UV-light induced domino type reactions: Synthesis and photophysical properties of unreported nitrogen ring junction quinazolines

Article abstract of DOI:10.1039/c5ra00229j

An expedient method for the synthesis of 5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]quinazolines by UV light has been developed. Our aim was to synthesize various α, β-unsaturated carbonyl compounds and to further react them with different amines in DMF, in

Full text of DOI:10.1039/c5ra00229j

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UV-light induced domino type reactions: synthesis
and photophysical properties of unreported
nitrogen ring junction quinazolines†
Cite this: RSC Adv., 2015, 5, 37415
*
Jeyakannu Palaniraja and Selvaraj Mohana Roopan
An expedient method for the synthesis of 5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]quinazolines by UV light
has been developed. Our aim was to synthesize various a, b-unsaturated carbonyl compounds and to
further react them with different amines in DMF, in the presence of potassium hydroxide as base, which
leads to cyclization and the aromatized products in a single step using UV irradiation at 254 nm. We have
performed the reaction with various other bases and solvents that lead to the desired product with a
lower yield. The synthesized ring junction compounds have been characterized by suitable
spectroscopic techniques. The fluorescence emission spectra of the synthesized compounds were
recorded in DMF.
Received 6th January 2015
Accepted 1st April 2015
DOI: 10.1039/c5ra00229j
www.rsc.org/advances
conventional energy sources like microwave irradiation, ultra-
violet light,24,25 ultrasonic waves, etc. To bring novelty to the
Introduction
existing work, our interest was mainly to focus on the synthesis
of triazoloquinazoline ring junction nitrogen compounds using
UV-irradiation via a domino type reaction.26 The cascade reac-
tion or domino reaction or tandem reaction has drawn special
focus in organic transformations. Despite their biological
activity, there are limited reports of uorescence studies of tri-
azoloquinazoline fused systems. This gap was identied by our
research group and so we planned the synthesis of a series of
triazoloquinazolines and to subject them to uorescence
studies.
Quinazoline derivatives are nitrogen-containing heterocyclic
compounds which have a universal impact due to their bio-
logical and pharmaceutical activities.1 Researchers have already
determined many therapeutic activities of quinazoline deriva-
tives, including anti-cancer,2–4 anti-inammation,5,6 anti-bacte-
rial,7–9 analgesia,10 anti-virus,11 anti-cytotoxin,12 anti-spasmodic,13
anti-tuberculosis,14 anti-oxidation,15 antimalarial,16 anti-hyper-
tension,17 anti-obesity,18 anti-psychotic,19 anti-diabetes,20 etc.,
along with the quinazoline core motif. We have also found
several triazolo pyrimidine core structures with highly impor-
tant medical activities for neurological disorders, anti-cancer,
anti-bacterial, anti-viral cases, and also with cytotoxic activi-
ties. Over past decades, researchers have been focusing on fused
heterocyclic compounds with a nitrogen ring junction due to
their biologically potent properties.21–23 Unfortunately, the
majority of ring junction systems do not occur naturally, but
they have more importance than just a theoretical viewpoint.
Replacement of a carbon atom and its attached hydrogen atoms
by heteroatoms like nitrogen, sulphur or oxygen, either in ve or
six-membered rings, leads to a wide variety of heterocycles.
Their pharmacological activities also vary hugely. Some of the
ring junction nitrogen analogues have been used as dyes as well.
Recent literature has been enriched with an overview on the
syntheses of various heterocyclic compounds using non-
Results and discussion
We have also reported a series of short reviews on arylation via
transition metal free conditions.27 The background literature
revealed that Scheme 1 was closely related to our present
research experiments. Drizin et al. (2002), synthesized dihy-
dropyrolopyrimidine fused rings by a one pot methodology with
excellent yields.28 The reactions were carried out in the absence
of a catalyst. In 2005, Shikhaliev et al. demonstrated the neat
reaction to synthesise dihydrotriazolo pyrimidine derivatives
with excellent yields.29
In 2008, Majid et al. synthesised dihydrotriazolo pyrimidine
derivatives via a one pot multi component methodology using a
tungsten catalyst.30
Desenko et al., in 1991, synthesized a set of tetrahydro tri-
azoloquinazolines from chalcones and 2H-[1,2,4]triazol-
3-ylamine in DMF.31 Many literature reports record either the
synthesis of ring junction nitrogen compounds without
aromatization or two step procedures were necessary to get the
aromatized ring junction nitrogen compound.32–34 To aromatize
Chemistry of Heterocycles & Natural Product Research Laboratory, Organic Chemistry
Division, School of Advanced Sciences, VIT University, Vellore, Tamil Nadu – 632014,
India; Web: www.mohanaroopan.com. E-mail: mohanaroopan.s@gmail.com;
mohanaroopan.s@vit.ac.in; Fax: +91-416-224-3092; Tel: +91-416-220-2352
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra00229j
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triazol-3-ylamine in the presence of potassium hydroxide as a
base in DMF under UV-irradiation (Scheme 1). The reaction
mixture was irradiated for 3 h at 254 nm and led to the cycliza-
tion, followed by the aromatized products, in a single step with
good to excellent yields. We have synthesised an array of 5,6-
dihydrobenzo[h][1,2,4]triazolo[5,1-b]quinazoline derivatives.
