A Novel Synthesis of 1,2,3-Benzotriazinones from 2-(o -Aminophenyl)oxazolines

Article abstract of DOI:10.1155/2017/2384780

1,2,3-Benzotriazinones were synthesized in excellent yields by the reaction of 2-(o-aminophenyl)oxazolines and isoamyl nitrite in methanol. The crystal structure of the acetyl derivative of one of the 1,2,3-benzotriazinones provided additional support for

Full text of DOI:10.1155/2017/2384780

Hindawi
Journal of Chemistry
Volume 2017, Article ID 2384780, 5 pages
https://doi.org/10.1155/2017/2384780
Research Article
A Novel Synthesis of 1,2,3-Benzotriazinones from
2-(o-Aminophenyl)oxazolines
Fernando Rocha-Alonzo,1 Daniel Chávez,2 Adrián Ochoa-Terán,2 David Morales-Morales,3
Enrique F. Velázquez-Contreras,1 and Miguel Parra-Hake2
1
´
´
Departamento de Ciencias Quımico Biologicas, Universidad de Sonora, Hermosillo, SON, Mexico
2
3
´
´
´
Centro de Graduados e Investigacion en Quımica, Instituto Tecnologico de Tijuana, Tijuana, BC, Mexico
´
´
´
´
Instituto de Quımica, Universidad Nacional Autonoma de Mexico, Ciudad de Mexico, Mexico
Correspondence should be addressed to Fernando Rocha-Alonzo; fernando.rocha@guayacan.uson.mx
Received 29 September 2016; Accepted 13 December 2016; Published 19 January 2017
Academic Editor: Hakan Arslan
Copyright © 2017 Fernando Rocha-Alonzo et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1,2,3-Benzotriazinones were synthesized in excellent yields by the reaction of 2-(o-aminophenyl)oxazolines and isoamyl nitrite in
methanol. e crystal structure of the acetyl derivative of one of the 1,2,3-benzotriazinones provided additional support for the
spectroscopic structural characterization of the title compounds.
1. Introduction
In this report, we describe facile access to the title com-
pounds from chiral and nonchiral 2-(o-aminophenyl)oxa-
zolines. Since racemization is not possible during the reac-
tion, this method allows the preparation of enantiopure 1,2,3-
benzotriazinones in excellent yields.
1,2,3-Benzotriazinones are compounds widely investigated
due to their interesting biological and chemical proper-
ties. ese heterocyclic compounds have been studied as
anaesthetic [1], anti-inflammatory [2], anticancer [3, 4], and
antitumoral [5, 6] agents. In organic synthesis, triazinones
are used as an activating moiety in coupling agents for the
preparation of peptides and amino acids [7–9]. As a result
of their biological and synthetic importance, there is still
interest in the development of methods for the synthesis of
compounds which contain the 1,2,3-triazinone moiety.
In general, 1,2,3-benzotriazinones are prepared via intra-
molecular cyclization through diazonium ion condensation
with an adjacent nucleophilic function. Using this strategy,
1,2,3-triazinones have been obtained from aminobenzamides
[10–12], aminonitriles [13, 14], and triazenes [15–17]. Other
workers have reported the synthesis of 1,2,3-benzotriazinones
by the oxidation of indazol-3-amines with hydrogen peroxide
in the presence of sodium carbonate, though in low yields,
and by the cyclization of 2-azido-N-4-toluoylbenzamide in
moderate yields [18].
2. Results and Discussion
e first step for the synthesis of 1,2,3-benzotriazinones was
the preparation of 2-(o-aminophenyl)oxazolines 3a–3c (see
(1)). ese oxazolines were prepared in high yields (58–
80%) by cyclization of anthranilonitrile with ethanolamines
under basic conditions in a mixture of glycerol and ethylene
glycol, following the methodology reported by Go´mez and
coworkers [19]. In the literature, it has been reported that
oxazolines 3a and 3b were obtained as oils, whereas in our
work both were isolated as solids; we believe this fact is due
to problems in the purification process in the previous report.
Nevertheless, NMR and IR spectroscopic and mass spec-
trometry data are consistent with those previously reported
[20].

