Arens Product Research Articles

Ni‐Catalyzed [2+2+2] Cycloaddition of Alkynes To Form Arenes and Pyridines at Low Catalyst Loadings

AbstractWe report the Ni‐catalyzed cyclotrimerization of terminal alkynes at very low loadings of catalysts (0.05 mol% for all substrates). The nickel catalyst containing a terphenyl phosphine ligand allows carrying out the reactions at room temperature in only 30 min, providing the arene products as a single regioisomer in most cases. The Ni complex is also competent for the synthesis of polysubstituted pyridines through the cycloadditions of diynes and nitriles at mild temperatures (25 ° or 50 °C) and low Ni loadings (1 mol%). Experimental data and computational studies support the involvement of monoligated PNi species in all fundamental steps of the catalytic cycle.

Cascade Reactions of Alkynyl Ketones and Amides to Generate Unsaturated Oxacycles and Aromatic Carbocycles.

We describe novel amine-mediated transformation of alkynyl ketones and amides to generate 2-methylene-2H-pyrans, substituted 3-hydroxy-9H-fluoren-9-ones, and amine-incorporated arenes. These cascade processes are initiated by conjugate addition of secondary amine followed by hydrolysis of the enamine/vinylogous amide intermediates. The product distribution is highly sensitive to the steric and electronic effects of the substituents on both the alkyne moieties, the tether structure connecting them, and the nature of the amine. Alkynyl amide participates in the Alder-ene reaction favorably to generate more reactive allene amide that reacts with amine to generate amine-incorporated arene products. These metal-free cascade reactions are a useful synthetic method that can be exploited for the construction of various hetero- and carbocyclic systems.

Catalytic Enantioselective Synthesis of Inherently Chiral Calix[4]arenes via Sequential Povarov Reaction and Aromatizations

AbstractInherently chiral calix[4]arenes represent a unique type of chiral molecules with significant applications, yet their catalytic enantioselective synthesis remains largely underexplored. We report herein the catalytic enantioselective synthesis of inherently chiral calix[4]arenes through the sequential organocatalyzed enantioselective Povarov reaction and aromatizations. The chiral phosphoric acid catalyzed three‐component Povarov reaction involving amino group‐substituted calix[4]arenes, aldehydes and (di)enamides desymmetrized the prochiral calix[4]arene substrates, which was followed by various aromatization methods, resulting in a diverse array of novel quinoline‐containing calix[4]arenes with good yields and high enantioselectivities (up to 75 % yield, 99 % ee). The large‐scale enantioselective synthesis and diverse derivatizations of the chiral calix[4]arene products highlight the value of this method. Furthermore, preliminary exploration into their photophysical and chiroptical properties demonstrate the potential applications of these novel calix[4]arene molecules.

Catalytic Enantioselective Synthesis of Inherently Chiral Calix[4]arenes via Sequential Povarov Reaction and Aromatizations.

Inherently chiral calix[4]arenes represent a unique type of chiral molecules with significant applications, yet their catalytic enantioselective synthesis remains largely underexplored. We report herein the catalytic enantioselective synthesis of inherently chiral calix[4]arenes through the sequential organocatalyzed enantioselective Povarov reaction and aromatizations. The chiral phosphoric acid catalyzed three-component Povarov reaction involving amino group-substituted calix[4]arenes, aldehydes and (di)enamides desymmetrized the prochiral calix[4]arene substrates, which was followed by various aromatization methods, resulting in a diverse array of novel quinoline-containing calix[4]arenes with good yields and high enantioselectivities (up to 75 % yield, 99 % ee). The large-scale enantioselective synthesis and diverse derivatizations of the chiral calix[4]arene products highlight the value of this method. Furthermore, preliminary exploration into their photophysical and chiroptical properties demonstrate the potential applications of these novel calix[4]arene molecules.

A Mixed-Valence Ti(II)/Ti(III) Inverted Sandwich Compound as a Regioselective Catalyst for the Uncommon 1,3,5-Alkyne Cyclotrimerization.

