One-pot microwave-assisted solvent-free synthesis, theoretical and experimental studies on barrier rotation of C-N bond of N-alkenyl-1,2,3-triazoles

Article abstract of DOI:10.1007/s11224-014-0422-6

The reactions on benzotriazoles continue to happen to reach interesting varieties of their derivatives. This study reports a fast one-pot microwave-assisted solvent-free synthesis of N-alkenyl-1,2,3-benzotriazole (3, 5, and 7) and 1-(2-Alkyloxycarbonyl-vi

Full text of DOI:10.1007/s11224-014-0422-6

Struct Chem
DOI 10.1007/s11224-014-0422-6
ORIGINAL RESEARCH
One-pot microwave-assisted solvent-free synthesis, theoretical
and experimental studies on barrier rotation of C–N bond
of N-alkenyl-1,2,3-triazoles
Maryam Malekdar
•
Avat Arman Taherpour
•
Issa Yavari Kambiz Larijani
•
Received: 7 August 2013 / Accepted: 5 March 2014
Springer Science+Business Media New York 2014
ꢀ
Abstract The reactions on benzotriazoles continue to
happen to reach interesting varieties of their derivatives.
This study reports a fast one-pot microwave-assisted sol-
vent-free synthesis of N-alkenyl-1,2,3-benzotriazole (3, 5,
and 7) and 1-(2-Alkyloxycarbonyl-vinyl)-1H-[1–3] tria-
zole-4-carboxylic acid methyl ester (8 and 9) derivatives by
nucleophilic addition reactions of 1,2,3-benzotriazole
Introduction
Triazoles are known to be relatively resilient to metabolic
degradation and have known utility in several medicinal
chemistry campaigns as isosteres for phenyl rings and
carboxyl functionalities [1]. In general, 1,2,3-triazole for-
mation requires harsh conditions, that is, high temperature
and longer reaction times. In the original description, the
explored examples showed that although these were rela-
tively clean processes, they could take from 12 to 48 h at
high temperatures (*110 ꢁC) [1]. The triazoles may dis-
play a wide range of biological activities as anti-HIV and
(
C H N ) (1) and 1H-[1–3] triazole-4-carboxylic acid
6 5 3
0
methyl ester (C H N O ) (1 ) with R-propiolates (R = Me,
4
4 3 2
Et; 2 & 4) and phenylacetylene 6 in good yields. The
values of activation energy for rotation around C–N bond
in the synthesized N-alkenyl-1,2,3-triazole compounds
were studied by DFT-B3LYP/6-31G* method.
anti-microbial agents as well as selective b -adrenergic
3
receptor agonist and anti-allergic agents [2–6]. Addition-
ally, 1,2,3-triazoles are found in herbicides, fungicides, and
dyes [7, 8]. As an aromatic heterocycle, Benzotriazole is a
commonly used corrosion inhibitor. Benzotriazoles are also
a class of compounds containing the benzotriazole skele-
ton. The [3 ? 2] cycloaddition reactions under microwave
irradiation and theoretical conditions were previously
investigated and reported to produce 1,2,3-triazoles [9–14].
The 1,2,3-triazole derivatives are produced by reaction of
o-phenylenediamine, sodium nitrite, and acetic acid. The
conversion proceeds via diazotization of one of the amine
groups [15, 16]. Benzotriazole is a complexing agent and
as such is a useful corrosion inhibitor, e.g., for silver pro-
tection in dishwashing detergents and an anti-fog agent in
photographic development. Aircraft deicer and anti-icer
fluid contain benzotriazole. Benzotriazole derivatives are
found in pharmaceuticals such as antifungal, antibacterial,
and anthelmintic drugs. Benzotriazole is fairly water sol-
uble, not readily degradable, and has a limited sorption
tendency. Hence, it is only partly removed in wastewater
treatment plants and a substantial fraction reaches surface
waters such as rivers and lakes [15, 16]. In 2008, Shi et al.
Keywords Microwave-assisted synthesis ꢀ 1,2,3-
Triazoles ꢀ N-alkenyl-1,2,3-benzotriazole ꢀ Solvent free ꢀ
Alkylpropiolates ꢀ Solvent-free synthesis ꢀ DFT-B3LYP
method ꢀ Molecular modeling
M. Malekdar
Chemistry Department, Science Faculty, Islamic Azad
University, Arak Branch, P.O. Box 38135-567, Arak, Iran
A. A. Taherpour (&)
Department of Organic Chemistry, Faculty of Chemistry, Razi
University, P.O. Box 67149-67346, Kermanshah, Iran
e-mail: avatarman.taherpour@gmail.com
I. Yavari
Department of Chemistry, Tarbiat Modares University,
P.O. Box 14115-175, Tehran, Iran
K. Larijani
Research Council of Science and Research Campus, Islamic
Azad University, P.O. Box 14155-4933, Tehran, Iran
123

Struct Chem
Fig. 1 The one-pot microwave-
assisted solvent-free with high-
oriented synthesis of simple N-
substituted-1,2,3-triazoles (3, 5,
3a
7a
N
4
7
3
5
6
2
N
1
N
3
a
N
Solvent free
MW
4
7
3
7
, 8, and 9)
5
6
H
2
N
β
α
2
00 W, 15 min.
8
1
N
H
R
9
7
a
H
R= -COOCH3
R= -COOCH CH3
2
4
6
3 (91%)
5 (87%)
7 (~15%)
R
H
2
(
1)
R= -Ph
7
OCH3
Compounds 2 and 4
7
4
N
3
6
O
H3CO
N
3
N
N
2
N
6
4
2
H
Solvent free
MW
1
N
5
1
8
2
00 W, 15 min.
O
5
9
R
H
(
1')
8 (92%)
(90%)
H
9
[
17] reported a rapid and easy entry to a variety of
irradiation in organic chemistry, the accelerated process
described has been a lure for chemists to further apply new
reactions to this technology [30]. Some of the different
methods to syntheses of compounds 3–7 were reported
before [38–40].
substituted, functionalized benzotriazoles under mild con-
ditions by a [3 ? 2] cycloaddition of azides to benzynes.
