One click to access push-triazole-pull fluorophores incorporating a pyrimidine moiety: Structure-photophysical properties relationships

Article abstract of DOI:10.1002/ejoc.201201033

Using copper-catalysed Huisgen 1,3-dipolar cycloaddition, we describe the synthesis of new A-π-D compounds containing a pyrimidine moiety as π-acceptor (A) and various para-substituted benzene rings as donors (D). Structure-photophysical properties relationships revealed the triazole ring to be a better π-conjugated linker than the triple bond. New push-triazole-pull (pyrimidine-triazole-para-substituted phenyl group) fluorophores were synthesized by using click chemistry, and were found to exhibit interesting photophysical properties.

Full text of DOI:10.1002/ejoc.201201033

FULL PAPER
DOI: 10.1002/ejoc.201201033
One “Click” to Access Push–Triazole–Pull Fluorophores Incorporating a
Pyrimidine Moiety: Structure–Photophysical Properties Relationships
Anne-Sophie Cornec,[a,b,c] Christine Baudequin,*[a,b,c] Catherine Fiol-Petit,[a,b,c]
Nelly Plé,[a,b,c] Georges Dupas,[a,b,c] and Yvan Ramondenc[a,b,c]
Keywords: Click chemistry / Nitrogen heterocycles / Fluorescence / Solvatochromism / Density functional calculations
Using copper-catalysed Huisgen 1,3-dipolar cycloaddition,
we describe the synthesis of new A-π-D compounds contain-
ing a pyrimidine moiety as π-acceptor (A) and various para-
substituted benzene rings as donors (D). Structure–photo-
physical properties relationships revealed the triazole ring to
be a better π-conjugated linker than the triple bond.
Huisgen 1,3-dipolar cycloaddition (CuAAC: copper-cata-
lysed azide–alkyne cycloaddition) by Sharpless and Meldal
ten years ago,[10] triazole rings have been used as compo-
nents of several fluorogenic probes,[11] as chelating ligands
in fluorescent metal sensors,[12] and less frequently as link-
ers in the conjugated backbone of push–pull fluoro-
phores.[13]
Introduction
During the last decade, a great deal of effort has been
put into the design and synthesis of new push–pull organic
dyes[1] due to their non-linear optical (NLO) properties,[2]
in particular in optoelectronics,[3] biological imaging,[4] and
dye-sensitized solar cells.[5] These push–pull dyes have also
attracted attention as fluorophores, and most of them act
as fluorescent sensors, as they have an emission response
that depends on their environment.[6] Generally, these push–
pull chromophores have an A-π-D structure, where A is an
acceptor moiety and D is an electron-donating group con-
nected by a π-conjugated linker. They have received much
interest due to their high polarizability. Extensive investi-
gations have been carried out into the synthesis of new A-π-
D chromophores and the evaluation of their light-emitting
properties.
Due to its electron-withdrawing character, the pyrimidine
moiety was chosen as the acceptor part incorporated into
the compounds reported in this paper. This diazine moiety
has already been incorporated as an electron-withdrawing
core or end-cap into linear, star- and banana-shaped oligo-
mers that show good light-emitting properties[7,8] and two-
photon absorption.[7,9]
In some cases, push–triazole–pull (PTP) chromophores
incorporating 1,2,3-triazole rings as linkers have been re-
ported to show low to moderate fluorescent properties.
However, some of them show a switchable fluorescence, be-
ing activated by the addition of metal cations.[13b] Others
have been developed as dual-fluorescent pH sensors,[13c]
and it may be noted that some of them have good quantum
yields.[13a] Previously, the synthesis and light-emitting prop-
erties of D-π-A-π-D or A-π-D fluorophores with diazine
moieties as acceptor (A), ethynyl or vinylene linkers (π), and
aromatic rings (D) have been reported in the literature. The
main advantages of the ethynyl linker over its vinylene
counterpart are the lack of possible (Z)/(E) isomerism and
its higher stability.[14] With the aim of comparing the influ-
ence of the backbones of A-π-D fluorophores on their light-
emitting properties, and to establish structure–photophysi-
cal properties relationships, “click chemistry” has been used
to incorporate a triazole linker instead of an ethynyl one to
access new PTP backbones.
The aim of this work was to synthesize a wide range of
new fluorophores to determine the influence of the different
parts (acceptor, π-conjugated linker, and donor) on the op-
tical properties. The use of readily available and cheap non-
fluorescent starting materials to synthesize new fluoro-
phores containing a triazole ring as the transmitter of con-
jugation was an interesting challenge. The light-emitting
properties were determined, and the results were compared
to theoretical calculations at the DFT6-31G* level. A study
of emission solvatochromism was also performed to deter-
mine the influence of solvent polarity on the intramolecular
charge transfer (ICT).