The synthesis, structure, and catalytic activity of a Ti(II)/Ti(III) inverted sandwich compound are presented in this study. Synthesis of the arene-bridged dititanium compound begins with the preparation of the titanium(IV) precursor [TiCl2(MesPDA)(thf)2] (MesPDA = N,N'-bis(2,4,6-trimethylphenyl)-o-phenylenediamide) (2). The reduction of 2 with sodium metal results in species [{Ti(MesPDA)(thf)}2(μ-Cl)3{Na}] (3) in oxidation state III. To achieve the lower oxidation state II, 2 undergoes reduction through alkylation with lithium cyclopentyl. This alkylation approach triggers a cascade of reactions, including β-hydride abstraction/elimination, hydrogen evolution, and chemical reduction, to generate the Ti(II)/Ti(III) compound [Li(thf)4][(TiMesPDA)2(μ-η6: η6-C6H6)] (4). X-ray and EPR characterization confirms the mixed-valence states of the titanium species. Compound 4 catalyzes a mild, efficient, and regiospecific cyclotrimerization of alkynes to form 1,3,5-substituted arenes. Kinetic data support a mechanism involving a binuclear titanium arene compound, similar to compound 4, as the resting state. The active catalyst promotes the oxidative coupling of two alkynes in the rate-limiting step, followed by a rapid [4 + 2] cycloaddition to form the arene product. Computational analysis of the resting state for the cycloaddition of trimethylsilylacetylene indicates a thermodynamic preference for stabilizing the 1,3,5-arene within the space between the two [TiMesPDA] fragments, consistent with the observed regioselectivity.

The order bidual of C(X) for a realcompact space

It is well known that the bidual of C(X) for a compact space X, supplied with the Arens product, is isometrically isomorphic as a Banach algebra to for some compact space . The space is unique up to homeomorphism. We establish a similar result for realcompact spaces: The order bidual of C(X) for a realcompact space X, when supplied with the Arens product, is isomorphic as an f-algebra to for some realcompact space . The space is unique up to homeomorphism.

Strategies for arene dissociation from transition metal η6-arene complexes.

Transition metal η6-arene complexes have unique properties that facilitate a variety of arene substitution reactions, rendering π-activation a powerful approach for arene functionalization. For decades, these complexes have been studied in the context of coordination chemistry and synthetic methodology via stoichiometric reactivity; one central challenge in expanding the utility of arene functionalization via transition-metal-π-activation is the dissociation of the arene product that remains bound to the transition metal. In this perspective, we highlight representative strategies and methods for the removal and/or exchange of arenes from such complexes. Recent studies that implement these strategies toward catalytic processes are discussed, along with remaining challenges in this area.

Geometry of Banach algebra [formula omitted] and the bidual of [formula omitted

This article is intended towards the study of the bidual of generalized group algebra L1(G,A) equipped with two Arens products, where G is any locally compact group and A is a Banach algebra. We show that the left topological center of (L1(G)⊗ˆA)⁎⁎ is a Banach L1(G)-module if G is abelian. Further it also holds permanence property with respect to the unitization of A. We then use this fact to extend the remarkable result of A.M. Lau and V. Losert [7], about the topological center of L1(G)⁎⁎ being just L1(G), to the reflexive Banach algebra valued case using the theory of vector measures. We further explore pseudo-center of L1(G,A)⁎⁎ for non-reflexive Banach algebras A and give a partial characterization for elements of pseudo-center using the Cohen's factorization theorem. In the running we also observe few consequences when A holds the Radon-Nikodym property and weak sequential completeness.

Palladium-Catalyzed Decarbonylative Coupling of (Hetero)Aryl Boronate Esters with Difluorobenzyl Glutarimides.

This report describes the Pd-catalyzed decarbonylative coupling of difluorobenzyl glutarimides with (hetero)aryl boronate esters to yield difluorobenzyl-substituted (hetero)arene products. The use of PAd2Bu as the phosphine ligand in combination with neopentylboronate ester nucleophiles proved critical for the selective formation of the decarbonylative coupling product versus analogous difluorobenzyl ketone. This transformation is effective for electronically diverse (hetero)aryl boronate esters and substituted difluorobenzyl glutarimides.

Electrochemical C-F bond activation of trifluoromethylarenes using silylium ions.

We report a mild, electrochemical trihydrodefluorination (e-THDF) for breaking highly stable C-F bonds in trifluoromethyl arenes to form the corresponding methyl arene products. Uniquely, this "green" approach relies on the in situ generation of Lewis acidic silyl cations that mediate fluoride abstraction. Overall, e-THDF has significantly improved functional group tolerance over current methods and should inspire the continued development of defluorinative processes.

