Efficient and convenient synthesis of pyrrolo[1,2- a ]quinazoline derivatives with the aid of tin(II) chloride

Article abstract of DOI:10.1021/cc100062e

An efficient, convenient, one-pot synthesis of 2,3,3a,4- tetrahydropyrrolo[1,2-a]quinazolin-5(1H)-one and 2,3,3a,4-tetrahydropyrrolo[1,2- a]quinazoline-1,5-dione was accomplished in good yields via the novel reductive cyclization of 2-nitrobenzamides with haloketones or keto acids mediated by SnCl₂2H₂O system. A variety of substrates can participate in the process with good yields, making this methodology suitable for library synthesis in drug discovery efforts.

Full text of DOI:10.1021/cc100062e

582
J. Comb. Chem. 2010, 12, 582–586
Efficient and Convenient Synthesis of Pyrrolo[1,2-a]quinazoline
Derivatives with the Aid of Tin(II) Chloride
Manman Wang, Guolan Dou, and Daqing Shi*
Key Laboratory of Organic Synthesis of Jiangsu ProVince, College of Chemistry, Chemical Engineering
and Materials Science, Soochow UniVersity, Suzhou, Jiangsu 215123, P. R. China
ReceiVed April 13, 2010
An efficient, convenient, one-pot synthesis of 2,3,3a,4-tetrahydropyrrolo[1,2-a]quinazolin-5(1H)-one and
2,3,3a,4-tetrahydropyrrolo[1,2-a]quinazoline-1,5-dione was accomplished in good yields via the novel
reductive cyclization of 2-nitrobenzamides with haloketones or keto acids mediated by SnCl2 · 2H2O system.
A variety of substrates can participate in the process with good yields, making this methodology suitable
for library synthesis in drug discovery efforts.
Introduction
7-8 h. Therefor, the development of more efficient methods
for the preparation of this kind of compounds is still an active
research area.
The quinazolinone skeleton is a building block for the
preparation of natural purine base,1 alkaloids, many biologi-
cally active compounds and intermediates in organic syn-
thesis.2 Quinazolinone derivatives are interesting because of
their diverse range of biological activities, such as antiin-
flammatory,2 antihypertensive,3 anticancer,4 antitumor,5 an-
ticonvulsant,6 and antibacterial activity.7 Hence, the synthesis
of quinazoline derivatives is currently of great interest in
organic synthesis. For example, our group has synthesized
a series of quinazoline derivatives using 2-nitrobenzamide
and aldehyde or ketone as reactants induced by low-valence
titanium.8 As an important quinazolinone derivative, the
pyrrolo[1,2-a]quinazolinone moiety, in particular, is a very
novel tricyclic compound. And some of them have antiedema
activity.9
In recent years, our interest has been focused on the usage
of SnCl2 reagent. We have previously reported the synthesis
of 2-aryl-2H-indazoles,15 1-hydroxyquinazolinones,16 qui-
noxaline derivatives,17 imidazo[1,2-c]quinazoline-5(6H)-
thione,18 and imidazo[1,2-c]quinazolin-5(6H)-one18 mediated
by the SnCl2 reagent. In this paper, we wish to describe a
new route to synthesize 2,3,3a,4-tetrahydropyrrolo[1,2-
a]quinazolin-5(1H)-one and 2,3,3a,4-tetrahydropyrrolo[1,2-
a]quinazoline-1,5-dione via the novel reductive cyclization
of 2-nitrobenzamides with haloketones or keto acids mediated
by SnCl2 · 2H2O system.
Results and Discussion
In a preliminary study, we selected o-nitrobenzamide 1a
and the 5-chloropentan-2-one 2a as model substrates to
optimize the experimental conditions for the proposed
reductive cyclization reaction. The results are summarized
in Table 1.
