Mild and efficient prepare disperse yellow 184, disperse yellow 232 and their analogues via LTTM promoted three-component reaction

Article abstract of DOI:10.1016/j.dyepig.2020.108415

A convenient protocol for the synthesis of disperse yellow 184, disperse yellow 232 and their analogues via a three-component one-pot reaction of salicylaldehyde, o-aminophenol and ethyl cyanoacetate has been established. Cheap and eco-friendly ethanol was employed as solvent. One drop of low-transition-temperature mixture (LTTM) which formed from l(?)-Proline and oxalic acid could smoothly promote the reaction of 0.5 mmol raw materials. Compared to the classical methodologies, the present pathway has broad reaction scope and affords all products in good to excellent yields. Furthermore, this process could reduce the reaction temperature from 135 to 85 °C and avoid the problems associated with catalyst cost, handling, safety and pollution. On the basis of comparative experiments and DFT calculation, possible mechanism of this strategy is discussed in detail.

Full text of DOI:10.1016/j.dyepig.2020.108415

Dyes and Pigments 179 (2020) 108415
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Mild and efficient prepare disperse yellow 184, disperse yellow 232 and
their analogues via LTTM promoted three-component reaction
Yudi Xiao, Ao Liu, Jiali Gao, Yizhen Zou, Chengwei Lü*, Yue An**
College of Chemistry and Chemical Engineering, Liaoning Normal University, Huanghe Road 850#, Dalian, 116029, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A convenient protocol for the synthesis of disperse yellow 184, disperse yellow 232 and their analogues via a
three-component one-pot reaction of salicylaldehyde, o-aminophenol and ethyl cyanoacetate has been estab-
lished. Cheap and eco-friendly ethanol was employed as solvent. One drop of low-transition-temperature mixture
(LTTM) which formed from L(À )-Proline and oxalic acid could smoothly promote the reaction of 0.5 mmol raw
materials. Compared to the classical methodologies, the present pathway has broad reaction scope and affords all
products in good to excellent yields. Furthermore, this process could reduce the reaction temperature from 135 to
85 �C and avoid the problems associated with catalyst cost, handling, safety and pollution. On the basis of
comparative experiments and DFT calculation, possible mechanism of this strategy is discussed in detail.
3-Benzoxazol-2-yl-chromen-2-one
Disperse yellow
Three-component method
Synthesis
LTTM
1. Introduction
[8–13]. There are only four reports employing multicomponent one-pot
method to prepare disperse yellow using ZSM-5 [2], benzoic acid as
Disperse yellow (Fig. 1), as we all know, is a class of functional dyes
with strong fluorescence [1]. The main scaffold is 3-Benzoxazol-2-yl--
chromen-2-one which contains coumarin (chromen-2-one) and ben-
zoxazole two units. In addition to coloring polymers, they are also
particularly useful in a wide range such as fluorescent paint and resins
for solar collectors, sensitive material and optical disc recording mate-
rials [2]. Although there is an increasing demand for these compounds
[3], developing novel, versatile, and efficient approaches to their
straightforward construction from common commercial materials has
not received intensive attention over the past decade. So far, only a few
references reported synthetic methodology and the main strategies are
as below. Multi-step procedures [4,5] which need several steps
increased the complexity of operation and typically afford diminished
yields (Scheme 1a). Synthesize the target products via coupling reaction
[6] (Scheme 1b) or via cyclization that starts from coumarin esters and
o-aminophenol [7]. These two-component methods usually employ
expensive reagents, require complex catalytic system and need to pre-
pare raw materials in advance. Multi-component reactions (MCRs) have
emerged as powerful and responsible alternative tools for constructing
various complex organic molecules. They are faster and cheaper than
classical reactions, since the reaction will be completed by just mixing
compounds together in one vessel without isolating any intermediate
catalyst [14,15] or under catalyst free condition [16]. Despite MCRs
have many advantages, the yields for above reaction are still not
completely satisfactory. The reaction temperature is relatively high and
solvent is not easy to remove. Thus, there is a need for the development
of more effective pathways for the preparation of such compounds in
higher yields and under minimal synthetic requirements.
