Hydrogen-Transfer-Mediated N-Arylation of Naphthols Using Indolines as Hydrogen Donors

Article abstract of DOI:10.1021/acs.joc.9b02558

Using a hydrogen-transfer-mediated activation mode, we report a new catalytic system for the transfer hydrogenation of naphthols. In the presence of the Pd/C catalyst and base, various naphthols reacted with indolines to afford N-aryl-substituted heterocyclic compounds. Indolines were found to act as novel hydrogen donors for naphthols under palladium catalysis. This method features good functional tolerance, operational simplicity, and a readily available catalyst.

Full text of DOI:10.1021/acs.joc.9b02558

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Article
Hydrogen-Transfer-Mediated N-Arylation of
Naphthols Using Indolines as Hydrogen Donors
Xiuwen Chen, Zhihai Yang, Xuyan Chen, Wanyi Liang, Zhongzhi Zhu, Feng Xie, and Yibiao Li
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b02558 • Publication Date (Web): 29 Nov 2019
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Hydrogen-Transfer-Mediated N-Arylation of Naphthols Using
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Indolines as Hydrogen Donors
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Xiuwen Chen,* Zhihai Yang, Xuyan Chen, Wanyi Liang, Zhongzhi Zhu,* Feng Xie and Yibiao Li
School of Biotechnology and Health Sciences, Wuyi University, Jiangmen 529020, China.
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E-mail: chenxiuwen2010@126.com; wyuchemzzz@126.com
OH
R1
N
R2
Pd/C
+
R2
+ H2O + H2
N
NaOCH3, p-xylene
R1
H
X
X
X = C, N
Hydrogen transfer reaction
Indolines as reagents and hydrogen donors
C-N bond formation
H2O and H2 as by-product
ABSTRACT: Using a hydrogen-transfer-mediated activation mode, we report a new catalytic
system for the transfer hydrogenation of naphthols. In the presence of Pd/C catalyst and base, various
naphthols reacted with indolines to afford N-aryl-substituted heterocyclic compounds. Indolines were
found to act as a novel hydrogen donors for naphthols under palladium catalysis. This method
features good functional tolerance, operational simplicity, and a readily available catalyst.
INTRODUCTION
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N-Arylheterocycles are important building blocks in medicinal, biological, and organic
chemistry.1 N-Arylindoles are of interest as antipsychotic agents,2 melatonin receptor agonists,
partial agonists,3 antipsychotic agents,4 and synthetic intermediates in the preparation of other
biologically active heterocyclic agents.5 Indoles and naphthalenes are common substructures in
natural products. The synthesis of these simple structures, or their introduction into complex
molecules, would not only have significant potential biological applications, but also represent a
significant contribution to synthetic methodology.6 In the last decades, much effort has been directed
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toward improving C–N bond formation reactions to synthesis of N-arylated heterocycles.7
Traditionally, Pd and Cu catalysts have been used for C–N bond formations. However, current aryl
halide-based strategies require the pre-synthesis of aryl halides and generate unwanted halide waste.8
Therefore, researchers should aim to develop more efficient and environmentally friendly
cross-coupling methods to construct N-arylindoles.
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Hydrogen transfer-mediated C–N bond formations have emerged as powerful tools in synthetic
organic chemistry.7b, 9 The direct coupling of phenols, instead of haloarenes, has long been a
synthetic aspiration and significant scientific challenge. Li’s group developed a highly efficient
Pd/C-catalyzed formal direct cross-coupling of phenols with various amines and anilines using
sodium formate as hydrogen donor (HD) under transfer hydrogenation conditions.10 More recently,
Li and coworkers described a palladium-catalyzed formal aromaticity transfer coupling reaction
between phenols and pyrrolidines or indolines to generate the corresponding N-cyclohexyl pyrroles
or indoles using NaBH4 as hydrogen donor (Scheme 1a).11 Recently, Li’s group have reported a
palladium-catalyzed formal direct cross-coupling of phenols with various amines and anilines
through a tandem reduction/condensation/dehydrogenation process (Scheme 1b).12 As part of our
continuing research interest in the construction of functional N-heterocycles through hydrogen
transfer,13 we have recently reported an iridium-catalyzed hydrogen-transfer-mediated
α-functionalization of 1,8-naphthyridines using tetrahydroquinolines (THQs) as inactive hydrogen
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donors . These previous studies prompted us to explore the transfer hydrogenation cross-coupling
of THQ with 2-naphthols, in which THQ serves as both reagent and hydrogen donor (Scheme 1c).
THQs does not react in this system because THQ is difficult to dehydrogenate relative to indoline in
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this catalytic system, so it cannot transfer hydrogenation process. Interestingly, we observed that,
using indoline instead of THQ under Pd/C catalysis and t-BuOK conditions, 2-naphthol was
successfully N-arylated to give desired product 3aa in 26% (Scheme 1d). Compared with
conventional HDs (such as alcohols,15 NH3BH3,16 Hantzsch esters,17 HCO2H,18 and NaCO2H10),
indolines derivatives, which are readily available, and easy to handle, were novel hydrogen donors in
hydrogen transfer reactions, providing a new and promising approach to future transfer
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hydrogenations.
