A new method for the synthesis of chalcone derivatives promoted by PPh3/I2under non-alkaline conditions

Article abstract of DOI:10.1080/00397911.2020.1847295

A straightforward and general method has been developed for the synthesis of chalcone derivatives by a Claisen-Schmidt reaction in the presence of PPh₃/I₂ in 1,4-dioxane under reflux temperatures. With the condensation of the aromatic ketone and aldehyde occurring at non-strongly alkaline conditions, our proposed method significantly expands the range of applicable substrates, especially for groups that are unstable under alkaline conditions.

Full text of DOI:10.1080/00397911.2020.1847295

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
A new method for the synthesis of chalcone
derivatives promoted by PPh3/I2under non-
alkaline conditions
Kangsheng Xue , Guoxiang Sun , Yanzhi Zhang , Xubing Chen , Yang Zhou ,
Jinjun Hou , Huali Long , Zijia Zhang , Min Lei & Wanying Wu
To cite this article: Kangsheng Xue , Guoxiang Sun , Yanzhi Zhang , Xubing Chen , Yang Zhou ,
Jinjun Hou , Huali Long , Zijia Zhang , Min Lei & Wanying Wu (2020): A new method for the
synthesis of chalcone derivatives promoted by PPh3/I2under non-alkaline conditions, Synthetic
Communications, DOI: 10.1080/00397911.2020.1847295
To link to this article: https://doi.org/10.1080/00397911.2020.1847295
View supplementary material
Published online: 20 Nov 2020.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=lsyc20

R
SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2020.1847295
A new method for the synthesis of chalcone derivatives
promoted by PPh3/I2under non-alkaline conditions
a
b
c
c
d,e
ꢀ
ꢀ
Kangsheng Xue , Guoxiang Sun , Yanzhi Zhang , Xubing Chen , Yang Zhou
Jinjun Houd,e, Huali Longd,e, Zijia Zhangd,e, Min Leid,e, and Wanying Wud,e
,
b
aCollege of Pharmacy, Changchun University of Chinese Medicine, Changchun, P. R. China; School of
Chemistry and Chemical Engineering, Yancheng Institute of Technology, Yancheng, Jiangsu, P. R. China;
d
cCollege of Pharmacy, Dali University, Dali, P. R. China; Shanghai Research Center for Modernization of
Traditional Chinese Medicine, National Engineering Laboratory for TCM Standardization Technology,
e
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, P. R. China; University
of Chinese Academy of Sciences, Beijing, P. R. China
ABSTRACT
ARTICLE HISTORY
Received 24 December 2019
A straightforward and general method has been developed for the
synthesis of chalcone derivatives by a Claisen-Schmidt reaction in
the presence of PPh3/I2 in 1,4-dioxane under reflux temperatures.
With the condensation of the aromatic ketone and aldehyde occur-
ring at non-strongly alkaline conditions, our proposed method sig-
nificantly expands the range of applicable substrates, especially for
groups that are unstable under alkaline conditions.
KEYWORDS
Aldehyde; chalcone; Claisen-
Schmidt reaction; ketone;
PPh3/I2
GRAPHICAL ABSTRACT
Introduction
Chalcone is an important type of natural product that is widely distributed in plants.
For example, licochalcone A, naringenin chalcone, bavachalcone, and pinocembrin chal-
cone are natural products that contain chalcone’s core (Figure 1).[1] Chalcone and its
analogs have diverse pharmacological properties, such as antineoplasticism,[2] antiplas-
modial properties,[3] antituberculosis activity,[4] anti-apoptotic properties,[5] Farnesoid X
Receptor antagonization,[4] Alzheimer’s Disease prevention,[6] et al.[7] Furthermore,
chalcones are also essential organic intermediates for the synthesis of dihydrochal-
cones,[8] 2-pyrazolines or pyrazoles,[9] pyrimidine-2-ones,[10] flavanones/flavones,[11] and
CONTACT Min Lei
mlei@simm.ac.cn; Wanying Wu
wanyingwu@simm.ac.cn;
Shanghai Research Center for
Modernization of Traditional Chinese Medicine, National Engineering Laboratory for TCM Standardization Technology,
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, P. R. China.
ꢀ
These two authors contributed equally to this work.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
K. XUE ET AL.
Figure 1. Natural products with chalcone’s core (highlighted in red).
others.[12] Thus, chalcones have significant value in both pharmaceutical and
organic chemistry.
Due to the importance of chalcones as biologically active compounds or as synthons
in organic synthesis, many methods for the synthesis of these compounds have been
developed.TheClaisen-Schmidt condensation reaction of an aromatic ketone and an
aldehyde is the essential method to synthesize these compounds under different condi-
tions, such as base,[13] ZnO,[14] CaO/MW,[15] SB3-Cy/CSA DES,[16] montmorillonite
clay,[17] IL,[18] ZrCl4,[19] and others.[20] Furthermore, chalcones can also be synthesized
by Heck reaction of 1-phenylprop-2-en-1-ones and aryl halide.[21] Although several
modified methods under improved conditions have been reported, many of them suffer
from drawbacks such as low yields, high reaction temperatures, and long reaction times.
In particular, the group intolerance under strong base conditions tend to cause the reac-
tion to fail. Therefore, there is a necessity to develop new methods for the synthesis of
chalcones under mild conditions.
Previous studies reported that PPh3/I2 could be used as a suitable dehydration
reagent.[22] Inspired by these results, we proposed that the Claisen-Schmidt reaction
could be promoted by PPh3/I2 to synthesize chalcones. To verify our assumption, we
chose acetophenone and benzaldehyde in the presence of PPh3/I2 in MeCN as the
model reaction. To our delight, the target product (E)-chalcone was formed, which
demonstrated the feasibility of our initial assumption. Therefore, in order to further
improve the yields of the reaction, we carried out a series of optimization experiments
(Table 1).
Results and discussion
A screening test of eight commonly-used solvents was performed to determine the most
suitable solvent to choose. As reported in Table 1, the product 3a was obtained in
MeCN, EtOAc, and 1,4-dioxane at 60 ꢁC with yields of 15%, 30%, and 60%, respectively.
However, only a trace amount of 3a was observed in the other solvents presented in
Table 1. Furthermore, to optimize the reaction temperature, we carried out the reaction
at temperatures ranging from room temperature to reflux temperature in the solvent
1,4-dioxane (Table 1, Entries 6, 9-12), finding that the yields of product 3a were
improved as the temperature increased. Therefore, 1,4-dioxane was selected as the solv-
ent under reflux temperature for all further reactions. Furthermore, when the reaction

