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1.
Density functional theory (DFT) calculations have been performed on the 7-alkylidenecephalosporin sulfone in order to study
the mechanism of producing the bicyclic intermediate. The solvent effect was considered via polarizable continuum model (PCM)
computations. The results show that in the acyl-enzyme intermediate, the side chain pyridine nitrogen atom attacks the C6
atom, which is followed by cleavage of the C6–S1 bond. The unsaturated C7 is attacked by the leaving sulfinate, and a tricyclic
structure yields. This structure is unstable, and the proton is transferred from C6 to the sulfone to yield the bicyclic end
product. Besides, the reactant can undergo enamine–imine tautomerism. This suggests the end products have two forms, viz.
imine and enamine.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
The reaction mechanism of the l-proline-catalyzed α-aminoxylation reaction between aldehyde and nitrosobenzene has been investigated using density functional theory (DFT) calculation. Our calculation results reveal following conclusions [1]. The first step that corresponds to the formation of C–O bond, is the stereocontrolling and rate-determining step [2]. Among four reaction channels, the syn-attack reaction channel is more favorable than that of the anti one, and the TS-ss channel dominates among the four channels for this reaction in the step of C–O bond formation [3]. The intermolecular hydrogen bond between the acidic hydrogen of l-proline and the N atom of the nitrosobenzene in an early stage of the process catalyzes very effectively the C–O bond formation by a large stabilization of the negative charge that is developing at the O atom along the electrophilic attack [4]. The effect of solvent decreases the activation energy, and also, the calculated energy barriers are decrease with the enhancement of dielectric constants for C–O bond formation step. These results are in good agreement with experiment, and allow us to explain the origin of the catalysis and stereoselectivity for l-proline-catalyzed α-aminoxylation of aldehyde reaction. The addition of H2O to substituted imine proline, intermolecular proton-transfer steps, and the l-proline elimination process were also studied in this paper. 相似文献
3.
Lszl Hazai Gyula Dek Jzsef Tams Gbor Doleschall Gabor Tth 《Journal of heterocyclic chemistry》1985,22(6):1491-1495
4-Benzylidene-1-phenyl-1,4-dihydro-3(2H)-isoquinolinone, the intermediary product of the carbonyl condensation reaction between 1-phenyl-1,4-dihydro-3(2H)-isoquinolinone and benzaldehyde, rearranges in the presence of an equivalent quantity of sodium hydride into 4-benzyl-1-phenyl-3(2H)-isoquinolinone. As the possibility of the migration of the hydrogen at C-1 in the form of a proton or a hydrogen atom (radical reaction) was excluded, the mechanism of the rearrangement could be depicted as an intermolecular hydride anion migration. In case of the 1-(4-pyridyl)- and 1-(3-pyridyl)-1,4-dihydro-3(2H)-isoquinolinones, however, the rearrangement can be carried out also in polyphosphoric acid and in this case a proton loss-proton gain mechanism was proved. 相似文献
4.
G. G. Tokmadzhyan 《Russian Journal of Organic Chemistry》2011,47(11):1746-1749
Beckmann rearrangement was performed of oximes of substituted 3-acetyl-4-methyl-5,5-dimethyl(pentamethylene)-2-oxo-2,5-dihydrofuranes
in the presence of boron trifluoride etherate. Aiming at establishing the spatial arrangement of the oximes the hydrolysis
was carried out of acid amides obtained by Beckmann rearrangement of oximes of methyl ketones belonging to unsaturated γ-lactone
series and also to aromatic and alicyclic series. The hydrolysis with 20% sulfuric acid led to the formation of the corresponding
acid and amine, and the hydrolysis with acetic and hydrochloric acids resulted in retrobeckmann rearrangement giving the initial
oximes. 相似文献
5.
V. Ya. Sosnovskikh A. Yu. Sizov B. I. Usachev M. I. Kodess V. A. Anufriev 《Russian Chemical Bulletin》2006,55(3):535-542
Reactions of chromones with methyl ketoximes in the presence of lithium diisopropylamide follow the nucleophilic 1,2-addition
mechanism to give spiro[4H-chromene-4,5′-isoxazolines] in good yields. The isoxazoline ring in spiro[4H-chromene-4,5′-isoxazolines] undergoes opening under the action of conc. H2SO4, yielding α,β-unsaturated oximes. Their nitrosation and bromination lead to the corresponding spiroisoxazolines, while the
Beckmann rearrangement, to α,β-unsaturated amides. The latter are also formed directly from spiro[4H-chromene-4,5′-isoxazolines] under the action of PCl5. N-Substituted acetophenone hydrazones in the presence of lithium diisopropylamide react at the C(4) atom of 2-trifluoromethylchromone,
while acetophenone anil under the same conditions, at the C(2) atom.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 516–522, March, 2006. 相似文献
6.