Deep eutectic solvents (DESs), also known as low-transition-
temperature mixture (LTTM) emerged in the last two decades as
promising green media for multiple applications. They can be used as
sustainable solvents or catalyst and bring unexpectedly favorable results
in organic synthetic chemistry [17,18]. Furthermore, MCRs with envi-
ronmentally benign solvents like DES are one of the most suitable stra-
tegies for green chemical process and developing the libraries of useful
scaffolds [19]. Our group has a continuing effort in the field of devel-
oping mild and green synthetic methodologies for organic trans-
formations. Based on these experiences especially in synthesis of
coumarin derivative [20–22], we decide to investigate the title reaction
by means of acidic LTTM formed from L(À )-Proline and oxalic acid as
catalyst and ethanol as solvent. The aim is to find a way which is milder
and easier to get disperse yellow and its analogues (Scheme 2). Due to
the high hydrophilicity of catalyst and solvent, separation of the prod-
ucts from the reaction mixture could be realized by adding water.
* Corresponding author.
** Corresponding author.
E-mail addresses: chengweilv@126.com (C. Lü), 18018928980@163.com (Y. An).
https://doi.org/10.1016/j.dyepig.2020.108415
Received 11 January 2020; Received in revised form 31 March 2020; Accepted 31 March 2020
Available online 5 April 2020
0143-7208/© 2020 Elsevier Ltd. All rights reserved.

Y. Xiao et al.
Dyes and Pigments 179 (2020) 108415
Scheme 2. Synthesis of 3-benzoxazol-2-yl-chromen-2-one promoted by LTTM
using ethanol as solvent.
Fig. 1. Fluorescent dyes containing 3-benzoxazol-2-yl-chromen-2-one nucleus.
Table 1
Effect of catalyst and solvent on synthesis of 3-benzoxazol-2-yl-chromen-2-one.
2. Results and discussion
Entrya
Catalyst (g)
Solvent
Yield (%)b
We had two main concerns at the outset of this work. One was
whether our approach could give the desired disperse yellow in
reasonable yields, which is critical for making present synthetic strategy
with the value in practical application. The other was to modify reaction
conditions including reduced temperature and simplified work-up pro-
cedure. Salicylaldehyde (0.50 mmol), o-aminophenol (0.55 mmol) and
ethyl cyanoacetate (0.55 mmol) were selected as model substrate for
optimization of the reaction parameters. Primarily, several acidic sys-
tems were chose to catalyze this reaction (Table 1 and Fig. 2). As ex-
pected, LTTM as catalyst and ethanol as solvent offered good yield at 80
�C (Table 1, entry 3). In order to determine the catalytic effect of the
LTTM system, we also conducted a separate comparison experiment
utilizing oxalic acid or L(À )-Proline as catalyst (Table 1, entries 1, 2).
The amount of L(À )-Proline and oxalic acid is determined according to
the mass of LTTM and the number of carboxyl groups contained in the
structure. Most surprisingly, L(À )-Proline had no catalytic activity and
oxalic acid offered a high yield too. However, the yield did not increase
when the subsequent conditions were optimized with oxalic acid.
Therefore, we chose LTTM (oxalic acid and L(À )-Proline) as promoter to
achieve this reaction. Further screening of solvents showed that both
ethanol and methanol provided better result in comparison to acetoni-
trile (Table 1, entries 4, 5). Considering the initiative from our point of
view, finally, ethanol turned into our selection. The volume of ethanol
was also explored (Table 2, entries 1–4).
1
2
3
4
5
L(À )-Proline (0.0466)
Oxalic acid (0.0390)
LTTM (0.0350)
ethanol
trace
77
ethanol
ethanol
83
LTTM (0.0350)
acetonitrile
methanol
65
LTTM (0.0350)
83
a
Salicylaldehydes (0.50 mmol), o-aminophenol (0.55 mmol) and ethyl cya-
noacetate (0.55 mmol) with 0.3 mL solvent reacted at 80 �C for 12 h.
b
Isolated yield.
Fig. 2. Effect of catalyst and solvent on synthesis of 3-benzoxazol-2-yl-chro-
According to the consequence of yield, 0.3 mL ethanol became the
best choice. Here, the yield could not be improved by increasing the
LTTM’s loading. 0.0350 g was found to be sufficient to promote reaction
(Table 2, entry 5), even while increasing the amount of catalyst would
lead to a lower yield. Testing material ratio found that a satisfied result
was obtained with 1:1.1:1.1 M ratio of salicylaldehyde, o-aminophenol
and ethyl cyanoacetate. Eventually, the effect of temperature and re-
action time were also investigated. It was found that increasing the re-
action temperature to 90 �C could improve the yield and inferior yields
were obtained at 100 �C (Table 2, entries 8, 9). The optimal reaction
duration was 12 h. Further extend or shorten the reaction time can’t
men-2-one.
favour the product yield (Table 2, entry 11). From above, the best result
was achieved when this transformation was carried out in ethanol at 90
�C for 12 h with 0.0350 g LTTM.
