Showing papers in "Organic chemistry frontiers in 2018"
TL;DR: In this paper, the authors focused on the recent advances in the chemistry of sulfur dioxide fixation through a radical process and showed that diverse sulfonyl compounds can be obtained efficiently under mild conditions.
Abstract: This review is focused on the recent advances in the chemistry of sulfur dioxide fixation through a radical process. Diverse sulfonyl compounds can be obtained efficiently under mild conditions. In general, aryl radicals, vinyl radicals, alkyl radicals, and nitrogen-centered radicals can react with sulfur dioxide, giving rise to sulfonyl radical intermediates. The resulting sulfonyl radicals can be captured by nucleophiles, olefins, and alkynes. The sources of aryl radicals from aryldiazonium salts, aryl halides, and diaryliodonium salts are demonstrated. It is believed that more amazing SO2-based achievements will be developed in the near future.
240 citations
TL;DR: This review aims at highlighting the pyridinium salts in terms of their synthetic routes, reactivity and their importance as pyrIDinium ionic liquids, as p Pyrid inium ylides, as anti-microbial, anti-cancer,Anti-malarial and anti-cholinesterase inhibitors, as well as their applications in materials science and biological issues related to gene delivery.
Abstract: Structurally diverse pyridinium salts are quite familiar structures in many natural products and bioactive pharmaceuticals. Over the centuries, these privileged scaffolds have played an intriguing role in a wide range of research topics and, thus, this review aims at highlighting the pyridinium salts in terms of their synthetic routes, reactivity and their importance as pyridinium ionic liquids, as pyridinium ylides, as anti-microbial, anti-cancer, anti-malarial and anti-cholinesterase inhibitors, as well as their applications in materials science and biological issues related to gene delivery.
190 citations
TL;DR: In this article, the authors summarized the advances of the highly enantioselective (≥90% ee) hydrofunctionalization reactions of minimally functionalized alkenes using earth-abundant transition metals (iron, cobalt, nickel, copper, titanium and zirconium) as catalysts.
Abstract: In recent years, earth-abundant transition metal catalysts have been used to make great achievements on homogenous catalysis, including the field of enantioselective hydrofunctionalization of alkenes Minimally functionalized alkenes are a class of challenging substrates for the catalytic asymmetric hydrofunctionalization reactions This review summarizes the advances of the highly enantioselective (≥90% ee) hydrofunctionalization reactions of minimally functionalized alkenes using earth-abundant transition metals (iron, cobalt, nickel, copper, titanium and zirconium) as catalysts
163 citations
TL;DR: The Rh(III)-catalyzed annulative C–H functionalization of arenes with sulfoxonium ylides has been realized and the coupling affords structurally diverse fused hetero- and carbocycles under redox-neutral conditions.
Abstract: The Rh(III)-catalyzed annulative C–H functionalization of arenes with sulfoxonium ylides has been realized. Arenes assisted by diverse nucleophilic directing groups are viable substrates, and the coupling affords structurally diverse fused hetero- and carbocycles under redox-neutral conditions.
131 citations
TL;DR: In this article, the dual hydrogen-bonded 1,4-bis-(3-hydroxy-4-oxo-4H-chromen-2-yl)-benzene (bisflavonol) system was investigated in detail.
Abstract: In this work, we investigate the dual hydrogen bonded 1,4-bis-(3-hydroxy-4-oxo-4H-chromen-2-yl)-benzene (bisflavonol) system in detail. Via optimizing stable structures and constructing potential energy curves, we confirm that two primary structures (i.e., anti-bisflavonol and syn-bisflavonol) can coexist in the S0 state. Calculating the reduced density gradient (RDG) versus sign(λ2)ρ and gradient isosurfaces, we confirm the formation of double hydrogen bonds for both anti-bisflavonol and syn-bisflavonol. Comparing the primary geometrical parameters involved in hydrogen bonds, we verify that the double intramolecular hydrogen bonds should be strengthened in the S1 state. In view of the photo-excitation process, we find that the charge redistributions around the hydrogen bonded moieties of both anti-bisflavonol and syn-bisflavonol facilitate the excited state intramolecular proton transfer (ESIPT) reaction. Given the reaction paths for the ESIPT process, the S0-state and S1-state potential energy surfaces (PESs) are constructed for both anti-bisflavonol and syn-bisflavonol along with two hydrogen bonds to reveal the overall excited state dynamical behavior. Searching for the transition state (TS) structure and calculating the intrinsic reaction coordinate (IRC) energetic profile, we confirm the ESIPT reaction. Combining it with Born–Oppenheimer molecular dynamics (BOMD) simulations, we study the ESIPT dynamical behaviors in detail. We present that only the single proton transfer process occurs in the S1 state in aprotic solvents, which makes up for the deficiency of previous experiments. The theoretical electronic spectra further confirm our attribution. This work not only illustrates that anti-bisflavonol and syn-bisflavonol coexisting in the S0-state can promote the respective ESIPT reaction, but also makes a new attribution to previous experiments.
