Dienophiles global electrophilicity

Table 1 Global electrophilicity scale and global properties3 for some common dienes and dienophiles involved in Diels-Alder reactions...

The classification based on the global electrophilicity scale presented in Table 1, correctly describing activating and deactivating effects promoted by chemical substitution on the diene/dienophile pair, may be complemented with a static analysis of the charge transfer pattern expected for transition state structures involved in DA reactions. This aspect is useful to discuss since the difference in polar character of these structures... 

Table 10.9. DFT Global Electrophilicity of Representative Dienes and Dienophiles ...

Domingo investigated the global electrophilic parameter, w, as an indicator of relative reactivity. Table 10.9 gives the value of this parameter calculated for a number of dienes and dienophiles. 

Domingo, L. R., Aurell, M. J., Perez, P, Contreras, R. (2002b). Quantitative characterization of the global electrophilicity power of common diene dienophile pairs in Diels-Alder reactions. Tetrahedron 58, 4417 423. 

Table 3.2 Global electrophilicity of some dienophiles in D-A reactions with 1,3-butadiene (Ara = 1.05 eV). 55...

The global electrophilicity index (q), introduced by Parr (Parr, et al, 1999) is a useful descriptor of the reactivity that allows a quantitative classification of the global electrophilicity character of a molecule within a unique scale. Current studies based on the DFT and applied to DA reactions, have shown this classification of the diene/ dienophile pair is a powerful tool to predict the feasibility of the process and the type of mechanism involved. This index defined as Eq. 3... 

Normally the polarity of the normal electron demand DA process has been studied by means of global electrophilicity index difference between reactants and the regioselectivity of the normal electron demand DA reaction using the local electrophilidty index for dienophiles (electrophiles in the reaction) and the local nudeophilicity index for dienes (nucleophiles in the reaction). 

On the other hand, the differences in the global electrophilicity power between the dienophile/diene pair (Aco) are higher for the Danishefsky s diene than for isoprene. Therefore, we can expect a high reactivity and a high regioselectivity for the pair dienophile/Danishefsky s diene. This fact is also consistent with the experimental researches in both molecular solvent and IL s. 

According to the global electrophilicity index co shown, the dienes will act as nucleophiles and the dienophiles as electrophiles. To study the regioselectivity we used the local... 

The reactions of naphthalenes properly mono- and disubstituted with an electron-withdrawing and a series of dienes in thermal conditions, were evaluated with the frontier molecular orbitals (FMO) theory which provide qualitative information about the feasibility of these DA reactions. Besides, the global electrophilicity index (co) is employed to estimate the electrophilic character of the dienophiles used in the cycloaddition reactions. 

It has been demonstrated a good correlation between the difference in the global electrophilicity of the diene/dienophile interacting pair (Aco) and the feasibility of the cydoaddition. 

Using the 8-nitroquinoline we showed specifically the interactions models with the lowest energy between the dienophile and the solvents (chloroform, EAN and HMIM) (Figure 24). For these structures were calculated the global electrophilicity and nucleophihcity values (Table 7). 

In Chart 7 we included a short series of benzylidenemalononitriles as well as a-nitrostilbenes.116 Note that the most common functionalities associated with the chemistry of the nucleophilic addition to the C=C bond, namely aldehydes, ketones, esters, anhydrides and nitriles, are EW substituents present in dienophiles and dipolarophiles used in NED DA and 1,3 dipolar cycloadditions, and they are included in Table l.121 In Table 14, we summarize the global properties and local electrophilicity values for the series of benzylidenemalononitriles and a-nitrostilbenes. Both series present ethylene derivatives with large electrophilicity values, to > 2.3 eV, they being classified as strong electrophiles within the theoretical electrophilicity scale.39... 

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