Scheme 1. Unexpected new transfer hydrogenation system
Previous work
Pd/C (10 mol %)
N
+
(a)
(b)
(c)
OH
N
TfOH (25 mol %)
Add HD (50 mol %)
H
R2
R2
Pd/C
OH
+
N
R3
N
H
R1
R1
R3
Add HD
This work
OH
Pd/C (10 mol %)
+
N
H
t-BuOK (50 %)
N
Toluene
OH
Pd/C (10 mol %)
N
(d)
+
N
t-BuOK (50 %)
H
1a
2a
Toluene
Indoline
3aa, 26%
as both reagent and HD
RESULTS AND DISCUSSION
Our initial studies focused on developing a more efficient catalyst system for the coupling of
indoline 1a and 2-naphthol 2a as a model reaction. First, conventional bases were tested by
performing the reaction in toluene at 130 C for 12 h under N2 protection. Many bases were tested,
including t-BuOK, t-BuONa, HCO2Na, NaOH, and NaOCH3 (Table 1, entries 1–5). The results
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showed that NaOCH3 was the most effective base, affording product 3aa in 49% yield. However,
using CF3CO2H or no base failed to afford any desired product (entries 6 and 7). A control
experiment without catalyst afforded no product, confirming that the catalyst was essential to the
reaction (Table 1, entry 8). When various palladium catalysts were tested, Pd/C gave the best results
(Table 1, entries 9–11). Next, several solvents were examined in combination with NaOCH3 (entries
12–15), with p-xylene giving the best result (59% yield, entry 13). The best yield of 3aa (68%) was
obtained when the reaction was conducted in p-xylene at 130 C for 24 h. Finally, by changing the
reaction temperature to 140 C, the yield was increased to 76% yield (entry 17). When we reduce the
content of Pd/C catalyst, we find that the yield of Pd/C catalyst (10 wt%, 10 mol% based on Pd
content) is greatly reduced. Therefore, the conditions shown in entry 17 (Table 1) were selected as
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optimal conditions.
Table 1. Screening of optimal reaction conditionsa
OH
N
Cat.
+
N
additive, solvent
H
1a
2a
3aa
Additive
Entry
Cat. (10 mol %)
Solvent
3aa (yield %)b
(50 mol %)
1
2
Pd/C
Pd/C
t-BuOK
Toluene
Toluene
31
34
t-BuONa
3
4
5
Pd/C
Pd/C
Pd/C
HCO2Na
NaOH
Toluene
Toluene
Toluene
44
22
49
NaOCH3
6
7
Pd/C
Pd/C
TFA
-
Toluene
Toluene
Trace
Trace
8
9
-
NaOCH3
NaOCH3
NaOCH3
NaOCH3
Toluene
Toluene
Toluene
Toluene
-
-
PdCl2
10
11
Pd(PPh3)4
Pd(dba)2
-
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Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
Pd/C
NaOCH3
NaOCH3
NaOCH3
NaOCH3
NaOCH3
NaOCH3
NaOCH3
Dioxane
40
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p-xylene
DMSO
DMF
Trace
Trace
68c
(76, 74, 71)d
(62, 41)e
p-xylene
p-xylene
p-xylene
aReaction conditions: Unless otherwise stated, all reactions were performed with 1a (42.8 mg, 0.36 mmol), 2a (43.2
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mg, 0.3 mmol), catalyst (31.8mg, 10 mol%), and base (8.1mg, 50 mol%) in solvent (1.5 mL) at 130 C by oil-bath
b
c
d
heating for 16 h under N2 protection. Isolated yield. After reacting for 24 h. Yields obtained at temperatures at
e
140, 150, and 160 C, respectively. Pd/C (6 mol%, 2 mol %).
With optimized conditions in hand, the indoline substrate scope was explored. As shown in
Scheme 2, different indolines reacted efficiently with 2-naphthol 2a, furnishing desired products
3aa–3oa in moderate to good isolated yields. Various indolines bearing electron-withdrawing and
electron-donating groups all reacted smoothly. Furthermore, substituent positioning at the meta- or
para-positions of the benzene ring only slightly affected the product yields (Scheme 2, 3ca and 3da).
Obvious electronic effects were observed in the reactions of substituted indolines, with
electron-donating groups resulting in relatively high yields (3ca–3ga) and electron-withdrawing
groups (3ha-3la) resulting in relatively low yields. This phenomenon was attributed to the
electron-donating substituents enhancing the nucleophilicity of the corresponding indoles, which
favored the trapping of cyclohexenone intermediates (Scheme 2). Similarly, disubstituted indolines
(1m–1o) underwent effective coupling to give desired products 3ma–3oa. We tested some
pyrrolidines and found that no target products were obtained. It may be that pyrrolidines are more
difficult to dehydrogenate relative to indoline in this catalytic system. According to the literature,19
we have tried to test the coupling reaction of indoles and naphthol under this conditions using
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HCO2H/HCO2K as hydrogen source, but failed to give product, probably because the N atom on the
indole is weakly nucleophilic.
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Scheme 2. Substrate scope of indolines a
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OH
R1
N
Pd/C
NaOCH3, p-xylene
+
N
R1
H
1
2a
3
N
N
N
3aa,73%
3ba, 68%
3ca, 79%
PhH2CO
N
N
N
H3CO
3da, 75%
3ea, 78%
3fa, 72%
F
N
N
3ga, 75%
N
N
F
PhH2CO
3ha, 68%
3ia, 66%
H3CO2C
N
3la, 58%
N
N
NC
H3CO2C
3ja, 61%
3ka, 63%
N
N
F
3ma, 59%
3na, 50%
3oa, 52%
a Standard conditions: 1a (0.36 mmol), 2 (0.3 mmol), Pd/C (10 mol %), and base (50 mol %) in
p-xylene (1.5 mL) at 140 C for 24 h.
Scheme 3. Variation of both coupling partners
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OH
R1
N
R2
Pd/C
NaOCH3, p-xylene
+
R2
N
R1
H
X
X
X = C, N
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N
N
N
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CO2CH3
OCH3
OCH3
3ab, 70%
3cb, 71%
3ac, 65%
N
N
N
PhH2CO
CO2CH3
F
OH
3gc, 61%
3ad, 57%
3ae, 55%
N
OH
N
N
3af, 56%
3ag, 52%
3ah, 18%
N
N
N
N
N
3ai, 53%
3di, 56%
3aj, 0%
Next, we focused on varying both coupling partners (Scheme 3). Reactions of indolines 1 with
various naphthols 2 were explored. Similar to the results described in Scheme 3, all reactions
proceeded efficiently to afford the desired products in moderate to good isolated yields (3ab–3di).