R
SYNTHETIC COMMUNICATIONSV
3
Table 1. Solvent and temperature screeningsa.
Entry
Solvent
MeCN
DCM
THF
EtOAc
Temperature (oC)
Yield of 3a (%)b
1
2
3
4
60
60
60
15
Trace
Trace
30
60
5
6
7
8
Toluene
1,4-dioxane
DMF
60
60
60
60
rt
40
80
reflux
reflux
TRACE
60
Trace
Trace
Trace
15
DMSO
9
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
10
11
12
13d
78
91 (84)c
20
aReaction conditions: 1a (240 mg, 2.0 mmol), 2a (254 mg, 2.4 mmol, 1.2 equiv), PPh3 (629 mg, 2.4 mmol, 1.2 equiv), I2
(609 mg, 2.4 mmol, 1.2 equiv), solvent (4 mL), 8 h.
bYields were determined by LC-MS.
cIsolated yields.
dPPh3 was not added in this case.
was carried out under PPh3-free conditions, only a 20% yield of the desired product 3a
was obtained (Table 1, Entry 13).
Then, the equivalents of PPh3/I2 (mole ratio, 1: 1) were investigated in 1,4-dioxane
under reflux temperature. The results indicated that increasing the equivalent of PPh3/I2
from 0.5 to 1.0 could increase the product yield from 70% to 84%. However, the yields
did not increase further when an excessive amount of PPh3/I2 was used in this Claisen-
Schmidt reaction. Therefore, 1.0 equivalents of PPh3/I2 was considered appropriate. To
examine the scope and generality of this procedure, we extended the methodology to
evaluate the yields with different substrates, and the results are presented in Table 2.
Initially, we studied the condensation of acetophenone with o-, m-, p-substituted ben-
zaldehyde to investigate the steric effect of the aldehyde motif (Table 2, Entries 2–7).
According to the yields of related products, steric hindrance had no significant effect on
the reaction (76–85%). However, the reaction yields were significantly affected by the
electron effect. The desired products formed smoothly when the benzaldehyde carried
EDG. On the contrary, the reactions were sluggish when the benzaldehyde carried EWG
(–CN, –NO2). Although the fluorine atom was an EWG, the p–p conjugation weakened
its electron absorption effect, which led to the reaction proceeding smoothly and the
target product 3j being obtained in a 90% yield. Furthermore, heteroaromatic aldehydes
(furyl and indolyl) were also selected as substrates for Claisen-Schmidt condensation.
Unfortunately, only low yields of desired products 3m–n (13%) were obtained in these
cases, and prolonging the reaction time would only reduce the yield.
The steric hindrance effect of acetophenone was not similar to that of benzaldehyde.
The acetophenones with o-substitution led to moderate yields (45–64%), which indi-
cated that steric hindrance affected the reaction. The electron effect of acetophenones
was consistent with that of benzaldehydes. To be specific, the reaction was carried out