128 citations
TL;DR: In this article, the first metal and reductant-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process is reported.
Abstract: The first example of a metal- and reductant-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process is reported. In this reaction, sodium sulfinates play dual roles of a sulfonylation reagent and activating agent. This procedure is expected to complement the current methods for the radical reaction of quinoline N-oxides.
123 citations
TL;DR: The methodology shows broad substrate scope, excellent functional group tolerance, high atom economy and high efficiency, thus enabling the preparation of diverse potentially valuable 3-alkyl quinoxalin-2(1H)-one derivatives.
Abstract: A convenient and efficient transition-metal-free protocol for the synthesis of 3-alkyl quinoxalin-2(1H)-ones from the radical reaction of quinoxalin-2(1H)-ones with ethers was developed with moderate to good yields. The methodology shows broad substrate scope, excellent functional group tolerance, high atom economy and high efficiency, thus enabling the preparation of diverse potentially valuable 3-alkyl quinoxalin-2(1H)-one derivatives.
105 citations
TL;DR: The methodology demonstrates a broad substrate scope, excellent functional group tolerance, high atom economy and high efficiency, thus enabling the preparation of diverse potentially valuable hydroxyl-containing quinoxalin-2(1H)-ones.
Abstract: An efficient copper-catalyzed protocol for the synthesis of hydroxyl-containing quinoxalin-2(1H)-ones from the radical reaction of quinoxalin-2(1H)-ones with alcohols was developed with moderate to good yields. Quinoxalin-2(1H)-ones were coupled with alkyl radicals through direct catalytic functionalization of the α sp3 C–H bond of alcohols. The methodology demonstrates a broad substrate scope, excellent functional group tolerance, high atom economy and high efficiency, thus enabling the preparation of diverse potentially valuable hydroxyl-containing quinoxalin-2(1H)-ones.
98 citations
TL;DR: Palladium-catalyzed regioselective electrocarboxylation of homostyrenyl acetates with CO2 has been successfully developed, providing α-aryl carboxylic acids with good selectivity and yield as discussed by the authors.
Abstract: Palladium-catalyzed regioselective electrocarboxylation of homostyrenyl acetates with CO2 has been successfully developed, providing α-aryl carboxylic acids with good selectivity and yield. In addition, the catalytic asymmetric carboxylation of cinnamyl acetate has been demonstrated, despite moderate enantioselectivity.
90 citations
TL;DR: This review proposes a concept of a supramolecular gelaton, which is a structural unit or molecule for the design and construction of the supramolescular gels, to show how to design the targeted functional gels.
Abstract: The fabrication and application of supramolecular gels have achieved great progress in the past few decades. Although several reviews and books have well summarized the design, properties and functions of certain supramolecular gels, a comprehensive overview is still lacking to reveal the design strategy of the supramolecular gels. In this review, we propose a concept of a supramolecular gelaton, which is a structural unit or molecule for the design and construction of the supramolecular gels, to show how to design the targeted functional gels. We classify the gelaton into two types. One is a covalent gelaton that when covalently connects with other functional groups results in a molecule that can become a gelator. The other type is a non-covalent gelaton, which is a gelator molecule that can assist other gelator or non-gelator molecules to form gels. We hope that the concept of supramolecular gelatons will provide useful guidance and understanding of the design of gelator molecules and preparation of supramolecular gels.
89 citations
TL;DR: An enthralling and exceptionally close race to garner the top position within the electron deficient molecules unfolds, which has immense implications with regard to stability and potential applications.
