Synthesis of 2-amino-1,3,4-oxadiazoles and 2-Amino-1,3,4-thiadiazoles via sequential condensation and I2-mediated oxidative C-O/C-S bond formation

Article abstract of DOI:10.1021/jo502518c

2-Amino-substituted 1,3,4-oxadiazoles and 1,3,4-thiadiazoles were synthesized via condensation of semicarbazide/thiosemicarbazide and the corresponding aldehydes followed by I₂-mediated oxidative C-O/C-S bond formation. This transition-metal-free sequential synthesis process is compatible with aromatic, aliphatic, and cinnamic aldehydes, providing facile access to a variety of diazole derivatives bearing a 2-amino substituent in an efficient and scalable fashion.

Full text of DOI:10.1021/jo502518c

Article
pubs.acs.org/joc
Synthesis of 2‑Amino-1,3,4-oxadiazoles and 2‑Amino-1,3,4-
thiadiazoles via Sequential Condensation and I2‑Mediated Oxidative
C−O/C−S Bond Formation
Pengfei Niu, Jinfeng Kang, Xianhai Tian, Lina Song, Hongxu Liu, Jie Wu, Wenquan Yu,*
and Junbiao Chang*
College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou, Henan 450001, China
S
* Supporting Information
ABSTRACT: 2-Amino-substituted 1,3,4-oxadiazoles and
1,3,4-thiadiazoles were synthesized via condensation of
semicarbazide/thiosemicarbazide and the corresponding alde-
hydes followed by I2-mediated oxidative C−O/C−S bond
formation. This transition-metal-free sequential synthesis
process is compatible with aromatic, aliphatic, and cinnamic
aldehydes, providing facile access to a variety of diazole derivatives bearing a 2-amino substituent in an efficient and scalable
fashion.
Scheme 1. Various Methods for the Construction of the 2-
Amino-Substituted 1,3,4-Oxadiazole Skeleton
INTRODUCTION
■
1,3,4-Oxadiazoles and 1,3,4-thiadiazoles are important five-
membered nitrogen-containing heterocycles with a wide range
of applications1−4 in medicinal chemistry, material science, and
organic synthesis. In particular, these diazole structural motifs
bearing a 2-amino substituent are valuable building blocks in
drug design. For example, 2-amino-1,3,4-oxadiazole derivatives
exhibit a broad spectrum of biological and pharmaceutical
activities including antimicrobial,5a anticonvulsant and sedative-
hypnotic,5b antiepileptic,5c antitubercular,5d antimitotic,5e and
muscle relaxing.5f In addition, they can also be used as histone
deacetylase inhibitors5g and antagonists of Pseudomonas
quorum sensing receptor (PqsR).5h On the basis of
bioisosterism between −S− and −O−,6 2-amino-1,3,4-
thiadiazole could act as a bioisostere of 2-amino-1,3,4-
oxadiazole and, therefore, produce biological properties broadly
similar to those of the latter.7 Thus, development of synthetic
methods to access these 2-amino-substituted diazoles is of great
importance to the drug discovery community.
To date, various methods have been reported in the literature
for the synthesis of 2-amino-1,3,4-oxadiazoles (Scheme 1): (a)
cyclodesulfurization of acyl thiosemicarbazide using desulfurat-
ing reagents such as carbodiimides,8a−c tosyl chloride,8d IBX,8e,f
oxone,8g mercury oxide,8h methyl iodide,8i and ethyl
bromoacetate;8j (b) cyclodehydration of acyl semicarbazides
using SOCl2,8i Ph3P,9 or POCl3;10e (c) reaction of acylhy-
drazides with reagents, such as cyanogen bromide,10a,b
isocyanides,10c trimethylsilyl isothiocyanate,10d isocyanide di-
chloride,10e,f di(benzotriazol-1yl)methanimine;10g and (d)
direct amination of oxadiazol-2-ones11a or 1,3,4-oxadiazo-
les.11b−f Yet, there are still disadvantages associated with
these methodologies, such as harsh reaction conditions, the use
of expensive and/or toxic reagents, and limited scalability.
Owing to the easy accessibility of substrates, oxidative
cyclization has been extensively used for the synthesis of 1,3,4-
oxadiazoles from the corresponding acylhydrazones.2,12a
However, preparation of 2-amino-substituted 1,3,4-oxadiazoles
through direct oxidative cyclization of semicarbazones (path e,
Scheme 1) is rarely reported in the literature.13 This could be
due to the presence of the amino group (NH2) in the substrate
(6, Scheme 2), which will compete with the oxygen atom
during the cyclization process to form byproduct triazolone 8,14
and may also lead to undesired byproducts under the oxidation
conditions. An ideal methodology for this transformation could
not only convert the precursor 6 to the desired oxadiazole 1
selectively but also avoid side reactions of the 2-amino group.
Herein, we report such a reaction for the construction of the 2-
amino-1,3,4-oxadiazole framework (1) via I2-mediated oxidative
cyclization. Moreover, this transition-metal-free protocol can
Received: November 3, 2014
© XXXX American Chemical Society
A
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Scheme 2. Two Possible Cyclization Pathways of Semicarbazone 6 or Thiosemicarbazone 7
also be utilized to synthesize 2-amino-1,3,4-thiadiazole
derivatives from the corresponding thiosemicarbazones 7 via
C−S bond formation.
well with a range of benzaldehydes (3a−k) bearing ortho-,
meta-, para-, or multisubstituents. Under the optimal reaction
conditions, both electron-donating groups and electron-with-
drawing groups with substituted benzaldehydes were converted
to the desired 2-amino-1,3,4-oxadiazoles (1a−k) in good to
excellent yields. Among them, the 3-trifluoromethylphenyl
analogue has been reported as a novel antagonist of PqsR.5h
Other aromatic aldehydes, such as α-naphthaldehyde, α-
picolinaldehyde, and furfural (3l−n), also gave the target
products (1l−n). The structure of 5-naphthyl-substituted 2-
amino-1,3,4-oxadiazole (1l) was further confirmed by X-ray
crystallography (see Supporting Information). In addition, this
synthetic process is compatible with both aliphatic (3o−q) and
cinnamic aldehydes (3r), which formed 2-amino-1,3,4-
oxadiazoles 1o−r in satisfactory yields, as well.
