An efficient green synthesis and antibacterial activity of 1,3-benzoxazine and 1,3-naphthoxazine using NaCl.SiO2 as solid catalyst in neat condition

Article abstract of DOI:10.1002/jhet.4059

A series of 1,3-oxazine derivatives were synthesized by a one-pot three-component (ie, phenol, formaldehyde, amine) method where SiO₂ bonded with NaCl was used as a reusable, more efficient, easily prepared, and available solid catalyst. The reactions were also carried out at room temperature for greener approach. in vitro studies for the synthesized compounds were also done against two gram-positive (Bacillus subtilis and Staphylococcus aureus) and two gram-negative bacteria (Escherichia coli and Klebsiella pneumonia) to check for their applicability as an antibacterial agent where some of the synthesized compounds gives the best antibacterial activity against selected bacterial strains. Streptomycin was used as a standard control for all the microbial test.

Full text of DOI:10.1002/jhet.4059

Received: 10 December 2019
DOI: 10.1002/jhet.4059
Revised: 27 April 2020
Accepted: 29 May 2020
A R T I C L E
An efficient green synthesis and antibacterial activity
of 1,3-benzoxazine and 1,3-naphthoxazine using NaCl.SiO2
as solid catalyst in neat condition
Putusenla Imchen1 | Betokali K. Zhimomi1 | Lensayula Longkumer1
Shokip Tumtin2 | Toka Swu3 | Tovishe Phucho1
|
1Department of Chemistry, Nagaland
Abstract
University, Zunheboto, India
2Department of Chemistry, Kirori Mal
College, Delhi University, Delhi, India
3Department of Chemistry, Pondicherry
University, Puducherry, India
A series of 1,3-oxazine derivatives were synthesized by a one-pot three-
component (ie, phenol, formaldehyde, amine) method where SiO2 bonded with
NaCl was used as a reusable, more efficient, easily prepared, and available solid
catalyst. The reactions were also carried out at room temperature for greener
approach. in vitro studies for the synthesized compounds were also done
against two gram-positive (Bacillus subtilis and Staphylococcus aureus) and two
gram-negative bacteria (Escherichia coli and Klebsiella pneumonia) to check for
their applicability as an antibacterial agent where some of the synthesized com-
pounds gives the best antibacterial activity against selected bacterial strains.
Streptomycin was used as a standard control for all the microbial test.
Correspondence
Tovishe Phucho, Department of
Chemistry, Nagaland University, Lumami
798627, Zunheboto, Nagaland, India.
Email: itphucho@nagalanduniversity.
ac.in
Funding information
Science and Engineering Research Board,
Grant/Award Number: EEQ/2016/000260
dated 28-02-2017
1 | INTRODUCTION
single step and also its variation can be simply developed
by changing the reacting components.[8]
Oxazine, due to their wide and diverse range of biological
activities are considered as an important type of heterocycles
and are therefore, a special interest for the synthetic areas.
The 1, 3-oxazine nucleus features prominently in many
biologically important natural products and other bioactive
molecules.[1–4] They have gained much importance
due to their many biological activities like antitubular,[3]
antibacterial,[4] anticancer,[5] anticonversant,[2] and analge-
sic.[1] Benzo-1,3-oxazines are also generally known to pos-
sess biologically properties like cytotoxic,, antianginal,
antihypertensive effects, demonstrating antirheumatic, and
antiosteoclastic bone resorption activity.[6]
Multicomponent reactions (MCRs) have become
highly efficient as they avoid time consumption, has eco-
nomic purification processes, formation of several bonds
in a single step and manufacture of complex molecular
architectures.[7] This type of MCRs incorporate synthetic
strategy as the products formed are obtained in just a
Recently, there is a consideration on the use and
design of environmentally friendly heterogeneous catalysts
to reduce the amount of toxic waste. Among them, nano
scale metal oxides[9] have been efficiently used as catalysts
for organic transformations.[10–12] Solid-support catalyst
has become prominently important in the recent years as
they are easily available/easily prepared and are generally
less expensive. They can also be easily separated from
reaction mixtures and can be reused which make them
eco-friendly and also simple to use. This is one of the main
reasons why silica-supported catalyst in MCRs has gained
much importance and attention.[13] Gabbas et al also syn-
thesized a series of 3,4-dihydro-2H-benzo- and naphtho-
1,3-oxazine derivatives using methylene bromide for ring-
closure reaction where they also confirmed the presence
of antibacterial property in almost all of their synthesized
compounds via in vitro antimicrobial studies.[14a] As deriv-
atives containing oxazine ring system have shown to
J Heterocyclic Chem. 2020;1–6.
