Hafnium Triflate as an Efficient Catalyst for Direct Friedel–Crafts Reactions of Chromene Hemiacetals

The direct Friedel–Crafts reaction of chromene hemiacetals with indoles, furans and sterically hindered anilines has been accomplished with high selectivity and excellent yields in the presence of a catalytic amount of hafnium triflate [Hf(OTf)₄, 0.1 mol%, 0–40 °C]. The mild conditions tolerate various sensitive functional and protecting groups, and the products were confirmed unambiguously from their spectra and by single‐crystal X‐ray analysis. This direct Friedel–Crafts reaction of chromene hemiacetals should inspire and encourage the consideration of hafnium triflate in the development of mild reaction conditions for the efficient derivatization of hemiacetal‐containing compounds.     

Chlorinated crosslinked adsorbents

High crosslinked copolymers based on poly(ethylstyrene-co-divinylbenzene), bead shaped, have chlorinated, resulting in adsorbents with a high content of chlorine (45.0% Cl). The chlorination process of the copolymer beads (0.40–0.80 mm in diameter) was carried out in 1,2-dichloroethane in the presence of a Friedel–Crafts catalyst (AlCl₃, FeCl₃), at 5–40°C, yielding yellow beads without any cracks and good mechanical strength. The chlorination degree of the samples is high because each vinyl aromatic unit contains 1.8–2.2 chlorine atoms. The chlorinated copolymer samples were used to retain Cephalosporine C from standard solutions comparatively with commercial adsorbents (Amberlite XAD-4 Rohm, Haas Co.; SP-206/7, Mitsubishi Kasai Corp., Japan). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1579–1587, 1998     

Synthesis and characterization of novel copolymers of poly(ether ketone ketone) and poly(ether ketone sulfone imide)

A new monomer containing sulfone and imide linkages, bis{4-[4-(p-phenoxyphenylsulfonylphenoxy)benzoyl]-1,2-benzenedioyl}-N,N,N′,N′-4,4′-diaminodiphenyl ether (BPSPBDADPE), was prepared by the Friedel–Crafts reaction of bis(4-chloroformyl-1,2-benzenedioyl)-N,N,N′,N′-4,4′-diaminodiphenyl ether with 4,4′-diphenoxydiphenyl sulfone. Novel copolymers of poly(ether ketone ketone) and poly(ether ketone sulfone imide) were synthesized by electrophilic Friedel–Crafts solution copolycondensation of terephthaloyl chloride with a mixture of DPE and BPSPBDADPE. The polymers were characterized by different physico-chemical techniques. The polymers with 10–25?mol% BPSPBDADPE are semicrystalline and had increased T _gs over commercially available PEEK and PEKK (70/30) due to the incorporation of sulfone and imide linkages in the main chains. The polymer IV with 25?mol% BPSPBDADPE had not only high T _g of 194?°C but also moderate T _m of 338?°C, having good potential for melt processing and exhibited high thermal stability and good resistance to common organic solvents.     

Gold(III) Chloride‐Catalyzed Addition Reactions of Electron‐Rich Arenes to Methyl Vinyl Ketone

For the reaction of α,β‐unsaturated ketones with electron‐rich arenes catalyzed by gold(III) chloride both, a Friedel–Crafts‐type mechanism and an initial metallation, are evaluated. Gold(III) chloride has proven to be an efficient catalyst under very moderate reaction conditions, however, in the case of sterically demanding products HBF₄ turned out to be the superior catalyst.     

Regioselective Cleavage of Unstrained C?C Bond and C?H Bond: Palladium–Copper Catalyzed Deacetophenonylative Arylation of Coumarin Derivatives

A C_α C_β bond activation of the carbonyl group in unstrained ketones catalyzed cooperatively by palladium and copper(II) with the departure of the acetophenone has been developed, and the subsequent coupling with a variety of aromatics via the formal C H activation similar to the Friedel–Crafts reaction affords the skeleton‐reconstructed coumarin derivatives with high regioselectivity.     