The synthesized triazoloquinazolines were characterized by
spectral analyses. The synthesised compounds were subjected
to uorescence studies and the quantum yields of uorescent-
active compounds were calculated. During ne tuning of the
reaction conditions, no product conversion was observed with
ethanol or with neat conditions (entry 1 and 2, Table 1). A
moderate yield was observed when using strong bases like
tBuOK, NaOH and KOH.
Aer performing the reaction under different conditions, we
found that the KOH/DMF combination with 1 h at room
temperature in the presence of UV irradiation at 254 nm
provided the best yield (entry 21). The reaction time also played
an important role in increasing the yield of the product (Table 1).
With optimized conditions in hand, the scope of the method-
ology was examined. We synthesized 22 a,b-unsaturated
carbonyl compounds and known compounds were conrmed by
Scheme 1 Synthesis of nitrogen ring junction quinazoline derivatives
by various methodologies.
the compound, DDQ35/toluene, PhCl/p-chloranil36 or CAN/
acetone37 were used. However, these methodologies require a
longer time for the completion of the reaction and provide a
lower yield. These gaps prompted us towards the synthesis of a
couple of 5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]quinazolines.
Our research methodology involves the reaction between a
series of a,b-unsaturated carbonyl compounds and 2H-[1,2,4]-
1
their melting points and H NMR data matching with reported
data. The compounds 5a and 5n formed with 92% product
(isolated yield). From the above result, the substitution on the
Table 1 Fine tuning the optimal reaction conditions for the compound 5aa
Entry
Base
Solvent
Temp. (ꢀC)
Source
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
—
—
—
100
80
80
80
80
D
16
16
16
16
16
16
16
16
16
16
3
5
3
3
3
5
3
0.5
3
1
NR
NR
NR
NR
Trace
75
40
30
50
56
45
25
16
16
87
67
50
60
EtOH
EtOH
EtOH
MeOH
EtOH
t-BuOH
t-BuOH
EtOH
EtOH
DMSO
DMSO
THF
D
Triethylamine
Piperidine
NaOMe
NaOEt
NaOtBu
KOtBu
NaOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
D
D
D
80
D
100
100
80
80
80
80
80
80
80
60
100
80
RT
RT
RT
RT
D
D
9
D
10
11
12
13
14
15
16
17
18
19
20
21
22
D
D
D
D
ACN
D
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
D
D
D
MW (100 W)
US
UV (254 nm)
UV (312 nm)
UV (365 nm)
55
92
67
55
3
3
a
Where D ¼ conventional heating, MW ¼ microwave, UV ¼ ultraviolet irradiation, US ¼ ultra sonication, NR ¼ no reaction and RT ¼ room
b
temperature. The optimal conditions are shown by bold letters. Isolated yield.
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Table 2 Synthesis of 5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]quina-
On the basis of the above ne-tuned reaction conditions, we
utilized the same methodology for different amines and a,b-
unsaturated carbonyls to provide compounds with fair to good
yields. The synthesized compounds 2-benzylidene cyclohexanone
6e and 2-benzylidene cyclopentanone 6d failed to afford the
required products under the same conditions (Table 3).
The compound 5a was also synthesized by a one pot multi
component reaction. The conditions involved equimolar
amounts of the three reactants with a KOH/DMF combination
under UV irradiation to afford the product with an isolated yield
of 20% (Scheme 2). In the multistep reaction, the compounds 3a
and 5a were synthesized with 94% yield38 and 92% isolated
yield, respectively. Compared with the above conditions, the
Multi Component Reaction (MCR) gave 20% product (isolated
yield).
zoline derivativesa
The uorescence emission spectra of the synthesized
compounds 5a–v were recorded in DMF (10ꢁ5 M). Among these
compounds 5d, 5e, 5h, 5k, 5l, 5m, 5o, 5q, 5u and 5v showed
uorescence properties (Fig. 1).
