed mild generally applicable platform using quinuclidin-3-yl acetate triisopropylsilanethiol highly reagent 1d). Considering valuable synthetic utilities radicals, establishment mechanistically readily available remains desirable but synthetically challenging. Scheme 1 | (a–e) Representative produce Organic electrosynthesis utilizes electron reactive intermediates sustainable manner. Its application carbon- heteroatom-centered therefore flourishing over past decade.40–55 comparison carbon electrochemical largely unexplored. Lin coworkers56 reported elegant electroreductive Si–Cl-containing compounds Mg sacrificial anode. Aligned our ongoing electrosynthesis,57–59 intrigued possibility electrochemically generating starting trialkylsilanes. direct hydrides results compatibility selectivity, mainly due hydrides.60 Since without limitation potentials,61,62 synergy opportunities at much lower operating than those analogous electrooxidations. Among many reagents, envision should ideal following reasons: (1) Hydrogen abstraction (BDE up 96 mol−1)63 O–H: 105 mol−1)64 thermodynamically favorable; (2) electronegative (electronegativity 2.2 vs 1.9 Pauling scale), triggered would preferably occur according effect65; (3) byproduct MeOH generated process easily removed reaction mixture. success proposal hinges facile energetically challenging potential subsequently trigger afford desired Motivated seminal works Zuo66–71 who proved RO· alcohols via cerium-catalyzed herein combines LMCT, methoxyl-radical-mediated 1e). BDEs activated through polarized transition state. utility electrophotocatalytic72–79 demonstrated compatibility, which prevalent biologically active molecules advanced materials.80,81 Our working hypothesis inspired recent reports demonstrating alkoxy LMCT excitation Ce(IV)-OR complexes.66–70,82–89 2, anodically could coordinate transient Ce(IV)-OMe, can undergo give MeO·. MeO · preference situ chlorine cannot excluded moment.90 Subsequently, intercepted compound B, triggers cyclization followed proton release deliver isoquinolinone E product. two main challenges must solved realize mechanistic hypothesis. First, relatively low concentration. Otherwise, competition between during lead selectivity. Second, Ce(IV)-OMe complex quickly avoid its cathodic reduction. 2 Experimental Methods General procedure electrophotochemical synthesis: An undivided cell equipped felt anode (1.0 × 1.0 cm2) foamed nickel cathode connected current (DC) regulated power supply. To added (0.3 mmol), mL), CeCl3·7H2O (0.06 mmol, 20 mol %), CH3CN:cholorobenzene (5 mL, V/V 1:1). placed 3 cm away light-emitting diodes (LEDs) (390 nm, W). mixture electrolyzed constant (2 mA) 50 °C under magnetic stirring. When thin-layer chromatography (TLC) analysis indicated electrolysis complete (witnessed disappearance 1), solvent distillation. product then extracted dichloromethane (DCM) (3 dried Na2SO4, concentrated vacuo. residue purified column silica gel pure Further details including experimental procedures additional data Supporting Information. Results Discussion Following hypothesis, parameters established 1a triethylsilane ( 2a) model (Table 1). Ni foam catalyst, MeOH/CH3CN/chlorobenzene electrolytic solution, while being irradiated W 390 nm LEDs 9 h, polycyclic 3aa obtained 66% yield (entry Replacing graphite plate changing led decreased yields (entries 3). optimization density showed mA/cm2 optimal 4 5). Reducing amount silane Ce catalyst 6 7). Anhydrous similar efficiency compared 8). choice precursor had significant influence chemical yield. Decreasing increasing afforded 10). chlorobenzene other halogenated benzenes PhCF3 PhBr failed 11 12). Irradiation 440 white light reduced 49% 31%, respectively 13 14). series control experiments cerium MeOH, irradiation, all transformation 15–18), showcasing cooperation photocatalysis. Table Optimization Reaction Conditionsa Entry Deviation Standard Conditions Yield (%)b None 66 Graphite 43 44 I mA 5 42 Et3SiH (0.7 mL) 37 7 (0.03 mmol) 31 8 67 (0.05 39 10 (0.2 56 PhCl Trace 12 1,3-Dichlorobenzene 0 49 14 White 15 No 16 17 18 electricity aReaction conditions: 2a (1 (0.1 CH3CN:chlorobenzene (1:1, (working area: cm2), cell, mA, (20 W), °C, h. bIsolated With established, began examine substrate scope 3, excellent affording corresponding products 3a– 3f 81% yield, competitive adjacent not observed. Aromatic tolerated well, Si-products 3g– 3i 73% 1,4-bis(dimethylsilyl)benzene employed substrate, one underwent tandem furnish 3j 39% (TMS)3SiH, BDE, suitable generate 3k 72% trimethoxysilane 3l probably instability radical. unstable even electrolysis, decomposition major side these transformations. hydrosilanes. 2a–2l mL liquid hydrides, mmol solid hydrides), CH3CN: (V/V 1:1, h; isolated Having hydride scope, next focused determining N-substituted benzimidazole derivatives. 4, variety benzimidazoles reactions smoothly Si-incorporated 4– good moderate yields. For Ar1 moiety, presence electron-donating groups systems containing electron-withdrawing substituents 6). Ar2 both (OMe) -withdrawing (CN) well-tolerated 16). alkene 11), borate 13), ester 14), sulfonate 15), nitrile 16) compatible conditions, giving 67% R methyl phenyl 17). Notably, derived l-menthol, (–)-nopol, diacetone-d-glucose also 18– 64% thus preparative transformation. benzimidazoles. 2c addition benzimidazoles, indole 22 71% construction indole-based gain insight into mechanism, cyclic voltammetry (CV) conducted (Figure (curves b c), suggests might proceed simultaneously. CV did display obvious peak (curve e), 0.68 V g). tetrabutylammonium salts n-Bu4NI, n-Bu4NBr, n-Bu4NPF6 (see Information Figure S3–S5 details). These reveal exogenous chloride Ce(III) species subsequent needed reagent. information coupled reagents moiety 1a, leads us proposed cycle Ce(IV). related 0.1 M LiClO4/CH3CN/PhCl/MeOH Pt disk electrode, wire counter Ag/AgNO3 CH3CN) reference electrode: Background, mM), (4) background, (5) (6) (7) (9 mM) + mM). further demonstrate electrooxidative assisted chloride, UV–vis carried out. CH3CN/MeOH absorption band λmax 250 nm. After min, appeared 395 consistent evidence highest irradiation when replace n-Bu4NPF6, no shift after S7 spectra solution 1:1 before (black line) (red line). Conclusions We synergistically combining BDEs. scenario makes electrons clean oxidants earth-abundant salt induce turn acts activate selectively effect. entry diversified isoquinolinones. methodology basis functionalization inert currently investigation laboratory. includes general considerations, detailed procedures, spectral characterization, voltammograms, data. Conflict Interest There conflict report. Funding work supported grants National Key Technology R&D Program (no. 2017YFB0307502), Natural Science Foundation China 21871019), Municipal Education Committee Project (nos. KZ202110005003 KM202110005006). References 1. Ramesh R.; Reddy D. S.Quest Novel Chemical Entities Incorporation Silicon Drug Scaffolds.J. Med. Chem.2018, 61, 3779–3798. Google Scholar 2. Franz A. K.; Wilson S. 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Язык: Английский

