Synthesis of new thioxanthenes by organocatalytic intramolecular Friedel–Crafts reaction

An efficient organocatalytic route has been developed to synthesize novel substituted thioxanthenes (2a–2v) starting from diaryl thioether alcohols (1a–1v) using the intramolecular Friedel–Crafts reaction. The starting materials were obtained in two stages via a coupling reaction followed by the Grignard reaction. In this study, we tried for the first time to use some organic Brønsted acids as organocatalysts (3a–3h) in the intramolecular Friedel–Crafts cyclization reaction of thioether alcohols. The synthesis of original substituted thioxanthenes was achieved within 15?minutes by using N-triflylphosphoramide (3h) with quantitative yields in THF at room temperature.     

Asymmetric intramolecular Friedel–Crafts reaction catalyzed by a spiropyrrolidine organocatalyst: Enantioselective construction of indolizine and azepine frameworks

The asymmetric intramolecular Friedel–Crafts type Michael reaction of α,β-unsaturated aldehyde with pyrrole, catalyzed by a spiropyrrolidine (SP)-type organocatalyst, has been accomplished, which allows the construction of a series of azepine and indolizine frameworks with high to excellent enantioselectivities (up to 98% ee). Moreover, the substrate scope could be extended to generate a quaternary center in indolizine frameworks (up to 96% ee).     

Synthesis of highly substituted indene derivatives by Brønsted acid catalyzed Friedel–Crafts reaction of homoallylic alcohols

An efficient synthetic method to prepare highly substituted indenes in moderate to excellent yields that relies on Brønsted acid catalyzed Friedel–Crafts reaction of homoallylic alcohols under mild conditions is described.     

Synthesis of extended π-conjugated hypercrosslinked polymers via a Friedel–Crafts reaction and an intramolecular Scholl coupling reaction

Long-range conjugated structures are important for increasing the conductivity and broadening the application scope of hypercrosslinked polymers (HCPs). It is, however, difficult to fabricate long-range conjugated structures using conventional HCP synthesis methods. Herein, we report a simple and efficient strategy for the synthesis of HCPs with extended π-conjugated structures through Friedel–Crafts and intramolecular Scholl-coupling reactions from readily available aromatic compounds under mild conditions. Two conjugated HCPs (C-HCPs), namely, C-HCP-ATA and C-HCP-TPB, were prepared from anthracene (ATA) and triphenylbenzene (TPB), respectively, using this method. The proposed strategy not only ensures a high specific surface area of materials but also introduces a long-range conjugated structure into HCPs. The lithium-ion battery applications of the C-HCPs were investigated. As anode materials, C-HCP-ATA and C-HCP-TPB displayed higher lithium storage capacities, better conductivity, and higher stability than their precursors, HCP-ATA and HCP-TPB, which were prepared using the conventional method.     

Tandem five membered-ring selective Prins reaction and Friedel–Crafts reaction

A tandem reaction consisting of five membered-ring selective Prins cyclization and subsequent Friedel–Crafts cyclization was developed. The reactions of phenyl homoallylic alcohol 3 and benzaldehyde derivatives 6 afforded tetrahydroindenofurans 7 or pentacyclic products 8, depending upon the quantity of 6. Also homoallylic alcohol 12 having an alkyne–cobalt moiety reacted with 6 to give rise to tetrahydroindenofurans 13 in good yields.     

Lithium perchlorate accelerated Friedel–Crafts addition of furans to β-nitrostyrenes

The Friedel–Crafts alkylation of furans by the Michael acceptor, β-nitrostyrene, is greatly accelerated by the use of the Lewis acid catalyst and solvent, 5 M lithium perchlorate in diethyl ether (LDPE).     