Inspired by the optimized conditions, our attention was then focused
on the synthesis of dispersed yellow molecules (4b, 4c in Table 3).
Satisfactorily, this reaction could perform readily and afford 4b, 4c with
good yield. To check the generality as well as the effectiveness of our
newly developed protocol, different salicylaldehydes and o-
Scheme 1. Synthesis of the 3-benzoxazol-2-yl-chromen-2-one, (a) via multi-step procedure, (b) by coupling reaction.
2

Y. Xiao et al.
Dyes and Pigments 179 (2020) 108415
and fluorescence emission wavelength only had
a little change
Table 2
Screening of reaction conditions.
compared to 4a. The substituent on salicylaldehyde and o-aminophenol
had on dramatic effect on photophysical properties.
Entrya
Vol.
Temp. (�C)
Time (h)
Yield (%)b
Only very few articles describe the synthesis of disperse yellow via a
three-component one-pot method and all of these methods employ harsh
reaction conditions combined with cumbersome workup procedure.
Taking disperse yellow 232 as example (Table 4), our major strengths lie
in offering higher product yield and successfully reduce the reaction
temperature to 85 �C. Choosing green and common ethanol as solvent
has advantage of that separation of product from reaction mixture could
add water.
1
0.1 ml
0.2 mL
0.3 mL
0.4 mL
0.3 mL
0.3 mL
0.3 mL
0.3 mL
0.3 mL
0.3 mL
0.3 mL
80
80
80
80
80
80
80
90
100
90
90
12
12
12
12
12
12
12
12
12
10
14
80
83
87
87
64
77
82
90
81
81
77
2
3
4
5c
6d
7e
8
9
10
To explore the reaction mechanism in-depth, some comparative ex-
periments were examined. When starting the reaction, there are three
possibilities between raw materials of salicylaldehyde, o-aminophenol
and ethyl cyanoacetate (Scheme 3). They would form five probable
compounds. Compounds 4 and 5 (Scheme 3c) are by-products and
others are the intermediates which had reported in the references [23].
Most reports suggest that o-aminophenol and ethyl cyanoacetate firstly
form compound 3 (Scheme 3b) by tandem nucleophilic reactions [2,14].
According to our experiments, we draw different conclusions from the
literature. The o-aminophenol could not rapidly react with ethyl cya-
noacetate at 50 �C with 0.0350 g LTTM and 0.5 mL ethanol. In this case,
cycloadduct 3 isn’t obtained as expected. Then we carried out the re-
action of salicylaldehyde with ethyl cyanoacetate at 50 �C with 0.0350 g
LTTM and 0.5 mL ethanol (Scheme 3a), which produces the Knoeve-
nagel condensation and a subsequent heterocyclization to give coumarin
derivatives 1 or 2. After purification, product 1 was obtained with 93%
yield. So we conclude that salicylaldehyde and ethyl cyanoacetate
would firstly react in this three-component one-pot reaction via the
Knoevenagel condensation and a subsequent heterocyclization to give
ester-coumarin intermediate 1.
11
a
reaction condition: add salicylaldehydes (0.5 mmol), o-aminophenol (0.55
mmol) and ethyl cyanoacetate (0.55 mmol) at the same time.
b
c
Isolated yield.
0.0700 g LTTM.
d
Molar ratio was 1:1:1.
e
Molar ratio was 1:1.2:1.2.
Table 3
Substrate scope of condensation cyclization of salicylaldehydes, o-aminophenol
and ethyl cyanoacetatea.
Density functional theory (DFT) calculations at C-PCM/B3LYP/6-
31G** levels of theory were utilized to evaluate detailed energy profiles
for each possible step of this route and explain why product 1 was the
major intermediate, not the product 2. Intrinsic reaction coordinate
(IRC) calculations of each transition states were carried out to confirm
the connectivity of these transition states to the right intermediates. The
3D images of the calculated structures were prepared using CYL view.
