An efficient and rapid dehydrogenation of 4-aryl-3,4-dihydropyrimidin-2(1H) -ones (DHPMs) using CAN/HCl

Article abstract of DOI:10.1016/j.tetlet.2012.08.017

An efficient and operationally simple method for the dehydrogenation of 4-aryl-3,4-dihydropyrimidin-2(1H)-ones (DHPMs) has been developed using CAN/HCl. 2012 Elsevier Ltd. All rights reserved.

Full text of DOI:10.1016/j.tetlet.2012.08.017

Tetrahedron Letters 53 (2012) 5541–5543
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An efficient and rapid dehydrogenation of
4-aryl-3,4-dihydropyrimidin-2(1H)-ones (DHPMs) using CAN/HCl
⇑
Hitendra N. Karade, Jyotiranjan Acharya, Mahabir Parshad Kaushik
Process Technology Development Division, Defence R & D Establishment, Jhansi Road, Gwalior 474 002, M.P., India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and operationally simple method for the dehydrogenation of 4-aryl-3,4-dihydropyrimidin-
2(1H)-ones (DHPMs) has been developed using CAN/HCl.
Received 3 June 2012
Revised 2 August 2012
Accepted 4 August 2012
Available online 10 August 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Dehydrogenation
CAN
DHPM
Oxidation
In 1893 Biginelli1 reported the one pot three-component
synthesis of 4-aryl-3,4-dihydropyrimidin-2(1H)-ones (DHPMs). Li-
brary of the structurally diverse DHPMs can be synthesized by
using the combination of different aldehydes, 1,3-dicarbonyl com-
pound, and urea or thiourea.2 This reaction has gained much
importance because the compounds containing pyrimidine/DHPM
unit have various biological properties3 such as antitumor, antihy-
pertensive, calcium channel blocker, alpha-1a-antagonism, neuro-
peptide Y (NPY) antagonism, antibacterial, and anti-inflammatory
activities. DHPM-derived structures are also present in the skele-
ton of several natural marine polycyclic guanidine alkaloids such
as crambine, batzelladine B (potent HIV gp-120CD4 inhibitors),
and ptilomycalin alkaloids.4 Thus DHPMs can be considered as
valuable structures for the drug discovery research.
Since pyrimidine derivatives are found in various biologically
important molecules, derivatization of DHPM has attracted the
attention of researches in the last decade.5 Dehydrogenation of
DHPM is one of the typical transformations, essentially because
DHPM contains two sensitive functionalities, one is allylic methyl
group at C-6 position and another is –CH–NH bond at C-4 position.
Thus under oxidative conditions mixture of products can be
obtained and hence for the development of an efficient and clean
methodology choice of reagents and reaction conditions become
very important. The allylic methyl group at C-6 position is sensitive
to the oxidizing agents such as SeO26 and hence the dehydrogena-
tion of the DHPMs is difficult as compared to the easy oxidation of
Hantzsch 1,4-dihydropyridines (DHPs) to pyridine.7
DHPM ring also shows the inertness toward the strong oxidiz-
ing agents like DDQ.8 Classical oxidizing agents such as (PCC),
chloranil, KMnO4/clay,9 and HNO3 were also tried for the dehy-
10
drogenation of DHPM, among which HNO3 has been proved to give
the satisfactory result. Palladium on charcoal requires a high tem-
perature of 230 °C and this method is also not suitable for the
DHPM containing ester at C-5 position.11 Myriad of other methods
and reagents are available in the literature12–18 for the dehydroge-
nation of DHPM, however all of them have some drawbacks such as
regioselectivity, requirement of
a high reaction temperature,
formation of undesired side product, long reaction time (1–18 h),
and involve tedious column chromatographic purification. Thus
there is still a need for the development of a novel method for
the dehydrogenation of DHPM which will minimize the reaction
time and formation of undesired side products with easy purifica-
tion process to isolate the pure product. Since last decade ceric
ammonium nitrate (CAN) has been explored for its wide range of
O
R2
O
R2
CAN (2 equi.),
50% aq. HCl
4
5
R1
N
R1
3NH
2
6
1
N
AcOH, RT, 20 min.
N
H
O
O
H
1a-1l
2a-2l
R1 = -OEt, -CH3
R2 = Aryl
⇑
Corresponding author. Fax: +91 751 2340042.
