Showing papers on "Aryl radical published in 2018"
TL;DR: It is demonstrated that this copper oxidative addition problem can be overcome with an aryl radical–capture mechanism, wherein the ariesl radical is generated through a silyl radical halogen abstraction in dual copper-photoredox catalysis.
Abstract: Transition metal–catalyzed arene functionalization has been widely used for molecular synthesis over the past century. In this arena, copper catalysis has long been considered a privileged platform due to the propensity of high-valent copper to undergo reductive elimination with a wide variety of coupling fragments. However, the sluggish nature of oxidative addition has limited copper’s capacity to broadly facilitate haloarene coupling protocols. Here, we demonstrate that this copper oxidative addition problem can be overcome with an aryl radical–capture mechanism, wherein the aryl radical is generated through a silyl radical halogen abstraction. This strategy was applied to a general trifluoromethylation of aryl bromides through dual copper-photoredox catalysis. Mechanistic studies support the formation of an open-shell aryl species.
266 citations
TL;DR: The key to controlling the chemoselectivity toward alkene 1,2-diarylation is the employment of a 2,2'-bipyridine base, thus allowing the formation of two new C(sp3)-C(sp2) bonds via aryl radical formation from aryldiazonium salts.
47 citations
TL;DR: The authors show the γ-arylation of aliphatic alcohols via a two-step radical translocation and subsequent radical aryl migration and subsequent radicals migration at unactivated secondary and tertiary C(sp3)−H bonds.
Abstract: Site selective chemical functionalization at unactivated C(sp3)−H bonds is highly challenging and recent successful studies mostly focus on the use of transition metal catalysis in combination with directing groups. Radical chemistry offers a complementary approach with the Barton and the Hofmann-Loffler-Freytag reactions being landmark contributions in the area of remote C−H functionalization at unactivated aliphatic sites. Herein we introduce the concept of radical translocation arylation at unactivated secondary and tertiary C(sp3)−H bonds in various alcohols. The straightforward two-step sequence comprises an ionic alcohol sulfonylation with especially designed ortho-iodoaryl sulfonyl chlorides followed by a radical cascade reaction including aryl radical generation, remote radical translocation, aryl migration, reduction, and SO2 extrusion to give the corresponding γ-arylated alcohols. Moderate to good yields are obtained, remote C−H arylation occurs with excellent regioselectivity and for secondary C(sp3)−H bonds good to excellent stereoselectivity is achieved. Selective remote functionalization of aliphatic C(sp3)−H bonds is highly challenging and often requires transition metals and/or directing groups. Here, the authors show the γ-arylation of aliphatic alcohols via a two-step radical translocation and subsequent radical aryl migration.
46 citations
TL;DR: Nitration of a biologically and environmentally relevant aromatic compound, guaiacol (2-methoxyphenol), under mild aqueous-phase conditions was investigated by a temperature-dependent experimental modeling coupled to extensive ab initio calculations to obtain the activation energies of the modeled reaction pathways.
Abstract: Many ambiguities surround the possible mechanisms of colored and toxic nitrophenols formation in natural systems. Nitration of a biologically and environmentally relevant aromatic compound, guaiacol (2-methoxyphenol), under mild aqueous-phase conditions (ambient temperatures, pH 4.5) was investigated by a temperature-dependent experimental modeling coupled to extensive ab initio calculations to obtain the activation energies of the modeled reaction pathways. The importance of dark nonradical reactions is emphasized, involving nitrous (HNO2) and peroxynitrous (HOONO) acids. Oxidation by HOONO is shown to proceed via a nonradical pathway, possibly involving the nitronium ion (NO2+) formation. Using quantum chemical calculations at the MP2/6-31++g(d,p) level, NO2• is shown capable of abstracting a hydrogen atom from the phenolic group on the aromatic ring. In a protic solvent, the corresponding aryl radical can combine with HNO2 to yield OH• and, after a subsequent oxidation step, nitrated aromatic products....
37 citations
TL;DR: Mechanistic studies revealed that rongalite could act as a radical initiator, a sulfur dioxide surrogate and a reducing reagent simultaneously in this reaction.
34 citations
TL;DR: A novel 1,2-bis(trifluoromethylation) of arynes using [CuCF3] is described.
Abstract: We herein describe an unprecedented 1,2-bis(trifluoromethylation) of arynes with [CuCF3] in the presence of an oxidant DDQ. The method allows the rapid construction of a new class of 1,2-bis(trifluoromethyl)arenes in one-step from aryne precursors under mild conditions. Its synthetic utility has been demonstrated in the preparation of bis(trifluoromethylated) molecules with potential pharmaceutical and materials science applications. Mechanistic studies indicated the presence of an o-trifluoromethyl aryl radical intermediate via CF3 group transfer from [CuCF3] to the aryne.
28 citations
TL;DR: In this article, the authors established distinct reaction pathways based on kinetic analysis and intermediate identification for selective hydrodehalogenation of a variety of aromatic halides (e.g., halogen subsitute phenones and hexafluorobenzene).