The cascade reaction of methyl cyanoacetate with salicylaldehyde was
chose as model reaction to pursue deeper understandings on the
mechanism. The calculated energy profiles are shown in Fig. 4 and
Fig. 5. The key transition states in the reaction are shown in Fig. 6. Our
results show that, the reaction starts from formation of a complex be-
tween two reactants, methyl cyanoacetate and salicylaldehyde. The
Knoevenagel condensation step takes place with no stereoselectivity.
Two competing transition states have similar activation energy around
14.0 kcal/mol. In transition state TS1, the forming C–C bond distance is
2.16 Å. The dehydration process could via two pathways. One is intra-
molecular hydrogen atom transfer from tertiary carbon atom to hy-
droxyl. The activation energy is 41.5 kcal/mol which is impossible to
accomplish.
aminophenol were employed. Affected by electronic effect, the reac-
tivity of some substituted salicylaldehydes and o-aminophenol changed,
so the reaction temperature was lowered uniformly to 85 �C and ethanol
was added 0.5 mL. No matter electron-donating or -withdrawing sub-
stituents on the salicylaldehyde and o-aminophenol, they tolerated the
reaction conditions well enough to furnish the corresponding products
in 77–94% yields (4d~4o). Interestingly, when only salicylaldehyde or
o-aminophenol had a substituent, the yield is slightly lower than model
reaction (4d, 4e, 4f, 4h, 4i, 4n, 4o). If both materials had an electron
withdrawing group (4g), the yield was similar to the above. Higher
yields of products were observed for one side bearing an electron-
donating group, the other side containing an electron-withdrawing
group or both sides having electron-donating groups (4j, 4k, 4l).
These results indicated this strategy is general and has broad substrate
scope. The UV–Vis absorption and fluorescence spectra of all products
were measured (Fig. 3). Except 4b and 4c, the maximum UV absorption
Another case is intra-molecular proton transfer from carbonyl to
hydroxyl. Dehydration step via TS2 and followed step forming a new
double bond via TS3 could occur effortlessly. The critical and rate-
determining step is nucleophilic reaction of hydroxyl to form C–O
bond. As shown in Fig. 5, there are two possibilities for this step. One is
hydroxyl attacking with carbonyl to give P-2. An alternative path is
hydroxyl attacking cyano group, which is then connected by hydrolysis
step to give ester-coumarin. The first probability proceeded could via
two route in concerted way. Hydrogen and oxygen atoms of hydroxyl
simultaneously added to the carbon oxygen double bonds. The
computed activation free energy is 36.6 kcal/mol. The other is hydrogen
and oxygen atoms of hydroxyl simultaneously adding to the carbon
oxygen bonds and removing methanol at the same time. The computed
activation free energy is 35.6 kcal/mol.
Focusing on the favored reaction pathway which proceeded in a
3

Y. Xiao et al.
Dyes and Pigments 179 (2020) 108415
Fig. 3. The ultraviolet spectra and fluorescence spectra of compounds 4a to 4o.
3. Conclusions
Table 4
Comparison of different conditions for the synthesis of disperse yellow 232.
In summary, a three-component one-pot method using salicylalde-
hyde, o-aminophenol, and ethyl cyanoacetate as raw materials was
developed and improved. As an application, disperse yellow 232 and
disperse yellow 184 were prepared in good yields. This method also had
good functional group tolerance and a series of coumarin derivatives
could be synthesized in good to excellent yields under mild conditions.
Employing LTTM formed from L(À )-Proline and oxalic acid as promoter
and less ethanol as solvent were the major features too. Under these
circumstances, we successfully reduced the reaction temperature from
135 to 85 �C and simplified the post-treatment procedure. Supported by
mechanistic experiments and DFT calculations, a possible mechanism of
this strategy was suggested. Coumarin-3-carboxylate acts as modular
components for the construction of final product.
Entry
Catalyst
Solvent
Conditions
Time
(h)
Yield
(%)
Year
[Ref.]