To extend the conjugation along the scaffold of the push–
pull chromophores, various conjugated linkers have been
described, such as ethynyl or vinyl linkers. More recently,
and since the independent discoveries of the CuI-catalysed
[a] Université de Rouen, Laboratoire COBRA UMR 6014 and FR
3038, IRCOF,
1 rue Tesnière, 76821 Mont-Saint-Aignan CEDEX, France
Fax: +33-2-35522971
E-mail: christine.baudequin@univ-rouen.fr
Homepage: http://ircof.crihan.fr/V2/
rubrique.php3?id_rubrique=77
[b] INSA de Rouen, Avenue de l’Université,
76800 St Etienne du Rouvray, France
[c] CNRS délégation Normandie,
14 Rue Alfred Kastler, 14052 Caen CEDEX, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201033.
1908
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Push–Triazole–Pull Fluorophores
Scheme 1. Synthesis of 2-azido-4,6-dimethylpyrimidine.
Table 1. Synthesis of push–triazole–pull fluorophores by CuAAC.
Results and Discussion
Compound[a]
R
Isolated yield [%]
Azidopyrimidine starting material 1 was obtained by two
pathways A and B (Scheme 1). Pathway A involved nucleo-
philic aromatic substitution of 2-chloro-4,6-dimethylpyrim-
idine by NaN3 to give 1 in a moderate 44% yield. Path-
way B, involving a cyclodehydration of pentane-2,4-dione
with 5-aminotetrazole, gave 1 in an excellent yield of
98%.[15] Although pathway A was discarded due to a lower
yield, this nucleophilic substitution has the advantage that
it could potentially be applied to a wider range of π-de-
ficient azaheterocycles.
3a
3b
3c
3d
3e
3f
NMe2
NPh2
NH2
OMe
F
CH3
H
79
96
58
99
82
72
89
75
3g
3h
CF3
[a] All reactions were performed on a 0.03 mmol scale with equi-
molar proportions of azide 1 and alkyne 2.
A tautomeric equilibrium between the major tetrazolo
form (i.e., 1b) and 2-azido-4,6-dimethylpyrimidine (1a) was
observed by 1H NMR spectroscopy in CDCl3 (see Support-
ing Information). Tetrazole 1b arises from a spontaneous
cyclization between the azido group and the adjacent pyr-
imidine nitrogen atom (Scheme 1). Such an equilibrium has
been described previously in π-deficient heterocycles like
pyrimidine that have an azido substituent at C-2.[15,16]
Generally, to induce the copper-catalysed Huisgen 1,3-
dipolar cycloaddition, the use of CuI salts is necessary.
Classical conditions involving the in situ reduction of CuII
salts by sodium ascorbate were used to synthesize 1,4-di- Scheme 3. Synthesis of 6, an isomer of 3a.
substituted-1,2,3-triazolo derivatives 3a–h (Scheme 2) in
good to excellent yields (58–99%, Table 1). This efficient
method allowed us to access various chromophores.
ine ring was synthesized. The CuAAC of commercially
available 4-ethynyl-N,N-dimethylaniline (2a) and 4-azido-
benzonitrile[19] (7) gave PTP fluorophore 8 in a low yield
(Scheme 4).
Scheme 2. Copper-catalysed azide–alkyne cycloaddition.
Scheme 4. CuAAC synthesis of cyanobenzene PTP derivative.
A similar strategy was used to obtain compound 6
(Scheme 3), a regioisomer of 3a, by carrying out the “click”
reaction between 4-azido-N,N-dimethylaniline[17] (5) and 2-
ethynyl-4,6-dimethylpyrimidine[18] (4).
The final part of this study consisted of the evaluation
of the influence of the π-linker on the photophysical prop-
In order to study the influence of the electron-with- erties. To this end, an ethynyl linker was introduced into the
drawing part on the photophysical properties, an analogue backbone in place of the triazole by a Sonogashira cross-
of 3a bearing a 4-cyanophenyl moiety instead of a pyrimid- coupling reaction (Scheme 5), which led to 10 in 81% yield.
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C. Baudequin et al.
FULL PAPER
(244 nm) and λem (389 nm) and a dramatic decrease of the
quantum yield ΦF (0.01). An examination of the data for
compounds 3e–h reveals similar values for the absorption
wavelengths λabs (244–254 nm). Compounds 3g and 3h,
with a hydrogen atom or an electron-withdrawing CF3
group, are non-emissive, whereas slightly electron-donating
groups such as the methyl group (inductive donor effect) in
compound 3e or the fluorine atom (deactivating substitu-
ent, mesomeric donor effect) in compound 3f result in low
emission wavelengths λem (345–364 nm) and lower quantum
yields ΦF (Ͻ0.01). Generally, large Stokes shifts were ob-
served. For the first series (compounds 3a–h), the corre-
Scheme 5. Sonogashira cross-coupling reaction.
All new compounds were characterized by using a vari- lations of the maximum absorbance and emission wave-
ety of analytical techniques. These materials are perfectly lengths with the Hammett reaction constants[20] are repre-
stable in the solid state, and can be stored without special sented in Figure 1 and were found to be linear.
precautions.