We calculated the quantum yield (F) of the uorescence
active compounds. The F was calculated using the formula,
F ¼ (FR ꢂ IS ꢂ ODR ꢂ hs)/(IR ꢂ ODS ꢂ hR)
where FR ¼ quantum yield of the reference, IS and IR ¼ integral
area of the sample and the reference, respectively, ODS and
ODR ¼ excited absorbance of the sample and the reference,
respectively, hs and hR ¼ refractive index of the sample solvent
and the reference solvent, respectively. We used tryptophan40–43
as a standard for calculating the quantum yield (Table 4). For
the standard we used water as a solvent and for the synthesised
compounds we used DMF.
Conclusions
In conclusion, we have developed an efficient and easy protocol
for the synthesis of triazoloquinazoline fused ring systems
through a domino type transformation. Moreover, this method
offers shorter reaction times, remarkable yields and transition
metal free reaction conditions. Some of the derivatives showed
uorescence activity and we have calculated the quantum yield
for these uorescence active compounds. In the future, we plan
to investigate the biological activities of the synthesized
compounds.
Experimental section
a
Reactions were carried out with 1.0 equivalent of 3, 4 and 1.2
b
All commercially available reagents were used without further
purication and the reactions were monitored by TLC. The H
equivalent of KOH in 10 mL DMF for 3 h. Isolated yields.
1
and 13C NMR spectra were obtained using a Bruker Avance 400
MHz spectrometer in CDCl3 solvent with TMS as an internal
standard. Chemical shi values (d) were expressed in parts per
million (ppm). Abbreviations are as follows: s, singlet; d,
doublet; t, triplet; m, multiplet. The melting points were
measured on an Elchem Microprocessor based DT apparatus
using open capillary tubes and are uncorrected. The mass
spectra were obtained by high resolution mass spectrometry.
a,b-unsaturated carbonyl compounds were not playing any
important role in the product formation. The synthesized a,b-
unsaturated carbonyl compounds were reacted with 2H-[1,2,4]
triazol-3-ylamine in the presence of KOH/DMF to afford the
product with good to excellent yield (Table 2).
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Table 3 Scope for various amines and a,b-unsaturated carbonyls
vial containing 10 mL of dimethylformamide and potassium
hydroxide (1.2 mmol) was added at room temperature. The
mixture was irradiated under UV at 254 nm (8 lamps) with
constant stirring. The progress of the reaction was monitored by
TLC. Aer the completion of the reaction, the reaction mixture
was poured into crushed ice and the solid was ltered. The solid
was dissolved in EtOAc and mixed with water and the organic
layer was separated. The separated organic layer was dried over
sodium sulphate and the solvent was evaporated. The crude
product was further puried by column chromatography to
afford the product as a solid.
Characterization data for the compounds [5a–i & 6a–f]
7-Phenyl-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]quinazo-
line (5a). Brown solid; isolated yield – 92%; mp: 201–203 ꢀC; 1H
NMR (400 MHz, CDCl3) d 8.62–8.59 (m, 1H), 8.39 (s, 1H), 7.62–
7.61 (m, 5H), 7.46 (t, J ¼ 4.4 Hz, 2H), 7.29 (d, J ¼ 4.0 Hz, 1H), 2.95
(bs, 4H); 13C NMR (100 MHz, CDCl3) d 24.7, 27.9, 117.8, 127.3,
127.7, 127.9, 128.9, 129.0, 129.5, 130.7, 131.7, 132.7, 139.5,
144.5, 155.7, 158.5; HRMS: m/z calcd for C19H14N4 298.1218
found 298.1210.
Scheme 2 Synthesis of 7-phenyl-5,6-dihydrobenzo[h][1,2,4]triazolo
[5,1-b]quinazoline via a multi component one pot methodology.
7-(p-Tolyl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]quinazo-
line (5b). Off-white solid; isolated yield – 75%; mp: 240–242 ꢀC;
1H NMR (400 MHz, CDCl3) d 8.61–8.59 (m, 1H), 8.38 (s, 1H),
7.51–7.42 (m, 6H), 7.29–7.26 (m, 1H), 3.00–2.91 (m, 4H), 2.49 (s,
3H); 13C NMR (100 MHz, CDCl3) d 21.6, 24.7, 27.9, 117.7, 126.0,
127.2, 127.6, 127.9, 129.4, 129.6, 131.6, 132.8, 139.6, 141.1,
144.7, 154.9, 155.6, 158.5; HRMS: m/z calcd for C20H16N4
312.1375 found 312.1370.