1
2
3
4
Benzoic
acid
n-
oil bath,
12
65
2008
pentanol
n-
138 �
C
[14]
ZSM-5
reflux
7
78.6
73
2012 [2]
butanol
n-
Catalyst
free
reflux
7
2016
[16]
butanol
ethanol
LTTM
85 �
C
12
83
present
work
4. Experimental
4.1. General
Unless otherwise stated, all reagents were obtained from commercial
sources and were used without further purification. Melting points were
determined on a Beijing Tech X-5 Melting point detector and were un-
corrected. The IR spectra were measured with a Bruker Shimadzu IR-460
spectrometer. 1H NMR and 13C NMR spectra were recorded on a Bruker
Avance III 500 MHz or Bruker Avance NEO 600. The chemical shifts (δ)
were reported in parts per million (ppm) and coupling constants (J) in
Hertz. Absorption spectra were obtained using a UV-1000 spectrometer.
Fluorescence spectrometer (F-7000) detected the spectrum.
Scheme 3. Control experiments for mechanistic studies.
concerted but asynchronous way. The O–H band cleavage and proton
transfer to the nitrogen atom of cyano group transition state TS4 could
be located. However, transition state for the second C–O bond formation
could not be found. IRC calculations from TS4 directly gave the final
adduct, implying that this step is barrierless. The relative Gibbs free
energy is 28.5 kcal/mol. In addition, the following intra-molecular
proton transfer from carbonyl to cyano group is an exothermic pro-
cess, so, this pathway is a preferential process. Based on the above ob-
servations, the plausible mechanism for the one-pot reaction is that
salicylaldehyde first react with ethyl cyanoacetate to form an ester-
coumarin intermediate, and this intermediate will further react with
o-aminophenol to give the final product. The calculated evaluation is in
good agreement with experimental results.
4.2. Typical experimental procedure for synthesis of 3-(benzo[d]oxazol-
2-yl)-2H- chromen-2-one
A mixture of salicylaldehyde (0.50 mmol), o-aminophenol (0.60
mmol) and ethyl cyanoacetate (0.55 mmol) was placed in a 10-mL
Schlenk tube, then 0.0350 g LTTM and 0.5 mL ethanol were added.
The reaction mixture was stirred at the indicated temperature for 12 h.
After completion of the reaction, Na2CO3 solution and DMF were added
to the mixture and vigorously stirred for a moment. Finally, the pre-
cipitate was separated by filtration and washed with ethanol without
further purification to afford the corresponding pure adducts.
3-(benzo[d]oxazol-2-yl)-2H-chromen-2-one (4a) [16]: Yellow solid.
m.p. 189–191 �C; IR (KBr)
ν
: 3030, 1741, 1604, 1566, 750 cmÀ 1
;
1H
NMR (500 MHz, CDCl3) δ 8.77 (s, 1H), 7.85–7.87 (m, 1H), 7.69–7.62 (m,
3H), 7.43–7.36 (m, 4H); 13C NMR (125 MHz, CDCl3) δ 158.02, 156.54,
154.50, 150.51, 145.10, 141.72, 133.86, 129.16, 126.08, 125.00,
4

Y. Xiao et al.
Dyes and Pigments 179 (2020) 108415
Fig. 4. Computed energy surface of reaction between salicylaldehyde and methyl cyanoacetate.
Fig. 5. Calculated energy barriers of cyclization procedure.
Fig. 6. The key transition states in the reaction of salicylaldehyde and methyl cyanoacetate.
5

Y. Xiao et al.
Dyes and Pigments 179 (2020) 108415
120.79, 118.32, 116.81, 115.09, 110.77.
(125 MHz, CDCl3) δ 164.70, 158.74, 157.04, 156.77, 148.81, 144.99,
142.01, 134.70, 130.24, 126.89, 120.35, 113.76, 112.20, 111.53,
110.06, 100.58, 56.01, 21.53.
3-(5-chlorobenzo[d]oxazol-2-yl)-7-(diethylamino)-2H-chromen-2-
one (4b) [14]: Yellow solid. m.p. 183–185 �C; IR (KBr)
ν: 3091, 1729,
1622, 1585, 692 cmÀ 1
;
1H NMR (600 MHz, DMSO‑d6) δ 8.78 (s, 1H),
6-bromo-3-(5-methylbenzo[d]oxazol-2-yl)-2H-chromen-2-one (4k)
7.96–7.54 (m, 3H), 7.41 (d, J ¼ 8.1 Hz, 1H), 6.80 (d, J ¼ 8.1 Hz, 1H),
6.58 (s, 1H), 3.49 (d, J ¼ 6.4 Hz, 4H), 1.15 (s, 6H); 13C NMR (150 MHz,
DMSO‑d6) δ 162.03 (s), 158.01 (s), 157.19 (s), 153.14 (s), 149.14 (s),
147.02 (s), 143.25 (s), 131.99 (s), 129.33 (s), 125.39 (s), 119.36 (s),
112.33 (s), 110.50 (s), 108.12 (s), 104.54 (s), 96.51 (s), 44.89 (s), 12.83
(s).
