A highly efficient way to capture CX2 (O, S) mildly in reusable ReILs at atmospheric pressure

Article abstract of DOI:10.1039/c4gc00190g

The highly efficient transformation of CX₂ (O, S) into valuable chemicals at atmospheric pressure is an attractive topic. A novel method of preparing quinazoline derivatives by capturing CX₂ (O, S) in reusable, room-temperature, reversible ionic liquids (ReILs) with high yields (up to 98%) at 40 °C and atmospheric pressure was developed in this paper. The different reaction conditions were optimized and the products were easily separated from the ReILs which could be reused at least six times without considerable loss in yield. The plausible mechanism of capturing CX₂ (O, S) in the ReILs was proposed and it provides a green, efficient protocol to capture CX₂ (O, S) in ReILs to synthesize quinazoline derivatives. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4gc00190g

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A highly efficient way to capture CX2 (O, S) mildly
in reusable ReILs at atmospheric pressure†
Cite this: Green Chem., 2014, 16,
3142
Hui Zheng,* Xianting Cao, Kui Du, Jun Xu and Pengfei Zhang
The highly efficient transformation of CX2 (O, S) into valuable chemicals at atmospheric pressure is an
attractive topic. A novel method of preparing quinazoline derivatives by capturing CX2 (O, S) in reusable,
room-temperature, reversible ionic liquids (ReILs) with high yields (up to 98%) at 40 °C and atmospheric
pressure was developed in this paper. The different reaction conditions were optimized and the products
were easily separated from the ReILs which could be reused at least six times without considerable loss in
yield. The plausible mechanism of capturing CX2 (O, S) in the ReILs was proposed and it provides a green,
efficient protocol to capture CX2 (O, S) in ReILs to synthesize quinazoline derivatives.
Received 4th February 2014,
Accepted 26th February 2014
DOI: 10.1039/c4gc00190g
www.rsc.org/greenchem
pressure, high temperature, expensive catalysts, etc., so devel-
oping efficient and green methods to transform CO2 into valu-
Introduction
Carbon dioxide, as an abundant, cheap, renewable and non- able chemicals under mild conditions is still an interesting
toxic C1 resource, has received extensive attention in recent topic.
years.1,2 Efficient transformation of CO2 into useful chemicals
Reversible ionic liquids (ReILs), as novel, switchable, recycl-
at atmospheric pressure is an ideal method which benefits the able solvents, are becoming an effective medium in organic
sustainable development of the chemical industry. The utili- synthesis. The Jessop group reported the first example of
zation of CO2 as an inexpensive source for constructing carbon reversible ionic liquids,17 which can convert back into mole-
building blocks in organic synthesis is very interesting and it cular liquid by bubbling N2 or argon through them and/or
has been performed during the past decade.3 Researchers have applying heat. The smart switchable ReILs can improve
carried out a lot of fruitful exploration and many promising specific classes of chemical reactions and processes, and
strategies for capturing CO2 have been proposed for synthesis provide facile separation techniques. Han and co-workers pre-
of high value-added chemicals, such as methanol,4 formic pared a functional IL to perform the utilization of CO2 by a
acid,5 esters,6 ureas,7 benzimidazoles,8 formamidine deriva- cycloaddition reaction.11 Enlightened by these reports, we syn-
tives,9 etc. Han and co-workers discovered a green and interest- thesized the ReIL shown in Scheme 1 and employed it to
ing synthesis of quinazoline-2,4(1H,3H)-diones from CO2 in capture CX2 (O, S) by synthesizing valuable quinazoline deriva-
water.10 They also reported the CO2 cycloaddition reactions tives mildly at atmospheric pressure.