wileyonlinelibrary.com/journal/jhet
© 2020 Wiley Periodicals LLC.
1

2
IMCHEN ET AL.
possess great potential as antimicrobial agents,[14] synthe-
sis of some oxazine derivatives as well as their in vitro
antibacterial investigation were assessed and presented in
this work.
TABLE 2 Reaction of β-napthanol with aniline and 4-ipropyl
to form compounds 6(a-b)
Product
R
Yield in %
8017
6a
6b
H
4-ipropyl
81
2 | RESULTS AND DISCUSSION
TABLE 3 Reaction of α-napthanol with aniline and 4-ipropyl
to form compounds 8(a-c)
In continuation with our investigation on the methodol-
ogy of green synthesis of oxazines,[15] this present study,
focused on a greener and economical approach, for the
synthesis of various substituted [1.3-oxazines] by MCRs
which were carried out at room temperature using a
solid-support catalyst, SiO2.NaCl. The catalyst we have
chosen proves to be an inexpensive, easily available, non-
toxic, environmental friendly, and an efficient catalyst.
The catalyst also acts as a solid-support medium and also
slightly makes the medium acidic which inhances the
reaction rate.16
Product
R
Yield in %
8a
8b
8c
H
82
79
79
4-ipropyl
CH3
MIC of 0.023 for Bacillus subtilis (B.s.), Escherichia coli
(E.c.), and Staphylococcus aureus (S.a.) and 0.005 for Kleb-
siella pneumonia (K.p.) Whereas, compound 4a, 4c, and
4d showed no activity against S.a., B.s., and E.c., respec-
tively. Overall, compound 8a, 4e, and 4f shows promising
property as it gave the best antibacterial activity against
all bacterial strains.
Using the catalyst, the completion of the reactions
was achieved within 5 to 10 minutes at room temperature
with continuous stirring. The products 4(a-f) were
obtained using substituted phenols (Table 1), while prod-
ucts 6(a-c) and 8(a, b) were obtained using 2-naphthol
(Table 2), and 1-naphthol (Table 3), respectively. We also
observed the production of heat as the reaction prog-
ressed which was then monitored and the structure of
2.1 | Spectral and analytical data
1
the purified compounds were deduced by their IR, H
NMR, 13C NMR and mass spectroscopy (Schemes 1-4).
The compounds were also screened for their
antibacterial activity which revealed that almost all the
compounds which were tested showed moderate to good
activity against the bacterial strains. Compounds 4b, 8a,
and 4f showed promising results. The results of the
antibacterial screening are as shown in Table 4. Further,
to quantify its antibacterial activity minimum inhibitory
concentration (MIC) of all the compounds were deter-
mined. The results are as shown in Table 5.
(4a) 6-bromo-3,4-dihydro-3-phenyl-2H-benzo[e][1,3]
oxazine- mp: 58ꢀC; IR (KBr, cm−1): 2853.83 and 2924.75
( CH2), 504.45 ( C Br), 1515.44 (C C), 1081.78
(CH2 O), 1261.07 (C N), 1314.83 (C O), 1612.79
(C O); 1H NMR (400 MHz, CDCl3): δ 4.351 (s, 2H, CH2),
4.150 (s, 2H, CH2), 6.760-7.060 (m, 7H, ArH); 13C NMR
(400 MHz, CDCl3): δ 60.45, 79.10, 115.30, 116.21, 117.81,
121.30, 129.63, 131.00, 132.8, 133.4, 147.8, 152.7; MS:
m/z = 289.
