A theoretical study of the mechanism, stereoselectivity and Lewis acid catalyst on the Diels–Alder cycloaddition between furan and activated alkenes

A molecular electron density theory study of asymmetric Diels-Alder [4 + 2] reaction's mechanism of furan with three substituted alkynes (5-R substituted-3-(3-(phenylsulfonyl)-propioloyl)-oxazolidin-2-one)

CONTEXT

The [4 +2 ] cycloaddition reactions between furan and three substituted alkynes (5-R-substituted-3-(3-(phenylsulfonyl)-propioloyl)-oxazolidin-2-one) have been investigated using the MEDT approach. Reactivity indices, reaction pathways, and activation energies are calculated. In an investigation of conceptual DFT indices, furan acts as a nucleophile, while the three substituted alkynes (5-R-substituted-3-(3-(phenylsulfonyl)-propioloyl)-oxazolidin-2-one) function as electrophiles in this reaction. The cycloaddition is regioiselective, as demonstrated by the activation and reaction energies, in clear agreement with the experiment's results. Hetero Diels-Alder [4 + 2] cycloadditions occur following a non-concerted two stages one-step molecular mechanism.

METHODS

For the purpose of this study, all calculations were performed using the Gaussian 09 software. Optimization was achieved through Berny's computational gradient optimization method, employing the B3LYP functional and the 6-31G(d) basis set. Analysis of both local and global reactivity indices provided insights into the reactivity tendencies of the reactants, distinguishing between electrophilic and nucleophilic characteristics via Parr functions. Frequency calculations were employed to identify and characterize stationary points, with transition states indicated by a single imaginary frequency and positive values of all frequencies for reactants and product. The electron localization function (ELF) was investigated using the Multiwfn software within the context of topological analyses.

New Experimental Conditions for Diels-Alder and Friedel-Crafts Alquilation Reactions with Thiophene: A New Selenocyanate with Potent Activity against Cancer

The reactivity of thiophene in Diels-Alder reactions is investigated with different maleimide derivatives. In this paper, we have synthesized for the first time the Diels-Alder adducts of thiophene at room temperature and atmospheric pressure. Maleimido-thiophene adducts were promoted by AlCl₃. The effects of solvent, time, temperature and the use of different Lewis acids were studied, showing dramatic effects for solvent and Lewis acid. Furthermore, the catalysis with AlCl₃ is highly stereoselective, preferably providing the exo form of the adduct. Additionally, we also discovered the ability of AlCl₃ to catalyze the arylation of maleimides to yield 3-aryl succinimides in a straightforward manner following a Friedel-Crafts-type addition. The inclusion of a selenocyanate group contributes to the cytotoxic activity of the adduct. This derivatization (from compound 7 to compound 15) results in an average GI₅₀ value of 1.98 µM in the DTP (NCI-60) cell panel, resulting in being especially active in renal cancer cells.

A computational investigation of the selectivity and mechanism of the Lewis acid catalyzed oxa-Diels-Alder cycloaddition of substituted diene with benzaldehyde

The selectivity and the mechanism of the uncatalyzed and AlCl₃ catalyzed hetero-Diels-Alder reaction (HDR) between ([E]-4-methylpenta-2,4-dienyloxy)(tert-butyl)dimethylsilane 1 and benzaldehyde 2 have been studied using density functional theory at the MPWB1K/6-31G(d) level of theory. The uncatalyzed HDR between diene 1 and alkene 2 is characterized by a polar character and proceeds via an asynchronous one-step mechanism for the meta paths and synchronous for the ortho ones. In the presence of AlCl₃ catalyst, the mechanism changes to be stepwise, while the first step is the rate-determining step. The activation energies widely decrease, and the polar character increases dramatically. A large analysis of the mechanism is performed using the activation strain model/energy decomposition analysis (ASM/EDA) model, the natural bond orbital (NBO) and state specific dual descriptors (SSDDs). The obtained results indicate that the combined interaction energy associated with the distortion of the reactants in these HDR are at the origin of the observed kinetics. NBO analyses were applied to estimate the Lewis-acid catalyst donor-acceptor interaction with the molecular system. The SSDD analysis shed light into the orientation effects on the reaction kinetics by providing important information about charge transfer interactions during the chemical reaction. It indicates that the more favorable HDR pathway have the lowest excitation energies, facilitating the interaction between diene 1 and benzaldehyde 2 moieties. Non-covalent interaction (NCI) and QTAIM analyses of the meta-endo structure indicate that the presence of several weak NCIs formed at this approach is at the origin of the meta-endo selectivity.