2
Journal of Chemistry
HO
NH2
K2CO3
+
3
NH2
NH2
a, R = H, 58%
Glycerol/ethylene glycol, 105∘C
R
(1)
CN
O
N
(R)-b, R = Ph, 72%
1
2
(R)-c, R = Et, 80%
R
Once the necessary 2-(o-aminophenyl)oxazolines were
with new signals for the acetyl moiety at ꢀ 1.95 and ꢀ 21.5
H
C
obtained, the next step was the synthesis of the 1,2,3-
benzotriazinones 4a–4c. Compounds 4a–4c were synthe-
sized by diazotization reaction involving oxazolines 3a–
3c and methanolic isoamyl nitrite. In all cases, the new
1,2,3-benzotriazinones were obtained in quantitative yields
(Scheme 1).
for the methyl group and ꢀ 171.9 for the ester carbonyl.
C
O(Ac)2
pyr., r.t.
N
N
N
N
It is assumed that the reaction takes place by the
intermediacy of the diazonium ion 5 formed from 2-(o-
aminophenyl)oxazoline (3) using a large excess of isoamyl
nitrite in order to ensure formation of the diazonium salt
(Scheme 1). e electron withdrawing effect of the diazonium
group in 5 could promote oxazolinyl ring hydrolysis, taking
water from the alcoholic media, and producing the 2-
carbamoylbenzenediazonium 6. e 1,2,3-triazinone moiety
in 4 is then achieved by ring closure between the amide
and the adjacent diazonium group in 6. Similar mechanistic
assumptions were proposed by Colomer and Moyano in the
synthesis of this kind of compound from aminonitriles [13,
21].
(2)
O
O
N
N
OAc
7a
OH
4a
Suitable crystals for X-ray diffraction studies of 1,2,3-
benzotriazinone 7a were grown by slow vapor diffusion of
hexane into a saturated solution in ethyl acetate. Compound
7a crystallized in the triclinic system with the space group P¯ı.
Molecular structure of 1,2,3-benzotriazinone 7a is shown in
Figure 1, which confirms the presence of the 1,2,3-triazinone
system and indirectly corroborates the hydroxyl group in
1,2,3-benzotriazinones 4a–4c.
Infrared spectroscopy of compounds 4a–4c showed a
single band at ca. (]) 3430 cm−1 due to the O-H stretching;
the bands at ca. (]) 1687 cm−1 and at ca. (]) 1657 cm−1
correspond to the N=N and the C=O stretching, respec-
tively. 1H NMR spectroscopy showed the following: aromatic
hydrogen from the 1,2,3-benzotriazinone moiety appeared
as an ABCD system with the characteristic two doublets
and two triplets between 8.29 and 7.87 ppm, slightly shifed
to lower field relative to the 2-(o-aminophenyl)oxazolines;
aliphatic protons appeared between 6.39 and 0.90 ppm. For
compound 4b, the phenyl protons are at (ꢀ) 7.43 ppm.
13C NMR spectroscopy showed carbonyl carbon at ca. (ꢀ)
156.5 ppm; aromatic carbon appeared in the range 146.1–
120.3 ppm and aliphatic carbon in the range 64.2–10.8 ppm.
e proton of hydroxyl group in the proposed structure
In the molecular structure of 7a, the N1=N2 bond
˚
[1.2715(19) A] is longer than the typical value for N=N double
˚
˚
bond (1.236 A) [22], whereas the N2-N3 bond [1.3728(19) A]
is slightly shorter than the typical value for N-N single
bond (1.404 A) [22]. e structure shows coplanarity between
˚
the two rings. ese data are in agreement with crystal
structure reports of related 1,2,3-benzotriazinones [17, 23–
25]. Crystallographic data of 7a are included as supplemen-
tary material (in Supplementary Material available online at
https://doi.org/10.1155/2017/2384780).
Of interest to pharmaceutical applications, Reingruber
et al. have suggested that the coplanar structure in 1,2,3-
benzotriazinones could have DNA-intercalating abilities such
as those displayed by some anticancer agents [17].
