Unusual anisotropic effects from 1,3-dipolar cycloadducts of 4-azidomethyl coumarins

Article abstract of DOI:10.1002/jhet.273

(Chemical Equation Presented) 4-Bromomethylcoumarins (1) reacted with sodium azide in aqueous acetone to give 4-azidomethyl-coumarins (2), which underwent 1,3-dipolar cycloaddition with acetylenic dipolarophiles to give triazoles (3). These triazoles (3)

Full text of DOI:10.1002/jhet.273

January 2010
Unusual Anisotropic Effects from 1,3-Dipolar Cycloadducts of
4-Azidomethyl Coumarins
91
Raviraj A. Kusanur,a Manohar V. Kulkarni,a* Geetha M. Kulkarni,by
Susanta K. Nayak,c Tayur N. Guru Row,c Kilivelu Ganesan,d
and Chung-Ming Sund
aDepartment of Chemistry, Karnatak University, Dharwad 580003, Karnataka, India
bDepartment of Chemistry, Karnatak Science College, Dharwad 580003, Karnataka, India
cSolid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012,
Karnataka, India
dDepartment of Applied Chemistry, National Chiao-Tung University, Hsinchu 300-10, Taiwan,
Republic of China
*E-mail: manohar274@gmail.com
yIn memoriam; deceased July 2009.
Received April 27, 2009
DOI 10.1002/jhet.273
Published online 29 December 2009 in Wiley InterScience (www.interscience.wiley.com).
4-Bromomethylcoumarins (1) reacted with sodium azide in aqueous acetone to give 4-azidomethyl-
coumarins (2), which underwent 1,3-dipolar cycloaddition with acetylenic dipolarophiles to give tria-
zoles (3). These triazoles (3) have been found to exhibit interesting variations in the chemical shifts of
C3AH and C4-methylene protons. Protonation studies indicate that the shielding effect of the C3AH of
coumarin is due to p-electrons of the triazole ring, further supported by diffraction and computational
studies.
J. Heterocyclic Chem., 47, 91 (2010).
INTRODUCTION
RESULTS AND DISCUSSION
Organic azides are an important class of 1,3-dipoles,
which have been recently recognized as crucial func-
tional groups in click chemistry [1]. The exergonic reac-
tion of azides with acetylenic dipolarophiles has resulted
in one of the best synthetic routes to 1,2,3-triazoles [2].
This single-step transformation has been investigated for
its regioselectivity in aqueous systems [3], in ionic
liquids [4], in copper (I) catalysis [5], and by the solid-
phase approach [6]. In view of the wide range of biolog-
ical activities of 1,2,3-triazoles [7,8] and in continuation
of our study on biologically active and fluorescent 4-
substituted coumarins [9,10], it was thought of substan-
tial intellectual appeal to link the 1,2,3-triazole moiety
at the allylic position with respect to the biogenetically
important C3AC4 double bond of coumarin. There are
very few reports on pyranone-substituted 1,3 dipoles
except for the reactions of coumarin 4-nitrile oxides
[11].
The required dipolar azide intermediates (2) were syn-
thesized by the reaction of sodium azide with various 4-
bromomethylcoumarins (1) [12] in aqueous acetone at
room temperature and were quite stable even above
100ꢀC. The first acetylenic dipolarophile used in
this investigation was dimethylacetylenedicarboxylate
(DMAD), giving rise to triazolomethylcoumarins (3) in
1
refluxing xylene (Scheme 1). In the H NMR spectrum
of the azide, (2a, R1 ¼ 6-CH3) as expected, the
C4ACH2 protons linked to the azido group were
observed at 4.57 ppm and the C3AH of coumarin,
appeared as a singlet at 6.52 ppm. The 1H NMR of
DMAD adduct 3a showed two interesting features such
as (i) C4ACH2 protons showed a downfield shift and
were observed at 6.05 ppm when compared with 4.56
ppm observed in the case of 4-anilinomethylcoumarins
or 5.20 ppm observed in the case of 4-phenoxymethyl-
coumarins. (ii) The C3AH of coumarin in the DMAD
C
V
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R. A. Kusanur, M. V. Kulkarni, G. M. Kulkarni, S. K. Nayak, T. N. Gururow, K. Ganesan,
and C. M. Sun
Vol 47
Scheme 1. Synthesis of triazolomethylcoumarins from click chemistry.
