Studies with 2-arylhydrazononitriles: A novel simple, efficient route to 5-acyl-2-substituted-1,2,3-triazol-4-amines

Article abstract of DOI:10.1002/jhet.5570440335

(Chemical Equation Presented) Efficient route to 5-acyl-2-substituted-1,2, 3-triazol-4-amines via reaction of 3-oxo-2-(arylhydrazono)-pentanenitrile with hydroxylamine hydrochloride is reported. X-ray crystal structure has been made to confirm the structu

Full text of DOI:10.1002/jhet.5570440335

May-Jun 2007
725
Studies With 2-Arylhydrazononitriles: A Novel Simple, Efficient
Route To 5-Acyl-2-Substituted-1,2,3-Triazol-4-Amines
Suzan Ibrahim Aziz [a], Hany Fakhry Anwar* [a], Daisy Hanna Fleita [b]
and Mohamed Hilmy Elnagdi [a]
[a] Chemistry Department; Faculty of Science; Cairo University; Giza; A. R. Egypt.
[b] Chemistry Department; American University in Cairo; Egypt.
e-mail: hany_fahkry@yahoo.com
Received June 9, 2006
OH
O
N
NH2
O
N
O
NH
Ar
O
N
CN
N
O
N
NH
Ar
N
O
N
NH2
Ar
N
N
N
Ar
Efficient route to 5-acyl-2-substituted-1,2,3-triazol-4-amines via reaction of 3-oxo-2-(arylhydrazono)-
pentanenitrile with hydroxylamine hydrochloride is reported. X-ray crystal structure has been made to
confirm the structure of reaction products.
J. Heterocyclic Chem., 44, 725 (2007).
INTRODUCTION
O
O
CN
CN
ArN NCl
O
H
Arylhydrazononitriles are readily obtainable materials
[1-3] and their chemistry has been extensively
investigated in our laboratories [4-6]. The utility of some
of the arylhydrazononitriles by several other authors in
published [7] and patent [8,9] literature prompted us to
explore further interesting synthetic potentials of such
compounds as precursors for heteroaromatic amines that
could be utilized as intermediates in dye and
pharmaceutical industries [10]. In the present article we
report a novel route for 5-acyl-2-aryl-1,2,3-triazole-4-
amines that may be interesting as precursors for the
synthesis of the potentially biologically active condensed
1,2,3-triazole ring. The biological importance of Zaprinast
[11], Tazobactam [12] and some anti-HIV agents [13,14]
that incorporate such ring in their structures has been well
established.
CN
N
N
N
NH
Ar
2a-c
Ar
1
3
NH2OH.HCl/
CH3COONa/
DMF
NH2OH.HCl/
CH3COONa/
EtOH
O
OH
O
N
NH2
(Et)3N
EtOH
NH2
N
N
N
N
NH
Ar
Ar
5a-c
4a
Ac2O
Ar
Ac2O
PhNCS
O
O
O
N
O
N
NHCSNHPh
N
N
N
O
O
RESULTS AND DISCUSSION
N
N
N
N
N
N
O
Reaction of 2-oxopentanenitrile (1) with aromatic
diazonium salts afforded the corresponding coupling
products (Scheme 1). Although these can be represented
as 2 or 3, several authors [15,16] have assumed the
predominance of 3 to account for the deshielding of NH.
However, X-ray crystal structure (cf. Figure 1 and Table 1
for selected bond lengths and bond angles), clearly
indicates that these compounds exit in the antiform 2a.
Thus deshielding of hydrazone NH may be due to the
creation of positive charge on hydrazone NH through lone
Ar
Ar
6a
8a-c
7a
a, Ar= p-Cl-C6H4
b, Ar=o-Cl-C6H4
c, Ar=p-CH3-C6H4
Scheme 1
pair delocalization. Similar assumption has been recently
made by El-Dusouqui et al [16]. Possible deschielding via
hydrogen bonding with NMR solvent (DMSO) cannot be

726
S. I. Aziz, H. F. Anwar, D. H. Fleita and M. H. Elnagdi
Vol 44
over looked as in CDCl3 the hydrazone NH resonance
appears at 9.23 ppm.
zation has afforded the 1,2,3-triazole 7a. Later, this was
confirmed by X-ray crystal structure (cf. Figure 2 and
Table 2 for selected bond lengths and bond angles), which
indicates that the N-2 lone pair is extensively delocalized
at both N-1 and N-3. Although routes to amino-1,2,3-
triazoles are well established [19], but these routes could
not be adapted for the preparation of 2-substituted-1,2,3-
triazol-4-amines (Scheme 1).