I. Yu. Bagryanskaya Yu. V. Gatilov S. A. Osadchii A. A. Martynov M. M. Shakirov E. E. Shul'ts G. A. Tolstikov 《Chemistry of Natural Compounds》2005,41(6):657-662
Oximation of oreoselone to produce a mixture the E- and Z-oximes was investigated. The crystal and molecular structures of
oreoselone Z-oxime and the Beckmann rearrangement product of oreoselone E- or Z-oximes and PCl5, 7-(1-chloro-2-methylpropoxy)-2-oxo-2H-1-benzopyran-6-carbonitrile, were established by XSA. Hydrolysis of the latter produced
7-hydroxy-2-oxo-2H-1-benzopyran-6-carbonitrile.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 541–545, November–December, 2005. 相似文献
7.
E. S. Shubina N. V. Belkova E. V. Bakhmutova L. N. Saitkulova A. V. Ionidis L. M. Epstein 《Russian Chemical Bulletin》1998,47(5):817-822
The results of experimental and theoretical studies of intermolecular MH...HX and BH...HX hydrogen bonds with the hydride
hydrogen atom acting as a proton accepting site are analyzed. Spectral (IR and NMR) criteria for their formation are presented.
The spectral, structural, and thermodynamic characteristics of these unusual hydrogen bonds obey the regularities found for
classical hydrogen bonds. It was shown that the MH...HX bonds participate in the proton transfer with the formation of nonclassical
cationic hydrides and the |M(η2-H2|+ hydrogen bonds are formed in low-polarity media. Problems arising in this new line of investigations are discussed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–851, May, 1998. 相似文献
8.
The substituent effects and product stereoselectivity of the title reaction has been studied using density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level of theory. It was found that the substituents do not perturb the mechanism of intermolecular formal aza-[3+3] cycloaddition. Our calculations also show that methyl or benzyl groups on the N atom of vinylogous amide favor the addition step, but alkyl substituents on the either N atom or terminal C atom of α,β-unsaturated imine cation have opposite effects. Alkyl substituents on the N atom of α,β-unsaturated imine cation may lower the activation barriers for elimination of amide. The steric interaction between two substituents leads to the formation of major product both thermodynamically and kinetically. 相似文献
9.
The reductive amination reaction of acetone by cyclohexylamine over hydrogenation metal catalysts was investigated. The study
is focused on the formation of side products in the reaction. It was verified that the formation of amines having unusual
combinations of alkyls is caused by the metal-catalyzed rearrangement of the double bond around the nitrogen atom in an imine
intermediate and consequent reactions of the isomeric imine. It was found that the isomerization reactions occur over virtually
all of the hydrogenation catalysts studied, while their respective activities for the imine isomerization decreases in the
order Ni = Co > Ru > Pt = Rh > Pd. 相似文献
10.
A systematic calculation of the potential curves or surfaces for 1,2-shift has been realized by using MNDO or other models in MOPAC programs. By referring to the previous authors' viewpoints, the 1,2-shift can be divided into two categories. 1,2-electron-deficient shift is that the electronic configuration of the atom which accepts the migrating group is a cation or an electron-deficient atom, and 1,2-anion shift is the one that the accepted atom of the migration group is a negative ion. In terms of the experimental facts and the calculation of the potential surfaces, in electron-deficient shift such as Beckmann or Baeyer-Villiger rearrangement, the migration occurs through a transition complex formed between the 7i-bond and the cation or electron-deficient migrating group, but in anion shift such as Wittig or Stevens rearrangement, the electron pair in it-orbit excites at first to π* orbit, and then the migration occurs through the new formed complex between the anion migration group and the vacant rc 相似文献
11.
Sirijaraensre J Truong TN Limtrakul J 《The journal of physical chemistry. B》2005,109(24):12099-12106
The mechanism of the Beckmann rearrangement (BR) catalyzed by the ZSM-5 zeolite has been investigated by both the quantum cluster and embedded cluster approaches at the B3LYP level of theory using the 6-31G(d,p) basis set. Single-point calculations were carried out at the MP2/6-311G(d,p) level of theory to improve energetic properties. The embedded cluster model suggests that the initial step of the Beckmann rearrangement is not the O-protonated oxime but the N-protonated oxime. The energy barriers derived from the proton shuttle of the N-bound to the O-bound isomer are determined to be approximately 99 and approximately 40 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. The difference in the activation energy is due mainly to the effect of the Madelung potential from the zeolite framework. The next step is the rearrangement step, which is the transformation of the O-protonated oxime to be an enol-formed amide compound, formimidic acid. The activation energy, at the rearrangement step, is calculated to be approximately 125 and approximately 270 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. The final step is the tautomerization step which transforms the enol-form to the keto-form, formamide compound. The energy barrier for tautomerization is calculated to be 123 and 151 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. These calculated results suggest that the rate-determining step of the vapor phase of the Beckmann rearrangement on H-ZSM-5 is the rearrangement or tautomerization step. 相似文献
12.
