A dramatic change of kinetic conditions and molecular mechanism of decomposition processes of nitroalkyl carboxylates catalyzed by ethylammonium cations

Energetic Aspects and Molecular Mechanism of 3-Nitro-substituted 2-Isoxazolines Formation via Nitrile N-Oxide [3+2] Cycloaddition: An MEDT Computational Study

Regioselectivity and the molecular mechanism of the [3+2] cycloaddition reaction between nitro-substituted formonitrile N-oxide 1 and electron-rich alkenes were explored on the basis of the wb97xd/6-311+G(d) (PCM) quantum chemical calculations. It was established that the thermodynamic factors allow for the formation of stable cycloadducts along all considered models. The analysis of the kinetic parameters of the main processes show that all [3+2] cycloadditions should be realized with full regioselectivity. In all cases, the formation of 5-substituted 3-nitro-2-isoxazolidines is clearly preferred. It is interesting that regiodirection is not determined by the local electrophile/nucleophile interactions but by steric effects. From a mechanistic point of view, all considered reactions should be treated as polar, one-step reactions. All attempts to locate the hypothetical zwitterionic intermediates along the cycloaddition paths were, however, not successful.

On the Mechanism of the Synthesis of Nitrofunctionalised Δ2-Pyrazolines via [3+2] Cycloaddition Reactions between α-EWG-Activated Nitroethenes and Nitrylimine TAC Systems

We investigated the reactivity of different substituted nitrylimine-type three atom components (TACs) in [3+2] cycloaddition (32CAs) reactions with electrophilically activated nitroethenes within molecular electron density theory (MEDT). In parallel research, the molecular mechanism of the considered transformation was examined through analysis of all possible reaction channels and full optimization of all critical structures. In particular, the existence of zwitterionic intermediates on reaction paths was verified. On the basis of the bonding evolution theory (BET), the mechanism of the 32CA reaction between C,N-diphenylnitrylimine and (E)-2-phenyl-1-cyano-1-nitroethene should be treated as a one-step two-stage mechanism.

Organocatalysis for the Asymmetric Michael Addition of Cycloketones and α, β-Unsaturated Nitroalkenes

Michael addition is one of the most important carbon–carbon bond formation reactions. In this study, an (R, R)-1,2-diphenylethylenediamine (DPEN)-based thiourea organocatalyst was applied to the asymmetric Michael addition of nitroalkenes and cycloketones to produce a chiral product. The primary amine moiety in DPEN reacts with the ketone to form an enamine and is activated through the hydrogen bond formation between the nitro group in the α, β-unsaturated nitroalkene and thiourea. Here, the aim was to obtain an asymmetric Michael product through the 1,4-addition of the enamine to an alkene to form a new carbon–carbon bond. As a result, the primary amine of the chiral diamine was converted into an enamine. The reaction proceeded with a relatively high level of enantioselectivity achieved using double activation through the hydrogen bonding of the nitro group and thiourea. Michael products with high levels of enantioselectivity (76–99% syn ee) and diastereoselectivity (syn/anti = 9/1) were obtained with yields in the range of 88–99% depending on the ketone.

The Molecular Mechanism of the Formation of Four-Membered Cyclic Nitronates and Their Retro (3 + 2) Cycloaddition: A DFT Mechanistic Study

In the present work, the formation of the four-membered cyclic nitronates and the retro (3 + 2) cycloaddition (retro-32CA) reaction of the 4H-[1,2]oxazete 2-oxide were studied using the density functional theory method at the MPWB1K/6-311G(d,p) theoretical level. The electronic structure of 3-tert-butyl-4,4-dimethyl-1,2-dinitro-pent-2-ene was known through electron localization function analysis, natural population analysis, and molecular electrostatic potential analysis. The formation of 4,4-di-tert-butyl-3-nitromethyl-4H-[1,2]oxazete 2-oxide proceeds through a one-step mechanism. The mechanism of the retro-32CA leading to di-tert-butyl ketone and nitrile oxide derivative should be described as an asynchronous two-stage one-step process. The bonding evolution theory study was carried out to clarify the mechanisms of the formation of 4H-[1,2]oxazete 2-oxide and their retro-32CA.

Understanding the molecular mechanism of γ-elimination of nitrous acid in the framework of the molecular electron density theory

The reactions of γ-dehydronitration of furaxanenitrolic acids have been studied within the density functional theory using molecular electron density theory scheme at the MPWB1K(PCM)/6-311G(d,p) level of theory. The alteration of bonding along the course of the reaction is studied in the topology of the electron density functional within the bonding evolution theory perspective. The characteristics of electron density changes indicate that we can distinguish six different phases in the nitrous acid extrusion from furaxanenitrolic acid 1a. These different phases related to the intrinsic reaction coordinate path of the analyzed reaction denote the non-concerted nature of the molecular mechanism.