Benzotriazole-containing polymers have recently emerged
in organic electronic applications and are increasingly
attracting a great deal of attention. These polymers are
reviewed from a general perspective in terms of their
potential use in three main fields, electrochromics, organic
solar cells, and organic light-emitting diodes [18]. It is well
This study reports a fast one-pot microwave-assisted
(200 W/100 ꢁC and 15 min.) solvent-free with high-ori-
ented synthesis of N-alkenyl-1,2,3-triazoles (3, 5, 7, new
derivatives 8 & 9) by the nucleophilic addition reactions of
1,2,3-benzotriazole (1) and 1H- [1–3] triazole-4-carboxylic
demonstrated that substitution reactions on triazoles (1 and
0
0
1
) and its N-substituent derivatives have not been widely
acid methyl ester (1 ) with alkyl-propiolates (2 and 4) in
good yields. The GC yield of 7 was about 15 %. There was
utilized. This is due to the triazole action as a deactivating
group on the benzene ring while the orientation is largely
influenced by the nature and the position of the substituent
0
not any successful reaction between 1 and 1 with DMAD
and DEAD in the conditions and by changing the MW-
irradiation conditions. Another (Fig. 1) aspect of this study
was the molecular modeling of the values of activation
energy for rotation around C–N Bond in the synthesized N-
alkenyl-1,2,3-triazole compounds. This study was carried
out by DFT-B3LYP/6-31G* method.
groups [19]. The microwave solvent-free synthesis of 1H-
0
[
1–3] triazole-4-carboxylic acid methyl ester (1 ) was
1
reported before [10]. The C-NMR analysis of the
3
chemical shifts of carbon atoms in the benzotriazoles was
1
3
already investigated by Carta et al. [20]. The results of C-
NMR analysis in benzotriazole derivatives demonstrated
bearing a substituent on the ring, and an alkyl substituent
on the nitrogen position of the triazole moiety proved to be
a tool for identification of the N-alkyl isomers [20]. By the
Experiments
1
3
use of the reported C-NMR data [20], it is possible to
observe that the chemical shifts assigned to the quaternary
carbon atoms C-3a and C-7a fall in different regions no
matter if they are close to the ring substituent or not. The
results have prompted investigations to see if these recur-
ring differences were maintained in both ring and N1(2)(3)
structure benzotriazoles [20]. Using the analysis of results
The N -alkenyl-1,2,3-triazole derivatives that were syn-
1
thesized (3, 5, 7, 8, and 9) were known by their physical
1
13
data, FT-IR, H-NMR, C-NMR, mass (MS) spectra, and
CHN analysis. The FT-IR spectra were recorded as KBr
1
pellets on a Shimadzu FT-IR 8000 spectrometer. H-NMR
1
3
and C-NMR spectra were determined on a 300 MHz
Br u¨ ker spectrometer. The solvent for NMR recording was
1
3
obtained from C-NMR method, it is obviously possible to
distinguish different isomers. [20] Microwave-assisted
synthesis has been utilized as a powerful and effective
technique to promote a group of chemical reactions [21–
CDCl . GC and GC–MS analysis were performed on a
3
Shimadzu QP5050A GC–MS instrument, injector 200 ꢁC;
temperature program: 100 ꢁC (2 min), then 16 ꢁC per min
till 250 ꢁC on a Zebron capillary column ZB-5 (0.25 lm
thickness, 0.32 mm diameter, and 30 m length). It should
3
7]. Since the first publications on the use of microwave
1
23

Struct Chem
Conformer(3A); 2167 = 0°
Conformer(3B); 2167 =180°
Conformer(5A); 2167 = 0°
Conformer(5B); 2167 =180°
Conformer(7A); 2167 = 0°
Conformer(7B); 2167 =180°
Fig. 2 The structure and the conformers (A and B with U2167 = 0ꢁ and 180ꢁ, respectively) of the 1,2,3-triazoles 3, 5, and 7
be noted that a limited amount of compounds is required
for the experiment. Therefore, some small quantity of
vapor is evolved during irradiation. A Labmate microwave
reactor (Milstone-Ethos 1.; 2,540 Hz, Max 1,200 W) was
used for the MW-assisted syntheses; temperatures were
measured externally by infrared fiber optics.
calculations have been performed by Spartan ‘10 package
[41]. To calculate the values of activation energy for
rotation around the C–N bond in the synthesized triazoles,
appropriate dihedral angle change around the C–N bond
(reaction coordinate method) and optimization in each step
were utilized. The Hartree’s energy was converted to
-
1
kcal mol , and the relative energies were calculated. The
graphs and the related tables demonstrated the appropriate
data. All of the graphing operations for the synthesized N-
alkenyl-1,2,3-triazoles were performed using the Microsoft
Office Excel-2013 program. The optimized structures of the
synthesized N-alkenyl-1,2,3-triazole (3, 5, 7, 8, and 9) were
Molecular modeling
The calculations on the structures of the synthesized N-
alkenyl-1,2,3-triazole (3, 5, 7, 8, and 9) have been per-
formed by the density functional theory (DFT) method.