adduct experienced an upfield shift and was observed as
a singlet at 5.60 ppm, as against 6.60–6.70 ppm in the
case of both 4-anilinomethyl or 4-phenoxymethyl cou-
marins [13,14]. To the best of our knowledge, there is
only one report in the literature on this type of shielding
effect of coumarin C3AH in 7-methoxy-4-platinomethyl-
coumarin complex coordinated with 1,10-phenanthroline
[15]. This rare type of shielding effect of coumarin
C3AH and simultaneous pronounced deshielding of the
C4-methylene protons were due to the triazole on the
C4ACH2 group, which has been consistently observed in
all the cycloaddition adducts of the azides and DMAD
(Table 1). It is interesting to note that benzylic azides
have also been reported to undergo similar dipolar
cycloaddition reaction [16], but no effects on the chemi-
cal shifts of the ortho protons have been observed. The
chemical shift for the methylene protons in p-hydroxy-
benzyl azide and DMAD adduct is around 5.60 ppm,
whereas the aromatic ortho protons were found to reso-
nate at 7.11 ppm [17].
Table 1
Chemical shift values of C4ACH2 and C3AH in azides (2) and cycloadducts (3) (CDCl3).
C4ACH2
C3AH
DMAD adduct (3)
Entry
R
Azide (2)
DMAD adduct (3)
Azide (2)
a
b
c
d
e
f
6-CH3
7-CH3
4.57
4.56
4.96
4.63
4.57
4.61
4.55
4.54
6.05
6.03
6.54
6.10
6.01
6.08
6.01
6.06
6.52
6.47
6.71
6.57
6.53
6.53
6.58
6.56
5.60
5.67
5.46
5.78
5.80
5.89
5.77
5.81
5,6-benzo
7,8-benzo
6-OCH3
7-OCH3
6-Cl
g
h
7-Cl
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January 2010
Unusual Anisotropic Effects from 1,3-Dipolar Cycloadducts
of 4-Azidomethyl Coumarins
93
Table 2
Temperature dependence of chemical shifts of C4ACH2 and C3AH of
(3a) in DMSO-d6.
Chemical shifts (d ppm)
Temperature (K)
C4ACH2
C3AH
303.1
313.1
323.1
333.1
343.1
353.1
373.1
393.1
6.1790
6.1710
6.1645
6.1565
6.1475
6.1405
6.1245
6.1090
5.638
5.654
5.670
5.689
5.706
5.725
5.758
5.790
sence of any intramolecular hydrogen bonding between
C3AH and triazole nitrogen via a six-membered ring.
Protonation behavior. Qualitative protonation stud-
ies were performed by adding two drops of trifluoroace-
tic acid (CF3CO2H) in CDCl3, which resulted in signifi-
cant changes in the chemical shifts of C3AH and
C4ACH2 protons. In the case of 3a, the C3AH proton
was further shifted downfield to 6.01 ppm from 5.60
ppm and C4ACH2 protons were also deshielded to 6.30
ppm from 6.05 ppm. This trend was observed for all the
substituted cycloadducts (3) (Table 3). In the case of
acetylene adduct 3i, the trend was also similar, whereas
the C4ACH2 protons showed downfield shift from 5.77
to 6.16 ppm and the C3AH from 5.94 to 6.41 ppm.
Probable structures of the protonated species 5 and 6
(Scheme 2) indicate that N1 of the triazole ring can be
quaternized and inductively withdraw the electron den-
sity at C4ACH2, which would cause deshielding effect.
