An Efficient One-Pot Multicomponent Synthesis of Tetracyclic Quinazolino[4,3- b ]quinazolines by Sequential C-N Bond Formation and Copper-Mediated Aerobic Oxidative Cyclization

Article abstract of DOI:10.1055/s-0036-1591578

An efficient one-pot synthesis of quinazolino[4,3- b ]quinazoline derivatives has been accomplished, starting from 2-(2-bromophenyl)quinazolin-4(3 H)-one, aldehydes, and various nitrogen sources under aerobic conditions. The multicomponent protocol is med

Full text of DOI:10.1055/s-0036-1591578

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© Georg Thieme Verlag Stuttgart · New York
2018, 29, A–F
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G. R. Potuganti et al.
Letter
Synlett
An Efficient One-Pot Multicomponent Synthesis of Tetracyclic
Quinazolino[4,3-b]quinazolines by Sequential C–N Bond
Formation and Copper-Mediated Aerobic Oxidative Cyclization
Gal Reddy Potugantia
Divakar Reddy Indukuria
Manjula Alla*a,b
O
R
O
N
Br
HN
NaN3
or
CuI, L-proline
O
N
N
a Division of Crop Protection Chemicals, CSIR-Indian Institute
of Chemical Technology, Tarnaka, Hyderabad 500 007, India
b AcSIR–Indian Institute of Chemical Technology, Tarnaka,
Hyderabad 500 007, India
NH3 H2O
N
DMSO, 80 °C
12 h, air
R
manjula@iict.res.in
R = aromatic and heteroaromatic
aldehydes
18 examples
Yields up to 80%
Good substrate scope
Three C–N bond formations
Received: 06.02.2018
Accepted after revision: 05.04.2018
Published online: 04.05.2018
O
O
N
O
N
H2N
DOI: 10.1055/s-0036-1591578; Art ID: st-2018-d0123-l
N
N
N
Abstract An efficient one-pot synthesis of quinazolino[4,3-b]quinazo-
line derivatives has been accomplished, starting from 2-(2-bromo-
phenyl)quinazolin-4(3H)-one, aldehydes, and various nitrogen sources
under aerobic conditions. The multicomponent protocol is mediated by
copper(I) salts and involves amination of 2-(2-bromophenyl)quinazolin-
4(3H)-one, followed by condensation with the aldehyde and an oxida-
tive cyclization to give the target compounds in moderate to good
yields.
N
N
O
Tryptanthrin
Lutonin A
Batracylin
OH
O
O
N
N
O
OH
N
N
NH
N
O
OH
Key words quinazolinoquinazoline, copper catalysis, oxidative cycliza-
tion, C–N bond formation.
Ophiuroidine
Auranthine
Figure 1 Representative examples of natural products and biologically
active quinazolinone derivatives
The synthesis of N-fused polycyclic heterocycles and
their analogues has attracted much attention, not only be-
cause of their presence in many bioactive natural products,
but also due to their status as privileged scaffolds in drug
design.1 Among these compounds, tetracyclic benzimidaz-
ole and quinazoline compounds containing a bridgehead
nitrogen atom are frequently encountered in pharmaceuti-
cals.2 Molecules containing the quinazoline core have been
known to bind to an array of receptors with enhanced affin-
ity.3 Therapeutic applications of quinazolines cover a wide
range of disease states,4 and the compounds show anti-
inflammatory, antihypertensive, anticancer, antibacterial,
and analgesic properties.5–7 Many potential drug molecules
and natural products possessing the quinazolinone moiety
in a tetracyclic framework, such as luotonin A,8 batracylin,9
tryptanthrin,10 ophiuroidine,11 and auranthine12 have been
reported (Figure 1).