UV/Vis and Photoluminescence (PL) Data
The optical properties of the fluorophores synthesized
(3a–h, 6, 8, and 10) were investigated in CH2Cl2 at 25 °C
by UV/Vis and photoluminescence (PL) spectroscopy.
These data are summarized in Table 2. All of the com-
pounds have absorption wavelengths (λabs) in the UV region
(244–357 nm), and have their emission wavelengths (λem) in
the UV or green region (345–527 nm). For compounds 3a–
h, the fluorescence properties are influenced by the nature
of the para substituent on the benzene ring.
Figure 1. Linear dependences of the maximum absorbance (dia-
monds) and emission (dots) wavelengths on the Hammett substitu-
ent constants for compounds 3a–h.
Table 2. UV/Vis and photoluminescence data.
[b]
Compound[a] λabs,max
ε
λem,max
[nm]
ΦF
Stokes shift
[cm–1]
To evaluate the influence of the structural parts of the
scaffold on the light-emitting properties, we compared the
data of compounds 3a, 6, 8, and 10. The backbone of these
chromophores differs in the nature of the π-linker between
the pyrimidine ring and the para-(dimethylamino)phenyl
group for 3a, 6, and 10, whereas compounds 3a and 8 differ
in the nature of the electron-withdrawing ring, a pyrimidine
for 3a, and a benzonitrile for 8.
Triazolo isomers 3a and 6 show similar photophysical
properties in terms of both quantum yields and Stokes
shifts. However, hypsochromic shifts were observed in the
absorption and emission wavelengths for 6 and compared
to its analogue 3a, which had a higher molar extinction
coefficient (ε). Replacement of the triazole ring in 3a by the
ethynyl linker in compound 10 resulted in a higher molar
extinction coefficient ε (42161 vs. 24386), but a dramatic
[nm]
[m–1 cm–1]
3a
3b
3c
3d
3e
3f
3g
3h
6
289
333
267
254
244
250
246
254
250
285
357
24386
21427
25698
46211
18069
18943
25697
20753
13893
19887
42161
486
476
476
389
345
364
–
0.47[c]
0.45[c]
0.30[c]
0.01[c]
Ͻ0.01[c]
Ͻ0.01[c]
–
14026
9022
16445
13663
11998
12527
–
–
–
–
434
527
447
0.33[c]
0.36[c]
0.04[d]
16958
16112
5640
8
10
[a] All spectra were recorded in CH2Cl2 at 25 °C. [b] Quantum yield
(Ϯ10%) of fluorescence determined by using harmane in 0.1 m
H2SO4 as a standard (ΦF = 0.83). [c] Excitation at 300 nm. [d] Exci-
tation at 360 nm.
A comparison of the amino compounds 3a–c reveals that decrease of both quantum yield ΦF (0.04 vs. 0.47) and
the λabs values are dependent on the substituents on the Stokes shift (5640 vs. 14026) was observed. When the pyr-
nitrogen atom. With a dimethylamino group (in compound imidine ring was replaced by the benzonitrile group, a com-
3a), the λabs and λem values and the quantum yield ΦF were parison of the data of compounds 3a and 8 revealed similar
found to be higher than with an amino group (in compound values for the absorption wavelength and quantum yield,
3c). This bathochromic shift is due to the highly electron- and a slightly higher Stokes shift for 8. Moreover, a signifi-
donating character of the dimethylamino group. The di- cant redshift of the emission wavelength was observed for
phenylamino group (in compound 3b) resulted in a high compound 8. These results could indicate that compound 8
λabs (333 nm) and a good quantum yield ΦF (0.45). The is a better fluorophore than 3a, but in spite of this, the
methoxy group (in compound 3d), which is a less effective much better yields observed in the synthesis of 3a make this
donor than the amino group, gave lower values for λabs compound attractive for further applications.
1910
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Push–Triazole–Pull Fluorophores
Molecular Orbital Calculations
established that the low percentage of exact orbital ex-
change in B3LYP can lead to an underestimation of the
charge-transfer interactions for extended systems.[24] The
use of CAM-B3LYP, which is a Coulomb-attenuated func-
tional, usually provides significantly improved long-range
excitation energies.[25] However, it must be noted that the
use of the CAM-B3LYP functional gave bad results, proba-
bly because our systems are not very extended, so allowing
the classic B3LYP functional to still be efficient. Moreover,
it can be seen that the HOMO–LUMO gaps are also in
good agreement with the observed absorption properties.
Increasing the strength of the donor group connected to the
benzene ring led to a decrease in the gap, which explains
the bathochromic effect. The lower absorption wavelength
observed with compound 8 is due to the above-mentioned
deconjugation of the (dimethylamino)phenyl moiety.
Changing the triazole linker (in compound 3a) into a triple
bond (in compound 10) slightly increased the HOMO–
LUMO gap. However, this fact does not explain the ba-
thochromic shift observed. It must also be pointed out that
the UV spectrum of compound 10 showed two absorption
bands, probably due to the topology of the triple bond.
