Simple Aryl Research Articles

Revisiting Claims of the Iron-, Cobalt-, Nickel-, and Copper-Catalyzed Suzuki Biaryl Cross-Coupling of Aryl Halides with Aryl Boronic Acids

Intrigued by recent reports on the surprisingly excellent activity of a range of cobalt-, iron-, copper-, and nickel-based catalysts in the Suzuki biaryl cross-coupling of simple aryl boronic acids with aryl halides, we undertook a reexamination of the syntheses of representative examples of the reported precatalysts and their application to the catalytic reaction. A reported PNP−Fe pincer complex proved to be a mixture of starting materials; a mono-Schiff base cobalt complex in fact the bis-ligated adduct and a monomeric copper(II) PNP–pincer complex a di- or oligomeric copper(I) species. In our hands, neither these complexes nor any other of the selected precatalysts investigated showed any activity in a Suzuki cross-coupling reaction of an electronically activated aryl bromide with phenyl boronic acid. Meanwhile, switching the nucleophile to the BuLi-activated phenyl boronic pinacol ester gave some promising activity with cobalt precatalysts.

Intramolecular Energy Transfer in Dithienogermole Derivatives.

Dithienogermole (DTG) has been applied as a useful building unit of optical/semiconducting materials for organic optoelectronic devices because of its extended conjugation, high chemical stability, and good emissive properties. Although DTG has two substituents on the Ge atom, the substituents have been limited to simple alkyl and aryl groups in previous work. In this work, to further uncover the new functionalities of this useful building unit, various π-conjugated groups were introduced on Ge of DTG. It was expected that the introduction of π-conjugated groups would give rise to efficient energy transfer between the substituents and the DTG core, which are in proximity and linked by a Ge atom. The thus-prepared DTG compounds with fluorene, terthiophene, and pyrene units on Ge possessed well-separated frontier orbitals on the substituents and the DTG core, as proved by the absorption spectra and DFT calculations. The substituted DTG derivatives showed clear emission only from the energy acceptor even though the energy donor was photoexcited. This indicated the highly efficient energy transfer in these compounds. We also prepared more π-extended compound DTGFl2-Ph with phenyl groups on the DTG thiophene rings. DTGFl2-Ph showed strong emission in the visible region with efficient energy transfer properties. These results clearly indicate the potential application of the present DTG system as optical functional materials.

A “Thiocarbonyl‐Directed” Regiospecific C−H/S−H Annulation of Quinoline‐4(1H)‐thiones with Alkynes

AbstractA regiospecific C−H/S−H annulation of quinoline‐4(1H)‐thiones with alkynes have been demonstrated using a ruthenium(II) catalyst. This C−H/S−H annulation is directed via the C=S group, where preferential annulation takes place at the sterically hindered position even in the presence of three other competing sites viz. two C−H/N−H and one C−H/O−H. This type of annulation is unsuccessful for simple aryl thiol such as 1‐naphthylthiol, giving only an oxidative dimerized product. The reaction proceeds via ruthenium‐catalyzed oxidative annulation followed by a hydrolytic cleavage of an amidic bond (loss of −COPh group), leading to the synthesis of thiopyrano[2,3,4‐de]quinolines. Isotopic labelling experiments suggest an irreversible initial C−Ru bond formation and the cleavage of C−H bond to be the rate‐limiting step. The reaction with unsymmetrical and terminal alkynes gave single regioisomeric product, where the new C−S bond formation takes place at the sp‐carbon of alkyne having more electron density. The reaction shows wide substrate scope both for quinoline‐4(1H)‐thiones as well as alkynes giving up to 91% product yields.magnified image

Palladium/Norbornene-Catalyzed Indenone Synthesis from Simple Aryl Iodides: Concise Syntheses of Pauciflorol F and Acredinone A.

To show the synthetic utility of palladium/norbornene (Pd/NBE) cooperative catalysis, here we report concise syntheses of indenone-based natural products, pauciflorol F and acredinone A, which are enabled by direct annulation between aryl iodides and unsaturated carboxylic acid anhydrides. Compared to the previous indenone-preparation approaches, this method allows simple aryl iodides to be used as substrates with complete control of the regioselectivity. The total synthesis of acredinone A features two different Pd/NBE-catalyzed ortho acylation reactions for constructing penta-substituted arene cores, including the development of a new ortho acylation/ipso borylation.