catalyzed by a highly cross-linked polymer matrix-supported
Quinazoline derivatives have received much attention for
IL.11 He and co-workers reported a silica-supported quaternary their multiple biological activities.18 Recently, the synthesis of
ammonium salt as an efficient and recyclable catalyst for the quinazoline-2,4(1H,3H)-diones from CO2 and 2-aminobenzo-
synthesis of PC from PO and CO2.12,13 They have also syn- nitriles has attracted much interest and various different kinds
thesized amorphous silica supported [BMIm]X (X = BF4, PF6, of catalyst have been studied to promote the reactions, such as
Br) which can be used to synthesize cyclic carbonates from 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),19 Cs2CO3,20 MgO–
epoxides and CO2.13,14 Liu and co-workers found a new way to ZrO2,21 [Bmim]OH,22 [Bmim]Ac,23 N-methyl-tetrahydropyrimi-
synthesize 2-benzimidazolones with CO2 catalyzed by a DBU- dine,24 1,1,3,3-tetramethylguanidine or guanidines,25 mono-
based ionic liquid at 120 °C and 9 MPa.15 Nolan and co- meric tungstate26 and so on. Despite the variety of catalysts
workers reported chemical fixation of CO2 via the carboxyl- available, development of a more efficient and green catalyst
ation of C–H using N-heterocyclic carbene gold(I) complexes.16
Generally, the common ways to capture CO2 need high
College of Material, Chemistry and Chemical Engineering, Hangzhou Normal
University, Hangzhou, China. E-mail: huizheng@hznu.edu.cn
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4gc00190g
Scheme 1 The synthesis of two types of ReIL by capturing CX2 (O, S).
3142 | Green Chem., 2014, 16, 3142–3148
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Scheme 2 Synthesis of quinazoline derivatives in the ReILs by capturing CX2 (O, S).
for synthesis of cyclic quinazoline derivatives under mild catalyzed by DBU and the ReILs. The results revealed that qui-
conditions still remains a challenging issue. nazoline-2,4(1H,3H)-dione was obtained with a low yield (44%)
In order to develop a green and highly efficient route to when catalyzed by DBU (entry 6, Table 1). Moreover, the
capture CX2 (O, S), herein, we reported a novel method to residue needed to be treated with 1 N HCl during the post-
synthesize quinazoline-2,4(1H,3H)-diones and quinazoline-2,4 reaction treatment and the DBU cannot be reused. Under com-
(1H,3H)-dithiones by capturing CX2 (O, S) in ReILs (I, II), parable conditions, the product could be obtained with high
which is shown in Scheme 2. It was discovered that the ReILs yields (>92%) in the ReILs (entries 7–8, Table 1) and the ReILs
(I, II) showed excellent catalytic ability for this reaction under could be recycled, so the advantages of using the ReILs as the
mild conditions (40 °C and 1 atm) with high yields (up to catalyst and the solvent to capture CX2 (O, S) were obvious for
98%), and the ReILs (I, II) could also be reused at least six the present examples of synthesizing quinazoline derivatives.
times as the solvents without considerable loss in yield.
Effects of reaction time and temperature
To obtain the optimum conditions, the reaction time and
temperature were screened and the results are summarized in
Fig. 1 and 2. As shown in Fig. 1, the yields increased with the
reaction time but did not change after 15 h, so the effect of
Results and discussion
Effect of different catalysts
Initially, the various catalysts Cs2CO3, TMG, K2CO3 and Et3N temperature on the yield was studied under these conditions
were investigated for the synthesis of quinazoline derivatives at (Fig. 2). The reaction was conducted in the temperature range
40 °C and 1 atm for 15 h, and the results are given in Table 1. of 20–45 °C. Generally, the isolated yields of the product
The results showed that these catalysts had no catalytic effect increased with the increasing temperature but increased
in this reaction (entries 1–5, Table 1).
slowly after 40 °C, because the reactants had almost comple-
It is known that the reaction could be catalyzed by DBU at tely reacted. Therefore, the optimum conditions were 15 h at
high temperature (>120 °C).18 We did the control experiments 40 °C for this reaction.
Table 1 Synthesis of quinazoline derivatives catalyzed by different catalysts
Entry
Catalyst
Yieldc (%)
1
2
3
4
5
6
7
8
Without catalyst
Cs2CO3
K2CO3
TMG
Et3N
DBU
ReILs (I)
ReILs (II)
0a/0b
0/0
0/0
0/20
0/0
44/70
92a
95b
a Reaction conditions: 1a 3 mmol, catalyst 5 mmol, solvent-free, CO2 1 atm, 15 h, 40 °C. b Reaction conditions: 1b 1 mmol, catalyst 3 mmol,
solvent-free, 10 h, 40 °C. c Isolated yield.
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Catalyst recyclability
A series of reaction cycles were run in order to examine the
stability of the catalytic system for capture of CX2 (O, S). The
general operation is similar to that used before. Taking
the synthesis of quinazoline-2,4(1H,3H)-dione 2a as an
example, the product was filtered under vacuum from the ReIL
(I) by adding about 1 mL ethanol to disperse the solid pro-
ducts, and then the filtrate was used directly for the next run.