However, the simultaneous deshielding effect of
C3AH under this condition strongly supports an argu-
ment that the C3AH proton falls in the shielding zone
of the triazole moiety, which is perturbed due to proto-
nation. Further, the higher deshielding of the methylene
protons was observed, which can also be explained in
Figure 1. ORTEP diagram of triazole adduct 3i. [Color figure can be
viewed in the online issue, which is available at www.interscience.
wiley.com.]
Effect of substituents. The possible role played by
the two ester groups in this observation was verified by
using other dipolarophiles such as acetylene, phenylace-
tylene, and diphenylacetylene in this reaction with azide
2a (Fig. 1). This led to the formation of adducts 3i, 3j,
and 3k, respectively (Scheme 1). In all these cases, sim-
ilar trend has been observed. Hence, the origin of this
effect lies in the triazole ring rather than the
substituents.
Temperature effect. To understand the nature of this
phenomenon, we recorded the temperature-dependent
NMR for one of the DMAD adducts (3a) at various
temperatures. Up to a temperature of 393 K, there was a
regular decrease in the chemical shift values of C4-
methylene protons from 6.1790 to 6.1090 d ppm. The
C3AH protons showed a slight increase from 5.638 to
5.790 ppm (Table 2). This behavior indicated the ab-
Table 3
Chemical shifts of C4ACH2 and C3AH upon protonation (CDCl3 þ TFA) in DMAD adducts (3a–3h).
C4ACH2 C3AH
Compound
R
CDCl3
CDCl3 þ TFA
CDCl3
CDCl3 þ TFA
3a
3b
3c
3d
3e
3f
6-CH3
7-CH3
6.05
6.03
6.54
6.10
6.01
6.08
5.94
6.06
6.30
6.21
6.73
6.33
6.21
6.29
6.19
6.17
5.60
5.67
5.46
5.78
5.85
5.89
5.77
5.81
6.01
5.94
5.87
6.06
6.09
6.02
6.16
6.00
5,6-benzo
7,8-benzo
6-OCH3
7-OCH3
6-Cl
3g
3h
7-Cl
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R. A. Kusanur, M. V. Kulkarni, G. M. Kulkarni, S. K. Nayak, T. N. Gururow, K. Ganesan,
and C. M. Sun
Vol 47
Scheme 2. Schematic representation of protonation behavior.
Figure 2. Optimized geometries of compounds 3a and 3k. [Color figure
can be viewed in the online issue, which is available at www.interscience.
wiley.com.]
formed according to the density functional theory at the
B3LYP method with standard Gaussian split-valence 6-
31G (d,p) basis set. The two structures clearly revealed
the relative orientations of the triazole ring with respect
to the C3 proton of the coumarin (Fig. 2). The aniso-
tropic effect observed on the C3AH of coumarin is due
to the angularly oriented triazole ring, the p-electron
cloud of which will have a shielding effect.
terms of enhanced contribution of the dipolar form 4 to
the ground-state resonance of compound 3.
Diffraction studies. We have performed a single
crystal analysis of the acetylene adduct 3i. The ORTEP
diagram (Fig. 1) clearly shows that the planar triazole
ring is oriented at an angle of 78.88ꢀ with respect to the
coumarin ring. This supports our argument that the
shielding of the C3AH is due to the triazole ring and
not because of any substituents.
CONCLUSIONS
The unusual anisotropic effects observed in the 4-tria-
zolomethyl coumarins synthesized from 4-azidomethyl-
coumarins 2 and a variety of acetylenic dipolarophiles
are due to the angularly oriented triazole, which has
been shown by NMR, X-ray diffraction, and computa-
tional studies.
Computational support. We have also performed
the geometry optimization of the triazoles 3a and 3k
molecules, which are shown in the Figure 2 using the
Gaussian 03 program [18]. The minimization was per-
Table 4
Synthesis of 4-azidomethyl-chromen-2-ones (2a–2h)and 1-(2-oxo-2H-chromen-4-ylmethyl)-1H-[1,2,3]triazoles (3a–3k).