Fig. 1 Fluorescence emission spectra of the synthesised compounds.
The UV-Visible spectra were obtained on a UV-2550, Shimadzu
Corporation, Kyoto, Japan. The uorescence spectra were
obtained on a Hitachi F-7000 FL spectrophotometer. Column
chromatography was performed using 60–120 mesh silica gel.
UV-irradiation was carried out in a Heber multi-wavelength
multi-lamp photo reactor (Model HML-LP88).
7-(4-Chlorophenyl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5c). Off-white solid; isolated yield – 77%; mp: 266–
268 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.60–8.58 (m, 1H), 8.38 (s,
1H), 7.62–7.55 (m, 4H), 7.47–7.43 (m, 2H), 7.29–7.28 (m, 1H),
2.95 (bs, 4H); 13C NMR (100 MHz, CDCl3) d 23.7, 26.7, 116.9,
126.2, 126.2, 126.7, 126.9, 128.3, 130.0, 130.8, 131.5, 136.0,
General procedure for the synthesis of 5,6-dihydrobenzo[h]-
[1,2,4]triazolo[5,1-b]quinazolines [5a–i & 6a–f]
A mixture of the a,b-unsaturated carbonyl compound (1 mmol) 138.4, 142.2, 153.8, 154.7, 157.5; HRMS: m/z calcd for
and amine (1 mmol) were mixed in a 50 mL quartz UV reaction
C19H13ClN4 332.0829 found 332.0820.
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Table 4 Photophysical data for the fluorescence active compoundsa
Entry
lmax (abs, nm)
lmax (em, nm)
Stokes shi (nm)
OD
I
F
Tryptophan39
5d
280
271
253 (Sh)
259
277 (Sh)
265
275 (Sh)
264 (Sh)
277
276 (Sh)
264
274 (Sh)
261
266
355
392
392
365
365
415
415
391
391
386
386
423
423
430
428
450
450
384
384
75
0.384
0.823
0.671
0.948
0.547
1.137
0.712
1.117
0.724
0.679
0.430
0.592
0.302
0.745
0.983
0.707
0.638
1.178
0.575
158 517
15 887
15 887
9773
0.130
0.006
0.008
0.003
0.006
0.002
0.004
0.003
0.005
0.009
0.014
0.010
0.020
0.004
0.013
0.008
0.010
0.001
0.002
121
139
106
88
5e
5h
5k
5l
9773
9029
9029
150
140
127
114
110
122
149
162
164
161
180
204
124
133
11 363
11 363
18 578
18 578
17 844
17 844
9546
37 482
18 747
18 747
5181
5m
5o
5q
5u
267
270 (Sh)
246
260
251 (Sh)
5v
5181
a
Sh ¼ shoulder; abs ¼ absorbance; em ¼ emission; OD ¼ excited absorbance; I ¼ integral area; F ¼ quantum yield.
7-(4-Bromophenyl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5f). Off-white solid; isolated yield – 85%; mp: 218–
220 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.61–8.58 (m, 1H), 8.39 (s,
1H), 7.78–7.76 (m, 2H), 7.51–7.45 (m, 4H), 7.29–7.26 (m, 1H),
2.96 (bs, 4H); 13C NMR (100 MHz, CDCl3) d 24.7, 27.8, 117.9,
125.4, 127.3, 127.7, 127.9, 129.5, 131.2, 131.8, 132.3, 132.6,
139.4, 143.3, 154.9, 155.7, 158.6; HRMS: m/z calcd for
7-(4-Methoxyphenyl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5d). Brown solid; isolated yield – 89%; mp: 204–206
ꢀC; 1H NMR (400 MHz, CDCl3) d 8.60–8.58 (m, 1H), 8.38 (s, 1H),
7.58 (d, J ¼ 8.4 Hz, 2H), 7.46–7.44 (m, 2H), 7.29–7.26 (m, 1H),
7.13 (d, J ¼ 8.8 Hz, 2H), 3.92 (s, 3H), 3.02–2.92 (m, 4H); 13C NMR
(100 MHz, CDCl3) d 24.9, 28.0, 55.5, 114.3, 117.6, 120.9, 127.2,
127.6, 127.8, 131.3, 131.6, 132.8, 139.5, 144.5, 154.9, 155.6, 158.5,
161.3; HRMS: m/z calcd for C20H16N4O 328.1324 found 328.1320.
C
19H13BrN4 376.0324 found 376.0320.