Abstract: Selective hydrodehalogenation of a variety of aromatic halides (e.g., halogen subsitute phenones and hexafluorobenzene) using isopropanol as the hydrogen source was successfully achieved over supported Au nanoparticles. Distinct reaction pathways were established based on kinetic analysis and intermediate identification. Surface hydrides generated by isopropanol oxidation mediate the hydrodehalogenation by nucleophilic attack without the involvement of carbon centered radical. On the other hand, engeretic electrons on Au nanoparticles populated by visible light irradiation trigger the dissciation of carbon halogen bond (C X) by injection to the substrates’ lowest unoccupied molecular orbitals (LUMO). The super-linear dependency on light intensity, shape of the action spectrum and formation of aryl radical revealed that electron transfer dominates the hydrodehalogneation process, which features a significantly lower activation barrier than transfer of surface hydride. The observed activity is correlated to energy levels of the substrate electron accepting states.
28 citations
TL;DR: A facile visible-light photocatalytic conjugate addition to prepare 1,4-dicarbonyl compounds has been developed by employing readily available aroyl chlorides as aryl radical sources.
Abstract: A facile visible-light photocatalytic conjugate addition to prepare 1,4-dicarbonyl compounds has been developed by employing readily available aroyl chlorides as aryl radical sources. This operationally simple method shows a broad scope with regard to both aroyl chlorides and Michael acceptors. As a result, a variety of 1,4-diketones were efficiently synthesized in moderate to good yields.
27 citations
TL;DR: The recently discovered futalosine-dependent menaquinone biosynthesis pathway employs radical chemistry for the naphthoquinol core assembly and has resulted in the discovery of novel reaction motifs.
27 citations
TL;DR: Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox-neutral azocycloamination and cyclize in a photocatalytic reaction with visible light and an organic dye, and a range of functional groups is tolerated.
Abstract: Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox-neutral azocycloamination. In general, N-aryl O-prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron-deficient diazonium salts, electronic matching with an electron-rich N-aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen-atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton-coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated.
22 citations
TL;DR: A catalytic procedure using poly(ethylene glycol) (PEG-400) as a greener alternative organic solvent has been developed and can achieve 99% targeted yield with a mild reaction temperature and short reaction time.
Abstract: The catalytic activities of eight copper(i) halide clusters assembled from copper(i) halide and ferrocenyltelluroethers, 1-8, were investigated in C-N formation under various conditions. A catalytic procedure using poly(ethylene glycol) (PEG-400) as a greener alternative organic solvent has been developed. The PEG-400/5 system can achieve 99% targeted yield with a mild reaction temperature and short reaction time. After the isolation of the products by extraction with diethyl ether, this PEG-400/cluster system could be easily recycled. Spectroscopic studies elucidate a stepwise mechanism: firstly, proton-coupled electron transfer (PCET) involving the transfer of an electron from Cu+ and a proton from imidazole results in the formation of a labile penta-coordinated Cu2+ and aryl radical; the following effective electron transfer from the ferrocene unit reduces Cu2+ and forms the target product; finally, the ferrocenium unit is reduced by the I- anion. The merits of this eco-friendly synthesis are the efficient utilization of reagents and easy recyclability.
TL;DR: A cascade radical addition/cyclization reaction of 2-vinylanilines with alkynes for the synthesis of biologically important naphthalene derivatives is reported.
Abstract: A cascade radical addition/cyclization reaction of 2-vinylanilines with alkynes for the synthesis of biologically important naphthalene derivatives is reported. In this transformation, the in-situ-formed diazonium salts from 2-vinylanilines served as efficient aryl radical precursors and the reaction was run under metal-free conditions.
TL;DR: In this paper, the intramolecular cross-coupling of sulfonic acid derivatives occurs in the presence of tris(trimethylsilyl)silane (TTMSS) at room temperature and in air to form biaryl compounds.
Abstract: The intramolecular cross-coupling of sulfonic acid derivatives occurs in the presence of tris(trimethylsilyl)silane (TTMSS) at room temperature and in air to form biaryl compounds. A photoredox-catalyzed procedure is also described. These protocols provide mild and convenient alternatives to standard tin-mediated reactions. Combined with the trivial preparation of the substrates from activated sulfonic acids and 2-halophenols or anilines, this work presents a useful means to employ sulfonic acid derivatives in cross-coupling transformations. A modified linker to realize high regioselectivity is also presented. Finally, a one-pot cross-coupling procedure is demonstrated.
TL;DR: In this article, a series of para-substituted tetraarylborates were investigated as aryl radical generator for photopolymerization reactions, using 2-hydroxyethyl methacrylate as monomer.
