Simple efficient synthesis of 4-aminoquinazoline via amidine of N-arylamidoxime

Article abstract of DOI:10.1002/jhet.572

Preparation of 4-amino-2-aryl quinazolines by reduction of N-(2-cyanoaryl) amidoximes via amidines using SnCl₂ in ethanol.

Full text of DOI:10.1002/jhet.572

652
Simple Efficient Synthesis of 4-Aminoquinazoline via Amidine
of N-Arylamidoxime
Vol 48
Sachin S. Patil,* Pravin C. Mhaske, Sachin V. Patil, and Vivek D. Bobade*
Department of Chemistry, HPT Arts and RYK Science College, Nasik 422005, India
*E-mail: spatilsachin@yahoo.co.in or v_bobade31@rediffmail.com
Received March 1, 2010
DOI 10.1002/jhet.572
Published online 28 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
Preparation of 4-amino-2-aryl quinazolines by reduction of N-(2-cyanoaryl) amidoximes via amidines
using SnCl2 in ethanol.
J. Heterocyclic Chem., 48, 652 (2011).
INTRODUCTION
The obtained amidoximes were then subjected to
reduction using SnCl2 in ethanol in which intermediate
amidine was not isolated, but rather immediately con-
verted in situ to 4-aminoquinazolines (Scheme 2). We
anticipate that the reduction of amidoxime to amidine
by SnCl2 is analogy to the reported work [15].
Quinazoline, owing to its pharmacological properties, is
an important heterocycle [1]. Quinazolines are well known
to possess an array of physiological activities, e.g., anti-
cancer [2], antifungal [3], antimalarial [4], anti-inflamma-
tory [5], and antihypertensive [6]. Because of numerous
applications in medicinal chemistry, the preparation of
4-aminoquinazoline derivatives has gained considerable
attention. Many procedures are reported in literature, most
of them start from cyanophenyltriazenes [7], o-azidobenzo-
nitrile and nitrile [8], o-aminobenzonitrile, and benzonitrile
[9], rearrangement of 3-amino-1-benzylindazone [10], reac-
tion of N-arylbenzimidoyl chloride with cyanamide in the
presence of TiCl4 [11], and reaction of 2-aminobenzonitrile
with orthoesters and ammonium acetate under solvent-free
and microwave condition [12]. Recently in literature, cop-
per-catalyzed reaction of 2-bromobenzonitrile and amidines
has been reported [13]. However, these methodologies were
not applicable for synthesis of halo-substituted quinazoline
derivatives. All these above methods suffer from drawbacks
such as harsh reaction condition (high temperature and
pressure [9]) and use of toxic reagents. Anthranilonitrile
undergoes self-condensation reaction forming 4-amino-2-
(2-aminophenyl) quinazoline as a side product (entry 2k).
Therefore, this methodology is not useful for the preparation
of cyano-substituted quinazoline derivatives.
To optimize the reaction conditions for the conversion
of N-(2-cyanoaryl) amidoximes to 4-aminoquinazoline,
the reactions were carried out with different molar ratios
of SnCl2 in appropriate solvents (Table 1). From these
studies, ethanol was found to be the best solvent. Reac-
tion also proceeded in DMF but required 48–50 h for
completion. In the ethereal solution, the reaction was
incomplete; this could be attributed to low solubility of
the amidoximes in THF.
As reported in Table 2, a variety of aromatic and het-
eroaromatic substrates undergo facile reactions within
8–10 h in high yields. An obvious result was found for
nitro-substituted derivative of amidoxime, which gave
4-amino-2-(2-aminophenyl) quinazoline (entry 2k) using
the optimized reaction condition. A noteworthy feature of
this reaction is that the extra cyano-substituent of N-(2-
cyanophenyl)-3-cyanobenzamidoxime remains unaffected
(entry 2l Table 2).
In conclusion, we have developed a rapid high-yield-
ing procedure for conversion of N-arylamidoximes to
4-aminoqunazolines via amidine. This method provides
a significant improvement over the existing methodology
for the synthesis of 4-amino-2-aryl quinazolines.
