Copper-Catalyzed One-Pot Synthesis of 2,3-Dihydroquinazolin-4(1 H)-ones from 2-Nitrobenzonitriles and Carbonyl Compounds Mediated by Diboronic Acid in Methanol-Water

Article abstract of DOI:10.1055/s-0037-1610740

A copper-catalyzed one-pot synthesis of 2,3-dihydroquinazolin-4(1 H)-ones with diboronic acid as a reductant in an aqueous medium is described. Various 2,3-dihydroquinazolin-4(1 H)-ones were prepared with good functional-group tolerance in good yields under mild conditions from readily available 2-nitrobenzonitriles and various carbonyl compounds.

Full text of DOI:10.1055/s-0037-1610740

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© Georg Thieme Verlag Stuttgart · New York
2019, 30, A–E
letter
A
en
Q. Liu et al.
Letter
Synlett
Copper-Catalyzed One-Pot Synthesis of 2,3-Dihydroquinazolin-
4(1H)-ones from 2-Nitrobenzonitriles and Carbonyl Compounds
Mediated by Diboronic Acid in Methanol–Water
Qixing Liu §
Yuebo Sui §
O
CN
O
CuCl/B2(OH)4, 60 °C, 3 h
H2O/MeOH
NH
R
+
R
R2
R1
R2
Yin Zhang
R1
NO2
N
H
Kaili Zhang
simple and easily available starting materials
mild reaction conditions and high reactivity
aqueous medium and noble-metal-free
Yongsheng Chen
Haifeng Zhou*
30 examples
63–93% yields
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2-2
7
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7
0
Research Center of Green Pharmaceutical Technology and Process,
Hubei Key Laboratory of Natural Products Research and Development,
College of Biological and Pharmaceutical Sciences, China Three Gorges
University, Yichang 443002, P. R. of China
zhouhf@ctgu.edu.cn
§ The authors contributed equally.
Received: 29.09.2019
Accepted after revision: 02.12.2019
Published online: 12.12.2019
In recent decades, numerous strategies have been devel-
oped for the construction of DHQs and their analogues;
these methods can be divided into four broad categories: (i)
cyclocondensations of anthranilamides with aldehydes cat-
alyzed by Brønsted acids,2 Lewis acids,3 or other catalysts4;
(ii) one-pot reductive cyclizations of o-nitrobenzamides or
o-azidobenzamides with aldehydes promoted by Fe/AcOH,
TiCl4/Zn,5 or Sm/I2;6 (iii) one-pot syntheses from 2-amino-
benzonitriles and aldehydes catalyzed by ZnCl2, K3PO4, Am-
berlyst A26OH, choline hydroxide, or N-heterocyclic car-
benes;7 and (iv) one-pot reactions of isatoic anhydrides, al-
dehydes, and ammonium acetate under acidic conditions8
(Scheme 1a). Although several examples of methods for
preparing DHQs have been reported, these have several
drawbacks, such as the use of strong Brønsted or Lewis ac-
ids or noble metals as catalysts, harsh reaction conditions,
and a limited substrate scope. Therefore, the development
of a step-economical method that proceeds from readily
available simple materials with good functional--group tol-
erance under mild conditions is still desirable.
DOI: 10.1055/s-0037-1610740; Art ID: st-2019-l0518-l
Abstract A copper-catalyzed one-pot synthesis of 2,3-dihydro-
quinazolin-4(1H)-ones with diboronic acid as a reductant in an aqueous
medium is described. Various 2,3-dihydroquinazolin-4(1H)-ones were
prepared with good functional-group tolerance in good yields under
mild conditions from readily available 2-nitrobenzonitriles and various
carbonyl compounds.
Key words copper catalysis, diboronic acid, dihydroquinazolinones,
carbonyl compounds, nitrobenzonitriles
2,3-Dihydroquinazolinones (DHQs), as privileged scaf-
folds, are present in a wide range of drugs and biologically
active molecules.1 Several marketed drugs containing DHQ
cores are shown in Figure 1. Consequently, the development
of efficient methods for the synthesis of DHQs and ana-
logues has attracted increasing amounts of attention.
