Showing papers on "Intramolecular force published in 2020"
TL;DR: In this paper, a novel intramolecular g-C3N4-based donor-acceptor (D-A) conjugated copolymers with a porous structure and large specific surface area, have been facilely prepared by copolymerizing urea with melamine-formaldehyde (MF) resin.
188 citations
TL;DR: In this paper, a multicomponent reductive cross-coupling involving an inorganic salt (sodium metabisulfite) for the straightforward construction of sulfones is disclosed.
Abstract: Conventionally, sulfones are prepared by oxidation of sulfides with strong oxidants. Now, a multicomponent reductive cross-coupling involving an inorganic salt (sodium metabisulfite) for the straightforward construction of sulfones is disclosed. Both intramolecular and intermolecular reductive cross-couplings were comprehensively explored, and diverse sulfones were accessible from the corresponding alkyl and aryl halides. Intramolecular cyclic sulfones were systematically obtained from five- to twelve-membered rings. Naturally occurring aliphatic systems, such as steroids, saccharides, and amino acids, were highly compatible with the SO2 -insertion reductive cross-coupling. Four clinically applied drug molecules, which include multiple heteroatoms and functional groups with active hydrogens, were successfully prepared via a late-stage SO2 insertion. Mechanistic studies show that alkyl radicals and sulfonyl radicals were both involved as intermediates in this transformation.
134 citations
TL;DR: To date, intramolecular electrophilic C-H borylation is utilised mainly for accessing boron containing conjugated organic materials, however recent developments have highlighted the applicability of this methodology for forming synthetically versatile organo-boronate esters and bor on containing bioactives.
Abstract: The intramolecular C-H borylation of (hetero)arenes and alkenes using electrophilic boranes is a powerful transition metal free methodology for forming C-B bonds. These C-H borylation reactions are preceded by intermolecular bond (both dative and covalent) formation, with examples proceeding via initial C-B and N-B bond formation dominating this field thus both are discussed in depth herein. Less prevalent intramolecular electrophilic C-H borylation reactions that proceed by intermolecular O-B, S-B and P-B bond formation are also summarised. Mechanistic studies are presented that reveal two mechanisms for C-H borylation, (i) electrophilic aromatic substitution (prevalent with B-X electrophiles); (ii) σ-bond metathesis mediated (prevalent with B-H and B-R electrophiles). To date, intramolecular electrophilic C-H borylation is utilised mainly for accessing boron containing conjugated organic materials, however recent developments, summarized herein alongside early studies, have highlighted the applicability of this methodology for forming synthetically versatile organo-boronate esters and boron containing bioactives. The multitude of synthetic procedures reported for intramolecular electrophilic C-H borylation contain many common features and this enables key requirements for successful C-H borylation and the factors effecting regioselectivity and substrate scope to be identified, discussed and summarized.
103 citations
TL;DR: The pnictogen bond (PnB) is a noncovalent attraction between electrophilic pnivictogen atoms, originated from the anisotropic distribution of electron density on Pn in a molecular entity, and a nucleophilic (Nu) region in the same (intramolecular) or another molecular entity as mentioned in this paper.
95 citations
TL;DR: Density Functional Theory (DFT) and Natural Bond Orbital (NBO) calculations support the role of orbital delocalization (occurring via intramolecular chalcogen bonding) in determining the conformation, equilibrium population, and reactivity of N -acylated intermediates.
Abstract: The importance of 1,5-O⋅⋅⋅chalcogen (Ch) interactions in isochalcogenourea catalysis (Ch=O, S, Se) is investigated. Conformational analyses of N-acyl isochalcogenouronium species and comparison with kinetic data demonstrate the significance of 1,5-O⋅⋅⋅Ch interactions in enantioselective catalysis. Importantly, the selenium analogue demonstrates enhanced rate and selectivity profiles across a range of reaction processes including nitronate conjugate addition and formal [4+2] cycloadditions. A gram-scale synthesis of the most active selenium analogue was developed using a previously unreported seleno-Hugerschoff reaction, allowing the challenging kinetic resolutions of tertiary alcohols to be performed at 500 ppm catalyst loading. Density functional theory (DFT) and natural bond orbital (NBO) calculations support the role of orbital delocalization (occurring by intramolecular chalcogen bonding) in determining the conformation, equilibrium population, and reactivity of N-acylated intermediates.