E-mail address: mpkaushik@rediffmail.com (M.P. Kaushik).
Scheme 1. Dehydrogenation of DHPM to pyrimidine-2(1H)-one using CAN/50%
aqueous HCl.
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.08.017

5542
H. N. Karade et al. / Tetrahedron Letters 53 (2012) 5541–5543
catalytic applications.19 Single electron oxidizing properties of CAN
can be altered by the addition of various additives such as KBr, LiBr,
NaHCO3, NaBrO3 or KBrO3, and H2O2.20 Herein we used the combi-
nation of CAN and HCl for the rapid and efficient dehydrogenation
of DHPM at room temperature (Scheme 1).
Table 2
Dehydrogenation of 4-aryl-3,4-dihydropyrimidin-2(1H)-ones (DHPMs) using CAN/
50% aqueous HCl
Entry
DHPM
R2
R1
Product
Yielda (%)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
1i
C6H5
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
CH3
CH3
2a
2b
2c
2d
2e
2f
2g
2h
2i
85
82
75
72
80
78
83
80
76
70
78
76
The model reaction was carried out using DHPM (1g)23. In a
50 mL round bottomed flask containing stirred solution of acetic
acid (15 mL) and DHPM (1g, 3 mmol), 50% aqueous hydrochloric
acid (5 mL) was added at room temperature. CAN (6 mmol) was
added portion-wise to the reaction mixture and stirring was con-
tinued at room temperature. The color of the reaction mixture
slowly changes from dark orange to transparent pale yellow. After
twenty minutes the TLC (6:4 EtOAc:Hexane) shows completion of
reaction. Stoichiometry of CAN was optimized to two equivalents
(Table 1). If we use CAN less than two equivalents then the reaction
time increases and DHPM remains unreacted even after 1.5 h. The
yield of the product decreased when we used CAN and conc. HCl.
Thus by using the optimized stoichiometry of CAN, DHPM, and
HCl we achieved the dehydrogenation of various substituted
DHPMs (Table 2).
4-CH3OC6H4
3-CH3OC6H4
2-CH3OC6H4
4-CH3C6H4
3-CH3C6H4
4-ClC6H4
2-ClC6H4
3-NO2C6H4
2-CH3O-5-BrC6H3
4-ClC6H4
10
11
12
1j
1k
1l
2j
2k
2l
4-CH3C6H4
a
Isolated Yield.
isolated using simple precipitation (DCM/hexane), instead of col-
umn chromatography. There is no formation of undesired side
products such as pyrimidin-2,4(1H, 3H)-dione and C-6 side chain
chlorination product. Thus the combination of CAN/HCl can be
used efficiently for the oxidative dehydrogenation of DHPM.
Similar kind of oxidative dehydrogenation of DHPM is also re-
ported in the literature using CAN/NaHCO3.18 This reported meth-
odology requires CAN more than two equivalents, longer reaction
time (1-6 h), controlled reaction temperature (À5–0 °C) and the
pure product was isolated by column chromatographic purifica-
tion. As compared to this reported methodology of CAN/NaHCO3,
our proposed methodology using CAN/HCl is mild (reaction occurs
at room temperature), rapid (reaction time 20 min.) and pure prod-
uct can be separated easily, just by precipitation (DCM/hexane). In
addition, we never observed the formation of pyrimidin-2,4(1H,
3H)-dione during the course of reaction by using CAN/HCl. During
the reaction of 1l, we did not observe any side chain chlorination of
benzylic methyl, acetyl methyl (C-5), or allylic methyl (C-6) groups.
Thus the above described method using CAN/HCl is much more
convenient and operationally simple than the reported methods.
The synthesized products (2a–2l) were characterized using IR, 1H
NMR, and MS. In all the cases, good to excellent yields of the prod-
ucts were obtained.
Acknowledgments
We are very much thankful to Mr. Ajay Pratap and Mr. Ashish
Kumar Srivastava for recording the 1H NMR and MS of synthesized
compounds respectively. We also thank the Director, DRDE Gwal-
ior for his keen interest and encouragement.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.08.
017.
References and notes
Since CAN acts as single electron oxidant, we tried the same
reaction using the additives such as NaCl, KBr, and LiBr (Table 1).
