Bromothiophene reactions. I. Friedel-crafts acylation

Friedel-Crafts acylation of 2,5-dibromo- and 2,3,5-tribromothiophenes with different acyl chlorides and anhydrous aluminium trichloride has been studied. The reaction afforded a mixture of acyl derivatives and tetrabromothiophene. The results obtained suggest a mechanism which involves the formation of bromine cations in the reaction medium. Several products obtained in this reaction are described.     

Friedel-crafts acylation of benzimidazolin-2-ones with aliphatic acid chlorides

The acylation of benzimidazolin-2-one and its 5,6-disubstituted derivatives with aliphatic acid chlorides in the presence of anhydrous aluminum chloride was studied. The corresponding 5(6)-acyl-, 5-R-6-acyl-, and 5,6-dimethyl-4-acylbenzimidaz-olin-2-ones, the structures of which were confirmed by the results of elementary analysis and IR, PMR, and mass spectroscopy, were obtained. The yields of the acylation products depend on the electronic effects of the substituents in the benzene ring of the benzimidazolin-2-one and on steric factors.Translated from Khimiya Geterotsiklieheskikh Soedinenii, No. 6, pp. 808–811, June, 1984.     

Friedel-crafts acylation of 2-methoxynaphthalene over h-beta catalysts: effect of Si/Al ratio

The acylation of 2-methoxynaphthalene with acetic anhydride was carried out over zeolite beta catalysts having various Si/Al ratios. It was found that the reaction performance is strongly dependent on the Si/Al ratio of the catalyst. The catalytic reaction features were elucidated in terms of the acidic properties of the catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Friedel-crafts cyclisation—IV: Intramolecular vs intermolecular acylation with β-aryl derivatives of propionyl chloride in aromatic substrates

Studies on the aluminium chloride-catalysed behaviour of β-phenylpropionyl, β,β-diphenylpropionyl, and β,β,β-triphenylpropionyl chlorides in anisole and some other aromatic stubstrates under standardised conditions are discussed. β,β-Diphenylpropionyl chloride gave yields of up to 27% 3-phenylindan-1-one in anisole and is one of the most easily cyclised acid chlorides so far reported. β,β,β-Triphenylpropionyl is less easily cyclised in anisole to 3,3-diphenylindan-1-one and its transformation product 2,3-diphenylind-1-one. The expected open-chain ketone is completely decomposed into products of αβ-ketonic cleavage and a subsequent redox reaction. Differences in ratios of intermolecular to intramolecular acylation (now called o/c ratios) are discussed.In benzene, β-bis-(p-chlorophenyl)propionyl chloride gave, in addition to the previously noted β-bis-(p-chlorophenyl)propiophenone (48%), the folloowing compounds: 6-chloro-3-(p-chlorophenyl)indan-1-one (4%) (the intramolecular acylation product), β-(p-chlorophenyl)-β-phenylpropiophenone (2·3%), ββ-diphenylpropiophenone (0·5%), 3-(p-chlorophenyl)-indan-1-one (5·2%). The transformation processes are discussed. Aluminium chloride-catalysed β-aryl exchange in acid chlorides is reported for the first time, but β-aryl exchange does not occur in ββ-(or 3,3-)di-aryl derivatives of indan-1-one.     

Molecular structure of arsabenzene by gas-phase electron diffraction

Vapor-phase molecules of C₅H₅As were found, assuming C_2v symmetry, to have the following structure parameters and uncertainties (2.5σ): r_g(C-As)= 1.850 ± 0.003 Å, r_g(C₂–C₃) = 1.390 ± 0.032 /rA, r_g(C₃–C₄) = 1.401 ± 0.032 /rA, r_g(C-C_ave) = 1.395₄ ± 0.002 Å, ∠CAsC = 97.3 ± 1.7°, ∠AsCC = 125.1 ± 2.8°, and ∠C₃C₃C₄ = 124.2 ± 2.9°. Amplitudes of vibration were also determined. Auxiliary information is more restrictive than pure electron diffraction intensities as evidence that the molecule is rigorously planar. Structural characteristics of arsabenzene reinforce prior indications that the heterocyclic molecule is genuinely aromatic.     

Thoughts about the electrophilic aromatic substitution mechanism: the Friedel-crafts alkylation and acylation of benzene with acetyl and t-butyl cations in the gas phase

Structural Chemistry - The mechanism of electrophilic aromatic substitution (SEAr) is still matter of debate and interest in the literature. In this work, the Friedel-Crafts alkylation and the...     