ON THE ALGEBRAS AND OF AN ULTRASPHERICAL HYPERGROUP

AbstractLet H be an ultraspherical hypergroup and let $A(H)$ be the Fourier algebra associated with $H.$ In this paper, we study the dual and the double dual of $A(H).$ We prove among other things that the subspace of all uniformly continuous functionals on $A(H)$ forms a $C^*$ -algebra. We also prove that the double dual $A(H)^{\ast \ast }$ is neither commutative nor semisimple with respect to the Arens product, unless the underlying hypergroup H is finite. Finally, we study the unit elements of $A(H)^{\ast \ast }.$

Photoinduced Pd-Catalyzed Csp2-H/Csp3-H Dehydrocoupling Reaction Employing Polyhaloaromatics as the Dehydrogenating Agent.

A mild strategy for intermolecular cross-dehydrocoupling of Csp2-H bonds and Csp3-H bonds has been developed with the aid of photoinduced Pd catalysis. Polyhalogenated arenes can be used as the efficient dehydrogenating agent, which enables multifold transfer of carbon radical to avoid the production of stoichiometric or excess wasted arenes. In this strategy, substituted styrenes and N-arylacrylamides with simple ethers or amides as the coupling partners gives the corresponding internal alkenes and benzolactams with moderate to good yield.

THE EXISTENCE OF NONZERO COMPACT RIGHT MULTIPLIERS AND ARENS REGULARITY OF WEIGHTED BANACH ALGEBRAS

Let ω be a weight function on a locally compact group 𝒢 and let M(𝒢,ω)0∗ be the subspace of M(𝒢,ω)∗ consisting of all functionals that vanish at infinity. We first introduce an Arens product on (M(𝒢,ω)0∗)∗ under which it is a Banach algebra. We then show that the existence of a nonzero compact right multiplier on (M(𝒢,ω)0∗)∗ is equivalent to compactness of 𝒢. We also prove that if (M(𝒢,ω)0∗)∗ is Arens regular, then 𝒢 is discrete.

Facile synthesis of multifunctional poly(ionic liquid)s as an advanced three-way catalyst for the efficient production of lignite-derived arenes

The precise synthesis of multifunctional poly(ionic liquid)s (MFPILs) featuring basic sites, mesoporous channels, and hydrophobicity continues to be a substantial challenge. Moreover, the directional conversion of lignite to monocyclic arenes (MCAs) is highly attractive but particularly challenging on account of its geometrical complexity and chemical inertness. The efficiency of lignite directional conversion to MCAs over solid bases is substantially decreased by the presence of water molecules leading to the deactivation and leaching of basic sites. Herein, the novel solid bases, i.e., MFPILs with dibasic sites, unique hydrophobicity, and abundant mesoporous channels, were successfully fabricated by a radical multicomponent cross-linked copolymerization for the first time. Even more excitedly, the resulting MFPILs were demonstrated to be very efficient for directional catalytic hydroconversion of extraction residue from Dahuangshan lignite (DLER) into MCAs with 32.3 wt% yield, which is by far the highest value reported for lignite-derived MCAs by solid bases under similar conditions. The synergistic catalysis, i.e., hydrophobic microenvironment, mesoporous confinement, and synergistic effect of dibasic sites, for active hydrogen transfer of DLER conversion into MCAs over MFPILs is confirmed by characterization methods. The work not merely sheds substantial light on developing the novel solid bases, but also exhibits a potentially powerful catalyzing strategy to synthesize MCAs.

Light-Driven Hydrodefluorination of Electron-Rich Aryl Fluorides by an Anionic Rhodium-Gallium Photoredox Catalyst.

An anionic Rh-Ga complex catalyzed the hydrodefluorination of challenging C-F bonds in electron-rich aryl fluorides and trifluoromethylarenes when irradiated with violet light in the presence of H2 , a stoichiometric alkoxide base, and a crown-ether additive. Based on theoretical calculations, the lowest unoccupied molecular orbital (LUMO), which is delocalized across both the Rh and Ga atoms, becomes singly occupied upon excitation, thereby poising the Rh-Ga complex for photoinduced single-electron transfer (SET). Stoichiometric and control reactions support that the C-F activation is mediated by the excited anionic Rh-Ga complex. After SET, the proposed neutral Rh0 intermediate was detected by EPR spectroscopy, which matched the spectrum of an independently synthesized sample. Deuterium-labeling studies corroborate the generation of aryl radicals during catalysis and their subsequent hydrogen-atom abstraction from the THF solvent to generate the hydrodefluorinated arene products. Altogether, the combined experimental and theoretical data support an unconventional bimetallic excitation that achieves the activation of strong C-F bonds and uses H2 and base as the terminal reductant.