Palladium/Norbornene‐Catalyzed Indenone Synthesis from Simple Aryl Iodides: Concise Syntheses of Pauciflorol F and Acredinone A

AbstractTo show the synthetic utility of palladium/norbornene (Pd/NBE) cooperative catalysis, here we report concise syntheses of indenone‐based natural products, pauciflorol F and acredinone A, which are enabled by direct annulation between aryl iodides and unsaturated carboxylic acid anhydrides. Compared to the previous indenone‐preparation approaches, this method allows simple aryl iodides to be used as substrates with complete control of the regioselectivity. The total synthesis of acredinone A features two different Pd/NBE‐catalyzed ortho acylation reactions for constructing penta‐substituted arene cores, including the development of a new ortho acylation/ipso borylation.

Stereoretentive C( sp3)-S Cross-Coupling.

We report a stereoretentive cross-coupling reaction of configurationally stable nucleophiles with disulfide and N-sulfenylsuccinimide donors promoted by Cu(I). We demonstrate the utility of this method in the synthesis of thioglycosides derived from simple alkyl and aryl thiols, thioglycosides, and in the glycodiversification of cysteine residues in peptides. These reactions operate well with carbohydrate substrates containing common protective groups and reagents with free hydroxyl and secondary amide functionalities under standardized conditions. Competition experiments in combination with computational DFT studies established that the putative anomeric intermediate is an organocopper species that is configurationally stable and resistant to epimerization due to its short lifetime. The subsequent reductive elimination from the Cu(III) intermediate is rapid and stereoretentive. Taken together, the glycosyl cross-coupling is ideally suited for late stage glycodiversification and bioconjugation under highly controlled installation of the aliphatic carbon-sulfur bonds.

Synthesis of Indoles through Palladium-Catalyzed Three-Component Reaction of Aryl Iodides, Alkynes, and Diaziridinone

The three-component reaction of aryl iodides, alkynes, and diaziridinone is described. The reaction provides an innovative synthetic approach for indoles. The approach features high efficiency, broad substrate scope, and excellent regioselectivity. C, C-Palladacycles should act as the intermediates. The C, C-palladacycles are obtained from simple aryl halides and alkynes and then reacted with diaziridinone to afford indoles.

Copper-catalyzed Cross-coupling Reaction between Aryl(trialkyl)silanes and Alkyl Halides

We report that simple aryl(trialkyl)silanes undergo cross-coupling reaction with alkyl (pseudo)halides in the presence of copper iodide/phenanthroline catalyst and cesium fluoride. Various aryl(trialkyl)silanes and alkyl electrophiles having iodine, bromine, chlorine, and tosyloxy group are applicable to the present reaction. Because such silanes are stable and readily accessible by catalytic C–H silylation, this protocol allows us to synthesize alkylarenes rapidly.

A Mechanism-Based Approach to Screening Metagenomic Libraries for Discovery of Unconventional Glycosidases.

Functional metagenomics has opened new opportunities for enzyme discovery. To exploit the full potential of this new tool, the design of selective screens is essential, especially when searching for rare enzymes. To identify novel glycosidases that employ cleavage strategies other than the conventional Koshland mechanisms, a suitable screen was needed. Focusing on the unsaturated glucuronidases (UGLs), it was found that use of simple aryl glycoside substrates did not allow sufficient discrimination against β-glucuronidases, which are widespread in bacteria. While conventional glycosidases cannot generally hydrolyze thioglycosides efficiently, UGLs follow a distinct mechanism that allows them to do so. Thus, fluorogenic thioglycoside substrates featuring thiol-based self-immolative linkers were synthesized and assessed as selective substrates. The generality of the approach was validated with another family of unconventional glycosidases, the GH4 enzymes. Finally, the utility of these substrates was tested by screening a small metagenomic library.