A Copper(II) Triflate‐Catalyzed Tandem Friedel–Crafts Alkylation/Cyclization Process towards Dihydroindenes

A one‐pot synthesis of dihydroindenes from substituted benzenes and haloalkenes was developed. The reaction proceeded via a copper(II) triflate [Cu(OTf)₂]‐catalyzed tandem Friedel–Crafts alkylation/cyclization process with high efficiency under relatively mild conditions.     

Synthesis of novel poly(ether ketone diphenyl ketone ether ketone ketone)s by electrophilic Friedel–Crafts solution polycondensation

4,4′‐Bis(4‐phenoxybenzoyl)diphenyl was prepared by the Friedel–Crafts reaction of 4‐bromobenzoyl chloride and diphenyl followed by condensation with potassium phenoxide. Novel aromatic poly(ether ketone diphenyl ketone ether ketone ketone)s were obtained by the electrophilic Friedel–Crafts solution copolycondensation of 4,4′‐bis(4‐phenoxybenzoyl)diphenyl with a mixture of isophthaloyl chloride and terephthaloyl chloride over a wide range of isophthaloyl chloride/terephthaloyl chloride molar ratios in the presence of anhydrous aluminum chloride and N‐methylpyrrolidone in 1,2‐dichloroethane. The influence of the reaction conditions on the preparation of the copolymers was examined. The copolymers were characterized with different physicochemical techniques. Because of the incorporation of diphenyl, the resulting copolymers exhibited outstanding thermal stability. The glass‐transition temperatures were above 174°C, the melting temperatures were above 342°C, and the 5% weight loss temperatures were above 544°C in nitrogen. All these copolymers were semicrystalline and insoluble in organic solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rate enhancement in palladium catalyzed Heck reactions by Lewis acid promoters

Significant enhancement in the rate of Heck reactions has been achieved when catalytic amounts of Lewis acid (like FeCl₃) promoters in the presence of trace amounts of water (>2000 ppm) are used along with Pd complex catalysts. Experiments with different aryl halides, bases as well as olefins have been carried out to demonstrate the role of Lewis acid promoters. The increase in the reaction rates is due to the weakening of Ar–X bond by the Lewis acid in the manner similar to Friedel–Crafts reaction.     

Brønsted Acid Generation over Alumina-Supported Niobia by Calcination at 1173 K

Alumina-supported niobium oxide promotes Friedel–Crafts reaction of benzyl alcohol and anisole effectively. The optimized condition of the catalyst was 16 wt% as Nb₂O₅ and calcination temperature of 1173 K. The catalyst exhibits the Brønsted acidity despite calcination at such high temperatures.     

One-pot synthesis of Ga-SBA-15: Activity comparison with Ga-post-treated SBA-15 catalysts

Gallium containing SBA-15 mesoporous materials with different Si/Ga ratio were synthesized using an in situ sol–gel procedure with an aqueous solution of Ga(NO₃)₃. The materials were characterised by means of elemental analysis, BET, XRD, TEM, and H/D isotope exchange techniques. It appears that depending their loading, stable Ga-species were either anchored to the siliceous matrix of SBA-15 or introduced in the framework via isomorphous substitution, thus generating acid properties in their host material.The catalytic activity of Ga-SBA-15 materials has been evaluated in the Friedel–Crafts acylation of anisole with benzoyl chloride and in the alkylation of benzene using benzyl chloride as alkylating agent. The activity of these catalysts was compared with the one of Ga-modified SBA-15 by post-treatment. A complete conversion of benzyl chloride over Ga-SBA-15 materials has been reached after 3 h of reaction with a 75% selectivity toward diphenylmethane. In contrast to Ga-samples prepared by post-treatment, in situ Ga-SBA-15 present a lower stability in the acylation reaction. However, the catalytic results indicate that Ga-SBA-15 mesoporous materials can be used as versatile and stable acid catalysts for Friedel–Crafts reactions with appropriate behavior depending on their preparation mode.     

