Di-n-butyl ammonium chlorosulfonate ionic liquids as an efficient and recyclable catalyst for the synthesis of 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylates under solvent-free ultrasound irradiation

Article abstract of DOI:10.1007/s11164-015-2328-3

Abstract: In this study, we present a straightforward, efficient and convenient approach for the synthesis of medicinally important 1,4-dihydrobenzo[4,5] imidazo [1,2-a]pyrimidine-3-carboxylates via three-component reactions of aldehydes, 1H-benzo[d]imida

Full text of DOI:10.1007/s11164-015-2328-3

Res Chem Intermed
DOI 10.1007/s11164-015-2328-3
Di-n-butyl ammonium chlorosulfonate ionic liquids
as an efficient and recyclable catalyst for the synthesis
of 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-
carboxylates under solvent-free ultrasound irradiation
Mudumala Veeranarayana Reddy1
•
Avuthu Vidya Sagar Reddy1 Yeon Tae Jeong1
•
Received: 8 September 2015 / Accepted: 17 October 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract In this study, we present a straightforward, efficient and convenient
approach for the synthesis of medicinally important 1,4-dihydrobenzo[4,5] imidazo [1,2-
a]pyrimidine-3-carboxylates via three-component reactions of aldehydes, 1H-
benzo[d]imidazol-2-amine and active methylene compounds in the presence of di-n-
butyl ammonium chlorosulfonate ionic liquids (DBA IL) under ultrasound irradiation.
This process develops the synthetic potential of ultrasound irradiation with DBA IL
combination and presents much compensation, such as outstanding product yields,
reusable catalyst, less reaction periods, gainful cost, easy work-up/purification and
environmentally benign reaction conditions.
Graphical Abstract The attractive features of this methodology are simple procedure,
green reaction, reusability and high efficiency of the catalyst, and easy workability.
O
l
C
S
O
O
O
NH2
R
O
O
OR1
R2
N
+
+
CHO
R
NH2
N
R2
OR1
N
H
°
Neat, 50 C, ))))US
N
H
N
(1)
(2a-y)
(3a-d)
(4a-y)
Keywords 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylates Á Di-
n-butyl ammonium chlorosulfonate ionic liquids Á Ultrasound (US) irradiation Á Neat
conditions
Electronic supplementary material The online version of this article (doi:10.1007/s11164-015-2328-3)
contains supplementary material, which is available to authorized users.
&
Yeon Tae Jeong
ytjeong@pknu.ac.kr
1
Department of Image Science and Engineering, Pukyong National University,
Busan 608-737, Republic of Korea
123

M. V. Reddy et al.
Introduction
Because of their wide application in bioorganic medicinal chemistry, pharmaceutic
agents, and important ligands in catalysis, nitrogen-containing heterocycles and
their derivatives have been the focus of various synthetic efforts [1–6]. 1,4-
dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylates are nitrogen-containing
heterocycles and their partially or completely reduced analogues are pharmaceu-
tically important scaffolds widely found in naturally occurring, as well as synthetic
biologically active, molecules [7, 8]. These molecules demonstrate a wide variety of
biological activities [9–17]. Considering the biological importance of these
compounds, the development of efficient syntheses of 1,4-dihydrobenzo[4,5]imi-
dazo[1,2-a]pyrimidine-3-carboxylates from nitrogen-containing heterocycles has
gained substantial interest [18–24]. Although known methodologies have conve-
nient protocols with good yields, the reported methods still suffer from shortcom-
ings, such as long reaction times, expensive catalyst, low yields, toxic solvents, high
temperature and the use of non-recyclable catalysts. Thus, it is essential to further
develop an efficient and suitable method to build this type of heterocyclic
compound.
Currently, multi-component one-pot synthesis and ultrasound (US) irradiation
reactions are simple and efficient methods in the sustainable, diversity-oriented
synthesis of biologically active heterocycles, affording one of the greatest platforms
to admission multiplicity, as well as difficulty in a partial numeral of reaction steps
[25–32]. In the development of a method with shorter reaction time, that is less
expensive, high-yield, and has enhanced reaction rates, cleaner products, manip-
ulative simplicity, and product selectivity, an improved novel and green synthetic
route for the synthesis of advanced heterocyclic compounds of medicinal
significance, a challenge at the forefront of the modern path, can be reached using
multi-component chemical reaction protocols [33–35].
Ionic liquids (ILs) technology has been used extensively as a new and
environmentally friendly approach towards modern synthetic organic chemistry. It
has a several attractive advantages, such as extremely low vapor pressure, high
chemical and thermal stability, reusability and convenience in product separation
[36–39]. Although ionic liquids have become commercially available, their cost is
still reduced compared to that of traditional solvents. Therefore, currently a new
approach, so-called sulfonic acid supported catalyst with ionic liquid, is the focus of
much attention. It is unique and attractive as it is environmentally compatible,
minimizes the cost of ionic liquids, has greater selectivity, maintains the catalytic
properties of the catalyst and allows ease of separation and recycling of the catalyst.
Several organic reactions are reported in the literature of sulfonic acid supported
ionic liquid being used as both solvent and catalyst [40–44]. Due to its importance,
the development of an easy and efficient method for the preparation of
chlorosulfonic acid supported di butyl amine ionic liquids (DBA IL) has been
successfully used for the synthesis of N-containing bisphosphonates in high yields
[45]. Combining the merits of ultrasound-assisted and ionic liquids, a numerous
organic transformations have recently been reported in synthetic organic chemistry
[46, 47].
123