H3C
O
O
O
S
O
S
O
H2N
H2N
O
S
H2N
NH
NH
O
O
N
O
Cl
N
H
Cl
N
H
Cl
N
CH3
H
Quinethazone
Fenquizone
Metolazone
(antihypertensive, diuretic)
(diuretic)
(antihypertensive, diuretic)
CH3
O
O
R
N
N
N
N
H
CH3
Ph
H
N
H
H3C
Evodiamine (R = H)
Hydroxyevodiamine (R = OH)
(thermogenic, stimulant)
VU0092145
(neurotransmitter)
Figure 1 Some marketed drugs with a DHQ core
© 2019. Thieme. All rights reserved. Synlett 2019, 30, A–E
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
Q. Liu et al.
Letter
Synlett
a) Previous work
O
O
X
(ii)
(i)
O
O
+
NH2
NH2
R'
R'
+
R'
H
R
H
R
NH2
O
X = NO2 or N3
NH
R'
O
O
NH4OAc
O
N
H
R
CN
+
O
+
R'
H
R
(iii)
(iv)
NH2
N
H
O
H
R
b) Our previous work (Org. Chem. Front. 2017, 4, 2175)
H
N
R1
R2
NH2
O
R1
B2(OH)4/H2O, 80 °C, 6 h
R
+
R
R
R2
NO2
N
H
O
c) This work
R
O
CN
O
CuCl/B2(OH)4, 60 °C, 3 h
H2O/MeOH (v/v = 1:1)
NH
+
R2
R1
R1 R2
NO2
N
H
Scheme 1 Methods for the synthesis of DHQs
In 2015, Kumar’s group developed an iron-catalyzed
tandem synthesis of 4(3H)-quinazolinones from o-nitro-
benzonitriles and phenylglycines.9 We recently developed a
novel B2(OH)4–H2O system for the reduction of nitro com-
pounds and tandem reactions of amino groups,10 for exam-
ple, the one-pot three-step synthesis of tetrahydroquinox-
alines from 2-nitroanilines and 1,2-dicarbonyls (Scheme
1b).11 To expand the range of applications of the B2(OH)4-
H2O system and in continuation of our research interest in
the preparation of quinazolinones,12 we report a Cu-cata-
lyzed one-pot synthesis of DHQs from readily available 2-
nitrobenzonitriles and carbonyl compounds mediated by
B2(OH)4 in an aqueous medium under mild conditions
(Scheme 1c).
The reaction of 2-nitrobenzonitrile (1a) with benzalde-
hyde (2a) was selected as a model reaction (Table 1). First,
we tried the reaction in the presence of 5.0 equivalents of
B2(OH)4 in 1:1 v/v H2O–MeOH at 60 °C for 12 hours, but the
desired 2-phenyl-2,3-dihydroquinazolin-4(1H)-one (3a)
was obtained in only 10% yield (Table 1, entry 1). When a
Brønsted acid (AcOH, TFA, PivOH, or BzOH) was added to
the reaction mixture, product 3a was obtained in a higher
yield (entries 2–5).5a Next, we screened several Lewis acids
[CuCl, CuCl2, CuBr, CuI, CuOAc, ZnCl2, FeCl2, FeCl3, In(OTf)3,
InCl3, and Yb(OTf)3] (entries 6–16). To our delight, the high-
est yield of 3a (92%) was obtained by using 20 mol% of CuCl
as the catalyst. The use of H2O or MeOH as solvent led to a
decreased yield compared with that in aqueous MeOH (en-
tries 17 and 18). The use of B2pin2 as the boron reagent gave
a lower yield of 3a (entry 19). The reaction time was then
optimized (entries 20 and 21), and a high yield was still ob-
tained on shortening the reaction time to three hours.13
When the amount of CuCl was halved, the yield decreased
markedly (entry 22). Finally, 1:1 H2O–EtOH, a greener sol-
vent system, was tested, but gave a lower yield (entry 23).
