A theoretical investigation of the regio- and stereoselectivities of the 1,3-dipolar cycloaddition of C-diethoxyphosphoryl-N-methylnitrone with substituted alkenes

Unveiling the Origin of the Selectivity and the Molecular Mechanism in the [3+2] Cycloaddition Reaction of N-aryl-C-carbamoylnitrone with N-arylitaconimide

The [3+2] cycloaddition reaction of N-aryl-C-carbamoylnitrone (nitrone 1) with N-arylitaconimide (ethylene 2) was computationally studied using the B3LYP/6-31G(d) level of theory. An analysis of the different energetic profiles and the transition states’ optimized structures clearly indicated that this 32CA occurred through a non-polar, asynchronous, one-step mechanism, favoring the formation of the ortho–endo cycloadduct, as observed experimentally. The analysis of the reactivity indices derived from the conceptual DFT explains well the low polarity of this 32CA reaction. Parr functions and a dual reactivity descriptors analysis correctly explained the regioselectivity ortho of this 32CA reaction. Solvent effects did not modify the obtained selectivity but it increased the activation energies and decreased the exothermic character of this 32CA reaction. A thermodynamic parameters analysis indicated that this 32CA wascharacterized by an ortho regioselectivity and endostereoselectivity and exothermic and exergonic characters.

Regio- and stereoselectivity of the [3+2] cycloaddition of nitrones with methyl-acetophenone: A DFT investigation

A theoretical study of the regio- and stereoselectivities of the [3 + 2] cycloaddition reactions of nitrones with substituted alkene (methyl acetophenone) is investigated using density functional theory (DFT) and carried out at B3LYP/6-311+G(d,p) level. The reactivity of these cycloadditions is rationalized by FMO model, activation energy calculations, and philicity indexes. The electronic populations have been calculated from natural orbital, which based on charges by using NBO analysis, MK and CHelpG electrostatic population. The four possible pathways, fused and bridged regioisomeric modes, and the two stereoisomeric approaches endo and exo for the cycloaddition reactions are analyzed and discussed. Analysis of TS geometries and bond lengths demonstrate that these reactions follow a one-step mechanism with asynchronous transition states. The activation energy indicated a favored endo approach along the four reaction pathways.

Unprecedented Regio- and Stereoselective Synthesis of Pyrene-Grafted Dispiro[indoline-3,2'-pyrrolidine-3',3″-indolines]: Expedient Experimental and Theoretical Insights into Polar [3 + 2] Cycloaddition

A series of dispiro[indoline-3,2'-pyrrolidine-3',3″-indolines] was synthesized via a multicomponent polar [3 + 2] cycloaddition (32CA) reaction of isatin derivatives, sarcosine and (E)-3-(2-oxo-2-(pyren-1-yl)ethylidene)indolin-2-one derivatives. The regio- and stereochemistries of the cycloadducts were established on the basis of one-dimensional (1D) (1H-, 13C-, 13C-CRAPT NMR) and two-dimensional (2D) homonuclear and heteronuclear correlation NMR spectrometry experiments (1H-1H gDQFCOSY, 13C-1H-HSQCAD, 13C-1H-HMBCAD, 1H-1H-ROESYAD). The molecular mechanism and regio- and stereoselectivities of the cycloaddition (CA) reaction have been investigated utilizing a density functional theory (DFT) method and were thoroughly explained based on the transition-state stabilities and global/local electrophilicity/nucleophilicity reactivity indices of the reactants.

Investigating the regio-, stereo-, and enantio-selectivities of the 1,3-dipolar cycloaddition reaction of C-cyclopropyl-N-phenylnitrone derivatives and benzylidenecyclopropane derivatives: A DFT study

The biomedical importance of spirocyclopropane isoxazolidine derivatives is widely known. The 1,3-dipolar cycloaddition (1,3-DC) of C-cyclopropyl-N-phenylnitrone derivative and benzylidenecyclopropane derivatives leading to the formation of 5- and 4-spirocyclopropane isoxazolidines derivatives have been studied using density functional theory (DFT) at M06-2X/6-311G (d,p) level of theory. An extensive exploration of the potential energy surface shows that the 1,3-dipole adds across the dipolarophile via an asynchronous concerted mechanism. While electron-donating groups (EDGs) on the benzylidenecyclopropane favor the formation of the 4-spirocyclopropane isomer, electron-withdrawing groups (EWGs) favor the reaction channels that furnish the 5-spirocyclopropane isoxazolidine isomer. Both EWDs and EDGs on the 1,3-dipole favor the formation of the 5-spirocyclopropane isoxazolidine isomer. Irrespective of the electronic nature of substituents on the C-cyclopropyl-N-phenylnitrone, the reaction channels that regioselectively lead to the formation of the 5-spirocyclopropane isoxazolidine isomer are favored. In all reactions considered, the channels that selectively lead to the formation of the cis-diastereoisomers proceed with lower activation barriers than the trans-diastereoisomers. In all cases, the observed selectivities in the title reaction are kinetically controlled.

Theoretical Study on Regioselectivity of the Diels-Alder Reaction between 1,8-Dichloroanthracene and Acrolein

A theoretical study of the regioselectivity of the Diels-Alder reaction between 1,8-dichloroanthracene and acrolein is performed using DFT at the B3LYP/6-31G(d,p) level of theory. The FMO analysis, global and local reactivity indices confirmed the reported experimental results. Potential energy surface analysis showed that the cycloadditions (CAs) favor the formation of the anti product. These results are in good agreement with the reported results obtained experimentally where the anti is the major product.

A DFT study of the role of the Lewis acid catalysts in the [3 + 2] cycloaddition reaction of the electrophilic nitrone isomer of methyl glyoxylate oxime with nucleophilic cyclopentene

The mechanism and stereoselectivity of the BH₃-catalysed 32CA reaction between C-methoxycarbonyl nitrone and cyclopentene has been studied using MPWB1K/6-31G(d) computational level.

Mechanism and Regioselectivity of the 1,3-Dipolar Cycloaddition of Methyleneamine N-Oxide with Cyclopent-3-Ene-1,2-Dione and its Aza, Oxa and Thia Analogues: A Dft Approach

A theoretical study on the regioselectivity of 1,3-dipolar cycloaddition reactions between methyleneamine N-oxide (nitrone) and cyclopent-3-Ene-1,2-Dione (DPhl), pyrrole-2,3-dione (DPh2), furan-2,3-dione (DPh3) and thiophene-2,3- dione (DPh4) has been carried out by means of several theoretical approaches, namely, activation energies, Houk's rule based on FMO theory and DFT reactivity indices. The calculations were performed at the DFT-B3LYP/6-31G(d) level of theory using Gaussian 03. The present analysis shows that these reactions have an NED character. Moreover, the results obtained from energetic and electronic approaches, with the exception of Gazquez - Mendez rule based on NPA analysis, confirm that 1,5-regioisomer is the major product.

Investigation into the regiochemistry of some isoxazoles derived from 1,3-dipolar cycloaddition of 4-nitrobenzonitrile oxide with some dipolarophiles: a combined theoretical and experimental studies

Reaction of 4-nitrobenzonitrile oxide (2) which was generated in situ with acrylo nitrile (3), methyl methacrylate (4) and allyl bromide (5) as dipolarphile afforded the new 7a, 8a and 9a compounds respectively. Reactivity and regiochemistry of these reactions were investigated using activation energy calculations and density functional theory (DFT)-based reactivity indexes. The theoretical 13C NMR chemical shifts of the cycloadducts which were obtained by GIAO method were comparable with the observed values.