Di-n-butyl ammonium chlorosulfonate ionic liquids as an…
Based on our previous studies on the use of ionic liquid as solvent and catalyst,
and as part of our continuing interest in the development of economic viability,
greater selectivity, green and efficient new synthetic methods in the organic
reactions [48], we now report the synthesis of 1,4-dihydrobenzo[4,5]imidazo[1,2-
a]pyrimidine-3-carboxylates by the reactions of aldehydes, 1H-benzo[d]imidazol-2-
amine, and active methylene compounds in the presence of catalytic amount
(10 mol%) of DBA IL under solvent-free US condition at 50 °C (As Shown in
Scheme 1). Here, DBA IL is used as a solvent and catalyst, and can be recycled and
reused. To the best of our knowledge, this methodology has not been reported in the
literature.
Results and discussion
In order to explore the efficiency of DBA IL as a catalyst for one-pot, multi-
component reactions, we select the model reaction between 1H-benzo[d]imidazol-2-
amine (1, 1.0 mmol), 4-fluorobenzaldehyde (2a, 1.0 mmol) and ethyl benzoylac-
etate (3a, 1.0 mmol). The effect of different reaction parameters, such as the effect
of solvents, catalytic concentration, temperature and reaction conditions, were
evaluated to optimize the reaction conditions under conventional thermal heating
(CTH). It was noteworthy that, in the absence of DBA IL and solvent at 60 °C, no
desired compound was identified under similar reaction conditions (Table 1, entry
1). In non-polar solvents such as benzene, toluene and chloroform, the reaction did
not take place in the presence of DBA IL as a catalyst even after prolonged reaction
time at various temperatures (Table 1, entries 2–4). Conducting the reactions in
polar aprotic solvents, such as dichloromethane, acetonitrile and acetone, the
reaction was very slow and resulted in lower product yield (Table 1, entries 5–7).
Next, we tested polar protic solvents such as methanol and ethanol, which improved
both the reaction rates as well as product yields at 70 °C (Table 1, entries 8, 9).
However, when the same reaction was carried out in water as a solvent for the
reaction in the presence of DEA IL, the expected product was obtained in moderate
yield even after 8 h (Table 1, entry 10) at 100 °C. Interestingly, there was a
substantial enhancement in the yield when the multi-component reaction was
carried out under solvent-free conditions in the presence of DBA IL at 60 °C
(Table 1, entry 11). The yield of the reaction was good and the reaction time was
shorter than under solvent conditions. The yield of the product increased to 92 %
O
S
O
O
Cl
O
NH2
R
O
O
OR1
R2
N
+
+
CHO
R
N
NH2
R2
OR1
N
H
Neat, 50 C, ))))
°
US
N
H
N
(1)
(2a-y)
(3a-d)
(4a-y)
Scheme 1 Synthesis of 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylates catalyzed by
DBA IL under US condition
123

M. V. Reddy et al.
Table 1 Optimization of reaction conditions for the synthesis of 4a
Entry Catalyst (10 mol%) Solevnt (5 mL) Methodsa Tem (°C) Time (min) Yieldb (%)
1
Neat
Neat
dCTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
CTH
eUS
60
80
100
60
40
65
55
70
70
100
60
90
90
90
90
90
90
90
90
90
50
50
50
50
600
480
420
480
600
360
480
240
240
480
120
120
300
240
300
360
180
240
150
120
30
18
2
DBA IL
DBA IL
DBA IL
DBA IL
DBA IL
DBA IL
DBA IL
DBA IL
DBA IL
DBA IL
DBA IL
Dibutyl amine
FeF3
Benzene
Toluene
Chloroform
DCM
28
3
32
4
30
5
35
6
Acetonitrile
Acetone
Methanol
Ethanol
Water
45
7
40
8
65
9
75
10
11
12
13
14
15
16
17
18
19
20
21c
22
23
24
a
50
Neat
75
Neat
90
Neat
55
Neat
60
GaCl3
Neat
45
K-10
Neat
55
[TMGTfa]
Neat
75
[DMDBSI]. 2HSO4 Neat
80
[TMGIL]
Neat
Neat
78
[bmim][MeSO4]
82
DBA IL (10 mol%) Neat
DBA IL (2 mol%) Neat
DBA IL (5 mol%) Neat
DBA IL (20 mol%) Neat
95, 93, 90, 89, 87
US
90
70
85
95
US
60
US
30
Reaction of 1H-benzo[d]imidazol-2-amine (1, 1 mmol), 4-fluorobenzaldehyde (2a, 1 mmol), ethyl
benzoylacetate (3a, 1 mmol)
b
Isolated yield
c
Catalyst was reused five times
d
Conventional thermal heating (CTH)
e
Ultrasound (US) irradiation
when the reaction was carried out at elevated temperature of 90 °C (Table 1, entry
12), and a small amount of yellow colored product was formed, which can be
attributed to the imine form of amine and aldehyde under basic conditions. It is
worth mentioning that the order of mixing the substrates did not influence the
product yield. DBA IL exhibited equivalent or superior catalytic behavior as a
sulfonic acid-supported IL catalyst under solvent-free conditions, compared to other
commonly used catalysts such as dibutyl amine, FeF3, GaCl3 and K-10 under
similar reaction conditions (Table 1, entries 13–16). For comparison, we performed
the synthesis in the presence of other supported IL catalysts such as tetra methyl
123