Various naphthols bearing electron-withdrawing or electron-donating groups were all suitable
substrates in this transformation, with the corresponding products obtained in moderate to good
yields. Furthermore, naphthols bearing electron-donating substituents provided the desired products
in higher yields than those bearing electron-withdrawing substituents (3ab–3gc). When
2,6-naphthalenediol and 2,7-dihydroxynaphthalene were used as starting materials, only one C–N
bond was formed (3ae, 3af). Interestingly, 2-hydroxyanthracene reacted smoothly with indoline to
afford desired N-arylation product 3ag. However, the reaction of phenol 2h with indoline 1a afforded
only a low yield (3ah, 18%), it is possible that phenol is more difficult to hydrogenate than naphthol
in this catalytic system using indoline as hydrogen donor. Interestingly, the catalytic system was also
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compatible with the transformation of 6-hydroxyquinoline, affording the new indole-quinoline linked
biheteroarenes (3ai, 3di). When using 1-naphthol as a substrate, unfortunately no target product (3aj)
was obtained.
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Scheme 4. Control experiments
N
+
standard
conditions
OH
N
H
+
1a',
11%
3aa'
OH
, 12%
N
3h
(eq 1)
H
1a
2a
3aa
+
, 51% +
2a'
, 4%
OH
+
standard conditions
3aa
3aa'
, 0%
N
, 0% +
(eq 2)
(eq 3)
H
1a
2a'
O
standard
conditions
N
+
3aa
, 41% +
N
H
1a
1a
2a''
3aa''
, 36%
O
N
N
3ah
+
(eq 4)
(eq 5)
(eq 6)
+
standard conditions
N
H
3ah'
, 71%
, 22%
N
standard conditions
standard conditions
3aa
, 94%
3aa'
35%
25%
46%
76%
20%
25%
48%
48%
N
65%
2a
+
N
48%
48%
47%
30%
H
30%
20%
3aa d (D%)
1a-dn (D%)
-
n
To gain insight into the reaction mechanism, several control experiments were performed
(Scheme 4). The model reaction was interrupted after 3 h to analyze the intermediates. Product 3aa,
indole 1a’, 3aa’, and 1,2,3,4-tetrahydro-2-naphthalenol 2a’ were detected in 51%, 11%, 12%, and
4% yields, respectively (Scheme 4, Eq. 1). The reaction of 2a’ with indoline 1a under the standard
conditions failed to give product 3aa (Eq. 2), supporting that suppressing the formation of
over-hydrogenated tetrahydronaphthalenol 2a’ was the key factor in chemoselective generation of
product 3aa. The reaction of 1a reacting with β-tetralone gave products 3aa and 3aa” in 41% and
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36% yields, respectively (Eq. 3). When we tried to separate 3aa’’, we found that 3aa’’ rapidly
converts to the other intermediate. Further control experiments suggested that both cyclohexanone
and cyclohexenone might be reaction intermediates (Eq. 4). Furthermore, reacting 3aa’ under the
standard reaction conditions gave product 3aa in 94% yield (Eq. 5), indicating that 3aa’ was a key
reaction intermediate. The deuterium-labelling experiment of indoline 1a-dn with 2a resulted in
product 3aa-dn, with incorporation of deuterium on the naphthalene unit, suggesting that hydrogen
was transferred from indoline 1a to 2-naphthol 2a (Eq. 6). The naphthol 2a is initially activated by
hydrogen transfer of [DPd(II)D] arising from the metal catalyst, affording cyclohexen-1-ol
intermediate and its tautomer cyclohexen-2-ol (in this tautomeric process, the D ratio was different
on the naphthol ring).
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Based on the above results, a tentative mechanism for this hydrogen transfer reaction was
proposed, as shown in Scheme 5. Initially, the Pd-catalyzed dehydrogenation of indoline 1a (1.5 eq.)
forms an active HPdIIH species, which performs the first hydrogenation of the 2-naphthol ring to
form activated intermediate 2a-A and regenerated the active palladium catalyst. Under NaOMe
conditions, intermediate 2a-A undergoes fast condensation with indoline 1a to give key intermediate
3aa-B. The role of NaOMe is to promote the conversion of naphthol to cyclohexenone intermediate
under this condition. Next, desired product 3aa can be obtained by palladium-catalyzed
dehydrogenation of intermediate 3aa-B to regenerate the HPdIIH species.
Scheme 5. Plausible reaction pathways
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Pd0
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HD
O
NaOMe
+
N
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OH
2a-A
NaOMe
1a
H
N
1a'
H
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2a
N
3aa-B
HPdIIH
N
3aa
CONCLUSIONS
In summary, a hydrogen-transfer-mediated activation mode for non-activated naphthols has been
developed to achieve the simple, efficient, and novel N-arylation of naphthols using indolines as both
reagent and hydrogen donor. The developed chemistry features operational simplicity, a readily
available catalyst, good functional tolerance, and a wide substrate scope. This method offers a
significant basis for the further development of new protocols for directly transforming or
functionalizing inert N-arylated indoles. In addition, the reaction employed indoline as the hydrogen
donor, avoiding the use of a potentially hazardous pressurized H2 atmosphere. Indoline is a novel
hydrogen donor in hydrogen transfer reactions, providing a promising new approach to future
transfer hydrogenations.
EXPERIMENTAL SECTION
General Information. All experiments were carried out under the standard conditions. Flash column
chromatography was performed over silica gel (200−300 mesh). All the obtained products were
1
characterized by melting points (m.p), H NMR and 13C {1H} NMR spectra were recorded on a
Bruker-AV (400 and 100 MHz, respectively) instrument internally referenced to TMS, chloroform
and DMSO signals. MS analyses were performed on an Agilent 5975 GC−MS instrument (EI). High
resolution mass spectra (HRMS) were recorded using electrospray ionization (ESI) and
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time-of-flight (TOF) mass analysis. Melting points were uncorrected. The new compounds were
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characterized by H NMR, C {1H} NMR, MS and HRMS. Unless otherwise stated, all the reagents
were purchased from commercial sources (J&KChemic, TCI, Fluka, Acros, SCRC), used without
further purification.
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Typical procedure for the synthesis of 3. In a 25 mL Schlenk tube was combined Indolines 1
(0.36 mmol), Naphthols 2 (0.30 mmol), Pd/C (10 wt%, 10 mol% based on Pd content) and NaOCH3
(50 mol%) in P-xylene (1.5 mL). The mixture was then stirred at 140 °C under oil-bath heating for
24 h. After cooling down to room temperature, the reaction mixture was concentrated by removing
the solvent under vacuum, and the residue was purified by preparative TLC on silica, eluting with
petroleum ether (60-90 °C): ethyl acetate (50:1) to give 3.