The results in Fig. 3 indicated that the ReILs (I, II) could be
reused at least six times without considerable loss in yield. Of
particular note is that a small amount of CO2 and CS2 should
be replenished into the filtrate before the next run because of
their consumption in the previous run.
Fig. 1 The effect of reaction time on the isolated yield of 2a (A)/3b (B).
Reaction conditions: (A) reactant 3 mmol, CO2 1 atm, 40 °C, ReIL (I)
1 mL; (B) reactant 1 mmol, 40 °C, ReIL (II) 1 mL.
Reaction mechanism
A plausible mechanism for the capture of CX2 (O, S) by synthe-
sizing quinazoline derivatives (2, 3) in ReILs (I, II) from 2-ami-
nobenzonitriles 1 is proposed as depicted in Scheme 3. Firstly,
the ROCX2 anion attacks the amino group, then captures a
proton, and activates the reactant 1 to produce an intermediate
4. Then, the CX2 reacts rapidly with amide 4, leading to gen-
eration of 5. After that, 6 is formed via an intramolecular
nucleophilic cyclization of 5. Subsequently, the rearrangement
of 6, via the intermediate 7, gives 8. Finally, the final
product (2, 3) is obtained from the protonation of 8.
In addition, the formation of the intermediate 7 assisted
by the o-cyano group appears to be important in the whole
catalytic cycle.10,19
Conclusions
Fig. 2 The effect of reaction temperature on the isolated yield of 2a
(A)/3b (B). Reaction conditions: (A) reactant 3 mmol, CO2 1 atm, 15 h,
ReIL (I) 1 mL; (B) reactant 1 mmol, 10 h, ReIL (II) 1 mL.
In conclusion, we discovered a novel green method to capture
CX2 (O, S) by preparing quinazoline derivatives in reusable,
room-temperature, reversible ionic liquids ReILs (I, II) with
high yields (up to 98%) at 40 °C and atmospheric pressure.
The separation of the products from the reversible ionic
liquids was simple and the ReILs could be reused at least six
times without considerable loss in yield. This work provides a
green protocol to capture CO2 and CS2 in the ReILs which
acted as a catalyst and solvent at the same time. This highly
efficient, green, cheap and reusable catalytic system has a
potential application in the synthesis of quinazoline deriva-
tives from CO2 and CS2 under mild conditions.
Different substrates
In order to demonstrate the generality of substrates, we
studied the reactions of seven kinds of reactant with CX2 (O, S)
at 1 atm and 40 °C in the ReILs (I, II), and the data are pres-
ented in Table 2. The substrate bearing the electron-donating
group OCH3 (entry 2) reacted smoothly with yields of up to
96%. The substrate bearing the electron-withdrawing group
NO2 (entry 7) also reacted well with yields of up to 75%. The
yield was lower than that of entry 2, which may be attributed
to the electronic effect of the electron-donating group activat-
ing the substrates. In addition, the substrates bearing halogen
groups (entries 3–6) reacted very well with yields of up to 98%.
It can be concluded from the results that the ReILs (I, II) had
broad applicability to substrates in this reaction. Additionally,
the reaction time for entries 2 and 4–7 (Table 2) was longer
than the optimum time of 15 h because of the low solubilities
of the reactants in the ReILs. The synthesis of quinazoline-2,4-
(1H,3H)-dithiones in the ReIL (II) at 40 °C was also studied
(Table 2).
Experimental
Materials
CO2 was purchased from Hangzhou special gases factory with
a purity of 99.99%. Absolute ethanol (>99.7%) was provided by
Shanghai Lingfeng Chemical Reagent Co. Ltd. n-Hexanol
(98%), 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU, 99%), Cs2CO3
(99.99%), 1,1,3,3-tetramethyl-guanidine (TMG, 99%), K2CO3
(99.99%), and Et3N (>99.5%) were provided by Aladdin
Chemistry Co. Ltd. 2-Aminobenzonitrile (1a) (purity >98%)
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Table 2 Synthesis of various quinazoline derivatives 2a–gaand 3a–gb by capture of CX2 (O, S)
Time (h)
Yieldc (%)
Entry
1
Substrate
Product (X = O, S)
X = O
15
X = S
15
X = O
92
X = S
94
2
24
10
96d
95
3
4
15
15
10
18
97
98
92
94
5
6
7
30
15
48
30
18
24
92d
44
80
75
89
75d
a Reaction conditions: reactant 3 mmol, CO2 1 atm, 40 °C, ReIL (I) 1 mL. b Reaction conditions: reactant 1 mmol, 40 °C, ReIL (II) 1 mL. c Isolated
yield. d Reactant: 2 mmol, ReIL (I): 1 mL.
