Mechanistic studies and quantification of the electrophilicity of aromatic triflones in σ-complexation and SNAr reactions

Article abstract of DOI:10.1016/j.jfluchem.2014.01.003

The reactions of anilines (N-nucleophiles) and enamines (C-nucleophiles) with NO₂ and SO₂CF₃ substituted aromatic triflones were investigated spectrophotometrically in acetonitrile at 20 C. We found that the second-order rate constants k₁ related to the C-N and C-C bond forming step of these nucleophilic aromatic substitution reactions (S_NAr) and σ-complexation reactions follow the three-parameter equation log k_{(20 C)} = s_N(N + E), allowing the determination of the electrophilicity E of such aromatic triflones for the first time. The ranking of these neutral electron-deficient compounds on the comprehensive electrophilicity scale defined by Mayr et al. reveals that the most electrophilic triflone, the 1,3,5-tris(trifluoromethanesulfonyl)benzene (TTSB), has an electrophilicity higher than that of the 1,3,5-trinitrobenzene (TNB) the common reference aromatic electrophile in anionic σ-complexation chemistry, by roughly 6 units of E. This finding holds promise for expanding the range of coupling reactions which can be envisioned between this series of electron-deficient neutral aromatics and nucleophiles.

Full text of DOI:10.1016/j.jfluchem.2014.01.003

Accepted Manuscript
Title: Mechanistic studies and quantification of the
Electrophilicity of Aromatic Triflones in ␴-complexation and
SNAr reactions
Author: Nizar El Guesmi Guillaume Berionni Basim H.
Asghar
PII:
S0022-1139(14)00013-X
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2014.01.003
FLUOR 8250
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
1-12-2013
22-12-2013
5-1-2014
Please cite this article as: N.E. Guesmi, G. Berionni, B.H. Asghar, Mechanistic
studies and quantification of the Electrophilicity of Aromatic Triflones in
rmsigma-complexation and SNAr reactions, Journal of Fluorine Chemistry (2014),
http://dx.doi.org/10.1016/j.jfluchem.2014.01.003
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Graphical Abstract
super electrophilicity reactivity
normal electrophilicity reactivity
reactions of aromatics triflones with methoxide ion
OCH3
O2N
SO2CF3
OCH3
SO2CF3
SO2CF3 CF3O2S
OCH3
CF3O2S
SO2CF3
CF3O2S
SO2CF3
NO2
SO2CF3
SO2CF3
-13
-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
-16
0
-20 -19
-17
-15 -14
-18
E
OCH3
OCH3
CF3O2S
SO2CF3
O2N
SO2CF3
CF3O2S
SO2CF3
OCH3
CF3O2S
SO2CF3
SO2CF3
SO2CF3
SO2CF3
NO2
reactions of aromatics triflones with enamines
reactions of aromatics triflones with anilines
Page 1 of 21

Mechanistic studies and quantification of the
Electrophilicity of Aromatic Triflones in σ-
complexation and SNAr reactions
Nizar El Guesmi a,c*, Guillaume Berionni b, Basim H. Asghar c
a Departement de chimie, Faculté des Sciences de Monastir, Avenue de l’Environnement,
5019 Monastir, Tunisia.
b Universud Paris, Institut Lavoisier de Versailles – UMR CNRS 8180, Université de
Versailles, 45, Avenue des Etats-Unis, 78035 Versailles Cedex, France
c Department of Chemistry, Faculty of Applied Sciences, Umm Alqura University, P.O. Box
9569, Makkah, Saudi Arabia.
* Corresponding author. Tel.: +966 55 1516795
E-mail addresses : nizar_chem@yahoo.fr, naguesmi@uqu.edu.sa
(N. El Guesmi).
Page 2 of 21