RESULTS AND DISCUSSION
■
Due to the numerous advantages associated with this eco-
friendly element, molecular iodine has been extensively used in
organic synthesis.15 Recently, we have reported I2-mediated
oxidative intramolecular C−O/C−N bond formation reactions
for the preparation of 1,3,4-oxadiazoles12a and pyrazoles,12b
respectively. In this work, initially, we investigated the oxidative
cyclization of the purified semicarbazone 6a, which was readily
prepared via the condensation of 4-methylbenzaldehyde (3a)
and aminourea hydrochloride (4a) in a mixture of water and
methanol (Scheme 3). However, treatment of substrate 6a with
Encouraged by the success of 2-amino-1,3,4-oxadiazole
synthesis, we sought to further extend the scope of this
practical approach by replacing semicarbazide hydrochloride 4
with thiosemicarbazide 5 to prepare 2-amino-1,3,4-thiadiazoles.
Upon the completion of the condensation of thiosemicarbazide
5 and the corresponding aldehyde 3, the reaction mixture was
concentrated and then redissolved in 1,4-dioxane, followed by
the treatment with molecular iodine and potassium carbonate.
To our delight, stirring the resulting mixture at the refluxing
temperature for 1−4 h (see the Experimental Section)
produced the desired 2-amino-1,3,4-thiadiazole 2 with a new
C−S bond formed. This sequential synthesis protocol also
tolerates aromatic, aliphatic, and cinnamic aldehydes to provide
a series of 2-amino-1,3,4-thiadiazole derivatives in moderate to
good yields (Table 2).
Scheme 3. Synthesis of 2-Amino-1,3,4-oxadiazole 1a from 4-
Methylbenzaldehyde (3a) and Semicarbazide Hydrochloride
(4)
a
a
Optimal reaction conditions: (1) condensation of 3a (0.5 mmol) and
CONCLUSIONS
■
4a (0.5 mmol) in the presence of NaOAc (0.5 mmol) in MeOH/H2O
(1:1) at room temperature; (2) I2 (0.6 mmol), K2CO3 (1.5 mmol),
1,4-dioxane, 80 °C.
In summary, we have developed a practical I2-mediated
oxidative C−O/C−S bond formation methodology for the
synthesis of 2-amino-substituted 1,3,4-oxadiazoles and 1,3,4-
thiadiazoles. Under the optimal sequential synthesis conditions,
semicarbazide/thiosemicarbazide and the corresponding alde-
hydes were smoothly converted into the desired diazoles 1 and
2 without purification of the condensation intermediates. This
versatile and transition-metal-free protocol allows the efficient
synthesis of a variety of aryl-, alkyl-, and alkenyl-substituted
diazole derivatives bearing a 2-amino group in a scalable
fashion.
I2 in the presence of K2CO3 in dimethylsulfoxide (DMSO)12a
did not afford the desired 2-amino-1,3,4-oxadiazole 1a at all.
Screening of the reaction solvent indicated that, when it was
switched to 1,4-dioxane, the transformation proceeded
smoothly at 80 °C. With no need for further optimization,
product 1a was generated in 95% yield (Scheme 3). Next, we
attempted to probe the feasibility of sequential synthesis of
compound 1a without purification of the intermediate 6a. After
the first-step condensation of 3a and 4 was complete
(monitored by TLC), the solvents were evaporated under
reduced pressure. The resulting crude semicarbazone 6a was
directly subjected to the above optimal reaction conditions (I2,
K2CO3, 1,4-dioxane, 80 °C), which also produced product 1a in
equally good yield (99%, Scheme 3). Furthermore, the reaction
can be successfully conducted in gram scale (Table 1, entry 1).
With good reaction conditions in hand, we set out to
examine the substrate scope of this methodology (Table 1). As
illustrated in Table 1, this sequential synthesis protocol works
EXPERIMENTAL SECTION
■
General Information. 1H and 13C NMR spectra were recorded on
a 400 MHz (100 MHz for 13C NMR) spectrometer. Chemical shift
values are given in parts per million with tetramethylsilane as an
internal standard. The peak patterns are indicated as follows: s, singlet;
d, doublet; t, triplet; q, quartet; quint, quintet; sext, sextet; m,
multiplet; dd, doublet of doublets; dt, doublet of triplets. The coupling
constants (J) are reported in hertz (Hz). Melting points were
determined on a micromelting point apparatus without corrections.
Flash column chromatography was performed over silica gel 200−300
B
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a
Table 1. Synthesis of 2-Amino-1,3,4-oxadiazoles 1
a
Optimal reaction conditions: (1) condensation of 3 (0.5 mmol) and 4 (0.5 mmol) in the presence of NaOAc (0.5 mmol) in MeOH/H2O (1:1) at
b
c
room temperature; (2) I2 (0.6 mmol), K2CO3 (1.5 mmol), 1,4-dioxane, 80 °C. Isolated yields. The reaction was conducted on gram scale (8 mmol
scale).
mesh, and the eluent was a mixture of ethyl acetate (EA) and
petroleum ether (PE). High-resolution mass spectra (HRMS-ESI)
were obtained on a Q-TOF mass spectrometer. 1,4-Dioxane was dried
over 4 Å molecular sieves before use.
MHz, DMSO-d6) δ 7.64 (d, J = 7.6 Hz, 2H), 7.28 (d, J = 7.6 Hz, 2H),
7.17 (br s, 2H), 2.30 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ
164.1, 157.8, 140.6, 130.2, 125.4, 122.1, 21.4; HRMS (m/z) [M +
Na]+ calcd for C9H9N3ONa 198.0638, found 198.0633.
5-Phenyl-1,3,4-oxadiazol-2-amine (1b): yield 78 mg, 97%; white
solid, mp 242−243 °C (lit.13e mp 241−242 °C); Rf = 0.40 (EA/PE
75:25); 1H NMR (400 MHz, DMSO-d6) δ 7.82−7.79 (m, 2H), 7.54−
7.52 (m, 3H), 7.26 (br s, 2H); 13C NMR (100 MHz, DMSO-d6) δ
164.3, 157.7, 130.8, 129.6, 125.4, 124.8; HRMS (m/z) [M + H]+ calcd
for C8H8N3O 162.0662, found 162.0661.
General Procedure for the Synthesis of 2-Amino-1,3,4-
oxadiazoles 1. To a stirred solution of semicarbazide hydrochloride
(4, 0.5 mmol) and sodium acetate (0.5 mmol) in H2O (1 mL) was
added a solution of the aldehyde (3, 0.5 mmol) in MeOH (1 mL).