But the reaction is very slow and starting material remains unre-
acted even after six hours with a number of unidentified side prod-
uct formation. Mechanistically, the combination of CAN and HCl
may generate a in situ chlorine radical which can act as oxidizing
agent21 for the proposed oxidative dehydrogenation of DHPM.
But surprisingly, we did not observe any chlorination at C-6 methyl
group during the course of reaction.22 Hence additionally we as-
sumed that the in situ generated HNO3 in aqueous media may be
responsible for the oxidative dehydrogenation.10
1. Biginelli, P. Gazz. Chim. Ital. 1893, 23, 360.
2. (a) Shaabani, A.; Bazgir, A. Tetrahedron Lett. 2004, 45, 2575; (b) Abelman, M. M.;
Smith, S. C.; James, D. R. Tetrahedron Lett. 2003, 44, 4559; (c) Tu, S.; Shao, Q.;
Zhou, D.; Cao, L.; Shi, F.; Li, C. J. Heterocyclic. Chem. 2007, 44, 1401; (d) Shaabani,
A.; Rahmati, A.; Naderi, S. Bioorg. Med. Chem. Lett. 2005, 15, 5553.
3. (a) Atwal, K. S.; Swanson, B. N.; Unger, S. E.; Floyd, D. M.; Moreland, S.; Hedberg,
A.; O’Reilly, B. C. J. Med. Chem. 1991, 34, 806; (b) Grover, G. J.; Dzwonczyk, S.;
McMullen, D. M.; Normandin, D. E.; Parham, C. S.; Sleph, P. G.; Moreland, S. J.
Cardiovasc. Pharmacol. 1995, 26, 289; (c) Rovnyak, G. C.; Kimball, S. D.; Beyer,
B.; Cucinotta, G.; Dimarco, J. D.; Gougoutas, J.; Hedberg, A.; Malley, M.;
McCarthy, J. P.; Zhang, R.; Moreland, S. J. Med. Chem. 1995, 38, 119; (d) Atwal, K.
S.; Rovnyak, G. C.; O’Reilly, B. C.; Schwartz, J. J. Org. Chem. 1989, 54, 5898; (e)
Hu, E. H.; Sidler, D. R.; Dolling, U. H. J. Org. Chem. 1998, 63, 3454; (f) Kappe, C.
O.; Fabian, W. M. F.; Semones, M. A. Tetrahedron 1997, 53, 2803.
4. (a) Franklin, A. S.; Ly, S. K.; Mackin, G. H.; Overman, L. E.; Shaka, A. J. J. Org.
Chem. 1999, 64, 1512; (b) Kappe, C. O. Eur. J. Med. Chem. 2000, 1043, 35.
5. (a) Lengar, A.; Kappe, C. O. Org. Lett. 2004, 6, 771; (b) Dondoni, A.; Massi, A.;
Sabbatini, S. Tetrahedron Lett. 2002, 43, 5913; (c) Singh, K.; Singh, S. Tetrahedron
Lett. 2006, 47, 8143; (d) Shah, T. B.; Gupte, A.; Patel, M. R.; Chatudhari, V. S.;
Patel, H.; Patel, V. C. Indian J. Chem. 2009, 48B, 88; (e) Hamouly, W. S. E.;
Khamry, A. M. A. E.; Abbas, E. M. H. Indian J. Chem. 2006, 45B, 2091.
6. Khanina, E. L.; Duburs, G. Khim. Geterotsikl. Soedin 1982, 535.
7. (a) Bagley, M. C.; Lubinu, M. C. Synthesis 2006, 8, 1283; (b) Han, B.; Liu, Z.; Liu,
Q.; Yang, L.; Liu, Z. L.; Yu, W. Tetrahedron 2006, 62, 2492; (c) Anniyappan, M.;
Muralidharan, D.; Perumal, P. T. Tetrahedron 2002, 58, 5069; (d) Nakamichi, N.;
Kawashita, Y.; Hayashi, M. Org. Lett. 2002, 4, 3955.
In summary, we have developed an efficient and operationally
simple method for the dehydrogenation of DHPM using CAN/HCl.