7-(4-Bromophenyl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5g). Off-white solid; isolated yield – 70%; mp: 208–
210 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.60–8.58 (m, 1H), 8.39 (s,
1H), 7.76–7.74 (m, 2H), 7.56–7.43 (m, 4H), 7.29–7.26 (m, 1H),
2.95 (s, 4H); 13C NMR (100 MHz, CDCl3) d 24.6, 27.8, 118.1,
123.0, 127.3, 127.7, 127.9, 128.2, 130.5, 130.8, 131.9, 132.4,
132.5, 133.8, 139.5, 142.8, 155.8, 158.6; HRMS: m/z calcd for
7-(4-Isopropylphenyl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5e). Off-white solid; isolated yield – 90%; mp: 190–
192 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.61–8.58 (m, 1H), 8.40 (s,
1H), 7.56–7.44 (m, 6H), 7.28–7.26 (m, 1H), 3.07–2.91 (m, 5H),
1.34 (d, J ¼ 7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) d 23.6, 24.1,
26.9, 33.4, 117.7, 126.1, 126.3, 126.4, 127.3, 128.2, 129.9, 131.5,
132.4, 140.0, 144.5, 150.9, 154.2, 155.3, 157.4; HRMS: m/z calcd
for C22H20N4 340.1688 found 340.1680.
C
19H13BrN4 376.0324 found 376.0320.
7-(Naphthalen-1-yl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5h). Yellow solid; isolated yield – 85%; mp: 203–
205 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.69–8.66 (m, 1H), 8.34 (s,
1H), 8.12 (d, J ¼ 8.0 Hz, 1H), 8.01 (d, J ¼ 8.0 Hz, 1H), 7.72–7.43
(m, 6H), 7.29–7.26 (m, 2H), 2.92–2.86 (m, 2H), 2.80–2.67
(m, 2H); 13C NMR (100 MHz, CDCl3) d 24.4, 27.7, 119.5, 124.1,
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125.4, 126.7, 126.9, 127.3, 127.6, 127.7, 128.0, 129.0, 130.3, NMR (100 MHz, CDCl3) d 25.6, 27.9, 118.4, 127.1, 127.3, 127.7,
131.2, 131.8, 132.6, 133.7, 139.7, 155.0, 155.9, 158.3; HRMS: m/z 128.2, 130.7, 131.6, 132.8, 132.9, 138.8, 139.2, 155.4, 158.3;
calcd for C23H16N4 348.1375 found 348.1370.
HRMS: m/z calcd for C17H12N4S 304.0783 found 304.0780.
3-Methoxy-7-phenyl-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5m). Off-white solid; isolated yield – 85%; mp:
182–184 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.55 (d, J ¼ 8.4 Hz, 1H),
8.34 (s, 1H), 7.65–7.58 (m, 5H), 6.99–6.96 (m, 1H), 6.77 (d, J ¼ 2.4
Hz, 1H), 3.89 (s, 3H), 2.96–2.88 (m, 4H); 13C NMR (100 MHz,
CDCl3) d 24.7, 28.2, 55.4, 112.9, 113.4, 117.2, 125.7, 128.9, 129.1,
129.3, 129.5, 130.6, 141.7, 144.2, 154.9, 155.4, 158.5, 162.5;
HRMS: m/z calcd for C20H16N4O 328.1324 found 328.1320.
7-(2,4-Dimethoxyphenyl)-5,6-dihydrobenzo[h][1,2,4]triazolo
[5,1-b]quinazoline (5i). Yellow solid; isolated yield – 80%; mp:
194–196 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.62–8.60 (m, 1H), 8.37 (s,
1H), 7.47–7.42 (m, 2H), 7.28–7.26 (m, 1H), 7.13–6.95 (m, 3H), 3.82
(s, 3H), 3.72 (s, 3H), 2.96–2.83 (m, 4H); 13C NMR (100 MHz, CDCl3)
d 24.3, 27.7, 55.8, 56.2, 112.9, 115.9, 117.2, 118.6, 119.2, 127.2,
127.6, 127.9, 131.5, 132.8, 139.8, 142.0, 151.2, 153.6, 154.9, 155.5,
158.0; HRMS: m/z calcd for C21H18N4O2 358.1430 found 358.1400.
7-(4-Chlorophenyl)-3-methoxy-5,6-dihydrobenzo[h][1,2,4]tri-
azolo[5,1-b]quinazoline (5n). Off-white solid; isolated yield –
92%; mp: 210–212 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.54 (d, J ¼
8.8 Hz, 1H), 8.34 (s, 1H), 7.61–7.54 (m, 4H), 6.99–6.96 (m, 1H),
6.78 (d, J ¼ 2.4 Hz, 1H), 3.89 (s, 3H), 2.92 (bs, 4H); 13C NMR (100
MHz, CDCl3) d 24.7, 28.1, 55.4, 112.9, 113.5, 117.2, 125.5, 127.4,
129.3, 129.4, 131.0, 137.0, 141.6, 142.9, 155.4, 158.5, 162.6;
HRMS: m/z calcd for C20H15ClN4O 362.0934 found 362.0930.