After being stirred at room temperature for 10 min, the solvent was
evaporated under reduced pressure, and the resulting residue was
redissolved in 1,4-dioxane (5 mL), followed by addition of potassium
carbonate (1.5 mmol) and iodine (0.6 mmol) in sequence. The
reaction mixture was stirred at 80 °C until the conversion was
complete (monitored by TLC, 1−4.5 h). After being cooled to room
temperature, it was treated with 5% Na2S2O3 (20 mL) and extracted
with CH2Cl2/MeOH (10:1, 10 mL × 4). The combined organic layer
was dried over anhydrous sodium sulfate and concentrated. The given
residue was purified through silica gel column chromatography using a
mixture of EtOAc and petroleum ether as eluent to afford the
corresponding 2-amino-1,3,4-oxadiazoles 1 in 85−99% yield.
5-(4-Methoxyphenyl)-1,3,4-oxadiazol-2-amine (1c): yield 90 mg,
94%; white solid, mp 252−253 °C (lit.13e mp 252−253 °C); Rf = 0.25
1
(EA/PE 75:25); H NMR (400 MHz, DMSO-d6) δ 7.76−7.72 (m,
2H), 7.16 (br s, 2H), 7.10−7.07 (m, 2H), 3.83 (s, 3H); 13C NMR
(100 MHz, DMSO-d6) δ 163.9, 161.2, 157.7, 127.2, 117.4, 115.1, 55.8;
HRMS (m/z) [M + Na]+ calcd for C9H9N3O2Na 214.0587, found
214.0584.
5-(4-Chlorophenyl)-1,3,4-oxadiazol-2-amine (1d): yield 94 mg,
96%; white solid, mp 260−262 °C (lit.10d mp 260−264 °C); Rf = 0.40
1
(EA/PE 75:25); H NMR (400 MHz, DMSO-d6) δ 7.80 (d, J = 8.4
5-(p-Tolyl)-1,3,4-oxadiazol-2-amine (1a): 0.5 mmol scale, yield 87
mg, 99%; 8 mmol scale, yield 1.28 g, 91%; white solid, mp 261−262
°C (lit.10d mp 261−263 °C); Rf = 0.35 (EA/PE 75:25); 1H NMR (400
Hz, 2H), 7.60 (d, J = 8.8 Hz, 2H), 7.33 (br s, 2H); 13C NMR (100
MHz, DMSO-d6) δ 164.4, 157.0, 135.3, 129.8, 127.2, 123.6; HRMS
(m/z) [M + Na]+ calcd for C8H6ClN3ONa 218.0092, found 218.0092.
C
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a
Table 2. Synthesis of 2-Amino-1,3,4-thiadiazoles 2
a
Optimal reaction conditions: (1) condensation of 3 (0.5 mmol) and 5 (0.5 mmol) in the presence of HOAc (0.5 mmol) in MeOH/H2O (1:1) at
b
room temperature; (2) I2 (0.75 mmol), K2CO3 (1.6 mmol), 1,4-dioxane, reflux. Isolated yields.
4-(5-Amino-1,3,4-oxadiazol-2-yl)benzonitrile (1e):8g yield 90 mg,
96%; white solid, Rf = 0.40 (EA/PE 75:25); mp 255−257 °C; H
NMR (400 MHz, DMSO-d6) δ 8.01−7.99 (m, 2H), 7.95−7.93 (m,
2H), 7.49 (br s, 2H); 13C NMR (100 MHz, DMSO-d6) δ164.9, 156.6,
133.7, 128.7, 125.9, 118.8, 112.7; HRMS (m/z) [M + Na]+ calcd for
C9H6N4ONa 209.0434, found 209.0434.
Hz), 132.9 (d, JC−F = 8.3 Hz), 128.8 (d, JC−F = 1.9 Hz), 125.5 (d, JC−F
= 3.6 Hz), 117.3 (d, JC−F = 20.6 Hz), 113.0 (d, JC−F = 12.0 Hz);
HRMS (m/z) [M + H]+ calcd for C8H7FN3O 180.0568, found
180.0577.
5-(2,4-Dichlorophenyl)-1,3,4-oxadiazol-2-amine (1j): yield 105
mg, 91%; white solid, mp 209−210 °C (lit.16 mp 210−211 °C); Rf
= 0.50 (EA/PE 75:25); 1H NMR (400 MHz, DMSO-d6) δ 7.84−7.82
(m, 2H), 7.60 (dd, J = 8.8, 2.0 Hz, 1H), 7.41 (br s, 2H); 13C NMR
(100 MHz, DMSO-d6) δ 164.6, 154.9, 135.9, 132.2, 131.6, 130.9,
128.4, 122.8; HRMS (m/z) [M + Na]+ calcd for C8H5Cl2N3ONa
251.9703, found 251.9705.
1
5-(4-Nitrophenyl)-1,3,4-oxadiazol-2-amine (1f): yield 102 mg,
99%; yellow solid, mp 251−252 °C (lit.13e mp 250−251 °C); Rf =
1
0.40 (EA/PE 75:25); H NMR (400 MHz, DMSO-d6) δ 8.38−8.35
(m, 2H), 8.04−8.01 (m, 2H), 7.54 (br s, 2H); 13C NMR (100 MHz,
DMSO-d6) δ 165.0, 156.5, 148.3, 130.2, 126.4, 125.0; HRMS (m/z)
[M + H]+ calcd for C8H7N4O3 207.0513, found 207.0523.
5-Mesityl-1,3,4-oxadiazol-2-amine (1k): yield 87 mg, 86%; white
1
5-(3-Nitrophenyl)-1,3,4-oxadiazol-2-amine (1g): yield 93 mg,
solid, mp 247−248 °C; Rf = 0.50 (EA/PE 75:25); H NMR (400
90%; yellow solid, mp 252−253 °C (lit.13e mp 253−254 °C); Rf =
MHz, DMSO-d6) δ 7.09 (br s, 2H), 7.00 (s, 2H), 2.28 (s, 3H), 2.18 (s,
6H); 13C NMR (100 MHz, DMSO-d6) δ 164.3, 156.2, 140.2, 138.3,
128.9, 122.4, 21.2, 20.3; HRMS (m/z) [M + Na]+ calcd for
C11H13N3ONa 226.0951, found 226.0951.