The structure of the N-alkenyl-1,2,3-triazole (3, 5, 7, 8, and
1
carried out to calculate the H-NMR by DFT-B3LYP/6-
1
31G* method. The experimental and calculated H-NMR
9
) was optimized by DFT-B3LYP/6-31G* method. All
by the DFT method were compared and discussed.
123

Struct Chem
Conformer(8A); 2167 = 0°
Conformer(8B); 2167 = 180°
Conformer(9A); 2167 = 0°
Conformer(9B); 2167 = 180°
Conformer(10A); 2167 = 0°
Conformer(10B); 2167 = 180°
Fig. 3 The structure and the conformers (A and B with U2167 = 0ꢁ and 180ꢁ, respectively) of the 1,2,3-triazoles 8, 9, and 10
Results and discussion
have enough d? charge for the nucleophilic addition
reactions of 1 and 1 on 2, 4, and 6. The symmetry reactants
of DMAD and DEAD do not have this suitable condition
0
Synthesis the N-substituted-1,2,3-triazoles
for this regio- and chemo-selectivity. The results of the GC,
1
13
In accordance with the method explained in the experi-
0
Mass, FT-IR, H-NMR, and C-NMR of the products have
been investigated. The GC spectrum of 3-benzotriazol-1-
yl-acrylic acid methyl ester (3) shows a signal at retention
time R.T. = 9.608 min that is related to the product 3. The
mass (MS) spectrum of 3-benzotriazol-1-yl-acrylic acid
methyl ester (3) was investigated. The results have shown
the omission of –N , –CO CH , –N–CH=CH–CO CH ,
mental section, the mixture of 1,2,3-triazole 1 and 1 with
the propyolate derivatives (2, 4, and 6) in different exper-
iments was exposed to 200 W/100 ꢁC microwave irradia-
1
13
tion for 15 min. The FT-IR, H-NMR, C-NMR, MS
spectrums, and CHN analysis of the MW-irradiation pro-
cess are demonstrated in the experimental section. No
details are given about the by-products, and only the final
products are considered. The results demonstrate high-
2
2
3
2
3
?
and –N –CH=CH–CO CH from [M] = 203 in the MS
3
2
3
1
13
spectrum of 3. The data of the FT-IR, H-NMR, and C-
NMR spectrums of 3-Benzotriazol-1-yl-acrylic acid methyl
ester (3) were demonstrated in the experimental section.
The GC spectrum of 3-Benzotriazol-1-yl-acrylic acid ethyl
ester (5) showed a signal at retention time R.T. = 10.150
that is related to the product 5. The mass spectrum of
3-benzotriazol-1-yl-acrylic acid ethyl ester (5) has shown
the omission of –N , –CO C H , –N–CH=CH–CO C H ,
oriented synthesis of simple N -alkenyl-1,2,3-triazole (3, 5,
1
7
, 8, and 9) products. Even after changing the conditions of
0
the reactions, the reaction between the triazoles 1 and 1
with DMAD and DEAD did not show any result. Consid-
ering this and the low yield (about 15 % by GC method) of
the nucleophilic addition reactions of 1 and 6 (H–C:C–
Ph), it seems that the C of the reactants 2 and 4 should
b
2
2
2
5
2 2 5
1
23

Struct Chem
Fig. 4 The rotation process to
interconversion of the
3
conformers (3A, [T.S.] , and 3B
with U2167 = 0ꢁ, 94ꢁ, and 180ꢁ,
respectively) of the 1,2,3-
triazole 3
Fig. 5 The rotation process to
interconversion of the
5
conformers (5A, [T.S.] , and 5B
with U2167 = 0ꢁ, 90ꢁ, and 180ꢁ,
respectively) of the 1,2,3-
triazole 5
–
N –CH=CH–CO C H , and –CO H group by the
5
the products 8 and 9 have been demonstrated in the
experimental section.
3
2
2
2
?
Mclafferty rearrangement from [M] = 217 in the MS
1
13
spectrum of 5. The FT-IR, H-NMR, and C-NMR spec-
trums of 3-benzotriazol-1-yl-acrylic acid ethyl ester (5)
have been demonstrated in the experimental section. The
The FT-IR spectrums show the C=O of ester functional
-
1
group at 1,712 and 1,704 cm for 3 and 5, respectively.
The –N – function vibration frequencies of 1,2,3-benzo-
3
1
13
results of the GC, Mass, FT-IR, H-NMR, and C-NMR of
triazole (1) rings appeared at 1,437 & 1,279 & 1,456 and
123

Struct Chem
Fig. 6 The rotation process to
interconversion of the
7
conformers (7A, [T.S.] , and 7B
with U2167 = 0ꢁ, 94ꢁ, and 180ꢁ,
respectively) of the 1,2,3-
triazole 7
Fig. 7 The rotation process to
interconversion of the
8
conformers (8A, [T.S.] , and 8B
with U2167 = 0ꢁ, 91ꢁ, and 180ꢁ,
respectively) of the 1,2,3-
triazole 8
-
1
2
2
1
,276 cm for the products 3 and 5, respectively. The
C=C stretching of N -alkene branch of the products 3 and
spectrums, the trans pattern of H–C =C –H of the pro-
sp sp
ducts 3 and 5 appeared as an AX doublet of doublet in
6.72–6.77 & 8.48–8.53 ppm (d.d-AX, 2H, 15 Hz) and
6.71–6.76 & 8.47–8.52 ppm (d.d-AX, 2H, 15 Hz),
1
-
appeared at 1,656 and 1,650 cm , respectively. The
1
5
C –H stretching of the products appeared at 3,000–3,150
2
sp
-
1
3
and 3,000–3,100 cm for 3 and 5, respectively. The C -
sp
13
respectively. The C-NMR results show 10 and 11
H stretching of the products 3 and 5 appeared at 2,958 and
2
C-atom types for 3 and 5, respectively. See the results at
?