The proposed methodology is rapid and the pure product can be
Table 1
Optimization of stoichiometry for the dehydrogenation of DHPM 1
Entry Additives
CAN (equiv.) Reaction time (min) Yield (%)
1
2
3
4
5
6
7
8
9
5 mL (Conc. HCl)
2.5 mL (Conc. HCl)
5 mL (50% aq. HCl)
5 mL (50% aq. HCl) 2.5
5 mL (50% aq. HCl)
5 mL (50% aq. HCl) 1.8
5 mL (50% aq. HCl) 1.5
NaCl
KBr
LiBr
2
2
2
45
45
20
20
20
50
60
85
85
85
45
30
15
20
20
8. Eynde, J. J. V.; Audiart, N.; Canonne, V.; Michel, S.; Haverbeke, Y. V.; Kappe, C. O.
Heterocycles 1997, 45, 1967.
9. Vanden Eynde, J. J.; Audiart, N.; Canonne, V.; Michel, S.; Van Haverbeke, Y.;
Kappe, C. O. Heterocycles 1997, 45, 1967.
10. Puchala, A.; Belaj, F.; Bergman, J.; Kappe, C. O. J. Heterocycl. Chem. 2001, 38,
1345.
11. Kappe, C. O.; Roschger, P. J. Heterocycl. Chem. 1989, 26, 55.
12. (a) Liu, Q.; Li, Y.-N.; Zhang, H.-H.; Chen, B.; Tung, C.-H.; Wu, L.-Z. J. Org. Chem.
2011, 76, 1444; (b) Esfahani, M. N.; Montazerozohori, M.; Abdi, K. ARKIVOC
2009, 255.
3
90
120
360
360
360
3
3
3
10

H. N. Karade et al. / Tetrahedron Letters 53 (2012) 5541–5543
5543
13. Memarian, H. R.; Farhadi, A.; Sabzyan, H.; Soleymani, M. J. Photochem. Photobio.
A: Chem. 2010, 209, 95.
Ethyl 4-(3-methoxyphenyl)-6-methyl-2-oxo-1,2-dihydropyrimidine-5-carboxylate
(2c). IR (KBr):
= 3316, 2836, 1718, 1658, 1600, 1438, 798 cmÀ1 1H (400 MHz,
m
.
14. Kadysh, V.; Stradins, J.; Khanina, H.; Duburs, G. Electrochim. Acta 1989, 34, 899.
15. Memarian, H. R.; Farhadi, A. Ultrason. Sonochem. 2008, 15, 1015.
16. (a) Yamamoto, K.; Chen, Y. G.; Buono, F. G. Org. Lett. 2005, 21, 4673; (b) Karade,
N. N.; Gampawar, S. V.; Kondre, J. M.; Tiwari, G. B. Tetrahedron Lett. 2008, 49,
6698.
17. Shanmugam, P.; Perumal, P. T. Tetrahedron 2007, 63, 666.
18. Shanmugam, P.; Perumal, P. T. Tetrahedron 2006, 62, 9726.
19. Nair, V.; Deepthi, A. Chem. Rev. 2007, 107, 1862.
DMSO-d6): d 0.84 (t, 3H, J = 7.2 Hz, –CH3), 2.38 (s, 3H, –CH3), 3.78 (s, 3H, –
OCH3), 3.94 (q, 2H, J = 7.2 Hz, –CO2CH2–), 6.98 (m, 2H, Ar-H), 7.06 (d, J = 8.4 Hz,
1H, Ar-H), 7.35 (t, 1H, J = 8.4 Hz, Ar-H), 13.67 (s, –NH). ESI-MS: m/z 289.5007
(M+1).
Ethyl 4-(2-methoxyphenyl)-6-methyl-2-oxo-1,2-dihydropyrimidine-5-carboxylate
(2d). IR (KBr): m .
= 3362, 3005, 2805, 1691, 1590, 1428, 726 cmÀ1 1H (400 MHz,
DMSO-d6): d 0.79 (t, 3H, J = 7.2 Hz, –CH3), 2.41 (s, 3H, –CH3), 3.68 (s, 3H, –
OCH3), 3.85 (q, 2H, J = 7.2 Hz, –CO2CH2–), 7.0 (t, 2H, J = 7.2 Hz, Ar-H), 7.31 (d,
J = 7.2 Hz, 1H, Ar-H), 7.42 (t, 1H, J = 7.2 Hz, Ar-H), 13.67 (s, –NH). ESI-MS: m/z
289.5120 (M+1).
20. (a) Sridharan, V.; Mene´ndez, J. C. Chem. Rev. 2010, 110, 3805. and references
given in it.; (b) Savitha, G.; Niveditha, S. K.; Muralidharan, D.; Perumal, P. T.