Therefore, the optimal reaction conditions were set as 20
mol% of CuCl, 5.0 equivalents of B2(OH)4, 1:1 v/v H2O–
MeOH (2 mL), 60 °C, and three hours.
Having established the optimal reaction conditions for
the one-pot transformation of 2-nitrobenzonitriles and car-
bonyl compounds into 2,3-dihydroquinazolin-4(1H)-ones,
we then examined the scope of the reaction. As shown in
Scheme 2, the reaction of 2-nitrobenzonitrile with various
benzaldehydes bearing either an electron-withdrawing
group (F, Cl, Br, CN) or an electron-donating group (CH3,
OCH3, OH) in the para-, meta-, or ortho-position proceeded
smoothly under the optimal conditions to provide the cor-
responding 2,3-dihydroquinazolin-4(1H)-ones 3a–k in
yields of 60–91%. Interestingly, the nitrile group of 3k from
4-cyanobenzaldehyde remained unchanged, showing that
hydrolysis of the nitrile to an amide had not occurred.
When 1,4-phthalaldehyde (2l) was subjected to this reac-
tion, product 3l with one intact formyl group was isolated
exclusively in 40% yield. In addition, the hetaryl aldehydes
2-pyridinecarboxaldehyde (2m) and furfural (2n) also un-
derwent this transformation to give products 3m and 3n in
yields of 71 and 77%, respectively. Next, the aliphatic chain
aldehydes 2o–r and cycloalkyl aldehydes 2s and 2t were
also subjected to this one-pot process to give the corre-
sponding 2,3-dihydroquinazolin-4(1H)-ones 3o–t in yields
of 70–81%. Next, we attempted the reactions of various cy-
clic and acyclic ketones. Cyclic ketones 2u–y gave lower
yields (63–68%) of the corresponding products than did the
acyclic ketones 2z and 2aa (71 and 74% yield). Finally, the
reactions of benzaldehyde (2a) with 2-nitrobenzonitriles
containing an F, Cl, or Me group were also found to proceed
successfully, giving 3ab, 3ac, and 3ad in 93, 86, and 79%
© 2019. Thieme. All rights reserved. Synlett 2019, 30, A–E

C
Q. Liu et al.
Letter
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Table 1 Optimization of Reaction Conditionsa
O
CuCl (20 mol%)
B2(OH)4 (5 equiv)
CN
O
R1 R2
2
NH
R2
R1
+
R
R
O
H2O/MeOH (1:1)
60 °C, 3 h
NO2
N
H
CN
CHO
catalyst
NH
+
3
1
B2(OR)4, solvent
N
H
NO2
O
O
O
1a
2a
3a
NH Br
NH Cl
NH
N
H
N
H
N
H
Entry Boron
reagent
Catalyst
t
(h)
Solvent
Yieldb
(%)
3a: 91% yield
84% yielda
O
3c: 83% yield
3b: 82% yield
1
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
B2pin2
–
12
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O
10
50
38
42
25
92
53
72
62
65
66
<5
35
31
10
25
30
38
42
91
85
70
82
O
O
2
AcOH (1.2 equiv)
TFA (1.2 equiv)
PivOH (1.2 equiv)
BzOH (1.2 equiv)
CuCl (20 mol%)
CuCl2 (20 mol%)
CuBr (20 mol%)
CuI (20 mol%)
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
3
NH OH
NH
NH
F
Br
3
N
H
N
H
N
H
4
3e: 87% yield
3d: 73% yield
3f: 80% yield
5
O
O
O
6
NH
NH
NH
OCH3
CH3
7
N
H
N
H
N
H
8
Br
3h: 81% yield
3i: 76% yield
3g: 82% yield
9
O
O
O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