Bifunctional Redox Active Materials for Flow Battery Applications

Nonaqueous redox flow batteries (RFBs) may provide a cost-effective and durable means of energy storage for grid applications, but numerous problems remain. For example, the ion exchange membrane that is generally required is expensive, prone to inefficiencies, and adds significant cell resistance. To avoid these problems, the use of redox polymers or redox-active clusters along with a simple separator has been explored. However, these systems often suffer from inaccessible sites and low mobility. Recently, we reported a promising approach based on covalently linking an electron acceptor moiety A to an electron donor moiety D to form a bifunctional compound D-L-A (where L represents a simple alkyl or aryl linker). Such systems have at least three accessible stable redox states: the “parent” D-L-A state, an oxidized form D+-L-A (catholyte), and a reduced form D-L-A- (anolyte). Since operation of the RFB would involve formation of the same product D-L-A at both anode and cathode, crossover is only a problem if the electrode reactions are inefficient. Numerous D-L-A compounds have been prepared using a wide variety of donor and acceptor groups. Many of these bifunctional compounds undergo chemically and electrochemically reversible oxidation and reduction, yielding predicted RFB cell voltages over 2 V. Additionally, multiple examples of the related D-L-A-L-D compounds incorporating 2e- acceptors A have also been synthesized and characterized. Several of these latter materials are of particular interest, and may provide the basis for RFBs with 2e- operation at 2.4-2.7 V and excellent stability. The electrochemical properties of several representative D-L-A and D-L-A-L-D systems will be described, and recent progress in the development of nonaqueous RFBs employing covalently linked anolyte-catholyte compounds as active materials will be presented.

Thorpe-Ingold Effect in Branch-Selective Alkylation of Unactivated Aryl Fluorides

Presented herein is a general protocol for the alkylation of simple aryl fluorides with unbiased secondary Grignard reagents by means of nickel catalysis. This study revealed a general Thorpe–Ingold effect in the ligand backbone which confers a high degree of selectivity for the secondary carbon center in the C−C coupling event. This protocol is characterized by mild reaction conditions, robustness, and simplicity. Both electron-rich and electron-deficient aryl fluorides are suitable candidates in this transformation. Equally amenable are a variety of heterocycles, permitting the coupling without over alkylation at the electrophilic sites.

Thorpe-Ingold Effect in Branch-Selective Alkylation of Unactivated Aryl Fluorides.

Presented herein is a general protocol for the alkylation of simple aryl fluorides with unbiased secondary Grignard reagents by means of nickel catalysis. This study revealed a general Thorpe-Ingold effect in the ligand backbone which confers a high degree of selectivity for the secondary carbon center in the C-C coupling event. This protocol is characterized by mild reaction conditions, robustness, and simplicity. Both electron-rich and electron-deficient aryl fluorides are suitable candidates in this transformation. Equally amenable are a variety of heterocycles, permitting the coupling without over alkylation at the electrophilic sites.

Site-Selective γ-C(sp3 )-H and γ-C(sp2 )-H Arylation of Free Amino Esters Promoted by a Catalytic Transient Directing Group.

The first selective PdII -catalysed γ-C(sp3 )-H and γ-C(sp2 )-H arylation of free amino esters using a commercially available catalytic transient directing group. A variety of free amino esters, including α-amino esters and β-amino esters, amino monoesters and amino bis-esters, are shown to react with a diverse range of simple aryl and heteroaryl iodide reagents.

Read-across of 90-day rodent repeated-dose toxicity: A case study for selected simple aryl alcohol alkyl carboxylic acid esters

Aryl alcohol alkyl carboxylic acid esters constitute a wide-employed class of fragrance materials. Outcomes presented within this study illustrate formulation of a read-across protocol for 90-day, repeat-dose toxicity within a series of these compounds, extending in scope to the dodecanoic acid esters of both benzyl and 2-phenylethyl alcohol. Central to the filling of data gaps is the hypothesis that adverse impact – mediated through mechanisms analogous to narcosis-associated non-specific basal cytotoxicity – is as a consequence of the hydrolysis of parent compounds to their corresponding alcohol. High-quality in vivo data (equivalent to either OECD Test Guideline 408 or 411) relating the toxicodynamic and toxicokinetic profiles of benzyl alcohol, 2-phenylethyl alcohol and benzyl acetate within rodents were retrieved, permitting extrapolation to each ester derivative with great confidence. NOAEL values of 250–500 mg/kg/day were assigned to esters, with a greater toxicity present within females. In order to greater enhance reliability, further theoretical support for the read-across prediction is provided through the integration, where appropriate, of in vitro and in silico data.