In an earlier study, the formation of N-oxide on cyclizing
amidoxime has normally been observed [19]. In this work,
when the amidoxime 4a was refluxed in DMF in the
presence of excess of triethylamine, the 1,2,3-triazole-4-
amine 5 was produced. Typical for heteroaromatic amines,
the amino function in 5a-c reacted with phenylisothio-
cyanate yielding the thiourea derivative 8a-c. However,
attempts to diazotize this amino function failed.
Similar to the behaviour of 2 the nitrile 9, recently
obtained in our laboratories via reacting 11 with benzene-
diazonium chloride [3], reacted with hydroxylamine
hydrochloride in DMF solution to yield the arylazo-1,2,3-
triazoleamime 10. In addition, when compound 11 reacted
with hydroxylamine hydrochloride, the amidoxime 12 was
produced and then cyclized in Ac2O into acetylamino-
isoxazole 13 (Scheme 2). These results agree with our
earlier report [3], but contradict our findings shown above.
Figure 1. X-ray crystal structure for compound 2a.
Table 1 selected bond lengths and bond angles.
Geometric parameters (Å, °.), for compound 2a
Bond
Bond lengths
O2—C6
N3—N4
N3—C11
N4—C9
C6—C11
1.213
1.301
1.313
1.415
1.475
NC
CHO
NC
OH
Ph
N
CN
N
N
N
N
N
NH
Ar
NH
Bond
Bond angles
NHPh
Ar
N4—N3—C11
N3—N4—C9
O2—C6—C11
O2—C6—C15
C11—C6—C15
N4—C9—C5
N4—C9—C8
N3—C11—C6
N3—C11—C13
C6—C11—C13
121.47
118.97
118.5
122.2
119.3
121.2
118.5
118.8
123.9
117.3
9
11
12
NH2OH.HCl/
NaOAc/
DMF
O
Ar
N
HN
N
Ph
N
NH2
N
N
O
N
N
13
11-13, Ar= p-Cl-C6H4
N
Ph
10
El-Bannany et al [17] have earlier reported the formation
of 1,2,3-triazoles from reaction of some hydrazononitriles
with phenylhydrazine. This synthesis however is rather
atom non economic as it involves elimination of aniline.
We thus believe that the utility of hydroxylamine in these
transformations is more attractive approach.
Compound 2a, reacted readily with hydroxylamine
hydrochloride in ethanolic sodium acetate to yield
amidoxime 4a, in 91 % yield. This was cyclized on reflux
with acetic anhydride to yield diacylated dehydration
products. At first glance we assumed formation of
isoxazoles 6a in analogy to well established structures
suggested for the products of cyclization of amidoximes
in acid and base media [18]. However, we noted in 13C
NMR the presence of low field carbonyl carbon at ꢀ 195.7
ppm. We thus considered the possibility that the cycli-
Scheme 2
In conclusion we succeeded to offer a new and efficient
general route to synthesize substituted 1,2,3-triazole
amines that could be of importance for utility in dyes,
pharmaceutical and agrochemical industries.
EXPERIMENTAL
All melting points are uncorrected. IR spectra were recorded in
KBr disks using a Pye-Unicam SP-3000 IR spectrophotometer
and Testscan Shimadzu FT-IR 8000 series. H and 13C NMR
spectra were measured in DMSO-d6 at 400/100 and 300/75 MHz
on a Varian Gemini relative to DMSO (2.50 ppm for 1H and 39.5
ppm for 13C); chemical shifts are reported in ꢀ (ppm). Mass
spectra were measured on a GCMS-QP 1000-EX Shimadzu.
1

May-Jun 2007
A Novel Simple, Efficient Route To 5-Acyl-2-Substituted-1,2,3-Triazol-4-Amines
727
nitrile) the product was separated on standing, collected by
filtration and crystallized from ethanol.
2-[(4-Chloro-phenyl)-hydrazono]-3-oxo-pentanenitrile (2a).