Asymmetric Brønsted Acid‐Catalyzed Friedel–Crafts Reactions of Indoles with Cyclic Imines ‐ Efficient Generation of Nitrogen‐Substituted Quaternary Carbon Centers

A new enantioselective Brønsted acid‐catalyzed Friedel–Crafts reaction of indole with cyclic imines has been develeoped. This organocatalytic reaction provides for the first time optically active indolindolinone derivatives in high yields and with excellent enantioselectivities (up to 91% ee) under mild reaction conditions.     

Synthesis and characterization of soluble aromatic poly(ether amide amide ether ketone ketone)s by electrophilic Friedel–Crafts solution polycondensation

A new monomer, N,N′-bis(4-phenoxybenzoyl)-m-phenylenediamine (BPBMPD), was prepared by condensation of m-phenylenediamine with 4-phenoxybenzoyl chloride in N,N-dimethylacetamide (DMAc). Novel soluble aromatic poly(ether amide amide ether ketone ketone)s (PEAAEKKs) were synthesized by electrophilic Friedel–Crafts solution copolycondensation of BPBMPD with a mixture of terephthaloyl chloride (TPC) and isophthaloyl chloride (IPC) in the presence of anhydrous aluminum chloride and N-methylpyrrolidone (NMP) in 1,2-dichloroethane (DCE). The influences of reaction conditions on the preparation of polymers were examined. The polymers obtained were characterized by different physico-chemical techniques such as FT-IR, DSC, TGA, and wide-angle X-ray diffraction (WAXD). All the polymers were amorphous and the solubility of the polymers was improved by the incorporation of 1,3-dibenzoylaminobenzene moieties in the main chain. Thermal analyses showed that the polymers had high T_gs of 220–231 °C and exhibited high thermal stability. All the polymers formed transparent, strong, and flexible films, with tensile strengths of 102.9–108.5 MPa, Young’s moduli of 2.44–2.86 GPa, and elongations at break of 9.8–13.7%.     

Structure and Catalytic Mechanism of a Bacterial Friedel–Crafts Acylase

C−C bond-forming reactions are key transformations for setting up the carbon frameworks of organic compounds. In this context, Friedel–Crafts acylation is commonly used for the synthesis of aryl ketones, which are common motifs in many fine chemicals and natural products. A bacterial multicomponent acyltransferase from Pseudomonas protegens (PpATase) catalyzes such Friedel–Crafts C-acylation of phenolic substrates in aqueous solution, reaching up to >99 % conversion without the need for CoA-activated reagents. We determined X-ray crystal structures of the native and ligand-bound complexes. This multimeric enzyme consists of three subunits: PhlA, PhlB, and PhlC, arranged in a Phl(A₂C₂)₂B₄ composition. The structure of a reaction intermediate obtained from crystals soaked with the natural substrate 1-(2,4,6-trihydroxyphenyl)ethanone together with site-directed mutagenesis studies revealed that only residues from the PhlC subunits are involved in the acyl transfer reaction, with Cys88 very likely playing a significant role during catalysis. These structural and mechanistic insights form the basis of further enzyme engineering efforts directed towards enhancing the substrate scope of this enzyme.     

An Efficient Bismuth(III) Chloride‐Catalyzed Synthesis of 1,1‐Diarylalkenes via Friedel–Crafts Reaction of Acyl Chloride or Vinyl Chloride with Arenes

In the presence of catalytic amount of bismuth(III) chloride, the reactions of acyl chlorides or vinyl chlorides with arenes afforded 1,1‐diarylalkenes in 25–82 % isolated yield. In the case of the reaction of acyl chlorides with arenes, the procedure includes an initial Friedel–Crafts acylation, subsequent formation of vinyl chlorides and final Friedel–Crafts‐type vinylation of another arene molecule with vinyl chloride. This paper reports the first Lewis acid‐catalyzed cleavage of the C Cl bond of vinyl chloride and its application in the synthesis of multiply subtituted alkenes.     

