Efficient Synthesis in Three Steps and Spectral Determination of Methyl-5-[(o-, m-, and p-substituted-phenylthio]-2-Benzimidazolecarbamates

Article abstract of DOI:10.1002/jhet.5570410220

The preparation and spectral properties of ten novel methyl 5-[(o-, m-, and p-substituted)-phenylthio]-2-benzimidazolecarbamates with possible pharmacological activity as antihelmintics is described; by condensation and cyclization between 5-methylthioures sulfate chloroformic acid methyl ester and 3,4-diaminophenyl-substituted-phenylthio ether dissolved in ethanol. The structures of all final products were corroborated by ir; ¹H-nmr, ¹³C-nmr and ms.

Full text of DOI:10.1002/jhet.5570410220

Mar-Apr 2004
273
Efficient Synthesis in Three Steps and Spectral Determination of
Methyl-5-[(o-, m-, and p-substituted-phenylthio]-2-
Benzimidazolecarbamates
Eduardo Cortés Cortés*[a][1], Rafael Sosa Mendoza [a], Maximiliano Santibáñez
Gutiérrez [a], and Olivia García-Mellado de Cortés [b]
[a] Instituto de Química [2], Universidad Nacional Autónoma de México. Circuito Exterior, Ciudad
Universitaria, Coyoacán 04510, México, D.F.
[b] F.E.S., Cuautitlán-UNAM, Av. 1° de Mayo s/n, Campo 1, Cuautitlán Izcalli, Edo. de México 5470 México.
Estancia Post-Doctoral, Instituto de Química, UNAM.
Received July 16, 2004
The preparation and spectral properties of ten novel methyl 5-[(o-, m-, and p-substituted)-phenylthio]-2-
benzimidazolecarbamates with possible pharmacological activity as antihelmintics is described; by conden-
sation and cyclization between 5-methylthioures sulfate chloroformic acid methyl ester and 3,4-
diaminophenyl-substituted-phenylthio ether dissolved in ethanol. The structures of all final products were
1
13
corroborated by ir; H-nmr, C-nmr and ms.
J. Heterocyclic Chem., 41, 273 (2004).
There have been many reports concerning pharmacolog-
ical interest of benzimidazole carbamate derivatives as
antihelmintics which have good efficacy against gastroin-
testinal nematodes of laboratory and domestic animals.
The addition of a phenylthio group to a chemotherapeuti-
cally active molecule can considerably increase its eff i-
cacy [3-8]. Recently, it has been reported that benzimida-
zole antihelmintics are useful for the treatment of crypto-
coccal infection, including meningitis, in particular for
AIDS patients [9].
In this report, we describe the synthesis of ten new
derivatives of 2-benzimidazole carbamates III, 1-10
(Figure 1). The synthesis of these compounds was carried
out by three steps as shown in Scheme I. The reaction of 5-
chloro-2-nitroaniline was heated six hours under reflux in
dimethylformamide anhydrous with the corresponding
substituted-phenylthiol in the presence of anhydrous
potassium carbonate.
After cooling, the reaction mixture was diluted with
water, the 3-amino-4-nitrophenyl-(R-phenyl-thio)ether, I,
that had precipitated, was collected by filtration with suc-
tion; the corresponding derivatives have been obtained in
60-98%.
To prepare the 3,4-diaminophyl-(substituted-phenylthio)
ethers we followed two routes.
Route 1.
This route was used only when the R-substituents are (o-,
m-, p-) CH3O- and H-. The 3-amino-4-nitrophenyl-(substi-
tuted-phenylthio)ether was hydrogenated in ethanol in pres-
ence of Pd/C 10% under a pressure of 60 pounds/inch2 at
room temperature, the catalyst was then removed by filtra-
tion and the solution was evaporated under reduced

274
E. Cortés Cortés, R. S. Mendoza, M. Santibáñez Gutiérrez, and
O. García-Mellado de Cortés
Vol. 41
pressure. The 3,4-diaminophenyl-(substituted-phenylthio)-
ethers have been obtained in 80-98% yield.
hydroxide solution were added dropwise, while stirring at
a temperature of 5-8°, in the mixture cooled with ice-
water. After been stirred for forty minutes, the reaction
mixture was neutralized with glacial acetic acid solution
and the 3,4-diaminophenyl-(substituted-phenylthio)-ether
dissolved in ethanol and the mixture was stirred and heated
at 95° for twenty four hours, during this time methylmer-
captan was removed.After having allowed the entire reac-
tion mixture to cool with ice-water, the methyl 5-[(o-, m-,
p-substituted)phenylthio]-2-benzimidazolecarbamate that
had formed was collected by suction filtration to yield III,
1-10 (57-90%).