4
K. XUE ET AL.
a
Table 2. Synthesis of chalcones in the presence of PPh3/I2 .
Yield (%)b
84
Entry
1
Time (h)
8
Product 3
3a
3b
2
8
85
3
4
5
12
10
10
76
79
3c
3d
85
3e
6
7
8
12
12
10
82
85
75
3f
3g
3h
(continued)

R
SYNTHETIC COMMUNICATIONSV
5
9
8
12
8
87
3i
10
11
12
13
90
3j
0
3k
8
0
3l
3
13c
3m
14
3
13c
3n
15
16
17
11
11
11
64
75
80
3o
3p
3q
18
19
11
11
50
75
3r
3s
(continued)

6
K. XUE ET AL.
20
11
10
12
76
85
45
3t
21
22
3u
3v
23
24
12
12
0
3w
78
3x
aReaction conditions: 1 (2.0 mmol), 2 (2.4 mmol, 1.2 equiv), PPh3 (524 mg, 2.0 mmol, 1.0 equiv), I2 (507 mg, 2.0 mmol,
1.0 equiv), 1,4-dioxane (4 mL), reflux.
bIsolated yields.
cProlonged reaction time leads to reduced yield.
Scheme 1. Plausible mechanism for the formation of compound 3.
smoothly with acetophenones bearing EDG, but the reaction would be blocked with
acetophenones bearing EWG.
A tentative mechanism to demonstrate the product 3 formation is shown in
Scheme 1. Initially, PPh3 reacts with I2 to form A, and ketones undergo enol alternation
to form B. Then, B undergoes an additional reaction with aldehyde 2 to form