(4b)
3,4-dihydro-8-nitro-3-phenyl-2H-benzo[e]
From Table 5, we can see that compound 8a showed
maximum inhibition against all bacterial strains with
[1,3]oxazine- mp: 50ꢀC; IR (KBr, cm−1): 3418.78 (C H),
2851.76 and 2921.42 ( CH2), 1538.76 (C NO2), 1507.07
(C C), 1076.22 (CH2 O), 1263.90 (C N), 1318.93
1
(C O), 1602.77 (C C); H NMR (400 MHz, CDCl3): δ
4.781(s, 2H, CH2), 5.610 (s, 2H, CH2), 6.743-7.912 (m, 8H,
ArH); 13C NMR (400 MHz, CDCl3): δ 54.79, 87.51,
114.37, 115.59, 118.71, 121.40, 124.12, 123.02, 129.95,
141.05, 149.82, 157.94; MS: m/z = 157 (M+).
TABLE 1 Reaction of phenol/substituted phenols with aniline
and 4-ipropyl to form compounds 4(a-f)
Product
R'
R
Yield in %
4a
4b
4c
4d
4e
4f
4-Br
2-NO2
4-NO2
2-NH2
4-Br
H
H
78
75
76
70
73
76
(4c)
3,4-dihydro-6-nitro-3-phenyl-2H-benzo[e]
[1,3]oxazine- mp: 52ꢀC; IR (KBr, cm−1): 1506.97
(C NO2), 3411.85 ( CH), 2926.28-2854.30 ( CH2),
1074.30 (CH2 O), 1261.46 (C N), 1453.69 (C O),
H
H
H
1
1602.70 (C C); H NMR (400 MHz, CDCl3): δ 4.896 (s,
4-ipropyl
4-ipropyl
2H, CH2), 5.298 (s, 2H, CH2), 6.854-7.200 (m, 8H, ArH);
13C NMR (400 MHz, CDCl3): δ 53.57, 68.72, 108.9,

IMCHEN ET AL.
3
113.75, 115.22, 117.79, 121.04, 129.29, 129.41, 129.56,
148.72, 158.04; MS: m/z = 156.
(s, 2H, CH2), 3.487 (s, 2H, NH2), 4.686 (s, 2H, CH2),
6.704-7.138 (m, 8H, ArH), 13C NMR (400 MHz,
CDCl3): δ 57.95, 89.90, 115.27, 116.19, 117.17, 118.74,
119.64, 121.48, 129.43, 155.17, 144.27, 146.42; MS:
m/z = 226.
(4e) 6-bromo-3,4-dihydro-3-(4-isopropylphenyl)-
2H-benzo[e][1,3]oxazine- mp: 99ꢀC; IR (KBr, cm−1):
2861.26 (C CH3), 471.98 (C Br), 3276.63 (C H),
2960.40 and 2861.26 ( CH2), 1056.44 (CH2 O), 1260.80
(C N), 1489.13 (C O), 1613.22 (C C), 1514.17 (C C);
1H NMR (400 MHz, CDCl3): δ 2.317 (s, 3H, CH3), 2.991
(s, H, CH) 3.026 (s, 2H, CH2), 4.511 (s, 2H, CH2),
6.891-7.452 (m, 7H, ArH); 13C NMR (400 MHz, CDCl3): δ
24.112, 33.313, 49.067, 111.586, 116.298, 118.486, 124.865,
(4d) 3,4-dihydro-3-phenyl-2H-benzo[e][1,3]oxazine-
8-amine- mp: 52ꢀC; IR (KBr, cm−1): 3306.98 (C NH2),
3376.44 (C H), 2963.65 and 2850.57 ( CH2), 1095.68
(CH2 O), 1261.81 (C N), 1468.68 (C O), 1603.11 (C C),
1509.22 (C C); 1H NMR (400 MHz, CDCl3): δ 2.174
SCHEME 1 Synthesis of 1,3-benzoxazine 4(a-f)
SCHEME 2 Synthesis of
1,3-napthoxazine 6(a-b)
SCHEME 3 Synthesis of
1,3-napthoxazine 8(a-c)
SCHEME 4 Plausible
reaction mechanism showing
the role of catalyst

4
IMCHEN ET AL.