These two absorption bands were nicely predicted by TD-
DFT calculations (Table 4), and are related to different
transitions: HOMO–LUMO for the higher (calculated at
370 nm) and mainly (HOMO–1)–LUMO for the lower (cal-
culated at 240 nm). For these reasons, comparisons are not
easy to establish, and the above mentioned redshift could
be simply explained by the triazole linker’s having a better
electronic transfer than that of the triple bond. Moreover,
the fact that the LUMO of 10 is still slightly located on the
phenyl ring, in contrast to the LUMO of 3a, confirms the
better efficiency of the triazole linker, and could explain the
significant difference in the quantum yield.
To gain insight into the effect of the various substituents
on the geometrical and electronic properties of the chromo-
phores, density functional theory (DFT) and time-depend-
ent DFT (TD-DFT) calculations were carried out on the
synthesized compounds 3a–h, 6, and 10 by using the
Gaussian 03 and 09 program packages.[21] The geometries
of all of the studied systems were optimized by using the
B3LYP exchange–correlation hybrid functional together
with the 6-31G** basis set. The in vacuo structures were
further optimized by applying the self-consistent reaction
field (SCRF) under the polarizable continuum model (C-
PCM) incorporating dichloromethane as the solvent. The
DFT-computed HOMO (highest occupied molecular or-
bital) and LUMO (lowest unoccupied molecular orbital)
frontier molecular orbitals (FMOs) of chromophores 3a
and 10 are presented in Table 3 (see Supporting Infor-
mation for compounds 3b–h and 6). Examination of the
computer-modelled structures of the studied systems re-
veals some common features, such as an absolutely copla-
nar structure, except for 6, in which the phenyl ring is
slightly out of the plane of the rest of the molecule (dihedral
angle 35.9 °). A comparison of the electronic structures re-
veals that the localization and nature of the HOMO and
LUMO are almost the same for all of the individual homo-
logues (see Table 3), the only difference being in the energies
of these FMOs, which depend on the structure.[22] The
HOMO orbitals of all of the chromophores showed the
same character, being localized on the benzene and triazole
rings. Changing the nature of the R group connected to the
benzene ring had a great influence on the HOMO energy
level.
Table 3. HOMO and LUMO levels of chromophores 3a and 10.
Table 4. HOMO–LUMO gaps and TD-DFT predictions of λabs
.
Compound λabs,max λabs,calcd. Strongest
R
HOMO–LUMO
[nm]
[nm]
f
gap [eV]
3a
3b
3c
3d
3e
3f
3g
3h
6
289
333
267
254
244
250
246
254
250
281.2
333.2
267.8
254.9
245.5
249.4
245.1
255.7
244.6
0.603
0.566
0.790
0.706
0.704
0.921
0.775
0.326
0.617
1.183
NMe2
NPh2
NH2
OMe
F
CH3
H
CF3
3.57
3.51
3.77
4.18
4.54
4.47
4.55
4.79
4.11
3.67
NMe2
NMe2
10
242/357 240/370
To shed some light on the optical absorption process, we
used TD-DFT to study the vertical excitation in chromo-
phores 3a–h, 6, and 10. Singlet vertical excitation energies
were determined by using both B3LYP and CAM-
B3LYP[23] exchange–correlation functionals. The results of
Solvatochromism
The photophysical properties of regioisomers 3a and 6
the TD-DFT calculations with the B3LYP functional are were evaluated in different solvents. The aim of this study
reported in Table 4, in which the observed absorption wave- was to explore the effect of solvent polarity on the photo-
length is compared to the calculated value corresponding physical properties of the fluorophores and to correlate
to the largest oscillator strength (f). In most cases, the cal- these effects to their structures. The photoluminescence
culated and experimental values are well correlated, with a data in aprotic solvents are summarized in Table 5, Fig-
maximum difference of 2.8% for compound 3a. It is well ures 2, 3, 4, and 5. When a protic polar solvent such as
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C. Baudequin et al.
FULL PAPER
MeOH was used, a complete quenching of the fluorescence end-capping fluorophores in the ground state. In contrast,
was observed with both of the regioisomers. The ab- a solvent-polarity-dependent emission was shown by both
sorbance spectra showed only a slight dependence on the regioisomers 3a and 6. For both of these fluorophores, the
solvent polarity, which is characteristic of an insignificant maximum emission wavelength was plotted against ET(30)
intramolecular interaction between the donor and acceptor (the Dimroth–Reichardt polarity parameter; see Supporting
Table 5. Optical properties of 3a and 6 in different solvents.
