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N,O-Diprotonated forms (dications) of various quinolinecarbaldehydes were theoretically studied by DFT calculations. It was found that the most reactive electrophilic dications are expected to be generated from 2- and 4-quinolinecarbaldehydes compared to the other quinolinecarbaldehydes. Experimental studies of protonation of quinoline-2(6,8)-carbaldehydes in Bronsted acids (CF3SO3H, H2SO4) by means of 1H, 13C, and 15N NMR revealed the formation of the corresponding N-protonated O-protosolvated species. Reactions of quinoline-2(6,8)-carbaldehydes with arenes in the presence of Bronsted (TfOH) and Lewis acids (AlX3, X = Cl, Br) or acidic zeolites led to the formation of the corresponding 2(6,8)-(diarylmethyl)quinolines. However, 6- and 8-quinolinecarbaldehydes gave additionally unusual products – 6(8)-(arylmethyl)quinolines.

Acetylene derivatives of 1,2,4-oxadiazoles, i.e., 5-(2-arylethynyl)-3-aryl-1,2,4-oxadiazoles, have been obtained, for the first time reported, from 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles by their bromination at the carbon–carbon double bond followed by di-dehydrobromination with NaNH2 in liquid NH3. The reaction of the acetylenyl-1,2,4-oxadiazoles with arenes in neat triflic acid TfOH (CF3SO3H) at room temperature for 1 h resulted in the formation of E/Z-5-(2,2-diarylethenyl)-3-aryl-1,2,4-oxadiazoles as products of regioselective hydroarylation of the acetylene bond. The addition of TfOH to the acetylene bond of these oxadiazoles quantitatively resulted in E/Z-vinyl triflates. The reactions of the cationic intermediates have been studied by DFT calculations and the reaction mechanisms are discussed.

Trimethylsilyl ethers of 1,5-diaryl-3-(trifluoromethyl)-pent-1-en-4-yn-3-oles [Ar–C≡C–C(CF3)(OSiMe3)–CH═CH–Ar′] in the superacid TfOH give rise to reactive conjugated CF3-allylic-propargylic cation...

A novel catalyst-free synthesis of N-pyridin-2-yl, N-quinolin-2-yl, and N-isoquinolin-1-yl carbamates utilizes easily accessible N-hetaryl ureas and alcohols. The proposed environmentally friendly technique is suitable for the good-to-high yielding synthesis of a wide range of N-pyridin-2-yl or N-quinolin-2-yl substituted carbamates featuring electron-donating and electron-withdrawing groups in the azine rings and containing various primary, secondary, and even tertiary alkyl substituents at the oxygen atom (48-94%; 31 examples). The DFT calculation and experimental study showed that the reaction proceeds through the intermediate formation of hetaryl isocyanates. The method can be applied to obtain N-isoquinolin-1-yl carbamates, although in lower yields, and ethyl benzo[h]quinolin-2-yl carbamate has also been successfully synthesized (68%).

Preparative limitations of the reaction of chloroethynylphosphonates with 2-(alkylamino)malonates have been established. Unlike the reaction of chloroethynylphosphonates with 2-(arylamino)malonates which involve only the carbon nucleophilic center, 2-(alkylamino)malonates react through both carbon and nitrogen atoms. The geometric structural, energetic, and charge parameters of the optimized structures of aliphatic and aromatic diethyl 2-aminomalonates have been determined by quantum chemical calculations using Gaussian 03 software, and pKa values for both nucleophilic centers in their molecules have been calculated.

Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkylbenzimidazoles with arenes in the Brønsted superacid TfOH resulted in the formation of the corresponding Friedel–Crafts reaction products, 2-diarylmethyl and 2-arylmethyl-substituted benzimidazoles, in yields up to 90%. The reaction intermediates, protonated species derived from starting benzimidazoles in TfOH, were thoroughly studied by means of NMR and DFT calculations and plausible reaction mechanisms are discussed.

The reaction of CF3-propargyl alcohols [ArCCCH(OH)CF3] with arenes under the action of acidic HUSY zeolite CBV-720 was investigated. It was found that the reaction at 100 °C for 1 h gave rise to 3-aryl-1-CF3-indenes in up to 83% yield. Electronic characteristics of the reaction key intermediates, mesomeric CF3-propargyl-allenyl cations [ArCC−HC+(CF3) ↔ ArC+CCH(CF3)], were studied by DFT calculations. A plausible cationic reaction mechanism is discussed.