Tetrahedron Lett. 2007, 48, 2943; (c) Savitha, G.; Perumal, P. T. Tetrahedron Lett.
2006, 47, 3589; (d) Roy, S. C.; Rana, K. K.; Guin, C.; Banerjee, B. Arkivoc 2003, 34;
(e) Hamper, B. C.; Gan, K. Z.; Owen, T. J. Tetrahedron Lett. 1999, 40, 4973.
21. Tale, N. P.; Shelke, A. V.; Karade, N. N. Synth. Commun. 2012, 42, 2959.
22. Zigeuner, G.; Hamberger, H.; Blaschke, H.; Sterk, H. Monatsh. Chem. 1966, 97,
1408.
23. General experimental procedure for the oxidative dehydrogenation of DHPM (1g)
using CAN/HCl: In a 50 mL round bottomed flask containing stirred solution of
acetic acid (15 mL) and DHPM (1g, 3 mmol), 50% aqueous hydrochloric acid
(5 mL) was added at room temperature. CAN (6 mmol) was added portion-wise
to the reaction mixture and stirring was continued at room temperature. The
color of the reaction mixture slowly changed from dark orange to transparent
pale yellow. After twenty minutes the TLC (6:4 EtOAc/Hexane) showed
completion of reaction. Cold water (20 mL) was added to the reaction
mixture and extracted with DCM (20 mL). Organic layer was separated and
washed by bicarbonate solution followed by brine solution. Organic layer was
dried over anhydrous sodium sulfate and concentrated under vacuum. Crude
product was precipitated using DCM/hexane (1:6) and filtered off to give the
pure product (2g).
Ethyl 6-methyl-2-oxo-4-p-tolyl-1,2-dihydropyrimidine-5-carboxylate (2e). IR
(KBr):
m .
= 3308, 2884, 1714, 1642, 1601, 1438, 802 cmÀ1 1H (400 MHz,
DMSO-d6): d 0.98 (t, 3H, J = 7.2 Hz, –CH3), 2.39 (s, 3H, –CH3), 2.59 (s, 3H, –
CH3), 4.06 (q, 2H, J = 7.2 Hz, –CO2CH2–), 7.22 (m, 2H, Ar-H), 7.50 (m, 2H, Ar-H),
13.65 (s, –NH). ESI-MS: m/z 273.4701 (M+1).
Ethyl 6-methyl-2-oxo-4-m-tolyl-1,2-dihydropyrimidine-5-carboxylate (2f). IR
(KBr): m .
= 3411, 3316, 3212, 3100, 2984, 1712, 1441, 795 cmÀ1 1H (400 MHz,
DMSO-d6): d 0.95 (t, 3H, J = 7.2 Hz, –CH3), 2.38 (s, 3H, –CH3), 2.60 (s, 3H, -CH3),
4.04 (q, 2H, J = 7.2 Hz, –CO2CH2–), 7.26 (m, 4H, Ar-H), 13.64 (s, –NH). ESI-MS:
m/z 273.5500 (M+1).
Ethyl 4-(2-chlorophenyl)-6-methyl-2-oxo-1,2-dihydropyrimidine-5-carboxylate
(2h). IR (KBr):
m .
= 3324, 3225, 2810, 1709, 1668, 1431, 762 cmÀ1 1H
(400 MHz, DMSO-d6): d 0.72 (t, 3H, J = 7.2 Hz, –CH3), 3.32 (s, 3H, –CH3), 3.84
(q, 2H, J = 7.2 Hz, –CO2CH2–), 7.34–7.49 (m, 4H, Ar-H), 12.60 (s, –NH). ESI-MS:
m/z 293.4813 (M+1).
Ethyl
(2i). IR (KBr):
6-methyl-4-(3-nitrophenyl)-2-oxo-1,2-dihydropyrimidine-5-carboxylate
m
= 3412, 3319, 3217, 2986, 1533, 1448 cmÀ1 1H (400 MHz,
.
DMSO-d6): d 0.83 (t, 3H, J = 7.2 Hz, –CH3), 2.46 (s, 3H, –CH3), 3.95 (q, 2H,
J = 7.2 Hz, –CO2CH2–), 7.75 (m, 1H, Ar-H), 7.88 (m, 1H, Ar-H), 8.24 (s, 1H, Ar-H),
8.35–8.37 (m, 1H, Ar-H), 12.59 (s, –NH). ESI-MS: m/z 304.4072 (M+1).