Compound[a]
Solvent
λabs,max [nm]
ε [m–1 cm–1]
λem,max [nm][b]
Stokes shift [cm–1]
3a
toluene
dioxane
THF
EtOAc
CHCl3
CH2Cl2
DMF
305
284
278
284
289
289
288
291
288
15914
26057
1571
15090
16042
24386
19676
23177
19528
432
456
482
480
469
486
538
556
544
9639
13281
14464
14464
13280
14026
16134
16379
16340
DMSO
MeCN
6
toluene
dioxane
THF
EtOAc
CHCl3
CH2Cl2
DMF
305
301
305
300
305
250, 306
306
311
14659
18220
15291
19604
15807
390
421
428
428
420
434
488
503
496
7146
9469
9422
9968
9146
13893, 12834
18485
16958, 9638
12188
12274
13061
DMSO
MeCN
18809
18014
301
[a] All spectra were recorded at 25 °C. [b] Excitation at 300 nm.
Figure 4. Structure and colour changes of compound 6 in various
solvents.
Figure 2. Structure and colour changes of compound 3a in various
solvents.
Figure 3. Normalized emission spectra of compound 3a in various
solvents.
Figure 5. Normalized emission spectra of compound 6 in various
solvents.
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Push–Triazole–Pull Fluorophores
Information).[26] Furthermore, broad structureless emission
and larger Stokes shifts were observed when the solvent po-
larity was increased. Thus, a redshift of 124 and 113 nm for
3a and 6, respectively, was observed on changing from tolu-
ene to DMSO, which is characteristic of internal charge
transfer upon excitation.
0.15 mmol) was added, and the mixture was stirred for 5 min to
give colourless, homogeneous mixture. Pentane-2,4-dione
a
(0.15 mL, 1.50 mmol) and 1H-tetrazol-5-amine (127.5 mg,
1.50 mmol) were added, and the resulting mixture was stirred at
room temperature for 3 h. NH4Cl (satd. aq.; 15 mL) was added,
and the resulting suspension was extracted with EtOAc (5ϫ
30 mL). The organic extracts were dried with Na2SO4 and concen-
trated in vacuo to give a mixture of compounds 1a and 1b (219 mg,
98%, 1a and 1b combined) as a white powder.
Conclusions
1
Data for 1a: H NMR (300 MHz, CDCl3): δ = 2.42 (s, 6 H, CH3),
6.76 (s, 1 H, 5-H) ppm. 13C NMR (75 MHz, CDCl3): δ = 23.9
By using an efficient click-chemistry strategy, push–tri-
azole–pull chromophores were synthesized in good to excel-
lent yields, and interesting fluorescence properties were ob-
served. The influence of the para substituent borne by the
phenyl ring was evaluated, and this showed that increasing
the strength of the electron-donating group increased the
fluorescence properties and induced a bathochromic shift.
We also demonstrated that a triazole linker offers better
photoluminescence properties than an ethynyl linker.
Furthermore, theoretical calculations support our experi-
mental results. The PTPs 3a and 6 showed strong emission
solvatochromism, and redshifted broad structureless bands
were obtained in polar aprotic solvents, which is character-
istic of intramolecular charge-transfer in excited states.
Further development of new chromophores and evalu-
ation of these N-heterocyclic chelators in ligand–metal in-
teractions are currently underway in our laboratory.
(CH3), 116.2, 161.8, 169.3 ppm.
1
Data for 1b: H NMR (300 MHz, CDCl3): δ = 2.75 (s, 3 H, CH3),
2.95 (s, 3 H, CH3), 6.94 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 17.1, 25.5, 112.8, 144.7, 155.2, 169.1 ppm. HRMS: calcd. for
C6H8N5 [M + H]+ 150.0780; found 150.0777.
General Procedure for the [3 + 2] Cycloaddition of Azides and Ter-
minal Alkynes: Sodium ascorbate (9.3 mg, 0.047 mmol) and
CuSO4·5H2O (5.9 mg, 0.024 mmol) were added to a mixture of 5,7-
dimethyltetrazolo[1,5-a]pyrimidine (1; 35.0 mg, 0.235 mmol) and
alkyne 2 (0.235 mmol) in a mixture of H2O/tBuOH (1:1, 1 mL).
The mixture was stirred at 60 °C for 72 h. Then NH3 (dilute aque-
ous; 10 mL) was added, and the crude mixture was extracted with
EtOAc (3ϫ 10 mL). The organic layer was dried with MgSO4 and
filtered, and the solvents were evaporated. The title triazolyl com-
pounds were purified by column chromatography (EtOAc).
4-[1-(4,6-Dimethylpyrimidin-2-yl)-1H-1,2,3-triazol-4-yl]-N,N-di-
methylaniline (3a): By using the general procedure and starting
from 1 (32 mg) and 4-ethynyl-N,N-dimethylaniline (2a; 88 mg), title
compound 3a (27 mg, 79%) was isolated as a yellow powder; m.p.