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Electrophotocatalytic C−H Functionalization of N‐Heteroarenes with Unactivated Alkanes under External Oxidant‐Free Conditions

ChemSusChem, Год журнала: 2021, Номер 15(6)

Опубликована: Дек. 30, 2021

The Minisci alkylation of N-heteroarenes with unactivated alkanes under external oxidant-free conditions provides an economically attractive route to access alkylated but remains underdeveloped. Herein, a new electrophotocatalytic strategy alkyl radicals from strong C(sp3 )-H bonds was reported for the following reactions in absence chemical oxidants. This realized first example cerium-catalyzed reaction directly abundant excellent atom economy. It is anticipated that general design principle would enrich catalytic strategies explore functionalizations H2 evolution.

Язык: Английский

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Electrochemical C–H phosphorylation of arenes in continuous flow suitable for late-stage functionalization

Nature Communications, Год журнала: 2021, Номер 12(1)

Опубликована: Ноя. 16, 2021

Abstract The development of efficient and sustainable methods for carbon-phosphorus bond formation is great importance due to the wide application organophosphorus compounds in chemistry, material sciences biology. Previous C–H phosphorylation reactions under nonelectrochemical or electrochemical conditions require directing groups, transition metal catalysts, chemical oxidants suffer from limited scope. Herein we disclose a catalyst- external oxidant-free, reaction arenes continuous flow synthesis aryl phosphorus compounds. C–P formed through with anodically generated P-radical cations, class reactive intermediates remained unexplored despite intensive studies P-radicals. high reactivity cations coupled mild electrosynthesis ensures not only diverse electronic properties but also selective late-stage functionalization complex natural products bioactive synthetic utility method further demonstrated by production 55.0 grams one phosphonate products.

Язык: Английский

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