Synthesis of 1-(naphthalen-2-yl)-1H-indole (3aa): Under N2 atmosphere, Indoline 1a (0.4 g, 3.6
mmol), 2-Naphthol 2a (0.4 g, 3 mmol), Pd/C (318 mg, 10 wt%, 10 mol% based on Pd content) and
NaOCH3 (81 mg, 50 mol%) in P-xylene (5.0 mL) were introduced into a Schlenk tube (50 mL),
successively. Then, the Schlenk tube was closed and the resulting mixture was stirred at 140 °C for
24 h. Purification of the residue by column chromatography (50:1 petroleum ether: ethyl acetate)
gave 3aa as a yellow solid (0.5 g, 68% yield). Yellow solid; m.p: 90.9-92.7 °C; Rf = 0.3 (petroleum
ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.02 (d, J = 8.7 Hz, 1H), 8.01 – 7.88
(m, 3H), 7.80 (d, J = 6.7 Hz, 1H), 7.76 – 7.67 (m, 2H), 7.66 – 7.54 (m, 2H), 7.50 (d, J = 3.1 Hz, 1H),
7.39 – 7.26 (m, 2H), 6.81 (d, J = 3.2 Hz, 1H). 13C {1H} NMR (101 MHz, CDCl3) δ 137.4, 136.2,
133.9, 131.9, 129.7, 129.5, 128.23, 127.9, 127.8, 127.0, 126.1, 123.3, 122.6, 122.0, 121.3, 120.6,
110.7, 103.9. HRMS (ESI) m/z calcd for C18H14N [M+H]+ : 244.1121; found 244.1113.
2-methyl-1-(naphthalen-2-yl)-1H-indole (3ba). Yellow oil (54.7 mg, 56% yield); Rf = 0.3
(petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.02 (d, J = 8.6 Hz, 1H),
7.98 (dd, J = 6.0, 3.5 Hz, 1H), 7.91 (dd, J = 6.0, 3.5 Hz, 1H), 7.87 (d, J = 1.7 Hz, 1H), 7.67 – 7.62 (m,
1H), 7.60 (dd, J = 6.2, 3.3 Hz, 2H), 7.48 (dd, J = 8.6, 2.0 Hz, 1H), 7.21 – 7.10 (m, 3H), 6.49 (s, 1H),
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2.38 (s, 3H). C{1H} NMR (101 MHz, CDCl3) δ 138.4, 137.3, 135.5, 133.7, 132.6, 129.4, 128.4,
128.0, 127.9, 126.8, 126.6, 126.4, 126.2, 121.2, 120.2, 119.7, 110.1, 101.5, 13.5. HRMS (ESI) m/z
calcd for C19H16N [M+H]+ : 258.1277; found 258.1271.
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5-methyl-1-(naphthalen-2-yl)-1H-indole (3ca). Yellow solid (59.4 mg, 77% yield); m.p:
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164.9-167.3 °C; Rf = 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); H NMR (400 MHz, CDCl3) δ
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7.90 (d, J = 8.7 Hz, 1H), 7.88 – 7.77 (m, 3H), 7.60 (dd, J = 8.7, 1.9 Hz, 1H), 7.57 – 7.43 (m, 4H),
7.35 (d, J = 3.1 Hz, 1H), 7.04 (d, J = 8.3 Hz, 1H), 6.62 (d, J = 2.3 Hz, 1H), 2.46 (s, 3H). 13C{1H}
NMR (101 MHz, CDCl3) δ 137.6, 134.5, 134.0, 133.9, 131.8, 129.9, 129.6, 128.2, 127.9, 127.8,
126.9, 126.0, 124.2, 123.2, 121.6, 120.9, 110.4, 103.5, 21.5. HRMS (ESI) m/z calcd for C19H16N
[M+H]+ : 258.1277; found 258.1271.
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6-methyl-1-(naphthalen-2-yl)-1H-indole (3da). Yellow oil (57.8 mg, 75% yield); Rf = 0.3
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(petroleum ether/ethyl acetate = 50/1, v/v); H NMR (400 MHz, CDCl3) δ 8.02 (d, J = 8.7 Hz, 1H),
7.99 – 7.89 (m, 3H), 7.68 (dd, J = 15.9, 8.3 Hz, 2H), 7.62 – 7.53 (m, 2H), 7.49 (s, 1H), 7.41 (d, J =
3.1 Hz, 1H), 7.09 (d, J = 8.0 Hz, 1H), 6.73 (s, 1H), 2.52 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ
137.5, 136.6, 133.9, 132.4, 131.9, 129.6, 127.9, 127.8, 127.7, 127.3, 126.9, 126.1, 123.5, 122.3,
122.0, 120.9, 110.5, 103.7, 22.0. HRMS (ESI) m/z calcd for C19H16N [M+H]+ : 258.1277; found
258.1271.
5-methoxy-1-(naphthalen-2-yl)-1H-indole (3ea). Yellow oil (63.9mg, 78% yield); Rf = 0.3
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(petroleum ether/ethyl acetate = 50/1, v/v); H NMR (400 MHz, CDCl3) δ 7.99 (d, J = 8.7 Hz, 1H),
7.96 – 7.86 (m, 3H), 7.67 (dd, J = 8.7, 2.1 Hz, 1H), 7.62 – 7.52 (m, 3H), 7.45 (d, J = 3.1 Hz, 1H),
7.23 (s, 1H), 6.97 (d, J = 8.9 Hz, 1H), 6.70 (d, J = 3.0 Hz, 1H), 3.93 (s, 3H). 13C{1H} NMR (101 MHz,
CDCl3) δ 154.8, 137.5, 133.9, 131.8, 131.4, 130.1, 129.6, 128.6, 127.9, 127.7, 127.0, 126.0, 123.1,
121.5, 112.6, 111.5, 103.6, 102.9, 55.9. HRMS (ESI) m/z calcd for C19H16NO [M+H]+ : 274.1226;
found 274.1219.
