Search results for "Electrophile"
showing 10 items of 258 documents
Über die Synthese methylsubstituierter P-Oligopenylene. 5. Mitteilung
1959
Unsubstituierte p-Oligophenylene sind sehr schwer loslich. Die Loslichkeit dieser substanzen kann durch Substitution mit Methylgruppen verbessert werden. Fur die Synthese methylsubstituierter p-Oligophenylence wurden verschiedene Verfahren herangezogen. Durch ULIMANN-Kondensation entsprechender Jodaryle konnten zwei substitutionsisomere Tettamethyl-p-quaterphenyle, ein Tetramethoxy-p-quaterphenyl und ein Tetramethyl-p-sexiphenyl synthetisiert werden. Uber die Carbonyladdition aromatischer metallorganischer Verbindungen an cyclische Diketone wurden uber hydroaromatische Zwischenstufen ein Dimethyl-p-terphenyl, ein Tetramethyl-p- quinquiphenul, zwei substitutionsisomere Dimethyl-p-quaterpheny…
Theoretical Study of the Reaction of Dimethyl Acetylenedicarboxylate with 1-Methyl-2-(1-substituted vinyl)pyrroles
1995
Abstract A theoretical study of the transition structure for the electrophilic attack step of the 1-methyl-2-vinylpyrrole to dimethyl acetylenedicarboxylate is reported with analytical gradients at AM1 and PM3 semi-empirical levels and ab initio at 3-21G level. The geometry, electronic structure, and vector components are qualitatively computer level and model independent The competition of the Michael addition reactions and Diels-Alder reactions of 1-methyl-2-(1-substituted vinyl)pyrroles with dimethyl acetylenedicarboxylate has been studied at the PM3 semi-empirical level.
A theoretical study on the regioselectivity of 1,3-dipolar cycloadditions using dft-based reactivity indexes
2004
The regioselectivity for a series of four 1,3-dipolar cycloaddition reactions has been studied using global and local reactivity indexes. The results of the theoretical analysis suggest that for asynchronous cycloadditions associated to polar processes, the regioselectivity is consistently explained by the most favorable two-center interactions between the highest nucleophilic and electrophilic sites of the reagents.
Catalytic Asymmetric Formal [3+2] Cycloaddition of 2-Isocyanatomalonate Esters and Unsaturated Imines: Synthesis of Highly Substituted Chiral γ-Lacta…
2017
[EN] Unlike their isocyano and isothiocyanato analogues, isocyanato esters remain almost unexplored as formal 1,3-dipoles in asymmetric catalytic reactions. The first asymmetric formal [3+2] cycloaddition involving isocyanato esters and electrophilic alkenes is reported. Diisopropyl 2-isocyanatomalonate reacts with a,b-unsaturated N-(o-anisidyl) imines in the presence of a Mg(OTf)2¿BOX complex to give highly substituted chiral pyrrolidinones featuring a conjugate exocyclic double bond with excellent yields and enantiomeric excesses up to 99%. Several transformations of the resulting heterocycles, including the synthesis of a pyroglutamic acid derivative, have been carried out.
A molecular electron density theory study of the chemo- and regioselective [3 + 2] cycloaddition reactions between trifluoroacetonitrile N-oxide and …
2018
Abstract The [3 + 2] cycloaddition (32CA) reaction between trifluoroacetonitrile N-oxide (NO 7) and 2,2,4,4-tetramethyl-3-thioxocyclobutan-1-one (THK 12) as well as the self-dimerization of NO 7 as a competitive pathway were studied within the Molecular Electron Density Theory (MEDT) using several DFT functionals together with def2-TZVP basis set. Taking CCSD(T)/TZVP activation energies as reference, among the employed functionals, just the B2PLYP-D3(BJ) one is able to portray complete predominance of 32CA reaction over self-dimerization process in excellent agreement with the experimental outcomes. Analysis of the global reactivity indices permits to characterize NO 7 and THK 12 as a stron…
A molecular electron density theory study of the [3 + 2] cycloaddition reaction of nitrones with ketenes.
2017
The [3 + 2] cycloaddition (32CA) reaction between nitrones and ketenes has been studied within the Molecular Electron Density Theory (MEDT) at the Density Functional Theory (DFT) MPWB1K/6-311G(d,p) computational level. Analysis of the conceptual DFT reactivity indices allows the explanation of the reactivity, and the chemo- and regioselectivity experimentally observed. The particular mechanism of this 32CA reaction involving low electrophilic ketenes has been elucidated by using a bonding evolution theory (BET) study. It is determined that this reaction takes place in one kinetic step only but in a non-concerted manner since two stages are clearly identified. Indeed, the formation of the se…
Understanding the domino reaction between 1-diazopropan-2-one and 1,1-dinitroethylene. A molecular electron density theory study of the [3 + 2] cyclo…
2017
The reaction between 1-diazopropan-2-one and 1,1-dinitroethylene has been studied using the Molecular Electron Density Theory (MEDT) at the B3LYP/6-31G(d,p) computational level. This reaction comprises two domino processes initialised by a common [3 + 2] cycloaddition (32CA) reaction yielding a 1-pyrazoline, which participates in two competitive reaction channels. Along channel I, 1-pyrazoline firstly tautomerises to a 2-pyrazoline, which by a proton abstraction and spontaneous loss of nitrite anion yields the final pyrazole, while along channel II, the thermal extrusion of the nitrogen molecule in 1-pyrazoline gives a very reactive diradical intermediate which quickly yields the final gem-…
On the nature of organic electron density transfer complexes within molecular electron density theory.
2019
The structural features of a series of organic molecular complexes formed between the strong electrophilic tetracyanoethylene and twelve benzene derivatives with increased nucleophilic character, herein called Electron Density Transfer Complexes (EDTCs), have been studied using Molecular Electron Density Theory. The favourable nucleophilic/electrophilic interactions, which favour the global electron density transfer (GEDT) towards the electrophile, are responsible for the formation of these species. Molecular complexes presenting a GEDT above 0.05e are classified as EDTCs. Analysis of the Parr functions of the separated reagents and the topological analysis of the electron density of the ED…
Unravelling the strain-promoted [3+2] cycloaddition reactions of phenyl azide with cycloalkynes from the molecular electron density theory perspective
2020
The strain-promoted [3+2] cycloaddition (SP-32CA) reactions of phenyl azide with a series of five strained cycloalkynes C5–C9 have been studied within molecular electron density theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. These zwitterionic type SP-32CA reactions take place through a one-step mechanism, with activation enthalpies in acetonitrile between −4.2 and 19.9 kcal mol−1. An excellent linear correlation between the decrease in activation enthalpies and the ring size of this series of cycloalkynes can be established. The present study shows that the highly strained cycloalkynes C5 and C6 experience a different chemical reactivity than less strained cycloalkynes C7–C9,…
A molecular electron density theory study of the enhanced reactivity of aza aromatic compounds participating in Diels–Alder reactions
2019
The enhanced reactivity of a series of four aza aromatic compounds (AACs) participating in the Diels–Alder (DA) reactions with ethylene has been studied using Molecular Electron Density Theory (MEDT). The analysis of the electronic structure of these AACs allows establishing that the substitution of the C–H unity by the isoelectronic N: unity linearly decreases the ring electron density (RED) of these compounds and concomitantly decreases their aromatic character and increases their electrophilic character. These behaviours not only decrease drastically the activation energies of these DA reactions, but also increase the reaction energies when they are compared with the very unfavourable DA…