In summary, we have presented an efficient method for
the synthesis of 1,2,3-benzotriazinones from 2-(o-amino-
phenyl)oxazolines in high yields.
1
was not identified by H NMR, but the carbinol moiety
was inferred from the chemical shifs on 13C NMR data.
Since compounds 4a–4c are novel, high-resolution mass
spectrometry was run with no significant difference between
calculated and obtained values (less than 0.003 amu).
In general, the molecular formula assignment and the
spectroscopic characterization were consistent with their
structures.
3. Experimental Section
In order to corroborate the presence of the hydroxyl
group, the acetyl derivative 7a was obtained by reaction of
4a with acetic anhydride in pyridine (see (2)). NMR spectra
for the acetyl derivative 7a turned out to be similar to 4a, but
3.1. General Procedures. All reagents were purchased in the
highest quality available and were used without further
purification. e solvents used in column chromatography
were obtained from commercial suppliers and used without

Journal of Chemistry
3
crude product that was purified by flash chromatography on
neutral alumina (hexane/ethyl acetate, 20 : 1) to give the pure
product.
N2
N2
NH
O
O
N
2-[4,5-Dihydro-1,3-oxazol-2-yl]aniline (3a). White solid (58%
yield), mp 52-53∘C. FTIR (KBr): ] 3384, 3264, 1630,
R
R
1254 cm−1. 1H NMR [(CD ) CO, 200 MHz]: ꢀ 7. 69 (dd, ꢁ =
OH
3 2
5
6
7.9, 1.7 Hz, 1H), 7.19 (ddd, ꢁ ꢂ =.3, 7.1, 1.6 Hz, 1H), 6.66 (m,
2H), 6.04 (s, 2H), 4.30 (m, 2H), 4.08 (m, 2H). 13C NMR
[(CD ) CO, 50 MHz]: ꢀ 164.4, 148.1, 131.6, 129.3, 115.7, 115.4,
3 2
108.9, 65.6, 54.8. EI-MS (Int. %): [M]+ 162 (100), 131 (36), 118
(33).
a, R = H
(R)-b, R = Ph
(R)-c, R = Et
NH2
N
N
C2H11ONO
MeOH, r.t.
2-[(4R)-4-Phenyl-4,5-dihydro-1,3-oxazol-2-yl]aniline (3b).
O
N
O
N
Yellow solid (72% yield), mp 62-63∘C. [ꢃꢄ20 ꢂ −1=2 (c 0.22,
ꢀ
MeOH). FTIR (KBr): ] 3416, 3272, 1631, 1249 cm−1. 1H NMR
R
R
OH
[(CD ) CO, 200 MHz]: ꢀ 7. 70 (dd, ꢁ ꢂ =.0, 1.8 Hz, 1H), 7.32
3 2
3
4
(m, 5H), 7.21 (ddd, ꢁ ꢂ =.4, 7.0, 1.4 Hz, 1H), 6.83 (dd, ꢁ ꢂ =.6,
Scheme 1: Synthesis of 1,2,3-benzotriazinones 4a–4c.
0.8 Hz, 1H), 6.80 (br. s, 2H), 6.60 (ddd, ꢁ ꢂ =.2, 7.0, 1.2 Hz, 1H),
5.43 (dd, ꢁ ꢂ 10.0, 8.2 Hz, 1H), 4.66 (dd, ꢁ ꢂ 10.0, 8.3 Hz, 1H),
4.11 (dd, ꢁ ꢂ =.2, 8.2 Hz, 1H). 13C NMR [(CD ) CO, 50 MHz]:
3 2
ꢀ 165.0, 148.8, 142.7, 132.3, 129.8, 128.7, 127.5, 126.6, 116.0, 115.7,
108.6, 73.0, 70.2. EI-MS (Int. %): [M]+ 238 (100), 207 (48), 118
(50).