Abstract: The reactions of anilines (N–nucleophiles) and enamines (C–nucleophiles) with
NO2 and SO2CF3 substituted aromatic triflones were investigated spectrophotometrically in
acetonitrile at 20 °C. We found that the second-order rate constants k1 related to the C–N and
C–C bond forming step of these nucleophilic aromatic substitution reactions (SNAr) and σ-
complexation reactions follow the three-parameter equation log k(20 °C) = sN (N + E), allowing
the determination of the electrophilicity E of such aromatic triflones for the first time. The
ranking of these neutral electron-deficient compounds on the comprehensive electrophilicity
scale defined by Mayr et al. reveals that the most electrophilic triflone, the 1,3,5-
tris(trifluoromethanesulfonyl)benzene (TTSB), has an electrophilicity higher than that of the
1,3,5-trinitrobenzene (TNB) the common reference aromatic electrophile in anionic σ-
complexation chemistry, by roughly 6 units of E. This finding holds promise for expanding
the range of coupling reactions which can be envisioned between this series of electron-
deficient neutral aromatics and nucleophiles.
Keywords :
Aromatic triflones, Trifluoromethanesulfonyl group, SNAr reactions, Electrophilicity,
Kinetics.
Page 3 of 21

1. Introduction
The reactions of electron-deficient arenes and heteroarenes substituted by very strong
electron-withdrawing substituents such as SO2CF3 with O–, N– and C–nucleophiles are of
great interest from a synthetic and mechanistic point of view. [1-7] Indeed the anionic
Meisenheimer σ–complex intermediates are highly stabilized by the SO2CF3 substitutents and
can be characterized or isolated, and the resulting products are highly valuable aromatic
compounds [8-12].
Discussions of the substituent effects and of the mechanisms of these SNAr type reactions
through the use of empirical linear free–energy relationships is one of the preferred approach
in the literature. Indeed, since the introduction of the electrophilicity and nucleophilicity
concepts to describe the reactivity of electron–deficient (electrophile) and electron–rich
(nucleophile) species by Ingold in the 1930s [13], there has been a growing interest in
classifying molecules within scales of electrophilicity/nucleophilicity. From that time, the
classification and the quantification of the reactivity organic molecules within empirical and
hopefully unique scales of electrophilicity and nucleophilicity have been attempted. For
instance, several linear free-energy relationships (LFERs) such as the well–known Hammett
equation [14] and other relationships involving kinetic parameters instead of equilibrium
constants have been proposed in the literature [15-19]. The main objective of such
correlations was the development of absolute reactivity scales that could be independent on
the reactivity of the nucleophile/electrophile partners. This objective is ambitious if one
considers that a universal scale should accommodate a wide diversity of chemical species
presenting quite different structural and bonding properties.
Mayr and co–workers have, however, recently defined nucleophilicity and electrophilicity
parameters that are independent of the reaction partners and that describe the rates of many
reactions in organic and organometallic chemistry [20-23]. It has been well established, in
contrast to the accepted opinion about the relative character of the experimental
electrophilicity/nucleophilicity scales, that the rates of reactions of hundreds of carbenium
ions, Michael acceptors and other electrophiles with charged and uncharged σ−, π− and n−
nucleophiles obey the linear free-energy relationship given by:
log k(20 °C) = sN (N + E)
(1)
where k(20 °C) is the second-order constant in mol-1 dm3 s-1, sN is the nucleophile sensitivity
parameter, N is the nucleophilicity parameter, and E is the electrophilicity parameter. Based
on Eq. (1), general electrophilicity (E) and nucleophilicity (N) scales, each covering a
Page 4 of 21

reactivity range of more than 30 orders of magnitude have been defined and successfully used
to predict the feasibility and rate of many interactions [24-27].
Interestingly, it has recently been shown that the electrophilicity of an extended series of
neutral electron-deficient nitroaromatics and heteroaromatics of widely differing reactivity
and structure is appropriately described by this equation [28].
In this paper, we report on the determination of the electrophilicity of the four aromatic
triflones 1-4 shown in Scheme 1. Electrophilicity parameters E of 1-4 were determined from
the kinetics of their reactions with various anilines and enamines A-G of known
nucleophilicity parameters N and which are defined as reference nucleophiles (Table 1). This
extension of the applicability of Eq. (1) to SNAr and σ–complexation processes further
demonstrates the general utility of this relationship and the new kinetic data might allow
synthetic chemists to design new addition reactions of nucleophiles to NO2 and SO2CF3
substituted arenes.
OCH3
OCH3
OCH3
SO2CF3 CF3O2S
SO2CF3 O2N
SO2CF3 CF3O2S
SO2CF3
CF3O2S
SO2CF3
NO2
SO2CF3
SO2CF3
1
2
3
4
Scheme 1. Structures and numbering of the aromatic triflones
< Table 1 >
2. Results and Discussion
The kinetic study was performed under pseudo-first-order conditions with the concentration
of anilines or enamines in excess over the substrates concentration. All of the reactions
obeyed first-order kinetics. Pseudo-first-order rate constants (kobs) were calculated from the
equation ln (A∞ - At) = - kobs t + C. The kobs values with the reaction conditions are
summarized in Tables S1-S7 in the Supporting Information.
For anilines reactions, all pseudo–first–order rate constants kobs obey Eq. (2) with
negligible ko as illustrated in the plots of kobs vs. aniline concentration in the case of the
Page 5 of 21

