Double Group Transfer Reactions as Indicators of Aromatic Stabilization

Abstract

The main features of double hydrogen atom transfer reactions in syn‐sesquinorbornanes, which involve the concomitant formation of an aromatic ring, have been studied computationally within the framework of Density Functional Theory. The very good linear correlations, which exhibit high correlation coefficients between the recently available Aromatic Stabilization Energies (ASE) from the Energy Decomposition Analysis (EDA) method and the activation and reaction energies, as well as geometric features (C–C bond lengths) of the corresponding transition states of the transformations, suggest that the calculated values are useful in estimating the aromatic character of a molecule. The studied process may be used for benchmarking of energetic aromatic indices. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Studying Double Group Transfer Reactions by Means of Computational Methods

“…These results clearly indicate that the aromatic strength of the final products control the process since the reactions gathered in Scheme 8 involve formation of substituted benzene, furan, and cyclobutadiene (archetypal examples of aromatic and antiaromatic compounds, respectively). For this reason, it has been suggested [31] that the activation and reaction energies of concerted type II dyotropic reactions similar to those depicted in Scheme 8 may be used to quantify the aromatic stabilization of cyclic molecules, thus founding excellent linear correlations between activation and reaction energies and aromatic stabilization energies (ASE) [19a,b]. Interestingly, the model C 2v symmetric transition state TS1b (analogous to species 9) also exhibits the expected in-plane aromaticity.…”

“…Type II-Dyotropic Reactions computationally studied. See reference [31] for additional details. putations leave room for uncertainty about the reaction mechanism, namely whether the endo-R-sulfonyl hydrogen atoms migrate concertedly to the proximal double bond in a [ 2 s + 2 s + 2 s ] fashion or do so nonclassically through a stepwise mechanism, via a tunneling that would skirt the full energetic costs associated with the formation of biradical intermediates [32].…”

Combined activation strain model and energy decomposition analysis methods: a new way to understand pericyclic reactions

“…20 kcal mol À1 ). 44 Differently, in the MPV reduction of carbonyl groups, there occurs the formation of an intramolecular hydrogen-bond which approximates both reactants making the interaction energy between them stronger; as a consequence, the computed barrier for this process drops to ca. 25 kcal mol À1 .…”

Dyotropic Reactions: Mechanisms and Synthetic Applications

“…Thus, excellent linear correlations between activation and reaction energies and aromatic stabilization energies (ASE) 147 were found (Figure 3). 146 A double hydrogen transfer has been located computationally in the thermal dimerization of cyclopropenes (Scheme 90). 148 The features of transition structure 278, resulting from the degenerate dyotropic rearrangement of 277, are similar to those found for saddle points 269, 272, and 275.…”

“…Figure 3. Plot of the ASE values vs the activation (E a , circles)and reaction (E R , squares) energies for different dyotropic reactions involving aromatic, nonaromatic, and antiaromatic molecules 146. …”