[16]: Yellow solid. m.p. 245–246 �C; IR (KBr)
ν: 3045, 2916, 1747, 1600,
1566, 661 cmÀ 1; 1H NMR (500 MHz, CDCl3) δ 8.66 (s, 1H), 7.80 (d, J ¼
2.3 Hz, 1H), 7.73 (dd, J ¼ 8.8, 2.3 Hz, 1H), 7.65–7.63 (m, 1H), 7.51 (d, J
¼ 8.3 Hz, 1H), 7.31 (d, J ¼ 8.8 Hz, 1H), 7.24 (dd, J ¼ 8.4, 1.1 Hz, 1H),
2.50 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 157.61, 155.91, 153.26,
148.90, 143.20, 141.88, 136.34, 135.07, 131.12, 127.62, 120.68,
119.87, 118.56, 117.60, 116.38, 110.23, 21.53.
7-(diethylamino)-3-(5-methylbenzo[d]oxazol-2-yl)-2H-chromen-2-
one (4c) [14]: Yellow solid. m.p. 226–230 �C; IR (KBr)
ν: 3075, 1744,
6-chloro-3-(5-chlorobenzo[d]oxazol-2-yl)-2H-chromen-2-one (4l)
1622, 1585, 790 cmÀ 1; 1H NMR (500 MHz, DMSO‑d6 6) δ 8.78 (s, 1H),
7.69 (d, J ¼ 9.0 Hz, 1H), 7.63–7.49 (m, 2H), 7.21 (d, J ¼ 8.3 Hz, 1H),
6.81 (dd, J ¼ 9.0, 2.3 Hz, 1H), 6.61 (d, J ¼ 2.1 Hz, 1H), 3.50 (q, J ¼ 7.0
Hz, 4H), 2.45 (s, 3H), 1.16 (t, J ¼ 7.0 Hz, 6H); 13C NMR (125 MHz,
DMSO‑d6) δ 157.96, 157.33, 152.90, 148.64, 146.45, 142.15, 134.52,
131.78, 126.52, 119.61, 110.42, 109.13, 105.45, 96.57, 44.85, 21.49,
12.83.
[16]: Yellow solid. m.p. 228–230 �C; IR (KBr)
ν: 3051, 1751, 1606, 1568,
673 cmÀ 1; 1H NMR (500 MHz, CDCl3) δ 8.71 (s, 1H), 7.85 (d, J ¼ 2.0 Hz,
1H), 7.67 (d, J ¼ 2.4 Hz, 1H), 7.63 (dd, J ¼ 8.8, 2.4 Hz, 1H), 7.58 (d, J ¼
8.7 Hz, 1H), 7.42–7.38 (m, 2H); 13C NMR (125 MHz, CDCl3) δ 158.99,
155.81, 152.98, 149.25, 144.25, 142.70, 134.00, 130.73, 130.56,
128.20, 126.72, 120.74, 119.20, 118.41, 115.97, 111.69.
3-(5-chlorobenzo[d]oxazol-2-yl)-7-methoxy-2H-chromen-2-one
3-(benzo[d]oxazol-2-yl)-7-chloro-2H-chromen-2-one (4d) [15]:
(4m) [16]: Yellow solid. m.p. 242–246 �C; IR (KBr)
ν: 3058, 1747, 1564
Yellow solid. m.p. 248–251 �C; IR (KBr)
ν
: 3070, 1743, 1598, 746 cmÀ 1
;
cmÀ 1; 1H NMR (500 MHz, CDCl3) δ 8.72 (s, 1H), 7.79 (d, J ¼ 2.0 Hz, 1H),
7.57 (d, J ¼ 8.7 Hz, 1H), 7.54 (d, J ¼ 8.6 Hz, 1H), 7.35 (dd, J ¼ 8.6, 2.0
Hz, 1H), 6.95 (dd, J ¼ 8.7, 2.4 Hz, 1H), 6.88 (d, J ¼ 2.3 Hz, 1H), 3.94 (s,
3H); 13C NMR (125 MHz, CDCl3) δ 165.06, 160.06, 156.88, 149.10,
145.77, 142.89, 130.39, 125.96, 120.34, 113.92, 112.04, 111.44,
110.82, 100.60, 56.05.
