V. G. Shubin

Nitrenium Ions and Problem of Direct Electrophilic Amination of Aromatic Compounds

Published data on direct electrophilic amination of aromatic compounds are summarized and analyzed on the basis of nitrenium ion properties.

Electrophilic reactions of aromatic and heteroaromatic compounds in ionic liquids

The review summarizes and analyzes published data on electrophilic aromatic substitution reactions performed in ionic liquids.

Quantum-Chemical Study of Nitrosonium Complexes of Monocyclic Aromatic Compounds

With the use of Hartree-Fock and DFT methods we demonstrated that for the benzene derivatives with the substituents Me, Et, Pr, i-Pr, t-Bu, CF3, F, and Cl π-complexes are more favorable by energy, whereas with the substituents CHO, MeCO, PhCO, CN, NO, and NO2n-complexes are more feasible. The affi nity of aromatic compounds to the nitrosonium-cation (ANO+) at the formation of the π-complexes grows with the growing donor character of the substituents in the ring and with their number. The best agreement between the calculated and experimental ANO+ values for benzene was obtained with the use of RI-MP2/L1 method.

Fluorination of aromatic compounds with N-fluorobenzenesulfonimide under solvent-free conditions

Reactions of N-fluorobenzenesulfonimide with methylbenzenes, phenols, and phenol ethers were studied under solvent-free conditions. The rate constant ratio for the reactions with mesitylene and durene indicates polar mechanism of the process. Solvent-free fluorination of aromatic compounds with N-fluorobenzenesulfonimide in some cases is more selective than reactions with other N-F reagents in a solvent.

Molecular and crystal structure of 1-amino-X-pyrazinium mesitylenesulfonates

X-Ray diffraction analysis was performed of 1-amino-X-pyrazinium mesitylenesulfonates (X=H, 2-NH2, 3-NHCOMe, 3-OMe, 3-Cl). In all events save 1,2-diaminopyrazinium cation the bond length of N-NH2 was shorter than that of N-N bond but considerably longer than the length of the double bond N=N. In the 1,2-diaminopyrazinium cation the bond distance C2-NH2 was close to the length of a common double bond C=N indicating the iminium character of the cation. Quantum-chemical calculations [AM1, PM3, DFT/(PBE/3z), B3LYP/6-31G++(2d,p)] provided the geometry of cations similar to the experimental one. In the crystals under investigation motifs were observed of 0D, 1D, and 2D type mainly due to hydrogen bonds N-H···O and π-stacking interactions of the aromatic rings.

Mechanism of Electrophilic Fluorination of Aromatic Compounds with NF-Reagents *

Kinetic isotope effects H/D in electrophilic fluorination of aromatic compounds with NF-reagents were investigated. The small values of kH/kD (0.86–1.00) are in agreement with the polar reaction mechanism where the Wheland complex decomposition is not the limiting stage. The fluorination of 1,3,5-trideuterobenzene was established by 1H and 19F NMR spectroscopy to occur with a 1,2-migration of a hydrogen (deuterium) atom. The analysis of Brown-Stock relationship demonstrated that the activity of NF-reagents exceeded that of many known electrophilic systems including halogenation, but it was essentially less than the activity of elemental fluorine.

Degenerate rearrangement of detectable 9,10-dimethyl-9-vinyl-phenanthrenium ion : 1,2-shift of the vinyl group

Dynamic NMR study showed that 9,10-dimethyl-9-vinylphenanthrenium ion, generated under the conditions ensuring its “long life,” undergoes very fast (ΔG≠ = 24.4 kJ/mol at −103°C) degenerate 1,2-shift of the vinyl group. According to the DFT quantum-chemical calculations, the process is one-step, and the low energy of formation of the activated complex is determined by effective participation of π electrons of the vinyl group in delocalization of the positive charge; no such delocalization is intrinsic to the initial ion.

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.

Carbocationic Cyclizations: IX. Rearrangement of Long-Lived 4-(2-Biphenylyl)-1,2,3,4-tetramethylcyclobutenyl Cation into trans- and cis-4,5,6,6-Tetramethyl-4,5,6-trihydrocyclopenta[j,k]phenanthren-5-yl Cations

According to the 1H and 13C NMR data, long-lived 4-(2-biphenylyl)-1,2,3,4-tetramethylcyclobutenyl cation generated by protonation of 3-(2-biphenylyl)-1,2,3-trimethyl-4-methylenecyclobutene in super-acids undergoes cyclization which launches further rearrangements finally leading to formation of a mixture of trans- and cis-4,5,6,6-tetramethyl-4,5,6-trihydrocyclopenta[j,k]phenanthren-5-yl cations.

Quantum-chemical study on uracil and thymine nitrosonium complexes

AbstractQuantum-chemical calculations at the RI-MP2/L1 level of theory showed that the most energetically favorable complexes of uracil and thymine with nitrosonium cation are those of n-type with NO+ coordination at the nitrogen or oxygen atom. A correlation was found between the experimental and calculated affinities of the dioxo tautomer of thymine for nitrosonium ion (