This compound was obtained as yellow crystals, (yield 72%, 17.0 g)
mp 153-154°C; ir (KBr): ꢀmax 3436 (NH), 2212 (CN) 1667 cm-1
1
(CO); H nmr (400 MHz, DMSO-d6): ꢁ 1.05 (t, 3H, J = 7.3 Hz,
CH3), 2.89 (q, 2H, J = 7.3 Hz, CH2), 7.48 (d, 2H, J = 8.9 Hz, Ar-H),
7.54 (d, 2H, J = 8.9 Hz, Ar-H), 12.28 ppm (brs, 1H, NH); 13C nmr
(100 MHz; DMSO-d6): ꢁ 196.3, 142.0, 130.6, 130.4, 129.7, 119.2,
118.8, 114.6, 111.9, 30.5, 9.0 ppm; ms (70 eV) m/z 235 (M+, 40%),
+
111 (p-ClC6H4 ). Anal. calcd. for C11H10ClN3O: (235.67) C, 57.35;
H, 4.28; N, 17.83. Found: C, 57.35; H, 4.51; N, 17.34.
2-[(2-Chloro-phenyl)-hydrazono]-3-oxo-pentanenitrile (2b).
This compound was obtained as yellow crystals, (yield 66%,
15.5 g) mp 128-130°C; ir (KBr): ꢀmax 3420 (NH), 2217 (CN)
1
1654 cm-1 (CO); H nmr (300 MHz, DMSO-d6): ꢁ 1.07 (t, 3H, J
= 7.2 Hz, CH3), 2.87 (q, 2H, J = 7.2 Hz, CH2), 7.22-7.27 (m, 1H,
Ar-H), 7.42-7.76 (m, 3H, Ar-H), 11.00 ppm (brs, 1H, NH); ms
(70 eV) m/z 235 (M+, 39 %), 111 (o-ClC6H4 ). Anal. calcd. for
+
C11H10ClN3O: (235.67) C, 56.06; H, 4.28; N, 17.83. Found: C,
56.18; H, 4.20; N, 18.21.
3-Oxo-2-(p-tolyl-hydrazono)-pentanenitrile (2c). This
compound was obtained as yellow crystals, (yield 76%, 16.3 g)
mp 110-111°C; ir (KBr): ꢀmax 3240 (NH), 2215 (CN) 1683 cm-1
Figure 2. X-ray crystal structure for compound 7a.
1
(CO); H nmr (300 MHz, DMSO-d6): ꢁ 1.05 (t, 3H, J = 7.5 Hz,
CH3), 2.92 (s, 3H, CH3), 2.85 (q, 2H, J = 7.5 Hz, CH2), 7.20 (d,
2H, J = 8.4 Hz, Ar-H), 7.42 (d, 2H, J = 8.4 Hz, Ar-H), 12.12
Table 2 selected bond lengths and bond angles.
Geometric parameters (Å, °.), for compound 7a
+
ppm (brs, 1H, NH); ms (70 eV) m/z 215 (M+, 44%), 91 (C7H7 ).
Anal. calcd. for C12H13N3O: (215.25) C, 66.96; H, 6.09; N,
19.52. Found: C, 66.32; H, 6.34; N, 19.89.
Bond
N3—N7
Bond lengths
1.346
2-[(4-Chloro-phenyl)-hydrazono]-N-hydroxy-3-oxo-pentan-
amidine (4a). A mixture of 2a (0.235 g, 1 mmol) in 20 ml
EtOH, hydroxylamine hydrochloride (0.069 g, 1 mmol) and
sodium acetate (1 mmol) was heated under reflux for 2 hrs. the
reaction mixture was then poured into water, collected by
filtration and recrystallized from ethanol to give red crystal,
(yield 91%, 0.244 g) mp 110-112°C; ir (KBr): ꢀmax 3496 (NH),
N3—C12
N4—C12
N4—C23
O5—C10
N6—N7
N6—C14
N7—C9
Bond
N7—N3—C12
C10—N4—C12
C10—N4—C23
C12—N4—C23
N7—N6—C14
N3—N7—N6
N3—N7—C9
N3—C12—N4
N6—N7—C9
1.323
1.423
1.422
1.210
1.322
1.335
1.428
Bond angles
101.8
120.8
124.1
115.2
104.2
116.1
121.7
121.3
122.2
1
3379 (NH2, OH) 1647 cm-1 (CO); H nmr (400 MHz, DMSO-
d6): ꢁ 1.04 (t, 3H, J = 7.3 Hz, CH3), 2.97 (q, 2H, J = 7.3 Hz,
CH2), 6.53 (brs, 2H, NH2), 7.32 (d, 2H, J = 8.7 Hz, Ar-H), 7.45
(d, 2H, J = 8.7 Hz, Ar-H), 10.21 (brs, 1H, NH), 13.68 ppm (s,
1H, OH); 13C nmr (100 MHz; DMSO-d6): ꢁ 201.9, 151.9, 142.5,
129.5, 128.1, 127.3, 117.4, 31.6, 9.8 ppm; ms (70 eV) m/z 268
+
(M+, 34%) 251(M+- 17), (M+- p-ClC6H4), 111 (p-ClC6H4 ). Anal.
calcd. for C11H13ClN4O2: (268.70) C, 49.17; H, 4.88; N, 20.85.