Experimental Section
1
199–201 °C. H NMR (300 MHz, CDCl3): δ = 2.60 (s, 3 H), 2.99
(s, 6 H), 6.78 (d, J = 8.97 Hz, 2 H), 7.05 (s, 1 H), 7.82 (d, J =
8.97 Hz, 2 H), 8.66 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ
= 24.2, 40.6, 112.5, 116.8, 118.3, 119.6, 127.1, 148.5, 150.7, 154.3,
General Remarks: All chemicals were purchased from commercial
sources and used without further purification unless otherwise
specified. Analytical thin layer chromatography was performed on
silica gel plates (Merck® TLC Silica gel 60 F254), and compounds
were detected by irradiation with UV light (254 nm). Chromato-
graphic purification of compounds was achieved with silica gel
(mesh size 60–80 μm). IR spectra were recorded with a Perkin–
Elmer Spectrum 100 FT IR spectrometer. HRMS spectra (ESI+)
were recorded with an LC Waters Acquity coupled to a Waters
LCT Premier XE instrument. Elemental analyses were performed
with a Carlo Erba 1106 apparatus. Measurement accuracy is
around Ϯ0.4% on C. Melting points were measured with a Kofler
bench. The 1H, 19F, and 13C NMR spectra were recorded with a
Bruker Avance spectrometer operating at 300, 282, and 75 MHz,
respectively. The chemical shifts δ are reported in parts per million
(ppm), and the residual solvent peaks were used as an internal ref-
erence [δ = 7.26 (1H) and 77.16 (13C) ppm for CDCl3; δ = 0.00
(19F) ppm for CFCl3]. Data appear in the following order: chemical
shift in ppm, multiplicity (s, singlet; d, doublet; t, triplet; q, quartet;
m, multiplet), coupling constant J in Hz, number of protons.
169.6 ppm. IR (neat): ν = 3167, 2924, 2856, 2810, 1657, 1599, 1534,
˜
1510, 1421, 1345, 1227, 1194 cm–1. HRMS: calcd. for C16H19N6 [M
+ H]+ 295.1676; found 295.1671.
4-[1-(4,6-Dimethylpyrimidin-2-yl)-1H-1,2,3-triazol-4-yl]-N,N-di-
phenylaniline (3b): By using the general procedure and starting from
1 (45 mg) and 2b (81 mg), title compound 3b (120 mg, 96%) was
1
isolated as a white powder; m.p. 200–202 °C. H NMR (300 MHz,
CDCl3): δ = 2.62 (s, 1 H), 7.02–7.16 (m, 9 H), 7.25–7.30 (m, 4 H),
7.82 (d, J = 8.7 Hz, 2 H), 8.74 (s, 1 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 24.2, 117.9, 123.3, 123.7, 124.8, 127.2, 129.5, 147.6,
148.3, 169.8 ppm. IR (neat): ν = 3166, 2922, 2853, 1599, 1539,
˜
1488, 1470, 1424, 1329, 1269, 1240, 1177 cm–1. HRMS: calcd. for
C26H23N6 [M + H]+ 419.1984; found 419.1990.
4-[1-(4,6-Dimethylpyrimidin-2-yl)-1H-1,2,3-triazol-4-yl]aniline (3c):
By using the general procedure and starting from 1 (36 mg) and 4-
ethynylaniline (2c; 28 mg), title compound 3c (36 mg, 58%) was
isolated as a beige powder (58 %); m.p. 221–223 °C. 1H NMR
(300 MHz, CDCl3): δ = 2.59 (s, 6 H), 6.74 (d, J = 8.7 Hz, 2 H),
7.06 (s, 1 H), 7.73 (d, J = 8.7 Hz, 2 H), 8.66 (s, 1 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 24.1, 112.8, 115.3, 117.1, 119.6, 120.6,
2-Azido-4,6-dimethylpyrimidine (1a) and 5,7-Dimethyltetrazolo[1,5-
a]pyrimidine (1b)
Method A: A solution of 2-chloro-4,6-dimethylpyrimidine (1.06 g,
7.4 mmol) in DMF (48 mL) was treated with NaN3 (1.82 g,
31.3 mmol) at 100 °C for 21 h. The solvent was evaporated under
reduced pressure, and the residue was purified by silica gel flash
chromatography (EtOAc) to give 2-azido-4,6-dimethylpyrimidine
(486 mg, 44%, 1a and 1b combined).
127.4, 146.9, 148.3, 154.2, 169.7 ppm. IR (neat): ν = 3426, 3347,
˜
3241, 3176, 1640, 1616, 1602, 1534, 1504, 1472, 1421, 1348, 1299,
1226, 1182 cm–1. C14H14N6 (266.30): calcd. C 63.14, H 5.30, N
31.56; found C 63.34, H 5.03, N 31.60.