7-(Pyridin-2-yl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]qui-
nazoline (5j). Off-white solid; isolated yield – 85%; mp: 230–232
1
ꢀC; H NMR (400 MHz, CDCl3) d 8.89 (d, J ¼ 4.8 Hz, 1H), 8.62–
8.59 (m, 1H), 8.41 (s, 1H), 8.02–7.98 (m, 1H), 7.83 (d, J ¼ 7.6 Hz,
1H), 7.55–7.49 (m, 3H), 7.29–7.26 (m, 1H), 3.05–2.95 (m, 4H);
13C NMR (100 MHz, CDCl3) d 24.1, 27.6, 118.8, 125.0, 126.1,
127.3, 127.6, 127.9, 131.8, 132.5, 136.9, 139.7, 142.1, 148.5,
150.2, 154.9, 155.8, 159.0; HRMS: m/z calcd for C18H13N5
299.1171 found 299.1170.
7-(4-Bromophenyl)-3-methoxy-5,6-dihydrobenzo[h][1,2,4]tri-
azolo[5,1-b]quinazoline (5o). Off-white solid; isolated yield –
90%; mp: 206–208 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.54 (d, J ¼
8.8 Hz, 1H), 8.34 (s, 1H), 7.76 (d, J ¼ 8.4 Hz, 2H), 7.48 (d, J ¼ 8.4
Hz, 2H), 6.99–6.96 (m, 1H), 6.78 (d, J ¼ 2.0 Hz, 1H), 3.89 (s, 3H),
2.92 (bs, 4H); 13C NMR (100 MHz, CDCl3) d 24.7, 28.1, 55.4,
112.9, 113.5, 117.2, 125.5, 127.9, 129.4, 131.2, 132.2, 141.6,
142.9, 155.5, 158.5, 162.6; HRMS: m/z calcd for C20H15BrN4O
406.0429 found 406.0420.
7-(Furan-2-yl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]qui-
nazoline (5k). Off-white solid; isolated yield – 87%; mp: 196–198
1
ꢀC; H NMR (400 MHz, CDCl3) d 8.55 (t, J ¼ 6.8 Hz, 1H), 8.49
(s, 1H), 8.04 (d, J ¼ 3.6 Hz, 1H), 7.80 (s, 1H), 7.45 (t, J ¼ 4.4 Hz, 2H),
7.31–7.26 (m, 1H), 6.78 (d, J ¼ 2 Hz, 1H), 3.50 (t, J ¼ 6.8 Hz, 2H),
3.02 (t, J ¼ 7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 24.6, 27.7,
112.4, 116.9, 120.7, 127.3, 127.6, 127.6, 131.5, 132.8, 139.5, 145.3,
155.4; HRMS: m/z calcd for C17H12N4O 288.1011 found 288.1000.
3-Methoxy-7-(p-tolyl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5p). Off-white solid; isolated yield – 87%; mp: 182–
184 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.55 (d, J ¼ 8.8 Hz, 1H), 8.33
(s, 1H), 7.48 (d, J ¼ 8.0 Hz, 2H), 7.42 (d, J ¼ 8.0 Hz, 2H), 6.99–
6.96 (m, 1H), 6.78 (d, J ¼ 2.4 Hz, 1H), 3.89 (s, 3H), 2.96–2.90 (m,
4H), 2.48 (s, 3H); 13C NMR (100 MHz, CDCl3) d 21.5, 24.7, 28.2,
55.4, 112.9, 113.3, 117.0, 125.7, 126.1, 129.3, 129.4, 129.5, 141.0,
7-(Thiophen-2-yl)-5,6-dihydrobenzo[h][1,2,4]triazolo[5,1-b]-
quinazoline (5l). Off-white solid; isolated yield – 88%; mp: 226–
228 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.57–8.56 (m, 1H), 8.45 (s,
1H), 7.79–7.77 (m, 1H), 7.67–7.66 (m, 1H), 7.48–7.42 (m, 2H),
7.32–7.27 (m, 2H), 3.23–3.20 (m, 2H), 2.97 (t, J ¼ 7.6 Hz, 2H); 13
C
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141.7, 144.4, 155.4, 162.5; HRMS: m/z calcd for C21H18N4O 117.4, 122.9, 125.5, 128.2, 129.4, 130.5, 130.9, 132.4, 133.7,
342.1481 found 342.1480.