95 citations
TL;DR: A comprehensive survey of reported crystal structures of organic diselenides demonstrates the recurrent setting of intermolecular as well as intramolecular chalcogen bonding interactions (ChB) between the selenium atoms acting as ChB donors and Lewis bases.
80 citations
TL;DR: Results offer further support for the ability of non-covalent interactions to enforce stereoselectivity in reactions of transient and highly reactive open-shell intermediates.
Abstract: An enantioselective, radical-based method for the intramolecular hydroamination of alkenes with sulfonamides is reported. These reactions are proposed to proceed via N-centered radicals formed by proton-coupled electron transfer (PCET) activation of sulfonamide N-H bonds. Noncovalent interactions between the neutral sulfonamidyl radical and a chiral phosphoric acid generated in the PCET event are hypothesized to serve as the basis for asymmetric induction in a subsequent C-N bond forming step, achieving selectivities of up to 98:2 er. These results offer further support for the ability of noncovalent interactions to enforce stereoselectivity in reactions of transient and highly reactive open-shell intermediates.
72 citations
TL;DR: New symmetric and unsymmetric B,N,B-doped benzo[4]helicenes 3 - 6a/b have been achieved in good yields, using a three-step process, starting from N(tolyl) 3 in a highly divergent manner.
Abstract: New symmetric and unsymmetric B,N,B-doped benzo[4]helicenes 3-6 a/b have been achieved in good yields, using a three-step process, starting from N(tolyl)3 in a highly divergent manner (7 examples). A borinic acid functionalized 1,4-B,N-anthracene 1 was found to display unprecedented reactivity, acting as a convenient and highly effective precursor for selective formation of bromo-substituted B,N,B-benzo[4]helicenes 2 a/2 b via intramolecular borylation and sequential B-Mes bond cleavage in the presence of BBr3 . Subsequent reaction of 2 a/2 b with Ar-Li provided a highly effective toolbox for the preparation of symmetrically/unsymmetrically functionalized B,N,B-helicenes. Their high photoluminescence quantum yields along with the small ΔEST suggest their potential as thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs).
70 citations
TL;DR: A novel asymmetric total synthesis of CB2 receptor agonist MDA7 has been successfully developed using a ruthenium(II)-catalyzed asymmetric intramolecular hydroarylation assisted by a chiral transient directing group.
Abstract: A ruthenium(II)-catalyzed asymmetric intramolecular hydroarylation assisted by a chiral transient directing group has been developed. A series of 2,3-dihydrobenzofurans bearing chiral all-carbon quaternary stereocenters have been prepared in remarkably high yields (up to 98 %) and enantioselectivities (up to >99 % ee). By this methodology, a novel asymmetric total synthesis of CB2 receptor agonist MDA7 has been successfully developed.
69 citations
TL;DR: In this paper, the synthesis and detailed spectral calculations of a new azoimidazole compound 1-[2-(2-hydroxy-3-methoxy-5-phenylazobenzaldeneamino) ethyl]-3-methyl-3H-IMI (HMAI) and its further characterisations using different quantum mechanical and molecular modelling tools were presented.
69 citations
TL;DR: In this review, the recent advances in remote C-C bond formation via photoredox-catalyzed intramolecular HAT are summarized.
Abstract: Carbon-carbon bonds comprise the major framework of organic molecules, rendering their formation one of the most fundamental transformations in synthetic organic chemistry. Visible light photoredox catalysis has recently been established as a powerful technique to construct molecular architectures that would otherwise be inaccessible under mild conditions. Photoredox catalysis combined with intramolecular hydrogen atom transfer (HAT) can serve as a unique tool for achieving remote C-C bond formation. In this review, the recent advances in remote C-C bond formation via photoredox-catalyzed intramolecular HAT are summarized.
TL;DR: Indole-tethered ynones form an intramolecular electron donor–acceptor complex that can undergo visible-light-induced charge transfer to promote thiyl radical generation from thiols and initiates a novel radical chain sequence based on dearomatising spirocyclisation with concomitant C–S bond formation.
