Regioselective Synthesis of Emission Color-Tunable Pyrazolo[1,5-a]pyrimidines with β,β-Difluoro Peroxides as 1,3-Bis-Electrophiles

Article abstract of DOI:10.1002/adsc.202100298

The synthesis and photophysical properties of fluorescent pyrazolo[1,5-a]pyrimidines (PPs) are explored. An array of 5,7-disubstituted fluorescent PPs are prepared selectively by using β,β-difluoro peroxides as the 1,3-bis-electrophiles. The synthesized PPs display a fairly significant stokes shift (up to 211 nm) and a large window of tunable emission wavelength that covers most of the visible spectrum (400 nm to 800 nm). Theoretical calculation indicates that the distinguished variation of intramolecular charge transfer (ICT) ability upon the varied substituents is responsible for the color-tunable fluorescence emission. (Figure presented.).

Full text of DOI:10.1002/adsc.202100298

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DOI: 10.1002/adsc.202100298
Regioselective Synthesis of Emission Color-Tunable Pyrazolo[1,5-
a]pyrimidines with β,β-Difluoro Peroxides as 1,3-Bis-Electrophiles
Yangyang Ma,a Yuanjin Chen,a, b Leiyang Lv,a,* and Zhiping Lia,*
a
Department of Chemistry, Renmin University of China, Beijing 100872, People’s Republic of China
E-mail: lvleiyang2008@ruc.edu.cn; zhipingli@ruc.edu.cn
College of Chemistry, Peking University, Beijing 100871, People’s Republic of China
b
Manuscript received: March 9, 2021; Revised manuscript received: May 17, 2021;
Version of record online: ■■■, ■■■■
Dedicated to Professor Tamotsu Takahashi on the occasion of his retirement
Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.202100298
that effectively helps to reduce self-absorption of
Abstract: The synthesis and photophysical proper-
fluorescence.[3] In addition, fluorescent reagents based
ties of fluorescent pyrazolo[1,5-a]pyrimidines (PPs)
on the DÀ πÀ A skeleton could be easily modified to
are explored. An array of 5,7-disubstituted fluores-
cent PPs are prepared selectively by using β,β-
difluoro peroxides as the 1,3-bis-electrophiles. The
synthesized PPs display a fairly significant stokes
possess a wide range of fluorescence emmision that is
quite useful in many fields.[4] Therefore, the design and
synthesis of the DÀ πÀ A based fluorophore candidates
with tunable fluorescence emmision are of great
shift (up to 211 nm) and a large window of tunable
significance.[2,5]
emission wavelength that covers most of the visible
spectrum (400 nm to 800 nm). Theoretical calcula-
tion indicates that the distinguished variation of
Pyrazolo[1,5-a]pyrimidines (PPs) are important N-
heterocycles that involve in many biological processes
relevant to medicinal applications. The most common
intramolecular charge transfer (ICT) ability upon
strategy to construct this rigid bicyclic N-fused moiety
the varied substituents is responsible for the color-
tunable fluorescence emission.
was the cyclocondensation between 5-amino-1H-pyr-
azoles and 1,3-bis-electrophiles, such as 1,3-dicarbon-
yls and enones (Scheme 1a).[6] However, regioselective
installation of functional groups into this skeleton on
both the 5- and 7- positions (especially 5-position with
electron-withdrawing group) is still a great challenge
due to the lack of chemo-and regioselctivity in the
cyclocondensation step of common 1,3-bis-electro-
philes with 5-amino-1H-pyrazole. Therefore, the devel-
Keywords: Pyrizolol[1,5-a]pyrimidine;
Organic
peroxide; Fluorophores; Intramolecular charge trans-
fer; Emission color-tunable
Organic fluorophores are privileged structures that opment of efficient method to approach the functional-
have received increasing attention due to their wide ized PPs in a regioselective manner is higly desirable.