Di-n-butyl ammonium chlorosulfonate ionic liquids as an…
guanidinium triflate [TMGTfa], 1,3-dimethyl-2-oxo-1,3-bis(4-sulfobutyl)imidazo-
lidine-1,3-diium hydrogen sulfate [DMDBSI]. 2HSO4, tetramethylguanidine-based
ionic liquids [TMG IL] and 1-butyl-3-methyiImidazolium methylsulfate
[bmim][MeSO4] (Table 1, entries 14–17). These results clearly demonstrate that
DBA IL is a more efficient catalyst for the synthesis of the title products (Table 1,
entry 12).
US irradiation has received considerable importance in organic and medicinal
chemistry in recent years as a feasible reaction alternative to conventional thermal
heating (CTH). It already offers an adaptable and facile path in a wide variety of
organic transformations. As compared to conventional methods, ultrasound is a
more considerable and suitable method for enhancing reaction rates, the formation
of pure products, superior yields and high purity of compounds, repression of side
products, improved selectivity, easier experimental procedures, and use of milder
reaction conditions. When we performed the model reaction between 1H-
benzo[d]imidazol-2-amine (1, 1.0 mmol), 4-fluorobenzaldehyde (2a, 1.0 mmol)
and ethyl benzoylacetate (3a, 1.0 mmol) in an ultrasonicator bath under solvent-free
conditions using DBA IL as a catalyst, the reaction yield improved to 95 % in a
significantly reduced reaction time (30 min, Table 1, entry 21). Hence, it was
imperative for us to use ultrasonic irradiation for developing a synthetic
methodology for the synthesis of 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylates.
It is worth mentioning here that the substrate to catalyst ratio played an important
role in the rate of the coupling reaction. The quantity of the catalyst required for
obtaining maximum product yield was studied by using 2, 5,10 and 20 mol% of
DBA IL, and the obtained yields were 70, 85, 95 and 95 %, respectively (Table 1,
entries 21–24). These results indicated that 10 mol% of DBA IL was sufficient, and
further increase in the quantity of catalyst did not show any significant improvement
in the reaction rate and product yields. This shows that the rate of the reaction and
product yield depends on the nature and quantity of the catalyst.
One of the principal aims of our study was to investigate the recycling of DBA
ILs, as this is obviously imperative in the context of financial viability and
sustainable development. The DBA IL was recovered by the addition of water to the
reaction mixture; the water solution containing ILto be recycled was dried in
vacuum for several hours. The separated catalyst was run for five successive cycles,
furnishing the corresponding 4a, with 95, 93, 90, 89 and 87 % isolated yields, which
confirmed the effectiveness of the catalyst for multiple usages (Table 1, entry 21).
The reaction procedure explained above is exceedingly efficient and involves the
use of an economical, small amount of DBA IL (10 mol%), which is required for
the reaction, and works both as a solvent and a catalyst. The cost analysis of the
reaction protocol as compared to other reported methods makes it quite economical
due to the recyclability of the IL, high yield and ambient temperature condition.
Having optimized the reaction conditions for the synthesis of 1,4-dihy-
drobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylates (4a–y), the procedure was
extended to various aldehydes (2a–y) to explore its generality (Table 2). First, a
wide range of aromatic aldehydes bearing electron-withdrawing and electron-
donating groups were reacted as coupling partners with 1H-benzo[d]imidazol-2-
123

M. V. Reddy et al.
Table 2 Synthesis of 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylates (4a–y)
Entry
R
R1
R2
Product
Time (min)
Yielda (%)
MP (°C)
1
4–F–C6H4
Et
C6H5
C6H5
C6H5
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
4a
4b
4c
4d
4e
4f
30
28
30
25
25
30
24
20
30
20
20
25
20
27
30
31
23
30
28
27
30
24
27
32
30
95
92
91
90
92
89
94
95
91
93
92
89
93
91
90
89
92
89
91
90
91
92
88
90
91
261–263
281–283
238–240
223–225
204–206
244–246
251–253
246–248
245–247
290–292
262–264
246–248
253–255
292–294
278–280
265–267
192–194
261–263
247–249
189–191
293–295
283–285
241–243
281–283
282–284
2
4–Cl–C6H4
3–Cl–C6H4
CH3CH2
Et
3
Et
4
C(CH3)3
C(CH3)3
C(CH3)3
C(CH3)3
C(CH3)3
C(CH3)3
Et
5
CH3CH2CH2
C4H3S
6
7
4–NO2–C6H4
4–Me–C6H4
3–Cl–C6H4
4–CN–C6H4
4–OMe–C6H4
C7H5O2
4g
4h
4i
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
4j
Et
4k
4l
Et
4–OEt–C6H4
2–5–Me–C6H3
2–4–F2–C6H3
2–F–5–Br–C6H3
C6H11
Et
4m
4n
4o
4p
4q
4r
4s
Et
Et
Et
Et
2–F–4–Br–C6H3
2–F–4–Br–C6H3
C6H11
Et
Me
Me
4t
2–4–F2–C6H3
4–CN–C6H4
C7H5O2
Me
4u
4v
4w
4x
4y
Me
Me
2–F–5–Br–C6H3
2–5–Me–C6H3
Me
Me
Reaction of 1H-benzo[d]imidazol-2-amine (1, 1 mmol), aldehydes (2a–y, 1 mmol), active methylene
compounds (3a–d, 1 mmol) catalyzed by DBA IL under US at 50 °C in neat condition
a
Isolated yield
amine and active methylene compounds (3a–d), and they were smoothly
transformed to the corresponding 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylates in good to moderate yields. It is noteworthy that no reports exist for
the synthesis of bioactive 1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-car-
boxylates from tert-butyl 3-oxobutanoate and ethyl benzoylacetate. All the
substituted aldehydes were easily converted into the desired products, indicating
that steric factors did not significantly affect the reactivity. In this procedure, the
pure products were isolated by simple filtration of the reaction mixture without
chromatography or a cumbersome work-up procedure. After the reaction, the
catalyst was separated from the product and reused without significant decrease in
1
its catalytic activity. The structures of the new compounds were determined by H
NMR, 13C NMR and HRMS.
123