The Role of the Catalyst on the Reactivity and Mechanism in the Diels–Alder Cycloaddition Step of the Povarov Reaction for the Synthesis of a Biological Active Quinoline Derivative: Experimental and Theoretical Investigations

An experimental and theoretical study of the reactivity and mechanism of the non-catalyzed and catalyzed Povarov reaction for the preparation of a 4-ethoxy-2,3,4,4a-tetrahydro-2-phenylquinoline as a biological active quinoline derivative has been performed. The optimization of experimental conditions indicate that the use of a catalyst, namely Lewis acid with an electron-releasing group, creates the best experimental conditions for this kind of reaction. The chemical structure was characterized by the usual spectroscopic methods. The prepared quinoline derivative has been also tested in vitro for antibacterial activity, which displays moderate inhibitory activity against both Escherichia coli and Staphylococcus aureus. The antioxidant activity was investigated in vitro by evaluating their reaction with 1,1-diphenyl-2-picrylhydrazyl DPPH radical, which reveals high reactivity. The computational study was performed on the Diels–Alder step of the Povarov reaction using a B3LYP/6-31G(d,p) level of theory. The conceptual DFT reactivity indices explain well the reactivity and the meta regioselectivity experimentally observed. Both catalysts enhance the reactivity of the imine, favoring the formation of the meta regioisomers with a low activation energy, and they change the mechanism to highly synchronous for the Lewis acid and to stepwise for the Brønsted acid. The reaction of imine with allyl alcohol does not give any product, which requires high activation energy.

Theoretical investigation of the effect of hydrogen bonding on the stereoselectivity of the Diels–Alder reaction

Here, we report the computational prediction of high exo selectivities in a series of Diels–Alder reactions with H-bonding interaction.

Ring Rearrangement Metathesis in 7-Oxabicyclo[2.2.1]heptene (7-Oxanorbornene) Derivatives. Some Applications in Natural Product Chemistry

Metathesis reactions is firmly established as a valuable synthetic tool in organic chemistry, clearly comparable with the venerable Diels-Alder and Wittig reactions and, more recently, with the metal-catalyzed cross-coupling reactions. Metathesis reactions can be considered as a fascinating synthetic methodology, allowing different variants regarding substrate (alkene and alkyne metathesis) and type of metathetical reactions. On the other hand, tandem metathesis reactions such Ring Rearrangement Metathesis (RRM) and the coupling of metathesis reaction with other reactions of alkenes such as Diels-Alder or Heck reactions, makes metathesis one of the most powerful and reliable synthetic procedure.

In particular, Ring-Rearrangement Metathesis (RRM) refers to the combination of several metathesis transformations into a domino process such as ring-opening metathesis (ROM)/ring-closing metathesis (RCM) and ROM-cross metathesis (CM) in a one-pot operation. RRM delivers complex frameworks that are difficult to assemble by conventional methods constitutingan atom economic process. RRM is applicable to mono- and polycyclic systems of varying ring sizes such as cyclopropene, cyclobutene, cyclopentene, cyclohexene, pyran systems, bicyclo[2.2.1]heptene derivatives, bicyclo[2.2.2]octene derivatives, bicyclo[3.2.1]octene derivatives and bicyclo[3.2.1]octene derivatives.