141.6, 142.4, 154.9, 155.5, 158.5, 162.6; HRMS: m/z calcd for
C
20H15BrN4O 406.0429 found 407.0501.
7-(4-Isopropylphenyl)-3-methoxy-5,6-dihydrobenzo[h][1,2,4]-
triazolo[5,1-b]quinazoline (5q). Off-white solid; isolated yield –
84%; mp: 208–210 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.55 (d, J ¼ 8.8
Hz, 1H), 8.33 (s, 1H), 7.53 (d, J ¼ 8.4 Hz, 2H), 7.47 (d, J ¼ 8.4 Hz,
2H), 6.99–6.96 (m, 1H), 6.76 (d, J ¼ 2.4 Hz, 1H), 3.95 (s, 3H), 3.07–
2.88 (m, 5H), 1.33 (d, J ¼ 7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) d
23.8, 24.8, 28.3, 34.2, 55.4, 112.9, 113.3, 117.1, 125.8, 126.4, 127.0,
129.3, 129.6, 141.7, 144.4, 151.6, 155.0, 155.4, 158.4, 162.4; HRMS:
m/z calcd for C23H22N4O 370.1794 found 370.1790.
3-Methoxy-7-(naphthalen-1-yl)-5,6-dihydrobenzo[h][1,2,4]tri-
azolo[5,1-b]quinazoline (5u). Off-white solid; isolated yield –
88%; mp: 256–258 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.62 (d, J ¼
8.8 Hz, 1H), 8.29 (s, 1H), 8.11 (d, J ¼ 8.0 Hz, 1H), 8.00 (d, J ¼ 8.4
Hz, 1H), 7.69–7.01 (m, 6H), 6.76 (d, J ¼ 2.0 Hz, 1H), 3.89 (s, 3H),
2.88–2.66 (m, 4H); 13C NMR (100 MHz, CDCl3) d 24.4, 28.1, 55.4,
113.0, 113.5, 118.8, 124.1, 125.4, 125.6, 126.8, 127.5, 127.7,
129.0, 129.4, 130.4, 131.1, 133.7, 141.9, 143.3, 155.6, 158.2,
162.6; HRMS: m/z calcd for
C24H18N4O 378.1481 found
378.1480.
3-Methoxy-7-(4-methoxyphenyl)-5,6-dihydrobenzo[h][1,2,4]-
triazolo[5,1-b]quinazoline (5r). Yellow solid; isolated yield –
88%; mp: 196–198 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.54 (d, J ¼
8.8 Hz, 1H), 8.34 (s, 1H), 7.56 (d, J ¼ 8.8 Hz, 2H), 7.12 (d, J ¼ 8.4
Hz, 2H), 6.98–6.95 (m, 1H), 6.77 (d, J ¼ 2.0 Hz, 1H), 3.91 (s, 3H),
3.88 (s, 3H), 2.90–2.88 (m, 4H); 13C NMR (100 MHz, CDCl3) d
24.8, 28.3, 55.4, 55.4, 112.9, 113.3, 114.3, 117.0, 121.0, 125.8,
129.3, 131.3, 141.6, 144.2, 155.0, 155.3, 158.4, 161.2, 162.4;
HRMS: m/z calcd for C21H18N4O2 358.1430 found 358.1400.
4-(5,6-Dihydrobenzo[h][1,2,4]triazolo[5,1-b]quinazolin-7-yl)-
benzonitrile (5v). Off-white solid; isolated yield – 78%; mp: 250–
252 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.58 (t, J ¼ 6.8 Hz, 1H), 8.38
(s, 1H), 7.93 (d, J ¼ 8.0 Hz, 2H), 7.76 (d, J ¼ 8.4 Hz, 2H), 7.48–
7.44 (m, 2H), 7.30–7.27 (m, 1H), 2.98–2.92 (m, 4H); 13C NMR
(100 MHz, CDCl3) d 24.6, 27.7, 114.7, 117.8, 118.1, 127.3, 127.8,
128.0, 130.6, 132.0, 132.3, 132.6, 133.3, 139.3, 142.1, 154.8,
155.8, 158.7; HRMS: m/z calcd for C20H13N5 323.3507 found
323.5409.