4-(benzyloxy)-1-(naphthalen-2-yl)-1H-indole (3fa). Yellow oil (73.3 mg, 70% yield); Rf = 0.3
(petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 7.86 – 7.68 (m, 4H), 7.50
(d, J = 8.7 Hz, 1H), 7.46 – 7.35 (m, 4H), 7.28 (t, J = 7.4 Hz, 2H), 7.21 (d, J = 2.7 Hz, 2H), 7.14 (d, J
= 8.2 Hz, 1H), 7.02 (dd, J = 15.6, 7.6 Hz, 1H), 6.80 (s, 1H), 6.54 (d, J = 7.7 Hz, 1H), 5.13 (s, 2H).
13C{1H} NMR (101 MHz, CDCl3) δ 152.8, 137.7, 137.5, 133.9, 131.9, 129.6, 128.6, 127.9, 127.9,
127.8, 127.4, 127.0, 126.8, 126.2, 123.4, 123.4, 122.0, 120.5, 104.4, 102.0, 101.5, 70.1. HRMS (ESI)
m/z calcd for C25H20NO [M+H]+ : 350.1539; found 350.1531.
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5-(benzyloxy)-1-(naphthalen-2-yl)-1H-indole (3ga). Red solid (78.5 mg, 75% yield); m.p:
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115.2-117.3 °C; Rf = 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); H NMR (400 MHz, CDCl3) δ
8.00 (d, J = 8.7 Hz, 1H), 7.98 – 7.86 (m, 3H), 7.68 (dd, J = 8.7, 2.1 Hz, 1H), 7.65 – 7.54 (m, 5H),
7.51 – 7.43 (m, 3H), 7.40 (t, J = 7.2 Hz, 1H), 7.33 (d, J = 2.0 Hz, 1H), 7.08 (dd, J = 8.9, 2.1 Hz, 1H),
6.72 (d, J = 3.1 Hz, 1H), 5.21 (s, 2H). 13C{1H} NMR (101 MHz, CDCl3) δ 153.9, 137.8, 137.5, 134.0,
131.8, 131.6, 130.1, 129.7, 128.7, 128.6, 127.9, 127.9, 127.8, 127.6, 127.0, 126.1, 123.1, 121.5,
113.4, 111.5, 104.6, 103.7, 70.9. HRMS (ESI) m/z calcd for C25H20NO [M+H]+ : 350.1539; found
350.1528.
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5-fluoro-1-(naphthalen-2-yl)-1H-indole (3ha). Yellow oil (46.9 mg, 60% yield); Rf = 0.3
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(petroleum ether/ethyl acetate = 50/1, v/v); H NMR (400 MHz, CDCl3) δ 7.90 (d, J = 8.7 Hz, 1H),
7.82 (dd, J = 15.9, 8.5 Hz, 3H), 7.61 – 7.42 (m, 4H), 7.34 (dd, J = 3.1, 1.3 Hz, 1H), 7.28 (d, J = 7.6
Hz, 1H), 6.94 (dd, J = 8.4, 7.0 Hz, 1H), 6.65 (d, J = 2.6 Hz, 1H). 13C{1H} NMR (101 MHz, CDCl3) δ
160.4 (d, J = 237.9 Hz), 137.0, 136.2 (d, J = 12.0 Hz), 133.9, 132.0, 129.9, 128.7 (d, J = 3.5 Hz),
127.9, 127.8, 127.1, 126.3, 125.9, 122.9, 122.0, 121.9, 109.3 (d, J = 24.5 Hz), 103.9, 97.2 (d, J =
27.1 Hz). 19F NMR (376 MHz, CDCl3) δ -119.8. HRMS (ESI) m/z calcd for C18H13FN [M+H]+ :
262.1027; found 262.1021.
4-fluoro-1-(naphthalen-2-yl)-1H-indole (3ia). Yellow oil (47.7 mg, 61% yield); Rf = 0.3
(petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.01 (d, J = 8.7 Hz, 1H),
7.99 – 7.86 (m, 3H), 7.65 (dd, J = 8.7, 2.1 Hz, 1H), 7.63 – 7.53 (m, 2H), 7.50 – 7.37 (m, 2H), 7.18
(dd, J = 13.4, 7.8 Hz, 1H), 6.91 (t, J = 7.9 Hz, 1H), 6.86 (s, 1H). 13C{1H} NMR (101 MHz, CDCl3) δ
156.5 (d, J = 247.4 Hz), 138.7 (d, J = 11.0 Hz), 137.0, 133.8, 132.1, 129.7, 128.2, 127.9, 127.8,
127.1, 126.4, 123.2, 123.0 (d, J = 7.7 Hz), 122.3, 118.5 (d, J = 23.0 Hz), 106.8 (d, J = 3.4 Hz), 105.3
(d, J = 18.9 Hz), 99.8. 19F NMR (376 MHz, CDCl3) δ -121.7. HRMS (ESI) m/z calcd for C18H13FN
[M+H]+ : 262.1027; found 262.1038.
Methyl 1-(naphthalen-2-yl)-1H-indole-6-carboxylate (3ja). Yellow solid (46.1 mg, 51% yield);
m.p: 150-151 °C; Rf = 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ
8.37 (s, 1H), 8.05 (d, J = 8.7 Hz, 1H), 7.99 – 7.87 (m, 4H), 7.77 (d, J = 8.3 Hz, 1H), 7.68 (d, J = 8.6
Hz, 1H), 7.64 – 7.54 (m, 3H), 6.80 (d, J = 3.1 Hz, 1H), 3.94 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3)
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δ 168.0, 136.6, 135.7, 133.8, 132.9, 132.2, 131.4, 129.9, 127.9, 127.9, 127.1, 126.4, 124.3, 123.3,
122.5, 121.6, 120.8, 112.9, 103.9, 51.9. HRMS (ESI) m/z calcd for C20H16NO2 [M+H]+ : 302.1176;
found 302.1171.
