I. R. Elanov

Electrophilic Amination of Methylbenzenes with the System NaN3-AlCl3-HCl. Effects of the Solvent, Crown Ether, and Substrate Structure

Using mesitylene and o-xylene as examples, it was shown that the solvent nature strongly affects the conversion of methylbenzenes in electrophilic amination with the system NaN3-AlCl3-HCl. Two-parameter correlations were found between the substrate conversion, on the one hand, and dielectric constant and number of heavy atoms in the solvent, on the other. A considerable solvent effect on the regioselectivity of amination of o-xylene was observed. The presence of 18-crown-6 weakly affects the ratio of isomeric amines, but the conversion of o-xylene sharply decreases. Solid aromatic substrates, such as durene and pentamethylbenzene can also be involved in electrophilic amination with the system NaN3-AlCl3-HCl. On the basis of the experimental data and the results of quantum-chemical calculations, participation of a nitrenium intermediate in this reaction was postulated.

Fluorination of Bi- and polycyclic aromatic hydrocarbons with N -fluorobis(phenylsulfonyl)amine in the absence of solvent

Reactions of N-fluorobis(phenylsulfonyl)amine with naphthalene, 1-methylnaphthalene, phenanthrene, anthracene, and pyrene without solvent were investigated. Sometimes the fluorination of aromatic compounds with N-fluorobis(phenylsulfonyl)amine without solvent proceeded more selectively than at the use of fluorinating reagents in solution.

Nitrosonium complexes of [2.2]paracyclophane

The reaction of [2.2]paracyclophane with nitrosonium tetrachloroaluminate was studied by NMR (1H, 13C) spectroscopy using deuterium isotopic perturbation technique. The resulting cationic complexes containing one and two nitrosonium ions are involved in fast (on the NMR time scale) interconversion. Quantum-chemical calculations performed on the DFT level (using triple zeta basis set) indicate the higher stability of 2η single-charged π-complexes relative to σ complexes corresponding to the addition of NO+ ion at the ipso and ortho positions. The formation of the single-charged π-complex is energetically more favorable, compared to the double-charged π-complex. The affinity of NO+ for [2.2]paracyclophane is much greater than for p-xylene, presumably due to stacking interaction between the aromatic rings in the π-complex.

Electrophilic fluorination of 6-methyl- and 1,3,6-trimethyluracils in water

The reaction of 4-chloromethyl-1-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) with 6-methyl- and 1,3,6-trimethyluracil in water has been studied. According to the kinetic data, the fluorination follows a bimolecular mechanism with intermediate formation of cationic σ-complexes.

Promotional effect of ionic liquids in electrophilic fluorination of methylated uracils

A novel efficient protocol has been developed for fluorination of methylated uracils involving a stoichiometric amount of ionic liquid (IL) in alcohols. The fluorination of 6-methyluracil and 1,3,6-trimethyluracil has been carried out using the electrophilic fluorinating reagent Selectfluor™ (F-TEDA-BF4) in MeOH and EtOH solvents with the formation of 5-fluoro-6-methyluracil, 5-fluoro-1,3,6-trimethyluracil as well as α-fluoromethoxy- and α-fluoroethoxy ethers of difluorodihydrouracils as the main products. The use of a stoichiometric amount of ionic liquid as an additive results in acceleration of the reaction. It has been found that the effect of the anion of the IL on the rate of the reaction is more pronounced compared to that of the cation, the effectiveness of the anions decreasing in the following order: [HSO4−] > [OTf−] ∼ [NTf2−] > [BF4−] > [PF6−]. The influence of metal carbonates on the yields of fluorouracils has also been evaluated.

Nitrosonium Complexes of Fluorene and 9,9-Dimethylfluorene

The reaction of fluorene and 9,9-dimethylfluorene with nitrosonium tetrachloroaluminate was investigated using 1H and 13C NMR spectroscopy with deuterium perturbation. The arising positively charged complexes with one and two nitrosonium cations are involved into an interconversion fast in the NMR time scale. The data of quantum-chemical calculations performed by DFT method (basic Λ02) indicate the higher stability of single-charged π-complexes of 2η type compared with the π-complexes corresponding to the addition of two NO+ cations. In the dication π-complexes the transoid position of the NO groups is more favorable than the cisoid position.

Nitrosonium complexes of triptycene

According to the 1H and 13C NMR data, triptycene reacts with nitrosonium tetrachloroaluminate to form positively charged π-complexes with one and two nitrosonium ions, which are rapidly (on the NMR time scale) converted into each other. DFT quantum-chemical calculations with Λ02 basis set indicated higher stability of singly charged complexes relative to doubly charged. Addition of three nitrosonium ions to triptycene molecule is unfavorable from the energy viewpoint.