C8
N1
C2
C1
C8a
C4a
O2
N2
N3
C7
2-[(4R)-4-Ethyl-4,5-dihydro-1,3-oxazol-2-yl]aniline (3c). Brown
O3
ꢀ
oil (80% yield). [ꢃꢄ20 ꢂ +10 (c 0.22, MeOH). FTIR (NaCl): ]
C6
C10
3461, 3286, 1632, 1263 cm−1. 1H NMR [(CD ) CO, 200 MHz]:
3 2
C4
O1
C5
C9
ꢀ 7. 62 (dd, ꢁ ꢂ 7.9, 1.6 Hz, 1H), 7.15 (ddd, ꢁ ꢂ =.0, 6.0, 2.0 Hz,
1H), 6.77 (dd, ꢁ ꢂ =.5, 0.7 Hz, 1H), 6.74 (br. s, 2H), 6.55 (ddd,
ꢁ ꢂ =.2, 7.0, 1.2 Hz, 1H), 4.28 (m, 2H), 3.90 (m, 1H), 1.59 (m,
2H), 0.97 (t, ꢁ ꢂ 7.4 Hz, 3H). 13C NMR [(CD ) CO, 50 MHz]:
Figure 1: Molecular structure of 7a (ORTEP drawing showing 50%
3 2
ellipsoids).
ꢀ 164.1, 150.3, 132.4, 130, 116.1, 115.4, 109, 70.8, 68.8, 29.5, 10.4.
EI-MS (Int. %): [M]+ 190 (81), 161 (100), 133 (59), 118 (31).
distillation. Infrared spectra (FTIR) were recorded on a
Perkin Elmer FT-IR 1600 spectrophotometer. Nuclear mag-
netic resonance 1H (at 200 MHz) and 13C (at 50 MHz) spectra
were recorded on a Varian Mercury 200 MHz spectrometer
3.3. General Procedure for the Synthesis of 1,2,3-Benzotriazi-
nones. To a solution of 2-(o-aminophenyl)oxazoline (3)
(1 equiv.) in methanol, a solution of isoamyl nitrite (8 equiv.)
in methanol was added. e reaction mixture was stirred
at room temperature until the disappearance of the aniline
(followed by TLC, hexane/ethyl acetate, 3 : 1). e solvent was
evaporated under reduced pressure to give a crude product
that was purified by washing with petroleum ether and
recrystallization from hexane/ethyl acetate.
in (CD ) CO with TMS as internal standard. Melting points
3 2
were obtained on an Electrothermal 88629 apparatus. Optical
rotations were determined using an Autopol III polarimeter.
EIMS were recorded on an Agilent Technologies 5975C mass
spectrometer. e ESI-HRMS data were performed at High-
Resolution Mass Spectrometry Facility, UC Riverside.
3-(2-Hydroxyethyl)-1,2,3-benzotriazin-4(3H)-one (4a). White
3.2. General Procedure for the Synthesis of 2-(o-Aminophe-
nyl)Oxazoline (3). Anthranilonitrile (1 equiv.), potassium
carbonate (0.1 equiv.), and ethanolamine (1.7 equiv.) were
placed in a Schlenk flask, followed by a solution of glycerol
in dry ethylene glycol (5 : 9) (3.3 mL of solution per mmol of
anthranilonitrile). e resulting mixture was stirred at 105∘C
under argon until the disappearance of the nitrile (followed
by TLC, hexane/ethyl acetate, 3 : 1). e mixture was cooled
to room temperature and then poured over crushed ice.
e resulting white solid was filtered and then dissolved
in dichloromethane. e organic solution was washed with
water, dried over anhydrous Na SO , and filtered, and the
solid (>99% yield), mp 111-112∘C. FTIR (KBr): ] 3431, 1691,
1
1646, 1300 cm−1. H NMR [(CD ) CO, 200 MHz]: ꢀ 8.29
3 2
(ddd, ꢁ ꢂ 7.=, 1.5, 0.7 Hz, 1H), 8.15 (ddd, ꢁ ꢂ =.1, 1.5, 0.6 Hz,
1H), 8.06 (ddd, ꢁ ꢂ =.1, 7.0, 1.5 Hz, 1H), 7.91 (ddd, ꢁ ꢂ 7.9,
6.9, 1.6 Hz, 1H), 4.57 (t, ꢁ ꢂ 5.6 Hz, 2H), 4.02 (t, ꢁ ꢂ 5.6 Hz,
2H). 13C NMR [(CD ) CO, 50 MHz]: ꢀ 157.1, 146.1, 136.8,
3 2
134.2, 129.8, 126.5, 121.7, 61.2, 54.1. ESI-HRMS: 192.0778 (100),
calculated for [M+H]+, C H N O , 192.0768.
