Recognition of carboxylic acids and phosphonic acids using 1,8-diphenylnaphthalene-based diguanidine

Article abstract of DOI:10.1016/j.tet.2020.131770

A diphenylnaphthalene-based diguanidine (1) has been designed and synthesized for the recognition of dicarboxylic acids and diphosphonic acids. The diguanidine 1 forms 1:1 complexes with the dicarboxylic acids and the diphosphonic acid derivatives in a DM

Full text of DOI:10.1016/j.tet.2020.131770

Tetrahedron 77 (2021) 131770
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Recognition of carboxylic acids and phosphonic acids using 1,8-
diphenylnaphthalene-based diguanidine
Takahiro Kusukawa*, Ryosuke Mura, Masashi Ooe, Ryuki Sumida, Ayaka Nakagawa
Faculty of Molecular Chemistry and Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku Kyoto,
606-8585, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A diphenylnaphthalene-based diguanidine (1) has been designed and synthesized for the recognition of
dicarboxylic acids and diphosphonic acids. The diguanidine 1 forms 1:1 complexes with the dicarboxylic
acids and the diphosphonic acid derivatives in a DMSO solution, and the formation of the complexes was
determined by DOSY NMR spectroscopy. The weak yellowish fluorescence of the diguanidine 1 in a
DMSO solution turned to a strong bluish fluorescence after the addition of 1,3-benzenediacetic acids 3.
Received 24 October 2020
Received in revised form
9 November 2020
Accepted 12 November 2020
Available online 17 November 2020
However, after the addition of other types of aliphatic dicarboxylic acids, such as a,u-dicarboxylic acids,
only a weak yellowish fluorescence was observed and selective recognition of the 1,3-benzenediacetic
acids 3 was developed. On the other hand, for the recognition of diphosphonic acid derivatives (5e7),
a light blue, blue or pinkish fluorescence was observed. Interestingly, the binding mode on the guanidyl
group (two existing types of binding modes toward three nitrogen atoms) with oxoacids were suc-
cessfully determined by the 2D NOESY analysis. The fluorescence quantum yields (Ffl) were moderately
increased by the introduction of the guanidyl group and binding with dicarboxylic acids 3 than that of
the 1,8-diphenylnaphthalene itself. These fluorescence characteristics of the diguanidine 1 are applicable
for the detection of dicarboxylic acids and diphosphonic acids.
Keywords:
Guanidine
Fluorescence
Carboxylic acid recognition
Phosphonic acid recognition
© 2020 Elsevier Ltd. All rights reserved.
1. Introduction
“phosphonic acids” have been reported [2e-h].
On the other hand, the “amidino group” and “guanidyl group”
The “oxoacids” and “oxoanions” such as carboxylic acids
(carboxylate) and phosphoric acids (phosphate) play many roles in
biological systems and in industry. The recognition of carboxylic
acids (carboxylate) and phosphoric acids (phosphate) using fluo-
rogenic chemosensor is of particular important because of their
applications in the chemical, biological, medical, and environ-
mental sciences [1].
Until recently, numerous reports of fluorogenic chemosensors
for “carboxylate” as anionic form have been reported, but the flu-
orogenic chemosensors for the recognition of “carboxylic acids” are
relatively rare [1a-b].
Additionally, the recognition of the “phosphonic acid” is also
important target related to the trace of nerve gases that produce
phosphonic acid after hydrolysis (i.e., Sarin produces methyl-
phosphonic acid after hydrolysis) [2a-d]. However, only a few ex-
amples of the fluorogenic chemosensors for the recognition of the
have become extremely advantageous functional binding groups
for the oxoacids [3,4]. We previously reported that the synthesis of
anthracene-based “diamidine” and “diguanidine”, which recognize
dicarboxylic acids and diphosphonic acid derivatives as turn-on
and turn-off fluorogenic chemosensors, respectively [2g-h,3f,3h].
Additionally, we developed the diphenylnaphthalene-based dia-
midine for the recognition of a dicarboxylic acid as a turn-on
fluorescent chemosensor with high fluorescent quantum yields
[3g]. To explore the applicability of these functional chemosensors
for the recognition of oxoacids, we have synthesized the new
diphenylnaphthalene-based diguanidine 1 (Scheme 1). The ob-
tained diguanidine 1 recognized “dicarboxylic acids” and “diphos-
phonic acids” in a DMSO solution, and the formation of 1:1
complexes was determined by a DOSY NMR analysis. The weak
yellowish fluorescence of the diguanidine 1 in a DMSO solution
turned into a strong bluish fluorescence after the addition of 1,3-
benzenediacetic acids 3. However, after the addition of other
types of aliphatic carboxylic acids, such as
a,u-dicarboxylic acids,
* Corresponding author.
E-mail address: kusu@kit.ac.jp (T. Kusukawa).
only a weak yellowish fluorescence was observed and selective
https://doi.org/10.1016/j.tet.2020.131770
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T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
Scheme 1. Synthesis of diguanidine 1.
recognition of the 1,3-benzenediacetic acids 3 was developed.
Additionally, for the recognition of phosphonic acid diethyl ester
derivatives, a light blue, blue or pinkish fluorescence was observed.
Interestingly, the binding mode (Type I and Type II) on the guanidyl
group with oxoacids was successfully determined by the 2D NOESY
analysis.
1ꢀBoc4 and obtained the product in 84% yield by the reaction with
1,8-di(40-aminophenyl)naphthalene. The 1H NMR spectrum of the
Boc protected diguanidine 1ꢀBoc4 showed two types of NH signals
at 11.6 ppm (Ho) and 9.97 ppm (Hp) in Fig. 1a. The structure of the
1ꢀBoc4 (non-conjugated structure of the C]N double bond with
diphenylnaphtalene ring) was confirmed by the HMBC correlation
between Hp and Ca (see Fig. 1a and supporting information). The
obtained Boc protected product 1ꢀBoc4 was converted to the
diguanidine dihydrochloride 1ꢀ2HCl in an almost quantitative
yield. The diguanidine 1 was obtained from the diguanidine dihy-
drochloride 1ꢀ2HCl by treatment with NaOH aq. (yield: 97%).