7-(2,4-Dimethoxyphenyl)-3-methoxy-5,6-dihydrobenzo[h][1,2,4]-
triazolo[5,1-b]quinazoline (5s). Yellow solid; isolated yield – 89%;
mp: 190–192 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.57 (d, J ¼ 8.8 Hz,
1H), 8.34 (s, 1H), 7.37 (d, J ¼ 8.4 Hz, 2H), 7.28 (s, 1H), 7.00–6.97
(m, 1H), 6.79–6.67 (m, 3H), 3.92 (s, 3H), 3.90 (s, 3H), 3.77 (s, 3H),
2.98–2.78 (m, 4H); 13C NMR (100 MHz, CDCl3) d 24.5, 28.2, 55.4,
55.6, 55.6, 99.1, 105.2, 110.6, 112.9, 113.2, 118.7, 125.9, 129.2,
131.5, 141.9, 141.9, 155.1, 157.9, 158.4, 162.3, 163.0; HRMS: m/z
calcd for C22H20N4O3 388.1535 found 388.1530.
7-Phenyl-5,6-dihydrobenzo[h]pyrazolo[5,1-b]quinazoline (6a).
Brown solid; isolated yield – 70%; mp: 220–222 ꢀC; 1H NMR (400
MHz, CDCl3) d 8.46 (d, J ¼ 6.4 Hz, 1H), 8.02 (s, 1H), 7.59–7.55 (m,
5H), 7.43–7.37 (m, 2H), 7.25 (d, J ¼ 4 Hz, 1H), 6.73 (s, 1H), 2.87–
2.86 (m, 4H); 13C NMR (100 MHz, CDCl3) d 24.8, 28.3, 96.6, 115.4,
126.2, 127.4, 127.9, 128.8, 129.6, 130.1, 130.2, 130.6, 133.5, 139.3,
143.1, 144.5, 148.4, 153.0; HRMS: m/z calcd for C20H15N3
297.1266 found 297.1260.
7-(3-Bromophenyl)-3-methoxy-5,6-dihydrobenzo[h][1,2,4]tri-
azolo[5,1-b]quinazoline (5t). Off-white solid; isolated yield –
87%; mp: 210–212 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.54 (d, J ¼
8.4 Hz, 1H), 8.35 (s, 1H), 7.75–7.55 (m, 2H), 7.55–7.48 (m, 2H),
6.99–6.96 (m, 1H), 6.78 (d, J ¼ 2.4 Hz, 1H), 3.89 (s, 3H), 2.92 (bs,
4H); 13C NMR (100 MHz, CDCl3) d 24.6, 28.1, 55.4, 112.9, 113.5,
7-Phenyl-5,6-dihydrobenzo[h]benzo[4,5]imidazo[2,1-b]quinazo-
line (6b). Yellow solid; isolated yield – 82%; mp: 270–272 ꢀC; 1H
NMR (400 MHz, CDCl3) d 8.70–8.68 (m, 1H), 7.92–7.73 (m, 1H),
7.72–7.69 (m, 3H), 7.51–7.23 (m, 6H), 6.94 (t, J ¼ 7.6 Hz, 1H),
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6.18 (d, J ¼ 8.4 Hz, 1H), 2.95–2.91 (m, 2H), 2.78–2.74 (m, 2H);
13C NMR (100 MHz, CDCl3) d 23.8, 28.1, 113.9, 114.8, 119.9,
120.8, 125.4, 127.3, 127.5, 127.9, 127.9, 128.6, 129.9, 130.7,
131.4, 131.5, 133.1, 140.0, 144.6, 145.2, 151.4, 158.2; HRMS: m/z
calcd for C24H17N3 347.1422 found 347.1420.
Notes and references
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Yellow solid; isolated yield – 87%; mp: 290–292 ꢀC; 1H NMR (400
MHz, CDCl3) d 8.63 (d, J ¼ 7.6 Hz, 1H), 8.40 (d, J ¼ 8.0 Hz, 1H),
7.77 (d, J ¼ 8.4 Hz, 1H), 7.64–7.73 (m, 8H), 7.28–7.25 (m, 2H),
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[4,5-a]acridine (6f). Brown solid; isolated yield – 79%; mp: 342–
344 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.26 (s, 1H), 8.11 (d, J ¼ 8.4
Hz, 1H), 7.78 (d, J ¼ 7.2 Hz, 1H), 7.67–7.45 (m, 9H), 7.34 (bs, 2H),
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Acknowledgements
SMR thanks DST-SERB (no. SB/FT/CS-126/2012), Government of
India, New Delhi for providing the research grant. JP wishes to
express their gratitude to DST for providing a Research Assis-
tant Position. Furthermore, we thank the VIT management for
providing the research facility, and thanks to VIT-SIF and DST-
FIST for providing NMR facilities to carry out this work.
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