Light‐Driven Hydrodefluorination of Electron‐Rich Aryl Fluorides by an Anionic Rhodium‐Gallium Photoredox Catalyst

AbstractAn anionic Rh−Ga complex catalyzed the hydrodefluorination of challenging C−F bonds in electron‐rich aryl fluorides and trifluoromethylarenes when irradiated with violet light in the presence of H2, a stoichiometric alkoxide base, and a crown‐ether additive. Based on theoretical calculations, the lowest unoccupied molecular orbital (LUMO), which is delocalized across both the Rh and Ga atoms, becomes singly occupied upon excitation, thereby poising the Rh−Ga complex for photoinduced single‐electron transfer (SET). Stoichiometric and control reactions support that the C−F activation is mediated by the excited anionic Rh−Ga complex. After SET, the proposed neutral Rh0 intermediate was detected by EPR spectroscopy, which matched the spectrum of an independently synthesized sample. Deuterium‐labeling studies corroborate the generation of aryl radicals during catalysis and their subsequent hydrogen‐atom abstraction from the THF solvent to generate the hydrodefluorinated arene products. Altogether, the combined experimental and theoretical data support an unconventional bimetallic excitation that achieves the activation of strong C−F bonds and uses H2 and base as the terminal reductant.

Three-Component Coupling of Arenes, Ethylene, and Alkynes Catalyzed by a Cationic Bis(phosphine) Cobalt Complex: Intercepting Metallacyclopentenes for C-H Functionalization.

A cobalt-catalyzed intermolecular three-component coupling of arenes, ethylene, and alkynes was developed using the well-defined air-stable cationic bis(phosphine) cobalt(I) complex, [(dcype)Co(η6-C7H8)][BArF4] (dcype = 1,2-bis(dicyclohexylphosphino)ethane; BArF4 = B[(3,5-(CF3)2)C6H3]4), as the precatalyst. All three components were required for turnover and formation of ortho-homoallylated arene products. A range of directing groups including amide, ketone, and 2-pyridyl substituents on the arene promoted the reaction. The cobalt-catalyzed method exhibited broad functional group tolerance allowing for the late-stage functionalization of two drug molecules, fenofibrate and haloperidol. A series of control reactions, deuterium labeling studies, resting state analysis, as well as synthesis of substrate- and product-bound η6-arene complexes supported a pathway involving C(sp2)–H activation from a cobalt(III) metallacycle.

On Odd Duals of a Banach Algebra as a Banach Algebra

It is known that even duals of a Banach algebra A with one of Arens products are Banach algebras, these products are natural multiplications extending the one on A. But the essence of A*is completely different. We investigate some algebraic and spectral properties of odd duals of A, by defning the products ⃝a, ⃝F as in [12]. We will show relations between these products and Arens products, weak or weak-starcontinuity, commutativity and unit elements of these algebras. Also we determine the spectrum and multiplier algebra for A*, and we calculate the quasi-inverses, spectrum and spectral radius for elements of these kinds of algebras.

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

A cascade double 1,4-addition/intramolecular annulation strategy for expeditious assembly of unsymmetrical dibenzofurans

Existing synthetic routes for accessing dibenzofuran core have intrinsic regioselectivity, limiting the substitution patterns available in heteropolycyclic arene products. Here we report a double 1,4-conjugate addition/intramolecular annulation cascade reaction between propargylamines and two equivalents of imidazolium methylides that allows efficient access of structurally versatile dibenzofurans. This transition metal-free protocol proceeds smoothly under bench-top air atmosphere and offers easy manipulation of substituents on the dibenzofuran core, and also provides good-to-excellent product yields with good functional group tolerance, particularly the –Br and –Cl groups which are often incompatible with existing metal-catalyzed C–C and/or C–O bond ring-forming processes. It is worth noting that ladder-type π-systems with all-arene quarternary carbon structure can be straightforwardly generated upon simple late-stage functionalization.