the experimental section. The [M ] for 3, 5, and 7 were
-
,986 cm , respectively. The N -H stretching frequency
1
1
of benzotriazole 1 as a single absorption has been
removed from the FT-IR spectrum of the products 3 and 5,
203, 217, and 221, respectively. The mass spectrums of 3,
5, and 7 show m/z 175, 189, and 193, respectively,
meaning that each of the products under mass conditions
has lost 28 weight unit. This is due to the omission of
–N =N – from the structure of the products. These evi-
1
respectively. The H-NMR spectrum of 3 shows a singlet
signal for CH group at 3.84 ppm. The quartet and triplet
3
for –CH CH appeared at 1.33–1.38 ppm (q, 2H, 7.0 Hz)
2
3
2
3
1
and 4.28–4.35 ppm (t, 3H, 7.0 Hz) for 5. In H-NMR
13
dences and the reported results of C-NMR analysis
1
23

Struct Chem
Fig. 8 The rotation process to
interconversion of the
9
conformers (9A, [T.S.] , and 9B
with U2167 = 0ꢁ, 92ꢁ, and 180ꢁ,
respectively) of the 1,2,3-
triazole 9
Fig. 9 The rotation process to
interconversion of the
conformers (10A, [T.S.]10, and
1
1
0B with U2167 = 0ꢁ, 93ꢁ, and
80ꢁ, respectively) of the 1,2,3-
triazole 10
method by Carta et al. [20] confirm that the substituted
Activation energy for rotation around C–N bond
in the synthesized N-alkenyl-1,2,3-triazoles
alkene group was located on N in the structures of 3, 5,
1
and 7 products. There were almost the same interpreta-
tions for the structures of products 8 and 9 from com-
The principles of rotation about the C=C bond through the
dipolar transition state (the thermal mechanism of the Z, E-
isomerization) have been discussed in previous studies
[42–44]. The main factors concerning C=C rotation are:
increasing the electron-donating power and the acceptor
capacity promotes polarization of the C=C bond in the
0
pound 1 . The percentages of C, H, and N were explained
in the experimental section. Based on the results shown in
the experimental section, the MS spectrums and CHN
analysis demonstrated the formation of products during
the synthesis process.
123

Struct Chem
Table 1 The selected structural data of the 1,2,3-triazoles (3, 5, and 7) and the saddle form of interconversions of the conformers A and B
Selected data
3A $ 3B
5A $ 5B
5A
7A $ 7B
7A
3
A
[T.S.]
3
3B
[T.S.]
5
5B
[T.S.]
7
7B
DG = 0.45 DG* = 9.05
DG = 0.50 DG* = 9.41
DG = 0.36 DG* = 5.26
˚
Bond length (A)
N1–N2
1.386
1.283
1.386
1.405
1.378
1.388
1.341
1.474
1.085
1.083
2.461
2.669
–
1.386
1.283
1.385
1.406
1.379
1.388
1.341
1.474
1.085
1.083
3.511
3.512
3.771
2.965
1.396
1.278
1.386
1.409
1.381
1.385
1.343
1.475
1.085
1.081
–
1.386
1.284
1.385
1.406
1.378
1.389
1.341
1.475
1.085
1.083
2.466
2.664
–
1.386
1.283
1.385
1.406
1.379
1.388
1.341
1.474
1.085
1.083
3.453
3.463
3.883
2.992
1.395
1.278
1.386
1.409
1.381
1.385
1.343
1.476
1.085
1.081
–
1.377
1.289
1.381
1.408
1.375
1.402
1.343
1.464
1.084
1.086
2.442
2.535
–
1.377
1.289
1.381
1.408
1.375
1.402
1.343
1.464
1.084
1.086
3.496
3.403
3.711
2.950
1.385
1.284
1.382
1.410
1.377
1.399
1.344
1.466
1.084
1.086
–
N2–N3
N3–C4
C4–C5
C5–N1
N1–C6
C6–C7
C7–C8
C6–H16
C7–H17
H16ꢀꢀꢀH18
H17ꢀꢀꢀN2
H17ꢀꢀꢀH18
H16ꢀꢀꢀN2
Bond angle (ꢁ)
N1N2N3
N2N3C4
–
–
–
2.071
2.439
2.074
2.438
2.107
2.443
–
–
–
109.02
109.15
108.60
103.73
128.42
125.69
118.11
114.28
122.52
109.05
109.13
108.63
103.69
128.64
125.47
118.27
114.41
122.42
109.31
109.06
108.92
103.53
133.99
127.33
118.48
112.33
124.11
109.04
109.13
108.61
103.72
128.49
125.63
118.20
114.37
122.48
109.05
109.13
108.63
103.69
128.64
125.47
118.27
114.41
122.42
109.32
109.04
108.92
103.53
134.02
127.50
118.25
112.30
124.20
109.27
108.80
108.59
103.76
128.33
124.10
126.28
112.52
117.47
109.27
108.80
108.59
103.76
128.33
124.10
126.28
112.52
117.47
109.49
108.72
108.91
103.53
133.53
125.94
125.28
110.93
119.30
N3C4C5
C4C5N1
C5N1C6
N1C6C7
C6C7C8
N1C6H16
C6C7H17
Torsional angle (ꢁ)
N2N1C6C7
N2N1C6H16
N1C6C7C8
C8C7C6H16
0.00
180
180
0.00
94.14
-85.81
180
180
0.00
180
0.00
0.00
180
180
0.00
90.14
-89.81
180
180
0.00
180
0.00
0.63
94.00
-86.00
180
164.18
-14.13
178.57
-3.30
179.37
179.87
0.00
0.00
0.00
0.00
-
1
n
The values of DG and DG* were reported in kcal mol . [T.S.] means transition state form. See the graphs
molecular ground state and stabilizes the charges in the
transition state, thereby decreasing the values of activation
energy to rotation. An increase in the size of the substitu-
ents at the double bond increases steric strain in the
molecular ground state, which also decreases the rotation
values of activation energy. Increasing the dielectric con-
stant of the medium favors polarization of the C=C bond in
the ground state and separation of charges in the transition
saddle, which decreases the barrier to rotation about the
C=C bond. The values of activation energy for rotation
around the C–N bond are a very useful quantitative char-
acteristic of the structure of enamines [42–44].