1H NMR (500 MHz, CDCl3) δ 8.75 (s, 1H), 7.88–7.87 (m, 1H), 7.63 (dd, J
¼ 12.2, 7.9 Hz, 2H), 7.44–7.36 (m, 4H); 13C NMR (125 MHz, CDCl3) δ
157.77, 155.87, 154.73, 150.59, 144.11, 141.70, 140.10, 129.85,
126.25, 125.82, 125.07, 120.87, 117.24, 116.94, 115.07, 110.83.
3-(benzo[d]oxazol-2-yl)-6-chloro-2H-chromen-2-one (4e) [16]: Yel-
low solid. m.p. 234–235 �C; IR (KBr)
ν
: 3047, 1747, 1614, 1568, 744
3-(benzo[d]oxazol-2-yl)-6-bromine-2H-chromen-2-one (4n) [16]:
cmÀ 1; 1H NMR (500 MHz, DMSO‑d6) δ 9.00 (s, 1H), 8.09 (s, 1H), 7.84 (d,
J ¼ 7.7 Hz, 1H), 7.81 (d, J ¼ 7.9 Hz, 1H), 7.76 (d, J ¼ 8.6 Hz, 1H),
7.43–7.52 (m, 4H); 13C NMR (125 MHz, DMSO‑d6) δ 158.51, 155.93,
153.20, 150.54, 145.36, 141.51, 133.93, 129.20, 126.79, 125.65,
120.64, 120.17, 118.72, 115.92, 111.49.
Yellow solid. m.p. 238–240 �C; IR (KBr)
ν: 3047, 1751, 1602, 1566, 746
cmÀ 1; 1H NMR (600 MHz, CDCl3) δ 8.69 (s, 1H), 7.91–7.85 (m, 1H), 7.81
(d, J ¼ 2.3 Hz, 1H), 7.74 (dd, J ¼ 8.8, 2.3 Hz, 1H), 7.65 (d, J ¼ 7.5 Hz,
1H), 7.43 (m, 2H), 7.32 (d, J ¼ 8.8 Hz, 1H); 13C NMR (150 MHz, CDCl3)
δ 157.52, 155.91, 153.30, 150.56, 143.50, 141.68, 136.50, 131.17,
126.41, 125.14, 120.98, 119.81, 118.60, 117.66, 116.23, 110.87.
3-(benzo[d]oxazol-2-yl)-7-hydroxyl -2H-chromen-2-one (4o) [16]:
3-(5-chlorobenzo[d]oxazol-2-yl)-2H-chromen-2-one (4f) [16]: Yel-
low solid. m.p. 240–241 �C; IR (KBr)
ν: 3064, 1749, 1606, 1564, 752
cmÀ 1; 1H NMR (500 MHz, CDCl3) δ 8.78 (s, 1H), 7.82 (d, J ¼ 2.0 Hz, 1H),
Yellow solid. m.p. >300 �C; IR (KBr)
ν: 3319, 3180, 3049, 1732, 1612,
7.69 (d, J ¼ 7.6 Hz, 2H), 7.56 (d, J ¼ 8.7 Hz, 1H), 7.44–7.37 (m, 4H); 13
C
1544, 734 cmÀ 1; 1H NMR (500 MHz, DMSO‑d6) δ 8.41 (s, 1H), 7.65 (dd,
J ¼ 12.1, 7.6 Hz, 2H), 7.32–7.26 (m, 4H), 6.16 (d, J ¼ 9.0 Hz, 1H), 5.87
(s, 1H). 13C NMR (125 MHz, DMSO‑d6) δ 180.67, 162.48, 160.16,
158.81, 150.05, 144.54, 142.47, 131.51, 124.63, 124.17, 122.27,
118.94, 110.45, 105.98, 103.67.
NMR (125 MHz, CDCl3) δ 159.51, 156.45, 154.69, 149.22, 145.78,
142.77, 134.19, 130.56, 129.27, 126.42, 125.17, 120.61, 118.27,
116.96, 114.83, 111.62.