Friedel-crafts acetylation of durene,isodurene and prehnitene

Good yields of acetyl- and diacetyl-durene, acetyl- and diacetyl-isodurene, and acetylprehnitene can be obtained by Friedel-Crafts acylations. Products arising from methyl-migration prior to acetylation are also formed. A claim of the formation of diacetylprehnitene is shown to be incorrect.     

Friedel-crafts cyanation of some reactive aromatic hydrocarbons

Direct cyanation, using the heterogeneous Friedel-Crafts system cyanogen bromide/aluminium chloride, has given good yields of the following carbonitriles: anthracene-9-, chrysene-6-, 2-methyl-1-naphtho-, 4-methyl-1-naphtho-, 1-naphtho-, phenanthrene-9-, 2,4,6-trimethylbenzo-, triphenylene-1- and triphenylene-2-carbonitriles.     

Organocatalytic enantioselective Friedel-crafts reactions of 1-naphthols with aldimines

An organocatalytic enantioselective Friedel-Crafts reaction of 1-naphthols with aldimines has been developed. The method affords a direct access to chiral aminoarylnaphthols in good yields and with good to high enantioselectivities.     

Friedel-crafts reactions—XXVII : The mechanism for benzoylation of dichlorobenzenes

A search for mechanisms for benzoylation of dichlorobenzenes which are consistent not only with the nature and relative proportions of the eight products but also with the pattern of the non-additivity of substituent effects on the reaction rates, produced just one candidate. It involves chloronium ion migration and secondary protodechlorination in addition to the usual displacement of protons by acylium ions.     

Lanthanide triflate-catalyzed arene acylation. Relation to classical Friedel-Crafts acylation

Lanthanide trifluoromethanesulfonates, Ln(OTf) 3 (OTf (-) = trifluoromethanesulfonate), serve as effective precatalysts for the rapid, regioselective, intermolecular acylation of activated arenes. This contribution probes mechanism and metal ionic radius effects in the catalytic lanthanide triflate-mediated acylation of anisole with acetic anhydride. Kinetic studies of Ln(OTf) 3 (Ln = La, Eu, Yb, Lu)-mediated anisole acylation with acetic anhydride in nitromethane reveal the rate law nu approximately k 3 [Ln (3+)] (1)[acetic anhydride] (1)[anisole] (1). Eyring and Arrhenius analyses yield Delta H++ = 12.9 (4) kcal.mol (-1), Delta S++ = -44.8 (1.3) e.u., and E a = 13.1 (4) kcal.mol (-1) for Ln = Yb, with the negative Delta S++ implying a highly organized transition state. The observed primary kinetic isotope effect of k H/ k D = 2.6 +/- 0.15 is consistent with arene C-H bond scission in the turnover-limiting step. The proposed catalytic pathway involves precatalyst formation via interaction of Ln(OTf) 3 with acetic anhydride, followed by Ln (3+)-anisole pi-complexation, substrate-electrophile sigma-complex formation, and turnover-limiting C-H bond scission. Lanthanide size effects on turnover frequencies are consistent with a transition state lacking significant ionic radius-dependent steric constraints. Substrate-Ln (3+) interactions using paramagnetic Gd (3+) and Yb (3+) NMR probes and factors affecting reaction rates such as arene substituent and added LiClO 4 cocatalyst are also explored.     

Exhaustive acylation of dihydroquercetin

Reaction of dihydroquercetin with acid chlorides of higher and functionalized carboxylic acids was studied with the purpose of creation of new pharmaceuticals.     

The acylation of lepidine

A number of ketones have been prepared in good to high yields by acylating the methyl group of lepidine (III) with a variety of esters using sodium diisopropylamide (II) as the condensing agent. Two ketones, ethyl and isopropyl lepidyl ketone, have been shown to exist in two forms, the keto form and the intermolecular, hydrogen bonded, enolic form.     

Friedel-crafts cyclisation—VI: Polyphosphoric acid-catalysed reactions of crotonophenones and chalcones

Polyphosphoric acid-catalysed cyclisation of derivatives of crotonophenone and chalcone is shown to be a general reaction which occurs without migration of aryl substituents evident with other Friedel-Crafts catalysts. Two other reactions, however, may intervene: hydrogenation and α-carbonyl cleavage. Thus 4-bromochalcone gives 3 - (p - bromophenyl) -1 - phenylpropan -1 - one, 3 - (p - bromophenyl)indan -1 - one and some benzole acid. A mechanism for the cyclisation is discussed in comparison with those reported for cyclisations of α,β-unsaturated esters and divinyl ketones. The formation of intermediate Wheland complexes is predicted to be conrotatory.