2-[4-(4-Methoxyphenyl)-1H-1,2,3-triazol-1-yl]-4,6-dimethylpyrim-
idine (3d): By using the general procedure and starting from 1
(35 mg) and 1-ethynyl-4-methoxybenzene (2d; 31 mg), title com-
Method B: CuCl2 (20.1 mg, 0.15 mmol) was dissolved in EtOH
(4.5 mL), resulting in a green solution. Sodium ascorbate (26.4 mg,
Eur. J. Org. Chem. 2013, 1908–1915
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1913

C. Baudequin et al.
FULL PAPER
pound 3d (66 mg, 99%) was isolated as a beige powder; m.p. 138–
140 °C. H NMR (300 MHz, CDCl3): δ = 2.56 (s, 6 H), 3.80 (s, 3
1168 cm–1. HRMS: calcd. for C16H19N6 [M + H]+ 295.1671; found
295.1666.
1
H), 6.93 (d, J = 8.85 Hz, 2 H), 7.03 (s, 1 H), 7.84 (d, J = 8.85 Hz,
2 H), 8.68 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 24.0,
55.4, 114.2, 117.6, 119.7, 122.8, 127.4, 147.7, 154.0, 159.8,
4-{4-[4-(Dimethylamino)phenyl]-1H-1,2,3-triazol-1-yl}benzonitrile
(8): By using the general procedure and starting from 4-azido-
benzonitrile (7;[15] 43 mg) and 4-ethynyl-N,N-dimethylaniline (2a;
43 mg), title compound 8 (9 mg, 10%) was isolated as a brown
169.6 ppm. IR (neat): ν = 3161, 2959, 2928, 2836, 1600, 1534, 1501,
˜
1472, 1441, 1345, 1250, 1176 cm–1. HRMS: calcd. for C15H15N5O
[M + H]+ 282.1355; found 282.1337.
1
powder; m.p. 239–241 °C. H NMR (300 MHz, CDCl3): δ = 3.02
(s, 1 H), 6.80 (d, J = 9 Hz, 2 H), 7.77 (d, J = 8.7 Hz, 2 H), 7.85 (d,
J = 8.7 Hz, 2 H), 7.97 (d, J = 8.7 Hz, 2 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 40.5, 112.1, 112.5, 115.3, 117.6, 118.0, 120.5,
2-[4-(4-Fluorophenyl)-1H-1,2,3-triazol-1-yl]-4,6-dimethylpyrimidine
(3e): By using the general procedure and starting from 1 (35 mg)
and 1-ethynyl-4-fluorobenzene (2e; 28 mg), title compound 3e
(52 mg, 82%) was isolated as a beige powder; m.p. 199–201 °C. 1H
NMR (300 MHz, CDCl3): δ = 2.57 (s, 6 H), 7.06–7.13 (m, 3 H),
7.86–7.91 (m, 2 H), 8.74 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 24.1, 115.7, 116.0, 118.2, 119.9, 126.3, 126.4, 127.8, 127.9,
147.0, 154.0, 161.2, 164.5, 169.7 ppm. 19F NMR (282 MHz,
127.1, 134.0, 140.2, 149.8, 150.9 ppm. IR (neat): ν = 3111, 2925,
˜
2852, 2230, 1618, 1608, 1570, 1502, 1409, 1354, 1223, 1034 cm–1.
HRMS: calcd. for C17H16N5 [M + H]+ 290.1346; found 290.1351.
4-[(4,6-Dimethylpyrimidin-2-yl)ethynyl]-N,N-dimethylaniline (10):
Triethylamine (5 mL) and THF (5 mL) were added to 2-iodo-4,6-
dimethylpyrimidine (9; 157.1 mg, 0.671 mmol), 4-ethynyl-N,N-di-
methylaniline (2a; 126.7 mg, 0.873 mmol), CuI (10.2 mg,
0.044 mmol) and PdCl2(PPh3)2 (16.5 mg, 0.024 mmol) under ar-
gon. The resulting mixture was heated at 70 °C for 72 h and then
filtered through Celite®. After purification by column chromatog-
raphy (EtOAc/petroleum ether, 1:1), title compound 10 (137 mg,
CDCl ): δ = –113.6 ppm. IR (neat): ν = 3167, 3068, 2922, 2853,
˜
3
1729, 1600, 1498, 1432, 1414, 1343, 1222, 1025 cm–1. HRMS: calcd.
for C14H13N5F [M + H]+ 270.1155; found 270.1161.
4,6-Dimethyl-2-(4-p-tolyl-1H-1,2,3-triazol-1-yl)pyrimidine (3f): By
using the general procedure and starting from 1 (35 mg) and 1-
ethynyl-4-methylbenzene (2f; 27 mg), title compound 3f (45 mg,
1
81%) was isolated as a beige powder; m.p. 173–175 °C. H NMR
1
72%) was isolated as a beige powder; m.p. 169–171 °C. H NMR
(300 MHz, CDCl3): δ = 2.50 (s, 6 H, CH3), 3.00 (s, 6 H, CH3), 6.64
(m, 2 H, HAr), 6.91 (s, 1 H, 5-H), 7.55 (m, 2 H, HAr) ppm. 13C
NMR (75 MHz, CDCl3): δ = 24.0, 40.1, 87.2, 89.5, 107.7, 111.5,
(300 MHz, CDCl3): δ = 2.38 (s, 3 H), 2.60 (s, 6 H), 7.07 (s, 1 H),
7.22 (d, J = 7.8 Hz, 2 H), 7.84 (d, J = 7.8 Hz, 2 H), 8.77 (s, 1 H)
ppm. 13C NMR (75 MHz, CDCl3): δ = 21.4, 24.1, 118.2, 119.8,
118.2, 134.1, 150.8, 153.2, 167.0 ppm. IR (neat): ν = 3092, 2919,
˜
126.1, 127.4, 129.6, 138.5, 148.0, 154.2, 169.7 ppm. IR (neat): ν =
˜
2861, 2807, 2202, 1603, 1576, 1522, 1430, 1358, 1343, 1224, 1180,
1167 cm–1. HRMS: calcd. for C16H18N3 [M + H]+ 252.1501; found
252.1502.