R
SYNTHETIC COMMUNICATIONSV
7
intermediate C, while under the action of A. Lastly, the intermediate C decomposes to
form the desired product 3.
In conclusion, we demonstrate a simple and efficient procedure for the synthesis of
chalcone derivatives in the presence of PPh3/I2 in 1,4-dioxane. The mild reaction condi-
tions, short reaction time, easy set-up, and high compatibility with various
functional groups are some of the salient features of this reaction. The advantage of the
present procedure is that the reaction is performed under a non-strongly alkaline condi-
tion. The simplicity of the present procedure makes it an exciting alternative to
other approaches, especially for those substrates that are unstable under alka-
line conditions.
Experimental
Melting points were measured using a WRS-1B micromelting point apparatus and are
uncorrected. NMR spectra were recorded on a Bruker AMX 500 instrument using solv-
ent peaks as DMSO-d6 solutions. Yields of the condition-screening experiments were
determined by LC-MS (Waters LCMS/SQD þ UPLC H-class spectrometer). HRESIMS
were determined on a Micromass Q-TOF Global mass spectrometer, and ESIMS were
run on a Bruker Esquire 3000 Plus Spectrometer. TLC was performed on GF254 silica
gel plates (Yantai Huiyou Inc., China).
General procedures for synthesis of compounds 3
A mixture of PPh3 (524 mg, 2.0 mmol, 1.0 equiv), I2 (507 mg, 2.0 mmol, 1.0 equiv), and
1,4-dioxane (4 mL) was stirred at room temperature for 30 min. Then, compounds 1
(2.0 mmol) and 2 (2.4 mmol) were added to the mixture and stirred for the appropriate
time (Table 2) under reflux temperature. After completion of the reaction (TLC), DCM
(20 mL) was added, and the solution was washed with NaS2O3 (20 mL, 10%). Then, the
organic layer was washed with water (2 ꢂ 20 mL) and brine (2 ꢂ 20 mL) and dried over
anhydrous MgSO4. The organic layer was concentrated under reduced pressure, and the
crude product was purified by column chromatography to afford the corresponding
product 3.
3a: Pale yellow solid; Yield: 84% (349 mg); mp: 54.4–56.2 ꢁC.[23] 1H NMR (500 MHz,
DMSO-d6) d ¼ 8.16 (d, J ¼ 7.4 Hz, 2H), 7.95 (d, J ¼ 15.7 Hz, 1H), 7.90–7.88 (m, 2H),
7.76 (d, J ¼ 15.7 Hz, 1H), 7.67 (t, J ¼ 7.4 Hz, 1H), 7.58 (t, J ¼ 7.4 Hz, 2H), 7.47–7.45 (m,
3H); 13C NMR (126 MHz, DMSO-d6) d ¼ 189.21, 144.06, 137.56, 134.66, 133.17, 130.66,
128.93 (4c), 128.81 (2c), 128.55 (2c), 122.05; MS (ESI): m/z, 209 ([M þ H]þ); HRMS
(ESI): m/z [M þ H]þ calcd. for C15H13O: 209.0961, found: 209.0965.
Funding
This work was supported by the Special Fund for Strategic Pilot Technology of the Chinese
Academy of Sciences [XDA12020379], the National Natural Science Foundation of China [Grant
81973455], and the National Key R&D Program of China [2018YFC1707900].