1
0.35 (EA/PE 75:25); H NMR (400 MHz, DMSO-d6) δ 8.47 (t, J =
2.0 Hz, 1H), 8.34 (ddd, J = 8.4, 2.4, 0.8 Hz, 1H), 8.23−8.20 (m, 1H),
7.84 (t, J = 8.0 Hz, 1H), 7.47 (br s, 2H); 13C NMR (100 MHz,
DMSO-d6) δ 164.7, 156.2, 148.6, 131.6, 131.3, 126.2, 125.1, 119.8;
HRMS (m/z) [M + Na]+ calcd for C8H6N4O3Na 229.0332, found
229.0332.
5-(Naphthalen-1-yl)-1,3,4-oxadiazol-2-amine (1l):17 yield 105 mg,
1
99%; yellow solid, mp 175−176 °C; Rf = 0.60 (EA/PE 75:25); H
NMR (400 MHz, CD3OD) δ 9.01 (d, J = 8.8 Hz, 1H), 7.99−7.97 (m,
2H), 7.92 (d, J = 7.6 Hz, 1H), 7.62−7.50 (m, 3H); 13C NMR (100
MHz, CD3OD) δ 164.0, 158.3, 133.9, 131.2, 129.5, 128.3, 127.2, 126.7,
126.2, 125.5, 124.6, 120.5; HRMS (m/z) [M + Na]+ calcd for
C12H9N3ONa 234.0638, found 234.0638.
5-(3-(Trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-amine (1h):5h
yield 114 mg, 99%; white solid, mp 229−230 °C; Rf = 0.55 (EA/PE
1
75:25); H NMR (400 MHz, DMSO-d6) δ 8.09 (d, J = 8.0 Hz, 1H),
8.02 (s, 1H), 7.89 (d, J = 7.2 Hz, 1H), 7.79 (t, J = 8.0 Hz, 1H), 7.40
(br s, 2H); 13C NMR (100 MHz, DMSO-d6) δ 164.6, 156.6, 131.1,
130.3 (q, JC−F = 32.1 Hz), 129.2, 127.2, 125.8, 124.1 (q, JC−F = 271.1
Hz), 121.6 (q, JC−F = 3.9 Hz); HRMS (m/z) [M + H]+ calcd for
C9H7F3N3O 230.0536, found 230.0539.
5-(Pyridin-2-yl)-1,3,4-oxadiazol-2-amine (1m):5f yield 72 mg,
1
89%; white solid, mp 250−252 °C; Rf = 0.15 (EA/PE 75:25); H
NMR (400 MHz, DMSO-d6) δ 8.67 (dt, J = 4.8, 1.6 Hz, 1H), 8.00−
7.94 (m, 2H), 7.53−7.49 (m, 1H), 7.42 (br s, 2H); 13C NMR (100
MHz, DMSO-d6) δ 164.9, 157.7, 150.2, 144.0, 137.9, 125.3, 121.5;
HRMS (m/z) [M + Na]+ calcd for C7H6N4ONa 185.0434, found
185.0432.
5-(2-Fluorophenyl)-1,3,4-oxadiazol-2-amine (1i):8g yield 85 mg,
95%; white solid, mp 213-214 °C; Rf = 0.45 (EA/PE 75:25); 1H NMR
(400 MHz, DMSO-d6) δ 7.85 (td, J = 7.6, 1.6 Hz, 2H), 7.61−7.55 (m,
1H), 7.44−7.35 (m, 4H); 13C NMR (100 MHz, DMSO-d6) δ 164.5
(d, JC−F = 0.9 Hz), 158.9 (d, JC−F = 252.7 Hz), 154.1 (d, JC−F = 5.2
5-(Furan-2-yl)-1,3,4-oxadiazol-2-amine (1n): yield 68 mg, 90%;
yellow solid, mp 222−223 °C (lit.5f mp 225−226 °C); Rf = 0.45 (EA/
D
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PE 75:25); 1H NMR (400 MHz, DMSO-d6) δ 7.92 (m, 1H), 7.33 (br
s, 2H), 7.00 (d, J = 3.6 Hz, 1H), 6.72−6.70 (m, 1H); 13C NMR (100
MHz, DMSO-d6) δ 163.7, 151.1, 145.7, 139.8, 112.5, 111.6; HRMS
(m/z) [M + Na]+ calcd for C6H5N3O2Na, 174.0274, found 174.0270.
5-Propyl-1,3,4-oxadiazol-2-amine (1o):13a yield 54 mg, 85%;
5-(4-Nitrophenyl)-1,3,4-thiadiazol-2-amine (2f): yield 82 mg,
74%; brown solid, mp 250−252 °C (lit.20 mp 250−252 °C); Rf =
1
0.50 (EA/PE 75:25); H NMR (400 MHz, DMSO-d6) δ 8.30 (d, J =
8.8 Hz, 2H), 8.02 (d, J = 8.8 Hz, 2H), 7.73 (br s, 2H); 13C NMR (100
MHz, DMSO-d6) δ 170.4, 154.5, 147.8, 137.2, 127.5, 124.9; HRMS
(m/z) [M + H]+ calcd for C8H7N4O2S 223.0284, found 223.0281.
5-(3-(Trifluoromethyl)phenyl)-1,3,4-thiadiazol-2-amine (2h):22
yield 105 mg, 86%; white solid, mp 144−146 °C; Rf = 0.40 (EA/PE
1
white solid, mp 145−146 °C; Rf = 0.25 (EA/PE 75:25); H NMR
(400 MHz, DMSO-d6) δ 6.83 (br s, 2H), 2.59 (t, J = 7.6 Hz, 2H), 1.62
(sext, J = 7.6 Hz, 2H), 0.92 (t, J = 7.6 Hz, 3H); 13C NMR (100 MHz,
DMSO-d6) δ 163.9, 159.5, 26.8, 19.9, 13.8; HRMS (m/z) [M + Na]+
calcd for C5H9N3ONa 150.0638, found 150.0634.
1
50:50); H NMR (400 MHz, DMSO-d6) δ 8.07 (s, 1H), 8.03 (d, J =
7.6 Hz, 1H), 7.80 (d, J = 8.0 Hz, 1H), 7.72 (t, J = 8.0 Hz, 1H), 7.58 (br
5-Isopropyl-1,3,4-oxadiazol-2-amine (1p):13a yield 54 mg, 85%;
s, 2H); 13C NMR (100 MHz, DMSO-d6) δ 169.7, 155.1, 132.4, 130.9,
1
130.8 (q, JC−F = 1.4 Hz), 130.3 (q, JC−F = 31.9 Hz), 126.3 (q, JC−F
=
white solid, mp 181−182 °C; Rf = 0.25 (EA/PE 75:25); H NMR
3.8 Hz), 124.3 (q, JC−F = 271.2 Hz), 122.4 (q, JC−F = 3.8 Hz); HRMS
(m/z) [M + Na]+ calcd for C9H6F3N3SNa 68.0127, found 268.0123.