applications in fluorescent probes, biomedical imaging,
Recently, we realized the synthesis of a variety of
drug discovery and photoelectric materials.[1] The bench-stable β,β-difluoroalkyl peroxides from simple
electron-donating group (D) linked to an electron- and readily starting materials.[7] The unique reactivity
withdrawing one (A) via a π-conjugated bridge and advantage of these novel peroxides were exempli-
(DÀ πÀ A) skeletons that feature the strong push-pull fied by their application in the construction of various
electron system are particularly attractive among heterocyclic scaffolds.[8] Herein, we disclosed that β,β-
various fluorophores, due to their structural stability, difluoro peroxides could be manipulated as 1,3-bis-
relatively small conjugation systems, and the great electrophiles that underwent cyclocondensation with 5-
convenience of ready modifications.[2] Small fluoro- amino-1H-pyrazoles under base condition, thus allow-
phores that based on the DÀ πÀ A framework have great ing the regioselective construction of both 7-donor
advantages in biological applications, which can (aryl) and 5-accepter (Scheme 1b). In these structures,
dramatically avoid the destruction of metabolic trans- the electron-withdrawing character of the pyrazolo
porters in cells, and meanwhile hold large stokes shift [1,5-a]pyrimidine rings is reinforced by perfluoroalkyl
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(TMEDA) was used instead of DABCO, 3a was
obtained in a 54% yield (entry 11). While other bases,
such as triethylamine (NEt3), pyridine, 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) and K2CO3, led to poor
results (entries 12–15). These outcomes indicated
DABCO (pKa=8.8)[9] was exactly adequate to modu-
late the rate of Kornblum - DeLaMare rearrangement
of β,β-difluoro peroxide to form the corresponding
ketone and subsequent condensation with 5-amino-1H-
pyrazole. Dramatic decreased reaction efficiency was
observed when the reaction temperature was lowered
°
to 25 C (entries 16). In comparison, the yield of 3a
°
was almost not affected at 80 C (entries 17).
With the optimized conditions in hand, the scopes
of the substrates 1 and 2 were investigated (Table 2).
As shown in Table 2A, β-perfluoro peroxides 1 bearing
a variety of functional groups (R=aryl), including
t
both the electron-donating (À Bu, À Me, À OMe) and
electron-withdrawing (À F, À Cl, À Br, À CF3) groups,
reacted smoothly with 5-amino-1H-pyrazole 2. The
substituents, regardless of the ortho-, meta- or para-
position, were all tolerated to give the corresponding
5-perfluoro substituted pyrazolol [1,5-a] pyrimidines
3a–3k in good yields. The substrates with other
(hetero-) aromatic rings, such as naphthalene and
furan, could also react and give the desired products
(3k and 3l) in 67% and 74% yield, respectively. When
aliphatic substituent (e.g. R=C6H13) attached to the β-
perfluoro peroxide, the desired product 3n was
°
Scheme 1. Synthetic strategies for the preparation of pyrazolo
[1,5-a]pyrimidines.
or carbonyl substituents. Modification of the substitu- obtained in a 12% yield even at 120 C. The low
ents in the starting peroxides enabled the construction reaction efficiency was attributed to the difficult
of structure diverse PPs with D-π-A scaffold, which formation of corresponding alkyl ketone in the initial
displayed a fairly significant stokes shift (up to Kornblum-DeLaMare rearrangement.[10] Notably, when
211 nm) and a large window of tunable emission the peroxide assembled with strong electron donor
wavelength that covering most of the visible spectrum. (triphenylamine) or π-extended group (N,N-diphenyl-
Initially, we chose β,β-difluoro peroxide 1a (the [1,1’-biphenyl]-4-amine), the cyclocondensation reac-
decomposation temperture of the peroxide is approx tions delivered the corresponding products 3o and 3p
°
170 C, see the details in SI) and 5-amino-1H- in 58% and 47% yields, respectively. Besides, poly-
pyrazoles 2a as the model to optimize the reaction substituted PPs (3q and 3r) could be obtained
conditions (Table 1). To our delight, the 5-perfluoro efficiently when substituted 5-amino-1H-pyrazole 2
pyrazolo[1,5-a]pyrimidine product 3a was obtained as was tested. In the case of 1H-indazol-3-amine tested,
a single isomer in a 59% yield using 1,4-diazabicyclo the desired 3s was obtained in 50% yield along with
[2.2.2]octane (DABCO) as base in ethyl acetate (EA), the regioisomer 3s’ in 16% yield. We hypothesized
in which the other regioisomer 3a’ was formed in 7% that the regioselectivities of the transformation are also
yield (entry 1) (the determination of the structures of related with the reactivity of the amino group in 1H-
3a and 3a’ see SI). Preliminary investigation of the indazol-3-amine and thus leads to two regioisomers.