It was shown by quantum chemical methods and 1H NMR spectroscopy that in the series of prototropic tautomeric quinazolin-4-ones with hydrogenated 1,3-diazaheterocycles
annulated at positions 2 and 3, namely, imidazole, pyrimidine, or [1,3]diazepine (compounds 1–3, respectively), the 1H-tautomeric form strongly predominates in the gas phase and in solutions regardless of the nature of these cycles. Tautomerization
of tricycles 1–3 occurs via the intermolecular mechanism to form as intermediates hydrogen-bonded cyclodimers of these compounds or their cyclosolvates
with proton-donor solvents. The key step of the reaction is the intraassociated concerted double proton transfer, which can
proceed in nearly synchronous and asynchronous modes. In particular, double proton transfer in cyclodimers of quinazolinones
1–3 is asynchronous and proceeds with the formation of solvate-stabilized polar transition states, which are similar in structure
to ionic intermediates of the nonconcerted double proton transfer. 相似文献
13.
Multiple Reaction Pathways Operating in the Mechanism of Vinylogous Mannich‐Type Reaction Activated by a Water Molecule
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A systematic search for reaction pathways for the vinylogous Mannich‐type reaction was performed by the artificial force induced reaction method. This reaction affords δ‐amino‐γ‐butenolide in one pot by mixing 2‐trimethylsiloxyfuran, imine, and water under solvent‐free conditions. Surprisingly, the search identified as many as five working pathways. Among them, two concertedly produce anti and syn isomers of the product. Another two give an intermediate, which is a regioisomer of the main product. This intermediate can undergo a retro‐Mannich reaction to give a pair of intermediates: an imine and 2‐furanol. The remaining pathway directly generates this intermediate pair. The imine and 2‐furanol easily react with each other to afford the product. Thus, all of these stepwise pathways finally converge to give the main product. The rate‐determining step of all five (two concerted and three stepwise) pathways have a common mechanism: concerted Si? O bond formation through the nucleophilic attack of a water molecule on the silicon atom followed by proton transfer from the water molecule to the imine. Therefore, these five pathways have comparable barriers and compete with each other. 相似文献
14.
红霉素9,11-亚胺醚和乙腈分子加合物的合成和晶体结构 总被引:1,自引:0,他引:1
通过控制红霉素A (E)肟的贝克曼重排反应条件合成了一种关键中间体红霉素9,11-亚胺醚, 该化合物可与乙腈形成稳定的分子加合物(摩尔比为1∶1), 未见文献报道. 阐述了该化合物的合成、晶体结构、晶体学数据和结构参数. 该化合物为无色透明晶体, 属单斜晶系, 空间群P21. 对该加合物和已知化合物红霉素6,9-亚胺醚晶体结构的对照解析, 有助于对重排反应机理、异构化机理和两异构体还原差异性的分析, 对重排反应和还原反应起到积极的指导作用. 相似文献
15.
Sneh K. Dogra 《Journal of Chemical Sciences》1992,104(6):635-647
The present review describes the salient features of inter- and intramolecular proton transfer reactions of 2-(2′-aminophenyl)-,
2-(3′-aminophenyl)-, 2-(4′-aminophenyl)-, 2-(2′-hydroxyphenyl)-, 2-(3′-hydroxyphenyl)- and 2-(4′-hydroxyphenyl)-benzimidazoles,
benzoxazoles and benzothiazoles. Fluorescence quantum yield of the phototautomer produced by the intramolecular hydrogen bonding
decreases on going from benzimidazole to benzoxazole to benzothiazole. This indicates that the rate of internal conversion
increases in the order of compounds as mentioned above. The biprotonic phototautomerism or the presence of intermolecular
proton transfer has led to the formation of (i) nonfluorescent zwitterions in case of hydroxyphenyl derivatives and the ground
state precursor of this species in neutral molecules, (ii) nonfluorescent monoanions from fluorescent monoanions and (iii)
nonfluorescent monocations from monocations in case of aminophenyl derivatives. In the case of 2-(4′-aminophenyl)-substituted
compounds, the first protonation has always led to the formation of two types of monocations; one by protonating the amino
group and the other by protonating the tertiary nitrogen atom. The former is more stable in aqueous media and the latter in
non-polar media. 相似文献
16.