8, 9, and 10) were optimized for the first-order saddle point,
which was characterized with only one imaginary
frequency.
Due to the delocalization of the electron pair of the
nitrogen atom in the aromatic ring of 1,2,3-triazole, the
rotation around C–N bond in the structures of N-alkenyl-
1,2,3-triazole (3, 5, 7, 8, 9, and 10) calculated by DFT-
B3LYP/6-31G* was rather low. The delocalization of the
electron pair of the nitrogen atom (inside the aromatic rings
and out of the structures N–C=C–C=O) has been restricted
due to this reason; so, the energy rotation around C–N bond
is low. It is assumed, in this study, that the barrier rotation
around C–N is of a greater importance compared to C=C
bond. The stable conformers of the N-alkenyl-1,2,3-triazole
(3, 5, 7, 8, 9, and 10) were calculated and optimized by
The transition state forms of the compounds 3–10 were
confirmed by the applied DFT method. For this procedure,
in this study, the transition state forms ([T.S.] ; n = 3, 5, 7,
n
1
23

Struct Chem
Table 2 The selected structural data of the 1,2,3-triazoles (8, 9, and 10) and the saddle form of interconversions of the conformers A and B
Selected data
8A $ 8B
9A $ 9B
9A
10A $ 10B
10A
8
A
[T.S.]
8
8B
[T.S.]
9
9B
[T.S.]10
10B
DG = 0.22 DG* = 8.14
DG = 0.35 DG* = 8.56
DG = 0.60 DG* = 6.29
˚
Bond length (A)
N1–N2
1.378
1.289
1.374
1.376
1.358
1.398
1.338
1.479
1.085
1.083
2.582
2.632
–
1.384
1.286
1.375
1.376
1.358
1.395
1.339
1.479
1.084
1.084
3.342
3.427
3.826
2.938
1.384
1.286
1.375
1.376
1.358
1.395
1.339
1.479
1.085
1.081
–
1.378
1.289
1.374
1.377
1.358
1.399
1.338
1.480
1.085
1.083
2.581
2.632
–
1.384
1.286
1.375
1.376
1.358
1.395
1.339
1.479
1.084
1.084
3.332
3.414
3.846
2.945
1.383
1.286
1.376
1.376
1.359
1.395
1.339
1.480
1.084
1.085
–
1.362
1.301
1.367
1.373
1.363
1.411
1.332
–
1.367
1.298
1.368
1.372
1.363
1.406
1.332
–
1.367
1.298
1.368
1.372
1.363
1.406
1.332
–
N2–N3
N3–C4
C4–C5
C5–N1
N1–C6
C6–C7
C7–C8
C6–H16
1.085
1.084
2.543
2.622
–
1.084
1.085
3.294
3.396
3.856
2.929
1.084
1.084
–
C7–H17
H16…H18
H17…N2
H17…H18
H16…N2
Bond angle (ꢁ)
N1N2N3
N2N3C4
–
–
–
2.418
2.481
2.411
2.485
2.404
2.453
–
–
–
107.49
109.52
108.44
104.52
127.92
124.54
118.36
114.51
122.30
107.65
109.36
108.68
104.45
131.82
125.47
118.96
112.78
123.32
107.65
109.36
108.68
104.45
131.82
125.47
118.96
112.78
123.32
107.49
109.52
108.43
104.52
127.92
124.55
118.42
114.52
122.28
107.65
109.36
108.68
104.45
131.82
125.47
118.96
112.78
123.32
107.65
109.35
108.66
104.46
131.68
125.45
118.96
112.90
123.32
107.45
109.30
108.62
104.35
127.66
124.40
–
107.61
109.12
108.87
104.27
131.47
125.58
–
107.61
109.12
108.87
104.27
131.47
125.58
–
N3C4C5
C4C5N1
C5N1C6
N1C6C7
C6C7C8
N1C6H16
C6C7H17
Torsional angle (ꢁ)
N2N1C6C7
N2N1C6H16
N1C6C7C8
C8C7C6H16
112.68
121.78
111.02
123.28
111.02
123.28
0.00
180
180
0.00
91
180
0.00
180
0.00
0.00
180
180
0.00
92
180
0.00
180
0.00
0.00
180
–
93
-87
–
180
0.00
–
-89
180
0.00
-88
180
0.00
–
–
–
-
1
n
The values of DG and DG* were reported in kcal mol . [T.S.] means transition state form. See the graphs
DFT-B3LYP/6-31G* method. The results of the selected
˚
around the C–N bond and optimization in each step by
DFT-B3LYP/6-31G* method were employed. The reaction
coordinate method for A and B conformers of the N-