6-chloro-3-(5-methylbenzo[d]oxazol-2-yl)-2H-chromen-2-one (4g)
[15]: Yellow solid. m.p. 252–256 �C; IR (KBr)
ν: 3043, 2915, 1753, 1564,
671 cmÀ 1
;
1H NMR (500 MHz, DMSO‑d6) δ 8.97 (s, 1H), 8.09 (s, 1H),
Declaration of competing interest
7.76 (d, J ¼ 8.1 Hz, 1H), 7.68–7.62 (m, 2H), 7.52 (d, J ¼ 8.0 Hz, 1H),
7.28 (d, J ¼ 6.7 Hz, 1H), 2.45 (s, 3H); 13C NMR (125 MHz, DMSO‑d6) δ
158.54, 155.91, 153.14, 148.82, 145.08, 141.72, 135.13, 133.84,
129.17, 127.83, 120.23, 118.69, 115.95, 110.87, 21.46
The authors have declared that no conflict of interest exists.
CRediT authorship contribution statement
3-(benzo[d]oxazol-2-yl)-7-methoxy-2H-chromen-2-one (4h) [16]:
Yellow solid. m.p. 195–197 �C; IR (KBr)
ν
: 3060, 2914, 1747, 1612, 773
Yudi Xiao: Data curation, Writing - original draft. Ao Liu: Investi-
gation, Software. Jiali Gao: Formal analysis. Yizhen Zou: Formal
analysis. Chengwei Lü: Supervision, Project administration, Funding
acquisition. Yue An: Writing - review & editing, Funding acquisition.
cmÀ 1; 1H NMR (500 MHz, DMSO‑d6) δ 8.66 (s, 1H), 7.81 (d, J ¼ 7.7 Hz,
1H), 7.58 (d, J ¼ 7.2 Hz, 1H), 7.53 (d, J ¼ 8.6 Hz, 1H), 7.35 (p, J ¼ 7.4
Hz, 2H), 6.90 (d, J ¼ 8.6 Hz, 1H), 6.83 (s, 1H), 3.88 (s, 3H); 13C NMR
(125 MHz, CDCl3) δ 164.75, 158.57, 156.90, 156.72, 150.42, 145.11,
141.82, 130.30, 125.66, 124.76, 120.53, 113.70, 112.09, 111.21,
110.63, 100.55, 55.98.
Acknowledgements
3-(5-methylbenzo[d]oxazol-2-yl)-2H-chromen-2-one (4i) [16]: Yel-
We are grateful for financial support from the Department of Science
and Technology of Liaoning Province (No. 2019-ZD-0470 and 2019-MS-
215) and Students Program for Innovation and Entrepreneurship
Training of Liaoning Province.
low solid. m.p. 184–185 �C; IR (KBr)
ν: 3055, 2918, 1741, 1606, 1568,
763 cmÀ 1; 1H NMR (500 MHz, CDCl3) δ 8.74 (s, 1H), 7.68–7.63 (m, 3H),
7.50 (d, J ¼ 8.3 Hz, 1H), 7.35–7.42 (m, 2H), 7.21 (dd, J ¼ 8.3, 1.0 Hz,
1H), 2.49 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 158.13, 156.60, 154.49,
148.85, 144.86, 141.93, 134.86, 133.73, 129.10, 127.30, 125.02,
120.55, 118.39, 116.82, 115.28, 110.17, 21.51.
Appendix A. Supplementary data
7-methoxy-3-(5-methylbenzo[d]oxazol-2-yl)-2H-chromen-2-one
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2020.108415.
(4j) [16]: Yellow solid. m.p. 232–233 �C; IR (KBr)
ν: 3074, 2916, 1755,
1606 cmÀ 1; 1H NMR (500 MHz, CDCl3) δ 8.72 (s, 1H), 7.62 (s, 1H), 7.57
(d, J ¼ 8.7 Hz, 1H), 7.50 (d, J ¼ 8.3 Hz, 1H), 7.20 (d, J ¼ 8.3 Hz, 1H),
6.94 (d, J ¼ 8.7 Hz, 1H), 6.90 (s, 1H), 3.94 (s, 3H), 2.50 (s, 3H); 13C NMR
6

Y. Xiao et al.
Dyes and Pigments 179 (2020) 108415
[12] Zhang Z, You Y, Hong C. Multicomponent reactions and multicomponent cascade
reactions for the synthesis of sequence-controlled polymers. Macromol Rapid
Commun 2018;39(23):1800362.
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