The infrared spectrum of compounds 1-10 displayed
absorptions at 3342-3397 cm-1 for N-H stretching, at
2835-2625 cm-1 for NH-CO stretching, at 1721-1698 cm-1
for C=O stretching, at 1657-1627 cm-1 for C=N stretching,
at 1206-1264 cm-1 for C-O stretching, at 1196-1127 cm-1
and 1024-1006 cm-1 for C-N stretching and the corre-
sponding absorptions for the R-substituent. In the 1H-nmr
Route 2.
This route was used only when the R-substituents are Cl,
Br, NH2, and F. The 3-amino-4-nitrophenyl-(substituted-
phenylthio)ether was dissolved in ethanol, subsequently,
was added stannous chloride, sodium borohydride and the
mixture was stirred and heated at 60-80 °C for three hours.
After the reaction mixture was cooled with ice-water, sub-
sequently washed with cold water and aqueous sodium
hydroxide solution, until neutral pH was attained. The
ethanol was evaporated in vacuo and the residue was fil-
tered, the solution was extracted with dichloromethane and
dried with anhydrous sodium sulfate and evaporated to
obtain the 3,4-diaminophenyl-(substituted-phenylthio)
ethers in 60-90% yield.
The S-methylthiourea sulfate was dissolved in water and
then methyl chloroformate and an aqueous sodium
Table 1
C NMR Spectral Data for Compounds 1-10
13
Compounds
R
1
2
3
4
5
6
8
9
10
H
o-OCH
m-OCH
p-OCH
o-Br
p-Br
p-Cl
o-NH
2
p-F
3
3
3
C-2
C-3a
C-4
C-5
C-6
C-7
C-7a
C-1'
148.3
137.2
119.1
123.5
126.8
114.9
137.0
138.4
149.0
137.0
120.0
124.2
128.0
114.1
137.0
127.9
154.4
138.0
119.5
122.9
126.8
114.4
137.5
148.5
148.0
137.0
116.3
127.0
124.4
114.5
136.0
126.9
148.4
138.0
119.9
121.9
126.7
115.3
137.0
140.5
148.2
137.0
119.2
122.5
126.7
114.8
136.0
138.2
148.2
135.0
116.2
122.6
127.0
114.0
134.1
137.8
147.9
139.0
129.3
122.5
121.4
113.1
138.5
127.9
154.7
137.0
118.0
125.6
126.1
112.5
136.0
133.0 (d)
4
J
=3.3
C-F
C-2'
C-3'
C-4'
C-5'
C-6'
C=O
127.6
129.1
125.8
129.0
127.0
156.0
110.2
127.0
121.8
128.2
114.3
159.4
119.4
129.4
109.1
132.6
115.1
158.7
115.0
132.0
119.0
127.1
126.6
128.2
132.6
131.7
129.2
118.4
129.0
131.0
129.1
128.9
130.3
128.0
129.0
153.5
114.1
129.3
116.5
135.1
130.3 (d)
3
J
=7.7
C-F
115.3 (d)
2
J
=21.8
C-F
160.8 (d)
1
J
=243.6
C-F
115.3 (d)
2
J
=21.8
C-F
130.3 (d)
3
J
=7.7
C-F
154.5
52.5
-
155.8
52.2
56.0
154.3
52.1
54.7
154.6
52.5
55.2
154.4
52.5
-
154.4
52.3
-
154.4
52.6
-
154.5
51.8
-
154.6
52.5
-
OCH
R
3
13
Note: The numbering of the phenyl ring is only for the assignment of the chemical shifts of the carbon in C nmr spectra.