In this review our attention has focused on the RRM reactions in 7-oxabicyclo[2.2.1]heptene derivatives and on their application in the synthesis of natural products or significant subunits of them.

Effects of Solvent and Side-Chain Length on the Cycloaddition of Cyclopentadiene to N-alkylmaleimides: A Dft Study

Quantum chemistry calculations have been performed to investigate the kinetics and mechanism of the cycloaddition reaction between cyclopentadiene and N-alkylmaleimides in the gas phase and different solvents. To investigate the effects of side-chain length on the cycloaddition reaction, the rate constants and kinetic parameters of the reaction between cyclopentadiene with N-methyl-, N-ethyl-, N-propyl- and N-butyl-maleimide were calculated. The results obtained indicate that the reaction in solvents is faster than in the gas phase. Moreover, the dipole moments of the transition states are larger than those of the reactants. Therefore, the reactions in the most polar solvent (water) are faster than in ethanol, n-hexane, 2,2,2-trifluoroethanol (TFE) and acetonitrile. Quantum mechanics-molecular mechanics (QM/MM) calculations on the reactions using the explicit solvent model for water and TFE indicate that hydrogen bond interactions of the solvents have a key role in the rate of the reaction and these are more important than the polarity of the solvent. Natural bond orbital analysis reveals that the charge transfer between the reactants in solvents is more than in the gas phase. Finally, HOMO–LUMO analysis indicates that solvents increase the reactivity of the reactants in comparison to the gas phase.

Regio- and stereoselective synthesis of novel isoxazolidine heterocycles by 1,3-dipolar cycloaddition between C-phenyl-N-methylnitrone and substituted alkenes. Experimental and DFT investigation of selectivity and mechanism

A series of isoxazolidine heterocycles was synthesized through the 1,3-dipolar cycloaddition (13DC) reaction of C-phenyl-N-methylnitrone with different substituted alkenes.

Diels–Alder Reactions of α-Cyano α,β-Unsaturated Ketones with 2-Methyl-1,3-Butadiene: DFT Study of Mechanism, Reactivity and Regioselectivity

The mechanism, reactivity and regioselectivity of Diels–Alder cycloaddition reactions of 2-methyl-1,3-butadiene with four dienophiles, ( E)-2-benzylidene-3-oxobutanenitrile, ( E)-2-(furan-2-ylmethylene)-3-oxopentanenitrile, ( E)-2-benzylidene-4,4-dimethyl-3-oxopentanenitrile, and (E)-2-benzoyl-3-(furan-2-yl) acrylonitrile, have been studied by means of several theoretical approaches. The regioselectivity of these reactions has been confirmed by their activation energies, the Gazquez–Mendez rule, Houk's rule and global descriptors of the products. All the studied reactions have normal electron demand character and a polar nature. All calculations were done at the DFT-B3LYP/6-31G(d) level of theory.

Regioselective nucleophilic aromatic substitution reactions of 5,7-dinitroquinazoline-4-one and 5,7-dinitroquinazoline-4-thione with methylamine: a mechanistic consideration

Thiocarbonyls, similar to carbonyls, are able to provide regioselective control for the attack of amines at the peri-position of 5,7-dinitroquinazoline-4-thione through intramolecular N–H–SC hydrogen bonding.

Photoassisted diversity-oriented synthesis: accessing 2,6-epoxyazocane (oxamorphan) cores

The modular synthesis of photoprecursors and their photoinduced cyclization into substituted 1-benzazocanes of two distinct topologies is described. The key step producing an extended polyheterocyclic system involves the photogeneration of azaxylylenes and their subsequent intramolecular cycloaddition with furan-containing pendants tethered either via the aniline nitrogen or through the carbonyl group containing arm. The primary photoproducts-secondary or tertiary anilines which are not acylated at the nitrogen atom-undergo facile acid-catalyzed or spontaneous ring-opening-ring-closing rearrangement to yield fused polyheterocyclic structures possessing a 2,6-epoxyazocane (or oxamorphan) core.