Benzenes reactions, trifluoromethanesulfonic acid

In order to achieve high yields, the reaction usually is conducted by application of high pressure. For laboratory use, the need for high-pressure equipment, together with the toxicity of carbon monoxide, makes that reaction less practicable. The scope of that reaction is limited to benzene, alkyl substituted and certain other electron-rich aromatic compounds. With mono-substituted benzenes, thepara-for-mylated product is formed preferentially. Super-acidic catalysts have been developed, for example generated from trifluoromethanesulfonic acid, hydrogen fluoride and boron trifluoride the application of elevated pressure is then not necessary. 

Imines of acyclic and C10- to C15-membered carbocyclic ketones are prepared under the conditions described for cyclohexanone imines using trifluoromethanesulfonic acid or trifluoroacetic acid as additional catalyst. The reaction often takes several days in refluxing benzene or toluene9. 

Benzyne is an important reactive intermediate especially useful for the construction of polycyclic compounds via cycloaddition reactions with various dienes. Several benzyne precursors, including diphenyliodonium-2-carboxylate [ 1 ], have been previously used for the generation of benzyne by thermal decomposition. More recently, several new precursors that generate benzyne quantitatively under very mild conditions have been developed [105 -108]. An efficient benzyne precursor, iodonium triflate 109, can be readily prepared by the reaction of l,2-bis(trimethylsilyl)benzene 108 with [(diacetoxy)iodo]benzene in the presence of trifluoromethanesulfonic acid (Scheme 47) [105]. 

Oxetanes have also been used as alkylating agents in the Friedel-Crafts reaction for example, 2-isopropyloxetane was reacted with benzene in superacidic trifluoromethanesulfonic acid (TFSA) to give a mixture of alkylated aromatic products (Equation 9) <2003CAL1>. The main product of the reaction was the tetralin derivative 46 which could be isolated in up to 75% yield. Other notable side products are shown, resulting from monoalkylation or other skeletal rearrangements. 

Compounds lb - 4b were prepared in multistep syntheses according to Scheme 1, starting from dichlorodiphenylsilane (8), and were isolated as the hydrochlorides Ib-HCl - 4b-HCl. In the first step, 8 was reacted with vinylmagnesium chloride to afford diphenyldivinylsilane (9), which was treated with trifluoromethanesulfonic acid, followed by addition of triethylammonium chloride, to yield dichlorodivinylsilane (10). Reaction of 10 with hydrogen bromide, in the presence of dibenzoyl peroxide, gave bis(2-bromoethyl)dichlorosilane (11), which was reacted with 2-bromomagnesio-l-(3-(bromomagnesio)propyl)benzene (obtained by reaction of 15 (13 14 ->... 

The mixture of nitric acid and trifluoromethanesulfonic acid in CHjClj, CCI4, CF2CI2, CFQ3, and pentane solution is an excellent nitrating agent for benzene, toluene, m-xylene, chlorobenzene, nitrobenzene, and beozo-trifluoride (Table II). The reactions were carried out from —110 to 30 C. Mono- or dinitration of toluene can be controlled by specific reaction temperature. Mononitration of toluene is extremely rapid, the reaction being complete in one minute at -110X. The dinitration is complete in 30 min at 0 C. 

Various unsymmetrically substituted diaryliodonium triflates 269 can be synthesized by the reaction of iodosylbenzene [380] or (diacetoxyiodo)arenes [381] with arenes in trifluoromethanesulfonic acid (Scheme 2.76). This simple procedure affords diaryliodonium triflates in relatively high yields, but it is limited to aromatic substrates that are not sensitive to strong acids. In a milder, more selective variation of this procedure (diacetoxyiodo)benzene is reacted with arylboronic acids in the presence of triflic acid at -30 °C to afford aryl(phenyl)iodonium triflates in 74-97% yields [377]. 

Mechanistic studies of the diacetoxylation of alkenes using (diacetoxyiodo)benzene have demonstrated a protio-catalytic nature of this reaction [255]. Systematic studies into the catalytic activity in the presence of proton-trapping and metal-complexing additives indicate that strong acids act as catalysts in the reaction. When trifluoromethanesulfonic acid is used as catalyst, the selectivity and reaction rate of the conversion is similar or superior to most efficient metal-based catalysts, such as Pd(II) and Cu(II) metal cations. Based on a kinetic study as well as in situ mass spectrometry, a mechanistic cycle for the proton-catalyzed reaction was proposed in this work [255]. 

The efficient acylbenzyne precursors, [5-acyl-2-(trimethylsilyl)phenyl]iodonium triflates 705 have been prepared by reaction of the appropriate l,2-bis(trimethylsilyl)benzenes with PhI(OAc)2 in the presence of trifluoromethanesulfonic acid in dichloromethane at room temperature. Treatment of these reagents with BU4NF in dichloromethane generates acylbenzynes 706, which can be trapped by furan to give adducts 707 in high yield (Scheme 3.283) [927]. 

Preparative Methods diphenyliodonium triflate can be prepared by reaction of benzene with elemental iodine in tbe presence of potassium persulfate and trifluoroacetic acid in dicbloroetbane followed by ligand exchange with NaOTf in 71% yield. A one-pot reaction of iodobenzene and benzene with m-CPBA and trifluoromethanesulfonic acid at room temperature for 10 min also affords diphenyliodonium triflate in 92% yield. Diphenyliodonium triflate can be obtained in near-quantitative yield by reacting an excess of benzene (i.e., 4 equiv) with elemental iodine in the presence of m-CPBA and trifluoromethanesulfonic acid. More tedious and somewhat less efficient synthetic routes to diphenyliodonium triflate have been reported using iodosylbenzene (PhIO) or iodobenzene /J-diacetate (PhI(OAc)2), trifluoromethanesulfonic acid, and benzene as starting materials. Another preparation of diphenyliodonium triflate implies the reaction of phenylboronic acid with PhI(OAc)2 and trifluoromethanesulfonic acid in dichloromethane and proceeds in >90% yield. ... 

N-Tfa- and iV-Fmoc-a-amino ketones have been synthesized56 by reaction of some N -heterocycles or benzene with chiral AM Tfa- and Fmoc-a-aminoacyl)benzotriazoles [e.g. (49)] in the presence of aluminium trichloride. Full preservation of chirality was reported. Aromatic side-chains in some of the (a-amineacyl)benzotriazole compounds gave a competitive intramolecular cyclization, again with retention of chirality [e.g. (49) to (50)]. A full report57 on the intramolecular acylation of aromatics with Meldrum s acid derivatives catalysed by metal trifluoromethanesulfonates under mild reaction conditions has appeared [e.g. (51) to (52)]. The method tolerates many functional groups and was extended to the synthesis of 1-tetralones, 1-benzosuberones and donepezil (53). 

Friedel-Crafts Reactions. Aluminum trifluoromethanesulfonate has been used for the Friedel-Crafts alkylation reaction of toluene with isopropyl and tert-butyl chlorides (eq 1), and for the acylation of benzene and toluene with acetyl and benzoyl chlorides in low to moderate yields. Intramolecular Friedel-Crafts acylation of an aromatic compound with Meldrum s acid has also been reported using catalytic amounts of Al(OTf)3. Acylation of 2-methoxynaphthalene with acetic anhydride has been reported using Al(OTf)3 and lithium perchlorate as an additive to afford the corresponding 6-acetylated adduct in 83% yield. Effective acylation of arenes with carboxylic acids has also been disclosed using polystyrene-supported Al(OTf)3. ... 

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