Ethyl 4-(5-bromo-2-methoxyphenyl)-6-methyl-2-oxo-1,2-dihydropyrimidine-
Spectral data of 2g: mp 182–184 °C, IR (KBr):
m = 3309, 3216, 2983, 2811, 1707,
1649, 1434, 803 cmÀ1 1H (400 MHz, DMSO-d6): d 0.86 (t, 3H, J = 7.2 Hz, –CH3),
.
2.40 (s, 3H, -CH3), 3.95 (q, 2H, J = 7.2 Hz, –CO2CH2–), 7.44 (d, 2H, J = 8.4 Hz, Ar-
H), 7.53 (d, 2H, J = 8.4 Hz, Ar-H), 12.44 (s, –NH). ESI-MS: m/z 293.4886 (M+1).
Spectral data of the products (2a–2l):
5-carboxylate (2j). IR (KBr): m .
= 3327, 2974, 2844, 1715, 1654, 1441, 807 cmÀ1
1H (400 MHz, DMSO-d6): d 0.85 (t, 3H, J = 7.2 Hz, –CH3), 2.43 (s, 3H, –CH3), 3.68
(s, 3H, –OCH3), 3.89 (q, 2H, J = 7.2 Hz, –CO2CH2–), 7.01 (d, 1H, J = 8.4 Hz, Ar-H),
7.46 (s, 1H, Ar-H), 7.59 (d, 1H, J = 8.4 Hz, Ar-H), 12.38 (s, –NH). ESI-MS: m/z
367.3996 (M+1), 389.3737 (M+Na)
Ethyl 6-methyl-2-oxo-4-phenyl-1,2-dihydropyrimidine-5-carboxylate (2a). IR
(KBr):
m .
= 3309, 2981, 2816, 1730, 1652, 1602, 14, 682 cmÀ1 1H (400 MHz,
DMSO-d6): d 0.93 (t, 3H, J = 7.2 Hz, –CH3), 2.62 (s, 3H, –CH3), 4.02 (q, 2H,
J = 7.2 Hz, –CO2CH2–), 7.4 (m, 3H, Ar-H), 7.6 (m, 2H, Ar-H), 13.65 (s, –NH). ESI-
MS: m/z 259.452 (M+1).
5-acetyl-4-(4-chlorophenyl)-6-methylpyrimidin-2(1H)-one (2k). IR (KBr):
m
= 3361, 3059, 2806, 1641, 1573, 1426, 801 cmÀ1 1H (400 MHz, DMSO-d6):
.
d 1.91 (s, 3H, –CH3), 2.30 (s, 3H, –CH3), 7.48 (d, 2H, J = 8.4 Hz, Ar-H), 7.57 (d, 2H,
J = 8.4 Hz, Ar-H), 12.36 (s, –NH). ESI-MS: m/z 263.3372 (M+1).
Ethyl 4-(4-methoxyphenyl)-6-methyl-2-oxo-1,2-dihydropyrimidine-5-carboxylate
(2b). IR (KBr):
m
= 3422, 3084, 2986, 2836, 1667, 1594, 1438, 796 cmÀ1
.
1H
5-acetyl-6-methyl-4-p-tolylpyrimidin-2(1H)-one (2l). IR (KBr):
m = 3362, 30005,
(400 MHz, DMSO-d6): d 1.03 (t, 3H, J = 7.2 Hz,– CH3), 2.58 (s, 3H, –CH3), 3.85 (s,
3H, –OCH3), 4.09 (q, 2H, J = 7.2 Hz, –CO2CH2–), 6.93 (m, 2H, Ar-H), 7.6 (m, 2H,
Ar-H), 13.67 (s, -NH). ESI-MS: m/z 289.5029 (M+1).
2805, 1691, 1590, 1428, 830 cmÀ1 1H (400 MHz, DMSO-d6): d 1.85 (s, 3H, –
.
CH3), 2.28 (s, 3H, –CH3), 2.37 (s, 3H, –CH3), 7.31 (d, 2H, J = 8.0 Hz, Ar-H), 7.37 (d,
2H, J = 8.0 Hz, Ar-H), 12.25 (s, –NH). ESI-MS: m/z 243.3773 (M+1).