Mar-Apr 2004
Methyl-5-[(o-, m-, and p-substituted-phenylthio]-2-Benzimidazolecarbamates
275
cooling with an ice-water bath. After having stirred for forty min-
utes the reaction mixture was combined with aqueous glacial
acetic acid solution (0.6 ml of glacial acetic acid in 5.0 ml of
water) at room temperature and subsequently was added the 3,4-
spectra of derivatives 1-10 the presence of two broad pro-
ton signals at δ 11.8-11.6 that exchanges with deuterium
oxide was consistent with the presence of two amine
groups. One other proton signal at δ 7.5-7.4 as a doublet
was assigned to the proton joined to C-7. The other one-
proton signal at δ 7.6-7.3, a doublet was assigned to the
proton joined to C-4. The presence of a one-proton doublet
of doublets signal at δ 7.3-7.0 was consistent with the pres-
ence of the proton joined to C-6.
The aromatic protons appeared as a multiplet and an
AA'BB' system at δ 7.6-6.6. A three proton signal at δ 3.8-
3.7 as a singlet was assigned to the methoxy protons
joined to C-2" of the ester group, and the signals for the R-
substituents.
The 13C-nmr spectra of the compounds 1-10 are given in
Table 1. The signals were confirmed by using HETCOR;
LONG RANGE HETCOR, FLOCK, COSY and NOESY
nmr experiments operating at 300 and 500 MHz.
The mass spectra of compounds 1-1 0 exhibit a stable
molecular ion that is the base peak in most of the com-
pounds analyzed. The main fragmentation was consistent
with the assigned structures.
-3
diaminophenyl-phenyl-substituted-phenylthio ether (1.0 x 10
mole) dissolved in ethanol (5.0 ml). The mixture was stirred and
heated at 95° for twenty four hours, during which time
methylmercaptan separated. The entire reaction mixture was
cooled with ice-water, then the methyl 5-[(o-, m-, and p-substi-
tuted)phenylthio]-2-benzimidazolecarbamate that had formed
was collected by filtration to yield II, 1-10 (57-90%).
Methyl-5-phenylthio-2-benzimidazolecarbamate (1).
This compound was obtained as whitish needles in 88% yield,
mp 298°; ir (chloroform): ν NH 3339; NH-CO 2850-2667; C=O
-1
1709; C=N 1630; C-O 1273 and 1098; C-N 1194 and 1130 cm .
1
H-nmr (deuteriochloroform): δ 3.71 (s, 3H, COOCH ), 7.1 (dd,
3
1H, J=2.1, 8.1 Hz, 6-H), 7.1 (dd, 2H, J=1.2, 8.4 Hz, 2'-H and 6'-
H), 7.14 (dt, 1H, J=1.2, 7.2 Hz, 4'-H), 7.26 (dt, 2H, J=1.3, 7.5 Hz,
3'-H and 5'-H), 7.4 (d, 1H, J=8.4 Hz, 7-H), 11.8 (bs, 2H, N-H,
+
+
deuterium oxide exchangeable); ms: m/z 299 (M ); 301 [M+2] .
Anal. Calcd. for C N O S: C, 60.18; H, 4.38; N, 14.04.
Found. C, 60.29, H, 4.45; N, 14.13.
H
15 13
3 2
Methyl-5-(o-methoxy phenylthio)-2-benzimidazolecarbamate (2).
The relative abundance of the principal fragment ions in
the compounds 1-10 have some common features and the
proposed fragmentation pathways leading to the formation
of a number of important daughter ions have been con-
firmed by the corresponding parent ion spectra in colli-
sion-induced dissociation experiments. The elemental
composition of the molecular ion was determined by exact
mass measurements. The important fragment ions are: M+;
[M-32]+; [M-33]+; [M-58]+; [M-59]+ m/z 266; 239, 224;
211, 190; 171 and 109.
This compound was obtained as whitish needles in 57% yield,
mp 198°; ir (chloroform): ν NH 3396, NH-CO 2835-2625, C=O
-1
1729, C=N 1647, C-O 1271 and 1068, C-N 1190 and 1024 cm .
1
H-nmr (deuteriochloroform): δ 3.85 (s, 3H, COOCH ); 3.9 (s, 3H,
3
-OCH ), 6.8 (dt, 1H, J=1.3, 7.5 Hz, 5'-H), 6.82 (dd, 1H, J=1.2, 8.3
3
Hz, 6'-H), 6.86 (dd, 1H, J=1.2, 8.1 Hz, 3'-H), 7.12 (dt, 1H, J=1.4,
8.1 Hz, 4'-H), 7.31 (dd, 1H, J=1.2, 8.4 Hz, 6-H), 7.5 (d, 1H, J=8.4
Hz, 7-H), 7.67 (d, 1H, J=1.4 Hz, 4-H), 11.8 (bs, 2H, N-H, deu-
+
+
terium oxide exchangeable), ms: m/z 329 (M ), 331 [M+2] .