reaction solvent including dichloroethane (DCE),
We further extend this strategy to prepare PPs with
acetonitrile (MeCN), acetone, methanol, 1,2-dimeth- other electron-withdrawing substituents (Table 2B). To
oxyethane (DME), tetrahydrofuran (THF), ethyl ether our delight, esters (4a–4b), ketones (4c–4e), amides
(Et2O), methyl tert-butyl ether (MTBE) and 1,4- (4f–4i) as well as trifluoromethyl (4j) could be
dioxane was carried out (entries 2–10). The results effortlessly installed into the 5-position of the PP
indicated that the regioselectivities of the transforma- scaffold, as long as the corresponding β,β-difluoro
tion depend on the solvent (the determination of the peroxides reacted with 2 under the optimized con-
ratio of 3a and 3a’ see SI) and the best result was ditions. The large scale syntheses were also carried out
obtained in the case of 1,4-dioxane, affording 3a in an under the standard reaction conditions. To our delight,
77% yield (entry 10). The influence of base was next 3a (68%, 2.0 mmol) and 4a (72%, 4.7 mmol) were
surveyed. When N,N,N’,N’-tetramethylethylenediamine obtained. Control experiments were carried out to
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Table 1. Optimization of the reaction conditions.[a]
°
entry
solvent
base
T( C)
yield of 3a (%)[b]
yield of 3a’ (%)[b]
1
2
3
4
5
6
7
8
EA
DCE
MeCN
acetone
MeOH
DME
THF
ethyl ether
MTBE
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
TMEDA
pyridine
NEt3
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
25
80
59
30
45
67
42
27
65
59
7
7
15
13
5
N. D.[c]
6
5
9
8
9
60
10
11
12
13
14
15
16
17
77(73[c])
54
5
2
16
N. D.[c]
N. D.[c]
N. D.[c]
N. D.[c]
6
DBU
K2CO3
DABCO
DABCO
4
N.D.[c]
54
74
7
[a] Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), base (0.6 mmol), solvent (2.0 mL), 6 h.
[b] Reported yield was based on 1a and determined by 1H NMR using CH2Br2 as an internal standard; the isolated yield was given in
parenthesis.
[c] N.D. means not detected.
explore the possible reaction pathways (Scheme 2).
Based on the results and previous reports,[6,7,8,12]
When the reaction was carried out in the absence of tentative mechanisms were proposed (Scheme 3).
2a, β-fluoro enone 5 was obtained (eq 1).[11] Further DABCO initiated Kornblum-DeLaMare rearrangement
treatment of 5 with 2a afforded the desired product 3a of peroxide 1 generated ketone intermediate A, upon
in a 91% yield (eq 2). These results revealed that β- which further elimination of HF afforded the β-fluoro
fluoro enone 5 is most likely the intermediate of the enone B. Nucleophilic substitution of B with 2a
reaction. Importantly, 4,4,4-trifluoro-1-phenylbut-2-en- proceeded via the nucleophilic addition-elimination
1-one 6 could not deliver the expected product 4j, process produces the intermediate D (Path A), which
which indicated that the β-fluoro atom as a leaving underwent the intramolecular cyclization and re-
group is crucial in the present reaction.
aromatization to deliver the desired product 3 or 4 as
the major product.[13] On the other side, the condensa-
tion of B with 2a is also possible to deliver the
intermediate G,[14] which followed the intramolecular
cyclization and re-aromatization to give 3 or 4 as the
minor product.
Considering pyrazolo[1,5-a]pyrimidines are one
class of fluorophores, we then carried out photo-
physical studies of the synthesized functionalized PPs.