Di-n-butyl ammonium chlorosulfonate ionic liquids as an…
O
DBAIL
OH
R1O
O
DBA IL
OR1
R2
R
DBA IL
H
N
OH
O
O
O
O
2
R
N
+
R2
O
R
1
R2
OR1
+
H2N
NH
R
R2
NH2
H
N
N
N
N
4
-
H2O
-DBA IL
R
H
1
5
6
O
O
R2
OR1
3
Scheme 2 Plausible mechanism for the formation of 4a–y
The probable portraying sequence of mechanistic justification has been shown in
Scheme 2. At first, the reaction occurs via a Knoevenagel condensation between
enolic form of active methylene compound (3a) and aldehyde (2) in the presence of
DBA IL as catalyst to form the intermediate (5). Here, the solid catalyst will
facilitate the active hosting sites for the reactant molecules and accelerate the rate of
reaction. Second, the intermediate 5 immediately goes into one more intermediate,
6, by Michael addition of 1H-benzo[d]imidazol-2-amine (1) at conjugated C=C
bond of 5. Finally, by intramolecular concerted cyclisation of adduct, 6 formed the
titled compounds (4a–y) in good yields.
Conclusion
In summary, we have reported a simple, green, and efficient one-pot, ultrasound
irradiation synthesis of a variety of bioactive 1,4-dihydrobenzo[4,5]imidazo[1,2-
a]pyrimidine-3-carboxylates from easily available starting materials, using DBA IL
as a catalyst under solvent-free conditions. US/IL combination clearly has a strong
potential to broadly contribute to innovations in green and sustainable chemistry.
Materials and methods
Chemicals were purchased from Aldrich and Alfa aesar Chemical Companies. NMR
spectra were recorded in ppm in DMSO-d6 on a Jeol JNM ECP 400 NMR
instrument using TMS as internal standard. Mass spectra were recorded on a Jeol
JMS-700 mass spectrometer. All melting points were determined using open
capillaries on an Electrothermal-9100 (Japan) instrument.
Preparation of DBA IL
The solution of chlorosulfonic acid (2 mmol) in CH2Cl2 (10 mL) was added to a
solution of dibutylamine (DBA) (2 mmol) in CH2Cl2 (15 mL) in a 50-mL reaction
flask over a period of 5 min at 0 °C (Scheme 2). After completion of the addition,
the reaction mixture was stirred for 40 min at room temperature and then
concentrated by rotary evaporation. The obtained residue was washed with CH2Cl2
123

M. V. Reddy et al.
(30 mL) and dried at 70 °C by rotary evaporation to afford DBA IL as a colorless
solid, without using any further specific purification procedures (Scheme 3).
DBA IL: White solid, mp 75–77 °C and decomposition point (by thermogravi-
metric analysis (TGA)) 247.3 °C. IR (KBr): m (cm-1) 3166, 2972, 1583, 1225,
1
1179, 1060, 859, 746, 658, 590; H NMR (400 MHz, DMSO-d6): d (ppm) 8.26 (s,
2H, –NH2), 2.87–2.80 (m, 4H, N-CH2), 1.53–1.56 (m, 4H, –(CH2)2), 1.33–1.28 (m,
4H, –(CH2)2) 0.88 (t, J = 7.4 Hz, 6H, –(CH3)2); 13C NMR (100 MHz, DMSO-d6):
d (ppm) 46.6, 27.5, 19.2, 13.5. Anal. cacld for C8H20ClNO3S: C, 39.10; H, 8.20; N,
5.70; S, 13.05. Found: C, 39.06; H, 8.24; N, 5.90: S, 12.92.
The DBA IL was characterized by FT-IR, elemental analysis, NMR spectro-
scopies, and wide-angle X-ray scattering techniques, as well as thermogravimetric
analysis (all characterized spectral data and figures are given in supporting
information).
Synthesis of ethyl 4-(4-fluorophenyl)-2-phenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
a]pyrimidine-3-carboxylate (4a)
A mixture of 1H-benzo[d]imidazol-2-amine (1, 1.0 mmol), 4-fluorobenzaldehyde
(2a, 1.0 mmol) and ethyl benzoylacetate (3a, 1.0 mmol) in the presence of DBA IL
(10 mol%) was placed in a 25-mL beaker and exposed to ultrasonic irradiation in
solvent-free condition for 30 min at 50 °C. The progress of the reaction was
monitored by TLC. After completion of the reaction, the reaction mixture was
poured into 50 mL of water and filtered, washed thoroughly with water, dried and
recrystallized from hot ethanol (10 mL) to obtain a white solid. The ionic liquid was
recovered from the water by evaporation under reduced pressure, and was reused in
the next cycle.
Ethyl 4-(4-fluorophenyl)-2-phenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylate (4a) Yield 95 %; White solid; mp 261–263 °C. 1H-NMR
(400 MHz, DMSO-d6): d11.04 (s, 1H), 7.56–7.52 (q, 2H), 7.46–7.42 (m, 5H),
7.33 (t, J = 7.7 Hz, 1H), 7.28 (d, J = 7.8 Hz, 1H), 7.14 (t, J = 8.2 Hz, 2H), 7.05 (t,
J = 6.9 Hz, 1H), 6.98 (t, J = 6.9 Hz, 1H,), 6.58 (s, 1H), 3.72–3.69 (q, 2H), 0.72 (t,
J = 7.3 Hz, 3H); 13C NMR (100. MHz, DMSO-d6) d:164.8, 161.5 (d,
J = 243.3 Hz), 147.3, 145.5, 142.0, 138.0, 135.6, 131.2, 129.2, 129.1, 128.9,
128.4, 127.8, 121.9, 120.9, 116.5, 115.4, 115.2, 109.9, 98.9, 59.1, 55.4, 13.3; HRMS
(ESI, m/z): calcd for C25H20FN3O2 (M ? H?) 413.154, found: 413.147.
Ethyl 4-(4-chlorophenyl)-2-phenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylate (4b) Yield 92 %; White solid; mp 281–283 °C. 1H-NMR
O
O
S
O
CH2Cl2
RT
Cl S O
O
NH2
NH
+
Cl
OH
Scheme 3 Preparation of DBA IL
123