Abstract: Arylenediimides are inherently electron deficient and provide enormous opportunities to conjugate electron withdrawing substituents in different regions of the π-scaffold. This review article highlights the gradual emergence of diverse molecular design principles to realize exceptionally electron deficient arylenediimide molecules. Interestingly, non-conventional electron withdrawing substituents allow the realization of some of the strongest electron acceptors known from this class of molecules. Thus, an enthralling and exceptionally close race to garner the top position within the electron deficient molecules unfolds, which has immense implications with regard to stability and potential applications.
TL;DR: In this paper, the electrochemical trifluoromethylarylation of N-arylacrylamides catalyzed by bromide is described, and the synthetic utility of this methodology is demonstrated by transition metal-free and external oxidant-free conditions, and low catalyst loading.
Abstract: The electrochemical trifluoromethylarylation of N-arylacrylamides catalyzed by bromide is described. The synthetic utility of this methodology is demonstrated by transition metal-free and external oxidant-free conditions, and low catalyst loading.
TL;DR: A series of unsymmetrical β-diketimine coordinated magnesium(I) complexes have been successfully synthesized via reductions of related magnesium(II) halide complexes with a sodium reducing reagent in toluene or n-hexane solution as mentioned in this paper.
Abstract: A series of unsymmetrical β-diketimine coordinated magnesium(I) complexes have been successfully synthesized via reductions of related magnesium(II) halide complexes with a sodium reducing reagent in toluene or n-hexane solution. All the unsymmetrical magnesium(I) complexes prepared have been crystallographically and spectroscopically characterized. It was found, for the first time, that these well-defined unsymmetrical magnesium(I) complexes were highly active pre-catalysts for the hydroboration of alkynes, nitriles, aldehydes and ketones.
TL;DR: In this paper, a method for the synthesis of 3-tertiary alkylated 1,1-difluorostyrene derivatives via Cu-catalyzed alkylation of α-(trifluorsomethyl)styrenes with tertiary alklmagnesium reagents at room temperature was developed.
Abstract: A novel and efficient method for the synthesis of 3-tertiary alkylated 1,1-difluorostyrene derivatives via Cu-catalyzed alkylation of α-(trifluoromethyl)styrenes with tertiary alkylmagnesium reagents at room temperature was developed.
TL;DR: The present method provides a highly attractive and alternative approach to C–Se bond formation and preliminary mechanism studies suggest that oxidation-induced C–H functionalization may be involved in this transformation.
Abstract: A visible-light-promoted approach for the regioselective selenylation of 4-amino substituted coumarins has been developed under metal- and photocatalyst-free conditions at room temperature. Notably, dual selenylation products were also obtained selectively when N-substituted 4-(phenylamino)-2H-chromen-2-ones were employed. Preliminary mechanism studies suggest that oxidation-induced C–H functionalization may be involved in this transformation. The present method provides a highly attractive and alternative approach to C–Se bond formation.
TL;DR: This domino-type process offered an efficient method for the synthesis of 2,3-dihydrobenzofurans in good yields, exhibiting good functional group tolerance, scalability and high diastereoselectivity.
Abstract: A formal 1,6-conjugated addition-mediated [4 + 1] annulation of ortho-hydroxyphenyl-substituted para-quinone methides with sulfonium or ammonium bromides has been described. This domino-type process offered an efficient method for the synthesis of 2,3-dihydrobenzofurans in good yields, exhibiting good functional group tolerance, scalability and high diastereoselectivity.
TL;DR: In this article, a review of the recent developments involving the employment of organometallic reagents for palladium-catalysed non-directed C-H bond functionalisation of (hetero)arene C−H bonds is presented.
Abstract: Transition metal-catalysed C–H bond functionalisation is an attractive approach for assembling valuable complex intermediates for the synthesis of pharmaceuticals, natural products, agrochemicals and fine chemicals. Selective functionalisation of one specific C–H site within a complex molecule without the assistance of a directing group is one of the major challenges in organic synthesis. The non-directed functionalisation of C–H bonds is more attractive and straightforward than the directed approach. While several reviews have covered (hetero)aryl (pseudo)halides as coupling partners in non-directed C–H bond functionalisation, this review will complement these existing contributions by focusing on the recent developments involving the employment of organometallic reagents for palladium-catalysed non-directed C–H bond functionalisation of (hetero)arene C–H bonds. Additionally, C–H/C–H bond coupling and other coupling partners will also be fully described.