8
K. XUE ET AL.
References
[1] (a) Gou, S.; Liu, J.; He, M.; Qiang, Y.; Ni, J. Nat. Prod. Res. 2016, 30, 2130–2134. DOI: 10.
1080/14786419.2015.1114940. (b) Slimestad, R.; Fossen, T.; Verheul, M. J. J Agric Food
Chem. 2008, 56, 2436–2441. DOI: 10.1021/jf073434n. (c) Ng, C. H.; Rullah, K.; Aluwi, M.
F. F. M.; Abas, F.; Lam, K. W.; Ismail, I. S.; Narayanaswamy, R.; Jamaludin, F.; Shaari, K.
Molecules. 2014, 19, 11645–11659. DOI: 10.3390/molecules190811645. (d) Kim, D. H.; Li,
H.; Han, Y. E.; Jeong, J. H.; Lee, H. J.; Ryu, J.-H. Molecules. 2018, 23, 109. DOI: 10.3390/
molecules23010109.
[2] (a) Zhu, M.; Wang, J.; Xie, J.; Chen, L.; Wei, X.; Jiang, X.; Bao, M.; Qiu, Y.; Chen, Q.; Li,
W.; et al. Eur. J. Med. Chem. 2018, 157, 1395–1405. DOI: 10.1016/j.ejmech.2018.08.072.
(b) Park, S.; Kim, E. H.; Kim,J.; Kim, S. H.; Kim, I. Eur. J Med. Chem. 2018, 144,
435–443. DOI: 10.1016/j.ejmech.2017.12.056. (c) Abdelbaset, M. S.; Abdel-Aziz, M.;
Ramadan, M.; Abdelrahman, M. H.; Bukhari, S. N. A.; Ali, T. F. S.; Abuo-Rahma, G. E.
D. A. Bioorg. Med. Chem. 2019, 27, 1076–1086. DOI: 10.1016/j.bmc.2019.02.012. (d)
Kumar, S. K.; Hager, E.; Pettit, C.; Gurulingappa, H.; Davidson, N. E.; Khan, S. R. J. Med.
Chem. 2003, 46, 2813–2815. DOI: 10.1021/jm030213þ. (e) Srinivasan, B.; Johnson, T. E.;
Lad, R.; Xing, C. J. Med. Chem. 2009, 52, 7228–7235. DOI: 10.1021/jm901278z..
[3] Kumar, S.; Saini, A.; Gut, J.; Rosenthal, P. J.; Raj, R.; Kumar, V. Eur. J. Med. Chem. 2017,
138, 993–1001. DOI: 10.1016/j.ejmech.2017.07.041.
[4] Gomes, M. N.; Braga, R. C.; Grzelak, E. M.; Neves, B. J.; Muratov, E.; Ma, R.; Klein, L. L.;
Cho, S.; Oliveira, G. R.; Franzblau, S. G.; Andrade, C. H. Eur. J. Med. Chem. 2017, 137,
126–138. DOI: 10.1016/j.ejmech.2017.05.026.
ꢀ
[5] Dumontet, C.; Beck, G.; Gardebien, F.; Haudecoeur, R.; Mathe, D.; Matera, E. L.;
ꢁ
Tourette, A.; Mattei, E.; Esmenjaud, J.; Boyere, C.; et al. Eur. J. Med. Chem. 2018, 158,
405–413. DOI: 10.1016/j.ejmech.2018.09.033.
[6] (a) Sang, Z.; Wang, K.; Zhang, P.; Shi, J.; Liu, W.; Tan, Z. Eur. J. Med. Chem. 2019, 180,
238–252. DOI: 10.1016/j.ejmech.2019.07.021. (b) Cao, Z.; Yang, J.; Xu, R.; Song, Q.;
Zhang, X.; Liu, H.; Qiang, X.; Li, Y.; Tan, Z.; Deng, Y. Bioorg. Med. Chem. 2018, 26,
1102–1115. DOI: 10.1016/j.bmc.2018.01.030.
[7] (a) Rashid, H.; Xu, Y.; Ahmad, N.; Muhammad, Y.; Wang, L. Bioorg. Chem. 2019, 87,
335–365. DOI: 10.1016/j.bioorg.2019.03.033. (b) Yibcharoenporn, C.; Chusuth, P.; Jakakul,
C.; Rungrotmongkol, T.; Chavasiri, W.; Muanprasat, C. J. Pharmacol. Sci. 2019, 140,
273–283. DOI: 10.1016/j.jphs.2019.07.012. (c) Singh, G.; Arora, A.; Kalra, P.; Maurya, I. K.
; Ruizc, C. E.; Estebanc, M. A.; Sinha, S.; Goyal, K.; Sehgal, R. Bioorg. Med. Chem. 2019,
27, 188–195. DOI: 10.1016/j.bmc.2018.11.038. (d) Abuo-Rahma, G. E. D. A. A.; Abdel-
Aziz, M.; Mourad, M. A. E.; Farag, H. H. Bioorg. Med. Chem. 2012, 20, 195–206. DOI: 10.
1016/j.bmc.2011.11.012. (e) Kumar, V.; Kumar, S.; Hassan, M.; Wu, H.; Thimmulappa, R.
K.; Kumar, A.; Sharma, S. K.; Parmar, V. S.; Biswal, S.; Malhotra, S. V. J. Med. Chem.
2011, 54, 4147–4159. DOI: 10.1021/jm2002348.
[8] Zhang, D.; Iwai, T.; Sawamura, M. Org. Lett. 2019, 21, 5867–5872. DOI: 10.1021/acs.
orglett.9b01989.
[9] (a) Pise, A. S.; Jadhav, S. D.; Burungale, A. S.; Devkate, S. S.; Gawade, R. B. Asian J.
Chem. 2018, 30, 894–896.; DOI: 10.14233/ajchem.2018.21131. (b) Wang, X.; Pan, Y.;
Huang, X.; Mao, Z.; Wang, H. Org. Biomol. Chem. 2014, 12, 2028–2032. DOI: 10.1039/
c3ob42432d. (c) Zhu, X.; Li, Z.; Jin, C.; Xu, L.; Wu, Q.; Su, W. Green Chem. 2009, 11,
€ €
€ €
163.; DOI: 10.1039/b816788e. (d) Cho, H.; Torok, F.; Torok, B. Green Chem. 2014, 16,
3623–3634. DOI: 10.1039/C4GC00037D.;(e) Ananthnag, G. S.; Adhikari, A.; Balakrishna,
M. S. Catal. Commum. 2014, 43, 240–243. DOI: 10.1016/j.catcom.2013.09.002.
[10] (a) Kidwai, M.; Misra, P. Synth. Commum. 1999, 29, 3237–3250.; DOI: 10.1080/
00397919908085949. (b) Kankanala, K.; Venkata Reddy, L.; Ranga Reddy, V.; Mukkanti,
K.; Pal, S. LOC. 2011, 8, 53–59. DOI: 10.2174/157017811794557750.