alkenyl-1,2,3-triazole (3, 5, 7, 8, 9, and 10) was carried out
to gain the transition state forms by changing U2167 from 0ꢁ
to about 90ꢁ and 180ꢁ to about 90ꢁ. The values of the
activation energies around the C–N bond in the process of
the interconversion of the two stable conformers (A and
B in 3, 5, 7, 8, 9, and 10) are (DG*) 9.05, 9.41, 5.26, 8.14,
structural data i.e., bond lengths in A, bond angle, (h) and
dihedral angles (U) (in ꢁ) are demonstrated in the Figs. 2,
3
, 4, 5, 6, 7, 8 and 9 for the N-alkenyl-1,2,3-triazole (3, 5, 7,
, 9, and 10) and Tables 1 and 2. In N-alkenyl-1,2,3-tria-
8
zole (3, 5, 7, 8, 9, and 10), the conformers ‘‘A’’
(
(
(
U2167 = 0ꢁ) are more stable compared to ‘‘B’’ forms
U2167 = 180ꢁ). The 3A, 5A, 7A, 8A, 9A, and 10A are
DG = 0.45, 0.50, 0.36, 0.22, 0.35, and 0.60 kcal mol
-
1
)
-
1
more stable than 3B, 5B, 7B, 8B, 9B, and 10B, respec-
tively. See Tables 1 and 2. To calculate the values of
activation energy for rotation around the C–N bond and
investigate the interconversion process of the two stable
conformers (A and B) of the N-alkenyl-1,2,3-triazole (3, 5,
8.56, and 6.29 kcal mol , respectively. See Figs. 4, 5, 6,
7, 8, 9 and Tables 1 and 2.
The dihedral angles (U2167) in the process of the inter-
conversion of the two stable conformers (A and B in 3, 5,
7, 8, 9, and 10) are: 94ꢁ, 90ꢁ, 94ꢁ, 91ꢁ, 92ꢁ, and 93ꢁ,
respectively. Tables 1 and 2 have shown the calculated
7
, 8, 9, and 10), the change of the U2167 dihedral angle
123

Struct Chem
Table 3 The calculated chemical shifts (in vacuum) of H-16 and H-17 of the compounds 3–10
Compounds and data Chemical Shifts of H-16 and H-17 of the compounds 3–10
3
5
7
8
9
10
U
2167
U
2167
U
2167
U
2167
U
2167
U
2167
0
ꢁ
180ꢁ
0ꢁ
180ꢁ
0ꢁ
180ꢁ 0ꢁ
7.72 (6.80) 8.34
6.78 (6.65) 5.67
180ꢁ 0ꢁ
180ꢁ 0ꢁ
180ꢁ
H-16
H-17
8.16 8.72 (8.50) 8.14 (8.38) 8.79 (8.51) 7.58 8.24
6.69 5.86 (6.72) 6.73 (6.98) 5.88 (6.71) 7.52 6.57
7.71 8.33
6.81 5.71
6.77 7.45
6.36 5.12
3
The values in parentheses are the experimental values of H-16 and H-17 chemical shifts (in CDCl )
results for the distances between H6ꢀꢀꢀH18 and H7ꢀꢀꢀH18 in
the two stable conformers (A and B in 3, 5, 7, 8, 9, and 10).
The distances between H16ꢀꢀꢀH18 and N2ꢀꢀꢀH17 of the
stable conformers (A in 3, 5, 7, 8, 9, and 10) are: (2.461,
considering their medicinal effects, are closely related to the
structures of their isomers A and B. The physicochemical
properties as well as the structural properties are related to
this phenomenon. One of the important investigations rela-
ted to this property is the chemical shifts of the H-vinyl
atoms in the structures.
2
.669), (2.466, 2.664), (2.442, 2.535), (2.582, 2.632),
˚
2.581, 2.632), and (2.543, 2.622) A, respectively. The
(
distances between H17ꢀꢀꢀH18 and N2ꢀꢀꢀH16 of the B rota-
mers (in 3, 5, 7, 8, 9, and 10) are: (2.071, 2.439), (2.074,
The chemical shifts (in vacuum state) for H-16 and H-17
of the compounds 3–10 were calculated by DFT-B3LYP/6-
31G* method. The rotation around C–N bond (U2167) in the
structures of N-alkenyl-1,2,3-triazole (3, 5, 7, 8, 9, and 10)
has made different chemical shifts for the H-atoms. The
calculated chemical shifts in non-solvent conditions by
DFT-B3LYP/6-31G* method are demonstrated in Table 3.