RESULTS AND DISCUSSION
Herein, we wish to report a new general way for
preparation of 4-amino-2-aryl quinazolines from N-(2-
cyanoaryl) amidoximes which in turn are easily obtained
from reaction of the corresponding anilines and N-
hydroxyimidoyl chlorides [14] in Scheme 1.
EXPERIMENTAL
Chemicals were procured from Aldrich Chemical (Banga-
lore, India). Reactions were monitored, and purity of the prod-
ucts was checked by thin layer chromatography (TLC). TLC
C
V
2011 HeteroCorporation

May 2011
Simple Efficient Synthesis of 4-Aminoquinazoline via Amidine of N-Arylamidoxime
653
Scheme 1. Synthesis of N-(2-cyanoaryl) amidoximes from 2-
aminobenzonitriles.
4-Amino-6-chloro-2-phenyl-quinazoline: (2b). Pale yellow
solid, m.p. 167–170ꢀC, hydrochloride salt ꢂ233 to 235ꢀC (lit
[11] 230–231ꢀC) 1H-NMR (200 MHz, DMSO-d6): 7.46–7.54
(m, 3H), 7.56 (bs, 2H), 7.76–7.78 (m, 2H), 8.0 (s, 1H), 8.42
(m, 2H), 13C-NMR (50 MHz, DMSO-d6): d 117.6, 121.8,
128.4, 129.0, 129.4, 129.6, 130.5, 131.0, 136.3, 151.1, 160.3,
161.05. MS (EI): m/z ¼ 255(M þ 1 ¼ 256.2, M þ 2 ¼
258.1). Anal. Calcd. for C14H10ClN3: C, 65.73; H, 3.94; N,
16.43. Found: C, 65.68; H, 3.90; N, 16.39.
4-Amino-2-(p-tolyl)-quinazoline: (2c). Pale yellow solid
m.p. 134–136ꢀC, 1H-NMR (200 MHz, DMSO-d6): d 2.39 (s,
3H, ACH3), 7.29 (d, 2H, J ¼ 8.0 Hz), 7.42–7.50 (m, 3H),
7.80 (bs, 2H, NH2), 8.23 (d, 1H), 8.40 (d, 2H, J ¼ 8.0 Hz),
13C-NMR (50 MHz, DMSO-d6): d 21.4, 112.9, 121.7, 125.4,
128.2, 128.4, 129.1, 133.1, 135.7, 140.1, 150.8, 160.9, 161.6.
IR (KBr) gmax (cmꢂ1): 3317, 1645, 1566, 1436, MS (EI): m/
z¼235 (M þ 1¼ 235.9), Anal. Calcd. for C15H13N3: C, 76.57;
H, 5.57; N, 17.86. Found: C, 76.52; H, 5.58; N, 17.88.
4-Amino-6-chloro-2-(p-tolyl) quinazoline: (2d). Pale yellow
solid, m.p. 167–170ꢀC, 1H-NMR (200 MHz, DMSO-d6): d
2.38 (s, 3H, CH3), 7.24 (d, 2H, J ¼ 8.4 Hz), 7.75 (bs, 2H),
7.79–8.05 (m, 2H), 8.09 (s, 1H), 8.25 (d, 2H, J ¼ 8.4 Hz), MS
(EI): m/z¼269 (M þ 1¼270.2, Mþ2¼272.1). Anal. Calcd. for
C15H12ClN3 C, 66.79; H, 4.48; N, 15.58. Found: C, 66.72; H,
4.54; N, 15.54.
was performed on Merck60 F-254 silica gel plates with visual-
ization by UV light. Melting points were determined on a
Buchi Melting Point B-545 apparatus. The IR spectra (in KBr
pellets) were recorded on a Nicolet 6700 FTIR spectrometry.