For example, the fluorescence emission of 3n was
shifted from 445 nm to 472 nm in different solvents
(Figure 1a), and the fluorescence emmision of 3o was
shifted from 459 nm to 548 nm (Figure 1b), which
indicated that the intramolecular charge transfer (ICT)
in this D-π-A skeleton between the strong electron
donating triphenylamine (TPA) and electron-withdraw-
ing group. Besides, π-extended 3p exhibited a signifi-
cant shift from 397 nm to 608 nm (Figure 1c), which
revealed that further extension of the π-conjugation is
Scheme 2. Control experiments.
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Table 2. Scope of the substrates.[a]
[a]
°
Reaction conditions: 1 (0.2 mmol), 2 (0.4 mmol), DABCO (0.6 mmol), 1,4-dioxane (2.0 mL), 60 C, 6 h, unless otherwise noted.
Reported yields were the isolated yields.
[b]
[c]
[d]
[e]
°
25 C, 0.5 h.
°
120 C, 8 h.
°
1a (2.0 mmol), 2a (4.0 mmol), DABCO (6.0 mmol), 1,4-dioxane (20.0 mL), 60 C, 18 h.
°
1a (4.7 mmol), 2a (9.4 mmol), DABCO (14.1 mmol), 1,4-dioxane (47.0 mL), 60 C, 24 h.
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favorable for ICT and red-shift.[15] In polar solvents
such as DMF and ethanol, the intensity of fluorescence
emissions of pyrazolo[1,5-a]pyrimidines was weak.
The substitution pattern on PPs significantly influ-
enced their fluorescence properties, especially with the
original electron-deficient pyrimidine skeletons that
further attached with both 7-electron-donating and 5-
electron-withdrawing groups. Hence, to explore the
substituent effects on the optical properties, the
compounds 3b, 3d, 3n, 3o, 3p, 3q, 3r, 4a, 4b, 4d
and 4g were tested in dichloromethane (DCM), and
the photophysical spectrum and data were summarized
(Figure 1e and 1f and Table S1). Large stokes shift
(211 nm) was observed in the case of 3p that could
effectively help to reduce self-absorption of
fluorescence, which probably be utilized as sensor for
lipid contents or lipid droplets in cells.[16] The
fluorescence emission peak of 3q (540 nm) is 51 nm
red-shifted compared to the one without 5-perfluoro
group,[17] which indicated that the LUMO energy of
PPs was significantly lowed in the presence of 5-
electron-withdrawing group. Accordingly, when the
more electron-deficient ketone group 4d installed
instead, the fluorescence emission could be red-shifted
to 622 nm. More examples for the photophysical
properties data (molar absorptivity, quantum yield and
stokes shift) of the synthesized PPs were provided in
Figure S10 and Table S1 of SI.
Scheme 3. Proposed reaction mechanisms.
Theoretical calculation revealed that the
fluorescence emission of this DÀ πÀ A architecture was
attributed to the ICT, and the prominent red-shift was
due to the more electron-deficient pyrazolo[1,5-a]
pyrimidine skeleton (Figure 2).
Take 3o as an example, the charge distribution of
HOMO was mainly centered around the N,N-diphenyl
aniline fragment, while more charge accumulated in
the PP moiety in LUMO especially the attachement
with 5-perfluoro substituent. This phenomenon facili-
tated the formation of polarized excited state [D+À AÀ ]
upon increased dipole moments, thus exhibited reduced
ΔE value (2.55 eV vs 3.78 eV) and appreciable bath-
ochromic effect (540 nm vs 489 nm) compared with
the non-substitituted one.[15,18] ΔE value between
HOMO and LUMO was further reduced upon decreas-
ing the π-conjugation of donor (3p, 2.48 eV) or
decreasing the electron-density of acceptor (4d,
2.33 eV), which finally resulted in the fluorescence
emission shifted from blue to red.