3,3,3-Trihalogeno-1-nitropropenes C(Hal3)CH═CH(NO2) (Hal = F, Cl, Br) in reaction with arenes in the superacid CF3SO3H (TfOH) at room temperature in 1 h afford 3,3,3-trihalogeno-1,2-diarylpropan-1-one oximes C(Hal3)CH(Ar)–C(Ar)═NOH (CHal3-oximes) in yields of 23–99%. Such CHal3-oximes having one ortho-substituent in the aryl ring exist as atropoisomers in solutions at room temperature. Several cationic intermediates of this reaction were studied by means of NMR and DFT calculations, which proves the detailed reaction mechanism of the formation of CHal3-oximes in TfOH. CHal3-oximes (for Hal = Cl, Br) with DBU in DMF at microwave or thermal activation are cyclized into 5-halogeno-3,4-diarylisoxazoles in yields of 37–59%. CHal3-oximes under the conditions of Beckmann rearrangement with PCl5 in benzene at room temperature in 24 h are turned at first into imidoyl chlorides (yields of 94–96%), which undergo transformation into the corresponding benzamides PhCONHCHPh(CHal3) on silica gel (yields of 46–47%).

Reaction of 5-arylethynyl-2-methyl-2H-tetrazoles (acetylene tetrazoles) with arenes under the action of Bronsted superacid CF3SO3H or acidic zeolite HUSY CBV-720 gives rise to E-/Z-5-(2,2-diarylethenyl)-2-methyl-2H-tetrazoles, as products of hydroarylation of acetylene bond, in yields up to 98% with predominant formation of E-isomers. Cationic intermediates of these reactions have been studied theoretically by DFT calculations. Addition of CF3SO3H to the triple bond of acetylene tetrazoles leads to the corresponding E-/Z-vinyl triflates in high yields. Hydration of triple bond in these tetrazoles in H2SO4 results in the formation of 5-(2-aryl-2-oxoethyl)-2-methyl-2H-tetrazoles. Tandem hydroarylation-ionic hydrogenation of acetylene tetrazoles in the systems acid(CF3SO3H or AlCl3)-arene-cyclohexane affords 5-(2,2-diarylethyl)-2-methyl-2H-tetrazoles.

Reaction of linear conjugated enynones, 1,5-diarylpent-2-en-4-yn-1-ones, with malononitrile in the presence of lithium diisopropylamide LDA, as a base, in THF at room temperature for 3&ndash, 7 h resulted in the formation of the product of dimerization, multisubstituted polyfunctional cyclohexanes, 4-aryl-2,6-bis(arylethynyl)-3-(aryloxomethyl)-4-hydroxycyclohexane-1,1-dicarbonitriles, in yields up to 60%. Varying the reaction conditions by decreasing time and temperature and changing the ratio of starting compounds (enynone and malononitrile) allowed isolating some intermediate compounds, which confirmed a plausible reaction mechanism. The relative stability of possible stereoisomers of such cyclohexanes was estimated by quantum chemical calculations (DFT method). The obtained cyclohexanes were found to possess photoluminescent properties.

Protonation of diazodiketones N2C(COR)2 in Bronsted superacids (TfOH, FSO3H, TfOH–SbF5) gives rise to stable and non-reactive O,O-diprotonated at carbonyl oxygens species N2C(C( OH+)R)2, which were studied by means of 1H and 13C NMR. Diazomalonates N2C(CO2Alk)2, contrary to diazodiketones, react with TfOH or HF, releasing nitrogen and producing triflates of oxymalonates TfOCH(CO2Alk)2 or fluoromalonates FCH(CO2Alk)2, respectively. Diazoketoesters N2C(COR)(CO2Alk) react in the same way only with TfOH, but not with HF. The reactions of diazomalonates with arenes ArH (benzene, toluene, xylenes) in TfOH solution yield corresponding Friedel–Crafts reaction products ArCH(CO2Alk)2. According to performed DFT calculations, trication +CH(C( OH+)OMe)2, a possible intermediate, which is derived from protonation of dimethyl diazomalonate, should be the strongest cationic carbon-centered electrophile known up to date.

The formation of the corresponding benzyl cations [ArHC(+)-CH(X)CF3] takes place under protonation of E-/Z-2-halogeno-2-CF3 styrenes [ArCH═C(X)CF3, X = F, Cl, Br] in superacids. The structures of these new electrophiles were studied by means of NMR and theoretical DFT calculations. According to these data, in the case of bromo derivatives, the formed cations, most probably, exist as cyclic bromonium ions; however, in the cases of chloro and fluoro derivatives, open forms are more preferable. Subsequent reaction of these benzyl cations with arenes proceeds as Friedel-Crafts alkylation to afford 1,1-diaryl-2-halo-3,3,3-trifluoropropanes [Ar(Ar')CH-CH(X)CF3] in high yields (up to 96%) as a mixture of two diastereomers. The prepared halogenopropanes were easily converted into the corresponding mixtures of E-/Z-trifluoromethylated diarylethenes [Ar(Ar')C═CCF3] (in yields up to 96%) by dehydrohalogenation with base (KOH or t-BuOK). The mechanism of elimination (E2 and Ecb) depends on the nature of the leaving group and reaction conditions.