1H-NMR spectra were recorded on Bruker (200 MHz) spec-
trometer instruments, in and DMSO-d6. Chemical shifts were
recorded in parts per million downfield from tetramethylsilane.
Mass spectra were recorded on MS-3200Q trap spectrometer.
Elemental analysis was performed on a Carlo Erba Perkin-
Elmer model 240 analyzer. Analysis results were within 0.4%
of the calculated value. Column chromatography was performed
on silica gel (230–400 mesh) supplied by Acme Chemical
(Mumbai, India). The chemicals and solvents used were labora-
tory grade and were purified.
General experimental procedure for the synthesis 4-
amino-2-phenyl-quinazoline. The procedure for reaction entry
2a is illustrative. A 150-mL round-bottom flask equipped with
stir bar and reflux condenser was dried under an atmosphere of
nitrogen and charged with amidoxime (2.36 g, 1 mmol), fol-
lowed by 20 mL of anhydrous ethanol. Stannous chloride (9.48
g, 5 mmol) was added to this solution, and the mixture was
heated at 70ꢀC under nitrogen atmosphere for 8 h. The mixture
was distilled to half the volume and cooled at room temperature
and rendered basic (pH 8) with 150 mL of 10% aqueous sodium
bicarbonate. The mixture was extracted with 3 ꢁ 20 mL of eth-
ylacetate. The organic phase was washed thoroughly with satu-
rated NaCl (aq.), dried over sodium sulfate, and filtered through
celite. The solvent was removed in vacuo to obtain the crude
product. The product was purified by column chromatography
on silica (20% ethylacetate in hexane), and the desired quinazo-
line was obtained in 90% yield as pale yellow solid.
General procedure for preparation of hydrochloride salt
of 4-amino-2-phenyl-quinazoline. 4-Amino-2-phenyl-quinazo-
line base (1 g) was dissolved in methanol (5 mL), and dry
HCl gas was passed till pH 3. Ethyl acetate (5 mL) was added
dropwise to obtain the solid, which was filtered and washed
with 1:1 mixture of methanol:ethylacetate.
4-Amino-2-phenyl-quinazoline: (2a). Pale yellow solid,
m.p. 145–147ꢀC (lit. [9a] 145–146ꢀC), 1H-NMR (DMSO-d6,
200 MHz) d 7.53–7.50 (m, 4H), 7.89–7.80 (m, 4H), 8.07 (d,
1H, J ¼ 8.1 Hz, 1H), 8.54–8.51 (m, 2H), 13C-NMR (DMSO-
d6, 50 MHz) d 113.8, 124.1, 125.6, 128.2, 128.4, 128.7, 130.4,
133.5, 139.1, 150.9, 160.2, 162.6, IR (KBr) gmax (cmꢂ1):
3340, 1640, 1565. MS (EI): m/z ¼ 221 (M þ 1 ¼ 222). Anal.
Calcd. for C14H11N3: C, 76.00; H, 5.01; N, 18.19. Found: C,
76.06; H, 5.04; N, 18.13.
4-Amino-2-(4-flurophenyl)-quinazoline:(2e). Pale
yellow
1
solid, m.p. 170ꢀC, H-NMR (200 MHz, DMSO-d6): d 7.03 (m,
2H), 7.74 (m, 1H), 7.76 (m, 2H), 7.88 (bs, 2H), 8.24 (d, 1, H),
8.52 (m, 2H), 13C-NMR (50 MHz, DMSO-d6): d 111.9, 113.2,
113.6, 122.1, 123.7, 126.2, 128.7, 128.9, 131.4, 133.6, 149.0,
157.9, 160.8, 164.9. Anal. Calcd. for C14H10FN3 C, 70.28; H,
4.21; N, 17.56. Found: C, 70.21; H, 4.27; N, 17.53.