In summary, we have developed a selective method
for the synthesis of a series of multifunctionalized
fluorescent pyrazolo [1,5-a] pyrimidines by cyclo-
condensation of β,β-difluoro peroxides with 5-amine-
1H-pyrazols. This strategy enables the introduction of
both 7-electron-donating and 5-electron-withdrawing
groups onto the PP skeleton. Most importantly, by
modifying the substituents of this DÀ πÀ A scaffold,
PPs exhibited a large stokes shift (up to 211 nm) and
Figure 1. UV absorption and Fluorescence emission spectra of
PPs: a) Fluorescence emission of 3n in different solvents
(excitation maximum was 330 nm); b) Fluorescence emission
of 3o in different solvents (excitation maximum was 410 nm);
c) Fluorescence emission of 3p in different solvents (excitation
maximum was 400 nm); d) Structures of 3o, 3p, 3q and 4d; e)
UV-vis absorption spectra (1.0×10À 5 M) of 3n, 3o, 3p, 3q and
4d in DCM; f) Normalized fluorescence emission spectra (1.0×
10À 5 M) of 3n, 3o, 3p, 3q and 4d in DCM.
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Figure 2. HOMO-LUMO diagrams and the ΔE value for fluorophores 3o, 3p and 4d.
e) D. M. Jameson, J. A. Ross, Chem. Rev. 2010, 110,
2685.
displayed fairly a large window of tunable emission
wavelength that covering most of the visible spectrum.
Theoretical calculation indicated that distinguished
variation on ICT ability upon varied substituents was
responsible for the color-tunable fluorescence emis-
sion.
[2] a) T.-B. Ren, W. Xu, W. Zhang, X.-X. Zhang, Z.-Y.
Wang, Z. Xiang, L. Yuan, X.-B. Zhang, J. Am. Chem.
Soc. 2018, 140, 7716; b) H. M. Kim, B. R. Cho, Chem.
Rev. 2015, 115, 5014; c) X. Liu, Q. Qiao, W. Tian, W.
Liu, J. Chen, M. J. Lang, Z. Xu, J. Am. Chem. Soc. 2016,
138, 6960.
[3] a) L. D. Lavis, R. T. Raines, ACS Chem. Biol. 2008, 3,
142; b) Z. Xiang, Z.-Y. Wang, T.-B. Ren, W. Xu, Y.-P.
Liu, X.-X. Zhang, P. Wu, L. Yuan, X.-B. Zhang, Chem.
Commun. 2019, 55, 11462.
[4] a) S. Allard, M. Forster, B. Souharce, H. Thiem, U.
Scherf, Angew. Chem. Int. Ed. 2008, 47, 4070; b) Y.
Ohmori, Laser Photonics Rev. 2009, 4, 300; c) A. W.
Hains, Z. Liang, M. A. Woodhouse, B. A. Gregg, Chem.
Rev. 2010, 110, 6689; d) Y. Wu, W. Zhu, Chem. Soc. Rev.
2013, 42, 2039; e) J. N. Clifford, E. Mart'ınez-Ferrero,
A. Viterisi, E. Palomares, Chem. Soc. Rev. 2011, 40,
1635; f) M. Liang, J. Chen, Chem. Soc. Rev. 2013, 42,
3453.
Experimental Section
General Procedure for the Synthesis of PPs 3 and 4: To a
Schlenk tube was added DABCO (0.6 mmol), 5-amine-1H-
pyrazol 2a (0.4 mmol), peroxides 1 (0.2 mmol) and 1.4-dioxane
°
(2.0 mL) and the resulting solution was stirred at 60 C for 6 h.
After the reaction, solvent was evaporated in vacuo and the
residue was purified by flash column chromatography on silica
gel (eluent: ethyl acetate/ petroleum ether) to give the desired
PPs 3 and 4.
Acknowledgements
[5] a) E. Kim, M. Koh, B. J. Lim, S. B. Park, J. Am. Chem.
Soc. 2011, 133, 6642; b) D.-B. Sung, B. Mun, S. Park,
H.-S. Lee, J. Lee, Y.-J. Lee, H. J. Shin, J. S. Lee, J. Org.
Chem. 2019, 84, 379.
[6] a) J.-C. Castillo, A. Tigreros, J. Portilla, J. Org. Chem.
2018, 83, 10887 and references therein; b) S. Cheruku-
palli, R. Karpoormath, B. Chandrasekaran, G. A. Ham-
pannavar, N. Thapliyal, V. N. Palakollu, Eur. J. Med.
Chem. 2017, 126, 298 and references therein.