Reactions of 3-arylpropenenitriles [ArCH CHCN] with arenes [Ar’H] under the superelectrophilic activation conditions with Bronsted superacid TfOH (CF3SO3H) or strong Lewis acid AlBr3 result, first, in the formation of products of hydroarylation of the carbon-carbon double bond, 3,3-diarylpropanenitriles [Ar(Ar’)CHCH2CN]. Reactions may go further in TfOH leading to 3-arylindanones, as products of intramolecular aromatic acylation by the electrophilically activated nitrile group. Intermediate cationic species, derived at the protonation of the starting 3-arylpropenenitriles onto the carbon of C C bond and the nitrile nitrogen, have been studied by DFT calculation. A plausible reaction mechanism including the formation of highly reactive dications [(Ar)HC+–CH2C+ = NH] has been proposed. The obtained 3,3-diarylpropanenitriles have been transformed into pharmaceutically valuable 5-(2,2-diarylethyl)-1H-tetrazoles [Ar(Ar’)CHCH2Tetr] and 3-diarylpropylamines [Ar(Ar’)CH(CH2)2NH2] by the reactions with NaN3 and LiAlH4 correspondingly.

The TfOH-mediated reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-oles (CF3-substituted diaryl propargyl alcohols) with arenes in CH2Cl2 afford 1,3-diaryl-1-CF3-indenes in yields up to 84%. This new process for synthesis of such CF3-indenes is complete at room temperature within one hour. The synthetic potential, scope, and limitations of this reaction were illustrated by more than 70 examples. The proposed reaction mechanism invokes the formation of highly reactive CF3-propargyl cation intermediates that can be trapped at the two mesomeric positions by the intermolecular nucleophilic attack of an arene partner with a subsequent intramolecular ring closure.

Cinnamides ArCH CHCONRR′ in reactions with arenes Ar′H under the action of Bronsted (TfOH, FSO3H) or Lewis (AlBr3) superacids at rt for 1–2 h give C C bond hydroarylation products ArAr′CHCH2CONRR′ in yields of 63–98%. Reduction (LiAlH4/Et2O) of carbonyl group in the latter results in the formation of 3,3-diarylpropylamines ArAr′CHCH2CH2NRR′, valuable drugs. The reaction intermediates, superelectrophilic dications ArC+H–CH2C(OH+)NRR′, have been characterized by DFT calculations in terms of global electrophilicity index, natural charges, and atomic orbitals contributions.

An unusual ‘dimerization’ of CF3-allyl alcohols [ArCH CHCH(OH)CF3] under the action of anhydrous FeCl3 was found to give fluorinated indanes in 62–90% yields via the formation of intermediate allyl cations. Reactions of CF3-allyl alcohols with arenes (Ar′H) led to CF3-alkenes [Ar(Ar′)CHCH CHCF3] in 48–75% yields. The mechanisms of the transformations are discussed.

The metal-free reaction of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles with arenes in neat triflic acid (TfOH, CF3SO3H), both under thermal and microwave conditions, leads to 5-(2,2-diarylethyl)-3-aryl-1,2,4-oxadiazoles. The products are formed through the regioselective hydroarylation of the side chain carbon–carbon double bond of the starting oxadiazoles in yields up to 97%. According to NMR data and DFT calculations, N4,C-diprotonated forms of oxadiazoles are the electrophilic intermediates in this reaction.

The relative reactivity of ortho- and para-methyl-substituted iodoarenes in the Sonogashira reaction and palladium-catalyzed methoxycarbonylation, as well as of similarly substituted bromoarenes in the Suzuki reactions and cobalt-catalyzed methoxycarbonylation, was studied. Introduction of a methyl group into the para position of aryl halide slows down the cross-coupling. o-Methylhaloarenes are less reactive in palladiumcatalyzed reactions as compared to both unsubstituted haloarene and para-substituted analog. The presence of a methyl group in the ortho position with respect to the reaction center accelerates cobalt-catalyzed methoxycarbonylation.