better toxicity profile and the lower cost of the metal. Our
recent account on the convenient amination of the dihalide
of Tröger’s base14 by a copper-catalyzed protocol is an ex-
ample. This inspired us to probe the feasibility of a C–N
bond-formation protocol for the construction of tetracyclic
quinazolino[4,3-b]quinazolines. The present study explored
optimal conditions, suitable nitrogen sources, and the
scope of copper-catalyzed construction of quinazolino[4,3-
b]quinazolines from 2-(2-bromophenyl)quinazolin-4(3H)-
one and various aldehydes through oxidative C–N bond for-
mation.15
The optimum conditions for the protocol were assessed
by using 2-(2-bromophenyl)quinazolin-4(3H)-one (1a) and
benzaldehyde (3a) as model substrates together with vari-
ous nitrogen sources 2, including sodium azide (NaN3),
aqueous ammonia, and benzylamine. Initially the screening
was carried out with NaN3 as the nitrogen source, copper
iodide (CuI) as the catalyst, L-proline (L-Pro) as the ligand,
and DMSO as the solvent. The reaction proceeded at 80 °C
C–N bond formation plays a vital role in the construc-
tion of such tetracyclic bridgehead-nitrogen molecules.13
The coupling is usually carried out in the presence of
palladium derivatives as catalysts. Recently, copper-mediated
C–N bond formation has received attention owing to the
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–F

B
G. R. Potuganti et al.
Letter
Synlett
during 12 hours without the need for a base to yield the de-
sired quinazolino[4, 3-b]quinazoline 4a in 80% yield (Table
1, entry 1). Increasing the reaction time to 24 hours or the
reaction temperature to 100 °C did not alter the product
yield appreciably (entries 2 and 3). The reaction proceeded
more effectively in DMSO than in DMF, acetonitrile, or tolu-
ene (entries 4–6). The efficiency of the copper salts CuBr,
CuCl, (CuOAc)2, and CuOAc was then examined (entries 8–
11) but CuI was found to give the best results. The reaction
did not proceed in the absence of a catalyst (entry 12). L-
Proline was found to be a more effective ligand than N,N′-
dimethylethane-1,2-diamine (DMEDA) (entries 13 and14),
and the reaction yield fell in the absence of a ligand (entry
15).
When aqueous ammonia was used as the nitrogen
source, the reaction did not proceed under the standard
conditions. Modification of the reaction conditions by em-
ploying a base and heating the reaction in a sealed tube
(K2CO3, DMSO, 100 °C, 24 h), followed by aerial heating,
gave 4a in 61% yield (Table 1, entry 16). This version of the
reaction therefore takes longer, requires harsher conditions,
and gives a poorer yield compared with the use of NaN3 as
nitrogen source. The catalyst efficiency was also investigat-
ed (entries 18–20); again, CuI was found to be the best cata-
lyst. Subsequently, we examined the use of benzylamine as
the nitrogen source (K2CO3, DMSO, 80 °C; entry 21). How-
ever, the reaction yield was even lower (51%). Therefore, the
Table 1 Synthesis of 4a by Employing Various Reaction Parametersa
O
N
O
NaN3
Br HN
N
O
Cu(I) salts, ligand
or
N
solvent, temp, time, air
NH3.H2O
N
1a
2
3a
4a
Entry
Catalyst
Ligand
N Source
Base
Temp (°C)
Solvent
Time (h)
Yield (%)
NaN3
1
2
CuI
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
DMEDA
DMEDA
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
80
80
DMSO
DMSO
DMSO
DMF
12
24
12
12
12
12
24
12
12
12
12
12
12
12
12
24
24
24
24
24
24
80
CuI
NaN3
80
3
CuI
NaN3
100
80
80
4
CuI
NaN3
62
5
CuI
NaN3
80
MeCN
toluene
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
trace
trace
trace
56
6
CuI
NaN3
80
7
CuI
NaN3
r.t.