There are two isomeric structures for the target diguanidine (1
and 10) that have conjugated and non-conjugated C]N double
bonds between the diphenylnaphthalene ring, respectively
(Scheme 1). The 1H NMR spectrum of the obtained
diphenylnaphthalene-based diguanidine showed only one broad
NH signal at 4.88 ppm in DMSO‑d6 (Fig. 1b). The DFT optimized
structure of the conjugated structure 1 was 5.0 kcal/mol more
2. Results and discussion
2.1. Synthesis of diguanidine 1
The diphenylnaphthalene-based diguanidine 1 was prepared
according to Scheme 1. The 1,8-di(40-aminophenyl)naphthalene
was prepared using the Suzuki-Miyaura coupling from 1,8-
naphthalenediboronic anhydride and 4-bromoacetanilide fol-
lowed by deprotection of the acetyl group. For the synthesis of the
diphenylnaphthalene-based diguanidine 1, we used Goodman’s
reagent [5] for the synthesis of the Boc protected diguanidine
Figure 1. 1H NMR spectra of a) 1ꢀBoc4 in CDCl3, and b) diguanidine 1 in DMSO-d6.
2

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
stable than the non-conjugated structure 1’ (B3LYP/6-31G*,
Fig. S24). Recently, Antol [6] and co-workers also proposed the
conjugated structure of the aromatic guanidine derivatives using
DFT calculations.
calculated molecular volume of the complex 1ꢀ2 derived from the
observed diffusion coefficient (V ¼ 918 Å3) is slightly larger than the
sum of the volumes of the free building blocks (1: V ¼ 546 Å3, 2:
V ¼ 226 Å3), which indicated the formation of the stable 1:1
complex (Fig. 3, Table 1). There are two binding sites (Type I, Type II,
see reference 6) for the diguanidine 1, and two possible structures
exist for the formation of the 1:1 complex between the diguanidine
1 and the dicarboxylic acids (Chart 2). Additionally, the conforma-
tions of the dicarboxylic acid part also have two possibilities (up
and down) and there are four isomeric structures (Chart 2). The DFT
calculations of the 1:1 complex 1ꢀ2 of the diguanidine 1 and
dicarboxylic acid 2 showed that the “Type I-down” is the most
stable structure compared to the other structures (Relative energy;
Type I-down: 0.00 kcal/mol, Type I-up 2.77 kcal/mol, Type II-down
3.60 kcal/mol, Type II-up 2.31 kcal/mol, see Fig. S25).
2.2. Binding experiments of diphenylnaphthalene-based
diguanidine 1 with dicarboxylic acids (2e4)
To investigate the binding ability of the diguanidine 1 toward
the dicarboxylic acids (Chart 1), we observed the 1H NMR and DOSY
NMR spectra for the complexation of diguanidine 1 with slightly
rigid dicarboxylic acids (2 and 3). The formation of the 1:1 complex
1ꢀ2 was achieved by mixing the DMSO‑d6 solutions
([1] ¼ [2] ¼ 1.89 mM) of 1 and 2. The 1H NMR spectrum of the
obtained solution showed the characteristic upfield and downfield
shifts with respect to those of 1 and 2 (Fig. 2, S1). The downfield
shift of the guanidine unit (Ha, Hb) and the upfield shift of the
dicarboxylic acid unit (HA, HD) in the 1H NMR indicated the for-
mation of a cationic charge and an anionic charge in each unit after
complexation.
To obtain information about the formation of the 1:1 complex
1ꢀ2, the DOSY NMR spectroscopy was evaluated. The 1H DOSY
spectra showed that the diffusion coefficient of the complex 1ꢀ2 is
lower than those of the corresponding free building blocks (1, 2),
confirming the formation of the binding complex (Fig. 3). The
The complexation of the diguanidine
1 with the 1,3-
benzenediacetic acids 3a and 3b also showed the formation of
the stable 1:1 complexes 1ꢀ3a and 1ꢀ3b in DMSO‑d6, which were
confirmed by 1H NMR and DOSY NMR spectroscopies (Figures S2-3,
S11-12, Table 1). The binding mode and the stable conformation of
the 1:1 complex 1ꢀ3a was also evidenced by the DFT calculations as
the Type I-down structure (Fig. S26).
To explore the applicability of this diguanidine 1 for the recog-
nition of several dicarboxylic acids, we evaluated the recognition of
the conformationally flexible
a,u
ꢁdicarboxylic acids 4. The
Chart 1.
Figure 2. 1H NMR spectra (1.89 mM in DMSO-d6, 298 K) of a) diguanidine 1, b) 1ꢀ2 obtained by mixing equimolar solutions of 1 and 2, and c) dicarboxylic acid 2.
3

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
1
Figure 3. H DOSY spectra (1.89 mM in DMSO-d6, 25 ꢂC, diffusion time
D
¼ 200 ms) of a) complex 1ꢀ2, b) dicarboxylic acid 2, c) diguanidine 1.
formation of the 1:1 complex 1ꢀ4c (X¼(CH2)5) was also achieved by
mixing the DMSO‑d6 solution (1.89 mM) of both components. The
1H NMR spectrum of the obtained solution showed the character-
istic upfield and downfield shifts with respect to those of 1 and 4c,
which indicated the formation of the complex (Fig. S4). The mo-
lecular volume of 1ꢀ4c (V ¼ 869 Å3) derived from the observed
diffusion coefficient using DOSY NMR spectroscopy is similar to the
sum of the volumes of the free building blocks (1: V ¼ 546 Å3, 4c:
V ¼ 169 Å3), which also indicated the formation of the stable 1:1
complex (Table 1, Fig. S13). For the complexation of the diguanidine
1 with the dicarboxylic acids 4d (X¼(CH2)6) and 4e (X¼(CH2)7), it
also showed the formation of the stable 1:1 complexes 1ꢀ4d and
1ꢀ4e in DMSO‑d6, which was also confirmed by the 1H NMR and
DOSY NMR spectroscopies (Figures S5-6, S14-15, Table 1).
Table 1
Comparison of diffusion coefficients, molecular radii and volumes.a.