Abstract: Indole-tethered ynones form an intramolecular electron donor–acceptor complex that can undergo visible-light-induced charge transfer to promote thiyl radical generation from thiols. This initiates a novel radical chain sequence, based on dearomatising spirocyclisation with concomitant C–S bond formation. Sulfur-containing spirocycles are formed in high yields using this simple and mild synthetic protocol, in which neither transition metal catalysts nor photocatalysts are required. The proposed mechanism is supported by various mechanistic studies, and the unusual radical initiation mode represents only the second report of the use of an intramolecular electron donor–acceptor complex in synthesis.
TL;DR: A streamlined method for asymmetric synthesis of β-aryl β-lactams from propanoic acid and aryl iodides via Pd-catalyzed sequential C(sp3)–H functionalization is reported.
Abstract: β-Lactams are important scaffolds in drug design and frequently used as reactive intermediates in organic synthesis. Catalytic reactions featuring intramolecular C–H amidation of alkyl carboxamide ...
TL;DR: This method provides access to products with readily enolizable functional groups, incompatible with traditional Pd-catalyzed conditions, and offers access to valuable oxindole and isoindoline-1-one motifs.
Abstract: A mild visible-light-induced Pd-catalyzed intramolecular C-H arylation of amides is reported. The method operates by cleavage of a C(sp2 )-O bond, leading to hybrid aryl Pd-radical intermediates. The following 1,5-hydrogen atom translocation, intramolecular cyclization, and rearomatization steps lead to valuable oxindole and isoindoline-1-one motifs. Notably, this method provides access to products with readily enolizable functional groups that are incompatible with traditional Pd-catalyzed conditions.
TL;DR: This study underlines the development of C(sp3)-H bond functionalization chemistry that should find wide application in the context of drug discovery and natural product synthesis.
Abstract: A concept for intramolecular denitrogenative C(sp3)–H amination of 1,2,3,4-tetrazoles bearing unactivated primary, secondary, and tertiary C–H bonds is discovered. This catalytic amination follows ...
TL;DR: A mild and efficient protocol for the intramolecular aromatic C-H oxygenation of 2-biphenylcarboxylic acids has been achieved via iron photocatalysis and it is speculated that the aryl carboxylate-iron(III) complexes should generate the aroyloxy radicals and iron(II) upon visible light irradiation.
TL;DR: Interestingly, strong relationships for halogen and chalcogen bonding energies are found, especially for the V(r) energy density, thus allowing to estimate the interaction energy without computing the separate monomers.
Abstract: Halogen (X-bond) and chalcogen bond (Ch-bond) energies for 36 complexes have been obtained at the RI-MP2/def2-TZVP level of theory, involving the heavier halogen and chalcogen atoms (Br, I, Se, Te). We have explored the existence of linear relationships between the interaction energies and the local kinetic energy densities at the bond critical points that characterize the σ-hole interactions (both electronic G(r) and potential V(r) energy densities). Interestingly, we have found strong relationships for halogen and chalcogen bonding energies, especially for the V(r) energy density, thus allowing to estimate the interaction energy without computing the separate monomers. This is also useful to estimate the interaction in monomeric systems (intramolecular X/Ch-bonds), as illustrated using several examples. Remarkably, we have also found a good relationship when in the same representation both halogen and chalcogen atoms are included, thus allowing to use the same empirical correlation for both interactions.
TL;DR: In this article, a hydrazone derivative, 2-[(2,3-dimethylphenyl)amino]-N’-[(E)-thiophen-2-ylmethylidene]benzohydrazide, was synthesized and its three-dimensional structure was determined by X-ray crystallography.
TL;DR: A catalytic approach is reported that is highly effective for controlling enantioselectivity as well as reactivity of the intermolecular radical C-H amination of carboxylic acid esters with organic azides via Co(II)-based metalloradical catalysis (MRC).