R
SYNTHETIC COMMUNICATIONSV
9
[11] (a) Zheng, X.; Jiang, H.; Xie, J.; Yin, Z.; Zhang, H. Synth. Commum. 2013, 43, 1023–1029.;
DOI: 10.1080/00397911.2011.621096. (b) Eshghi, H.; Rahimizadeh, M.; Mousavi, S. M.
Nat. Prod. Res. 2014, 28, 438–443. DOI: 10.1080/14786419.2013.872103. (c) Liu, R.;
Zhang, Y.; Xu, K.; Tan, G. Synth. Commum. 2017, 47, 1–9. DOI: 10.1080/00397911.2016.
1230217.;(d) Du, Z.; Ng, H.; Zhang, K.; Zeng, H.; Wang, J. Org. Biomol. Chem. 2011, 9,
6930–6933. DOI: 10.1039/c1ob06209c.
[12] (a) Krishna, V.; Garapati, R.; Gravel, M. Org. Lett. 2018, 20, 6372–6375. DOI: 10.1021/acs.
orglett.8b02636. (b) Song, P.; Lu, C.; Fei, Z.; Zhao, B.; Yao, Y. J. Org. Chem. 2018, 83,
6093–6100. DOI: 10.1021/acs.joc.8b00783. (c) Ottenbacher, R. V.; Samsonenko, D. G.;
Talsi,E. P.; Bryliakov, K. P. ACS Catal. 2016, 6, 979–988. DOI: 10.1021/acscatal.5b02299.
(d) McLaughlin, N.; Duffy, C.; Alletto, F.; Ravelli, A.; Lancianesi, S.; Gillick-Healy, M.;
Adamo, M. F. A. Tetrahedron Lett. 2019, 60, 1313–1316.; DOI: 10.1016/j.tetlet.2019.03.
065. (e) Liu, T.; Zeng, Y.; Zhang, H.; Wei, T.; Wu, X.; Li, N. Tetrahedron Lett. 2016, 57,
4845–4849. DOI: 10.1016/j.tetlet.2016.09.059. (f) Allingham, M. T.; Bennett, E. L.; Davies,
D. H.; Harper, P. M.; Howard-Jones, A.; Mehdar, Y. T. H.; Murphy, P. J.; Thomas, D. A.;
Caulkett, P. W. R.; Potter, D.; et al. Tetrahedron. 2016, 72, 496–503. DOI: 10.1016/j.tet.
2015.11.058.
[13] (a) Mellado, M.; Madrid, A.; Reyna, M.; Weinstein-Oppenheimer, C.; Mella, J.; Salas,
ꢀ
C. O.; Sanchez, E.; Cuellar, M. Med. Chem. Res. 2018, 27, 2414–2425.; DOI: 10.1007/
s00044-018-2245-2. (b) Bashary, R.; Khatik, G. L. Bioorg. Chem. 2019, 82, 156–162. DOI:
10.1016/j.bioorg.2018.10.010. (c) Niu, C.; Yin, L.; Nie, L. F.; Dou, J.; Zhao, J. Y.; Li, G.;
Aisa, H. A. Bioorg. Med. Chem. 2016, 24, 5440–5448. DOI: 10.1016/j.bmc.2016.08.066. (d)
Lee, Y.-T.; Fong, T.-H.; Chen, H.-M.; Chang, C.-Y.; Wang, Y.-H.; Chern, C.-Y.; Chen, Y.-
H. Molecules. 2014, 19, 641–650. DOI: 10.3390/molecules19010641.
[14] (a) Li, Z.; Zhao, H.; Han, H.; Liu, Y.; Song, J.; Guo, W.; Chu, W.; Sun, Z. Tetrahedron
Lett. 2017, 58, 3984–3988. DOI: 10.1016/j.tetlet.2017.09.011. (b) Tamuly, C.; Saikia, I.;
Hazarika, M.; Bordoloi, M.; Hussain, N.; Das, M. R.; Deka, K. RSC Adv. 2015, 5,
8604–8608. DOI: 10.1039/C4RA14225J.