TL;DR: A visible-light-mediated radical allylation of primary amine-derived Katritzky salts with allylic sulfones via C(sp3)–N bond activation is reported, furnishing the corresponding alkenes in satisfactory yields.
Abstract: A visible-light-mediated radical allylation of primary amine-derived Katritzky salts with allylic sulfones via C(sp3)–N bond activation is reported, furnishing the corresponding alkenes in satisfactory yields. This mild protocol provides an efficient strategy for site-specific C(sp3)–C(sp3) bond formation using abundant feedstock primary amines, particularly α-amino acids as alkyl radical precursors. This photocatalytic reaction demonstrates a broad substrate scope and good functional group tolerance.
TL;DR: In this paper, the authors summarize recent advances in natural product synthesis, featuring late-stage functionalization of four-membered rings and novel strategies for the stereocontrolled assembly of cyclobutanes or cyclobutenes.
Abstract: Cyclobutanes, as the second most strained monocyclic all-carbon rings, are found in many complex natural products. Although recent methodological developments in the formation of cyclobutanes have been reviewed, few have focused on the topic of total synthesis of cylcobutane-containing natural products. Here we summarize recent advances in natural product synthesis, featuring late-stage functionalization of four-membered rings and novel strategies for the stereocontrolled assembly of cyclobutanes or cyclobutenes.
TL;DR: In this paper, the effects of atomic electronegativity (O, S and Se atoms) on the excited-state intramolecular proton transfer (ESIPT) properties of three compounds (3-HF, 3-HTF and 3-HSeF) were systematically studied using the density functional theory (DFT) and time-dependent DFT (TD-DFT).
Abstract: The effects of atomic electronegativity (O, S and Se atoms) on the excited-state intramolecular proton transfer (ESIPT) properties of three compounds (3-HF, 3-HTF and 3-HSeF) were systematically studied using the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. Furthermore, the antioxidant activities of the three compounds were evaluated using different parameters from the perspective of biological activities. The calculated results indicate that the generation of ESIPT is attributed to the excited-state intramolecular charge transfer owing to the change in electron density distribution on the frontier molecular orbitals and natural bond orbital (NBO) charge distribution of the O1 and O2 atoms at the S0 and S1 states. Moreover, 3-HTF shows the greatest red shift of the O1–H1 stretching peak and the lowest energy barrier at the S1 state among the three compounds, implying that 3-HTF would have the strongest intramolecular hydrogen bond at the S1 state, which is most beneficial for the occurrence of ESIPT. In addition, the decreased ionization potentials and energy gaps from 3-HF to 3-HTF and 3-HSeF means that the antioxidant activity of the compound would be enhanced along with the lowered atomic electronegativity. Interestingly, the lower ionization potentials and energy gaps of the compounds in keto forms suggest that the compound (3-HTF) easy to carry out ESIPT reaction would exhibit efficient antioxidant activity, which would establish the relationship between ESIPT reaction and antioxidant activity of the compound and provide a new notion for synthesizing more efficient antioxidants in experiments.
TL;DR: In this article, a decarboxylative cascade radical cyclization of tertiary carboxylic acids and o-(allyloxy)arylaldehydes was developed to synthesize 3-alkyl-substituted chroman-4-one derivatives.
Abstract: A convenient silver-catalyzed decarboxylative cascade radical cyclization of tertiary carboxylic acids and o-(allyloxy)arylaldehydes was developed to synthesize 3-alkyl-substituted chroman-4-one derivatives. A series of chroman-4-one derivatives were constructed with moderate to good yields. This procedure offers a practical method for the synthesis of 3-alkyl-substituted chroman-4-one derivatives by a one-pot reaction from easily available reagents.
TL;DR: In this article, various Ru(II) complexes bearing functionalized 2,2′-bipyridine ligands were synthesized and fully characterized, and a new N6,N6′-dimethyl-2, 2, 2′-, 6, 6′-diamine ligand was found to be the most electron-rich ligand as its corresponding Ru (II) complex (1a) displayed the lowest νco value and the highest efficiency in the β-alkylation of secondary alcohols with primary alcohols.