5-(2-Fluorophenyl)-1,3,4-thiadiazol-2-amine (2i):23 yield 82 mg,
(400 MHz, DMSO-d6) δ 6.83 (br s, 2H), 2.96 (heptet, J = 6.8 Hz,
1H), 1.21 (d, J = 6.8 Hz, 6H); 13C NMR (100 MHz, DMSO-d6) δ
163.9, 163.6, 25.8, 20.2; HRMS (m/z) [M + Na]+ calcd for
C5H9N3ONa 150.0638, found 150.0639.
1
84%; white solid, mp 210−212 °C; Rf = 0.35 (EA/PE 50:50); H
5-(tert-Butyl)-1,3,4-oxadiazol-2-amine (1q):18 yield 67 mg, 95%;
NMR (400 MHz, DMSO-d6) δ 8.09 (td, J = 8.0, 1.6 Hz, 1H), 7.52−
7.48 (m, 1H), 7.47 (br s, 2H), 7.41−7.32 (m, 2H); 13C NMR (100
MHz, DMSO-d6) δ 170.4 (d, JC−F = 4.5 Hz), 158.3 (d, JC−F = 247.0
Hz), 148.9 (d, JC−F = 7.9 Hz), 131.8 (d, JC−F = 8.5 Hz), 128.1 (d, JC−F
= 2.7 Hz), 125.6 (d, JC−F = 3.2 Hz), 119.1 (d, JC−F = 11.9 Hz), 116.7
(d, J = 21.6 Hz); HRMS (m/z) [M + Na]+ calcd for C8H6FN3SNa
218.0159, found 218.0159.
1
white solid, mp 193−194 °C; Rf = 0.30 (EA/PE 75:25); H NMR
(400 MHz, DMSO-d6) δ 6.84 (br s, 2H), 1.27 (s, 9H); 13C NMR (100
MHz, DMSO-d6) δ 165.8, 163.9, 32.0, 28.2; HRMS (m/z) [M + Na]+
calcd for C6H11N3ONa 164.0794, found 164.0791.
(E)-5-Styryl-1,3,4-oxadiazol-2-amine (1r):8g yield 83 mg, 89%;
1
yellow solid, mp 249−251 °C; Rf = 0.30 (EA/PE 75:25); H NMR
5-(2,4-Dichlorophenyl)-1,3,4-thiadiazol-2-amine (2j): yield 100
(400 MHz, DMSO-d6) δ 7.70−7.67 (m, 2H), 7.43−7.33 (m, 3H), 7.26
(br s, 2H), 7.17 (d, J = 16.4 Hz, 2H), 7.10 (d, J = 16.4 Hz, 1H); 13C
NMR (100 MHz, DMSO-d6) δ 163.7, 158.1, 135.6, 134.3, 129.5,
129.3, 127.7, 111.3; HRMS (m/z) [M + Na]+ calcd for C10H9N3ONa
210.0638, found 210.0638.
mg, 81%; white solid, mp 223−224 °C (lit.24 mp 225 °C); Rf = 0.45
1
(EA/PE 50:50); H NMR (400 MHz, DMSO-d6) δ 8.04 (d, J = 8.4
Hz, 1H), 7.99 (s, 1H), 7.55 (dd, J = 8.4, 2.0 Hz, 1H), 7.52 (br s, 2H);
13C NMR (100 MHz, DMSO-d6) δ 170.7, 151.0, 135.0, 131.7, 131.6,
130.3, 129.1, 128.4; HRMS (m/z) [M + H]+ calcd for C8H6Cl2N3S
245.9654, found 245.9654.
General Procedure for the Synthesis of 2-Amino-1,3,4-
thiadiazoles 2. To a stirred solution of thiosemicarbazide (5, 0.5
mmol) and acetic acid (0.5 mmol) in H2O (1 mL) was added a
solution of the aldehyde (3, 0.5 mmol) in MeOH (1 mL). After being
stirred at room temperature for 30 min, the solvent was evaporated
under reduced pressure, and the resulting residue was redissolved in
1,4-dioxane (5 mL), followed by addition of potassium carbonate (1.6
mmol) and iodine (0.75 mmol) in sequence. The reaction mixture was
heated to reflux under nitrogen atmosphere until the conversion was
complete (monitored by TLC, 1−4 h). After being cooled to room
temperature, it was treated with 5% Na2S2O3 (20 mL) and extracted
with EtOAc (15 mL x 3). The combined organic layer was dried over
anhydrous sodium sulfate and concentrated. The given residue was
purified through silica gel column chromatography using a mixture of
EtOAc and petroleum ether as eluent to afford the corresponding 2-
amino-1,3,4-thiadiazoles 2 in 39−86% yield.
5-Mesityl-1,3,4-thiadiazol-2-amine (2k):25 yield 89 mg, 81%;
1
white solid, mp 273−274 °C; Rf = 0.40 (EA/PE 50:50); H NMR
(400 MHz, DMSO-d6) δ 7.24 (br s, 2H), 6.96 (s, 2H), 2.27 (s, 3H),
2.09 (s, 6H); 13C NMR (100 MHz, DMSO-d6) δ 169.9, 153.9, 139.2,
137.7, 128.6, 127.7, 21.1, 20.2; HRMS (m/z) [M + H]+ calcd for
C11H14N3S 220.0903, found 220.0907.
5-(Naphthalen-1-yl)-1,3,4-thiadiazol-2-amine (2l):26 yield 80 mg,
1
70%; yellow solid, mp 207−208 °C; Rf = 0.25 (EA/PE 50:50); H
NMR (400 MHz, DMSO-d6) δ 8.79 (d, J = 8.0 Hz, 1H), 8.05−8.01
(m, 2H), 7.74 (dd, J = 7.2, 1.2 Hz, 1H), 7.66−7.57 (m, 3H), 7.47 (br s,
2H); 13C NMR (100 MHz, DMSO-d6) δ 169.1, 156.0, 134.0, 130.4,
130.2, 129.1, 128.9, 127.8, 126.9, 126.1, 125.9; HRMS (m/z) [M +
H]+ calcd for C12H10N3S 228.0590, found 228.0590.