reaction of the p–methoxyaniline A with the triflones 1, 2 and 3 (Fig. 1). The second–order
rate constants k1 were determined from the slopes of theses linear plots, based on Eq. (2).
kobs = ko + k1[An]
(2)
Furthermore, no higher–order terms were detected and no complications were found in the
determination of k1.
< Fig. 1 >
This suggests that there is no base catalysis or noticeable side reactions, and that the overall
reaction follows the mechanism described in Scheme 2. This is also in agreement with the
traditional interpretation of nucleophilic aromatic substitution by amines, and in agreement
with the SNAr–Ad.E mechanism, where the rate–limiting formation of the zwitterionic σ–
complex intermediate ZW± is followed by the fast expulsion of the methoxy leaving group
[31, 32].
X
X
OCH3
NH2
+
NH2
CH3O
Z
NH
Y
Z
SO2CF3
+
SO2CF3
Z
SO2CF3
+
k 1
k 2
-
CH3OH
fast
k - 1
X
Y
Y
+
ZW-
1 Y = Z = SO2CF3
2 Y = NO2 ; Z = SO2CF3
3 Y = SO2CF3 ; Z = NO2
A X = OCH3
B X = CH3
C X = H
Scheme 2
The second-order rate constants k1 of the SNAr reactions of anilines A-C (p-methoxyaniline A,
p-methylaniline B and aniline C) with aromatic triflones 1-3 at 20 °C in MeCN are
summarized in Table 2. The substitution of one nitro group of 2,6-bis(SO2CF3)-4-nitroanisole
2 and 2,4-bis(SO2CF3)-6-nitroanisole 3 by a SO2CF3 group to give the 2,4,6-
tris(SO2CF3)anisole 1 increases the rate of reactions with anilines by 15 and 40–fold,
respectively. These results emphasize that the SO2CF3 group has a stronger electron-
withdrawing character than a NO2 group, both in the ortho– and para–positions of a reactive
center in an aromatic ring. This behavior is consistent with the higher values of the Hammett
Page 6 of 21

constants of the SO2CF3 substituent (σm = 0.76, σp = 0.96, σp- = 1.65) obtained from studies
of the ionization of various AH-type acids (benzoic acids, anilinium ions and phenols) [6, 33,
34] than the Hammett constants of the NO2 substituent (σm = 0.71, σp = 0.78, σp- = 1.27).
Obviously, these substituent constants fit well the finding that the SO2CF3 group is markedly
more activating than a NO2 group on para than on ortho-position.
Interestingly, Table 2 shows that contrasting trends govern the reactivity of 2,4-
bis(trifluoromethanesulfonyl)-6-nitroanisole 3. This contrasting behavior is readily
understood in terms of steric effects. As revealed by X-ray crystallography, the NO2 groups in
the 2-and 6-positions are strongly twisted from the plane of the ring [35, 36].
For enamines reactions, Figures S1-S4 in the Supporting Information show the
oscilloscope traces illustrating the unique relaxation process corresponding to the formation of
the σ–adducts representative of the various electrophile
4
–
enamines D-G
E,
1-(N-
1-(N-morpholino)cyclopentene G) combinations
(morpholinoisobutylene
morpholino)cyclohexene
D,
and
1-(phenylmethylamino)cyclohexene
F
investigated. The observed pseudo first–order rate constant for the approach to equilibrium, as
illustrated in Scheme 3, is simply given by
kobs = k1[Enamine] + k-1
(3)
Figure 2 shows for a representative example that plots of kobs vs. enamine concentration were
also linear with negligible intercepts (k-1 ≈ 0), indicating that the resulting σ–adducts have a
high thermodynamic stability in acetonitrile solution and that the reverse reaction is not
observed.
O
+
N
H
Y
Y
O
N
Y
Y
_
k1
+
k-1
Y
Y
D
4 Y = SO2CF3
5 Y = NO2
Scheme 3
Page 7 of 21