Entry
Product
R1
R2
R3
Melting point (ꢀC)
Yield (%)
1
2
2a
2b
2c
2d
2e
2f
2g
2h
3a
3b
3c
3d
3e
3f
6-CH3
7-CH3
–
–
–
–
110
104
146
131
106
92
118
102
192
151
180
226
194
182
209
194
199
168
170
63
60
65
64
62
59
66
65
76
75
78
79
70
69
72
70
69
71
67
3
5,6-Benzo
7,8-Benzo
6-OCH3
7-OCH3
6-Cl
–
–
4
5
–
–
–
–
6
7
–
–
–
–
8
9
7-Cl
6-CH3
7-CH3
–
–
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
H
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
H
10
11
12
13
14
15
16
17
18
19
5,6-Benzo
7,8-Benzo
6-OCH3
7-OCH3
6-Cl
3g
3h
3i
3j
3k
7-Cl
6-CH3
6-CH3
6-CH3
H
Ph
Ph
Ph
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January 2010
Unusual Anisotropic Effects from 1,3-Dipolar Cycloadducts
of 4-Azidomethyl Coumarins
95
EXPERIMENTAL
6.53 (s, 1H, C3AH), 6.96 (d, 1H, C7AH, J ¼ 8.1 Hz), 7.26
(d, 1H, C8AH, J ¼ 8.1 Hz), 7.40 (s, 1H, C5AH). Anal. Calcd.
for C11H9N3O3; C, 57.14; H, 3.92; N, 18.17; Found: C, 57.11;
H, 3.83; N, 18.06.
Melting points were determined by open capillary method
and are uncorrected. The elemental analysis was performed
using Heraus CHN rapid analyzer. Analytical TLC was per-
formed on Merck precoated 60 F254 silica gel plates. IR spec-
tra (KBr disc) were recorded on a Nicolet-5700 FTIR spectro-
4-Azidomethyl-7-methoxy-chromen-2-one (2f). Colorless
solid (petroleum ether), mp. 92ꢀC, yield 59%; IR (KBr, m in
1
cmꢁ1): 1712 (lactone C¼¼O), 2116 (N3); H NMR (300 MHz,
photometer. H and 13C NMR spectra were recorded on Bruker
1
CDCl3): d 3.93 (s, 3H, C7AOCH3), 4.61 (s, 2H, CH2AN3),
6.53 (s, 1H, C3AH), 6.55–7.44 (m, 3H, ArAH). Anal. Calcd.
for C11H9N3O3; C, 57.14; H, 3.92; N, 18.17; Found: C, 57.09;
H, 3.86; N, 18.02.
300 MHz spectrometer using CDCl3 as a solvent and tetrame-
thylsilane as an internal standard. The chemical shifts are
expressed in d ppm scale down field from tetramethylsilane
and proton signals are indicated as s ¼ singlet, d ¼ doublet, t
¼ triplet and m ¼ multiplet. EI 70 EV and AUTOSPEC elec-
tron impact mass spectrometer was used to record mass
spectra.
Preparation of substituted 4-bromomethylcoumarins (1a–
1h). The required substituted 4-bromomethylcoumarins 1 [14]
have been synthesized by the Pechmann cyclization of various
phenols with 4-bromoethylacetoacetate.
4-Azidomethyl-6-chloro-chromen-2-one (2g). Colorless solid
(petroleum ether), mp. 118ꢀC, yield 66%; IR (KBr, m in
1
cmꢁ1): 1720 (lactone C¼¼O), 2121 (N3); H NMR (300 MHz,
CDCl3): d 4.55 (s, 2H, CH2AN3), 6.58 (s, 1H, C3AH), 7.32
(d, 1H, C7AH, J ¼ 8.2 Hz), 7.54 (d, 1H, C8AH, J ¼ 8.2 Hz),
7.70 (s, 1H, C5AH); LCMS m/z: 237 [M þ 2]. Anal. Calcd.
for C10H6ClN3O2; C, 50.97; H, 2.57; N, 15.05; Found: C,
50.82; H, 2.54; N, 15.01.