Abstract: Various Ru(II) complexes bearing functionalized 2,2′-bipyridine ligands were synthesized and fully characterized. Among them, a new N6,N6′-dimethyl-2,2′-bipyridine-6,6′-diamine ligand was found to be the most electron-rich ligand as its corresponding Ru(II) complex (1a) displayed the lowest νco value and the highest efficiency in the β-alkylation of secondary alcohols with primary alcohols (TON = 98 860). Complex 1a also exhibited a greater reactivity in the monoalkylation of acetonitrile, α-alkylation as well as α-methylation of arylacetonitriles. Compared to the other reported systems, in α-methylation of nitriles complex 1a presented superior catalytic activity. The potential of complex 1a was extended further in N-methylation of amines using methanol as a green methylating agent.
TL;DR: In this paper, the tetrahalogenoferrate(III) complexes were reported as a new kind of iron photocatalyst, which is easily prepared from FeCl3 with lithium bromide or ammonium bromides, and has a good and tunable photo-sensitivity in the visible light region.
Abstract: We report tetrahalogenoferrate(III) complexes as a new kind of iron photocatalyst. These complexes are easily prepared from FeCl3 with lithium bromide or ammonium bromides, and have a good and tunable photo-sensitivity in the visible light region. Their distinct catalytic mode with FeCl3 enables a highly chemoselective photooxygenation of benzylic sp3 C–H, providing a series of carbonyls in moderate to excellent yields. The method has also been employed in the challenging aerobic oxidative transposition of vinyl halides, thus facilitating a mild and highly efficient approach to access significant α-halo ketones with a broad substrate scope. The disclosure of tetrahalogenoferrate(III) complex photocatalysts should provide inspiration for their expansion to new aerobic oxidative reactions and even anaerobic variations.
TL;DR: In this paper, a copper-catalyzed enantioselective hydroboration of 1,3-enynes with the catalyst generated from Cu(OAc) and (S,S)-Ph-BPE was reported.
Abstract: We report a copper-catalyzed enantioselective hydroboration of 1,3-enynes with the catalyst generated from Cu(OAc) and (S,S)-Ph-BPE. A wide range of alkyl- and aryl-substituted 1,3-enynes undergo this asymmetric hydroboration with pinacolborane, yielding the corresponding allenes in good yields with high to excellent enantioselectivities (up to 99% ee). This asymmetric transformation tolerates a variety of reactive groups, such as chloro, bromo, trifluoromethyl ether, siloxy, carboxylic ester and imido functionalities.
TL;DR: In this paper, a photocatalyst was used to assist the single electron transfer during the reaction process, thus facilitating the formation of desired products in good yields, achieving the generation of sulfonated isobenzofuran-1(3H)-ones starting from 2-vinylbenzoic acids, aryldiazonium tetrafluoroborates, and sulfur dioxide surrogate of DABCO˙(SO2)2.
Abstract: Generation of sulfonated isobenzofuran-1(3H)-ones starting from 2-vinylbenzoic acids, aryldiazonium tetrafluoroborates, and sulfur dioxide surrogate of DABCO˙(SO2)2 under photocatalysis in the presence of visible light is achieved. The presence of a photocatalyst assists the single electron transfer during the reaction process, thus facilitating the formation of desired products in good yields. Additionally, the method can be extended to 4-phenylpent-4-enoic acid and 5-phenylhex-5-enoic acid.
TL;DR: A sustainable manganese-catalyzed acceptorless dehydrogenative coupling of alcohols with alkaline water to form carboxylates generating H2 as the sole byproduct is reported in this paper.
Abstract: The direct oxidation of alcohols into carboxylic acids is an essential reaction for the synthesis of bulky and fine chemicals Most current processes require the use of either strong and toxic oxidants or the presence of pressurized oxygen Herein, we report a sustainable manganese-catalyzed acceptorless dehydrogenative coupling of alcohols with alkaline water to form carboxylates generating H2 as the sole by-product This is a general applicable and efficient non-noble metal catalyzed dehydrogenative transformation of alcohols into carboxylates The reaction proceeded selectively in the presence of a well-defined manganese pincer complex at a very low catalyst loading A wide range of carboxylic acids (46 examples) were synthesized with high yields and excellent functional group tolerance Mechanistic studies including control experiments, NMR spectroscopy, and X-ray crystallography identified the resting state and key intermediates in the catalytic cycle
TL;DR: In this article, the radical tri-/difluoromethylation of para-quinone methides with readily available sodium tri- /dif fluoromethanesulfinate via organic photoredox catalysis is described, which is external oxidant free and exhibits wide functional group compatibility, providing the desired products in useful yields.