Compounds
D (m2S-1
)
rH (Å)
V (Å3)
1
2
1.96 0.01 x 10-10
2.63 0.03 x 10-10
1.65 0.06 x 10-10
2.80 0.02 x 10-10
1.65 0.02 x 10-10
2.60 0.03 x 10-10
1.66 0.02 x 10-10
2.90 0.03 x 10-10
1.68 0.05 x 10-10
2.80 0.01 x 10-10
1.58 0.09 x 10-10
2.69 0.03 x 10-10
1.63 0.05 x 10-10
5.07
3.78
6.03
3.55
6.03
3.82
5.99
3.43
5.92
3.55
6.29
3.70
6.10
546
226
918
187
918
233
900
169
869
187
1042
212
951
1ꢀ2
3a
1ꢀ3a
3b
1ꢀ3b
4c
1ꢀ4c
4d
1ꢀ4d
4e
1ꢀ4e
a
Diffusion coefficients were recorded at 298 K in DMSO-d6 (1.89 mM), and the
molecular radii were calculated using the Stokes-Einstein equation.
Chart 2.
4

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
2.3. Binding experiments of diphenylnaphthalene-based
diguanidine 1 with diphosphonic acid diethyl esters (5e7)
complex formation which was estimated by the DFT calculations
(Fig. 7, S27-28).
To compare the recognition ability between the “dicarboxylic
acids” and “diphosphonic acid derivatives”, we examined the
recognition of the diphosphonic acid derivatives 5, 7a (Y¼(CH2)3),
and 7c (Y¼(CH2)5) which have solubilizing Et groups after the
complex formation (protection of the hydroxy group to inhibit the
formation of a higher aggregate, Chart 3). The formation of the 1:1
complex 1ꢀ5 was also achieved by mixing the DMSO‑d6 solutions
(1.89 mM) of both components. The 1H NMR spectrum of the ob-
tained solution showed the characteristic downfield and upfield
shifts with respect to those of 1 and 5, respectively (Fig. 4, S7). The
resonance of the NH protons was observed at 10.8 and 8.0 ppm
indicating the formation of “guanidinium-phosphonate” salt
bridges (i.e., formation of a stable complex, Fig. 4b).
The DOSY spectra of the complex 1ꢀ5 confirmed the formation
of a stable complex (Fig. 5). The molecular volume of 1ꢀ5 derived
from the observed diffusion coefficient (V ¼ 1062 Å3) is similar to
the sum of the volumes of the free building blocks (1: V ¼ 546 Å3, 5:
V ¼ 352 Å3), which indicated the formation of the stable 1:1
complex (Table 2).
2.4. Fluorescence detection of carboxylic acids using diguanidine 1
To demonstrate the recognition ability of the diguanidine 1 to-
ward dicarboxylic acids, we observed the fluorescence spectra of
the diguanidine 1 with dicarboxylic acids 2e4 and benzoic acid 8 (2
eq.) in a DMSO solution. The diguanidine 1 itself shows a very weak
yellow fluorescence as a broad band (lmax ¼ 586 nm) in the DMSO
solution (Fig. 8). After the addition of 1 equivalent of the 1,3-
adamantanediacetic acid 2 and a,u-dicarboxylic acids 4, the yel-
low fluorescence of the diguanidine 1 had only slightly changed
and the small increasing of the fluorescence band around 420 nm
was observed as a yellowish color. Surprisingly, after the addition of
1 equiv. of 1,3-benzenediacetic acid 3a, a strong emission was
observed at lmax ¼ 417 nm as a bluish color. A similar strong
emission was observed after the addition of the 1,3-
benzenediacetic acid derivative 3b to the solution of diguanidine
1 (Fig. 8).
The Job’s plot analysis for the complexation of the diguanidine 1
and dicarboxylic acids 3a and 3b showed the formation of the 1:1
complex by fluorescence spectroscopy at a high concentration
The DFTcalculations of the 1:1 complex 1ꢀ5 of the diguanidine 1
and diphosphonic acid diethyl ester 5 also showed that the Type I-
down is a more stable structure than the other binding mode (Chart
2, Fig. S27). The NOESY spectrum of the 1:1 complex 1ꢀ5 of the
diguanidine 1 and diphosphonic acid diethyl ester 5 showed the
NOE correlations between Ha and HF (or HE), indicating the for-
mation of the Type I-down structure (Fig. 6, S29).
(200 mM, Figs. S20e21). For the complexation with the benzoic acid
8 (aromatic monocarboxylic acid, 2 equiv.) with diguanidine 1,
which corresponds to the formation of guanidinium, and the
fluorescence spectrum of the hydrochloric acid salt of 1 (1ꢀ2HCl,
corresponding to protonated guanidinium of 1), a weak fluores-
cence was observed around 410 nm (Fig. 8).
For the complexation of the diguanidine 1 with the diphos-
phonic acid diethyl esters having a methylene chain 7c (Y¼(CH2)5),
the 1H NMR spectra of the formed complexes showed reasonable
upfield and downfield shifts indicating the formation of stable
complexes (Fig. S9). For the 1:1 complex 1ꢀ7c, a slightly larger
molecular volume compared to the formation of 1ꢀ5 was observed
by the DOSY NMR spectroscopy which indicated the formation of a
stable 1:1 complex, and also the NOESY correlation was observed
for the formation of the Type-I down structure (Figs. S10 and S17,
Table 2). On the other hand, for the complexation of diguanidine 1
with the diphosphonic acid diethyl ester 7a (Y¼(CH2)3) which has a
shorter methylene chain length than 7c, two different diffusion
coefficients were observed derived from diguanidine 1 (G) and the
diphosphonic acid diethyl ester 7a (Y¼(CH2)3, P) in the DOSY
spectra (Figs. S8 and S16, Table 2) [7]. These observations showed
the formation of a weaker complex 1ꢀ7a (Y¼(CH2)3) than 1ꢀ7c
(Y¼(CH2)5) and 1ꢀ5 that may be caused by the absence and pres-
ence of the multiple hydrogen bonding interactions after the
To obtain evidence for the formation of the guanidinium-
carboxylate bonding and also to assign the fluorescence wave-
length (410 nm) of the guanidinium species (i.e., 1þ2Hþ), we
measured the fluorescence spectra of 1ꢀ3a after the addition of H2O
(Fig. 9, Chart 4). The intensity of the fluorescence spectrum of 1ꢀ3a
decreased and blue-shifted (lmax ¼ 403 nm) by the addition of H2O
(0e1000 mL) which indicated the formation and dissociation of the
guanidinium-carboxylate bonding.