6-Methyl-2-phenyl-4-aminoquinazoline: (2f). White crystal-
line solid hydrochloride salt, m.p. 262–264ꢀC (lit. [11] 260–
260ꢀC), 1H-NMR (200 MHz DMSO-d6) d 2.48 (s, 3H), 7.47
(m, 3H), 7.71–7.60 (m, 4H), 8.05 (m, 1H), 8.46–8.43 (m, 2H),
13C-NMR (50 MHz, DMSO-d6) d 21.7, 113.6, 123.1, 128.0,
128.2, 128.6, 130.2, 135.1, 135.1, 139.1, 149.6, 160.0, 162.2.
4-Amino-2-(4-pyridyl)-quinazoline: (2g). Pale yellow solid
hydrochloride salt, m.p. 280–283ꢀC (lit [6] 280ꢀC), 1H-NMR
(200 MHz, DMSO-d6): d 6.50 (bs, 2H), 7.52–7.63 (m, 2H),
7.66–7.94 (m, 2H), 8.22 (d, 2H, J ¼ 8.0 Hz), 8.66 (d, 2H, J ¼
8.0 Hz), 13C-NMR (50 MHz, DMSO-d6): 118.0, 121.1, 124.4,
128.4, 130.3, 132.9, 142.2, 149.5, 150.2, 160.4, 162.9. MS
(EI): m/z ¼ 222 (M þ 1¼ 223).
4-Amino-2-(2-pyridyl)-quinazoline: (2h). Yellow solid as
hydrochloride salt, m.p. 235–237ꢀC (lit [6] 235ꢀC), 1H-NMR
(200 MHz, DMSO-d6) d 7.59 (m, 1H), 7.72 (bs, NH2, 2H)
7.78 (ddd, J ¼ 8.2, 6.9, 1.2 Hz, 1H), 8.05 (m, 2H), 8.14 (m,
1H), 8.35 (d, J ¼ 8.2 Hz, 1H), 8.58 (d, J ¼ 7.7 Hz, 1H), 8.82
(1H, d, J ¼ 4.3 Hz,1H); 13C-NMR (50 MHz, DMSO-d6) d,
119.6 (C), 123.4, 124.3, 125.5, 126.2, 128.6, 129.3 (CH), 130.7
(C), 134.91 (CH), 149.9 (C), 150.1 (CH) 158.7, 169.7 (C).
Scheme 2. Synthesis 4-amino-2-phenyl substituted quinazolines from N-(2-cynoaryl) amidoximes via amidine using SnCl2.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

654
S. S. Patil, P. C. Mhaske, S. V. Patil, and V. D. Bobade
Vol 48
Table 1
Optimization of reagents and reaction condition.a
8.9 Hz, 1H), 8.42 (dt, J ¼ 8.7, 1.9 Hz, 2H); 13C-NMR (50
MHz, DMSO-d6): 122.0 (C), 124.0 (CH), 124.1 (C), 126.1,
128.2, 129.1, 130.7, 132.6 (CH), 136.2, 149.2, 158.1, 167.3 (C).
4-Amino-2-(2-aminophenyl)-quinazoline: (2k). Yellow solid
hydrochloride, m.p. 286–289ꢀC (lit [7] 287–288ꢀC) 1H-NMR
(200 MHz, DMSO-d6) d 3.73 (bs, 2H), 6.69–7.12 (m, 3H),
6.83 (bs, 2H), 7.63–7.98 (m, 4H), 8.23(m, 1H).
4-Amino-2-(3-cynophenyl)-quinazoline: (2l). Pale yellow
solid, m.p. 225–227ꢀC (lit [9b] 226–227ꢀC) 1H-NMR (200
MHz, DMSO-d6): d 7.62–7.97 (m, 5H), 8.20 (m, 1H), 8.39 (s,
1H), 8.59 (m, 1H), 9.75 (bs, 2H). 13C-NMR (50 MHz, DMSO-
d6): d 109.9, 113.6, 118.6, 118.7, 125.2, 127.0, 128.0, 129.1,
129.7, 132.3, 136.7, 139.4, 151.8, 160.3, 162.9.