127.326, 130.960, 131.776, 142.087, 144.448, 156.256; MS:
m/z = 333.
13C NMR (400 MHz, CDCl3): δ 24.23, 36.37, 60.96, 89.99,
114.01, 114.29, 121.07, 122.33, 127.33, 128.33, 128.15,
129.03, 138.71, 147.33, 158.07; MS: m/z = 253.
(4f) 3,4-dihydro-3-(4-isopropylphenyl)-2H-benzo
[e][1,3]oxazine- mp: 70ꢀC; IR (KBr, cm−1): 2855.58
(C CH3), 3294.92 (C H), 2958.34 and 2925.72 ( CH2),
1059.15 (CH2 O), 1262.48 (C N), 1490.97 (C O),
1611.19 (C C), 1512.35 (C C); 1H NMR (400 MHz,
CDCl3): δ δ 2.291 (s, 3H, CH3), 3.026 (s, 2H, CH2), 3.304
(s, H, CH), 4.651 (s, 2H, CH2), 6.748-7.954 (m, 8H, ArH);
(6a) 3,4-dihydro-3-phenyl- 2H-naphtho[2,1-e][1.3]
oxazine- mp: 160ꢀC;IR (KBr, cm−1): 3298.23(C H),
2863.55 ( CH2) 1575.87 (C C), 1050.75 ( CH2-O),
1
1268.70 (C N), 1243.04 (C O), 1600.10 (C C); H NMR
(400 MHz, CDCl3): δ 4.454 (s, 2H, CH2), 6.748-8.147 (m,
11H, ArH); 13C NMR (400 MHz, CDCl3): δ 49.60, 115.33,
116.33, 119.43, 121.28, 122.09, 125.23, 125.32, 126.32,
126.37, 127.47, 129.49, 134.16, 147.22, 152.80; MS:
m/z = 260 (M−1).
TABLE 4 Antibacterial activity of the compounds 4(a-f), 6(a-c),
and 8(a-b) (diameter of zone of inhibition in mm)
(6b) 3,4-dihydro-3-(4-isopropylphenyl)-2H-naph-
tho[2,1-e][1,3]oxazine-
mp:
130ꢀC;
IR
(KBr,
Zone of inhibition (mm)
cm−1):2863.90 (C CH3), 3275.32 (C H), 2955.69 and
2863.90 ( CH2), 1048.01 (CH2O), 1263.54 (C N),
Compounds (2 mg/mL DMSO) B.s.
E.c.
12
K.p.
12
S.a.
NI
10
16
12
14
13
11
13
17
12
11
22
1
1471.07 (C O), 1614.42(C C), 1511.56 (C C); H NMR
4a
10
11
NI
13
14
15
13
13
18
13
10
23
(400 MHz, CDCl3): δ 2.941 (s, 3H, CH3), 2.975 (s, 3H,
CH3), 3.141 (s, H, CH), 4.948 (s, 2H, CH2), 6.792-7.929
(m, 10H, ArH); 13C NMR (400 MHz, CDCl3): δ 24.124,
33.202, 112.712, 113.566, 118.263, 121.419, 121.724,
122.748, 126.447, 127.301, 128.834, 129.636, 141.815,
144.857, 145.085, 155.526; MS: m/z = 304 (M+).
(8a) 2,3-dihydro-2-phenyl-1H-naphtho[1,2-e][1,3]
oxazine- mp: 98ꢀC; IR (KBr, cm−1): 3294.07 (C H),
1582.25 (C C), 1068.10 (CH2 O), 1271.86 (C N),
1244.79 (C O), 1602 (C C); 1H NMR (400 MHz, CDCl3):
δ 4.50 (s, 2H, CH2), 5.487 (s, 2H, CH2), 6.547-7.894 (m,
11H, ArH); 13C NMR (400 MHz, CDCl3): δ 51.70, 98.33,
115.49, 116.28, 119.33, 121.83, 124.23, 125.43, 126.72,
127.32, 128.74, 129.50, 135.50, 135.78, 148.47, 155.28; MS:
m/z = 262 (M+).