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Methyl 1-(naphthalen-2-yl)-1H-indole-4-carboxylate (3ka). Yellow oil (47.9 mg, 53% yield); Rf =
0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.10 – 7.98 (m, 2H),
7.97 – 7.88 (m, 3H), 7.82 (d, J = 8.2 Hz, 1H), 7.65 – 7.54 (m, 4H), 7.45 (d, J = 3.0 Hz, 1H), 7.31 (t, J
= 8.0 Hz, 1H), 4.07 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ 167.9, 137.0, 136.8, 133.8, 132.1,
130.3, 129.8, 128.9, 127.9, 127.8, 127.1, 126.4, 124.0, 123.4, 122.6, 122.1, 121.7, 115.4, 104.9, 51.9.
HRMS (ESI) m/z calcd for C20H16NO2 [M+H]+ : 302.1176; found 302.1188.
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1-(naphthalen-2-yl)-1H-indole-5-carbonitrile (3la). Yellow solid (43.4 mg, 54% yield); m.p:
133.6-137.5 °C; Rf = 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ
8.06 – 7.96 (m, 2H), 7.94 – 7.89 (m, 1H), 7.86 (d, J = 5.7 Hz, 2H), 7.60 – 7.52 (m, 4H), 7.50 (d, J =
3.3 Hz, 1H), 7.41 (dd, J = 8.6, 1.2 Hz, 1H), 6.76 (d, J = 3.3 Hz, 1H). 13C{1H} NMR (101 MHz,
CDCl3) δ 137.7, 136.1, 133.7, 132.3, 130.6, 130.0, 129.1, 128.0, 127.9, 127.4, 126.7, 126.7, 125.4,
123.0, 122.7, 120.6, 111.5, 104.4, 103.6. HRMS (ESI) m/z calcd for C19H13N2 [M+H]+ : 269.1073;
found 269.1066.
2,3-dimethyl-1-(naphthalen-2-yl)-1H-indole (3ma). Yellow solid (48.0 mg, 59% yield); m.p:
87-89.1°C; Rf = 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.07 –
7.98 (m, 2H), 7.94 (dd, J = 6.0, 3.4 Hz, 1H), 7.89 (s, 1H), 7.71 – 7.59 (m, 3H), 7.51 (dd, J = 8.6, 1.5
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Hz, 1H), 7.28 – 7.10 (m, 3H), 2.44 (s, 3H), 2.36 (s, 3H). C{1H} NMR (101 MHz, CDCl3) δ 137.6,
135.9, 133.8, 133.1, 132.4, 132.4, 129.3, 129.0, 127.9, 127.9, 126.8, 126.5, 126.3, 121.3, 119.7,
118.0, 109.8, 108.3, 11.1, 8.9. HRMS (ESI) m/z calcd for C20H18N [M+H]+ : 272.1434; found
272.1426.
5-fluoro-2-methyl-1-(naphthalen-2-yl)-1H-indole (3na). Yellow oil (36.3 mg, 44% yield); Rf = 0.3
(petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 7.94 (d, J = 8.6 Hz, 1H),
7.93 – 7.88 (m, 1H), 7.86 – 7.81 (m, 1H), 7.77 (d, J = 1.6 Hz, 1H), 7.60 – 7.49 (m, 2H), 7.37 (dd, J =
8.6, 2.0 Hz, 1H), 7.22 (dd, J = 9.5, 2.4 Hz, 1H), 6.98 (dd, J = 8.9, 4.4 Hz, 1H), 6.79 (td, J = 9.1, 2.5
Hz, 1H), 6.38 (s, 1H), 2.30 (s, 3H). 13C{1H} NMR (101 MHz, CDCl3) δ 158.4 (d, J = 234.3 Hz), 139.1,
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135.3, 135.1, 133.7, 132.6, 129.6, 128.7 (d, J = 10.2 Hz), 127.9 (d, J = 4.2 Hz), 126.9, 126.8, 126.4,
125.9, 110.7 (d, J = 9.6 Hz), 109.3, 109.1, 104.6 (d, J = 23.6 Hz), 101.6 (d, J = 4.2 Hz), 13.59 . 19F
NMR (376 MHz, CDCl3) δ -124.6. HRMS (ESI) m/z calcd for C19H15NF [M+H]+ : 276.1183; found
276.1188.
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2,5-dimethyl-1-(naphthalen-2-yl)-1H-indole (3oa). Yellow solid (40.6 mg, 50% yield); m.p:
99.7-100.3 °C; Rf = 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ
7.95 (d, J = 8.6 Hz, 1H), 7.92 (dd, J = 6.0, 3.4 Hz, 1H), 7.85 (dd, J = 6.1, 3.3 Hz, 1H), 7.80 (d, J =
1.3 Hz, 1H), 7.59 – 7.51 (m, 2H), 7.42 (dd, J = 8.6, 2.0 Hz, 1H), 7.37 (s, 1H), 7.02 (d, J = 8.3 Hz,
1H), 6.90 (d, J = 8.2 Hz, 1H), 6.35 (s, 1H), 2.44 (s, 3H), 2.31 (s, 3H). 13C{1H} NMR (101 MHz,
CDCl3) δ 137.3, 136.8, 135.7, 133.7, 132.5, 129.4, 129.3, 128.6, 127.9, 127.9, 126.8, 126.5, 126.3,
126.1, 122.7, 119.5, 109.8, 101.2, 21.5, 13.5. HRMS (ESI) m/z calcd for C20H18N [M+H]+ :
272.1434; found 272.1426.
1-(6-methoxynaphthalen-2-yl)-1H-indole (3ab). White oil (55.7 mg, 68% yield); Rf = 0.3
(petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 7.97 – 7.90 (m, 2H), 7.83
(d, J = 8.9 Hz, 2H), 7.75 – 7.64 (m, 2H), 7.49 (d, J = 2.7 Hz, 1H), 7.39 – 7.26 (m, 4H), 6.82 (d, J =
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0.7 Hz, 1H), 4.02 (s, 3H). C{1H} NMR (101 MHz, CDCl3) δ 158.0, 136.3, 135.5, 133.2, 129.4,
129.3, 129.2, 128.3, 128.3, 123.9, 122.4, 122.2, 121.3, 120.4, 119.9, 110.6, 105.9, 103.6, 55.4.