General procedure for the preparation of 4-azidomethyl-
chromen-2-ones (2a–2h). 4-Bromo-methylcoumarin 1 (0.01
mol) was taken in acetone (20 mL) in a round bottom flask.
To this, sodium azide (0.012 mol) in 3 mL of water was added
dropwise with stirring. The stirring was continued for 10 h
(reaction was monitored by TLC). Then, the reaction mixture
was poured to ice cold water. The separated solid was filtered
and recrystallized using suitable solvent (Table 4).
4-Azidomethyl-7-chloro-chromen-2-one (2h). Colorless solid
(petroleum ether), mp. 102ꢀC, yield 65%; IR (KBr, m in
1
cmꢁ1): 1710 (lactone C¼¼O), 2120 (N3); H NMR (300 MHz,
CDCl3): d 4.54 (s, 2H, CH2AN3), 6.56 (s, 1H, C3AH), 7.21
(d, 1H, C6AH, J ¼ 8.1 Hz), 7.41 (s, 1H, C8AH), 7.71 (d, 1H,
C5AH, J ¼ 7.9 Hz). Anal. Calcd. for C10H6ClN3O2; C, 50.97;
H, 2.57; N, 15.05; Found: C, 50.91; H, 2.52; N, 15.00.
General procedure for the preparation of 1-(2-oxo-2H-
chromen-4-ylmethyl)-1H-[1,2,3]triazole-4,5-dicaboxylic acid
dimethyl ester (3a–3h). Mixture of 4-azidomethylcoumarin 2
(0.01 mol) and DMAD (0.01 mol) was taken in a dry xylene
(5 mL) in a round bottom flask. The mixture was refluxed in
an oil bath at 130ꢀC under dry conditions for 8 h (reaction
was monitored by TLC) and then cooled. The separated solid
was collected by filtration and recrystallized using suitable
solvent.
4-Azidomethyl-6-methyl-chromen-2-one (2a). Colorless
solid (ethanol), mp. 110ꢀC, yield 63%; IR (KBr, m in cmꢁ1):
1
1722 (lactone C¼¼O), 2109 (N3); H NMR (300 MHz, CDCl3):
d 2.44 (s, 3H, C6ACH3), 4.57 (s, 2H, CH2AN3), 6.52 (s, 1H,
C3AH), 7.30 (s, 1H, C5AH), 7.32 (d, 1H, C7AH, J ¼ 7.9
Hz), 7.40 (d, 1H, C8AH, J ¼ 8.3 Hz); LCMS m/z: 216 [M þ
1]. Anal. Calcd. for C11H9N3O2; C, 61.39; H, 4.22; N, 19.53;
Found: C, 61.36; H, 4.10; N, 19.51.
4-Azidomethyl-7-methyl-chromen-2-one (2b). Colorless
solid (petroleum ether þ benzene), mp. 104ꢀC, yield 60%; IR
(KBr, m in cmꢁ1): 1732 (lactone C¼¼O), 2098 (N3); 1H NMR
(300 MHz, CDCl3): d 2.47 (s, 3H, C7ACH3), 4.56 (s, 2H,
CH2AN3), 6.47 (s, 1H, C3AH), 7.27 (s, 1H, C8AH), 7.13 (d,
1H, C6AH, J ¼ 8.0 Hz), 7.41 (d, 1H, C5AH, J ¼ 8.0 Hz);
LCMS m/z: 216 [M þ 1]. Anal. Calcd. for C11H9N3O2; C,
61.39; H, 4.22; N, 19.53; Found: C, 61.32; H, 4.08; N, 19.47.