9
10
3
2
3-((R)-2-Hydroxy-1-phenylethyl)-1,2,3-benzotriazin-4(3H)-one
ꢀ
(4b). White solid (>99% yield), mp 79-80∘C. [ꢃꢄ20 ꢂ −1=3
2
4
solvent was evaporated under reduced pressure to give a
(c 0.22, MeOH). FTIR (KBr): ] 3419, 1683, 1661, 1294 cm−1.

4
Journal of Chemistry
1H NMR [(CD ) CO, 200 MHz]: ꢀ 8.27 (ddd, ꢁ ꢂ 7.=, 1.5,
Acknowledgments
3 2
0.6 Hz, 1H), 8.16 (ddd, ꢁ ꢂ =.1, 1.3, 0.6 Hz, 1H), 8.04 (ddd,
ꢁ ꢂ =.1, 7.1, 1.5 Hz, 1H), 7.87 (ddd, ꢁ ꢂ 7.=, 7.1, 1.3 Hz, 1H), 7.43
(m, 5H), 6.39 (dd, ꢁ ꢂ 9.7, 5.2 Hz, 1H), 4.70 (dd, ꢁ ꢂ 11.4,
9.7 Hz, 1H), 4.25 (dd, ꢁ ꢂ 11.4, 5.2 Hz, 1H). 13C NMR
e authors gratefully acknowledge support from Con-
sejo Nacional de Ciencia y Tecnolog´ıa (CONACyT Grant
36435-E and “Supramolecular Chemistry ematic Network”
Grant 271884), Programa de Mejoramiento del Profeso-
rado (Apoyo a la Incorporacio´n de Nuevos PTC Grant
Promep/103.5/11/4462), and Consejo del Sistema Nacional
de Educacio´n Tecnolo´gica (COSNET, Grant 486-02-P). e
authors are indebted to Ignacio Rivero Espejel and Ratnasamy
Somanathan for their support in this work.
[(CD ) CO, 50 MHz]: ꢀ 156.1, 144.6, 138.6, 136.0, 133.3, 129.4,
3 2
128.9, 128.9, 128.7, 125.7, 120.5, 64.0, 63.3. ESI-HRMS: 268.1094
(100), calculated for [M+H]+, C H N O , 268.1081.
15 14
3
2
3-((R)-1-Hydroxybutan-2-yl)-1,2,3-benzotriazin-4(3H)-one (4c).
ꢀ
White solid (>99% yield), mp 89-90∘C. [ꢃꢄ20 ꢂ −5 (c 0.22,
MeOH). FTIR (KBr): ] 3439, 1686, 1663, 1296 cm−1. 1H NMR
[(CD ) CO, 200 MHz]: ꢀ 8.29 (ddd, ꢁ ꢂ 7.9, 1.5, 0.6 Hz, 1H),
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8.16 (ddd, ꢁ ꢂ =.1, 1.5, 0.6 Hz, 1H), 8.07 (ddd, ꢁ ꢂ =.2, 7.0,
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4.10 (dd, ꢁ ꢂ 11.3, 8.4 Hz, 1H), 3.96 (dd, ꢁ ꢂ 11.3, 5.1 Hz,
1H), 1.99 (quin, ꢁ ꢂ 7.4 Hz, 2H), 0.90 (t, ꢁ ꢂ 7.4 Hz, 3H). 13C
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1
NMR [(CD ) CO, 200 MHz]: ꢀ 8.30 (ddd, ꢁ ꢂ 7.=, 1.5,
3 2
0.6 Hz), 8.17 (ddd, ꢁ ꢂ =.1, 1.6, 0.6 Hz), 8.09 (ddd, ꢁ ꢂ =.1, 7.0,
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˚
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Competing Interests
e authors declare that there are no competing interests
regarding the publication of this paper.

Journal of Chemistry
5
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