Abstract: The radical tri-/difluoromethylation of para-quinone methides with readily available sodium tri-/difluoromethanesulfinate via organic photoredox catalysis is described. This reaction is external oxidant free and exhibits wide functional group compatibility, providing the desired products in useful yields. However, the reaction of para-quinone methides with CH2FSO2Na and CH3SO2Na under the optimal conditions gives the nucleophilic conjugate addition products. The results indicate that the strong inductive effect of the fluorine atom may play a critical role in the reactivity of the sodium sulfinates.
TL;DR: In this paper, the state of the art development of heteropore COFs is summarized and personal perspectives on this new generation of porous organic materials are also discussed. But unlike traditional COFs which only hold uniform pores and thus display homogeneous porosity, heteropores exhibit heterogeneous/hierarchical porosities.
Abstract: Covalent organic frameworks (COFs), a class of crystalline porous organic polymers with designable and predictable structures which can be constructed by atomically precise integration of organic units via covalent bonds, have drawn considerable attention over the past decade due to their versatile applications in many fields. Very recently, we have devised a new class of COFs coined as heteropore COFs by introducing different kinds of pores into one COF structure. In contrast to the traditional COFs which only hold uniform pores and thus display homogeneous porosity, heteropore COFs exhibit heterogeneous/hierarchical porosities. In this review, the state of the art development of heteropore COFs is summarized and personal perspectives on this new generation of porous organic materials are also discussed.
TL;DR: In this paper, a trifluoromethylation of 8-aminoquinoline scaffolds in the C5 position with CF3SO2Na under visible light irradiation without an external photocatalyst has been developed.
Abstract: A highly selective remote C–H trifluoromethylation of 8-aminoquinoline scaffolds in the C5-position with CF3SO2Na under visible light irradiation without an external photocatalyst has been developed. The protocol employs commercially available sodium trifluoromethanesulfinate (CF3SO2Na) as a trifluoromethylation reagent and shows a broad substrate scope, generating various 5-trifluoromethylated quinolines in good yields under photocatalyst-free, simple and mild conditions. Investigations indicated that both the starting material and product act as photosensitizers and 1O2 coexists with O2˙− during the reaction through energy transfer and single electron transfer processes. It is important to note that the electronic effect of the CF3 group as a substituent introduced into quinoline rings makes their trifluoromethylation more efficient under photo-irradiation from ultraviolet to visible light in the absence of an external photocatalyst.
TL;DR: Pyridyltriazole-ligated ruthenium(II) complexes have been designed and synthesized, which were characterized by X-ray crystallography as mentioned in this paper, and the resulting complexes were revealed to have good stability through TG experiments and effective catalytic reactivity for selective alkylation and one-pot C-H hydroxylation of 2-oxindole with a variety of primary alcohols, via a hydrogen-borrowing process.
Abstract: Pyridyltriazole-ligated ruthenium(II) complexes have been designed and synthesized, which were characterized by X-ray crystallography. The resulting complexes were revealed to have good stability through TG experiments and effective catalytic reactivity for selective alkylation and one-pot C–H hydroxylation of 2-oxindole with a variety of primary alcohols, via a hydrogen-borrowing process. The mechanism experiments revealed that the catalytic activity of these catalysts was enhanced by non-coordinating anions. Isotopic labelling experiments were further explored to understand these transformations. In comparison with previous ruthenium systems, these catalysts are not only easily synthesized with cheap triazole as the ligand, but also triazole ruthenium complexes are effective new catalysts for hydrogen-borrowing reaction. This provided an efficient and green method for the synthesis of valuable 3-functionalized-2-oxindoles, 3-functionalized-3-hydroxy-2-oxindoles and quaternary α-hydroxy carbonyl compounds with excellent yields for the first time.