1-Azidomethyl-benzo[f]chromen-3-one (2c). Colorless solid
(ethanol), mp. 146ꢀC, yield 65%; IR (KBr, m in cmꢁ1): 1727
(lactone C¼¼O), 2099 (N3); 1H NMR (300 MHz, CDCl3): d
4.96 (s, 2H, CH2AN3), 6.71 (s, 1H, C3AH), 7.50 (d, 1H,
ArAH, J ¼ 8.8 Hz), 7.58 (t, 1H, ArAH, J ¼ 6.6 Hz), 7.69 (t,
1H, ArAH, J ¼ 6.6 Hz), 7.94 (d, 1H, C7AH, J ¼ 8.1 Hz),
8.02 (d, 1H, ArAH, J ¼ 8.9 Hz), 8.25 (d, 1H, C8AH, J ¼ 8.0
Hz). Anal. Calcd. for C14H9N3O2; C, 66.93; H, 3.61; N, 16.73;
Found: C, 66.90; H, 3.54; N, 16.70.
1-(6-Methyl-2-oxo-2H-chromen-4-ylmethyl)-1H-[1,2,3]tri-
azole-4,5-dicaboxylic acid dimethyl ester (3a). Colorless
solid (ethanol), mp. 192ꢀC, yield 76%; IR (KBr, m in cmꢁ1):
1
1722 (lactone C¼¼O), 1722 (ester C¼¼O); H NMR (300 MHz,
CDCl3): d 2.46 (s, 3H, C6ACH3), 3.95 (s, 3H, ACOOCH3),
4.02 (s, 3H, ACOOCH3), 5.60 (s, 1H, C3AH), 6.05 (s, 2H,
C4ACH2), 7.36 (d, 1H, C7AH, J ¼ 8.4 Hz), 7.51 (d, 1H,
C8AH, J ¼ 8.4 Hz), 7.67 (s, 1H, C5AH); 13C NMR (75 MHz,
CDCl3): 22, 50, 53, 54, 114, 117, 118, 124, 130, 134, 135,
141, 148, 152, 158, 161, 162; LCMS m/z: 358 [M þ 1]. Anal.
Calcd. for C17H15N3O6; C, 57.14; H, 4.23; N, 11.76; Found:
C, 57.18; H, 4.17; N, 11.69.
1-(7-Methyl-2-oxo-2H-chromen-4-ylmethyl)-1H-[1,2,3]tri-
azole-4,5-dicaboxylic acid dimethyl ester (3b). Colorless
solid (benzene), mp. 151ꢀC, yield 75%; IR (KBr, m in cmꢁ1):
1
1722 (lactone C¼¼O), 1754 (ester C¼¼O); H NMR (300 MHz,
CDCl3): d 2.48 (s, 3H, C7ACH3), 3.94 (s, 3H, ACOOCH3),
4.01 (s, 3H, ACOOCH3), 5.67 (s, 1H, C3AH), 6.03 (s, 2H,
C4ACH2), 7.17 (d, 1H, C6AH, J ¼ 7.2 Hz), 7.37 (s, 1H,
C8AH), 7.57 (d, 1H, C5AH, J ¼ 7.1 Hz); LCMS m/z: 358 [M
þ 1]. Anal. Calcd. for C17H15N3O6; C, 57.14; H, 4.23; N,
11.76; Found: C, 57.19; H, 4.16; N, 11.72.
4-Azidomethyl-benzo[h]chromen-2-one (2d). Colorless solid
(ethanol), mp. 131ꢀC, yield 64%; IR (KBr, m in cmꢁ1): 1716
(lactone C¼¼O), 2115 (N3); 1H NMR (300 MHz, CDCl3): d
4.63 (s, 2H, CH2AN3), 6.57 (s, 1H, C3AH), 7.26–8.54 (m,
6H, ArAH). Anal. Calcd. for C14H9N3O2; C, 66.93; H, 3.61;
N, 16.73; Found: C, 66.87; H, 3.53; N, 16.66.