The synthsis of pyrrolo[1,2-a]quinazolinone derivatives
have hitherto been reported by only few workers. For
example, Aeberli et al.10 synthesized 3-a-methyl- and 3-a-
phenyl-l,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinazoline-l,5-
dione by reaction of anthranilamide with 4-oxopentanoic acid
and 4-oxo-4-phenylbutanoic acid. Bell et al.11 prepared
pyrrolo[1,2-a]quinazolines from the reaction of anthranil-
amides with either γ-cyanopropionaldehyde or succinican-
hydride. Kurihara et al.12 also reported the reaction of ethyl
3-ethoxymethylene-2,4-dioxovalerate with 2-aminobenz-
amide derivatives to give pyrrolo[1,2-R]quinazoline-1,5-
dione derivatives. However, these synthetic methods are
considerably limited because of unsatisfactory yields, long-
reaction time, complex manipulation, and inaccessible start-
ing materials. Recently, Iminov et al.,13,14 reported the
synthesis of pyrroloquinazoline carboxylic acids and 7a,8,9,
10-tetrahydrocyclopenta[2,3]pyrrolo[1,2-a]quinazoline-
6,12(7H,11H)-diones from the reaction of 2-aminobenza-
mides with 2-oxoglutaric acid and 2-oxocyclopentaneheptane-
acetic acids esters, respectively. But, the reaction still needs
Table 1. Optimization of Temperature, Ratio, and Solvents in
the Synthesis of 3a
entry
solvent
temperature/°C
ratioa
yield/%
1
2
3
4
5
6
7
8
9
THF
reflux
reflux
reflux
reflux
rt
40
60
reflux
reflux
reflux
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:2
1:3
1:5
67
52
45
85
39
55
70
54
68
83
CH3CN
CHCl3
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
10
* To whom correspondence should be addressed. E-mail: dqshi@
suda.edu.cn.
a Ratio of 1 and SnCl2 · 2H2O system.
10.1021/cc100062e  2010 American Chemical Society
Published on Web 06/14/2010

Pyrrolo[1,2-a]quinazoline Derivatives
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4 583
Table 2. Synthesis of Compounds 3 from o-Nitrobenzamides 1 and Haloketones 2
entry
X
Y
Z
R1
R2
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
compound
yield (%)
1
2
3
4
5
6
7
8
H
H
CH3
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
H
H
H
H
H
H
H
H
H
H
H
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
85
80
78
86
82
79
65
69
73
67
75
70
76
73
75
76
72
68
CH3
H
OCH3
H
Cl
H
OCH3
Cl
H
H
H
H
H
4-CH3C6H4
4-OCH3C6H4
4-ClC6H4
4-FC6H4
4-FC6H4
2-ClC6H4
4-FC6H4CH2
C6H5CH2
H
H
H
H
H
H
H
H
H
9
10
11
12
13
14
15
16
17
18
Cl
H
H
H
Cl
H
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
H
H
H
H
H
CH3
H
Cl
Scheme 1. Synthesis of Compounds 3s and 3t
As shown in Table 1, we first examined the effect of
different organic solvents (entries 1-4) and concluded that
ethanol was the best solvent for this reaction. Then, we also
briefly examined the effect of different temperatures and ratio
of 1a/SnCl2 · 2H2O. The results showed that at refluxing
temperature the reaction preceded smoothly in high yield.
To further evaluate the influence of the ratio of 1a/
SnCl2 · 2H2O, the reaction was carried out in ethanol using
a 1:2 to 1:5 ratio of 1a/SnCl2 · 2H2O (Table 1, entries 8, 9,
4, 10), leading to 3a in 54%, 68%, 85%, and 83% yields,
respectively. We concluded the best ratio of 1a/SnCl2 · 2H2O
was 1:4.
(entries 1-14) and 1-(4-bromophenyl)-4-chlorobutan-1-one
(entries 15-18) can also give moderate to good yields.
However, the reaction was impeded by severe steric hin-
drance. For example, no desired product was obtained when
1-(4-bromophenyl)-4-chlorobutan-1-one reacted with N-aryl-
o-nitrobenzamides.
However, no desired products 2a-phenyl-2a,3-dihydro-1H-
azeto[1,2-a]quinazolin-4(2H)-one and 7-chloro-2a-phenyl-
2a,3-dihydro-1H-azeto[1,2-a]quinazolin-4(2H)-one were ob-
tained when we treated 3-chloro-1-phenylpropan-1-one with
o-nitrobenzamide or 4-chloro-2-nitrobenzamide under the
same conditions. To our surprise, compounds 3s and 3t were
obtained as our final products (Scheme 1).
Encouraged by these results, we next focused our attention
on the reaction of 2-nitrobenzamides with keto acids to
synthesis of 2,3,3a,4-tetrahydropyrrolo[1,2-a]quinazoline-1,5-
dione.
To demonstrate the efficiency and the applicability of the
present method, we performed the reaction of a variety of
o-nitrobenzamides 1 and keto acids 4 under the optimized
conditions. Table 3 summarizes our results on the reductive
cyclization of 1 and 4.
