Search

The regio- and stereoselectivity and the molecular mechanisms of the [3 + 2] cycloaddition reactions between Syn-propanethial S-oxide and selected conjugated nitroalkenes were explored theoretically in the framework of the Molecular Electron Density Theory. It was found that cycloadditions with the participation of nitroethene as well as its methyl- and chloro-substituted analogs can be realized via a single-step mechanism. On the other hand, [3 + 2] cycloaddition reactions between Syn-propanethial S-oxide and 1,1-dinitroethene can proceed according to a stepwise mechanism with a zwitterionic intermediate. Finally, we evaluated the affinity of model reaction products for several target proteins: cytochrome P450 14α-sterol demethylase CYP51 (RSCB Database PDB ID: 1EA1), metalloproteinase gelatinase B (MMP-9; PDB ID: 4XCT), and the inhibitors of cyclooxygenase COX-1 (PDB:3KK6) and COX-2 (PDB:5KIR). [ABSTRACT FROM AUTHOR]

The molecular mechanism of the reaction between 2-methoxyfuran and ethyl (Z)-3-phenyl-2-nitroprop-2-enoate was investigated using wb97xd/6-311+G(d,p)(PCM) quantum chemical calculations. It was found that the most probable reaction mechanism is fundamentally different from what was previously postulated. In particular, six possible zwitterionic intermediates were detected on the reaction pathway. Their formation is determined by the nature of local nucleophile/electrophile interactions. Additionally, the channel involving the formation of the exo-nitro Diels–Alder cycloadduct was completely ruled out. Finally, the electronic nature of the five- and six-membered nitronates as potential TACs was evaluated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper assesses various approaches that use captured greenhouse gases (GHG) as feedstocks for chemical synthesis. The analysis focuses mainly on the two most abundant anthropogenic GHG, such as carbon dioxide (CO2) and methane (CH4), as well, their conversion technologies to obtain methanol (MeOH), formic acid (FA) and dimethyl carbonate (DMC). These GHG conversions to chemicals technologies are compared with the conventional industrial methods based on fossil feedstocks. The essential information, such as the ranges of energy requirements, environmental footprint and economic production aspects, are summarised. According to the collected information and analysis, the conventional, non-GHG conversion methods are still more environmentally sustainable. Chemicals production technologies based on CO2, such as direct catalytic synthesis to obtain both MeOH and FA, as well as transesterification with MeOH to obtain DMC, are relatively good candidates for implementation on a large scale when a good source of co-reactants such as hydrogen, ethylene carbonate and urea will be provided. In turn, electrochemical methods to synthesise the target chemicals are less feasible due to energy consumption related to the concentration and purification stages of products being the main hotspots. Chemical synthesis based on captured CH4 is currently difficult to evaluate as too little information is available to draw a credible conclusion. However, it may be a trend in future. The limitations of GHG-based conversion for application are related to the capture and transport stages. [ABSTRACT FROM AUTHOR]

The molecular mechanism of the [3+2] cycloaddition reactions between aryl azides and ethyl propiolate was evaluated in the framework of the Molecular Electron Density Theory. It was found that independently of the nature of the substituent within the azide molecule, the cycloaddition process is realized via a polar but single-step mechanism. All attempts of localization as postulated earlier by Abu-Orabi and coworkers' zwitterionic intermediates were not successful. At the same time, the formation of zwitterions with an "extended" conformation is possible on parallel reaction paths. The ELF analysis shows that the studied cycloaddition reaction leading to the 1,4-triazole proceeds by a two-stage one-step mechanism. It also revealed that both zwitterions are created by the donation of the nitrogen atom's nonbonding electron densities to carbon atoms of ethyl propiolate. [ABSTRACT FROM AUTHOR]

The molecular mechanism of the Diels–Alder reaction with the participation of cyclopentadiene and isopropyl 3-nitroprop-2-enate was examined based on wb97xd/6-311+G(d) (PCM) quantum chemical calculations. It was found that the type of mechanism for the conversion of addends depends significantly on the reaction conditions. In less-polar environments, a one-step polar mechanism is realised. In more polar solvents, the formation of "extended"-type zwitterionic intermediates is possible. In contrast, in the presence of an LA-type catalyst, the one-step mechanisms are replaced by respective stepwise mechanisms with zwitterionic or heterocyclic intermediates. [ABSTRACT FROM AUTHOR]