Found: C, 49.65; H, 4.69; N, 20.40.
General procedure for the preparation of 1-(5-Amino-2-
aryl-2H-[1,2,3]triazol-4-yl)-propan-1-one (5a-c). Method A: A
mixture of 2a-c (1 mmol) in 15 ml DMF, hydroxylamine
hydrochloride (0.069 g, 1 mmol) and sodium acetate (1 mmol)
was heated under reflux for 40 min. the reaction mixture was
then poured into water, the solid collected by filtration and
recrystallized from ethanol to give 5a-c in 72, 63, 69 % yield,
respectively. Method B: A mixture of 4a (0.27 g, 1 mmol) and 5
ml triethylamine in 10 ml absolute EtOH was heated under
reflux for 3 hrs, left to cool, then poured into H2O, neutralized
by HCl. The solid product, so formed, was collected by filtration
and crystallized from EtOH to give 5a in 83 % yield.
Crystal structures were performed using Envaf Nonius 591 Kappa
CCD single crystal diffraction. Elemental analyses were carried
out by the Microanalytical Center of Cairo University, Giza,
Egypt. 3-Oxo-pentanenitrile 1 [15], phenylhydrazono(phenylazo)-
acetonitrile 9 [3, 20] were prepared as previously reported.
Structural date have been deposited at Cambridge Crystallo-
graphic Data Centre, deposition number for 2a and 7a CCDC
612931 and 612930.
General procedure for the preparation of 2-aryl-hydra-
zono-3-oxo-pentanenitrile (2b-d). To a mixture of 1 (9.70 g,
0.1 mol) in ethanol (100 ml), sodium acetate (20 g, 0.24 mol)
was added. The mixture was then added gradually with stirring
at room temperature to a cold solution of the appropriate
aryldiazonium salt (prepared from 0.1 mol of aromatic amine
and appropriate quantities of hydrochloric acid and sodium
1-[5-Amino-2-(4-chloro-phenyl)-2H-[1,2,3]triazol-4-yl]-
propan-1-one (5a). This compound was obtained as red
crystals, mp 135-137°C; ir (KBr): ꢀmax 3468, 3367 (NH2), 1667
1
cm-1 (CO); H nmr (300 MHz, DMSO-d6): ꢁ 1.11 (t, 3H, J = 7.2

728
S. I. Aziz, H. F. Anwar, D. H. Fleita and M. H. Elnagdi
Vol 44
Hz, CH3), 2.97 (q, 2H, J = 7.2 Hz, CH2), 6.22 (brs, 2H, NH2)
7.55 (d, 2H, J = 8.5 Hz, Ar-H), 7.90 ppm (d, 2H, J = 8.5 Hz, Ar-
H); 13C nmr (75 MHz; DMSO-d6): ꢀ 195.69, 154.49, 137.49,
131.75, 131.47, 129.50, 119.67, 31.65, 7.78 ppm; ms (70 eV)
m/z 250 (M+, 37%), 221 (M+- 29), 139 (M+- p-ClC6H4), 111 (p-
MHz; DMSO-d6): ꢀ 195.7, 154.5, 137.5, 131.8, 131.7 131.5,
129.7, 129.5, 128.6, 124.8, 120.5, 119.7, 31.7, 7.8 ppm; ms (70
+
eV) m/z 385 (M+, 33%), 249 (M+- PhNHCS), 111 (p-ClC6H4 ).
Anal. calcd. for C18H16ClN5OS: (385.87) C, 56.03; H, 4.18; N,
18.15. Found: C, 55.81; H, 4.39; N, 18.57.
+
1-[2-(2-Chloro-phenyl)-5-propionyl-2H-[1,2,3]triazol-4-yl]-
3-phenyl-thiourea (8b). This compound was obtained as red
crystals, (yield 75%, 0.29 g) m.p.175-177 °C; ir (KBr): ꢁmax
ClC6H4 ). Anal. calcd. for C11H11ClN4O: (250.68) C, 52.70; H,
4.42; N, 22.35. Found: C, 52.08; H, 4.67; N, 21.94.