1-(3-Oxo-3H-benzo[f]chromen-1-ylmethyl)-1H-[1,2,3]tria-
zole-4,5-dicaboxylic acid dimethyl ester (3c). Colorless solid
(ethanol), mp. 180ꢀC, yield 78%; IR (KBr, m in cmꢁ1): 1731
(lactone C¼¼O), 1731 (ester C¼¼O); 1H NMR (300 MHz,
CDCl3): d 3.85 (s, 3H, ACOOCH3), 4.03 (s, 3H, ACOOCH3),
4-Azidomethyl-6-methoxy-chromen-2-one (2e). Colorless
solid (petroleum ether), mp. 106ꢀC, yield 62%; IR (KBr, m in
1
cmꢁ1): 1710 (lactone C¼¼O), 2115 (N3); H NMR (300 MHz,
CDCl3): d 3.90 (s, 3H, C6AOCH3), 4.57 (s, 2H, CH2AN3),
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and C. M. Sun
Vol 47
5.46 (s, 1H, C3AH), 6.54 (s, 2H, C4ACH2), 7.52 (d, 1H, J ¼
8.9 Hz), 7.62 (t, 1H, J ¼ 7.3 Hz), 7.72 (t, 1H, J ¼ 7.5 Hz),
8.00 (d, 1H, C7AH, J ¼ 8.0 Hz), 8.07 (d, 1H, J ¼ 8.9 Hz),
7.66 (d, 1H, triazole), 7.82 (d, 1H, triazole); LCMS m/z: 242
[M þ 1]. Anal. Calcd. for C13H11N3O2; C, 64.72; H, 4.60; N,
17.42; Found: C, 64.68; H, 4.58; N, 17.40.
8.19 (d, 1H, C8AH,
J
¼
8.0 Hz). Anal. Calcd. for
Preparation of 6-methyl-4-(4-phenyl-[1,2,3]triazol-1-
ylmethyl)-chromen-2-one (3j). Mixture of 4-azidomethyl-
coumarin 2a (0.01 mol) and phenyl acetylene (0.01 mol) was
taken in a dry xylene (5 mL) in a dry round bottom flask. The
mixture was refluxed in an oil bath at 130ꢀC under dry condi-
tions for 10 h (reaction was monitored by TLC) and cooled.
The separated solid was filtered and recrystallized from alco-
hol.Colorless solid (ethanol), mp. 168ꢀC, yield 71%; IR (KBr,
m in cmꢁ1): 1738 (lactone C¼¼O); 1H NMR (300 MHz,
CDCl3): d 2.43 (s, 3H, C6ACH3), 5.77 (s, 2H, C4ACH2), 6.10
(s, 1H, C3AH), 7.28–7.84 (m, 9H, ArAH); LCMS m/z: 318
[M þ 1]. Anal. Calcd. for C19H15N3O2; C, 71.91; H, 4.76; N,
13.24; Found: C, 71.80; H, 4.72; N, 13.18.
C20H15N3O6; C, 61.07; H, 3.84; N, 10.68; Found: C, 61.01;
H, 3.79; N, 10.60.
1-(2-Oxo-2H-benzo[h]chromen-4-ylmethyl)-1H-[1,2,3]tria-
zole-4,5-dicaboxylic acid dimethyl ester (3d). Colorless solid
(ethanol þ dioxane), mp. 226ꢀC, yield 79%; IR (KBr, m in
cmꢁ1): 1711 (lactone C¼¼O), 1738 (ester C¼¼O); 1H NMR
(300 MHz, CDCl3): d 3.94 (s, 3H, ACOOCH3), 4.01 (s, 3H,
ACOOCH3), 5.78 (s, 1H, C3AH), 6.10 (s, 2H, C4ACH2),
7.20–8.54 (m, 6H, ArAH). Anal. Calcd. for C20H15N3O6; C,
61.07; H, 3.84; N, 10.68; Found: C, 61.04; H, 3.80; N, 10.63.
1-(6-Methoxy-2-oxo-2H-chromen-4-ylmethyl)-1H-[1,2,3]
triazole-4,5-dicaboxylic acid dimethyl ester (3e). Colorless
solid (ethanol þ dioxane), mp. 194ꢀC, yield 70%; IR (KBr, m
in cmꢁ1): 1720 (lactone C¼¼O), 1744 (ester C¼¼O); 1H NMR
(300 MHz, CDCl3): d 3.87 (s, 3H, C6AOCH3), 3.93 (s, 3H,
ACOOCH3), 4.00 (s, 3H, ACOOCH3), 5.85 (s, 1H, C3AH),
6.01 (s, 2H, C4ACH2), 7.16–7.34 (m, 3H, ArAH). Anal.