Di-n-butyl ammonium chlorosulfonate ionic liquids as an…
(400 MHz, DMSO-d6): d11.07 (s, 1H), 7.52 (d, J = 8.4 Hz, 1H), 7.46–7.39 (m, 8H),
7.32 (t, J = 8.0 Hz, 2H), 7.08 (d, J = 6.9 Hz, 1H), 6.98 (t, J = 6.9 Hz, 1H), 6.58 (s,
1H), 3.71–3.68 (q, 2H), 0.72 (t, J = 7.3 Hz, 3H); 13C NMR (100. MHz, DMSO-d6)
d:164.8, 145.5, 142.2, 140.6, 135.5, 132.5, 131.3, 129.0, 128.5, 128.4, 127.9, 121.9,
120.4, 116.7, 109.9, 98.6, 59.2, 55.5, 13.3; HRMS (ESI, m/z): calcd for C25H20ClN3O2
(M ? H?) 429.898, found: 429.890.
Ethyl 4-(3-chlorophenyl)-2-phenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylate (4c) Yield 91 %; White solid; mp 238–240 °C. 1H-NMR
(400 MHz, DMSO-d6): d11.10 (s, 1H), 7.60 (s, 1H), 7.46–7.30 (m, 10H),
7.09–6.98 (m, 2H), 6.60 (s, 1H), 3.75–3.68 (m, 2H), 0.73 (t, J = 6.9 Hz, 3H);
13C NMR (100. MHz, DMSO-d6) d:164.8, 147.6, 145.4, 144.3, 135.4, 133.0, 130.7,
129.0, 128.3, 127.9, 127.1, 125.5, 122.1, 120.5, 116.8, 109.9, 98.4, 59.2, 55.5, 13.3;
HRMS (ESI, m/z): calcd for C25H20ClN3O2 (M ? H?) 429.898, found: 429.888.
Tert-butyl 4-ethyl-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-car-
1
boxylate (4d) Yield 90 %; White solid; mp 223–225 °C. H-NMR (400 MHz,
DMSO-d6): d10.36 (s, 1H), 7.41–7.36 (m, 2H), 7.11–7.03 (m, 2H), 5.52 (t,
J = 3.6 Hz, 1H), 2.36 (s, 3H), 1.99–1.93 (m, 1H), 1.71–1.65 (m, 1H), 1.48 (s, 9H),
0.52 (t, J = 7.3 Hz, 3H); 13C NMR (100. MHz, DMSO-d6) d:165.0, 147.1, 147.0,
142.3, 131.4, 121.5, 120.5, 116.5, 109.3, 96.5, 79.4, 52.4, 28.0, 26.4, 18.6, 7.3;
HRMS (ESI, m/z): calcd for C18H23N3O2 (M ? H?) 313.179, found: 313.170.
Tert-butyl-2-methyl-4-propyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-
1
carboxylate (4e) Yield 92 %; White solid; mp 204–206 °C. H-NMR (400 MHz,
DMSO-d6): d10.39 (s, 1H), 7.41–7.35 (m, 2H), 7.01–7.03 (q, 2H), 5.49 (t,
J = 4.0 Hz, 1H), 2.34 (s, 3H), 1.91–1.85 (m, 1H), 1.65–1.60 (m, 1H), 1.48 (s, 9H),
1.26–1.19 (m, 1H), 0.81–0.68 (m, 4H); 13C NMR (100. MHz, DMSO-d6) d:165.0,
146.9, 142.3, 131.5, 121.5, 120.0, 116.7, 109.2, 97.3, 79.4, 51.6, 36.3, 28.0, 18.6,
16.5, 13.7; HRMS (ESI, m/z): calcd for C19H25N3O2 (M ? H?) 327.195, found:
327.191.
Tert-butyl-2-methyl-4-(thiophen-2-yl)-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrim-
idine-3-carboxylate (4f) Yield 89 %; White solid; mp 244–246 °C. 1H-NMR
(400 MHz, DMSO-d6): d10.79 (s, 1H), 7.48 (d, J = 7.7 Hz, 1H), 7.36–7.32 (m,
2H), 7.11–7.05 (m, 3H), 7.01 (t, J = 6.9 Hz, 1H), 6.72 (s, 1H), 2.42 (s, 3H), 1.37 (s,
9H); 13C NMR (100. MHz, DMSO-d6) d:164.6, 146.0, 145.5, 145.1, 142.3, 131.3,
126.4, 125.7, 125.5, 121.8, 120.1, 116.8, 110.0, 98.9, 79.6, 50.8, 27.9, 18.5; HRMS
(ESI, m/z): calcd for C20H21N3O2S (M ? H?) 367.135, found: 367.140.
Tert-butyl-2-methyl-4-(4-nitrophenyl)-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrim-
idine-3-carboxylate (4g) Yield 94 %; White solid; mp 251–253 °C. 1H-NMR
(400 MHz, DMSO-d6): d10.85 (s, 1H), 8.15 (d, J = 8.4 Hz, 2H), 7.66 (d,
J = 8.4 Hz, 2H), 7.35–7.30 (m, 2H), 6.88 (t, J = 6.9 Hz, 1H), 6.98 (t,
J = 6.9 Hz, 1H), 6.53 (s, 1H), 2.45 (s, 3H), 1.34 (s, 9H); 13C NMR (100. MHz,
DMSO-d6) d:164.3, 148.9, 146.6, 145.3, 142.2, 131.3, 128.6, 128.5, 123.6, 121.9,
123