CuOAc (20 mol%)
ZnCl2 (20 mol%)
FeCl2 (20 mol%)
FeCl3 (20 mol%)
In(OTf)3 (20 mol%)
InCl3 (20 mol%)
Yb(OTf)3 (20 mol%)
CuCl (20 mol%)
CuCl (20 mol%)
CuCl (20 mol%)
CuCl (20 mol%)
CuCl (20 mol%)
CuCl (10 mol%)
CuCl (20 mol%)
NH
NH
NH
N
H
N
H
N
H
CN
CHO
CH3
3j: 80% yield
3k: 60% yield
3l: 40% yield
O
O
O
NH
NH
NH
N
O
N
H
N
H
N
H
Ph
3m: 71% yield
3o: 81% yield
3n: 77% yield
O
O
O
MeOH
NH
NH CH3
CH3
NH
CH3
O
Ph
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–MeOH (1:1)
H2O–EtOH (1:1)
N
H
N
H
N
H
B2(OH)4
B2(OH)4
B2(OH)4
B2(OH)4
3r: 70% yield
3q: 74% yield
3p: 71% yield
O
O
O
1
NH
NH
NH
3
N
H
N
H
N
H
3
a Reaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), boron reagent (5
equiv), catalyst, 1:1 H2O–MeOH (2 mL), 60 °C.
b Isolated yield.
3u: 67% yield
3t: 80% yield
3s: 81% yield
O
O
O
NH
NH
NH
N
H
N
H
N
H
yield, respectively. To demonstrate the practicability of this
method, we also conducted a gram-scale synthesis of 3a
and obtained an 84% yield (Scheme 2).
Ph
3v: 65% yield
3w: 63% yield
3x: 68% yield
O
O
O
NH
NH
NH
To understand the reaction pathway, we conducted
some control experiments (Scheme 3). When 2-nitroben-
zonitrile (1a) was reduced by B2(OH)4, 2-aminobenzonitrile
(A) was obtained in 95% yield whereas 2-aminobenzamide
(B) was not detected. When CuCl (20 mol%) was added,
compound B was obtained in 22% yield (eq 1). The reaction
of A with benzaldehyde (2a) gave the desired product 3a in
only 10% yield in the absence of CuCl (eq 2). On adding CuCl
(20 mol%), 3a was obtained in 91% yield (eq 3). This indicat-
ed that CuCl is essential for the tandem reaction. In con-
CH3
Ph
CH3
CH3
N
H
N
H
N
H
3z: 74% yield
3aa: 71% yield
3y: 66% yield
O
O
O
NH
NH
NH
F
N
H
Cl
N
H
H3C
N
H
3ad: 79% yield
3ac: 86% yield
3ab: 93% yield
Scheme 2 Substrate scope. Reagents and conditions: 1 (0.5 mmol), 2
(0.6 mmol), CuCl (20 mol%), B2(OH)4 (5 equiv), 1:1 v/v H2O–MeOH (2
mL), 60 °C, 3 h. Isolated yields are reported. a Gram-scale reaction: 10
mmol.
© 2019. Thieme. All rights reserved. Synlett 2019, 30, A–E

D
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O
CN
CN
B2(OH)4 (5 equiv)
NH2
NH2
(1)
+
H2O/MeOH (1:1), 60 °C, 3 h
NO2
NH2
1a
A
B
without CuCl
95%
68%
0%
25%
with CuCl (20 mol%)
O
CN
CHO
B2(OH)4 (5 equiv)
NH
+
(2)
H2O/MeOH (1:1), 60 °C, 3 h
N
H
NH2
A
2a
3a
10%
O
CuCl (20 mol%)
CHO
CN
B2(OH)4 (5 equiv)
NH
+
(3)
H2O/MeOH (1:1), 60 °C, 3 h
N
H
NH2
A
2a
3a
91%
O
O
CuCl (20 mol%)
B2(OH)4 (5 equiv)
CHO
NH
NH2
+
(4)
H2O/MeOH (1:1), 60 °C, 3 h
N
H
NH2
B
2a
3a
38%
Scheme 3 Control experiments
trast, the reaction of B and 2a gave 3a in only 38% yield un-
der the standard conditions (eq 4). This suggests that B is
not a key intermediate of this tandem reaction.
the formation of the 2,3-dihydroquinazolin-4(1H)-one skel-
eton includes reduction of the nitro group followed by in-
tramolecular Pinner reaction and Dimroth rearrangement.