Determination of the second–order rate constants k1 from the slopes of the kobs vs [enamine]
plots was straightforward for all reactions studied, and the data are summarized in Table 2
together with the k1 values for the structurally analogue 1,3,5-trinitrobenzene (TNB) 5 [28].
A significant result is that the replacement of three NO2 groups of the TNB 5 by three SO2CF3
groups to give the 1,3,5-tris-(trifluoromethanesulfonyl)benzene 4 results in an enormous
increase in reactivity, as reflected by the ratios
/
in the order of ~ 104 for the reactions
with the enamines D-G. This huge reactivity differences emphasize again the much greater
activating effect exerted by the SO2CF3 groups relative to the NO2 groups in anionic σ–
complex formation and related SNAr processes. This effect is fully consistent with previous
observations, showing that the rate-constants of the formation of the adducts are strongly
influenced by the variation in the substitution pattern of the aromatic or heteroaromatic ring
[6, 7, 35-38].
< Fig. 2 >
< Table 2 >
Determination of the electrophilicity parameters of 1-4
In the recent years, much interest has been paid to the design of electron-deficient aromatics
and heteroaromatics exhibiting a high reactivity in σ-complex formation [8, 9, 41-44].
Although the electrophilicity of various aromatic substrates have been already measured by
studying the kinetics of attack of nucleophiles at unsubstituted CH positions of their π-system,
kinetics of the reactions of nucleophiles at a substituted position, for instance by a chloride,
fluoride or a methoxy substituent, have been less studied [45, 46].
The addition of nucleophiles at positions bearing a leaving group such as OMe is even of
higher synthetic potential because the leaving group facilitates the subsequent
rearomatizationa step by its expulsion, and hence facile achievement of the overall SNAr
substitution.
We have found that these σ–complexation and SNAr reactions described above follow the
three–parameters equation log k(20 °C) = sN (N + E) developed by Mayr and co-workers.
Assuming that the rate determining step of these reactions is the C-C or C-N bond formation,
the k1 values given in Table 2 have been used for the determination of the E parameters for 1-
4. The obtained E values and the derived standard deviations are given in Table 3. The
Page 8 of 21

resulting electrophilicity parameters
E
are, respectively, for each 2-Y-4-Z-6-
(trifluoromethanesulfonyl)anisole: E = -14.98 for 1 (Y = Z= SO2CF3), E = -16.69 for 2 (Y =
SO2CF3 ; Z = NO2), E = -17.34 for 3 (Y = NO2 ; Z = SO2CF3) and E = -7.98 for the 1,3,5-
tris(SO2CF3)benzene 4.
The quantitative ranking of the electrophiles 1-4 on the electrophilicity scale (Figure 3) make
possible a comparison of their electrophilic reactivity with that of related compounds
previously classified in the scale. The experimental E values of 1-3 show that the substitution
of one nitro group of 2,6-bis(SO2CF3)-4-nitroanisole 2 and 2,4-bis(SO2CF3)-6-nitroanisole 3
by a SO2CF3 group to give 1 increases their electrophilic strength by approx. 3 orders of
magnitude. Interestingly, The E values of 1-3 determined are comparable to those of other
electron-deficient aromatics, such as 1-Hal-2,4-dinitrobenzene: E = -14.1 for Hal = F, E = -
17.6 for Hal = Cl and Br, and E = -18.3 for Hal = I [46], that also engage in SNAr
displacement reactions.
< Table 3 >
Most importantly, the reactivity domain of neutral electrophilic aromatic substrates is greatly
expanded by the 1,3,5-tris(trifloromethanesulfonyl) benzene 4 which has an E values of -7.98,
i.e. almost 6 orders of magnitude more electrophilic than the trinitrobenzene 5 (E = -13.19),
however, considerably more electrophilic that the most reactive neutral substrate studied by
Mayr namely benzylidenemalonitrile (E = -9.42). The electrophilicity of 4 compares well with
that of the 6-cyano-4-nitrobenzofuroxan (E = -7.01) and found to approach that of 4-
nitrobenzodifuroxan NBDF (E = -6.25), an activated nitroolefin with a superelectrophilic
behavior. Anchoring to carbocationic reactivity, the electrophilicity of 4 is of the same order
of reactivity as that of a stabilized benzhydrylium cation such as Michler’s hydrol blue (E = -
7.02), but higher than that of other positively charged species such as triallyl cations or
arylallylpalladium complexes as shown in Figure 3.
< Fig. 3 >
The determination of the electrophilicity of the triflones 1-4 represents an extension of the
previously reported electrophilicities of neutral electron-deficient aromatics and
heteroaromatics of widely different reactivity and structure which were also appropriately
Page 9 of 21