M. V. Reddy et al.
120.2, 116.8, 109.8, 98.0, 79.9, 55.4, 27.9, 18.7; HRMS (ESI, m/z): calcd for
C22H22N4O4 (M ? H?) 406.164, found: 406.160.
Tert-butyl-2-methyl-4-(p-tolyl)-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-
1
carboxylate (4h) Yield 95 %; White solid; mp 246–248 °C. H-NMR (400 MHz,
DMSO-d6): d10.66 (s, 1H), 7.31(d, J = 8.1 Hz, 1H), 7.26–7.21 (m, 3H), 7.07–7.00
(m, 3H), 6.93 (t, J = 6.9 Hz, 1H), 6.30 (s, 1H), 2.41 (s, 3H), 2.18 (s, 3H), 1.32 (s,
9H); 13C NMR (100. MHz, DMSO-d6) d:164.6, 146.5, 145.6, 142.2, 139.0, 136.9,
131.6, 128.0, 127.1, 126.9, 116.5, 113.0, 99.6, 79.4, 55.9, 27.9, 20.6, 18.5; HRMS
(ESI, m/z): calcd for C23H25N3O2 (M ? H?) 375.195, found: 375.190.
Tert-butyl-4-(3-chlorophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrim
idine-3-carboxylate (4i) Yield 91 %; White solid; mp 245–247 °C. 1H-NMR
(400 MHz, DMSO-d6): d10.89 (s, 1H), 7.49 (d, J = 8.0 Hz, 1H), 7.39–7.28 (m,
4H), 7.06 (t, J = 6.9 Hz, 1H), 7.06 (t, J = 6.9 Hz, 1H), 6.47 (s, 1H), 2.47 (s, 3H),
1.35 (s, 9H); 13C NMR (100. MHz, DMSO-d6) d:164.8, 147.0, 146.2, 145.4, 144.3,
142.2, 132.7, 131.4, 130.4, 127.7, 127.1, 125.6, 121.9, 120.1, 116.8, 109.8, 97.8,
79.7, 55.3, 27.8, 18.7; HRMS (ESI, m/z): calcd for C22H22ClN3O2 (M ? H?)
395.140, found: 395.135.
Ethyl 4-(4-cyanophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylate (4j) Yield 93 %; White solid; mp 290–292 °C. 1H-NMR
(400 MHz, DMSO-d6): d11.08 (s, 1H), 7.74 (d, J = 6.9 Hz, 2H), 7.56 (d,
J = 6.9 Hz, 2H), 7.34 (t, J = 6.9 Hz, 1H), 7.27–7.21 (m, 1H), 7.04 (d,
J = 6.9 Hz, 1H), 6.95 (t, J = 6.9 Hz, 1H), 6.53 (s, 1H), 4.04–3.98 (m, 2H), 2.47
(s, 3H), 1.13 (t, J = 6.9 Hz, 3H); 13C NMR (100. MHz, DMSO-d6) d:164.9, 147.4,
147.1, 145.3, 142.1, 133.0, 132.4, 131.3, 128.1, 126.7, 122.0, 120.4, 118.4, 116.9,
110.6, 109.7, 96.8, 59.5, 55.4, 18.7, 14.0; HRMS (ESI, m/z): calcd for C21H18N4O2
(M ? H?) 358.143, found: 358.135.
Ethyl 4-(4-methoxyphenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylate (4k) Yield 92 %; White solid; mp 262–264 °C. 1H-NMR (400 MHz,
DMSO-d6): d10.75 (s, 1H), 7.33 (d, J = 8.0 Hz, 1H), 7.26 (d, J = 8.0 Hz, 3H), 7.02
(t, J = 6.9 Hz, 1H), 6.94 (d, J = 6.9 Hz, 1H), 6.80 (d, J = 8.0 Hz, 2H), 6.37 (s, 1H),
4.02–3.99 (q, 2H), 3.65 (s, 3H), 2.44 (s, 3H), 1.15 (t, J = 6.9 Hz, 3H); 13C NMR (100.
MHz, DMSO-d6) d:165.2, 158.7, 146.1, 145.5, 142.3, 134.1, 131.5, 128.2, 121.7,
120.0, 116.6, 113.6, 109.8, 98.1, 59.2, 55.2, 54.9, 18.4, 14.0; HRMS (ESI, m/z): calcd
for C21H21N3O3 (M ? H?) 363.158, found: 363.150.
Ethyl 4-(benzo[d][1, 3]dioxol-5-yl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
1
a]pyrimidine-3-carboxylate (4l) Yield 89 %; White solid; mp 246–248 °C. H-
NMR (400 MHz, DMSO-d6): d10.77(s, 1H), 7.32 (t, J = 6.9 Hz, 2H), 7.04 (t,
J = 6.9 Hz, 1H), 6.96 (t, J = 6.9 Hz, 1H), 6.85 (d, J = 8.8 Hz, 2H), 6.78 (d,
J = 7.7 Hz, 1H), 6.36 (s, 1H), 5.92 (d, J = 2.2 Hz, 2H), 4.06–4.01 (q, 2H), 2.44 (s,
3H), 1.16 (t, J = 6.9 Hz, 3H); 13C NMR (100. MHz, DMSO-d6) d:165.3, 147.1,
146.6, 146.3, 145.5, 142.6, 136.0, 122.1, 119.9, 116.5, 109.9, 107.2, 100.8, 97.7,
123