The formation of the corresponding benzyl cations [ArHC+–CH(X)CF3] takes place under protonation of E-/Z-2-halogeno-2-CF3 styrenes [ArCH═C(X)CF3, X = F, Cl, Br] in superacids. The structures of these new electrophiles were studied by means of NMR and theoretical DFT calculations. According to these data, in the case of bromo derivatives, the formed cations, most probably, exist as cyclic bromonium ions; however, in the cases of chloro and fluoro derivatives, open forms are more preferable. Subsequent reaction of these benzyl cations with arenes proceeds as Friedel–Crafts alkylation to afford 1,1-diaryl-2-halo-3,3,3-trifluoropropanes [Ar(Ar′)CH–CH(X)CF3] in high yields (up to 96%) as a mixture of two diastereomers. The prepared halogenopropanes were easily converted into the corresponding mixtures of E-/Z-trifluoromethylated diarylethenes [Ar(Ar′)C═CCF3] (in yields up to 96%) by dehydrohalogenation with base (KOH or t-BuOK). The mechanism of elimination (E2 and Ecb) depends on the nature of the leaving gro...

Protonation of diazodiketones N2C(COR)2 in Bronsted superacids (TfOH, FSO3H, TfOH–SbF5) gives rise to stable and non-reactive O,O-diprotonated at carbonyl oxygens species N2C(C( OH+)R)2, which were studied by means of 1H and 13C NMR. Diazomalonates N2C(CO2Alk)2, contrary to diazodiketones, react with TfOH or HF, releasing nitrogen and producing triflates of oxymalonates TfOCH(CO2Alk)2 or fluoromalonates FCH(CO2Alk)2, respectively. Diazoketoesters N2C(COR)(CO2Alk) react in the same way only with TfOH, but not with HF. The reactions of diazomalonates with arenes ArH (benzene, toluene, xylenes) in TfOH solution yield corresponding Friedel–Crafts reaction products ArCH(CO2Alk)2. According to performed DFT calculations, trication +CH(C( OH+)OMe)2, a possible intermediate, which is derived from protonation of dimethyl diazomalonate, should be the strongest cationic carbon-centered electrophile known up to date.

The reaction of 3-aryl-N-(aryl)propiolamides with arenes in TfOH at room temperature for 0.5 h led to 4,4-diaryl-3,4-dihydroquinolin-2-(1H)-ones in yields of 44-98%. The obtained dihydroquinolinones were further transformed into the corresponding N-acyl or N-formyl derivatives. For the latter, the superelectrophilic activation of the N-formyl group by TfOH in the reaction with benzene resulted in the formation of N-(diphenylmethyl)-substituted dihydroquinolinones.

Conjugated 1,5-diarylpent-2-en-4-yn-1-ones add the superacid CF3SO3H to the acetylenic bond with formation of the corresponding butadienyl triflates. Under superacidic reaction conditions, these triflates are transformed into indanone or indene derivatives depending on which substituents on the aromatic ring are conjugated with the butadiene fragment. In a less acidic system (10% vol pyridine in CF3SO3H) only the formation of butadienyl triflates takes place. Cationic reaction intermediates were studied by means of NMR and DFT calculations.

Reaction of 4-aryl-1,1,1-trifluorobut-3-en-2-ols [CF3-allyl alcohols, ArCH═CHCH(OH)CF3] with arenes under activation with anhydrous FeCl3 or FSO3H was studied. We found that the transformation led to trifluoromethylated alkenes [Ar(Ar′)CHCH═CHCF3] or 1-trifluoromethylated indanes (CF3-indanes). The formation of these two types of reaction products strongly depends on the nucleophilicity of the starting arene and the electrophilicity of cationic intermediates generated from CF3-allyl alcohols under reaction conditions. Benzene, anisole, veratrole, and ortho-xylene lead exclusively to CF3-alkenes with an E-configuration. More π-donating polymethylated arenes (pseudocumene, mesitylene) afford only CF3-indanes with a predominantly cis-orientation of substituents at positions 1 and 3 of the indane ring. Meta- and para-xylenes show an intermediate behavior; they may form both CF3-alkenes and/or CF3-indanes. The mechanisms of the investigated transformations are discussed.

The regioselective methoxycarbonylation of polychlorinated biphenyls (PCBs), 2,3,4′-trichlorobiphenyl (РСВ22), and 2,5,4′-trichlorobiphenyl (PCB31), carried out in the presence of modified Co 2 (CO) 8 cobalt carbonyl catalyst proceeds with substitution of chlorine atom in the position 3 for РСВ22 and yields methyl 2-chloro-3-(4-chlorophenyl)benzoate 1 , while for PCB31 results in methyl 4-chloro-2-(4-chlorophenyl)benzoate 2 . The substitution of methoxycarbonyl group for chlorine in ortho -position of trichlorobiphenyls seems not to affect the twist angle of the biphenyl unit. However, the twist angle of the methoxycarbonyl group relative to the phenyl ring was found to be significantly larger in the meta -derivative 1 than the ortho -derivative 2 . To rationalize conformational differences between the two esters 1 and 2 in their crystal structures the optimized geometries and potential energy curves (relative energy versus torsion angle) were calculated at the B3LYP/6-31+G(d,p) level of theory.