5-(tert-Butyl)-1,3,4-thiadiazol-2-amine (2q): yield 79 mg, 76%;
5-(p-Tolyl)-1,3,4-thiadiazol-2-amine (2a): yield 78 mg, 81%; white
white solid, mp 180−181 °C (lit.27 mp 181−184 °C); Rf = 0.25 (EA/
solid, mp 215−216 °C (lit.19 mp 214−216 °C); Rf = 0.50 (EA/PE
PE 50:50); H NMR (400 MHz, CDCl3) δ 5.77 (br s, 2H), 1.40 (s,
1
75:25); H NMR (400 MHz, DMSO-d6) δ 7.64 (d, J = 8.4 Hz, 2H),
9H); 13C NMR (100 MHz, CDCl3) δ 171.3, 168.2, 36.1, 30.7; HRMS
(m/z) [M + H]+ calcd for C6H12N3S 158.0746, found 158.0748.
(E)-5-Styryl-1,3,4-thiadiazol-2-amine (2r):28 yield 40 mg, 39%;
1
7.36 (br s, 2H), 7.27 (d, J = 7.6 Hz, 2H), 2.34 (s, 3H); 13C NMR (100
MHz, DMSO-d6) δ 168.6, 156.9, 139.7, 130.1, 128.7, 126.7, 21.3;
HRMS (m/z) [M + Na]+ calcd for C9H9N3SNa 214.0409, found
214.0406.
1
yellow solid, mp 230−232 °C; Rf = 0.20 (EA/PE 50:50); H NMR
(400 MHz, DMSO-d6) δ 7.65−7.63 (m, 2H), 7.43 (br s, 2H), 7.41−
7.32 (m, 4H), 7.06 (d, J = 16.4 Hz, 1H); 13C NMR (100 MHz,
DMSO-d6) δ 168.0, 157.2, 136.2, 134.7, 129.2, 129.0, 127.3, 120.0;
HRMS (m/z) [M + Na]+ calcd for C10H9N3SNa 226.0409, found
226.0402.
5-(4-Methoxyphenyl)-1,3,4-thiadiazol-2-amine (2c): yield 56 mg,
54%; white solid, mp 191−193 °C (lit.20 mp 192−194 °C); Rf = 0.40
1
(EA/PE 75:25); H NMR (400 MHz, DMSO-d6) δ 7.71−7.67 (m,
2H), 7.31 (br s, 2H), 7.04−7.00 (m, 2H), 3.81 (s, 3H),; 13C NMR
(100 MHz, DMSO-d6) δ 168.3, 160.7, 156.7, 128.2, 124.0, 114.9, 55.7;
HRMS (m/z) [M + Na]+ calcd for C9H9N3OSNa 230.0359, found
230.0357.
ASSOCIATED CONTENT
■
S
* Supporting Information
5-(4-Chlorophenyl)-1,3,4-thiadiazol-2-amine (2d): yield 64 mg,
Copies of 1H and 13C NMR spectra of compounds 1 and 2, and
X-ray structure and data of compound 1l (CIF). This material
is available free of charge via the Internet at http://pubs.acs.org.
60%; white solid, mp 224−225 °C (lit.21 mp 224−226 °C); Rf = 0.55
1
(EA/PE 75:25); H NMR (400 MHz, DMSO-d6) δ 7.77 (d, J = 8.4
Hz, 2H), 7.53 (d, J = 8.4 Hz, 2H), 7.48 (br s, 2H); 13C NMR (100
MHz, DMSO-d6) δ 169.2, 155.5, 134.4, 130.3, 129.6, 128.3; HRMS
(m/z) [M + Na]+ calcd for C8H6ClN3SNa 233.9863, found 233.9858.
4-(5-Amino-1,3,4-thiadiazol-2-yl)benzonitrile (2e):7f yield 66 mg,
AUTHOR INFORMATION
Corresponding Authors
*E-mail: (W.Y.) wenquan_yu@zzu.edu.cn.
*E-mail: (J.C.) changjunbiao@zzu.edu.cn.
■
1
65%; white solid, mp 243−244 °C; Rf = 0.40 (EA/PE 75:25); H
NMR (400 MHz, DMSO-d6) δ 7.96−7.90 (m, 4H), 7.66 (br s, 2H);
13C NMR (100 MHz, DMSO-d6) δ 170.1, 155.0, 135.5, 133.5, 127.2,
118.9, 111.9; HRMS (m/z) [M + Na]+ calcd for C9H6N4SNa
225.0205, found 225.0206.
Notes
The authors declare no competing financial interest.
E
DOI: 10.1021/jo502518c
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Heterocycl. Chem. 1984, 21, 1415. (i) Fulop, F.; Semega, E.; Dombi, G.;
Bernath, G. J. Heterocycl. Chem. 1990, 27, 951. (j) Kucukguzel, G.;
Kocatepe, A.; Clercq, E. D.; Sahin, F.; Gulluce, M. Eur. J. Med. Chem.
2006, 41, 353.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(Nos. 21172202, 81302637, 81330075, and J1210060) and the
China Postdoctoral Science Foundation (Nos. 2013M530341
and 2014T70690) for financial support.
̌
(9) Dumciute, J.; Martynaitis, V.; Holzer, W.; Mangelinckx, S.;
̇
̅
̌
Kimpe, N. D.; Sack
̌
us, A. Tetrahedron 2006, 62, 3309.
(10) (a) Patel, N. B.; Patel, J. C. Sci. Pharm. 2010, 78, 171.
(b) Kerimov, I.; Ayhan-Kılcıgil, G.; Ozdamar, E. D.; Can-Eke, B.;
̈
Çoban, T.; Ozbey, S.; Kazak, C. Arch. Pharm. Chem. Life Sci. 2012,
̈
REFERENCES
■
(1) For the application of 1,3,4-oxadiazoles in medicinal chemistry,
see: (a) Bhatia, S.; Gupta, M. J. Chem. Pharm. Res. 2011, 3, 137. (b) de
Oliveira, C. S.; Lira, B. F.; Barbosa-Filho, J. M.; Lorenzo, J. G.; de
Athayde-Filho, P. F. Molecules 2012, 17, 10192. (c) Khalilullah, H.;
Ahsan, M. J.; Hedaitullah, M.; Khan, S.; Ahmed, B. Mini-Rev. Med.