described by Eq (1) [28, 42-46]. Our data furthermore increase the scope and the applications
of this equation which was originally mostly developed by modulating the strength of the
electrophilic partner through variations of the substituents and structural variations of
carbocationic structures.
Thus, TTSB 4 represents a departure from the classical electrophilicity domain and an entry to
the superelectrophilic domain of reactivity (E ~ < -8) in σ–complex formation and related
reactivities of aromatic substrates. The E value that we correctly predicted earlier for 4, based
on an empirical correlation between E and pKa (eq. 4) was E = -7.56 from the value
=
9.12 [9].
E = - 0.662
-1.53 (4)
A similar approach has been used earlier in order to estimate the E values of the aromatic
triflones 1-3, where the nucleophilic attack occurs at a substituted position of the aromatic
ring, in contrast to 4. The predicted E values were E = -6.37 (
8.47 ( = 10.48) for 2 [9], E = -7.76 ( = 9.42) for 3 [47], suggesting that 1-3 are
very strong electrophiles.
= 7.32) for 1[8], E = -
These predicted E values were very far from the experimental values (Table 3) because eq.4.
refers to the methoxylation reaction at unsubstituted positions, i.e. reactions with negligible
steric effects, or it refers to the methoxylation reaction at substituted position (OMe
sustitutent) to give 1,1-dimethoxy adducts through σ-complexation reaction, i.e. reactions
with nucleophile of small sizes. The reactions of aromatic triflones 1-3 with anilines A-C,
nucleophiles of larger size attacking at a position substituted by OMe, gave experimental E
values of approx. 9 units of electrophilicity less than predicted earlier, illustrating in the
strong effect of substituent and of nature of nucleophile partner on the attacked position of
the aromatic ring.
3. Conclusions
Our study has established that the SO2CF3 group is markedly more activating than a NO2
group in σ-complex formation and therefore in related nucleophilic aromatic displacement
processes. Importantly, our results provide a quantitative demonstration that the tris-SO2CF3
benzene 4 exhibits a reactivity which surpasses that of conventional electron-deficient
aromatics, e.g. TNB, by several orders of magnitude.
Applying the general approach to nucleophilicity/electrophilicity developed by Mayr et al.,
the E parameters, quantifying the electrophilic reactivity of the triflones 1-4, have been
Page 10 of 21