Synthesis of 4,5-fused tricyclic quinolines via an acid-promoted intramolecular Friedel–Crafts allenylation of aniline derivatives

A novel method for synthesizing 4,5-fused tricyclic quinoline derivatives based on an acid-promoted intramolecular Friedel–Crafts allenylation of anilines. Using aryl group-substituted propargyl alcohol derivatives with a meta-substituted N-Boc aniline unit as substrates, a four-step reaction sequence involving an acid-promoted intramolecular Friedel–Crafts allenylation of anilines, an acid-promoted intramolecular C–N bond formation, deprotection of the Boc group, and air oxidation proceeded in a single pot, producing the corresponding 4,5-fused tricyclic quinoline derivatives in 31–84% yield.     

Highly stereoselective imidazolethiones mediated Friedel–Crafts alkylation of indole derivatives

The asymmetric Friedel–Crafts alkylation of indoles with α,β-unsaturated aldehydes was promoted by the novel imidazolethiones to afford the corresponding adducts in moderate to excellent yields and high enantioselectivities under mild reaction conditions.     

Triarylaminium salt facilitated Friedel–Crafts reaction of indoles with enamides and vinyl ethers

Commercially available stable radical cation triarylaminium salt can be used as an efficient initiator for Friedel–Crafts reaction of indoles with enamides to regioselectively construct complex indole derivatives and for double Friedel–Crafts reaction of indoles with vinyl ethers to offer 3,3′-Bis(indolyl)alkane derivatives. The ready availability of the starting materials and the usefulness of the products make this strategy attractive.     

The linkage between reversible Friedel–Crafts acyl rearrangements and the Scholl reaction

Structural Chemistry - Friedel–Crafts acyl rearrangements in PPA (at 80–240 °C) and Scholl reactions in AlCl3/NaCl (at 140–220 °C) of...     

Diastereoselective Friedel–Crafts reaction of α-trifluoromethyl imines derived from chiral amines

The Friedel–Crafts reactions of chiral N-(2,2,2-trifluoroethylidene)-1-arylethylamines 1a and 1b with various electron-rich aromatic compounds were examined. The reactions proceeded readily at room temperature in the presence of BF₃·Et₂O. Substituted products 2–12 were obtained in low to very high stereoselectivities (up to 100% d.e.). The absolute configuration of compound 12 was determined by X-ray analysis. Moreover, the chiral auxiliary from compounds 3 and 12 was selectively removed by palladium-catalyzed hydrogenolysis.     

Total synthesis of agomelatine via Friedel–Crafts acylation followed by Willgerodt–Kindler reaction

Total synthesis of antidepressant drug, agomelatine is reported. Regio selective Friedel–Crafts acylation followed by Willgerodt–Kindler reactions is used as the key steps for the synthesis of agomelatine.     

Biocatalytic Friedel–Crafts Acylation and Fries Reaction

The Friedel–Crafts acylation is commonly used for the synthesis of aryl ketones, and a biocatalytic version, which may benefit from the chemo- and regioselectivity of enzymes, has not yet been introduced. Described here is a bacterial acyltransferase which can catalyze Friedel–Crafts C-acylation of phenolic substrates in buffer without the need of CoA-activated reagents. Conversions reach up to >99 %, and various C- or O-acyl donors, such as DAPG or isopropenyl acetate, are accepted by this enzyme. Furthermore the enzyme enables a Fries rearrangement-like reaction of resorcinol derivatives. These findings open an avenue for the development of alternative and selective C−C bond formation methods.     

Chiral counteranion-directed silver-catalyzed asymmetric synthesis of 1,2-dihydroisoquinolines by Friedel–Crafts alkylation reactions

The reaction of ortho-alkynylaryl aldimines and indoles catalyzed by a silver binol-derived phosphate was realized to afford a series of enantioenriched 1,2-dihydroisoquinolines in moderate to good yields and ee. An interesting phenomenon that highly enantioenriched products could be obtained from their lower ee form by silica gel column chromatography was observed, providing an easy access to the enantiopure form of the product.     