The binding constants of the diguanidine 1 and dicarboxylic
acids 2, 3, 4c, 4e with a 1:1 stoichiometry were determined by
fluorescence titrations, and pKa values of the dicarboxylic acids are
summarized in Table 3. The binding constants of the diguanidine 1
and dicarboxylic acids are on the order of 104-106 (Mꢁ1) in the
DMSO solution. Surprisingly, higher binding constants were
observed for the complexation with the 1,3-benzenediacetic acid
derivatives 3a and 3b (K1:1 ¼ 1.5 ꢃ 106
M a,u-
ꢁ1) than with the
dicarboxylic acids 4c and 4e (Table 3). These higher binding con-
stants agreed with the observation of the higher fluorescence
Chart 3.
5

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
Figure 4. 1H NMR spectra (1.89 mM in DMSO-d6, 298 K) of a) diguanidine 1, b) 1ꢀ5 obtained by mixing equimolar solutions of 1 and 5, and c) diphosphonic acid diethyl ester 5.
Figure 5. 1H DOSY spectra (1.89 mM in DMSO-d6, 298 K, diffusion time
D
¼ 200 ms) of a) complex 1ꢀ5, b) diphosphonic acid diethyl ester 5, c) diguanidine 1.
intensities of the mixed solutions of diguanidine 1 with the dicar-
boxylic acids 3 compared to the dicarboxylic acids 4 (Fig. 8). Rela-
tively higher binding constants were observed for the
complexation with carboxylic acids having low pKa values.
2.5. Fluorescence detection of diphosphonic acids using diguanidine
1
To further understand the recognition ability of the diguanidine
1 toward diphosphonic acids, we observed the fluorescence spectra
6

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
Table 2
of the diguanidine 1 with diphosphonic acids 5e7 in a DMSO so-
lution. The diguanidine 1 itself showed a weak yellow fluorescence
as a broad band (lmax ¼ 586 nm) in the DMSO solution as already
discussed. After the addition of 1 equivalent of the diphosphonic
acids 5e7, the yellow fluorescence of the diguanidine 1 had
changed and the increasing of the fluorescence band around
420e430 nm was observed as a light blue, blue or pinkish color
(Fig. 10).
The Job’s plot analysis for the complexation of the diguanidine 1
and diphosphonic acids 5, 7c showed the formation of the 1:1
complex by fluorescence spectroscopy (Figs. S22e23). To obtain
evidence for the formation of the guanidinium-phosphonate
bonding and to also assign the fluorescence wavelength of the
1:1 complex of the diguanidine 1 and diphosphonic acids, we
measured the fluorescence spectra of 1ꢀ5 after the addition of H2O
Comparison of diffusion coefficients, molecular radii and volumes.a.
Compounds
D (m2S-1
)
rH (Å)
V (Å3)
1
5
1ꢀ5
7a
1ꢀ7a
1.96 0.01 x 10-10
2.27 0.03 x 10-10
1.57 0.03 x 10-10
2.50 0.04 x 10-10
1.58 0.03 x 10-10(G)b
1.99 0.03 x 10-10(P)c
2.39 0.05 x 10-10
1.38 0.06 x 10-10
5.07
4.38
6.33
3.98
6.29
5.00
4.16
7.21
546
352
1062
264
1042
524
7c
1ꢀ7c
a
302
1570
Diffusion coefficients were recorded at 298 K in DMSO-d6 (1.89 mM, diffusion
¼ 200 ms), and the molecular radii were calculated using the Stokes-Einstein
equation.
time
D
b
Derived from diguanidine 1.
Derived from diphosphonic acid diethyl ester 7a.
c
Figure 6. 1H NOESY spectrum (1.89 mM in DMSO-d6, 298 K, mixing time ¼ 2 sec.) of complex 1ꢀ5.
Figure 7. Schematic representation of the formation of the stable and unstable complexes with and without multiple hydrogen bonding interactions.
7

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
Table 3
Binding constants (K1:1
)
a of diguanidine 1 with dicarboxylic acids and diphosphonic
acids, and pKa values.b.
oxoacids
K1:1/M-1
pKa (obs)
pKa (calc)
2 (1,3-adamantanediacetic acid)
3a (1,3-benzenediacetic acid)
3b (5-methyl-1,3-benzenediacetic acid)
4c (pimelic acid, X¼ (CH2)5)
4e (azelaic acid, X¼ (CH2)7)
5 (Y¼ m-xylylene)
2.8 x 104
1.5 x 106
1.5 x 106
2.4 x 104
7.2 x 104
1.7 x 106
1.2 x 106
4.42
3.93
3.94
4.43
4.47
2.09
2.65
4.71
4.53
5.58
5.33
7c (Y¼ (CH2)5)
a
Binding constants were determined by fluorescent titration in DMSO (1: 25 mM,)
using the 1:1 model.
b
pKa (obs): pKa values of carboxylic acids in H2O, Lide D. R. Ed., CRC Handbook of
Chemistry and Physics, 88th ed., CRC Press, Boca Raton, FL, 2007-2008; pKa
:
(calc)
Calculated pKa values of carboxylic acids and phosphonic acids using Advanced
Chemistry Development (ACD/Laboratories) Software V11.02 (1994-2020 ACD/
Labs) taken from SciFinder Scholar.
(Fig. S19). The intensity of the fluorescence spectrum of 1ꢀ5 slightly
decreased and again increased around 400e410 nm by the addition
of H2O (0e1000 mL) which indicated the formation and dissociation
Figure 8. Fluorescence spectra of diguanidine 1 (25
m
M in DMSO, lex ¼ 313 nm) upon
of the guanidinium-phosphonate bonding. The binding constants
for the complexation of the diguanidine 1 with diphosphonic acid 5
(Y ¼ m-xylylene) and 7c (Y¼ (CH2)5) were obtained by the fluo-
the addition of carboxylic acids, and fluorescence spectrum of 1ꢀ2HCl (25
mM in
DMSO).
rescence titration (1ꢀ5: Ka
¼
1.7
ꢃ
106 Mꢁ1
,
1ꢀ7c:
Ka ¼ 1.2 ꢃ 106 Mꢁ1) as a 1:1 binding model (Table 3, Figs. S35e36).
2.6. Fluorescence quantum yields of carboxylic acids and
phosphonic acid binding complexes
The fluorescence quantum yields (Ffl) of the dicarboxylic acid
binding complexes 1ꢀ3a, 1ꢀ3b and diphosphonic acid binding
complexes 1ꢀ7b (Y¼(CH2)4), 1ꢀ7d (Y¼(CH2)6) in a DMSO solution
were determined by a calibrated integrating sphere (Table 4).