With the optimized conditions in hand, we then performed
the reaction of a variety of o-nitrobenzamides 1 and
haloketones 2 via SnCl2 · 2H2O system. The results are
summarized in Table 2.
As shown in Table 2, we were pleased to find that the
method was applicable to a broad substrate scope on both
substituted o-nitrobenzamides and haloketones. It can be seen
that this protocol can be applied not only to the o-
nitrobenzamides (entries 1-6, 15-17) with electron-
withdrawing groups (such as halide groups) or electron-
donatinggroups(suchasalkylgroups)butalsotoN-substituted
o-nitrobenzamides (entries 7-14, 18) under the same condi-
tions, which highlighted the wide scope of this reaction. The
yields of o-nitrobenzamides were superior to those of
N-substituted ones. Meanwhile, the effects of different
haloketones were also investigated. 5-Chloropentan-2-one
Similarly, it can be seen that either o-nitrobenzamides
(entries 1-3, 9, 10) or N-substituted ones (entries 4-8, 11)
were well tolerated. o-Nitrobenzamides containing electron-
donating and electron-withdrawing substituents were reacted
under the optimized conditions, and the corresponding
products were obtained in good yields. No remarkable

584 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4
Wang et al.
Table 3. Synthesis of Compounds 5 from o-Nitrobenzamides 1 and Keto Acids 4
entry
X
Y
Z
R1
R2
compound
yield (%)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
H
H
H
H
Cl
H
H
H
H
Cl
Cl
H
H
H
H
H
Cl
H
Cl
H
H
H
H
CH3
H
H
H
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
C6H5
C6H5
C6H5
5a
5b
5c
5d
5e
5f
5g
5h
5i
83
86
80
76
68
72
75
70
82
78
73
4-BrC6H4
4-CH3C6H4
4-OCH3C6H4
4-FC6H4
C6H5CH2
H
9
10
11
H
CH3
5j
5k
Table 4. Synthesis of Compounds 7
entry
X
n
compound
yield (%)
1
2
3
4
5
Cl
H
Cl
Cl
Cl
1
1
2
3
4
7a
7b
7c
7d
7e
85
86
83
82
85
Scheme 2. Supposed Reaction Mechanism
electronic effects on the reaction was observed. The effects
of different keto acids were also investigated. 4-Oxopentanoic
acid (entries 1-8) and 4-oxo-4-phenylbutanoic acid (entries
9-11) all reacted well to give moderate to good yields.
However, no desired product was obtained when 4-oxo-4-
phenylbutanoic acid reacted with N-aryl-o-nitrobenzamides
because of severe steric hindrance.
However, when we study the reaction of o-nitrobenz-
amides 1 and keto acids 6 under the same reaction, to our
surprise, compounds 7 were obtained as our final products.
The results are summarized in Table 4.
A plausible mechanistic pathway to products 3 from
o-nitrobenzamides and haloketones is illustrated in Scheme
2, although the details are still unclear. In the initial step,
o-nitrobenzamides 1 are reduced by tin(II) chloride to
intermediate A, and Sn(II) was oxidated to Sn(IV). The
amine compounds A then reacted with haloketones 2 with
the aid of Sn(IV) or excess Sn(II) to give the intermediate
B. Intermediate C was formed by attack of the amino group
onto the central carbon atom of the imine. Finally, products
3 were obtained by eliminating of a hydrogen chloride
molecule.

Pyrrolo[1,2-a]quinazoline Derivatives
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4 585
MS 1200/6200 (ESI+). X-ray crystallographic analysis was
performed with a Rigaku Mercury CCD/AFC diffractometer.
General Procedure for the Synthesis of Compounds
3, 5, and 7. A solution of o-nitrobenzamides 1 (1 mmol),
haloketones, or keto acids 2, 4, 6(1 mmol) and SnCl2 · 2H2O
(4 mmol) in EtOH (5 mL) was stirred at reflux for 2-4 h.
After this period, the TLC analysis of the mixture showed
the reaction to be completed. The mixture was quenched with
3% HCl (10 mL) and filtered to yield a crude product, which
was purified by recrystallization from 95% ethanol and DMF.