S. A. Soldatova G. S. Gimranova Zh. A. Mamyrbekova K. B. Polyanskii S. V. Akbulatov A. T. Soldatenkov 《Chemistry of Heterocyclic Compounds》2007,43(11):1420-1425
4-Aryl-1,2,3,6-tetrahydropyridinium quaternary salts which have a benzoylmethyl or ethoxycarbonylmethyl group on atom N-1
generate N-ylides when heated in the presence of NaH and they can rearrange in situ with contraction or expansion of the six-membered
heterocycle to give substituted pyrrolidines (as a result of a [2,3]-sigmatropic rearrangement) or 1H-tetrahydroazepine derivatives
(via Stevens rearrangement). The presence of an aryl substituent at position C-4 in the tetrahydropyridine ring allows to
avoid the formation of elimination products and changes the direction of the reaction towards the preparation of the tetrahydroazepines.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1670–1676, November, 2007. 相似文献
17.
Gian Pietro Miscione Marco Stenta Domenico Spinelli Ernst Anders Andrea Bottoni 《Theoretical chemistry accounts》2007,118(1):193-201
Some aspects of the catalytic mechanism of HCA have been investigated. Either a zinc-bound water or a zinc-bound hydroxide
has been considered as a nucleophile attacking CO
2. No reaction path exists in the former case, while a transition state for the nucleophilic attack has been located in the
latter (barrier of 7.6 kcal mol−1). This activation energy is determined by the breaking of the hydrogen-bond network that shields the zinc-bound hydroxide
when the CO
2 molecule approaches the reaction center. No ambiguity exists about the mechanism for the internal rearrangement of the zinc–bicarbonate
complex. The rotation pathway (Lindskog mechanism) proposed by many authors is too energy demanding since it causes the breaking
of the hydrogen-bond network around the bicarbonate. The only possible rearrangement mechanism is a proton transfer (Lipscomb)
that occurs in two steps (each step corresponding to a double proton transfer) and involves the Thr199 residue as a proton
shuttle.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Contribution to the Fernando Bernardi Memorial Issue. 相似文献
18.
Song T Hao Q Law CH Siu CK Chu IK 《Journal of the American Society for Mass Spectrometry》2012,23(2):264-273
In this study, we observed unprecedented cleavages of the Cβ–Cγ bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M•+) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory
(DFT) calculations to study the mechanism of this bond cleavage, which forms [M – 116]+ ions. The formation of an α-carbon radical intermediate at the tryptophan residue for the subsequent Cβ–Cγ bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported
by the identical product ion spectra of [LGGGH – 43]+ and [WGGGH – 116]+, obtained from the CID of [LGGGH]•+ and [WGGGH]•+, respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom,
leaving the radical centered formally on the indole nitrogen atom ([Ind]•-2), in agreement with the CID data for [WGGGH]•+ and [W1-CH3GGGH]•+; replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising
from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from Cβ–Cγ bond cleavage. Hydrogen atom transfer or proton transfer to the γ-carbon atom of the tryptophan residue weakens the Cβ–Cγ bond and, therefore, decreases the dissociation energy barrier dramatically. 相似文献
19.
N. A. Klyuev Yu. V. Shurukhin V. A. Konchits I. I. Grandberg V. L. Rusinov V. A. Zyryanov I. Ya. Postovskii 《Chemistry of Heterocyclic Compounds》1980,16(2):202-208
The thermolysis of 5-methyl-1-phenyltetrazole was studied at 20–350°C by derivatography and mass spectrometry, and it was
shown that thermal decomposition proceeds with the elimination of a molecule of nitrogen and is accompanied by skeletal rearrangement
of the intermediately formed nitrene to 2-methylbenzimidazole or migration of the methyl group to the nitrogen atom with the
formation of methylphenylcarbodiimide (MPCD). In addition, symmetrical dimethyl- and diphenylcarbodiimides, methylphenylguanidines,
and aniline are formed. It is assumed that the formation of these compounds in the pyrolyzate is due to polymerization of
MPCD and subsequent thermal destruction of the polymerization products. A scheme for the thermolysis of 5-methyl-1-phenyltetrazole
is proposed.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 265–271, February, 1980. 相似文献
20.
分子筛催化cis-2-丁烯的双键异构反应机理的DFT研究 总被引:1,自引:0,他引:1
基于含有两个Si和一个Al的分子筛3T簇模型, 利用密度泛函方法(DFT)研究了分子筛催化1-丁烯双键异构为cis-2-丁烯的反应机理. 在B3LYP/6-31G(d,p)计算水平上对反应各驻点进行了全优化, 并计算了反应的活化能. 研究发现, 分子筛上的酸性OH基团首先通过物理吸附靠近1-丁烯的双键, 形成了π配位复合物后, 丁烯双键的端基C原子逐渐抽取这个质子, 同时相邻酸性位的一个O原子也抽取丁烯碳链上的一个H原子, 形成吸附态的cis-2-丁烯, 最后通过脱附形成产物, 使分子筛复原, 反应按照协同反应机理发生. 计算得到的表观活化能是55.9 kJ/mol, 与实验结果接近. 相似文献