80
8
CuBr
CuCl
Cu(OAc)2
CuOAc
–
NaN3
9
NaN3
80
51
10
11
12
13
14
15
16
17
18
19
20
21c
NaN3
80
41
NaN3
80
36
NaN3
80
NRb
48
CuI
NaN3
80
CuI
NaN3
80
45
CuI
NaN3
80
34
CuI
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
L-Pro
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
BnNH2
K2CO3
100
100
100
100
100
80
61
–
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
NRb
32
CuCl
CuBr
Cu(OAc)2
CuI
36
31
51
a Reaction conditions: (Entries 1–15) 1 (1.66 mmol), PhCHO (3a; 2 mmol), CuI (10 mol%), ligand (20 mol%), NaN3 (3 mmol), DMSO (5 mL), 80 °C, air;16 (Entries
16–20) 1 (1.66 mmol), PhCHO (3a; 2 mmol), CuI (10 mol%), ligand (20 mol%), 25% aq NH3 (1 mL), K2CO3 (5 mmol), DMSO (5 mL), 100 °C, sealed tube then air.16
b No reaction.
c No aldehyde was used.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–F

C
G. R. Potuganti et al.
Letter
Synlett
preferred nitrogen source for this multicomponent protocol
is sodium azide (Scheme 1).
We assumed that the reaction proceeds mainly by a
copper-catalyzed Ullmann-type aryl amination, followed
by sequential C–N bond formations and aerobic oxidative
cyclization (Scheme 2).
To confirm the salient features of the pathway, we per-
formed a series of control experiments (Scheme 3). First,
we proved beyond doubt that aerobic oxidation indeed
occurs, as experiments performed under a nitrogen atmo-
sphere with all three nitrogen sources gave the nonoxidized
product 5.
In the case of benzylamine, the reaction seems to pro-
ceed by an Ullmann-type N-arylation17 in the presence of
CuI, L-proline, and K2CO3. The arylated product undergoes
C–H amidation, followed by oxidative cyclization.18 With
aqueous ammonia as the nitrogen source, the CuI-catalyzed
ligand-assisted arylation19 of NH3 affords intermediate C,
probably via intermediates A and B. This is followed by a
second C–N bond formation between the newly formed an-
Having successfully established optimal reaction condi-
tions, we examined the scope of the protocol with various
aldehydes. The reaction proceeded smoothly with a range
of aromatic and hetaromatic aldehydes (Scheme 1; 4a–r),
giving yields of 43–80 %. In general, aryl aldehydes (4a–l)
were more reactive than heteroaryl aldehydes (4m–o). Use
of a bulkier aldehyde (4p) had a negative influence on reac-
tion yield, probably due to steric crowding. Substituents on
the aryl ring also influenced the reaction yields; aromatic
aldehydes with electron-donating substituents seem to be
preferred compared with those with electron-withdrawing
substituents. This explains why the lowest yield was ob-
tained in case of 4-nitrobenzaldehyde (4i; 43%). The reac-
tion did not proceed with 1 (R1 = NO2). Aliphatic and unsat-
urated aldehydes did not undergo the copper-mediated
coupling reaction.
N
N
R3
O
NaN3
CuI, L-Proline
DMSO, 80 °C 12 h, air
R2
N
O
O
Br HN
or
R1
R3
NH3.H2O
N
R2
1
2
3
4a–r
R1
R3 = aromatic,
R1 = H, NO2
R2 = H, Cl
heteroaromatic carbaldehyde.
O
Cl
Cl
Cl
O
N
O
O
N
N
N
N
N
N
N
N
N
N
N
O
N
O
N
O
N
O
O
N
O
N
N
4a, (80%)
4b, (66%)
4c, (65%)
4d, (63%)
4e, (66%)
4f, (65%)
NO2
OCF3
CN
Br
O
N
N
N
N
N
N
N
N
N
N
N
N
O
N
O
N
O
N
O
N
O
N
O
N
4g, (72%)
4h, (57%)
4i, (43%)
4j, (61%)
4k, (53%)
4l, (70%)
S
N
O
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Br
N
O
N
O
O
N
O
O
N
O
Cl
Cl
4m, (70%)
4n, (66%)
4o, (59%)
4p, (55%)
4q, (62%)
4r, (56%)
Scheme 1 Synthesis of quinazolino[4,3-b]quinazolines
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–F

D
G. R. Potuganti et al.
Letter
Synlett
N2
N
O
O
N
O
N
O
N
Br
L
N2
N
L
Br HN
L Cu
HN
NaN3
Cu
HN
H2O
HN
Cu(L)
N
A
1a
K2CO3
NH3.H2O
-N2
KBr
O
+CO2
+H2O
O
NH2 HN
L
H2N
L
Cu(I)/L
Cu
HN
N
O
R
N
C
R
H2O
B
N
H
N
O
N
Cu, Air
N
O
N
N
NH
D
aerobic
oxidation
N
N
O
R
R
proposed mechanism
4a
Scheme 2
O
H3CO
iline and the aldehyde, resulting in formation of imine D.