3163, 2958, 2918, 2851, 1602, 1539, 1474, 1436, 1426, 1347, 1232,
1029 cm–1. HRMS: calcd. for C15H16N5 [M + H]+ 266.1406; found
266.1411.
Supporting Information (see footnote on the first page of this arti-
4,6-Dimethyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyrimidine (3g): By
using the general procedure and starting from 1 (32 mg) and ethyn-
ylbenzene (2g; 88 mg), title compound 3g (48 mg, 89%) was iso-
lated as a white powder; m.p. 179–181 °C. 1H NMR (300 MHz,
CDCl3): δ = 2.60 (s, 6 H), 7.07 (s, 1 H), 7.35 (m, 1 H), 7.44 (m, 2
H), 7.94 (m, 2 H), 8.81 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 24.1, 118.5, 119.8, 126.1, 128.5, 128.9, 130.1, 147.8, 154.0,
1
cle): General procedures, characterization data, H and 13C NMR
spectra.
Acknowledgments
This work was supported by MENRT (Ministère Education Na-
tionale, Recherche et Technologie). We thank Dr. Anthony Romieu
(Université de Rouen, UMR 6014) and Dr. Sylvain Achelle (Insti-
tut des Sciences Chimiques de Rennes) for helpful discussions. We
also warmly thank Maxine Junker for her contribution to the solva-
tochromism study.
169.7 ppm. IR (neat): ν = 3176, 3062, 2918, 1600, 1538, 1473, 1429,
˜
1346, 1296, 1234, 1013 cm–1. C14H13N5 (251.29): calcd. C 66.92, H
5.21, N 27.87; found C 66.87, H 5.22, N 27.82.
4,6-Dimethyl-2-{4-[4-(trifluoromethyl)phenyl]-1H-1,2,3-triazol-1-
yl}pyrimidine (3h): By using the general procedure and starting
from 1 (35 mg) and 1-ethynyl-4-(trifluoromethyl)benzene (2h;
40 mg), title compound 3h (56 mg, 75%) was isolated as a white
powder; m.p. 213-215 °C. 1H NMR (300 MHz, CDCl3): δ = 2.59
(s, 6 H), 7.08 (s, 1 H), 7.66 (d, J = 8.4 Hz, 2 H), 8.04 (d, J = 8.1 Hz,
2 H), 8.88 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 24.1,
119.5, 120.1, 125.8, 125.9, 126.2, 133.6, 146.5, 153.9, 169.9 ppm.
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19F NMR (282 MHz, CDCl ): δ = –63.1 ppm. IR (neat): ν = 3170,
˜
3
3098, 2923, 2852, 1605, 1539, 1471, 1429, 1321, 1298, 1029,
1015 cm–1. HRMS: calcd. for C15H13N5F3 [M + H]+ 320.1123;
found 320.1126.
4-[4-(4,6-Dimethylpyrimidin-2-yl)-1H-1,2,3-triazol-1-yl]-N,N-di-
methylaniline (6): By using the general procedure and starting from
4-azido-N,N-dimethylaniline (5;[13] 39 mg) and 2-ethynyl-4,6-di-
methylpyrimidine (4;[14] 32 mg), title compound 6 (34 mg, 75%)
was isolated as a white powder; m.p. 117–119 °C. 1H NMR
(300 MHz, CDCl3): δ = 2.57 (s, 6 H), 3.03 (s, 6 H), 117–119 (d, J
= 9 Hz, 2 H), 6.97 (s, 1 H), 7.63 (d, J = 9 Hz, 2 H), 8.56 (s, 1 H)
ppm. 13C NMR (75 MHz, CDCl3): δ = 24.1, 40.5, 112.3, 118.7,
122.0, 122.8, 126.6, 150.7, 158.6, 167.3 ppm. IR (neat): ν = 3467,
˜
3141, 2922, 2807, 1611, 1589, 1525, 1430, 1363, 1344, 1278,
1914
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 1908–1915

Push–Triazole–Pull Fluorophores
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Received: August 1, 2012
Published Online: February 8, 2013
Eur. J. Org. Chem. 2013, 1908–1915
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1915