Influence of Reactant Polarity on the Course of the Inverse-Electron-Demand Diels−Alder Reaction. A DFT Study of Regio- and Stereoselectivity, Presence of Lewis Acid Catalyst, and Inclusion of Solvent Effects in the Reaction between Nitroethene and Substituted Ethenes

Abstract

The molecular mechanisms for the inverse-electron-demand Diels−Alder reactions between nitroethene and three substituted ethenes (propene, methyl vinyl ether, and dimethylvinylamine) to give the corresponding nitroso cycloadducts have been characterized with density functional theory methods using the B3LYP/6-31G* calculational level. On the basis of stability arguments and molecular orbital analysis relative rates, regioselectivity, and stereoselectivity, the presence of Lewis acid catalyst modeled by the BH3 system and the inclusion of solvent effects as a function of the nature of substituent in the dienophile fragment are analyzed and discussed. The ortho attack mode presents transition structures more stable than the meta one. For the former, reactivity, endo selectivity, and asynchronicity are enhanced with the increase of the electron-releasing character of the substituent on dienophile fragment. The reaction between nitroethene and propene has dissymmetric concerted transition structures associated with a pericyclic process, while the reaction between nitroethene and dimethylvinylamine takes place along an asynchronous transition structure corresponding to a nucleophilic attack to nitroethene, with concomitant ring closure and without participation of zwitterionic intermediates. For the most unfavorable meta attack modes, the reactions have synchronous mechanisms that are not sensible to the substitution on the dienophile system. For the ortho channels, the inclusion of Lewis acid catalyst and solvent effects contributes to the charge-transfer process from the substituted ethenes to nitroethene and rate acceleration, as well as a significant increase of the endo stereoselectivity.

Understanding the Bond Formation in Hetero-Diels-Alder Reactions. An ELF Analysis of the Reaction of Nitroethylene with Dimethylvinylamine

“…In 1999, we studied the effects of the electron-releasing substitution on the dipolarophile in the HDA reactions of electrophilic nitroethylene 6 with three ethylenes of increasing nucleophilicity: propene 7, methyl vinyl ether 8, and dimethylvinylamine (DMVA) 9 (see Scheme 1) [11]. A good correlation between the acceleration of the reaction and the polar character of the TS was established.…”

“…A good correlation between the acceleration of the reaction and the polar character of the TS was established. The polar character measured by the CT at the TS of the reaction no only accelerates the reaction but also increases the endo stereo and ortho regioselectivity [11].…”

“…Herein, we present an ELF analysis of the electronreorganization along the most favorable endo/ortho reactive channel associated with the HDA reaction between nitroethylene 6 and DMVA 9, which corresponds to the most P-DA reaction of the series given in Scheme 1 [11]. The purpose of this paper is to shed light on the electronic changes during HDA reactions, and to provide new insight into the answer this question: how does the C-O bond in HDA reactions take place, and which is the origin of the asynchronicity in bond-formation and regioselectivity?…”

DFT study of the decomposition reactions of nitroethyl benzoates catalyzed by the 1,3-dimethylimidazolium cation

“…Recently published reports 26,[44][45][46][47][48] , indicate that a similar approach was used successfully for the exploration of a reaction involving several different nitrocompounds. These calculations proved that the first step of the decomposition of nitroethyl benzoate (1a) is the establishment of a pre-reaction complex ( [1][DMIM]) between the ester molecule and the 1,3-dimethylimidazolium cation.…”

Theoretical analysis of the mechanism and regioselectivity of the 1, 3-dipolar cycloaddition of E-3-(dimethylamino)-1-(10H-phenothiazin-2-yl)prop-2-en-1-one with some nitrilimines using DFT and the distortion/interaction model

“…The comparison of the results presented in Table 1 ] cycloaddition reactions that "for asymmetrically substituted dienophiles, the more asynchronous TS has the lower energy''. [36][37][38] The evaluation of the electronic nature of these 1,3-DC reactions showed that the atomic charges in the transition state were shared between the dipoles 1a-c and 2 (see Figure 1). In the gas phase, the charge transfer (CT) in the transition state, which fluxes from the dipolarophile 2 to the dipoles 1a-c, ranges from 0.06 to 0.18 e, indicating the polar nature of the 1,3-DC reactions.…”