1-[5-Amino-2-(2-chloro-phenyl)-2H-[1,2,3]triazol-4-yl]-
propan-1-one (5b). This compound was obtained as red
crystals, mp 135-136°C; ir (KBr): ꢁmax 3422, 3289 (NH2), 1627
1
3472, 3325 (NH2), 1678 cm-1 (CO); H nmr (300 MHz, DMSO-
d6): ꢀ 1.15 (t, 3H, J = 8.7 Hz, CH3), 3.11 (q, 2H, J = 8.7 Hz,
CH2), 6.80 (brs, 1H, NH), 7.10-7.84 (m, 8H, phenyl-H and Ar-
H) 14.57 ppm (brs, 1H, NH); ms (70 eV) m/z 385 (M+, 48%),
1
cm-1 (CO); H nmr (300 MHz, DMSO-d6): ꢀ 1.31 (t, 3H, J = 7.5
Hz, CH3), 3.12 (q, 2H, J = 7.5 Hz, CH2), 6.47 (brs, 2H, NH2)
7.41-7.48 (m, 2H, Ar-H), 7.66-7.71 ppm (m, 2H, Ar-H); 13C nmr
(75 MHz; DMSO-d6): ꢀ 176.4, 155.5, 147.2, 133.1, 131.9,
130.4, 128.0, 125.2, 116.7, 19.1, 11.2 ppm; ms (70 eV) m/z 250
249 (M+- PhNHCS), 111 (o-ClC6H4 ). Anal. calcd. for
+
C18H16ClN5OS: (385.87) C, 56.03; H, 4.18; N, 18.15. Found: C,
56.31; H, 4.27; N, 17.91.
(M+, 48%), 221 (M+- 29), 139.(M+- o-ClC6H4), 111 (o-ClC6H4 ).
+
1-Phenyl-3-(5-propionyl-2-p-tolyl-2H-[1,2,3]triazol-4-yl)-
thiourea (8c). This compound was obtained as dark red crystals,
(yield 77%, 0.28 g) mp 215-216 °C; ir (KBr): ꢁmax 3456, 3195
(NH2), 1682 cm-1 (CO); 1H nmr (300 MHz, DMSO-d6): ꢀ 1.17 (t,
3H, J = 8.7 Hz, CH3), 2.27 (s, 3H, CH3), 3.05 (q, 2H, J = 8.7 Hz,
CH2), 7.14-7.17 (m, 4H, phenyl-H and Ar-H), 7.40-7.42 (m, 5H,
phenyl-H and Ar-H), 8.10 (brs, 1H, NH), 9.71 ppm (brs, 1H,
Anal. calcd. for C11H11ClN4O: (250.68) C, 52.70; H, 4.42; N,
22.35. Found: C, 52.31; H, 4.13; N, 22.52.
1-(5-Amino-2-p-tolyl-2H-[1,2,3]triazol-4-yl)-propan-1-one
(5c). This compound was obtained as red crystals, mp 148-
149°C; ir (KBr): ꢁmax 3204 (NH2), 1708 cm-1 (CO); 1H nmr (300
MHz, DMSO-d6): ꢀ 1.25 (t, 3H, J = 8.4 Hz, CH3), 2.29 (s, 3H,
CH3) 2.66 (q, 2H, J = 8.4 Hz, CH2), 6.30 (brs, 2H, NH2) 7.23 (d,
2H, J = 9.8 Hz, Ar-H), 7.51 ppm (d, 2H, J = 9.8 Hz, Ar-H); 13C
nmr (75 MHz; DMSO-d6): ꢀ 205.0, 163.4, 13.9.0 135.7, 129.8,
118.9, 116.8, 30.6, 20.48, 10.4 ppm; ms (70 eV) m/z 231 (M++1,
20%), 202 (M+-29), 140 (M+- p-CH3C6H4). Anal. calcd. for
C12H14N4O: (230.27) C, 62.59; H, 6.13; N, 24.33. Found: C,
62.22; H, 6.42; N, 23.98.
+
NH); ms (70 eV) m/z 365 (M+, 46%), 91 (C7H7 ). Anal. calcd.
for C19H19N5OS: (365.45) C, 62.44; H, 5.24; N, 19.16. Found: C,
62.47; H, 5.03; N, 18.87.