Chem. 2012, 12, 789. (d) Li, Z.; Zhan, P.; Liu, X. Mini-Rev. Med. Chem.
2011, 11, 1130. (e) Sahu, V. K. R.; Singh, A. K.; Yadav, D. Int. J.
ChemTech Res. 2011, 3, 1362. (f) Sharma, S.; Sharma, P. K.; Kumar,
N.; Dudhe, R. Pharma Chem. 2010, 2, 253. (g) Singh, A. K.; Sahu, V.
K. R.; Yadav, D. Int. J. Pharm. Sci. Res. 2011, 2, 135. (h) Sun, J.;
Makawana, J. A.; Zhu, H. L. Mini-Rev. Med. Chem. 2013, 13, 1725.
(2) For the application of 2,5-disubstituted 1,3,4-oxadiazoles in
material science, see: Guin, S.; Ghosh, T.; Rout, S. K.; Banerjee, A.;
Patel, B. K. Org. Lett. 2011, 13, 5976 and references cited therein.
(3) For the application of 1,3,4-oxadiazoles in organic synthesis, see:
(a) Campbell, E. L.; Skepper, C. K.; Sankar, K.; Duncan, K. K.; Boger,
D. L. Org. Lett. 2013, 15, 5306. (b) Lajiness, J. P.; Jiang, W.; Boger, D.
L. Org. Lett. 2012, 14, 2078. (c) Sasaki, Y.; Kato, D.; Boger, D. L. J.
Am. Chem. Soc. 2010, 132, 13533. (d) Xie, J.; Wolfe, A. L.; Boger, D. L.
Org. Lett. 2013, 15, 868.
(4) For the application of 1,3,4-thiadiazoles, see recent reviews:
(a) Hu, Y.; Li, C.-Y.; Wang, X.-M.; Yang, Y.-H.; Zhu, H.-L. Chem. Rev.
2014, 114, 5572. (b) Jain, A. K.; Sharma, S.; Vaidya, A.; Ravichandran,
V.; Agrawal, R. K. Chem. Biol. Drug Des. 2013, 81, 557. (c) Sharma, B.;
Verma, A.; Prajapati, S.; Sharma, U. K. Int. J. Med. Chem. 2013,
No. 348948.
(5) (a) Mishra, P.; Rajak, H.; Mehta, A. J. Gen. Appl. Microbiol. 2005,
51, 133. (b) Kashaw, S. K.; Gupta, V.; Kashaw, V.; Mishra, P.; Stables,
J. P.; Jain, N. K. Med. Chem. Res. 2010, 19, 250. (c) Rajak, H.; Thakur,
B. S.; Singh, A.; Raghuvanshi, K.; Sah, A. K.; Veerasamy, R.; Sharma, P.
C.; Pawar, R. S.; Kharya, M. D. Bioorg. Med. Chem. Lett. 2013, 23, 864.
(d) Sonia, G.; K, R. T. Med. Chem. Res. 2013, 22, 3428. (e) Rai, K. M.
L.; Linganna, N. Il Farmaco 2000, 55, 389. (f) Yale, H. L.; Losee, K. J.
Med. Chem. 1966, 9, 478. (g) Rajak, H.; Agarawal, A.; Parmar, P.;
Thakur, B. S.; Veerasamy, R.; Sharma, P. C.; Kharya, M. D. Bioorg.
Med. Chem. Lett. 2011, 21, 5735. (h) Zender, M.; Klein, T.; Henn, C.;
Kirsch, B.; Maurer, C. K.; Kail, D.; Ritter, C.; Dolezal, O.; Steinbach,
A.; Hartmann, R. W. J. Med. Chem. 2013, 56, 6761.
345, 349. (c) Fang, T.; Tan, Q.; Ding, Z.; Liu, B.; Xu, B. Org. Lett.
2014, 16, 2342. (d) Guda, D. R.; Cho, H. M.; Lee, M. E. RSC Adv.
2013, 3, 7684. (e) Zeevaart, J. G.; Wang, L.; Thakur, V. V.; Leung, C.
S.; Tirado-Rives, J.; Bailey, C. M.; Domaoal, R. A.; Anderson, K. S.;
Jorgensen, W. L. J. Am. Chem. Soc. 2008, 130, 9492. (f) Barreiro, G.;
Kim, J. T.; Guimaraes, C. R. W.; Bailey, C. M.; Domaoal, R. A.; Wang,
̃
L.; Anderson, K. S.; Jorgensen, W. L. J. Med. Chem. 2007, 50, 5324.
(g) Katritzky, A. R.; Vvedensky, V.; Cai, X.; Rogovoy, B.; Steel, P. J.
ARKIVOC 2002, 6, 82.
(11) (a) Levins, C. G.; Wan, Z.-K. Org. Lett. 2008, 10, 1755.
(b) Kawano, T.; Hirano, K.; Satoh, T.; Miura, M. J. Am. Chem. Soc.
2010, 132, 6900. (c) Matsuda, N.; Hirano, K.; Satoh, T.; Miura, M.
Org. Lett. 2011, 13, 2860. (d) Wang, J.; Hou, J.-T.; Wen, J.; Zhang, J.;
Yu, X.-Q. Chem. Commun. 2011, 47, 3652. (e) Wertz, S.; Kodama, S.;
Studer, A. Angew. Chem., Int. Ed. 2011, 50, 11511. (f) Joseph, J.; Kim, J.
Y.; Chang, S. Chem.Eur. J. 2011, 17, 8294.
(12) (a) Yu, W.; Huang, G.; Zhang, Y.; Liu, H.; Dong, L.; Yu, X.; Li,
Y.; Chang, J. J. Org. Chem. 2013, 78, 10337. (b) Zhang, X.; Kang, J.;
Niu, P.; Wu, J.; Yu, W.; Chang, J. J. Org. Chem. 2014, 79, 10170.
(13) Several recent developments achieved this oxidative cyclization
through electro-oxidation: (a) Kumar, S. J. Korean Chem. Soc. 2009, 53,
159. (b) Kumar, S. Proc. Natl. Acad. Sci., India, Sect. A 2012, 82, 157.
(c) Lotfi, B.; Mustafa, B.; Leila, L.; Salima, M. Int. J. Electrochem. Sci.
2011, 6, 1991. (d) Sharma, L. K.; Kumar, S.; Singh, S.; Singh, R. K. P.