Anal. Calcd. For C N O S: C, 58.34; H, 4.59; N, 12.76.
Found. C, 58.22; H, 4.67, N, 12.64.
H
16 15
3 3
Methyl-5-(m-methoxyphenylthio)-2-benzimidazolecarbamate (3).
EXPERIMENTAL
This compound was obtained as whitish needles in 88% yield,
mp 180°, ir (chloroform): ν NH 3342, NH-CO 2840-2674, C=O
1706; C=N 1632, C-O 1266 and 1060, C-N 1143 and 1020 cm-1.
The ir spectra were recorded on a Nicolet Magna TR-750 spec-
1
trophotometer. The H-nmr spectra were recorded on a Varian
1
13
Unity 300 spectrometer operating at 300 MHz and the C-nmr
H-nmr (deuteriochloroform): δ 3.7 (s, 3H, COOCH ), 3.8 (s,
3
3H, OCH ), 6.61 (d, 1H, J=1.7 Hz, 2'-H), 6.67 (dd, 1H, J=1.4, 7.9
spectra were recorded on a Varian Unity 500 spectrometer oper-
ating at 125 MHz in deuteriochloroform solution containing
tetramethylsilane as the internal standard with chemical shifts δ
(ppm) expressed downfield from tetramethylsilane. The mass
spectra were measured on a JEOL JMS-AC505 and JEOL MS-
SX 102A high-resolution mass spectrometer with accurate mass
determination of the molecular ion and the principal fragment
ions, using the direct inlet system. The spectra were recorded by
electron impact at an ionization chamber temperature of 190° and
ionizing electron energy of 70 eV.
3
Hz, 4'-H), 6.69 (dd, 1H, J=1.4, 7.9 Hz, 6'-H), 7.1 (5, 1H, J=8.9
Hz, 5'-H), 7.2 (dd, 1H, J=1.6, 8.2 Hz, 6-H), 7.5 (d, 1H, J=8.2 Hz,
7-H), 7.6 (d, 1H, J=1.4 Hz, 4-H), 11.7 (bs, 2H, N-H, deuterium
+
+
oxide exchangeable); ms: m/z 329 (M ), 331 [M+2] .
Anal. Calcd. For C N O S: C, 58.34; H, 4.59; N, 12.76.
Found: C, 58.45; H, 4.46; N, 12.84.
H
16 15
3 3
Methyl-5-(p-methoxy phenylthio)-2-benzimidazolecarbamate (4).
This compound was obtained as whitish needles in 67% yield,
mp 223°, ir (chloroform): ν NH 3359; NH-CO 2835-2670; C=O
Compounds I and II were prepared following methods devel-
oped by us, with modifications [9-10].
-1
1716; C=N 1642; C-O 1267 and 1065; C-N 1193 and 1015 cm .
1
H-nmr (deuteriochloroform): δ 3.73 (s, 3H, COOCH ), 3.74 (s,
3
3H, OCH ), 6.91 and 7.25 (AA'BB', 4H, J=8.7 Hz, phenyl pro-
General Procedure for the Synthesis of the Methyl 5-[(o-, m-, and
p-substituted)phenylthio-2-benzimidazolecarbamates, III, 1-10.
3
tons of "C" ring); 7.06 (dd, 1H, J=1.8, 8.1 Hz, 6-H), 7.34 (d, 1H,
J=1.5 Hz, 4-H); 7.35 (d, 1H, J=8.4 Hz, 7-H); 11.7 (bs, 2H, N-H,
-3
S-Methylthiourea sulfate (1.25 x 10 mole) was dissolved in
+
+
-3
deuterium oxide exchangeable). ms: m/z 329 (M ); 331 [M+2] .
Anal. Calcd. For C N O S: C, 58.34; H, 4.59; N, 12.76.
Found: C, 58.43; H, 4.68; N, 12.87.
water (3.0 ml) and then chloroformic acid methyl ester (2.4 x 10
mole) and 25% aqueous sodium hydroxide solution (10 ml)
were added dropwise, while stirring at a temperature of 3° to 6°
H
16 15
3 3

276
E. Cortés Cortés, R. S. Mendoza, M. Santibáñez Gutiérrez, and
O. García-Mellado de Cortés
Vol. 41
Methyl-5-(o-bromo phenylthio)-2-benzimidazolecarbamate (5).