Compared to the fluorescence quantum yield of 1,8-
diphenylnaphthalene (Ffl ¼ 0.03 in DMSO) [3g], the introduction
of the guanidium-carboxylate and guanidium-phosphonate groups
to the 1,8-diphenylnaphthalene unit moderately improved
(
Ffl ¼ 0.13e0.27) fluorescence quantum yields in the DMSO solu-
tion were observed. The reason for the improvement of the fluo-
rescence quantum yields is not clear at the moment, but there are
some possibilities such as the formation of rigid complex or sub-
stituent of electron withdrawing groups (i.e., guanidinium-
carboxylate or guanidinium-phosphonate groups).
3. Conclusions
Figure 9. Fluorescence spectra of 1ꢀ3a (25 M, 3 mL in DMSO, lex ¼ 313 nm) upon the
m
addition of H2O.
We have synthesized the diphenylnaphthalele-based diguani-
dine 1 for the recognition of carboxylic acids and phosphonic acid
derivatives. The diguanidine 1 forms 1:1 complexes with dicar-
boxylic acids in a DMSO solution and the formation of the com-
plexes were confirmed by the DOSY NMR analysis. For the
recognition of the diphosphonic acid diethyl esters, the formation
of 1:1 complexes were also evidenced by the DOSY NMR analysis.
For the fluorescence detection of the dicarboxylic acids, the weak
yellowish fluorescence of the diguanidine 1 in a DMSO solution
turned into a strong bluish fluorescence after the addition of the
1,3-benzenediacetic acids 3, and selective recognition of 3 was
developed. On the other hand, after the addition of the diphos-
phonic acid derivatives, several types of fluorescence colors were
observed. Interestingly, the binding mode on the guanidyl group
with oxoacids (Type I-down) was successfully determined by the
2D NOESY analysis. These fluorescence characteristics of the
diguanidine 1 are applicable for the detection of dicarboxylic acids
and diphosphonic acids.
Chart. 4.
8

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
Figure 10. Fluorescence spectra of diguanidine 1 (25
mM in DMSO, lex ¼ 313 nm) upon the addition of diphosphonic acids, and fluorescence spectrum of 1ꢀ2HCl (25
mM in DMSO).
B(OMe)3 is ꢁ34 ꢂC). The solution was stirred for 20 min. at ꢁ80 ꢂC,
then gradually warmed to room temperature over 2 h and stirred
overnight at room temperature. The reaction was quenched with
H2O (5 mL) followed by 2 M HCl (10 mL), then stirred at room
temperature for 45 min. The organic phase was separated and the
water phase was additionally extracted with Et2O (15 mL x 3). The
combined organic phase was extracted with 10% NaOH aq. (10 mL x
3), then the obtained alkaline fraction was acidified with conc. HCl
(10 mL). The obtained colorless solids were collected and vacuum
dried (208 mg, 80%)
Table 4
Fluorescence quantum yields (Ffl) of dicarboxylic acid-binding
complexes and diphosphonic acid-binding complexes in
DMSOa.
compound
Ffl
1,8-Diphenylnaphthalene
1
0.03b
0.07
0.27
0.26
0.13
0.20
1ꢀ3a
1ꢀ3b
1ꢀ7b (Y¼(CH2)4)
1ꢀ7d (Y¼(CH2)6)
Colorless solid; mp > 300 ꢂC; 1H NMR (500 MHz, DMSO‑d6)
a
Fluorescence quantum yields were determined by a cali-
brated integrating sphere.
d
¼ 9.14 (s, 2H, BeOH), 8.17 (dd, J ¼ 6.8 Hz, 1.2 Hz, 2H), 8.09 (dd,
b
in DMSO, from reference 3g.
J ¼ 8.3 Hz, 1.1 Hz, 2H), 7.59 (t, J ¼ 7.5, 2H). 13C NMR (125 MHz,
DMSO‑d6);
d
¼ 141.3 (Cq), 134.1 (CH), 131.5 (CH), 131.4 (Cq), 125.5
(CH), missing one carbon (CeB) due to interaction with the boron
4. Experimental section
atom.
4.1. General methods
4.1.2. Synthesis of 1,8-di(40-acetoamidophenyl)naphthalene [9]
1,8-Naphthalenediboronic anhydride (303 mg, 1.53 mmol), 4-
bromoacetanilide (976 mg, 4.56 mmol), and Pd(PPh3)4 (175 mg,
0.15 mmol) were mixed in DME (60 mL), then a 0.5 M Na2CO3
aqueous solution (15 mL, 7.50 mmol) was added. The obtained
mixture was degassed 3 times by a freeze-pump-through method,
then the mixture was heated at 85 ꢂC for 20 h in an Ar atmosphere.
After removing the solvent in vacuo and adding water (20 mL), the
mixture was extracted with CH2Cl2 (20 mL x 3), then evaporated.
The target product was also precipitated as a gray solid in the water
phase, then recovered by filtration. All the fractions were com-
bined, then 1,8-di(40-acetoamidophenyl)naphthalene was isolated
(225 mg, 37%) by column chromatography (SiO2, CHCl3/
MeOH ¼ 19/1).
The 1H NMR and 13C NMR spectra were recorded using Avance
III 500 (500 and 125 MHz) spectrometers. The FAB-mass spectra
were recorded by a JEOL JMS-700 mass spectrometer. The absorp-
tion spectra were recorded by a SHIMADZU UV-2550 UVeVisible
spectrometer. The fluorescence spectra were recorded by a JASCO
FP-6200 spectrometer, and the fluorescence spectra were corrected
using rhodamine B as the reference. The absolute PL quantum
yields (Ffl) were determined by a Quantaurus-QY (Hamamatsu
Photonics) instrument. All solvents and reagents were purified
according to standard procedures. For the NMR measurement using
CDCl3, the acidic impurity in the CDCl3 solvent was removed by
passage
through
basic
Al2O3
(Merck, 101,076). 1,3-
Bis(cyanomethyl)-5-methylbenzene was purchased from TCI
(Tokyo Chemical Industry Co., Ltd).
1H NMR (500 MHz, DMSO‑d6)
d
¼ 9.71 (s, 2H), 8.00 (d, J ¼ 7.2 Hz,
2H), 7.58 (t, J ¼ 7.6 Hz, 2H), 7.36 (d, J ¼ 7.0 Hz, 2H), 7.19 (d, J ¼ 8.5 Hz,
4H), 6.84 (d, J ¼ 8.5 Hz, 4H), 1.99 (s, 6H).