4b
16
15
4c
12
14
4d
NI
13
10
4e
14
4f
11
12
6a
13
14
6b
13
12
8a
18
19
8b
>10
11
>10
13
8c
Streptomycin
22
22
Abbreviations: B.s., Bacillus subtilis; E.c., Escherichia coli; K.p., Kleb-
siella pneumonia; NI, no inhibition; S.a., Staphylococcus aureus.
TABLE 5 Determination of MIC
of compounds 4(a-f), 6(a-c), and 8(a-b)
MIC (mg/ml)
Compounds (2 mg/mL DMSO)
B.s
E.c.
K.p.
S.a.
4a
0.75
0.375
0.046
0.375
—
0.375
0.046
0.187
0.75
—
4b
0.75
0.75
4c
—
0.046
0.375
0.187
0.187
0.375
0.187
0.023
0.375
0.375
0.0058
4d
0.187
0.187
0.187
0.187
0.187
0.023
0.187
0.75
4e
0.187
0.375
0.187
0.187
0.023
0.75
0.187
0.375
0.187
0.375
0.005
0.75
4f
6a
6b
8a
8b
8c
0.375
0.00729
0.187
0.0029
Streptomycin
0.00729
Abbreviations: B.s., Bacillus subtilis; E.c., Escherichia coli; K.p., Klebsiella pneumonia; MIC, mini-
mum inhibitory concentration; S.a., Staphylococcus aureus.

IMCHEN ET AL.
5
(8b) 2,3-dihydro-2-(4-isopropylphenyl)-1H-naph-
continuously stirred for 20 minutes in a magnetic stirrer.
The whole mixture was further heated gently on a hot
magnetic stirrer plate with occasional stirring until the
white solid is free flowing. The resultant catalyst was fur-
ther activated in a hot air oven maintained at 120ꢀC for at
24 hours prior to use.
tho[1,2-e][1,3]oxazine- mp: 129ꢀC; IR (KBr, cm−1):
2863.90 (C CH3), 3275.46 (C H), 2955.50 and 2890.97
( CH2), 1049.92 (CH2 O), 1263.31 (C N), 1470.97
(C O), 1614.38 (C C), 1510.80 (C C); 1H NMR
(400 MHz, CDCl3): δ 2.299 (s, 3H, CH3), 2.992 (s, 2H,
CH2), 3.010 (s, H, CH), 4.966 (s, 2H, CH2), 6.760-7.942
(m, 10H, ArH); 13C NMR (400 MHz, CDCl3): δ 24.216,
33.313, 115.283, 116.123, 119.227, 121.218, 122.746,
122.874, 126.649, 126.744, 127.128, 128.748, 128.920,
129.476, 132.011, 133.124, 146.858, 154.321; MS:
m/z = 304 (M+).
3.2 | General procedure for the synthesis
of compounds 4(a-f), 6(a-c), and 8 (a-b)
To a mixture of 1 mmol of Amine (2), 2 mmol of Formalde-
hyde (3) was added. Subsequently 1 mmol of Substituted-
Phenol (1)/naphthol (5 or 7) and 1 g of the prepared
catalyst was added and then stirred at room temperature
for 5 to 10 minutes. The progress of the reaction was moni-
tored by TLC. After the completion of the reaction, the
reaction mixture was first washed with ethyl acetate and
the filtrate was dried using BUCHI Rotavapor R-300. The
catalyst after washing was kept to dry in a hot air oven for
further use. The synthesized compound was then separated
and purified by Column chromatography using hexane:
ethylacetate mixture. Further confirmation of the synthe-
sized compound was done by spectral analysis data such as
melting point, IR, NMR, and mass spectroscopy.