2848-2670; C=O 1707; C=N 1628; C-O 1278 and 1099; C-N
-1
1137 and 980 cm . H-nmr (deuteriochloroform): δ 3.75 (s, 3H,
1
This compound was obtained as brownish nedles in 58% yield.
mp>300°; ir (chloroform): ν NH 3397; NH-CO 2854-2650; C=O
COOCH ); 6.64 (dt, 1H, J=1.5, 7.5 Hz, 5'-H); 6.8 (dd, 1H, J=1.2,
3
8.1 Hz, 3'-H); 7.03 (dd, 1H, J=1.6, 8.2 Hz, 6-H); 7.15 (dt, 1H,
J=1.5, 7.6 Hz, 4'-H); 7.27 (d, 1H, J=1.5 Hz, 4-H); 7.37 (d, 1H,
J=8.4 Hz, 7-H); 7.38 (dd, 1H, J=1.8, 7.6 Hz, 6'-H); 11.8 (bs, 2H,
-1
1
1721; C=N 1657; C-O 1278 and 1100; C-N 1196, 1011 cm ; H-
nmr (deuteriochloroform): δ 3.76 (s, 3H, COOCH ); 6.58 (dd,
3
1H, J=1.4, 8.1 Hz, 3'-H); 7.04 (dt, 1H, J=1.3, 8.1 Hz, 4'-H); 7.18
(dt, 1H, J=1.3, 8.1 Hz, 5'-H); 7.23 (dd, 1H, J=1.4, 8.4 Hz, 6-H);
7.51 (d, 1H, J=8.4 Hz, 7-H); 7.58 (d, 1H, J=1.5 Hz, 4-H); 7.59
(dd, 1H, J=1.4, 7.8 Hz, 6'-H); 11.8 (bs, 2H, N-H, deuterium oxide
+
N-H, deuterium oxide exchangeable); ms: m/z 314 (M ); 316
+
[M+2] .
Anal. Calcd. For C H N O S: C, 57.31; H, 4.49; N, 17.83.
15 14 4 2
Found: C, 57.19; H, 4.37; N, 17.93.
+
+
+
exchangeable). ms: m/z 377 (M ), 379 [M+2] ; 381 [M+4] .
Anal. Calcd. for C BrN O S: C, 47.63; H, 3.20, N, 11.11.
Found: C, 47.72, H, 3.12; N, 11.18.
H
Methyl-5-(p-fluorophenylthio)-2-benzimidazolecarbamate (10).
15 12
3 2
This compound was obtained as brownish needles in 80%
yield; mp 187°; ir (chloroform): ν NH 3343; NH-CO 2856-2680;
C=O 1705; C=N 1639; C-O 1275 and 1127; C-N 1135 and 1010
Methyl-5-(p-bromophenylthio)-2-benzimidazolecarbamate (6).
This compound was obtained as brownish needles in 90%
yield; mp 230°; ir (chloroform): ν NH 3376; NH-CO 2855-2674,
C=O 1698; C=N 1648; C-O 1272 and 1104, C-N 1198 and 1006
-1
1
cm ; H-nmr (deuteriochloroform): δ 3.85 (s, 3H, COOCH ),
3
6.95 and 7.22 (AA'BB', 4H, J =8.7 Hz; J =8.4 Hz, 3'-H and
H-H
H-F
5'-H; J =9.1 Hz; J =5.4 Hz, 2'-H and 6'-H); 7.23 (dd, 1H,
-1
1
H-H
H-F
cm ; H-nmr (deuteriochloroform) δ 3.76 (3, 3H, COOOH ),
3
J=1.5, 7.9 Hz, 6-H); 7.45 (d, 1H, J=7.5 Hz, 7-H); 7.6 (d, 1H,
J=1.5 Hz, 4-H); 11.8 (bs, 2H, N-H, deuterium oxide exchange-
7.04 and 7.44 (AA'BB', 4H J=8.4 Hz, phenyl protons of "C"
ring), 7.2 (dd, 1H, J=1.4, 8.1 Hz, 6-H), 7.45 (d, 1H, J=8.4 Hz, 7-
H), 7.53 (d, 1H, J=1.5 Hz, 4-H), 11.6 (bs, 2H, N-H, deuterium
+
+
able); ms: m/z 317 (M ); 319 [M+2] .