was provided by J & K Scientific Ltd. 2-Amino-4,5-dimethoxy- vided by Apollo Scientific Limited. 2-Amino-5-nitro benzo-
benzonitrile (1b) (>98%), 2-amino-5-fluorobenzonitrile (1c) nitrile (1g) (>98%) was purchased from Tokyo Chemical
(>98%), 2-amino-5-chloro benzonitrile (1d) (>98%), and Industry. Co. Ltd. The deuterated solvent (DMSO-d6) was pro-
2-amino-5-bromobenzonitrile (1f) were provided by Adamas vided by Adamas Reagent Co. Ltd. All of the chemicals were
Reagent Co. Ltd. 2-Amino-4-chlorobenzonitrile (1e) was pro- used without further purification.
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ReIL (II): a solution of CS2, DBU, and 1-hexanol (0.5 mol of
each) was added into a 10 mL tube and magnetically stirred at
room temperature until reacted (nearly 2 h). Then it was
cooled to about 0 °C to get the solid which was dried under
vacuum and characterized with 1H, 13C NMR.28
Reaction
The general procedure is similar for all products. As an
example, the synthesis of compound 2a was carried out in a
10 mL tube with a magnetic stirrer. As a typical experiment, we
describe the procedures for the reaction of CO2 and 2-amino-
benzonitrile. 2-Aminobenzonitrile (3 mmol) and ReIL (I)
(1 mL) were added into the reactor. The air in the reactor was
removed by blowing CO2 through it. Then the CO2 pressure
was kept at 1 atm. The reactor was placed in a heating mag-
netic stirrer at the desired temperature and the reaction
mixture was stirred. When the reaction ended, after adding
about 1 mL ethanol to disperse the solid product, the product
could be separated simple by filtration under vacuum, and
then the precipitate was washed with tert-butyl methyl ether 3
times (15 mL each time) and dried under vacuum at 60 °C for
4 h to afford the desired product.
Fig. 3 (A) The recyclability of the ReIL (I) for the synthesis of 2a. Reac-
tion conditions: reactant 3 mmol, CO2 1 atm, 40 °C, 15 h. Conditions for
the second to sixth cycles: 20 h, ReIL (I) 1 mL. (B) The recyclability of the
ReIL (II) for the synthesis of 3b. Reaction conditions: reactant 1 mmol,
40 °C, 10 h, ReIL (II) 1 mL.
Preparation of ReILs
ReIL (I): CO2 was bubbled at atmospheric pressure through the
mixture of DBU and ethanol (0.5 mol of each) for 2 h to form
the ionic liquid. Then it was cooled to about 0 °C to get the
solid which was washed with ethyl acetate (3 × 5 mL)
and dried under vacuum, then characterized with 1H and
13C NMR.27
The method of synthesis of quinazoline-2,4(1H,3H)-
dithiones: in
a typical experiment, 2-aminobenzonitrile
Scheme 3 A plausible mechanism for the capture of CX2 (O, S) by synthesizing quinazoline derivatives in ReILs.
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(1 mmol) and ReIL (II) (1 mL) were added into a 10 mL bottle. (126 MHz, DMSO-d6) δ 185.88, 169.94, 156.83, 147.91, 133.11,
The reactor was placed in a heating apparatus at 40 °C. By 117.20, 109.95, 98.14, 56.67, 56.23.
adding about 1 mL n-hexanol after the reaction to disperse the
6-Fluoroquinazoline-2,4(1H,3H)-dithione (3c). New com-
solid product, the product could be separated simply by fil- pound, Mp > 300 °C, IR (KBr), vmax 3124, 1627, 1574, 1503,
1
tration under vacuum. Then the precipitate was washed with 1392, 1341, 1266, 1146. H NMR (500 MHz, DMSO-d6) δ 13.79
tert-butyl methyl ether 3 times (10 mL each time) and dried (s, 1H), 13.17 (s, 1H), 7.95 (dd, J = 9.4, 2.9 Hz, 1H), 7.69–7.65
under vacuum at 60 °C for 4 h to afford the desired product.