3a-Methyl-2,3,3a,4-tetrahydropyrrolo[1,2-a]quinazolin-
5(1H)-one (3a): mp 166-167 °C; IR (KBr) ν 3170, 3042,
2972, 2893, 2850, 1661, 1652, 1505, 1384, 1366, 1308, 1187,
1145, 800, 749, 627 cm-1; 1H NMR (300 MHz, DMSO-d6)
δ 1.22 (3H, s, CH3), 1.91-2.07 (4H, m, 2CH2), 3.39-3.45
(2H, m, CH2), 6.58 (1H, d, J ) 8.1 Hz, ArH), 6.68 (1H, t,
J ) 7.5 Hz, ArH), 7.32 (1H, t, J ) 7.2 Hz, ArH), 7.65 (1H,
dd, J1 ) 7.8 Hz, J2 ) 1.2 Hz, ArH), 8.25 (1H, s, NH); HRMS
[found m/z 202.1089 (M+), calcd for C12H14N2O M, 202.1106].
3a-(4-Bromophenyl)-8-chloro-2,3,3a,4-tetrahydropyr-
rolo[1,2-a]quinazolin-5(1H)-one (3o): mp 148-150 °C; IR
(KBr) ν 3161, 3030, 2975, 2899, 1661, 1602, 1482, 1302,
Figure 1. Molecular structure of 3e.
1
1196, 1082, 989, 822, 645 cm-1; H NMR (300 MHz,
DMSO-d6) (δ, ppm) 1.63-1.73 (1H, m, CH), 2.03-2.07
(1H, m, CH), 2.16-2.21 (1H, m, CH), 2.33-2.41 (1H, m,
CH), 3.47-3.56 (1H, m, CH), 3.84-3.91 (1H, m, CH), 6.67
(1H, dd, J1 ) 8.1 Hz, J2 ) 1.8 Hz, ArH), 6.91 (1H, d, J )
1.5 Hz, ArH), 7.21 (2H, d, J ) 8.7 Hz, ArH), 7.49 (3H, dd,
J1 ) 8.4 Hz, J2 ) 5.4 Hz, ArH), 9.24 (1H, s, NH); HRMS
[Found m/z 375.9978 (M+), calcd for C17H14N2O35Cl79Br M,
375.9978].
7-Chloro-2-(2-ethoxyethyl)-2-phenyl-2,3-dihydroquinazo-
lin-4(1H)-one (3s): mp 216-218 °C; IR (KBr) ν 3355, 3306,
3065, 2971, 2890, 1644, 1605, 1482, 1402, 1266, 1119, 930,
Figure 2. Molecular structure of 5g.
All the products were characterized by IR, 1H NMR, 13
C
1
765, 702 cm-1; H NMR (300 MHz, DMSO-d6) (δ, ppm)
NMR, and HRMS spectra. The structures of 3e and 5g were
further confirmed by X-ray diffraction analysis.19 The
molecular structures of the products 3e and 5g are shown in
Figures 1 and 2, respectively.
1.08(3H, t, J ) 7.2 Hz, CH3), 2.05-2.11 (2H, m, CH2),
3.37-3.41 (2H, m, CH2), 3.53 (2H, t, J ) 7.2 Hz, CH2),
6.58 (1H, d, J ) 8.4 Hz, ArH), 6.82 (1H, s, ArH), 7.19 (1H,
t, J ) 6.9 Hz, ArH), 7.30 (2H, t, J ) 7.5 Hz, ArH), 7.44
(3H, d, J ) 8.4 Hz, ArH), 7.84 (1H, s, NH), 8.74 (1H, s,
NH); HRMS [Found m/z 331.1207(M+ + H), calcd for
C18H20N2O235Cl M + H, 331.1213].
In conclusion, a series of 2,3,3a,4-tetrahydropyrrolo[1,2-
a]quinazolin-5(1H)-one and 2,3,3a,4-tetrahydropyrrolo[1,2-
a]quinazoline-1,5-dione compounds were synthesized by the
reaction of 2-nitrobenzamides with haloketones or keto acids
mediated by SnCl2 · 2H2O system. A variety of substrates
can participate in the process with moderate to good yields.
Our protocol is characterized by (i) faster reaction times,
(ii) accessible materials and handy manipulation (only one
pot), and (iii) isolation of products via simple recrystallization
to give higher purities.