Russ. J. Electrochem. 2010, 46, 34. Employing bromine: (e) Chatto-
padhyay, G.; Ray, P. S. Synth. Commun. 2011, 41, 2607. (f) Gupta, V.;
Kashaw, S. K.; Jatav, V.; Mishra, P. Med. Chem. Res. 2008, 17, 205.
(g) Bansal, R. K.; Bhagchandani, G. J. Indian Chem. Soc. 1982, 59, 277
and also see 5g.
(14) Scott, F. L.; Lambe, T. M.; Butler, R. N. J. Chem. Soc., Perkin
Trans. 1 1972, 1918.
(15) (a) Banerjee, A. K.; Vera, W.; Mora, H.; Laya, M. S.; Bedoya, L.;
Cabrera, E. V. J. Sci. Ind. Res. 2006, 65, 299. (b) Togo, H.; Iida, S.
Synlett 2006, 2159. (c) Ren, Y.-M.; Cai, C.; Yang, R.-C. RSC Adv.
2013, 3, 7182. (d) Finkbeiner, P.; Nachtsheim, B. J. Synthesis 2013, 45,
979.
(16) Mitsuhiko, M.; Takuji, S.; Toshimi, M.; Kinichi, I. Chem. Pharm.
Bull. 1976, 24, 2871.
(17) Rai, G.; Kenyon, V.; Jadhav, A.; Schultz, L.; Armstrong, M.;
Jameson, J. B., II; Hoobler, E.; Leister, W.; Simeonov, A.; Holman, T.
R.; Maloney, D. J. J. Med. Chem. 2010, 53, 7392.
(6) Meanwell, N. A. J. Med. Chem. 2011, 54, 2529.
(7) (a) Kumar, C. T. K.; Keshavayya, J.; Rajesh, T. N.; Peethambar, S.
K.; Ali, A. R. S. Org. Chem. Int. 2013, No. 370626. (b) Siddiqui, S. M.;
Salahuddin, A.; Azam, A. Med. Chem. Res. 2013, 22, 1305. (c) Siddiqui,
N.; Ahuja, P.; Malik, S.; Arya, S. K. Arch. Pharm. Chem. Life Sci. 2013,
(18) Hayman, D. F.; Petrow, V.; Stephenson, O. J. Pharm. Pharmacol.
1964, 16, 538.
́
346, 819. (d) Juszczak, M.; Walczak, K.; Langner, E.; Karpinska, M.;
Matysiak, J.; Rzeski, W. Ann. Agric. Environ. Med. 2013, 20, 575.
(e) Hou, Z.; Nakanishi, I.; Kinoshita, T.; Takei, Y.; Yasue, M.; Misu,
R.; Suzuki, Y.; Nakamura, S.; Kure, T.; Ohno, H.; Murata, K.; Kitaura,
K.; Hirasawa, A.; Tsujimoto, G.; Oishi, S.; Fujii, N. J. Med. Chem. 2012,
55, 2899. (f) Ferrari, S.; Morandi, F.; Motiejunas, D.; Nerini, E.;
(19) Guda, D. R.; Cho, H. M.; Lee, M. E. RSC Adv. 2013, 3, 6813.
(20) Tu, G.; Li, S.; Huang, H.; Li, G.; Xiong, F.; Mai, X.; Zhu, H.;
Kuang, B.; Xu, W. F. Bioorg. Med. Chem. 2008, 16, 6663.
(21) Carvalho, A. S.; Gibaldi, D.; Pinto, A. C.; Bozza, M.; Boechat, N.
Lett. Drug Des. Discovery 2006, 3, 98.
(22) Lalezari, I.; Sharghi, N. J. Heterocycl. Chem. 1966, 3, 336.
(23) Liu, X. H.; Shi, Y. X.; Ma, Y.; Zhang, C. Y.; Dong, W. L.; Pan, L.;
Wang, B. L.; Li, B. J.; Li, Z. M. Eur. J. Med. Chem. 2009, 44, 2782.
(24) Dutta, M. M.; Goswami, B. N.; Kataky, J. C. S. J. Indian Chem.
Soc. 1990, 67, 603.
(25) Hilfiker, M. A.; Wang, N.; Hou, X.; Du, Z.; Pullen, M. A.; Nord,
M.; Nagilla, R.; Fries, H. E.; Wu, C. W.; Sulpizio, A. C.; Jaworski, J. P.;
Morrow, D.; Edwards, R. M.; Jin, J. Bioorg. Med. Chem. Lett. 2009, 19,
4292.
̀
Henrich, S.; Luciani, R.; Venturelli, A.; Lazzari, S.; Calo, S.; Gupta, S.;
Hannaert, V.; Michels, P. A. M.; Wade, R. C.; Costi, M. P. J. Med.
Chem. 2011, 54, 211.
(8) (a) Coppo, F. T.; Evans, K. A.; Graybill, T. L.; Burton, G.
Tetrahedron Lett. 2004, 45, 3257. (b) Yang, S. J.; Lee, S. H.; Kwak, H.
J.; Gong, Y. D. J. Org. Chem. 2013, 78, 438. (c) Kilburn, J. P.; Lau, J.;
Jones, R. C. F. Tetrahedron Lett. 2001, 42, 2583. (d) Dolman, S. J.;
Gosselin, F.; O’Shea, P. D.; Davies, I. W. J. Org. Chem. 2006, 71, 9548.
(e) Chaudhari, P. S.; Pathare, S. P.; Akamanchi, K. G. J. Org. Chem.
2012, 77, 3716. (f) Prabhu, G.; Sureshbabu, V. V. Tetrahedron Lett.
2012, 53, 4232. (g) Shinde, V. N.; Ugarkar, B. G.; Ghorpade, S. R. J.
Chem. Res. 2013, 37, 53. (h) Omar, A. M. E.; Aboulwafa, O. J.
(26) Zhao, Z.; Li, L.; Liu, M.; Mei, Q. J. Chem. Res. 2012, 36, 218.
(27) Chubb, F. L.; Nissenbaum, J. Can. J. Chem. 1959, 37, 1121.
F
DOI: 10.1021/jo502518c
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The Journal of Organic Chemistry
Article
(28) Jatav, V.; Mishra, P.; Kashaw, S.; Stables, J. P. Eur. J. Med. Chem.
2008, 43, 135.
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DOI: 10.1021/jo502518c
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