Diastereo- and enantioselective conjugate addition of 3-substituted oxindoles to enones via bifunctional catalysts

This paper presents a synthetically challenging vicinal quaternary-tertiary C–C forming reaction of 3-substituted oxindoles and chalcones by a simple aryl substituted bifunctional thiourea catalyst. The reactions work with a broad range of chalcones, giving chiral 3,3′-substituted oxindoles type compounds with adjacent quaternary-tertiary stereocenters in high yields (up to 99%), very good dr (up to >98:2) and very good ee (up to 96%).

Direct Cyclization of Tertiary Aryl Amines with Iodonium Ylides.

Described herein is a direct cyclization of simple tertiary aryl amines with iodonium ylides leading to a broad range of N-heterocycles. Completely different from the known reactivity of iodonium ylides, the finding reported herein is that an iodonium ylide is capable of cleaving a C(sp3 )-H bond and accepting two hydrogen atoms of a tertiary aryl amine, thus inducing a novel cyclization process. This transformation can proceed without the assistance of a transition-metal catalyst and eliminates the need for the premodification of the amine or the use of an additional initiator/oxidant.

Direct Cyclization of Tertiary Aryl Amines with Iodonium Ylides

AbstractDescribed herein is a direct cyclization of simple tertiary aryl amines with iodonium ylides leading to a broad range of N‐heterocycles. Completely different from the known reactivity of iodonium ylides, the finding reported herein is that an iodonium ylide is capable of cleaving a C(sp3)−H bond and accepting two hydrogen atoms of a tertiary aryl amine, thus inducing a novel cyclization process. This transformation can proceed without the assistance of a transition‐metal catalyst and eliminates the need for the premodification of the amine or the use of an additional initiator/oxidant.

Direct Palladium‐Catalyzed β‐Arylation of Lactams

AbstractA direct and catalytic method is reported here for β‐arylation of N‐protected lactams with simple aryl iodides. The transformation is enabled by merging soft enolization of lactams, palladium‐catalyzed desaturation, Ar−X bond activation, and aryl conjugate addition. The reaction is operated under mild reaction conditions, is scalable, and is chemoselective. Application of this method to concise syntheses of pharmaceutically relevant compounds is demonstrated.

Direct Palladium-Catalyzed β-Arylation of Lactams.

A direct and catalytic method is reported here for β-arylation of N-protected lactams with simple aryl iodides. The transformation is enabled by merging soft enolization of lactams, palladium-catalyzed desaturation, Ar-X bond activation, and aryl conjugate addition. The reaction is operated under mild reaction conditions, is scalable, and is chemoselective. Application of this method to concise syntheses of pharmaceutically relevant compounds is demonstrated.

Selective chloroform sensor using thiol functionalized reduced graphene oxide at room temperature

This paper presents a highly selective chloroform sensor using functionalised reduced graphene oxide (RGO) as a sensing layer. Thiol group is covalently attached on the basal plan of RGO film by a simple one-step aryl diazonium chemistry to improve its selectivity. Several spectroscopic techniques like X-ray photoelectron, Raman and Fourier transform infrared spectroscopy confirm successful thiol functionalization of RGO. Finally, the fabricated chemiresistor type sensor is exposed to chloroform in the concentration range 200–800 ppm (parts per million). The sensor shows a 4.3% of response towards 800 ppm chloroform. The selectivity of the sensor is analyzed using various volatile organic compounds as well. The devices show enhanced response and faster recovery attributed to the physiosorption of chloroform onto thiol functionalized graphene making them attractive for 2D materials based sensing applications.