determined in acetonitrile, through kinetic investigations of σ-complexation and SNAr
substitution reactions involving anilines and enamines as N- and C-nucleophiles. It has been
shown that this reactions form an integral part of electrophile-nucleophile interactions through
the definition of general electrophilicity (E) and nucleophilicity (N) scales.
Overall, this relationship appears as being a nice probe to predict the feasibility of the
reactions of SNAr substitutions and related σ-complexation processes, which will be of real
benefit for broadening the range of synthetic and analytical applications in this field.
4. Experimental
Materials. 2,4,6-tris(trifluoromethanesulfonyl)anisole 1, 2,6-bis(trifluoromethanesulfonyl)-4-
nitroanisole 2, 2,4-bis(trifluoromethanesulfonyl)-6-nitroanisole 3, and 1,3,5-tris(trifluoro-
methanesulfonyl)benzene 4 was prepared as previously described by Yagupolskii et al. [48-
50]. Anilines A-C were of the highest quality available (Aldrich products) and were
recrystallized or distilled before use whenever necessary. Enamines D-G were prepared by
condensation of the ketone or aldehyde with the corresponding secondary amine [51].
Acetonitrile was distilled over P2O5 and stored under nitrogen.
Kinetics. Kinetic determinations were performed on an Applied Photophysics SX-18MV
stopped-flow apparatus or a conventional Shimadzu (model 1650 PC) UV–Vis
spectrophotometer, the cell compartments of which were maintained at 20 ± 0.1 °C. All
kinetic runs were carried out in triplicate under pseudo-first-order conditions with a triflone
concentration of ~ 3 x 10-5 mol dm-3 and an concentration in the range of 5 x 10-3 - 1 mol dm-3
for anilines and an concentration in the range of 5 x 10-4 – 0.1 mol dm-3 for enamines. In a
given experiment, the rates were found to be reproducible to 2–3 %.
Acknowledgments. We are grateful to Prof. F. Terrier for the use of his laboratory and to
Prof. T. Boubaker for discussions.
Page 11 of 21

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[42] S. Lakhdar, R. Goumont, F. Terrier, T. Boubaker, J. M. Dust, E. Buncel, Org. Biomol.
Chem. 5 (2007) 1744-1751.
[43] E. Buncel, F. Terrier, Org. Biomol. Chem. 8 (2010) 2285-2308.
[44] F. Terrier, S. Lakhdar, T. Boubaker, D. Vichard, R. Goumont, E. Buncel, Chem.
Sustainable Dev. 16 (2008) 59-70.
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74 (2009) 3305-3315.
[46] I-H. Um, L-R. Im, J-S. Kang, S. S. Bursey, J. M. Dust, J. Org. Chem. 77 (2012) 9738-
9746.
[47] N. El Guesmi, F. Terrier, unpublished results.
[48] V. N. Boiko, G. M. Shchupak, L. M. Yagupolskii, Zh. Org. Khim. 15 (1979) 1245-1252.
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[50] L. M. Yagupolskii, N. V. Kondratenko, V. P. Sambur ,Synthesis. (1975) 721-723.
[51] Organikum, Edition dt. Verlag der Wissenschaften, 19th ed., Berlin -Germany (1993).
Page 13 of 21

Table 1
Nucleophilicity N and nucleophile sensitivity parameter sN of the anilines A-C and of the
enamines D-G used as reference nucleophiles in this study.
Nucleophiles
N
sN
13.42a
0.73a
H3CO
H3C
NH2
A
B
C
13.19a
12.64a
0.69a
0.68a
NH2
NH2
N
O
10.04b
10.73b
0.82b
0.81b
D
E
N
11.40c
13.41b
0.83c
0.82b
N
O
F
N
O
G
a From ref. [29]. b From ref. [30]. c From ref. [22]
Page 14 of 21

Table 2
Second–order rate constants k1 (mol-1 dm3 s-1) for coupling of the electrophiles 1-5 with the
reference nucleophiles A-G in acetonitrile at 20 °C.
Nucleophile
1
2
3
4
5 d
8.73 x 10-2 4.99 x 10-3 1.72 x 10-3
5.42 x 10-2 3.54 x 10-3 1.31 x 10-3
2.21 x 10-2 1.49 x 10-3 5.32 x 10-4
A
B
C
9.11 x 101
1.65 x 102
3.8 x 10-3
6 x 10-3
D
E
F
6.53 x 102 1.14 x 10-2
1.61 x 104
5.0
G
d From ref. [28]
Page 15 of 21