(m, 1H), 7.40 (dd, J = 9.0, 4.7 Hz, 1H). 13C NMR (126 MHz,
The products were characterized by IR, H NMR, 13C NMR DMSO-d6) δ 187.29, 170.68, 160.27, 158.34, 133.72, 124.61 (d,
and HRMS. NMR was carried out with a Bruker AV500 J = 25.0 Hz), 124.36 (d, J = 8.6 Hz), 119.45 (d, J = 8.3 Hz), 115.06
(500 MHz) spectrometer with DMSO-d6 as the solvent. Spectral (d, J = 25.4 Hz). HRMS calcd for C8H5FN2S2 (M + H)+ 212.9951,
characterizations of the products (2a–g, 3a–g) were obtained as found 212.9947.
1
follows.
6-Chloroquinazoline-2,4(1H,3H)-dithione (3d).31 1H NMR
Quinazoline-2,4(1H,3H)-dione (2a).25 1H NMR (500 MHz, (500 MHz, DMSO-d6) δ 13.81 (s, 1H), 13.18 (s, 1H), 8.20 (d, J =
DMSO-d6) δ 11.18 (s, 2H), 7.89 (dd, J = 8.4, 1.4 Hz, 1H), 2.4 Hz, 1H), 7.79 (dd, J = 8.8, 2.4 Hz, 1H), 7.36 (d, J = 8.8 Hz,
7.65–7.62 (m, 1H), 7.18 (t, J = 7.5 Hz, 2H). 13C NMR (126 MHz, 1H). 13C NMR (126 MHz, DMSO-d6) δ 187.03, 171.04, 136.15,
DMSO-d6) δ 162.53, 150.63, 142.42, 139.75, 129.47, 122.92, 135.70, 129.71, 129.18, 124.31, 119.04.
115.15, 113.78.
7-Chloroquinazoline-2,4(1H,3H)-dithione (3e).32 1H NMR
6,7-Dimethoxyquinazoline-2,4(1H,3H)-dione (2b).25 1H NMR (500 MHz, DMSO-d6) δ 13.75 (s, 1H), 13.10 (s, 1H), 8.27 (d, J =
(500 MHz, DMSO-d6) δ 11.10 (s, 1H), 10.92 (s, 1H), 7.26 (s, 1H), 9.3 Hz, 1H), 7.37–7.35 (m, 2H). 13C NMR (126 MHz, DMSO-d6)
6.68 (s, 1H), 3.83 (s, 3H), 3.79 (s, 3H). 13C NMR (126 MHz, δ 187.06, 171.03, 140.63, 137.20, 132.15, 125.35, 121.64,
DMSO-d6) δ 162.87, 155.39, 150.86, 145.50, 137.01, 107.68, 115.45.
106.67, 98.25, 56.27, 56.19.
6-Fluoroquinazoline-2,4(1H,3H)-dione
6-Bromoquinazoline-2,4(1H,3H)-dithione (3f).33 1H NMR
NMR (500 MHz, DMSO-d6) δ 13.81 (s, 1H), 13.17 (s, 1H), 8.35 (d, J =
(2c).25 1H
(500 MHz, DMSO-d6) δ 11.39 (s, 1H), 11.17 (s, 1H), 7.60–7.53 2.3 Hz, 1H), 7.90 (dd, J = 8.7, 2.3 Hz, 1H), 7.29 (d, J = 8.7 Hz,
(m, 2H), 7.21 (dd, J = 8.9, 4.4 Hz, 1H). 13C NMR (126 MHz, 1H). 13CNMR (126 MHz, DMSO-d6) δ 186.90, 171.07, 138.82,
DMSO-d6) δ 162.56 (d, J = 2.9 Hz), 157.74 (d, J = 239.8 Hz), 136.02, 132.26, 124.68, 119.15, 117.58.
150.51, 138.01, 123.33 (d, J = 24.2 Hz), 118.03 (d, J = 7.9 Hz),
115.83 (d, J = 7.5 Hz), 112.39 (d, J = 23.7 Hz).
6-Chloroquinazoline-2,4(1H,3H)-dione
6-Nitroquinazoline-2,4(1H,3H)-dithione (3g).30 1H NMR
(500 MHz, DMSO-d6) δ 13.73 (s, 2H), 8.98 (d, J = 2.6 Hz, 1H),
(2d).25 1H
NMR 8.49 (dd, J = 9.0, 2.6 Hz, 1H), 7.46 (d, J = 9.0 Hz, 1H). 13C NMR
(500 MHz, DMSO-d6) δ 11.33 (s, 2H), 7.82 (d, J = 2.5 Hz, 1H), (126 MHz, DMSO-d6) δ 187.38, 172.19, 144.16, 141.08, 130.41,
7.68 (dd, J = 8.7, 2.5 Hz, 1H), 7.19 (d, J = 8.7 Hz, 1H). 13C NMR 126.33, 123.02, 118.44.