Anal. Calcd. For C FN O S: C, 56.77; H, 3.81; N, 13.24.
Found: C, 56.60; H, 3.88; N, 13.15.
H
+
+
15 12
3 2
oxide exchangeable); ms: m/z 377 (M ); 379 [M+2] , 381
+
[M+4] .
Anal. Calcd. for C
H BrN O : C, 47.63, H, 3.2, N. 11.11.
15 12 3 2
Found: C, 47.48; H, 3.10; N, 11.01.
Acknowledgements.
We wish to thank H. Ríos for the nmr determination; and R.
Patiño and M. Adaya for the ir determination.
Methyl-5-(m-chlorophenylthio)-2-benzimidazolecarbamate (7).
This compound was obtained as brownish needles in 60%; mp
215°, ir (KBr): ν NH 3346, NH-CO 2840-2655, C=O 1708, C=N
1649; C-O 1274 and 1095, C-N 1144 and 1005 cm ; H-nmr
(deuteriochloroform): it was not possible to obtain the spectrum,
+
because it is not soluble; ms. m/z 333 (M ); 335[M+2]+; 337
+
[M+4] .
REFERENCES AND NOTES
-1
1
[1] Author to whom correspondence should be addressed.
[2] Contribution No. 2458 from Instituto de Química, UNAM.
[3] H. Loewe, Proceedings 3rd International Congress of
Anal. Calcd. for C
H ClN O S: C, 53.97; H, 3.62, N, 12.59.
15 12 3 2
Found: C, 53.83; H, 3.70; N, 12.45.
Chemotherapy, 1552 (1964); H. Loewe, J. Urbanietz and H. Mieth;
th
5
International Congress of Chemotherapy, 645 (1967).
Methyl-5-(p-chlorophenylthio)-2-benzimidazolecarbamate (8).
[4] H. Mrozik, H. Jones, F. Friedman, G. Schwartzkopf, R. A.
Schardt, A. A. Patchett, D. R. Hoff, J. J. Yakstis, R. F. Riek, D. A.
Ostlind, G. A. Plishker, R. W. Butler, A. C. Cuckler and W. C.
Campbell, Experientia, 25, 883 (1969).
This compound was obtained as brownish needles in 61%, mp
225°, ir (chloroform): ν NH 3372; NH-CO 2847-2640; C=O
-1
1702, C=N 1649; C-O 1275 and 1102, C-N 1127 and 1020 cm ;
[5]
G e r. Offen. 2,063,857 (Cl. C 07d), Janssen
1
H-nmr (deuteriochloroform): δ 3.75 (s, 3H, COOCH ); 7.08 and
3
Pharmaceutica N. V. (1971): Chem. Abstr .75, 118319n (1971).
[6] P. Actor, Nature, 215, 321 (1967).
[7] Ger. Offen. 2,131,361 (Cl. C07d) Farbwerke Hoechst AG
(1972); Chem. Abstr 78, 84413h (1973).
7.32 (AA'BB', 4H, J=8.7 Hz, phenyl protons of "C" ring); 7.2 (dd,
1H, J=1.7, 8.1 Hz 6-H); 7.46 (d, 1H, J=8.4 Hz, 7-H); 7.53 (d, 1H,
J=1.5 Hz, 4-H); 11.7 (bs, 2H, N-H, deuterium oxide exchange-
+
+
+
able); ms: m/z 333 (M ); 335 [M+2] ; 337 [M+4] .
Anal. Calcd. For C ClN O S: C, 53.97; H, 3.62; N, 12.59.
Found: C, 54.08; H, 3.56; N, 12.71
H
[8] Q. A. McKellar and E. W. Schott, J. Vet. Pharmacol.
Therap., 13, 223 (1990).
15 12
3 2
[9] E. Cortés and L. A. Araluce, J. Heterocyclic Chem., 34,
745 (1997).
Methyl-5-(o-amine phenylthio)-2-benzimidazolecarbamate (9).
This compound was obtained as brownish needles in 60%
yield, mp 245°; ir (chloroform): ν NH 3462 and 3334; NH-CO
[10] E. Cortés and M. P. Sánchez, J. Heterocyclic Chem., 36,
611 (1999).