Abstract: Radical reactions hold a number of inherent advantages in organic synthesis that may potentially impact the planning and practice for construction of organic molecules. However, the control of enantioselectivity in radical processes remains one of the longstanding challenges. While significant advances have recently been achieved in intramolecular radical reactions, the governing of asymmetric induction in intermolecular radical reactions still poses challenging issues. We herein report a catalytic approach that is highly effective for controlling enantioselectivity as well as reactivity of the intermolecular radical C-H amination of carboxylic acid esters with organic azides via Co(II)-based metalloradical catalysis (MRC). The key to the success lies in the catalyst development to maximize noncovalent attractive interactions through fine-tuning of the remote substituents of the D2-symmetric chiral amidoporphyrin ligand. This noncovalent interaction strategy presents a solution that may be generally applicable in controlling reactivity and enantioselectivity in intermolecular radical reactions. The Co(II)-catalyzed intermolecular C-H amination, which operates under mild conditions with the C-H substrate as the limiting reagent, exhibits a broad substrate scope with high chemoselectivity, providing effective access to valuable chiral amino acid derivatives with high enantioselectivities. Systematic mechanistic studies shed light into the working details of the underlying stepwise radical pathway for the Co(II)-based C-H amination.
TL;DR: The present report summarizes the construction of four to eight-membered heterocyclic compounds containing nitrogen, oxygen and sulphur atoms through phosphine-catalyzed intramolecular annulations and intermolecular Annulations of electron-deficient alkenes, allenes, alkynes and Morita-Baylis-Hillman carbonates.
TL;DR: In this paper, the effects of different -NH2 group positions on the excited-state intramolecular proton transfer (ESIPT) mechanisms and its photophysical properties were investigated by using time-dependent DFT calculations.
TL;DR: A dual CuI /chiral phosphoric acid (CPA) catalytic system for radical-involved enantioselective intramolecular C(sp3 )-H amination of not only allylic positions but also benzylic positions with broad substrate scope is described.
Abstract: Radical-involved enantioselective oxidative C-H bond functionalization by a hydrogen-atom transfer (HAT) process has emerged as a promising method for accessing functionally diverse enantioenriched products, while asymmetric C(sp3 )-H bond amination remains a formidable challenge. To address this problem, described herein is a dual CuI /chiral phosphoric acid (CPA) catalytic system for radical-involved enantioselective intramolecular C(sp3 )-H amination of not only allylic positions but also benzylic positions with broad substrate scope. The use of 4-methoxy-NHPI (NHPI=N-hydroxyphthalimide) as a stable and chemoselective HAT mediator precursor is crucial for the fulfillment of this transformation. Preliminary mechanistic studies indicate that a crucial allylic or benzylic radical intermediate resulting from a HAT process is involved.
TL;DR: The proposed mechanism of rapid iminyl formation, rate-determining HAA, and subsequent radical recombination was corroborated by intramolecular isotope labeling experiments and theoretical calculations and provided facile preparation of indolizidine framework that is commonly found in a variety of alkaloids.
Abstract: A dipyrrin-supported nickel catalyst (AdFL)Ni(py) (AdFL: 1,9-di(1-adamantyl)-5-perfluorophenyldipyrrin; py: pyridine) displays productive intramolecular C-H bond amination to afford N-heterocyclic products using aliphatic azide substrates. The catalytic amination conditions are mild, requiring 0.1-2 mol% catalyst loading and operational at room temperature. The scope of C-H bond substrates was explored and benzylic, tertiary, secondary, and primary C-H bonds are successfully aminated. The amination chemoselectivity was examined using substrates featuring multiple activatable C-H bonds. Uniformly, the catalyst showcases high chemoselectivity favoring C-H bonds with lower bond dissociation energy as well as a wide range of functional group tolerance (e.g., ethers, halides, thioetheres, esters, etc.). Sequential cyclization of substrates with ester groups could be achieved, providing facile preparation of an indolizidine framework commonly found in a variety of alkaloids. The amination cyclization reaction mechanism was examined employing nuclear magnetic resonance (NMR) spectroscopy to determine the reaction kinetic profile. A large, primary intermolecular kinetic isotope effect (KIE = 31.9 ± 1.0) suggests H-atom abstraction (HAA) is the rate-determining step, indicative of H-atom tunneling being operative. The reaction rate has first order dependence in the catalyst and zeroth order in substrate, consistent with the resting state of the catalyst as the corresponding nickel iminyl radical. The presence of the nickel iminyl was determined by multinuclear NMR spectroscopy observed during catalysis. The activation parameters (ΔH‡ = 13.4 ± 0.5 kcal/mol; ΔS‡= -24.3 ± 1.7 cal/mol·K) were measured using Eyring analysis, implying a highly ordered transition state during the HAA step. The proposed mechanism of rapid iminyl formation, rate-determining HAA, and subsequent radical recombination was corroborated by intramolecular isotope labeling experiments and theoretical calculations.