[7] Y. Chen, L. Li, Y. Ma, Z. Li, J. Org. Chem. 2019, 84,
5328.
[8] a) Y. Chen, L. Li, X. He, Z. Li, ACS Catal. 2019, 9,
9098; b) Y. Ma, Y. Chen, C. Lou, Z. Li, Asian J. Org.
Chem. 2020, 9, 1018; c) X.-Q. Chu, B.-Q. Cheng, Y.-W.
Zhang, D. Ge, Z.-L. Shen, T.-P. Loh, Chem. Commun.
2018, 54, 2615.
This work was supported by the National Natural Science
Foundation of China (22071266), and Public Computing Cloud
Platform, Renmin University of China, The research was also
supported by the Fundamental Research Funds for the Central
Universities, and the Research Funds of Renmin University of
China (21XNLG04).
References
[1] a) H. M. Kim, B. R. Cho, Chem. Rev. 2015, 115, 5014;
b) F. J. Williams, D. A. Fiedler, ACS Chem. Biol. 2015,
10, 1958; c) K. M. Dean, A. E. Palmer, Nat. Chem. Biol.
2014, 10, 512; d) H. Kobayashi, M. Ogawa, R. Alford,
P. L. Choyke, Y. Urano, Chem. Rev. 2010, 110, 2620;
Adv. Synth. Catal. 2021, 363, 1–8
6
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

COMMUNICATIONS
asc.wiley-vch.de
[9] The pKa data can be obtained free of charge at https:// [14] J. Palaniraja, S. M. Roopan, G. M. Rayalu, N. A. Al-
organicchemistrydata.org/hansreich/resources/pka/#pka_-
water_compilation_evans.
[10] N. Kornblum, H. E. DeLaMare, J. Am. Chem. Soc. 1951,
73, 880.
Dhabi, M. V. Arasu, Molecules 2016, 21, 1571.
[15] a) S. Kumar, P. Rajamalli, D. B. Cordes, A. M. Z.
Slawin, E. Zysman-Colman, Asian J. Org. Chem. 2020,
9, 1277; b) M.-J. Kim, M. Ahn, J. H. Shim, K.-R. Wee,
Phys. Chem. Chem. Phys. 2020, 22, 3370.
[11] Synthesis of β-fluoroenones: a) Y.-b. Wu, G.-p. Lu, T.
Yuan, Z.-b. Xu, L. Wan, C. Cai, Chem. Commun. 2016, [16] J. S. Poli, H.-C. H. Lützhøft, D. B. Karakashev, P.
52, 13668; b) Y. Li, J. Liu, S. Zhao, X. Du, M. Guo, W.
Zhao, X. Tang, G. Wang, Org. Lett. 2018, 20, 917.
Valente, I. Angelidaki, Bioresour. Technol. 2014, 151,
388–391.
[12] C. Liu, E. Shi, F. Xu, Q. Luo, H. Wang, J. Chen, X. Wan, [17] a) M. Ahn, M.-J. Kim, D. W. Cho, K.-R. Wee, J. Org.
Chem. Commun. 2015, 51, 1214.
Chem. 2021, 86, 403; b) A. P. Kulkarni, X. Kong, S. A.
Jenekhe, Adv. Funct. Mater. 2006, 16, 1057; c) J.
Orrego-Hernandez, J. Portilla, J. Org. Chem. 2017, 82,
13376.
[13] a) E. E. Emelina, A. A. Petrov, S. I. Selivanov, Y. V.
Nelyubina, M. Y. Antipin, J. Fluorine Chem. 2009, 130,
861; b) A. M. Naglah, A. A. Askar, A. S. Hassan, T. K.
Khatab, M. A. Al-Omar, M. A. Bhat, Molecules 2020, [18] A. Tigreros, M. Macía, J. Portilla, Dyes Pigm. 2021, 184,
25, 1431.
108730.
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Regioselective Synthesis of Emission Color-Tunable
Pyrazolo[1,5-a]pyrimidines with β,β-Difluoro Peroxides as
1,3-Bis-Electrophiles
Adv. Synth. Catal. 2021, 363, 1–8
Y. Ma, Y. Chen, L. Lv*, Z. Li*