Di-n-butyl ammonium chlorosulfonate ionic liquids as an…
59.4, 55.5, 18.6, 14.1; HRMS (ESI, m/z): calcd for C21H19N3O4 (M ? H?) 377.138,
found: 377.132.
Ethyl 4-(4-ethoxyphenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-
3-carboxylate (4m) Yield 93 %; White solid; mp 253–255 °C. 1H-NMR
(400 MHz, DMSO-d6): d10.80 (s, 1H), 7.33 (d, J = 7.6 Hz, 1H), 7.25 (d,
J = 8.2 Hz, 3H), 7.03 (t, J = 6.9 Hz, 1H), 6.94 (d, J = 6.9 Hz, 1H), 6.78 (d,
J = 8.0 Hz, 2H), 6.36 (s, 1H), 4.06–3.99 (q, 2H), 3.92–3.87 (q, 2H), 2.45 (s, 3H),
1.23 (t, J = 6.9 Hz, 3H), 1.14 (t, J = 6.9 Hz, 3H); 13C NMR (100. MHz, DMSO-
d6) d:165.2, 157.9, 146.1, 145.6, 142.3, 134.0, 131.5, 128.2, 121.6, 120.0, 116.7,
114.0, 109.8, 98.1, 62.8, 59.3, 55.3, 18.5, 14.5, 14.0; HRMS (ESI, m/z): calcd for
C22H23N3O3 (M ? H?) 377.174, found: 377.165.
Ethyl 4-(2,5-dimethylphenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrim-
idine-3-carboxylate (4n) Yield 91 %; White solid; mp 292–294 °C. 1H-NMR
(400 MHz, DMSO-d6): d10.77 (s, 1H), 7.33 (d, J = 8.0 Hz, 1H), 7.04–6.94 (m,
6H), 6.53 (s, 1H), 4.03–3.95 (q, 2H), 2.42 (s, 6H), 2.15 (s, 3H), 1.10 (t, J = 6.9 Hz,
3H); 13C NMR (100. MHz, DMSO-d6) d:165.3, 145.8, 145.4, 142.1, 134.9, 132.0,
131.7, 130.6, 128.3, 128.3, 122.3, 121.6, 120.0, 116.7, 109.3, 95.6, 59.2, 52.0, 20.5,
18.6, 18.1, 14.0; HRMS (ESI, m/z): calcd for C22H23N3O2 (M ? H?) 361.179,
found: 361.173.
Ethyl 4-(2,4-difluorophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrim-
idine-3-carboxylate (4o) Yield 90 %; White solid; mp 278–280 °C. 1H-NMR
(400 MHz, DMSO-d6): d11.01 (s, 1H), 7.55–7.49 (m, 1H), 7.36 (d, J = 7.9 Hz,
1H), 7.16–6.97 (m, 5H), 6.61 (s, 1H), 4.01–3.94 (m, 2H), 2.46 (s, 3H), 1.10 (t,
J = 6.9 Hz, 3H); 13C NMR (100. MHz, DMSO-d6) d:164.9, 162.0 (d,
J = 218.0 Hz), 147.5, 145.3, 142.1, 131.3, 125.1, 121.9, 120.4, 116.9, 111.7,
108.8, 103.8, 95.5, 59.3, 50.3, 18.6, 13.9; HRMS (ESI, m/z): calcd for C20H17F2-
N3O2 (M ? H?) 369.129, found: 369.120.
Ethyl
4-(5-bromo-2-fluorophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
1
a]pyrimidine-3-carboxylate (4p) Yield 89 %; White solid; mp 265–267 °C. H-
NMR (400 MHz, DMSO-d6): d10.98 (s, 1H), 7.72 (d, J = 6.1 Hz, 1H), 7.35–7.30
(m, 1H), 7.36 (t, J = 8.0 Hz, 1H), 7.15–7.04 (m, 3H), 6.98 (t, J = 6.9 Hz, 1H), 6.61
(s, 1H), 4.07–3.91 (m, 2H), 2.46 (s, 3H), 1.12 (t, J = 6.9 Hz, 3H); 13C NMR (100.
MHz, DMSO-d6) d:164.8, 159.1 (d, J = 260.0 Hz), 147.9, 145.2, 142.1, 132.8,
131.3, 130.5, 122.0, 120.3, 118.2, 117.9, 116.1, 109.0, 94.8, 59.4, 51.0, 18.7, 13.8;
HRMS (ESI, m/z): calcd for C20H17BrFN3O2 (M ? H?) 430.270, found: 430.264.
Ethyl
4-cyclohexyl-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-
carboxylate (4q) Yield 92 %; White solid; mp 192–194 °C. 1H-NMR
(400 MHz, DMSO-d6): d10.48 (s, 1H), 7.47(d, J = 6.9 Hz, 1H), 7.37 (d,
J = 6.9 Hz, 1H), 7.11–7.04 (m, 2H), 5.43 (d, J = 3.8 Hz, 1H), 4.20–40.9 (m,
2H), 2.38 (s, 3H), 1.77–1.72 (m, 1H), 1.64–1.58 (m, 2H), 1.49–1.45 (m, 2H), 1.26 (t,
J = 6.9 Hz, 3H), 1.11–0.95 (m, 3H), 0.92–0.84 (m, 1H), 0.61–0.50 (m, 1H); 13C
NMR (100. MHz, DMSO-d6) d:165.8, 148.1, 147.5, 142.2, 132.0, 121.4, 119.9,
123