Abstract: A series of para-substituted tetraarylborates were investigated as aryl radical generator for photopolymerization reactions, using 2-hydroxyethyl methacrylate as monomer. The first steps of the photopolymerization process involve the use of tetraarylborate as monocomponent photoinitiator or combination of two-component systems (riboflavin and tetraarylborate anion) to generate the aryl radical species, which is used to initiate the radicalar polymerization of vinyl monomers. Both photoinitiator systems herein investigated are very attractive for vinyl polymerization upon light irradiation. The polymerization and photochemical results indicate that the changes on the para-substituted ligand may be used to improve the formation of aryl radical species and the rate constant of electron transfer into two-component systems. In consequence of this reaction, the kinetics of radical polymerization is also modulated by electron donor/acceptor features of para-substituent ligands.
TL;DR: In this paper, aryl-boronic acid addition to nitriles in the presence of inexpensive Mn/Cu catalytic system is reported, where the use of nonprecious Mn and Cu salts has been found to be highly advantageous both in terms of accessibility as well as cost effectiveness.
TL;DR: The combination of multistage mass spectrometry experiments employing the distonic radical approach together with DFT calculations are used to examine addition of the N-methyl-pyridinium-4-yl radical cation to iso(thio)cyanates in the gas-phase.
Abstract: The combination of multistage mass spectrometry experiments employing the distonic radical approach together with DFT calculations are used to examine addition of the N-methyl-pyridinium-4-yl radical cation (γ-NMP) to iso(thio)cyanates in the gas-phase. The type of products formed depend on the nature of the iso(thio)cyanate: (1) hydrogen atom abstraction occurs for alkyl isocyanates; (2) aryl isocyanates undergo radical-ipso substitution; (3) radical attack occurs at the C[double bond, length as m-dash]C bond of allyl isocyanate; (4) radical attack occurs at the C[double bond, length as m-dash]S bond of isothiocyanates to generate S adducts of γ-NMP and isonitriles. DFT calculations provide insight into the reactivity differences of these heterocumulenes towards the electrophilic C-centered γ-distonic radical cations. Translation of these gas phase results to the solution phase were hampered by dominating radical recombination reactions which appear to be favoured over the radical-iso(thio)cyanate reactions.
TL;DR: It is shown that Bmp7 can efficiently accept polychlorinated aryl substrates, in addition to the physiological polybrominated substrates for the biosynthesis of polyhalogenated marine natural products.
Abstract: Cytochrome P450 (CYP450) enzymes are ubiquitous catalysts in natural product biosynthetic schemes where they catalyze numerous different transformations using radical intermediates. In this protocol, we describe procedures to assay the activity of a marine bacterial CYP450 enzyme Bmp7 which catalyzes the oxidative radical coupling of polyhalogenated aromatic substrates. The broad substrate tolerance of Bmp7, together with rearrangements of the aryl radical intermediates leads to a large number of products to be generated by the enzymatic action of Bmp7. The complexity of the product pool generated by Bmp7 thus presents an analytical challenge for structural elucidation. To address this challenge, we describe mass spectrometry-based procedures to provide structural insights into aryl crosslinked products generated by Bmp7, which can complement subsequent spectroscopic experiments. Using the procedures described here, for the first time, we show that Bmp7 can efficiently accept polychlorinated aryl substrates, in addition to the physiological polybrominated substrates for the biosynthesis of polyhalogenated marine natural products.
Patent•
06 Mar 2018
TL;DR: In this article, a carbazole compound has been described and used as a sensitizing agent of a dye-sensitized solar battery, which can serve as a deterministic additive.
Abstract: The invention discloses a carbazole compound and application thereof. The carbazole compound has a structure as shown in a formula (I) (the formula is as shown in the description; and in the formula (I), R1 is C1-C12 hydrocarbyl or C1-C12 alkoyx or C4-C20 heterocyclic radical, the heteroatom of the heterocyclic radical is N or S or O, R2 is C1-C12 hydrocarbyl, and R3 is aryl radical or heterocyclic aromatic hydrocarbon. The compound provided by the invention can serve as a sensitizing agent of a dye-sensitized solar battery.
Patent•
29 Jun 2018
TL;DR: In this paper, a method for electrochemically producing arylalkyl carbonates or diaryl carbonates was proposed, which is characterized in that compounds of formula (1) R1-OH, wherein the radical R1 is an alkyl radical, preferably a radical from the range: C1 to C6alkyl, preferably methyl or ethyl, isopropyl or tert-butyl or cycloalkyl or cycle-cyclohexyl, with a compound of formula(2) R2-OH) where the radical is an
Abstract: The present invention relates to a method for electrochemically producing arylalkyl carbonates or diaryl carbonates, which is characterized in that compounds of formula (1) R1-OH, wherein the radical R1 is an alkyl radical, preferably a radical from the range: C1 to C6alkyl, preferably methyl or ethyl, isopropyl or tert-butyl or cycloalkyl, preferably cyclohexyl, with a compound of formula (2) R2-OH, wherein the radical R2 is an aryl radical, preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, particularly preferably is a phenyl radical, are subjected to anodic reaction with CO at an electrode with gold as heterogeneous electrocatalyst, and also the use thereof for producing polycarbonates.