The values in parentheses are the experimental values of
2
.438), (2.107, 2.443), (2.418, 2.481), (2.411, 2.485), and
˚
2.404, 2.453) A, respectively. In the transition state of
(
A $ B, the interatomic distances of H16ꢀꢀꢀH18, N2ꢀꢀꢀH17,
H16ꢀꢀꢀH18 and N2ꢀꢀꢀH17 (3, 5, 7, 8, 9, and 10) are: (3.511,
3
.512, 3.771 & 2.965), (3.453, 3.463, 3.883 & 2.992),
(
3.496, 3.403, 3.711 & 2.950), (3.342, 3.427, 3.826 &
2
3
.938), (3.332, 3.414, 3.846 & 2.945), and (3.294, 3.396,
˚
.856 & 2.929) A, respectively. Derivative 10 was not
H-16 and H-17 chemical shifts (in CDCl ). The different
3
chemical shifts are related to the different local shielding of
the H-atoms that occurs because of the interconversion
between the rotamers A and B of compounds 3–10. There
is good agreement between the theoretical and experi-
mental results. As it can be seen in Table 3, the calculated
chemical shifts of H-16 and H-17 for 3 and 5 were 8.72 and
synthesized here. This molecule was calculated to compare
its data with other molecules (structures 8 and 9). See
Figs. 4, 5, 6, 7, 8, 9 and Tables 1 and 2.
In the stable conformers 7A and 7B, the dihedral angles
U2167 are not 0 and 180ꢁ, respectively. The dihedral angles
U2167 for 7A and 7B were calculated as 0.63ꢁ and about 164ꢁ,
respectively. The conformer 7B in U2167 = 164ꢁ is
1
5.86 ppm, respectively, when U2167 was 180ꢁ. The H-
NMR experimental data for the introduced hydrogen atoms
-
1
0.018 kcal mol
more stable than this conformer in
in the structures and in CDCl were obtained: 8.50 and
3
U2167 = 180ꢁ. Because of aromatization in the 1,2,3-triazole
rings, the values of activation energy rotation around C–N
bond are lower than the ordinary enamines. See Tables 1 and
6.72 ppm, respectively. The experimental and calculated
data for the chemical shifts of H-16 and H-17 in 5 and 8
(when U2167 = 0ꢁ) were: {8.14 (8.38), 6.73 (6.98)} and
{7.72 (6.80), 6.78 (6.65)}, respectively. See Table 3.
2. Due to delocalization of the electron pair of the nitrogen
atom inside the 1,2,3-triazole aromatic rings, the calculated
magnitude of DG* for rotation around C–N bond in such
structures (N–C=C–C=O) is rather low (from about
Typical procedure for synthesis
-1
5–10 kcal mol ). An increase in electron-donating power and
acceptor capacity decreases the energy barrier to the rotation.
The two rotamers A and B for each of the structures were
obtained due to the low values of activation energy of C–N
bond rotation in the structures of N-alkenyl-1,2,3-triazole (3,
3-Benzotriazol-1-yl-acrylic acid methyl ester (3)
A mixture of benzotriazole 1 (0.06 g, 5 mmol) and methyl
propiolate 2 (0.8 g, 1.0 ml, 0.01 mol) was made in a dried
heavy wall Pyrex tube. The tube was sealed and then exposed
to microwave oven. After 15 min irradiation at 200 W
(100 ꢁC) power, the mixture was cooled to room tempera-
ture. The residue of compounds was evaporated under air and
reduced pressure. An off-white solid was afforded. The
product 3 can be recrystallized from dried diethyl ether.
5
, 7, 8, 9, and 10). The interconversion of the isomers A and
B is very simple because of the delocalization of the electron
pair of the nitrogen atom in the aromatic rings of the 1,2,3-
triazoles. So, there is no resonance between this nitrogen
atom and C=C (like the ordinary eneamines). The interac-
tions between these compounds with the receptors,
1
23

Struct Chem
Conclusion
11. Taherpour AA, Faraji M (2008) Molbank M577:1
1
2. Taherpour AA, Rajaian E (2008) J Mol Struct (THEOCHEM)
49:23
8
Here a fast one-pot microwave-assisted solvent-free with
1
3. Taherpour AA, Adams N, Wentrup C (2007) Fourth Heron island
conference on reactive intermediates and unusual molecules,
Queensland, Australia, 7–14 July 2007
high-oriented synthesis of simple N-alkenyl-1,2,3-triazole
(
3, 5, 7, 8, and 9) derivatives by nucleophilic addition
0
14. Taherpour AA, Rajaeian E, Shafiei H, Malekdar M (2013) Struct
Chem 24:523
reactions of 1,2,3-benzotriazole 1 and 1 with alkyl-propi-
olates (2 and 4) and phenylacetylene 6 is reported. The Cb
of the reactants 2 and 4 should have enough d? charge for
1
5. Smiley RA (2002) Phenylene- and toluene diamines in Ullmann’s
encyclopedia of industrial chemistry. Wiley, Weinheim
0
the reactions of 1 and 1 on 2 and 4. The symmetry reac-
16. Giger W, Schaffner C, Kohler HP (2006) Environ Sci Technol
0:7186
4
tants of 6, DMAD, and DEAD do not have this suitable
condition for this regio- and chemo-selectivity. The results
of the procedure confirmed the facility and rapidity of this
solvent-free with high-oriented synthesis of 3, 5, 7, 8, and 9
derivatives by the nucleophilic additional reaction. The
calculations on the structures of the synthesized N-alkenyl-
1
1
7. Shi F, Waldo JP, Chen Y, Larock RC (2008) Org Lett 10:2409
8. Balan A, Baran D, Toppare L (2011) Polym Chem 2:1029
19. Carta A, Piras S, Boatto G, Paglietti G (2005) Heterocycles
65(10):2471
2
0. Carta A, Sanna P, Paglietti G, Sparatore F (2001) Heterocycles
5(6):1133
1. Stadier A, Kappe CO (2005) Microw Assist Org Synth 2:177
6
2
1
,2,3-triazole (3, 5, 7, 8, and 9) were performed by the DFT
22. Kappe CO (2004) Angew Chem Int Ed 43:6250
23. Kappe CO, Stadler A (2005) Microwaves in organic and
medicinal chemistry. Wiley, Weinheim
method. In this study, the computational method employed
cover density functional theory (DFT) approaches. The
structure of the N-alkenyl-1,2,3-triazole (3, 5, 7, 8, and 9)
was optimized by DFT-B3LYP/6-31G* method. The val-
ues of activation energy for rotation around C–N bond in
the synthesized N-alkenyl-1,2,3-triazole compounds were
studied by DFT-B3LYP/6-31G* method.