4.1.1. Synthesis of 1,8-naphthalenediboronic anhydride [8]
To a solution of 1,8-diiodonaphthalene (501 mg, 1.32 mmol) in
Et2O (16 mL) was slowly added n-BuLi (1.85 M in hexane, 2.14 mL,
3.96 mmol) at ꢁ80 ꢂC over 15 min. After stirring the obtained
yellow solution for 20 min. at ꢁ80 ꢂC, B(OMe)3 (0.58 mL,
5.19 mmol) was smoothly added (attention: melting point of
4.1.3. Synthesis of 1,8-di(40-aminophenyl)naphthalene [9]
1,8-Di(40-acetoamidophenyl)naphthalene (175 mg, 0.44 mmol),
3 M HCl aq. (1.6 mL), and EtOH (8 mL) were mixed and refluxed for
29 h. After cooling to room temperature, 28% NH3 aq. (1.5 mL) was
9

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
added and extracted with CH2Cl2 (10 mL x 3). The combined
organic phase was dried (Na2SO4) and evaporated under reduced
pressure. The 1,8-di(40-aminophenyl)naphthalene (118 mg, 85%)
was isolated by column chromatography (SiO2, AcOEt).
was collected by filtration and washed with cold distilled water
(2 mL x 5) to give a colorless solid 1 (49 mg, 91%).
Colorless solid; mp 216.5e217.4 ꢂC; 1H NMR (500 MHz,
DMSO‑d6)
d
¼ 7.95 (d, J ¼ 7.5 Hz, 2H), 7.55 (t, J ¼ 6.8 Hz, 2H), 7.35 (d,
1H NMR (500 MHz, DMSO‑d6)
d
¼ 7.86 (d, J ¼ 8.2 Hz, 2H), 7.50 (t,
J ¼ 6.3 Hz, 2H), 6.76 (d, J ¼ 7.1 Hz, 2H), 6.38 (d, J ¼ 6.7 Hz, 2H); 13
C
J ¼ 7.6 Hz, 2H), 7.28 (d, J ¼ 7.1 Hz, 2H), 6.65 (d, J ¼ 8.4 Hz, 4H), 6.19
NMR (125 MHz, DMSO‑d6)
d
¼ 152.2 (Cq), 148.2 (Cq), 140.5 (Cq),
(d, J ¼ 8.4 Hz, 4H), 4.78 (s, 4H).
135.3 (Cq), 135.0 (Cq), 130.2 (CH), 130.0 (CH), 128.8 (Cq), 127.7 (CH),
125.2 (CH),121.5 (CH). HRMS (FAB, NBA) m/z ¼ 395.1985 (calculated
for [MþH]þ: 395.1984). Anal. Calcd. for C24H22N6ꢀ0.7H2O: C:70.81,
H:5.79, N:20.64. Found: C:70.84, H:5.44, N:20.41.
4.1.4. Synthesis of 1ꢀBoc4
1,8-Di(40-aminophenyl)naphthalene (102 mg, 0.33 mmol), 1,3-
bis(tert-butoxycarbonyl)-2-(trifluoro-methanesulfonyl)guanidine
(Goodman’s reagent, 315 mg, 0.81 mmol), and dry-Et3N (112
mL,
4.1.7. Synthesis of 5-methyl-1,3-benzenediacetic acid [10]
0.82 mmol) were mixed in 3 mL of dry CH2Cl2. The obtained
mixture was stirred for 1 day under an Ar atmosphere at room
temperature. During the course of the reaction, the amount of dry
CH2Cl2 (should not added a large amount of solvent) was main-
tained and the reaction was monitored by TLC (Rf ¼ 0.73 for 1ꢀBoc4,
Rf ¼ 0.37 for monoguanidineꢀBoc2, CHCl3 as the solvent). To obtain
the Boc-protected digauanidine 1ꢀBoc4, 1,3-bis(tert-butox-
ycarbonyl)-2-(trifluoromethanesulfonyl)guanidine (Goodman’s re-
agent, 88 mg, 0.23 mmol) was additionally added to reaction
mixture, and stirred for a total of 6 days under an Ar atmosphere at
40e45 ꢂC. To the reaction mixture, CH2Cl2 (10 mL) and 5% NaHCO3
aq. (10 mL) were added, additionally extracted with CH2Cl2 (10 mL
x 2), and the combined CH2Cl2 layer was dried (Na2SO4), and
evaporated under reduced pressure. The target product 1ꢀBoc4
(50 mg, 84%) was obtained by column chromatography (SiO2,
toluene).
1,3-Bis(cyanomethyl)-5-methylbenzene (1.0 g, 5.9 mmol), EtOH
(13 mL), and a 2.7 M KOH aqueous solution (13 mL, 35 mmol) were
mixed and refluxed for 6 h. After cooling to room temperature,11 M
HCl aq. (4 mL) was added, then extracted with AcOEt (15 mL x 2).
The combined AcOEt layer was washed with brine (50 mL x 2),
dried (Na2SO4), then evaporated under reduced pressure to give the
target product 5-methyl-1,3-benzenediacetic acid (778 mg, 63%).
Colorless solid; mp 180.0e181.0 ꢂC; 1H NMR (500 MHz,
DMSO‑d6)
d
¼ 6.93 (s, 2H), 6.91 (s, 1H), 3.47 (s, 4H), 2.25 (s, 3H).
4.2. Jobs plot analysis (fluorescence spectroscopy)
The stock solutions of 1, dicarboxylic acids and diphosphonic
acids in DMSO were prepared in separate volumetric flasks. Several
sample solutions containing both the diguanidine 1 and carboxylic
acids (or diphosphonic acids) in different ratios (1/9 to 9/1) were
prepared and maintained at 0.2 mM. The fluorescence spectra of
the mixtures were recorded, and the intensities were analyzed by
the Job’s method.