(126 MHz, DMSO-d6), δ 162.28, 150.51, 140.20, 135.23, 126.75,
−
[DBUH+][C2H5OCO2
]
(ReIL (I)).27 1H NMR (500 MHz,
126.36, 117.98, 116.23.
7-Chloroquinazoline-2,4(1H,3H)-dione
CD3OD) δ 3.62–3.64 (m, 4H), 3.57 (t, J = 5.5 Hz, 2H), 3.37–3.39
NMR (m, 2H), 3.32–3.33 (m, 2H), 2.69–2.72 (m, 2H), 2.04–2.09 (m,
(2e).25 1H
(500 MHz, DMSO-d6) δ 11.37 (s, 1H), 11.22 (s, 1H), 7.88 (d, J = 2H), 1.79–1.94 (m, 2H), 1.72–1.77 (m, 5H). 13C NMR (126 MHz,
8.4 Hz, 1H), 7.22–7.18 (m, 2H). 13C NMR (126 MHz, DMSO-d6) CDCl3) δ 162.84, 159.05, 60.40, 53.07, 48.30, 42.17, 35.47,
δ 163.30, 150.78, 141.32, 135.39, 122.77, 122.92, 115.78, 29.46, 27.97, 25.34, 21.56, 15.19.
114.79.
6-Bromoquinazoline-2,4(1H,3H)-dione
[DBUH+][C6H13OCS2−] (ReIL (II)).28 1H NMR (500 MHz,
NMR CD3CN) δ 7.32 (s, 1H), 4.31–4.34 (m, 2H), 3.53–3.55 (m, 2H),
(2f).25 1H
(500 MHz, DMSO-d6) δ 11.42 (s, 1H), 11.25 (s, 1H), 7.95–7.94 3.48–3.51 (m, 2H), 3.36–3.38 (m, 2H), 2.84–2.86 (m, 2H),
(m, 1H), 7.81–7.77 (m, 1H), 7.13 (d, J = 8.7 Hz, 1H). 13C NMR 1.97–1.99 (m, 2H), 1.68–1.74 (m, 8H), 1.33–1.38 (m, 6H),
(126 MHz, DMSO-d6) δ 162.25, 150.64, 140.75, 137.88, 129.35, 0.90–0.91 (m, 3H). 13C NMR (126 MHz, CD3CN) δ 231.92,
118.34, 116.69, 114.17.
6-Nitroquinazoline-2,4(1H,3H)-dione
165.77, 71.71, 61.58, 53.94, 48.40, 38.43, 32.33, 31.47, 28.85,
NMR 26.37, 25.74, 23.89, 22.38, 19.43, 13.43.
(2g).19 1H
(500 MHz, DMSO-d6) δ 11.77 (s, 1H), 11.71 (s, 1H), 8.59 (s, 1H),
8.46 (d, J = 9.0 Hz, 1H), 7.32 (d, J = 9.0 Hz, 1H). 13C NMR
(126 MHz, DMSO-d6) δ 162.04, 150.41, 146.07, 142.28, 129.99,
123.53, 117.10, 114.95.
Acknowledgements
We are grateful to the National Natural Science Foundation of
Quinazoline-2,4(1H,3H)-dithione (3a).29 1H NMR (500 MHz, China (21106026, 21376058) and Program for Changjiang
DMSO-d6) δ 13.68 (s, 1H), 13.12 (s, 1H), 8.30 (d, J = 8.1 Hz, 1H), Scholars and Innovative Research Team in Chinese University
7.79–7.73 (m, 1H), 7.34 (dd, J = 15.0, 7.9 Hz, 2H). 13C NMR (IRT 1231) for providing financial support.
(126 MHz, DMSO-d6) δ 188.37, 170.98, 136.78, 136.50, 130.60,
125.71, 123.16, 116.66.
6,7-Dimethoxyquinazoline-2,4(1H,3H)-dithione
Notes and references
(3b).30 1H
NMR (500 MHz, DMSO-d6) δ 13.44 (s, 1H), 12.96 (s, 1H), 7.69
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