Based on the results of the control experiments and re-
lated reports in the literature,7a,b,14 the reaction pathway
shown in Scheme 4 is proposed. First, 2-nitrobenzonitrile
(1) is reduced by B2(OH)4 giving 2-aminobenzonitrile (I).
Secondly, the addition of the amino group to a carbonyl
group gives hemiacetal II. Thirdly, attack by the hydroxy
group of hemiacetal II on the nitrile group catalyzed by
CuCl affords benzoxazine III (Pinner reaction), which then
converts into product 3 by a Dimroth rearrangement.
In summary, we have developed a Cu-catalyzed one-pot
process for the synthesis of 2,3-dihydroquinazolin-4(1H)-
ones from readily available 2-nitrobenzonitriles and car-
bonyl compounds with B2(OH)4 as a reductant in an aque-
ous medium under mild conditions. Furthermore, a possi-
ble reaction pathway is proposed. The tandem process for
Funding Information
Natural Science Foundation of Hubei Province of China (2018CFB241)
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Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1610740.
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References and Notes
(1) (a) Badolato, M.; Aiello, F.; Neamati, N. RSC Adv. 2018, 8, 20894.
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Q.; Le, U.; Conn, P. J.; Lindsley, C. W. Bioorg. Med. Chem. Lett.
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O
N
OH
CN
CN
R1 R2
B2(OH)4, H2O
R
R
R
R
R2
2
NO2
NH2
N
H
R1
1
II
I
O
NH
Dimroth rearrangement
Piner reaction
CuCl
NH
O
R
R2
R1
R2
N
H
N
R1
H
III
3
Scheme 4 A proposed reaction pathway
© 2019. Thieme. All rights reserved. Synlett 2019, 30, A–E

E
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Letter
Synlett
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(13) 2-Phenyl-2,3-dihydroquinazolin-4(1H)-one (3a); Typical Pro-
cedure
A 10-mL tube was charged with 2-nitrobenzonitrile (1; 0.5
mmol), benzaldehyde (2a; 0.6 mmol), B2(OH)4 (2.5 mmol), CuCl
(0.1 mmol), H2O (1 mL), and MeOH (1 mL), and the mixture was
stirred at 60 °C for 3 h. The mixture was then extracted with
EtOAc (3 × 5 mL) and the organic layers were combined, dried
(Na2SO4), filtered, and concentrated under reduced pressure.
The residue was purified by flash chromatography [silica gel,
PE–EtOAc (5:1)] to give a white solid; yield: 101.9 mg (91%); mp
224–225 °C.
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1H NMR (400 MHz, CDCl3):  = 7.99 (d, J = 7.2 Hz, 1 H), 7.66–7.63
(m, 2 H), 7.52–7.49 (m, 3 H), 7.39 (dt, J1 = 7.6 Hz, J2 = 1.6 Hz , 1
H), 6.95 (t, J = 7.6 Hz, 1 H), 6.72 (d, J = 8.0 Hz, 1 H), 5.95 (s, 1 H),
5.80 (s, 1 H), 4.44 (s, 1 H). 13C NMR (100 MHz, CDCl3):  = 164.7,
147.2, 138.6, 134.0, 130.2, 129.2, 128.8, 127.4, 119.7, 115.7,
114.6, 69.1.
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2424.
© 2019. Thieme. All rights reserved. Synlett 2019, 30, A–E