2
4. Zbancioc NG, Caprosu DM, Moldoveanu CC, Ionel II (2005)
ARKIVOC 10:189
25. Katrisky AR, Singh SK (2003) ARKIVOC 13:68
26. Ling MJ, Sun CM (2004) Synlett 4:663
2
7. Dai W-M, Guo D-S, Sun L-P, Huang X-H (2003) Org Lett
(16):2919
5
2
8. Finaru A, Berthault A, Besson T, Guillaument G, Berteina-Rab-
oin S (2002) Org Lett 4(16):2613
Acknowledgments The corresponding author gratefully acknowl-
edges Professor Curt Wentrup and the colleagues in Chemistry
Department of The University of Queensland, Australia, for their
useful suggestions and for permitting to use CEM Labmate micro-
wave reactor for some of the MW tests during the sabbatical oppor-
tunity. We have also acknowledged Theoretical and Computational
Research Center of Chemistry Faculty of Razi University, Kerman-
shah, Iran and the Research Council of Science and Research
Campus, Islamic Azad University, Tehran, Iran for permitting to use
the Labmate microwave reactor (Milstone-Ethos 1.; 2,540 Hz, Max
29. Hoel MLA, Nielsen J (1999) Tetrahedron Lett 40(20):3941
30. Gedye R, Smith F, Westaway K, Ali H, Baldisera L, Laberge L,
Rousell J (1986) Tetrahedron Lett 27:279
31. Katrisky AR, Singh SK (2002) J Org Chem 67:9077
32. Sha C-K, Mohanakrishnan AK (2002) In: Padwa A, Pearson WH
(eds) Chemistry of heterocyclic compounds, vol 59. Wiely, New
York
33. Gilchrist TL, Gymer GE (1974) In: Katrizky AR, Boulton AJ
(eds) Advances in heterocyclic chemistry, vol 16. Academic
Press, New York
1
,200 W).
34. Padwa A (1984) In: Taylor EC, Weissberger A (eds) 1,3-Dipolar
cycloaddition chemistry, vol 1. Wiely, New York
3
5. Sheradsky T (1971) In: Patai S (ed) The chemistry of the Azido
group. Wiley, New York
References
3
6. Guezguez R, Bougrin K, El Akriand K, Benhida R (2006) Tet-
rahedron Lett 47:4807
7. Molteni G, Del Buttero P (2005) Tetrahedron 61(21):4983
8. Kabir MS, Namjoshi OA, Verma R, Lorenz M, Phani Babu
Tiruveedhula VVN, Monte VVN, Bertz SH, Schwabacher AW,
Cook JM (2012) J Org Chem 77(1):300
9. Kabir MS, Namjoshi OA, Verma R, Verma R, Polanowski R,
Krueger SM, Sherman D, Rott MA, Schwan WR, Monte A, Cook
JM (2010) Bioorg Med Chem 18(12):4178
0. Katritzky AR, Rachwal S, Caster KC, Mahni F, Law KW, Rubio
O (1987) J Chem Soc Perkin Trans 1(4):781
1. (2011) All of the calculations were performed by: Spatran’10-
Quantum Mechanics Program: (PC/x86) 1.1.0v4. Wavefunction,
USA
2. Bakhmutov VI, Fedin EI (1982) Bull Mag Reson 6(3):142
3. Kalinowski HO, Kessler H (1972) In: Allinger NL, Eliel EL (eds)
Topics in stereochemistry, vol 7. Wiley, New York, p 296
4. Azzaro M, Geribaldi S, Videau B (1985) Magn Reson Chem
1
. Savin KA, Robertson M, Gernet D, Green S, Hembre EJ, Bishop
J (2003) Mol Diver 7:171
3
3
2
3
4
. Garanti L, Molteni G (2003) Tetrahedron Lett 44:1133
. Molteni G, Buttero PD (2005) Tetrahedron 61:4983
. Alvarez R, Velazquez S, San F, Aquaro S, De C, Perno C,
Karlsson A, Balzarini J, Camarasa JM (1994) J Med Chem
3
3
7:4285
5
6
7
8
. Velazquez S, Alvarez R, Perez C, Gago F, De C, Balzarini J,
Camarasa MJ (1998) Antivir Chem Chemother 9:481
. Genin MJ, Allwine DA, Andersn DJ, Barbachyn MR, Grega KC,
Hester JB et al (2000) J Med Chem 43:953
. Appukkuttan P, Dehaen W, Fokin VV, Van der Eyken E (2004)
Org Lett 6(23):4223
. Wamhoff H (1984) In: Katrizky AR, Rees CW (eds) Compre-
hensive heterocyclic chemistry, vol 5. Pergamon Press, New
York, p 669
4
4
4
4
4
9
. Taherpour AA, Kvaskoff D, Bernhardt PV, Wentrup C (2010) J
Phys Org Chem 23:382
2
3(1):28
1
0. Taherpour AA, Kheradmand K (2009) J Heterocycl Chem
46:131
2
123