3a-Methyl-2,3,3a,4-tetrahydropyrrolo[1,2-a]quinazoline-
1,5-dione (5a): mp 163-165 °C; IR (KBr) ν 3177, 3056,
2925, 1718, 1683, 1603, 1490, 1465, 1387, 1352, 1278, 1246,
1
1211, 1153, 1004, 791, 758 cm-1; H NMR (300 MHz,
CDCl3) δ 1.57 (3H, s, CH3), 2.39 (2H, t, J ) 7.8 Hz, CH2),
2.68-2.73 (2H, m, CH2), 7.29 (1H, t, J ) 7.8 Hz, ArH),
7.60 (1H, t, J ) 7.8 Hz, ArH), 7.99 (1H, s, NH), 8.06 (1H,
d, J ) 7.8 Hz, ArH), 8.16 (1H, d, J ) 8.1 Hz, ArH); HRMS
[found m/z 216.0894 (M+), calcd for C12H12N2O2 M,
216.0899].
Experimental Section
General Information. Commercial solvents and reagents
were used as received. Melting points are uncorrected. IR
spectra were recorded on Varian F-1000 spectrometer in KBr
7-Methyl-3a-phenyl-2,3,3a,4-tetrahydropyrrolo[1,2-a]-
quinazoline-1,5-dione (5j): mp 296-297 °C; IR (KBr) ν
3186, 3085, 2888, 1712, 1671, 1496, 1451, 1357, 1204, 1089,
1
with absorptions in cm-1. H NMR was determined on
1
Varian-300 MHz or Varian-400 MHz spectrometer in DMSO-
d6 solution. J values are in Hz. Chemical shifts are expressed
in ppm downfield from internal standard TMS. MS data were
obtained using microma GCT-TOF instrument (EI+) or LC/
863, 824, 756, 696 cm-1; H NMR (300 MHz, CDCl3) (δ,
ppm) 2.32 (3H, s, CH3), 2.46-2.56 (1H, s, CH), 2.74 (3H,
s, CH2 + CH), 7.23-7.29 (3H, m, ArH), 7.34-7.40 (3H,
m, ArH), 7.77 (1H, s, ArH), 8.11 (1H, d, J ) 8.4 Hz, ArH),

586 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4
Wang et al.
9.76 (1H, s, NH); 13C NMR (75 MHz, CDCl3) δ 16.40,
25.26, 30.89, 35.28, 115.72, 116.31, 120.28, 123.81, 124.02,
124.42, 129.74, 130.24, 130.61, 138.69, 160.31, 168.61;
HRMS [Found m/z 292.1214 (M+), calcd for C18H16N2O2
M, 292.1212].
(5) Godfrey, A. A. A. PCT Int. Appl. WO 2005012260 A2, 2005;
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Ethyl 4-(7-chloro-4-oxo-2-phenyl-1,2,3,4-tetrahydro-
quinazolin-2-yl)butanoate (7a): mp 226-228 °C; IR (KBr)
ν 3324, 3066, 2970, 1716, 1646, 1476, 1417, 1287, 1197,
1077, 916, 864, 771, 702 cm-1; 1H NMR (300 MHz, DMSO-
d6) (δ, ppm) 1.16 (3H, t, J ) 6.9 Hz, CH3), 1.70-1.82 (4H,
m, 2CH2), 2.27-2.31 (2H, m, CH2), 4.03 (2H, dd, J1 ) 14.4
Hz, J2 ) 7.2 Hz, OCH2), 6.58 (1H, dd, J1 ) 8.1 Hz, J2 )
1.8 Hz, ArH), 6.87 (1H, d, J ) 1.8 Hz, ArH), 7.20 (1H, t, J
) 7.2 Hz, ArH), 7.31(2H, t, J ) 7.5 Hz, ArH), 7.42-7.47
(3H, m, ArH), 7.80 (1H, s, NH), 8.83 (1H, s, NH); 13C NMR
(75 MHz, DMSO-d6) δ 14.80, 20.33, 34.09, 41.99, 60.46,
73.71, 114.16, 114.21, 117.46, 125.89, 127.95, 128.80,
129.85, 138.43, 147.70, 149.05, 163.85, 173.34; HRMS
[Found m/z 373.1334 (M+ + H), calcd for C20H22N2O335Cl
M + H, 373.1319].
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Acknowledgment. Financial support from the Foundation
of Key Laboratory of Organic Synthesis of Jiangsu Province
is gratefully acknowledged.
Supporting Information Available. Detailed descriptions
of experimental procedures and spectroscopic and analytical
data are available for compounds 3, 5, and 7. This material
is available free of charge via the Internet at http://pubs.
acs.org.
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References and Notes
(19) Crystallographic data for the structures of 3e and 5g have been
deposited at the Cambridge Crystallographic Data Centre,
deposit numbers are CCDC-777790 and CCDC-777791,
respectively. Copies of available material can be obtained free
of change on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk).
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