RESUMO
The reaction mechanism of tthe formation of azomethine ylides from isatins and sarcosine is addressed in the literature in a general manner. This computational study aims to explore the mechanistic steps for this reaction in detail and to assess the reactivity of formed ylide in a 1,3-dipolar cycloaddition reaction with 7-oxabenzonorbornadiene. For this purpose, density functional theory (DFT) calculations at the M06-2X(SMD,EtOH)/6-31G(d,p) level were employed. The results indicate that CO2 elimination is the rate-determining step, the activation barrier for 1,3-dipolar cycloaddition is lower, and the formed ylide will readily react with dipolarophiles. The substitution of isatine with electron-withdrawal groups slightly decreases the activation barrier for ylide formation.
Assuntos
Compostos Azo , Reação de Cicloadição , Sarcosina , Tiossemicarbazonas , Tiossemicarbazonas/química , Compostos Azo/química , Sarcosina/química , Sarcosina/análogos & derivados , Isatina/química , Modelos Moleculares , Teoria da Densidade Funcional , Norbornanos/química , Estrutura MolecularRESUMO
Synthesis of N,N'-Di-Boc-2H-isoindole-2-carboxamidine, the first representative of isoindoles containing guanidine functionality, was carried out. The cycloaddition reactivity of this new Diels-Alder heterodiene was studied and the title compound was employed as a cycloaddition delivery reagent for guanidine functionality. Higher reactivity was found in comparison with the corresponding pyrrole derivative. Substitution with fluorine or guanidine functionality does not change the reactivities of isoindoles, and these findings are in good accord with computational results.
Assuntos
Guanidinas , Isoindóis , Guanidina , Indicadores e Reagentes , Reação de CicloadiçãoRESUMO
The solution phase 1,2-debromination of polycyclic imides using the Zn/Ag couple was successfully transferred to solid state mechanochemical conditions. The Zn/Ag couple was replaced by the Zn/Cu couple which was prepared without any metal activation by in situ ball milling of zinc and copper dusts. The advantage of the ball milling process is that the whole procedure is operationally very simplified. The reactive alkene generated was trapped in situ by several dienes and the respective Diels-Alder cycloadducts were obtained. It was demonstrated that mechanochemical milling offers complementary conditions to solution (thermal) reaction by allowing chemical transformations to proceed which were not possible in solution and vice versa.
RESUMO
The dimer of the tetracyanoethylene (TCNE) radical anions represents the simplest and the best studied case of two-electron multicenter covalent bonding (2e/mc or pancake bonding). The model compound, N-methylpyridinium salt of TCNEâ¢-, is diamagnetic, meaning that the electrons in two contiguous radicals are paired and occupy a HOMO orbital which spans two TCNEâ¢- radicals. Charge density in this system is studied as a benchmark for comparison of charge densities in other pancake-bonded radical systems. Two electrons from two contiguous radicals indeed form a bonding electron pair, which is distributed between two central ethylene groups in the dimer, i.e., between four carbon atoms. The topology of electron density reveals two bond critical points between the central ethylene groups in the dimer, with maximum electron density of 0.185 e Å-3; the corresponding theoretical value is 0.118 e Å-3.