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![ORTEP plot of the single crystal X-ray structure of 4f (represented by 50% thermal ellipsoids) [see Footnote 1]](publication/324372543/figure/fig1/AS:962195273822210@1606416638307/ORTEP-plot-of-the-single-crystal-X-ray-structure-of-4f-represented-by-50-thermal.gif)
ORTEP plot of the single crystal X-ray structure of 4f (represented by 50% thermal ellipsoids) [see Footnote 1]
Source publication
2-Cinnamoylimidazolium ions 4 have been synthesized by treatment of 2-cinnamoylimidazoles 8 with methyl triflate. They were characterised by NMR and mass spectroscopy, in one case (4f) also by X-ray analysis. The kinetics of their reactions [and also those of cinnamoyl fluoride (1)] with stabilised carbanions 9a–e and silyl ketene acetal 9f (refere...
Citations
... [7] In this respect, the experimental scale proposed by Mayr's and coworkers in early 1990s [8] certainly stands as the most comprehensive one. Freely available online, it includes reagents used for a wide variety of polar organic reactions (such as Friedel-Crafts, [9,10] Michael additions, [11,12] Tsuji-Trost, Hosomi-Sakurai…), and is constantly updated and expanded. More precisely, this double scale is based on the following linear relationship: ...
In this paper, we assess the ability of various machine learning methods, either linear or non‐linear, to efficiently predict Mayr's experimental scale for electrophilicity. To this aim, molecular and atomic descriptors rooted in conceptual density functional theory and in the quantum theory of atoms‐in‐molecules as well as topological features defined within graph theory were evaluated for a large set of molecules widely used in organic chemistry. State‐of‐the‐art regression tools belonging to the support vector machines family and decision tree models were in particular considered and implemented. They afforded a promising predictive model, validating the use of such methodologies for the study of chemical reactivity.
The stereoselective intramolecular dearomatizing spirocyclization of indoles via oxidative N-heterocyclic carbene (NHC) catalysis to afford indolenines bearing an all-carbon quaternary center at the 3-position is reported. The reaction proceeds via the intramolecular nucleophilic addition of the indole to an in situ generated α,β-unsaturated acyl azolium. The cyclized indolenine bearing an acyl azolium functionality is trapped by a suitable external nucleophile that does not efficiently react with the α,β-unsaturated acyl azolium via direct acylation.
Through the linear free energy relationship log k=sN (N + E), the electrophilicity parameters E of 4‐nitrobenzochalcogenadiazoles 1 a and 1 b have been determined, at 20 °C, by kinetic investigations of their electrophilic addition reactions to a series of nitroalkyl anions 2 a‐c in aqueous solution. The derived E‐parameters of electrophiles 1 a (E=‐12.80) and 1 b (E=‐11.46) have been integrated into the electrophilicity scale established by Mayr. Interestingly the less activated compound (1 a) has an E value which is practically the same as that of the 1,3,5‐trinitrobenzene (E=‐13.19), the common reference aromatic electrophile. Mayr's approach was found to predict the rate constants for σ‐complexation reactions of our electrophiles 1 a and 1 b with aniline and 4‐chloroaniline in acetonitrile with a factor of 10−36. Good linear correlation (r²=0.9979) between the electrophilicity parameters E of 4,6‐dinitrobenzochalcogenadiazoles 3 a‐c and E values of their analogously 4‐nitrobenzochalcogenadiazoles 1 a‐c has been found and analysed. Furthermore, effect of basicity of nitronate anions 2 a‐c on their nucleophilic reactivity has also been examined quantitatively on the basis of kinetic data. Imbalance effect is suggested to be responsible for the finding of an inequality between the Brønsted αelec and βnuc values.
Calculated methyl anion affinities are known to correlate with experimentally determined Mayr E parameters for individual organic functional group classes, but not between neutral and cationic organic electrophiles. We demonstrate that methyl anion affinities calculated with a solvation model (MAA*) give linear correlation with Mayr E parameters for a broad range of functional groups. Methyl anion affinities (MAA*) plotted on the log scale of Mayr E, provide insight into the full range of electrophilicity of organic functional groups. On the Mayr E scale, the electrophilicity towards the methyl anion spans 180 orders of magnitude.
Through an alternative scheme of representation of energy as a function of the number of electrons, and using the canonical ensemble model, a new electrophilicity descriptor was developed. In our development, we accept the idea that when a system begins to accept electrons from the surroundings, its chemical potential increases, tending to zero when the system is saturated with the maximum amount of charge. In this way, the number of transferred electrons, and therefore the stabilization energy of the system, were modeled by means of a third order approximation which in the state of electronic saturation led to the definition of our electrophilic descriptor. This new reactivity parameter, was tested to reproduce relative electrophilicity tendencies of some chemical systems known for their electrophilic reactivity. Although the results reported here partially demonstrate the potentiality of our descriptor, more systems must be investigated to test the effectiveness of this new reactivity index.