Preparation of novel membrane from dianhydride-modified polystyrene with controlled pore size on micro- and macrolevels

A technique has been developed to prepare crosslinked, porous membrane from a chemical modification of polystyrene. Polystyrene was chemically modified by crosslinking with pyromellitic dianhydride in nitrobenzene using a Friedel–Crafts acylation reaction in the presence of AlCl₃ at 100°C. Solid-state cross polarization/magic angle spinning NMR of powdered membrane was reported. TGA of the membrane was verified in air and in nitrogen. The morphologies of the membranes were analyzed. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 709–717, 1998     

Chemoselective Cascade Synthesis of N‐Fused Heterocycles via Silver(I) Triflate‐Catalyzed Friedel–Crafts/N‐C Bond Formation Sequence

An efficient cascade methodology toward chemoselective synthesis of N‐fused heterocycles including 9H‐pyrrolo[1,2‐a]indole, 3H‐pyrrolo[1,2‐a]indole and 1H‐pyrrolo[1,2‐a]indole derivatives has been developed. This transformation proceeds via a silver(I) triflate‐catalyzed consecutive Friedel–Crafts reaction/N C bond formation sequence between readily available propargyl alcohols and 3‐substituted 1H‐indoles. Not only is excellent chemoselectivity observed according to the substitution patterns of propargyl alcohols, but also the Lewis acid‐catalyzed N C bond formation process can be carried out under base‐ and ligand‐free conditions.     

Efficient synthesis of benzophenone derivatives in Lewis acid ionic liquids

Benzophenone and its derivatives were prepared via Friedel–Crafts acylation reactions using ionic liquids (ILs) of BmimCl–FeCl₃, BmimCl–AlCl₃ and BmimCl–ZnCl₂ as dual catalyst–solvent. Among them, BmimCl–FeCl₃ showed much higher catalytic activity than that observed for the other two ILs, and in conventional organic solvents. In these reaction systems, good to excellent yields (up to 97%) of acylation products were obtained in a short reaction time. This method features high yield, a simple product isolation procedure, ILs reusability and reduced waste discharge, thus rendering this catalytic system both efficient and environmentally friendly.     

Synthesis of 2-Hydroxybenzo[a]pyrene,a Tumorigenic Phenol Derivative of Benzo[a]pyrene

An efficient synthesis of 2-hydroxybenzo[a]pyrene (1a) from 4,5,9,10-tetrahydropyrene via 2-methoxy-4,5,9,10-tetrahydropyrene (2e) is described. Friedel–Crafts acetylation of tetrahydropyrene affords the 2-acetyl derivative which is transformed to the 2-methoxy derivative 2e via Baeyer–Villager oxidation, hydrolysis, and treatment with dimethyl sulfate. Friedel–Crafts succinoylation of 2e with succinic anhydride and AlCl₃ takes place regiospecifically in the 7-position. The product is transformed to 1a via Clemmensen reduction, HF cyclization, Wolff–Kishner reduction, catalytic dehydrogenation, and demethylation with HBr.     

Facile Creation of 3‐Indolyl‐3‐hydroxy‐2‐oxindoles by an Organocatalytic Enantioselective Friedel–Crafts Reaction of Indoles with Isatins

The first direct enantioselective Friedel–Crafts reaction of indoles with isatins has been developed. The process is catalyzed by simple cupreine under mild reaction conditions and affords synthetically and biologically interesting, chiral 3‐indolyl‐3‐hydroxy‐2‐oxindoles in good yields (68–97%) and with high enantioselectivities (76–91%).     

Triarylaminium Salt‐Initiated Aerobic Double Friedel–Crafts Reaction of Glycine Derivatives with Indoles

A novel and efficient stable radical cation triarylaminium salt‐catalyzed aerobic double Friedel–Crafts alkylation reaction of glycine derivatives with indoles has been developed. The reaction was performed in the absence of any other additives under mild conditions and only requires an air atmosphere (or oxygen, 1 atm) as co‐oxidant.