[15] Kulkarni, P. CMIC. 2015, 2, 144–149. DOI: 10.2174/2213335601666141126220412.
[16] Tiecco, M.; Germani, R.; Cardellini, F. RSC Adv. 2016, 6, 43740–43747. DOI: 10.1039/
C6RA04721A.
ꢀ
ꢀ
[17] Rocchi, D.; Gonzalez, J. F.; Menendez, J. C. Molecules. 2014, 19, 7317–7326. DOI: 10.
3390/molecules19067317.
[18] Fang, D.; Chen, J.; Fei, Z.; Gong, K.; Liu, Z. Catal. Commum. 2008, 9, 1924.
[19] Kumar, A.; Akanksha, A. J. Mol. Catal. A: Chem. 2007, 274, 212. DOI: 10.1016/j.molcata.
2007.05.016.
[20] (a) Riadi, Y.; Abrouki, Y.; Mamouni, R.; El Haddad, M.; Routier, S.; Guillaumet, G.; Lazar,
S. Chem. Cent. J. 2012, 6, 60. DOI: 10.1186/1752-153X-6-60. (b) Downey, C. W.; Glist,
H. M.; Takashima, A.; Bottum, S. R.; Dixon, G. J. Tetrahedron Lett. 2018, 59, 3080–3083.
DOI: 10.1016/j.tetlet.2018.06.066. (c) Sebti, S.; Solhy, A.; Tahir, R.; Abdelatif, S.; Boulaajaj,
S.; Mayoral, J. A.; Garcıꢀa, J. I.; Fraile, J. M.; Kossir, A.; Oumimoun, H. J. Catal. 2003, 213,
1–6. DOI: 10.1016/S0021-9517(02)00017-9. (d) Sebti, S.; Solhy, A.; Smahi, A.; Kossir, A.;
Oumimoun, H. Catal. Commum. 2002, 3, 335–339. DOI: 10.1016/S1566-7367(02)00137-1.
(e) Lee, Y.-T.; Fong, T.-H.; Chen, H.-M.; Chang, C.-Y.; Wang, Y.-H.; Chern, C.-Y.; Chen,
Y.-H. Molecules. 2014, 19, 641–650. DOI: 10.3390/molecules19010641.
[21] (a) Wilson, K. L.; Murray, J.; Sneddon, H. F.; Jamieson, C.; Watson, A. J. B. Synlett. 2018,
29. 2293;(b) Bianco, A.; Cavarischia, C.; Guiso, M. Nat. Prod. Res. 2006, 20, 93–97. DOI:
10.1080/14786410500059474. (c) Bianco, A.; Cavarischia, C.; Farina, A.; Guiso, M.; Marra,
C. Tetrahedron Lett. 2003, 44, 9107–9109. DOI: 10.1016/j.tetlet.2003.10.060. (d) Bianco, A.
; Cavarischia, C.; Guiso, M. Eur. J. Org. Chem. 2004, 2004, 2894–2898. DOI: 10.1002/ejoc.
200400032.

10
K. XUE ET AL.
[22] (a) Sun, G.; Lv, X.; Zhang, Y.; Lei, M.; Hu, L. Org. Lett. 2017, 19, 4235–4238. DOI: 10.
1021/acs.orglett.7b01882. (b) Wang, Y.; Zhou, Y.; Lei, M.; Hou, J.; Jin, Q.; Guo, D.; Wu,
W. Tetrahedron. 2019, 75, 1180–1185. DOI: 10.1016/j.tet.2019.01.023. (c) Pathak, G.; Das,
D.; Rokhum, L. RSC Adv. 2016, 6, 93729–93740.; DOI: 10.1039/C6RA22558F. (d)
Wangngae, S.; Duangkamol, C.; Pattarawarapan, M.; Phakhodee, W. RSC Adv. 2015, 5,
25789–25793. DOI: 10.1039/C5RA03184B.
[23] Khaligh, N. G.; Mihankhah, T. Chin. J. Catal. 2013, 34, 2167–2173. DOI: 10.1016/S1872-
2067(12)60658-5.