(8c) 3,4-dihyro-3-(4-isopropylphenyl)-6-methyl-
2H-benzo[e][1,3]oxazine- mp: 100ꢀC; IR (KBr, cm−1):
2857.99 (C CH3), 3313.75 (C H), 2912.26 and 2885.41
( CH2), 1040.43 (CH2 O), 1266.52 (C N), 1465 (C O),
1614.62 (C C), 1512.13 (C C); 1H NMR (400 MHz,
CDCl3): δ 2.318 (s, H, CH3), 2.431 (s, 2H, CH2), 4.716
(s, 2H, CH2), 6.749-8.377 (m, 10H, ArH); 13C NMR
(400 MHz, CDCl3): δ 20.533, 50.006, 112.712, 115.200,
116.446, 119.170, 121.999, 125.116, 126.155, 126.179,
127.309, 129.866, 130.717, 134.007, 144.576, 152.847; MS:
m/z = 276 (M+).
3 | EXPERIMENTAL SECTION
All the chemicals and reagents were purchased from
Merck and HiMedia and were used without further purifi-
cation. The synthesized compounds were characterized by
checking its melting point, IR, H1 NMR, C13 NMR, and
Mass spectroscopy. All the evaporation process after reac-
tion completion and Column chromatography completion
was done using BUCHI Rotavapor R-300. Melting point
was determined in open capillary tubes using IKON melt-
ing point apparatus and the results were uncorrected. FT-
IR Perkin Elmer instrument was used to record the IR
spectra using Kbr and FT-NMR Bruker Avance-II spec-
3.3 | Antibacterial studies
All the synthesized compounds were screened for their
antibacterial activity against two gram-positive bacteria
viz. B.s. and S.a., and two gram-negative bacteria viz. E.c.,
and K.p.. Well diffusion method was used for the in vitro
antibacterial studies and the activity was determined by
measuring the diameter of inhibition zones (mm), also
the MIC were determined by means of standard 2-fold
serial broth dilution method.18 DMSO concentration of
2 mg/mL of was used where DMSO was used as a−ve
control and Streptomycin was used as a+ve control.
1
trometer (400 MHz) was used to record the H NMR and
13C NMR spectra where CDCl3 was used as the solvent.
For mass spectroscopy, Compact Mass Spectrophotometer
APCI Expression-S instrument was used. Progress of the
reaction was monitored by TLC using TLC silica gel 60 Alu-
minum backed F254 which was developed in UV chamber
as well as in iodine chamber. For isolation and separation
process Column Chromatography was performed using Sil-
ica Gel 100-200 mesh.
4 | CONCLUSIONS
In this present study we have successfully synthesized a
series of 1,3-oxazines using an efficient and environmen-
tal friendly catalyst through a one-pot, three-component
condensation reaction. The synthesized compounds were
characterized by their melting point, 1H NMR, 13C NMR,
and mass spectroscopy. They were also screened for their
antibacterial activity which included determination of
zone of inhibition and MIC. Compounds like 8a, 4e, and
4f showed promising property as it gave the best
antibacterial activity against all bacterial strains.
3.1 | Preparation of SiO2.NaCl (Catalyst)
About 4 g of NaCl was dissolved in 20 mL of distilled water
and to it 10 g of SiO2 (100-200 mesh) was added and then

6
IMCHEN ET AL.
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ACKNOWLEDGMENTS
The authors wish to thank the Head, SAIF, NEHU, Shil-
long and Pondicherry University for all the spectral anal-
ysis. The authors are also grateful to SERB-DST for
financial assistance through major research project grant.
ORCID
Tovishe Phucho https://orcid.org/0000-0003-3786-5107
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How to cite this article: Imchen P, Zhimomi BK,
Longkumer L, Tumtin S, Swu T, Phucho T. An
efficient green synthesis and antibacterial activity
of 1,3-benzoxazine and 1,3-naphthoxazine using
NaCl.SiO2 as solid catalyst in neat condition.
J Heterocyclic Chem. 2020;1–6. https://doi.org/10.
1002/jhet.4059
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