Determination of the electrophilic reactivities of 1,1,3-triarylallyl cations

Mayr, Herbert; Fichtner, Claudia; Ofial, Armin R.

doi:10.1039/b203554e

Cited by 19 publications

(21 citation statements)

References 30 publications

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“…Returning to Figure 5, it is to be noted that the electrophilicity of NBDF appears to be intermediate between those of 4-aza-6-nitrobenzofuroxan (E = À5.86) and 4-cyano-6-nitrobenzofuroxan (E = À6.41), [11] two derivatives the general behavior of which are representative of a superelectrophilic ranking. [28] It follows that NBDF is more electrophilic than some amino-substituted benhydrylium cations, such as Michlers hydrol blue (E = À7.02), [13] that is, the bis(4-dimethylaminophenyl)carbenium ion, as well as of other positively charged species such as triarylallylcations, for example, 12 (E = À8.97), [29] arylallylpalladium complexes, for example, 13 (E = À10.10, Figure 5), [30] or even the tricarbonylcycloheptadienylium cation 14 (E = À9.21, Figure 5). [31] Because it is often a key C À C bond-forming process on route to many biologically active compounds, the addition of indoles to C=C double bonds activated by the presence of adjacent electron-withdrawing groups, notably a nitro or carbonyl group has received considerable synthetic attention.…”

Section: Resultsmentioning

confidence: 99%

Superelectrophilicity of the Nitroolefinic Fragment of 4‐Nitrobenzodifuroxan in Michael‐Type Reactions with Indoles: A Kinetic Study in Acetonitrile

Lakhdar

Goumont

Berionni

et al. 2007

Chemistry A European J

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The kinetics of the coupling of 4-nitrobenzodifuroxan (NBDF) with a series of indoles 8 a-e to give the expected Michael-type adducts 9 a-e have been investigated in acetonitrile solution. No significant influence of the nature of the isotopic substitution at C-3 of the indole ring has been found, indicating that the NBDF addition step is the rate limiting step of the SEAr substitution of the indole moiety. This implies that the measured second-order rate constants (k) for the reactions are identical to the second order rate constants (k1NBDF) associated to the C--C coupling step. By using the known N and s parameters characterizing the nucleophilicity of indoles, the k1NBDF rate constants are found to fit nicely to the three parameters equation logk1=s(N+E) introduced by Mayr to describe the feasibility of nucleophilic-electrophilic combinations. Based on this, the electrophilicity parameter E of NBDF could be determined as E=-6.15. This corresponds to a positioning of the reactivity of the nitroactivated double bond of NBDF in the domain of superelectrophilicity previously defined for nitrobenzofuroxans, in accord with the finding that the rates of coupling of 8 a-e with NBDF are only one order of magnitude lower than those for the coupling of these indoles with 4,6-dinitrobenzofuroxan (DNBF). The theoretical scale of electrophilicity introduced by Domingo et al. on the basis of the global electrophilicity index omega defined by Parr is also a very useful tool to discuss the relative reactivities of NBDF, DNBF, and a number of differently activated C==C double bonds.

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Section: Resultsmentioning

confidence: 99%

Superelectrophilicity of the Nitroolefinic Fragment of 4‐Nitrobenzodifuroxan in Michael‐Type Reactions with Indoles: A Kinetic Study in Acetonitrile

Lakhdar

Goumont

Berionni

et al. 2007

Chemistry A European J

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“…[16] Finally, allylic alcohols, another type of substrate illustrated in this review, forms a carbocation that is electrophilic, and it is positioned above 1 in the Mayr scale. [17] Consequently, in all the reactions illustrated in this review, where Brønsted or Lewis acids are employed, a better understanding of the reactions can come from careful examination of the concepts established by the work of Mayr.…”

Section: S N 1 Nucleophilic Reaction Of Alcohols By Generation Of Carmentioning

confidence: 99%

Direct Nucleophilic S_N1‐Type Reactions of Alcohols

et al. 2010

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In 2005, the ACS Green Chemistry Institute (GCI) and the global pharmaceutical corporations developed the ACS GCI Pharmaceutical Roundtable to encourage the development of green chemistry and green engineering in the pharmaceutical industry. The Roundtable has established a list of key research areas including the direct nucleophilic reactions of alcohols. The substitution of activated alcohols is a frequently used approach for the preparation of active pharmaceutical ingredients. Alcohols are transformed into the reactive halides or sulfonate esters, thereby allowing their reaction with nucleophiles. Although the direct nucleophilic substitution of an alcohol should be an attractive process, as one of the byproducts from the reaction yields water, hydroxide is a poor leaving group that hinders the reaction. Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved through an SN1 reaction with catalytic amounts of Brønsted or Lewis acids. In this review, the approaches leading to a greener process are examined in detail, and the advances achieved to date in this important transformation are presented.

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“…The various electrophilicity descriptors reported in this section may be broadly classified into three categories: viz., the kinetic descriptor that measures the rate at which an electrophilic attack takes place, the thermodynamic descriptor which measures the ease of such an attack, and a combination of these two approaches through a linear free energy relationship. Among the kinetic scales, the most important is that of Mayr and co-workers. − They have rank ordered various nucleophiles and electrophiles in terms of their N and E parameters respectively obtained from the associated experimental rate constants. Ritchie's parameters 123,124 or Swain−Scott parameters 142 are similar in spirit.…”

Section: Electrophilicity Scalesmentioning

confidence: 99%