M. V. Reddy et al.
116.7, 109.9, 95.4, 59.3, 55.8, 45.9, 29.6, 27.1, 25.7, 26.6, 18.4, 14.2; HRMS (ESI,
m/z): calcd for C20H25N3O2 (M ? H?) 339.195, found: 339.191.
Ethyl 4-(4-bromo-2-fluorophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
1
a]pyrimidine-3-carboxylate (4r) Yield 89 %; White solid; mp 261–263 °C. H-
NMR (400 MHz, DMSO-d6): d11.05 (s, 1H), 7.50–7.43 (m, 2H), 7.41–7.36 (m,
2H), 7.12–6.97 (m, 3H), 6.61(s, 1H), 4.00–3.97 (q, 2H), 2.46 (s, 3H), 1.11 (t,
J = 6.9 Hz, 3H); 13C NMR (100. MHz, DMSO-d6) d:165.0, 159.3 (d,
J = 257.2 Hz), 147.7, 145.2, 142.2, 131.5, 131.2, 128.2, 127.9, 122.0, 121.4,
120.4, 117.6, 117.0, 108.7, 95.3, 59.4, 50.2, 18.6, 13.9; HRMS (ESI, m/zm/z): calcd
for C20H17BrFN3O2 (M ? H?) 430.270, found: 430.265.
2.Methyl 4-(4-bromo-2-fluorophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
1
a]pyrimidine-3-carboxylate (4s) Yield 91 %; White solid; mp 247–249 °C. H-
NMR (400 MHz, DMSO-d6): d11.26 (s, 1H), 7.48–7.41 (m, 2H), 7.37–7.33 (m,
2H), 7.12–7.05 (m, 2H), 6.97 (t, J = 6.9 Hz, 1H), 6.61 (s, 1H), 3.55 (s, 3H), 2.45 (s,
3H); 13C NMR (100. MHz, DMSO-d6) d:165.4, 159.3 (d, J = 255.4 Hz), 147.7,
145.2, 142.1, 131.5, 131.3, 127.9, 122.0, 121.4, 120.4, 117.5, 117.0, 109.8, 95.2,
56.8, 50.4, 18.7; HRMS (ESI, m/z): calcd for C19H15BrFN3O2 (M ? H?) 416.244,
found: 416.239.
Methyl 4-cyclohexyl-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-
carboxylate (4t) Yield 90 %; White solid; mp 189–191 °C. 1H-NMR
(400 MHz, DMSO-d6): d10.56 (s, 1H), 7.45(d, J = 6.9 Hz, 1H), 7.37 (d,
J = 6.9 Hz, 1H), 7.11–7.04 (m, 2H), 5.44 (d, J = 2.9 Hz, 1H), 3.68 (s, 3H), 2.39
(s, 3H), 1.74–1.72 (m, 1H), 1.64–1.43 (m, 4H), 1.08–1.00 (m, 3H), 0.92–0.83 (m,
1H), 0.60–0.51 (m, 1H); 13C NMR (100. MHz, DMSO-d6) d:166.3, 148.4, 147.5,
142.2, 132.0, 121.4, 119.9, 116.7, 109.9, 95.2, 55.7, 50.9, 45.8, 29.5, 27.0, 25.7,
25.6, 18.4; HRMS (ESI, m/z): calcd for C19H23N3O2 (M ? H?) 325.179, found:
325.170.
Methyl 4-(2,4-difluorophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrim
idine-3-carboxylate (4u) Yield 91 %; White solid; mp 293–295 °C. 1H-NMR
(400 MHz, DMSO-d6): d11.05 (s, 1H), 7.55–7.49 (m, 1H), 7.34 (d, J = 8.0 Hz,
1H), 7.15–6.95 (m, 5H), 6.61 (s, 1H), 3.54 (s, 3H), 2.45 (s, 3H); 13C NMR (100.
MHz, DMSO-d6) d:165.4, 162.1 (d, J = 260.0 Hz), 147.6, 14.3, 142.1, 131.3,
124.9, 121.9, 120.4, 118.0, 111.8, 108.8, 103.9, 95.5, 50.8, 50.3, 18.7; HRMS (ESI,
m/z): calcd for C19H15F2N3O2 (M ? H?) 355.113, found: 355.110.
Methyl 4-(4-cyanophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrim-
idine-3-carboxylate (4v) Yield 92 %; White solid; mp 283–285 °C. 1H-NMR
(400 MHz, DMSO-d6): d11.38 (s, 1H), 7.84 (d, J = 7.2 Hz, 1H), 7.74 (d,
J = 7.2 Hz, 1H), 7.54 (d, J = 8.0 Hz, 1H), 7.36 (d, J = 6.9 Hz, 1H), 7.26–7.21
(m, 1H), 7.12–7.03 (m, 2H), 6.95 (t, J = 6.9 Hz, 1H), 6.54 (s, 1H), 3.57 (s, 3H),
2.46 (s, 3H); 13C NMR (100. MHz, DMSO-d6) d:164.9, 147.4, 147.1, 145.3, 142.1,
133.0, 132.4, 131.3, 128.1, 126.7, 122.0, 120.4, 118.4, 116.9, 110.6, 109.7, 96.8,
123

Di-n-butyl ammonium chlorosulfonate ionic liquids as an…
55.4, 51.5, 18.7; HRMS (ESI, m/z): calcd for C20H16N4O2 (M ? H?) 344.127,
found: 344.121.
Methyl 4-(benzo[d][1, 3]dioxol-5-yl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
1
a]pyrimidine-3-carboxylate (4w) Yield 88 %; White solid; mp 241–243 °C. H-
NMR (400 MHz, DMSO-d6): d10.77 (s, 1H), 7.32 (t, J = 7.1 Hz, 2H), 7.04 (t,
J = 6.9 Hz, 1H), 6.98 (t, J = 6.9 Hz, 1H), 6.87 (br s, 2H), 6.78 (d, J = 7.7 Hz,
1H), 6.36 (s, 1H), 5.92 (d, J = 4.4 Hz, 1H), 3.58 (s, 3H), 2.44 (s, 3H); 13C NMR
(100. MHz, DMSO-d6) d:166.5, 148.6, 147.9, 143.8, 132.9, 123.1, 122.0, 121.8,
121.5, 118.0, 111.4, 109.5, 102.4, 99.3, 56.8, 52.3, 20.1; HRMS (ESI, m/z): calcd for
C20H17N3O4 (M ? H?) 363.122, found: 363.115.
Methyl 4-(5-bromo-2-fluorophenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
1
a]pyrimidine-3-carboxylate (4x) Yield 90 %; White solid; mp 281–283 °C. H-
NMR (400 MHz, DMSO-d6): d11.18 (s, 1H), 7.45 (d, J = 8.0 Hz, 1H), 7.37 (d,
J = 8.0 Hz, 1H), 7.13 (d, J = 7.7 Hz, 2H), 7.09–7.04 (m, 2H), 6.98 (t, J = 6.9 Hz,
1H), 6.62 (s, 1H), 3.56 (s, 3H), 2.45 (s, 3H); 13C NMR (100. MHz, DMSO-d6)
d:165.4, 159.2 (d, J = 235.0 Hz), 147.9, 145.2, 142.1, 132.9, 132.8, 132.4, 131.3,
122.0, 120.5, 118.2, 117.9, 117.0, 116.2, 108.9, 95.0, 50.8, 50.7, 18.8; HRMS (ESI,
m/z): calcd for C19H15BrFN3O2 (M ? H?) 416.244, found: 416.234.
Methyl 4-(2,5-dimethylphenyl)-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-
1
a]pyrimidine-3-carboxylate (4y) Yield 91 %; White solid; mp 282–284 °C. H-
NMR (400 MHz, DMSO-d6): d10.81 (s, 1H), 7.34 (d, J = 7.2 Hz, 1H), 7.08–6.97
(m, 3H), 6.91–6.84 (m, 3H), 6.53 (s, 1H), 3.52 (s, 3H), 2.42 (s, 6H), 2.12 (s, 3H);
13C NMR (100. MHz, DMSO-d6) d:165.3, 148.0, 145.3, 142.3, 139.1, 135.5, 131.9,
131.7, 130.4, 128.4, 120.2, 116.7, 109.6, 97.5, 59.1, 50.1, 20.6, 18.7, 18.1; HRMS
(ESI, m/z): calcd for C21H21N3O2 (M ? H?) 347.163, found: 347.155.
Supporting information
Analytical spectral data, NMR spectra and DBA IL data for all compounds are
provided as supplementary data.
References
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