Colorless solid; mp > 300 ꢂC; 1H NMR (500 MHz, CDCl3)
d
¼ 11.62 (brs, 2H, NH), 9.97 (brs, 2H, NH), 7.94 (dd, J ¼ 8.3, 1.3 Hz,
2H), 7.54 (dd, J ¼ 8.1, 7.0 Hz, 2H), 7.40 (dd, J ¼ 7.0, 1.3 Hz, 2H), 7.17 (d,
J ¼ 8.5 Hz, 4H), 6.89 (d, J ¼ 8.5 Hz, 4H), 1.53 (s, 18H), 1.49 (s, 18H). 13
C
NMR (125 MHz, CDCl3);
d
¼ 163.7 (Cq), 153.6 (Cq), 153.1 (Cq), 151.4
4.3. DOSY measurements
(Cq), 140.0 (Cq), 139.8 (Cq), 135.4 (Cq), 134.3 (Cq), 130.7 (CH), 130.1
(CH), 129.5 (Cq), 128.5 (CH), 125.1 (CH), 122.0 (CH), 86.0 (Cq), 83.2
(Cq), 79.2 (Cq), 28.2 (CH3), 27.8 (CH3). HRMS (FAB, NBA) m/
z ¼ 795.4083 (calculated for [MþH]þ: 795.4081). Anal. Calcd. for
For the DOSY experiments with the free building blocks as well
as the complexes, the concentrations of 1, 2, 3a, 3b, 4c-4e, 5, 7a, 7c,
1ꢀ2, 1ꢀ3a, 1ꢀ3b, 1ꢀ4c-1ꢀ4e, 1ꢀ5, 1ꢀ7a and 1ꢀ7c were kept constant at
1.89 mM. The 1H DOSY experiments were carried out at 298 K using
a Bruker Avance III 500 MHz spectrometer equipped with a 5-mm
BBFO probe with a z-axis gradient coil. The data were acquired and
processed using the Bruker TopSpin 3.0 software. A series of
diffusion ordered spectra were collected of the samples using the
LEDbp pulse sequence [11]. The pulse-fields were incremented in
50 steps from 2% to 95% of the maximum gradient strength in a
linear ramp. The gradient length was selected between 2.0 and
3.0 ms with a diffusion time of 200 ms and an eddy current delay of
5 ms.
C
44H54N6O8ꢀH2O: C:65.01, H:6.94, N:10.34. Found: C:65.23, H:6.69,
N:10.36.
4.1.5. Synthesis of 1,8-di(40-guanidinophenyl)naphthalene
dihydrochloride 1ꢀ2HCl
To a suspension of 1ꢀBoc4 (30 mg, 37.9
mmol) in Et2O (15 mL) at
0 ꢂC was added 10 mL of 1 M HCl. The reaction mixture was stirred
at 0 ꢂC for 10 min, then at room temperature for 7 h. The reaction
(water layer) was monitored by 1H NMR (D2O) to confirm the dis-
appearence of the Boc group. To complete the deprotection, 5 mL of
11 M HCl was added to the reaction mixture and stirred at room
temperature for an additional 4 h. After the addition of distilled
water (20 mL x 2), the water phase was separated, then concen-
trated to provide the title compound (17 mg, 93%).
4.4. Fluorescence titrations
A solution of the diguanidine 1 was prepared (3e25
mM in
Colorless solid; mp 250.4 ꢂC (dec.); 1H NMR (500 MHz,
DMSO), and an aliquot (3 mL) was transferred to a 1 cm fluores-
cence tube. To this solution was dropwise added a stock solution of
the dicarboxylic acid or diphosphonic acid (0.3e25 mM in DMSO)
in small portions. The fluorescence spectra were recorded by
excitation at 313 nm. The association constants were calculated
using the program HYPSPEC [12] and are summarized in Table 3.
DMSO‑d6)
d
¼ 9.82 (brs, 2H, NH), 8.10 (dd, J ¼ 8.3, 1.2 Hz, 2H), 7.65
(dd, J ¼ 8.1, 7.1 Hz, 2H), 7.41 (dd, J ¼ 7.1, 1.3 Hz, 2H), 7.35 (brs, 8H,
NH), 6.97 (d, J ¼ 8.5 Hz, 4H), 6.82 (d, J ¼ 8.4 Hz, 4H). 13C NMR
(125 MHz, DMSO‑d6);
d
¼ 155.9 (Cq), 140.7 (Cq), 138.7 (Cq), 135.1
(Cq), 132.7 (Cq), 130.8 (CH), 130.6 (Cq), 129.0 (CH), 128.5 (Cq), 125.5
(CH), 123.2 (CH). Anal. Calcd. for C24H22N6ꢀ3.4HCl: C:55.60, H:4.94,
N:16.21. Found: C:55.35, H:5.05, N:16.61.
4.5. Computational methods
4.1.6. Synthesis of 1,8-di(40-guanidinophenyl)naphthalene 1
The ground-state geometries were fully optimized using the
density functional theory (DFT) with the B3LYP hybrid functional at
the basis set level of 6e31G*. The frequency calculations allowed
verification that these structures did not present imaginary fre-
quencies and we had global minima. All of the calculations were
To a stirred solution of 4 M NaOH (13 mL), an aqueous solution
of 1,8-di(40-amidinophenyl)-naphthalene dihydrochloride 1ꢀ2HCl
(64 mg, 0.14 mmol, 10 mL) was dropwise added at 0 ꢂC over 15 min,
and additionally stirred at 0 ꢂC for 40 min. The resulting precipitate
10

T. Kusukawa, R. Mura, M. Ooe et al.
Tetrahedron 77 (2021) 131770
(b) Y. Deng, J.A. Roberts, S.M. Peng, C.K. Chang, D.G. Nocera, Angew. Chem. Int.
Ed. Engl. 36 (1997) 2124;
performed with Gaussian 09W [13].
(c) A. Kraft, L. Peters, H.R. Powell, Tetrahedron 58 (2002) 3499;
(d) T. Kusukawa, E.A. Tessema, Y. Hoshihara, Chem. Lett. 47 (2018) 1395;
(e) T. Kusukawa, H. Aramoto, T. Umeda, Y. Kojima, Tetrahedron 75 (2019)
1293;
(f) T. Kusukawa, K. Toyama, S. Takeshita, S. Tanaka, Tetrahedron 68 (2012)
9973;
Author contributions
T.K. designed study (conceptualization); T.K., R.M., M.O., R.S.,
A.N. implemented study; T.K., R.M., M.O., R.S., A.N. generated data;
T.K., R.M., M.O., R.S., A.N. did data curation and formal analysis; T.K.
wrote the original draft; T.K. reviewed and edited the manuscript;
T.K. took care of <grant-highlight > funding</grant-highlight >
acquisition and project management.