Cyclization through a third C–N bond formation, followed
by aerial oxidation results in the formation of the target
compound (Scheme 2).
H
N
Br
OCH3
H
CuI, L-proline
N
O
N
N
O
3
DMSO, 80 °C
12 h, N2
N
On the other hand, the reaction with NaN3 is probably
initiated by disproportion of NaN3 between CuI and L-pro-
line, resulting in the formation of CuN3 and the sodium salt
of L-proline. This is followed by coupling of CuN3 with the
aryl bromide and elimination of Br–. Subsequent loss of
nitrogen from the aryl azide followed by reduction (with
the assistance of trace amounts of water in the DMSO) leads
to corresponding aniline.20 Control experiments with the
substrate and sodium azide in the presence of a copper salt
and L-proline resulted in the formation of aniline 6 (Scheme
3).21 Only traces of the aniline 6 were found in the absence
of L-proline. The second C–N bond formed between the
aldehyde and the resulting aniline affords the correspond-
ing imine. Nucleophilic attack by the quinazolinyl N–H
moiety forms the third C–N bond, resulting in the dihydro
product. Aerobic oxidation assisted by the metal affords the
aza-fused polycyclic target (Scheme 2).
NaN3
5
1a
2
yield: 69%
m/z: 356, IR: 3355 cm–1 (NH)
1692 cm–1(C=O)
Br
N
NH2
H
H
N
O
N
O
CuI, L-proline
NaN3
N
DMSO, 80 °C
6 h
1a
2
6
yield: 86%
m/z: 238, IR: 3447 cm–1(NH2),
1672 cm–1 (C=O)
Br
NH2
H
H
N
N
O
O
CuI
NaN3
N
N
DMSO, 80 °C
6 h
1a
2
6
In conclusion, a facile method for the construction of
tetracyclic quinazolino[4,3-b]quinazolines through copper-
catalyzed C–N bond formation has been developed. Three
nitrogen sources were explored for the initial N-arylation,
and the optimal conditions for the transformation were
established. This one-pot multicomponent reaction is suc-
cessful for various N-nucleophiles and for a range of aryl or
heteroaryl aldehydes, with good functional-group toler-
yield: 56%
Br
H
O
N
O
CuI, L-proline
OCH3
no reaction
N
DMSO, 80 °C,
12 h
1a
3
Scheme 3 Control experiments
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–F

E
G. R. Potuganti et al.
Letter
Synlett
ance. The protocol uses simple substrates and reagents and
this, coupled with its generality, make it a valuable tool for
the synthesis of aza-fused polycyclic heterocycles.
2765. (d) Cai, Q.; Li, Z.; Wei, J.; Fu, L.; Ha, C.; Pei, D.; Ding, K. Org.
Lett. 2010, 12, 1500. (e) Tyagi, V.; Khan, S.; Bajpai, V.; Gauniyal,
H. M.; Kumar, B.; Chauhan, P. M. S. J. Org. Chem. 2012, 77, 1414.
(14) Reddy, M. B.; Reddy, P. G.; Shailaja, M.; Manjula, A.; Rao, T. P.
RSC Adv. 2016, 6, 98297.
(15) Xu, C.; Jia, F. C.; Zhou, Z.-W.; Zheng, S.-J.; Li, H.; Wu, A.-X. J. Org.
Chem. 2016, 81, 3000.