Time
(h)
Entry
Reagent (mol eq)
Solvent
Yieldb (%)
1
2
3
4
5
6
Amidoxime/SnCl2 (1:1) Ethanol
Amidoxime/SnCl2 (1:2) Ethanol
Amidoxime/SnCl2 (1:3) Ethanol
Amidoxime/SnCl2 (1:5) Ethanol
Amidoxime/SnCl2 (1:5) DMF
Amidoxime/SnCl2 (1:5) THF
5
5
No reaction
No reaction
4-Amino-2-(2-furanyl)-quinazoline:
(2m). Pale
yellow
10
8
48
10
30
90
solid, m.p. 216–218ꢀC (lit [6a] 219–221ꢀC) 1H-NMR (200
MHz, DMSO-d6) 6.53 (dd, J ¼ 3.4, 1.8 Hz, 1H), 7.38 (dd,
J ¼ 3.4, 0.8 Hz, 1H), 7.49 (ddd, J ¼ 8.2, 7.0,1.2 Hz, 1H),
7.60 (m, 1H), 7.77 (ddd, J ¼ 8.4, 6.9, 1.2 Hz, 1H), 7.99 (m,
2H) 13C-NMR (50 MHz, DMSO-d6): d 111.0, 112.7 (CH),
121.6 (C), 124.2, 126.0, 128.1, 132.7, 144.1 (CH), 147.8,
149.2, 164.2, 167.7 (C).
70
No reaction
a Reactions were carried out on a 1mmol scale at reflux temperature.
b Yields obtained after column chromatography.
4-Amino-2-(2-thiophenyl)-quinazoline:(2n). Pale yellow
solid, m.p. 189–190ꢀC (lit [9b]188–190ꢀC) 1H-NMR (200
MHz, DMSO-d6): d 7.59 (m, 1H), 7.69 (m, 3H), 7.85 (dd, J ¼
1.6 Hz), 8.22 (d, J ¼ 4.4 Hz, 1H), 8.25 (ddd, J ¼ 4.4 Hz, 1.6
Hz 1H), 13C-NMR (50 MHz, DMSO-d6): 112.0, 122.1, 123.6,
124.1,125.6, 126.1, 126.4, 131.5, 141.5, 149.1, 156.3, 160.9.
4-Amino-2-(4-methoxyphenyl)-quinazoline: (2i). Pale yel-
low solid hydrochloride, m.p. 255–257ꢀC (lit [16] 256–259ꢀC)
1H-NMR (200 MHz, DMSO-d6): d 3.83 ( s, OCH3, 3H), 6.97
(d, J ¼ 9.0 Hz, 2H), 7.50 (ddd, J ¼ 8.2, 7.0, 1.2 Hz, 1H), 7.76
(bs, NH2, 2H), 7.81 (m, 2H), 7.97(d, J ¼ 8.3 Hz, 1H), 8.50 (d,
J ¼ 9.0 Hz, 2H).
4-Amino-6-bromo-2-phenyl-quinazoline: (2j). Pale yellow
solid hydrochloride salt, m.p. 186–189ꢀC (lit [11] 188–190ꢀC)
1H-NMR (200 MHz, DMSO-d6) 6.58 (bs, NH2, 2H), 7.50 (td,
J ¼ 7.7, 1.1 Hz, 1H), 7.56 (dt, J ¼ 8.7, 1.9 Hz, 2H), 7.78 (td,
J ¼ 7.7, 1.4 Hz, 1H), 7.98 (d, J ¼ 8.9 Hz, 1H), 8.01 (d, J ¼
Acknowledgments. The authors are grateful to UGC, New Delhi
for financial support and National chemical laboratory pune for
providing facility for spectral analysis.
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Table 2
Synthesis of substituted 4-aminoquinazolines.a
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72
68
83
73
98
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59
72
87
83
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Journal of Heterocyclic Chemistry
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Simple Efficient Synthesis of 4-Aminoquinazoline via Amidine of N-Arylamidoxime
655
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Journal of Heterocyclic Chemistry
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