2-Phenyl-5-phenylazo-2H-[1,2,3]triazol-4-ylamine (10). A
mixture of 9 (0.25 g, 1 mmol) in DMF (10 ml), hydroxylamine
hydrochloride (0.069 g, 1 mmol) and sodium acetate (1 mmol)
was heated under reflux for 40 min. The reaction mixture was
then poured into water, the solid collected by filtration and
recrystallized from ethanol to give red crystal, (yield 68%, 0.18
g) mp 205°C; ir (KBr): ꢁmax 3472, 3355 (NH2), 1612 cm-1 (CO);
1H nmr (300 MHz, DMSO-d6): ꢀ 6.75 (brs, 2H, NH2), 7.54-7.56
(m, 6H, Ar-H), 7.97-8.00 ppm (m, 4H, Ar-H); ms (70 eV) m/z
264 (M+, 20%), 187 (M+- Ph), 105 (PhNN+), 77 (Ph+). Anal.
calcd. for C14H12N6: (264.28) C, 63.62; H, 4.58; N, 31.80.
Found: C 63.48; H, 4.29; N, 31.96.
N-Acetyl-N-[2-(4-chloro-phenyl)-5-propionyl-2H-[1,2,3]-
triazol-4-yl]-acetamide (7a). Method A: A mixture of 4a (0.27
g, 0.01 mol) and 15 ml of acetic anhydride was refluxed for 4.5
hrs then poured into H2O. The solid formed was collected by
filtration and crystallized from ethanol to yield 2.6 g (78 %).
Method B: A mixture of 5a (0.25 g, 0.01 mol) and 15 ml of
acetic anhydride was refluxed for 2 hrs then poured into H2O.
The solid that formed was collected by filtration and crystallized
from ethanol to yield 2.8 g (84 %). This compound was obtained
as red crystals, X-ray crystal structure figure 2, mp 154-155°C;
Acknowledgement: Facilities and financial support provided by
the; American University in Cairo; are gratefully acknowledged
1
ir (KBr): ꢁmax 1722 (CO), 1672 cm-1 (CO); H nmr (300 MHz,
DMSO-d6): ꢀ 1.10 (t, 3H, J = 7.2 Hz, CH3), 2.14 (s, 6H, 2CH3),
2.99 (q, 2H, J = 7.2 Hz, CH2), 7.60 (d, 2H, J = 9.0 Hz, Ar-H),
7.97 ppm (d, 2H, J = 9.0 Hz, Ar-H); 13C nmr (75 MHz; DMSO-
d6): ꢀ 194.66, 171.40, 144.36, 137.22, 132.78, 129.72, 120.20,
32.86, 23.11, 7.38 ppm; ms (70 eV) m/z 291 (M+- CH3CO), 248
(291-43). Anal. calcd. for C15H15ClN4O3: (334.76) C, 53.82; H,
4.52; N, 16.74. Found: C, 54.09; H, 4.31; N, 16.43.
REFERENCES AND NOTES
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General procedure for the preparation of 1-(2-aryl-5-
propionyl-2H-[1,2,3]triazol-4-yl)-3-phenyl-thiourea (8a-c).
A
mixture of 5a-c (1 mmol) in DMF (10 ml), phenylisothiocyanate
(0.135 g, 1 mmol) and KOH (0.056 g, 1 mmol) was stirred at room
temperature for 24 hrs. the reaction mixture was then poured into
ice water, and neutralize by HCl, the solid so formed was collected
by filtration and recrystallized from ethanol to give 8a-c.
1-[2-(4-Chloro-phenyl)-5-propionyl-2H-[1,2,3]triazol-4-yl]-
3-phenyl-thiourea (8a). This compound was obtained as orange
crystals, (yield 83%, 0.32 g) mp 190-191°C; ir (KBr): ꢁmax 3483
1
(NH), 3365 (NH), 1672 cm-1 (CO); H nmr (300 MHz, DMSO-
d6): ꢀ 1.09 (t, 3H, J = 8.7 Hz, CH3), 2.96 (q, 2H, J = 8.7 Hz,
CH2), 6.24 (brs, 1H, NH), 7.21-7.41 (m, 3H, phenyl-H), 7.53 (d,
2H, J = 10.5 Hz, Ar-H), 7.59-7.62 (m, 2H, phenyl-H), 7.87 (d,
2H, J = 10.5 Hz, Ar-H) 9.70 ppm (brs, 1H, NH); 13C nmr (75
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