(g) T. Kusukawa, S. Tanaka, K. Inoue, Tetrahedron 70 (2014) 4049;
(h) T. Kusukawa, K. Inoue, H. Obata, R. Mura, Tetrahedron 73 (2017) 661.
[4] (a) P. Blondeau, M. Segura, R. Perez-Frenandes, J. de Mendoza, Chem. Soc. Rev.
36 (2007) 198;
(b) M. Pushina, P. Anzenbacher Jr., Chem. Commun. 53 (2017) 10074;
(c) M.D. Best, S.L. Tobey, E.V. Anslyn, Coord. Chem. Rev. 240 (2003) 3;
(d) K.A. Schug, W. Lindner, Chem. Rev. 105 (2005) 67;
Declaration of competing interest
(e) C. Schmuck, Coord. Chem. Rev. 250 (2006) 3053;
(f) M. Haj-Zaroubi, N.W. Mitzel, F.P. Schmidtchen, Angew. Chem. Int. Ed. 41
(2002) 104;
(g) B. Linton, A.D. Hamilton, Tetrahedron 55 (1999) 6027;
(h) W. Wang, J. Gu, X. Zou, W. Tong, H. Gong, Tetrahedron Lett. 56 (2015)
2684;
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
(i) M. Sekutor, K. Mlinaric-Majerski, Tetrahedron Lett. 55 (2014) 6665;
(j) M. Irfan Ashiq, B.F. Tesfatsion, F. Gaggini, S. Dixon, J.D. Kilburn, Chem. Eur J.
16 (2010) 12387;
Acknowledgments
(k) C.L. Beck, S.A. Berg, A.H. Winter, Org. Biomol. Chem. 11 (2013) 5827. Beck
C. L.; Winter A. H. J. Org. Chem. 2014, 79, 3152.
[5] K. Feichtinger, C. Zapf, H.L. Sings, M. Goodman, J. Org. Chem. 63 (1998) 3804.
[6] I. Antol, Z. Glasovac, D. Margetic, R. Crespo-Otero, M. Barbatti, J. Phys. Chem.
120 (2016) 7088.
[7] For the complexation of the diguanidine 1 and diphosphonic acid 7a, two
different diffusion coefficients (molecular volumes) were obtained (derived
from 1: V ¼ 1042 Å3, derived from 7a: V ¼ 524 Å3) and the large molecular
volumes were observed even in the dissociated (weak binding) spectrum. In
the DOSY spectrum, the larger molecular volume will be obtained in the
separately observed spectrum for the weak complex than the strongly binding
complex, and these separately observed volumes (Diffusion Coefficients) will
be changed by the parameter setting (Big Delta, Small Delta) during the
measurement. Therefore, in the weak binding complex, the obtained molec-
ular volume should not discuss quantitatively.
This study was supported by KAKENHI (18K04634) from the
Ministry of Education, Culture, Sports, Science, and Technology
(MEXT), Japan. This study was the result of using research equip-
ment shared in the MEXT Project for promoting public utilization of
advanced research infrastructure (Program for supporting intro-
duction of new sharing system) Grant Number JPMXS0421800120.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2020.131770.
[8] Recently, the synthesis of the 1,8-naphthalenediboronic anhydride was
independently reported A.S. Scholz, J.G. Massoth, M. Bursch, J.-M. Mewes,
T. Hetzke, B. Wolf, M. Bolte, H.-W. Lerner, S. Grimme, M. Wagner, J. Am. Chem.
Soc. 142 (2020) 11072.
References
[9] M.W. Ghosn, C. Wolf, J. Org. Chem. 75 (2010) 6653.
[10] T. Aotsuka, H. Kanazawa, K. Kumazawa, PCT Int. Appl. (2009). WO
2009072581.
[1] (a) D. Curiel, M. Mas-Montoya, G. Sanchez, Coord. Chem. Rev. 284 (2015) 19
(and references cited therein);
(b) M. Shome, N. Mishra, Indian J. Adv. Chem. Sci. 4 (2016) 56;
(c) A.E. Hargrove, S. Nieto, T. Zhang, J.L. Sessler, E.V. Anslyn, Chem. Rev. 111
(2011) 6603 (and references cited therein);
[11] D. Wu, A. Chen, C.S. Johnson Jr., J. Magn. Reson. 115 (1995) 260.
[12] P. Gans, A. Sabatini, A. Vacca, Talanta 43 (1996) 1739.
[13] Gaussian 09, Revision C. 01, M.J. Frisch, G.W. Trucks, H.B. Schlegel,
G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov,
J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi,
N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi,
C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski,
G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas,
J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian, Inc., Wallingford CT,
2010.
(d) S. Lee, K.K.Y. Yuen, K.A. Jolliffe, J. Yoon, Chem. Soc. Rev. 44 (2015) 1749;
(e) D. Zhang, J.R. Cochrane, A. Martinez, G. Gao, RSC Adv. 4 (2014) 29735.
[2] (a) N.A. Esipenko, P. Koutnik, T. Minami, L. Mosca, V.M. Lynch, G.V. Zyryanov,
P. Anzenbacher Jr., Chem. Sci. 4 (2013) 3617;
(b) Y. Liu, M. Bonizzoni, J. Am. Chem. Soc. 136 (2014) 14223;
(c) K. Kim, O.G. Tsay, D.A. Atwood, D.G. Churchill, Chem. Rev. 111 (2011) 5345;
(d) J.Y. Lee, Y.H.J. Lee, Anal. Chem. 69 (2014) 909;
(e) N.A. Esipenko, P. Koutnik, T. Minami, L. Mosca, V.M. Lynch, G.V. Zyryanov,
P. Anzenbacher Jr., Chem. Sci. 4 (2013) 3617;
(f) Y. Liu, M. Bonizzoni, J. Am. Chem. Soc. 136 (2014) 14223;
(g) T. Kusukawa, H. Nagano, K. Nakaguchi, S. Takeshita, Y. Harumoto, Tetra-
hedron 74 (2018) 465;
(h) T. Kusukawa, R. Mura, Y. Ohtagaki, M. Ooe, Tetrahedron 76 (2020) 131065.
[3] (a) D. Papoutsakis, J.P. Kirby, J.E. Jackson, D.G. Nocera, Chem. Eur J. 5 (1999)
1474;
11