Table 3
Determination of the electrophilicity parameters E of 1-4 from reactions with different
reference nucleophiles A-G in acetonitrile at 20 °C.
Electrophiles
Nucleophiles
N
sN
log k1
E
OCH3
A
B
C
13.42
13.19
12.64
0.73
0.69
0.68
-1.06
-1.27
-1.65
-14.87
-15.03
CF3O2S
SO2CF3
-15.06
E (1) = -14.98 ± 0.10 e
SO2CF3
1
OCH3
13.42
13.19
12.64
0.73
0.69
0.68
-2.30
-2.45
-2.82
-16.57
-16.74
A
B
C
CF3O2S
SO2CF3
-16.78
E (2) = -16.69 ± 0.11 e
NO2
2
A
B
C
13.42
13.19
12.64
0.73
0.69
0.68
-2.76
-2.88
-3.28
-17.20
-17.36
OCH3
O2N
SO2CF3
-17.46
E (3) = -17.34 ± 0.13 e
SO2CF3
3
D
E
F
10.04
10.73
11.40
13.41
0.82
0.81
0.83
0.82
1.96
2.22
2.81
4.21
-7.65
-7.99
-8.00
CF3O2S
SO2CF3
SO2CF3
G
-8.27
4
E (4) = -7.98 ± 0.36 e
e
The E parameter is obtained by minimizing ∆2 = ∑ [logk1 – s (E + N)]2 and deviates
slightly from the arithmetic mean of E derived from the individual reactions [22].
Page 16 of 21

8
7
6
5
4
3
2
1
0
100
80
60
40
20
0
1
2
0
0.02 0.04 0.06 0.08
0.1
0.12
3
0
0.02
0.04
0.06
0.08
0.1
0.12
[p-methoxyaniline A] (mol dm -3)
Fig. 1. Influence of the concentration of p-methoxyaniline A on the observed first-order rate
constant for addition to 2,4,6-tris(SO2CF3)anisole 1, 2,6-bis(SO2CF3)-4-nitroanisole 2, and
4,6-bis(SO2CF3)-2-nitroanisole 3 in MeCN at 20 °C
Page 17 of 21

10
8
4
6
4
2
0
0
0,02
0,04
0,06
0,08
0,1
0,12
[enamine D] (mol dm-3)
Fig. 2. Influence of the concentration of enamine D on the observed first-order rate constant
for addition to 1,3,5-tris(trifluoromethanesulfonyl)benzene 4 in MeCN at 20 °C.
Page 18 of 21

O2N
O2N
O2N
N
N
N
N
+
Me
-
+
O
NO2
N
E
N+
O
-3
-4
H
+
N
-3.72
-5.17
NO2
NO2
N
N
NMe2
Me2N
-4.67
H
+
O
NO2
-5 -5.06
-5.32
-
O
N
O2N
N
+
N
Me
N
N
,
O
-6
O
Me
-6.25
+
N
O
-
+
+
O
N
–
N
-
O
N
O
Fe(CO)3
CN
+
NC
-7.01
-7
-8
-9
-7.02
-8.22
N
F3CO2S
SO2CF3
O
N
CN
Ph
Pd(P(OPh)3)2
E = -7.98
NO2
-8.37
-9.05
4
+
-
SO2CF3
O
N
N
+
O
-9.21
-9.42
N
n
O
N
MeO
O2N
-10.11
-10
-11
-12
-13
OMe
N
N
N
O
N
-11.32
-11.89
O
N
O2N
N
-12.33
-13.19
NO2
NO2
S
S
O
N
O2N
-13.30
-14.36
CN
OCH3
-14 -14.10
CN
NO2
F
F3CO2S
SO2CF3
E = -14.98
SO2CF3
Me2N
-15
-16
NO2
1
O
NO2
OCH3
NO2
Cl
F3CO2S
SO2CF3
-17
NO2
-17.29
E = -16.69
-17.60
2
-18
NO2
O
NMe2
-18.30
OCH3
NO2
Br
O2N
SO2CF3
-19
NO2
E = -17.34
3
SO2CF3
NO2
Fig. 3. The ranking of aromatic triflones 1-4 on the E scale, as defined by Mayr et al.
Page 19 of 21

Graphical Abstract
Applying the general approach to nucleophilicity/electrophilicity developed by Mayr et al.,
the E parameters, quantifying the electrophilic reactivity of four aromatic triflones , have been
determined in acetonitrile, through kinetic investigations of σ−complexation and SNAr
substitution reactions involving anilines and enamines as N- and C-nucleophiles.
Page 20 of 21

Highlights
We quantify the electrophilic reactivity for four aromatics triflones
We examine changes in the substitutent of aromatic ring about electrophilic strength
Ranking the neutral electro‐deficient electrophiles in Mayr’s scale
Increasing the scope and the applications of the Mayr equation
Expanding the range of coupling reactions
Page 21 of 21