HRMS (ESI) m/z calcd for C19H16NO [M+H]+ : 274.1226; found 274.1219.
1-(6-methoxynaphthalen-2-yl)-5-methyl-1H-indole (3cb). Yellow oil (60.3 mg, 70% yield); Rf =
0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 7.75 – 7.68 (m, 2H),
7.63 (d, J = 8.9 Hz, 1H), 7.47 (d, J = 8.6 Hz, 1H), 7.38 (s, 2H), 7.25 (d, J = 2.9 Hz, 1H), 7.15 – 7.03
(m, 2H), 6.94 (d, J = 8.5 Hz, 1H), 6.52 (s, 1H), 3.82 (s, 3H), 2.37 (s, 3H). 13C{1H} NMR (101 MHz,
CDCl3) δ 157.9, 135.7, 134.6, 133.0, 129.7, 129.7, 129.3, 129.2, 128.3, 128.2, 123.9, 123.8, 121.9,
120.8, 119.8, 110.3, 105.9, 103.1, 55.4, 21.4. HRMS (ESI) m/z calcd for C20H18NO [M+H]+ :
288.1383; found 288.1376.
Methyl 6-(1H-indol-1-yl)-2-naphthoate (3ac). Yellow solid (41.6 mg, 46% yield); m.p: 75-77.8 °C;
Rf = 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.66 (s, 1H),
8.15 – 8.06 (m, 2H), 7.95 (d, J = 1.2 Hz, 1H), 7.90 (d, J = 8.6 Hz, 1H), 7.75 – 7.70 (m, 2H), 7.67 (d,
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J = 8.1 Hz, 1H), 7.44 (d, J = 3.3 Hz, 1H), 7.30 – 7.17 (m, 2H), 6.75 (d, J = 3.2 Hz, 1H), 4.00 (s, 3H).
13C{1H} NMR (101 MHz, CDCl3) δ 167.1, 139.4, 136.1, 135.8, 131.1, 130.9, 130.7, 129.7, 127.9,
127.8, 127.5, 126.4, 123.8, 122.8, 121.4, 121.2, 120.8, 110.6, 104.6, 52.3. HRMS (ESI) m/z calcd for
C20H16NO2 [M+H]+ : 302.1176; found 302.1172.
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Methyl 6-(5-methoxy-1H-indol-1-yl)-2-naphthoate (3gc). White oil (54.9 mg, 45% yield); Rf = 0.3
(petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.69 (s, 1H), 8.16 (dd, J =
8.6, 1.4 Hz, 1H), 8.10 (d, J = 8.8 Hz, 1H), 7.99 – 7.90 (m, 2H), 7.74 (dd, J = 8.7, 2.1 Hz, 1H), 7.62 (d,
J = 9.0 Hz, 1H), 7.53 (d, J = 7.4 Hz, 2H), 7.44 (dd, J = 11.9, 5.3 Hz, 3H), 7.37 (d, J = 7.3 Hz, 1H),
7.28 (d, J = 2.7 Hz, 1H), 7.04 (dd, J = 8.9, 2.3 Hz, 1H), 6.69 (d, J = 3.2 Hz, 1H), 5.18 (s, 2H), 4.04 (s,
3H). 13C{1H} NMR (101 MHz, CDCl3) δ 167.1, 154.1, 139.5, 137.6, 136.2, 131.2, 131.1, 130.9,
130.6, 130.3, 128.6, 128.3, 127.9, 127.8, 127.5, 127.4, 126.4, 123.5, 120.7, 113.5, 111.4, 104.7,
104.4, 70.8, 52.3. HRMS (ESI) m/z calcd for C27H22NO3 [M+H]+ : 408.1594; found 408.1599.
1-(6-fluoronaphthalen-2-yl)-1H-indole (3ad). Yellow oil(42.3 mg, 54% yield); Rf = 0.3
(petroleum ether/ethyl acetate = 20/1, v/v); 1H NMR (500 MHz, CDCl3) δ 7.96 (dd, J = 5.3, 3.3 Hz,
2H), 7.90 (dd, J = 9.0, 5.5 Hz, 1H), 7.78 (d, J = 8.1 Hz, 1H), 7.73 (dd, J = 8.8, 1.8 Hz, 1H), 7.67 (d, J
= 7.5 Hz, 1H), 7.58 (dd, J = 9.6, 2.5 Hz, 1H), 7.47 (d, J = 3.2 Hz, 1H), 7.43 – 7.36 (m, 1H), 7.35 –
7.23 (m, 2H), 6.79 (dd, J = 3.2, 0.6 Hz, 1H). 13C{1H} NMR (126 MHz, CDCl3) δ 160.8 (d, J = 246.5
Hz), 136.8 (d, J = 2.7 Hz), 136.0, 132.5 (d, J = 9.2 Hz), 130.8, 130.1 (d, J = 8.8 Hz), 129.4, 128.9 (d,
J = 5.4 Hz), 128.1, 124.4, 122.6, 122.0, 121.3, 120.6, 117.5 (d, J = 25.6 Hz), 111.1 (d, J = 20.9 Hz),
110.5, 103.9. 19F NMR (471 MHz, CDCl3) δ -114.2. HRMS (ESI) m/z calcd for C18H13FN [M+H]+ :
262.1027; found 262.1021.
6-(1H-indol-1-yl)naphthalen-2-ol (3ae). Yellow oil (38.8 mg, 50% yield); Rf = 0.3 (petroleum
ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 7.72 (s, 1H), 7.68 – 7.59 (m, 3H), 7.47
(t, J = 8.1 Hz, 2H), 7.29 (d, J = 2.9 Hz, 1H), 7.17 – 6.99 (m, 4H), 6.61 (d, J = 2.9 Hz, 1H), 5.49 (s,
1H). 13C{1H} NMR (101 MHz, CDCl3) δ 153.8, 136.3, 135.4, 133.2, 129.7, 129.3, 129.1, 128.3, 127.9,
124.1, 122.4, 122.3, 121.2, 120.4, 118.9, 110.6, 109.7, 103.5. HRMS (ESI) m/z calcd for C18H14NO
[M+H]+ : 260.1070; found 260.1064.
