Circumambulatory Rearrangements of 5-Halo-1,2,3,4,5-pentaphenylcyclopentadienes

Russian Journal of Organic Chemistry - DFT quantum chemical calculations at the CAM-B3LYP/Def2TZVP level of theory showed that intramolecular migrations of halogens in...     

Reversible Migrations of Nitro Group in a Methyltetramethoxycarbonylcyclopentadiene System

Quantum chemical calculations by the density functional theory method at the B3LYP/6-311++G** level have shown that 5-nitro-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene (1) and 5-nitro-2-methyl- 1,3,4,5-tetramethoxycarbonylcyclopentadiene (2) undergo interconversion by consecutive 1,5-sigmatropic shifts via the formation of an unstable isomer, 5-nitro-1-methyl-2,3,4,5- tetramethoxycarbonylcyclopentadiene (3), rather than through the NMR-detected 1,3-shift of the nitro group over the cyclopentadiene ring perimeter. According to calculations in the gas phase, isomer 3 is by ΔE _ZPE of 3.6 kcal/mol less stable than isomer 1, while the activation barrier of the stepwise 1 → 2 process is 24.5 kcal/mol, which agrees well with NMR data (ΔG_25C^≠, chlorobenzene, 26.5 kcal/mol).     

Quantum-chemical Simulation of Migration of Proton and Methoxycarbonyl Group in Amidinylcyclopentadiene Derivatives

A quantum-chemical simulation by MNDO method of probable migration mechanisms of proton and methoxycarbonyl group in a series of amidinylcyclopentadiene derivatives taking in consideration methoxycarbonyl and aryl substituents attached respectively to the cyclopentadienyl and amidine moieties provided a theoretical confirmation of 1,4-shift occurrence for the methoxycarbonyl group in quantitative agreement with the experimental evaluation of the barrier in this reaction.     

Synthesis of 3-(2-hydroxyphenyl)-1,5-dialkyl-1<Emphasis Type="Italic">H</Emphasis>-1,2,4-triazoles and their Zn(II) complexes

It has been demonstrated by ¹³C NMR and quantum-chemical calculations that alkylation of 5-(2-hydroxyphenyl)-3-methyl(vinylphenyl)-1H-1,2,4-triazoles with dialkyl sulfates in aqueous DMSO in the presence of alkali occurs exclusively in the 2-position of the triazole ring to give 3-(2-hydroxyphenyl)-1,5-dialkyl(alkylvinylphenyl)-1H-1,2,4-triazoles. Emission spectra of these compounds show two weak bands (λ _max ^fl = 317–346 and 430–447 nm, φ = 0.002–0.007), whereas their zinc complexes emit in the violet range of the visible spectrum (λ _max ^fl = 373–377 nm, φ = 0.20–0.25).     

Structure and Tautomerism of Cyclopentadiene Derivatives: X. 1,5-Sigmatropic Shifts of the p-Nitrobenzyl Group in Tetramethyl 5-Methylcyclopentadienetetracarboxylate

The reaction of thallium 5-methyl-1,2,3,4-tetrakis(methoxycarbonyl)cyclopentadienide with p-nitrobenzyl bromide gave a mixture of isomeric p-nitrobenzylcyclopentadienes. The isomers were separated, and the structure of each isomer was established by ¹H and ¹³C NMR spectroscopy. 1,5-Sigmatropic shifts of the p-nitrobenzyl group along the cyclopentadienyl ring were revealed, their Gibbs activation energies G 120°C ranging from 29.5 to 30.6 kcal/mol.     

Migration of Phthalimido Group in the Cycloheptatriene System

Russian Journal of Organic Chemistry -