Preparation of Mg–Al hydrotalcite from the effluent of Friedel–Crafts reaction and its application as a catalyst in Knoevenagel reaction

Abstract

Hydrotalcite containing magnesium and aluminium (Mg–Al HT) with a molar ratio of Mg(II)/Al(III) = 2.5 has been prepared by a co-precipitation method using the effluent of a Friedel–Crafts acylation reaction. The HT was calcined at 500°C and reconstructed with deionized water. The synthesized HT was characterized by XRD and FT-IR spectroscopy and was successfully used as a catalyst in the Knoevenagel reaction of aldehydes and active methylene compounds. The catalyst was found to be reusable.     

Syntheses,structures, and catalytic activity in Friedel–Crafts acylations of substituted tetramethylcyclopentadienyl molybdenum carbonyl complexes

Reactions of the substituted tetramethylcyclopentadienes [C₅HMe₄R] [R =  ^t Bu, Ph, CH₂CH₂C(CH₃)₃] with Mo(CO)₃(CH₃CN)₃ in refluxing xylene gave a series of dinuclear molybdenum carbonyl complexes [(η⁵-C₅Me₄R)Mo(CO)₃]₂ [R =  ^t Bu (1), Ph (2), CH₂CH₂C(CH₃)₃ (3)], [(η⁵-C₅Me ^t Bu)Mo(μ-CO)₂]₂ (4)], and [(η⁵-C₅Me₄) ^t Bu]₂Mo₂O₄(μ-O) (5)], respectively. Complexes 1–5 were characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectroscopy. In addition, their crystal structures were determined by X-ray crystal diffraction analysis. The catalytic activities of complexes 1–3 in Friedel–Crafts acylation in the presence of o-chloranil has also been investigated; the reactions were achieved under mild conditions to give the corresponding products in moderate yields.     

Recent developments of heterogeneous solid catalysts for liquid-phase Friedel–Crafts type benzylation reaction

Liquid-phase Friedel–Crafts type benzylation of aromatics has been effected traditionally with catalysis by homogeneous protonic acid or Lewis acid. However, heterogeneous catalysts have the advantages, compared to their homogeneous counterparts, of facile recovering and recycling. This short article describes the recent advances in the liquid-phase Friedel–Crafts type benzylation by benzyl chloride of aromatics over redox metal: gallium (Ga), indium (In) and thallium (Tl) containing novel heterogeneous solid catalysts. Unlike conventional acidic catalyst, the benzylation activity of the Ga-, In- or Tl-based solids does not depend solely on their acidic properties, even present; these solids in their non-acidic or basic form also shows high benzylation activity. The catalytic activity order of Ga, In and Tl containing solid catalysts supported on chemically similar inert catalyst carrier is as follows: thallium/support > indium/support > gallium/support, which is quite similar to their redox potential values indicating the role of redox function in the benzylation process. A plausible reaction mechanism for the benzylation reaction over these catalysts is proposed. These heterogeneous solids are highly efficient for the Friedel–Crafts type benzylation, even in the presence of moisture, than the conventional strongly acidic solid acid catalysts.Dedicated to Dr.Vasanth R. Choudhary, National Chemical Laboratory, Pune, India     

Bismuth Triflate–Catalyzed Friedel–Crafts Acylations of Sydnones

Friedel–Crafts acylations of various 3-arylsydnones at the C4 position have been achieved in good yields using 4 equivalents of an alkyl anhydride and 25 mol% each of bismuth triflate and lithium perchlorate in anhydrous acetonitrile at 95 °C. Acylations appear to be faster with arylsydnones bearing electron-donating moieties and sterically unencumbered anhydrides.     

Synthesis of porous aromatic framework with Friedel–Crafts alkylation reaction for CO_2 separation

A novel porous aromatic framework, PAF-8, derived from tetraphenylsilane as basic building unit, was successfully synthesized via Friedel–Crafts alkylation reaction. This PAF material had high thermal stability as well as high surface area(785 m~2g~(-1)) calculated from the Brunauer–Emmett–Teller(BET)model. Meanwhile, PAF-8 possessed high performances in gas sorption and especially for CO_2 separation.