Acknowledgment
(16) Quinazolino[4,3-b]quinazolines 4a–r; General Procedures
Method 1 (NaN3 as the nitrogen source): CuI (10 mol%), L-proline
(20 mol %), and NaN3 (3 mmol) were added to a solution of
quinazolinone 1 (1.66 mmol) in DMSO (5 mL) at r.t., and a blue
complex formed. The appropriate aldehyde (2 mmol) was
added, and the mixture was stirred at 80 °C for 12 h until the
reaction was complete (TLC). The mixture was cooled then par-
titioned between ice-cold H2O (25 mL) and EtOAc (30 mL). The
organic layer was separated, and the aqueous layer was
extracted with EtOAc (2 × 30 mL). The organic layers were com-
bined, washed with brine, dried (Na2SO4), filtered, and concen-
trate in vacuo. The residue was purified by column chromatog-
raphy (silica gel).
We would like to thank the Director, CSIR-IICT and AcSIR for facilities.
P.G.R. thanks the CSIR and I.D.R. thanks the DST, New Delhi, for fellow-
ships.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1591578.
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Method 2 (aq NH3 as the nitrogen source): CuI (10mol %), L-
proline (20 mol %), 25% aq NH3 (1 mL), K2CO3 (5 mmol), and the
appropriate aldehyde (2 mmol) were added to a solution of
quinazolinone 122 (1.66 mmol) in DMSO (5 mL), and mixture
was stirred at 100 °C for 6 h in a sealed tube. The mixture was
then heated for 18 h open to the air until the reaction was com-
plete (TLC). The mixture was cooled to r.t. then partitioned
between ice-cold H2O (25 mL) and EtOAc (30 mL). The organic
layer was separated, and the aqueous layer was extracted with
EtOAc (2 × 30 mL). The organic layers were combined, washed
with brine, dried (Na2SO4), filtered, and concentrated in vacuo.
The residue was purified by column chromatography (silica gel).
6-(4-Bromophenyl)-8H-quinazolino[4,3-b]quinazolin-8-one
(4g)
White solid; yield: 482 mg (72%); mp 270–272 °C. IR (KBr):
1696 (C=O) cm–1. 1H NMR (400 MHz, CDCl3): δ = 8.81 (d, J = 8.0
Hz, 1 H), 8.24 (d, J = 7.9 Hz, 1 H), 7.88 (d, J = 3.5 Hz, 2 H), 7.85–
7.78 (m, 2 H), 7.66–7.63 (m, 1 H), 7.62–7.59 (m, 2 H), 7.52–7.50
(m, 1 H), 7.49 (d, J = 8.2 Hz, 2 H). 13C NMR (100 MHz, CDCl3):
δ = 160.54 (C=O), 148.96, 146.92, 146.15, 144.21, 142.28,
135.96, 135.58, 133.70, 131.40, 128.62, 127.99, 127.40, 127.18,
126.52, 126.01, 124.01, 121.42, 120.29. LC-MS (positive-ion
mode): m/z = 402 [M + H]+; HRMS (EI): m/z [M + H]+ calcd for
C
21H13BrN3O: 402.02404; found: 402.02365.
6-(4-Nitrophenyl)-8H-quinazolino[4,3-b]quinazolin-8-one
(4i)
Yellow solid; yield: 246 (43%); mp 288–290 °C. IR (KBr): 1692
(C=O) cm –1. 1H NMR (400 MHz, CDCl3): δ = 8.85 (d, J = 8.0 Hz, 1
H), 8.35 (d, J = 8.7 Hz, 2 H), 8.23 (d, J = 7.9 Hz, 1 H), 7.91 (d, J =
2.3 Hz, 2 H), 7.85 (d, J = 6.5 Hz, 2 H), 7.75 (d, J = 8.7 Hz, 2 H), 7.69
(t, J = 7.3 Hz, 1 H), 7.55–7.50 (m, 1 H). 13C NMR (100 MHz,
CDCl3): δ = 160.33 (C=O), 147.97, 147.81, 146.92, 145.70,
143.27, 141.97, 135.89, 133.91, 129.39, 128.26, 127.94, 127.37,
126.83, 126.13, 123.50, 121.39, 119.97. LC-MS (positive-ion
mode): m/z = 369 [M + H]+; HRMS (EI): m/z [M + H]+ calcd for
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