TL;DR: It is presented that the negative inductive effect exerted by electron-withdrawing groups, such as sulfone groups, can obviously improve the ionization potential of amino auxochromes, thereby effectively inhibiting twisted intramolecular charge transfer (TICT) and markedly improving the quantum yields of several families of fluorophores in aqueous solution.
TL;DR: The first iridium-catalyzed cyclative indenylation through sequential B(4)-C and intramolecular C-C bond formation from o-carboranes and propargyl alcohols is described, leading to the formation of B( 4)-indenylated-o- carboranes with excellent regioselectivity via direct B-H activation.
Abstract: Described herein is the first iridium-catalyzed cyclative indenylation through sequential B(4)–C and intramolecular C–C bond formation from o-carboranes and propargyl alcohols, leading to the forma...
TL;DR: It is found that intermolecular charge transport ability through different single-stacking junctions is approximately independent of molecular structures, which contrasts with the strong length dependence of conductance in single-molecule junctions with the same building blocks.
Abstract: The experimental investigation of intermolecular charge transport in pi-conjugated materials is challenging. Herein, we describe the investigation of charge transport through intermolecular and intramolecular paths in single-molecule and single-stacking thiophene junctions by the mechanically controllable break junction (MCBJ) technique. We found that the ability for intermolecular charge transport through different single-stacking junctions was approximately independent of the molecular structure, which contrasts with the strong length dependence of conductance in single-molecule junctions with the same building blocks, and the dominant charge-transport path of molecules with two anchors transited from an intramolecular to an intermolecular path when the degree of conjugation increased. An increase in conjugation further led to higher binding probability owing to the variation in binding energies, as supported by DFT calculations.
TL;DR: The bond stretching vibration of the pyrazine-containing unit in these molecules is vigorous and insensitive to the external environmental restraint, which efficiently transforms the absorbed photons to dark-state heat energy.
Abstract: Development of highly effective approaches to desirable photothermal conversion agents is particularly valuable. Herein, we report a concept, namely, bond stretching vibration-induced photothermy, that serves as a mechanism to construct advanced photothermal conversion agents. As a proof-of-concept, two compounds (DCP-TPA and DCP-PTPA) with donor-acceptor (D-A) structures were synthesized. The bond stretching vibration of the pyrazine-containing unit in these molecules is vigorous and insensitive to the external environmental restraint, which efficiently transforms the absorbed photons to dark-state heat energy. The nanoparticles (NPs) of DCP-TPA and DCP-PTPA show rather high photothermal conversion efficiency (52% and 59%) and stronger photoacoustic (PA) signal than commercial methylene blue and reported high-performance semiconducting polymer nanoparticles. The DCP-PTPA NPs perform better than DCP-TPA NPs in terms of photothermal conversion, PA signal production, and in vivo PA tumor imaging because of the increased bond stretching vibration in the former molecule.
TL;DR: By manipulating the solid-state intramolecular motion of tetraphenylethylene (TPE) in crystallizing polymer matrix, controlled fluorescent patterns with information storage and encoding functionality are developed and provide a correlation between microscopic molecular motions and macroscopic optical signals.
Abstract: Molecules have limited mobility in the solid state because of the strong intermolecular interactions, and therefore, applications based on solid-state molecular motions are seldom explored. Herein,...
TL;DR: An intramolecular nickel-catalyzed cross-electrophile coupling reaction of 1,3-diol derivatives is reported, utilized to synthesize a range of mono- and 1,2-disubstituted alkylcyclopropanes, including those derived from terpenes, steroids, and aldol products.
Abstract: Cross-electrophile coupling reactions of two Csp3–X bonds remain challenging. Herein we report an intramolecular nickel-catalyzed cross-electrophile coupling reaction of 1,3-diol derivatives. Notab...
TL;DR: To extend the synthetic utilisation, fluorescent pyranoisocoumarins were achieved by using Rh(iii)-catalyzed peri-C-H/O-H activation/annulation reactions.