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7-(1H-indol-1-yl)naphthalen-2-ol (3af). Yellow solid (31.9 mg, 41% yield); m.p: 90-91.4°C; Rf =
0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 8.7 Hz,
1H), 7.83 (d, J = 9.4 Hz, 1H), 7.77 (d, J = 7.8 Hz, 2H), 7.69 (d, J = 7.9 Hz, 1H), 7.53 (dd, J = 8.6, 2.0
Hz, 1H), 7.46 (d, J = 3.2 Hz, 1H), 7.33 – 7.22 (m, 2H), 7.20 – 7.14 (m, 2H), 6.77 (d, J = 2.9 Hz, 1H),
5.75 (s, 1H). 13C{1H} NMR (101 MHz, CDCl3) δ 154.5, 138.0, 136.1, 135.2, 129.8, 129.5, 129.4,
128.2, 127.3, 122.5, 121.25, 120.9, 120.5, 120.4, 118.1, 110.7, 109.4, 103.8. HRMS (ESI) m/z calcd
for C18H14NO [M+H]+ : 260.1070; found 260.1064.
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1-(anthracen-2-yl)-1H-indole (3ag). Yellow solid (29.9 mg, 34% yield); m.p: 186.6-189.9 °C; Rf
= 0.3 (petroleum ether/ethyl acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 8.44 (d, J = 18.3 Hz,
2H), 8.11 (d, J = 9.0 Hz, 1H), 8.06 – 7.93 (m, 3H), 7.71 (dd, J = 13.4, 7.9 Hz, 2H), 7.64 (dd, J = 9.0,
1.9 Hz, 1H), 7.53 – 7.42 (m, 3H), 7.29 – 7.16 (m, 2H), 6.74 (d, J = 3.2 Hz, 1H). 13C{1H} NMR (101
MHz, CDCl3) δ 136.7, 136.1, 132.4, 131.8, 131.8, 131.7, 130.1, 130.1, 129.5, 128.3, 128.1, 128.0,
126.5, 126.1, 126.0, 125.6, 123.4, 122.6, 121.3, 120.6, 110.8, 104.0. HRMS (ESI) m/z calcd for
C22H16N [M+H]+ : 294.1277; found 294.1270.
1-phenyl-1H-indole (3ah). Yellow oil (10.4 mg, 18% yield); Rf = 0.3 (petroleum ether/ethyl
acetate = 50/1, v/v); 1H NMR (400 MHz, CDCl3) δ 7.74 (d, J = 7.7 Hz, 1H), 7.62 (d, J = 8.2 Hz, 1H),
7.56 (d, J = 4.2 Hz, 4H), 7.44 – 7.38 (m, 2H), 7.31 – 7.19 (m, 2H), 6.74 (d, J = 3.2 Hz, 1H). 13C{1H}
NMR (101 MHz, CDCl3) δ 139.9, 135.9, 129.6, 129.4, 127.9, 126.5, 124.4, 122.4, 121.2, 120.4,
110.5, 103.6. HRMS (ESI) m/z calcd for C14H12N [M+H]+ : 194.0964; found 194.0981.
6-(1H-indol-1-yl)quinolone (3ai). Yellow oil (38.8 mg, 53% yield); Rf = 0.3 (petroleum
ether/ethyl acetate = 10/1, v/v); 1H NMR (500 MHz, CDCl3) δ 8.97 (d, J = 4.1 Hz, 1H), 8.29 (d, J =
8.9 Hz, 1H), 8.17 (d, J = 8.1 Hz, 1H), 7.94 – 7.86 (m, 2H), 7.77 (d, J = 7.7 Hz, 1H), 7.68 (d, J = 8.1
Hz, 1H), 7.50 – 7.43 (m, 2H), 7.33 – 7.23 (m, 2H), 6.79 (d, J = 3.2 Hz, 1H). 13C{1H} NMR (126 MHz,
CDCl3) δ 150.5, 146.6, 137.8, 135.9, 135.8, 131.2, 129.6, 128.8, 127.9, 126.6, 122.8, 122.0, 121.4,
121.2, 120.8, 110.5, 104.5. HRMS (ESI) m/z calcd for C17H13N2 [M+H]+ : 245.1073; found
245.1088.
6-(6-methyl-1H-indol-1-yl)quinoline (3di). Yellow oil (43.3 mg, 53% yield); Rf = 0.3 (petroleum
ether/ethyl acetate = 10/1, v/v); 1H NMR (500 MHz, CDCl3) δ 8.98 (d, J = 3.0 Hz, 1H), 8.31 (d, J =
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8.9 Hz, 1H), 8.25 (d, J = 8.3 Hz, 1H), 7.95 (dd, J = 8.9, 2.2 Hz, 1H), 7.92 (s, 1H), 7.63 (d, J = 8.0 Hz,
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1H), 7.52 (dd, J = 8.2, 4.1 Hz, 1H), 7.47 (d, J = 0.6 Hz, 1H), 7.40 (d, J = 3.3 Hz, 1H), 7.08 (dd, J =
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8
8.0, 0.9 Hz, 1H), 6.73 (dd, J = 3.3, 0.7 Hz, 1H), 2.50 (s, 3H). 13C{1H} NMR (126 MHz, CDCl3) δ
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150.2, 146.3, 138.1, 136.3, 136.1, 132.7, 130.9, 128.9, 127.4, 127.3, 126.9, 122.6, 121.9, 121.3,
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120.9, 110.3, 104.3, 21.9. HRMS (ESI) m/z calcd for C18H15N2 [M+H]+ : 259.1230; found 259.1213.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:
10.XXX.
1H and 13NMR spectra for the products (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: chenxiuwen2010@126.com.
*E-mail: wyuchemzzz@126.com.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the Foundation of the Department of Education of Guangdong Province
(2018KZDXM070, 2017KZDXM085), the Foundation for Young Talents (2018KQNCX272,
2018KQNCX273), Jiangmen City Science and Technology Basic Research Project (2019JC01004,
2019JC01024), Science Foundation for Young Teachers of Wuyi University (2019td06) and
National innovation and entrepreneurship training program for college students (201911349030) for
financial support.
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