Calcd. for C17H15N3O7; C, 54.69; H, 4.05; N, 11.26; Found:
C, 54.62; H, 4.17; N, 11.25.
1-(7-Methoxy-2-oxo-2H-chromen-4-ylmethyl)-1H-[1,2,3]
triazole-4,5-dicaboxylic acid dimethyl ester (3f). Colorless
solid (ethanol þ dioxane), mp. 182ꢀC, yield 69%; IR (KBr, m
in cmꢁ1): 1722 (lactone C¼¼O), 1742 (ester C¼¼O); 1H NMR
(300 MHz, CDCl3): d 3.89 (s, 3H, C7AOCH3), 3.96 (s, 3H,
ACOOCH3), 4.01 (s, 3H, ACOOCH3), 5.89 (s, 1H, C3AH),
6.08 (s, 2H, C4ACH2), 7.21–7.92 (m, 3H, ArAH). Anal.
Calcd. for C17H15N3O7; C, 54.69; H, 4.05; N, 11.26; Found:
C, 54.60; H, 4.13; N, 11.21.
Preparation of 4-(4,5-diphenyl-[1,2,3]triazol-1-ylmethyl)-6-
methyl-chromen-2-one (3k). Mixture of 4-azidomethylcou-
marin 2a (0.01 mol) and diphenylacetylene (0.01 mol) was
taken in a dry xylene (5 mL) in a dry round bottom flask. The
mixture was refluxed in an oil bath at 130ꢀC under dry condi-
tions for 10 h (reaction was monitored by TLC) and cooled.
The separated solid was filtered and recrystallized from
alcohol.
Colorless solid (ethanol), mp. 170ꢀC, yield 67%; IR (KBr, m
1
in cmꢁ1): 1732 (lactone C¼¼O); H NMR (300 MHz, CDCl3):
d 2.39 (s, 3H, C6ACH3), 5.58 (s, 2H, C4ACH2), 5.70 (s, 1H,
C3AH), 7.24–7.58 (m, 13H, ArAH); LCMS m/z: 394 [M þ
1]. Anal. Calcd. for C25H19N3O2; C, 76.32; H, 4.87; N, 10.68;
Found: C, 76.26; H, 4.84; N, 10.65.
Acknowledgments. CMS and KG thank National Council of
Science, Taiwan for financial assistance and Dr. P. Raghunath,
NCTU, Taiwan for nice discussion regarding computational stud-
ies. MVK and GMK thank the authorities of the Karnatak Univer-
sity, Dharwad, India for providing laboratory facilities and
fellowship to RAK.
1-(6-Chloro-2-oxo-2H-chromen-4-ylmethyl)-1H-[1,2,3]tri-
azole-4,5-dicaboxylic acid dimethyl ester (3g). Colorless
solid (ethanol), mp. 209ꢀC, yield 72%; IR (KBr, m in cmꢁ1):
1
1726 (lactone C¼¼O), 1726 (ester C¼¼O); H NMR (300 MHz,
CDCl3): d 3.96 (s, 3H, ACOOCH3), 4.02 (s, 3H, ACOOCH3),
5.77 (s, 1H, C3AH), 6.01 (s, 2H, C4ACH2), 7.35 (d, 1H,
C7AH, J ¼ 8.8 Hz), 7.57 (d, 1H, C8AH, J ¼ 8.7 Hz), 7.70 (s,
1H, C5AH); LCMS m/z: 379 [M þ 2]. Anal. Calcd. for
C16H12ClN3O6; C, 50.87; H, 3.20; N, 11.12; Found: C, 50.79;
H, 3.15; N, 11.05.
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1-(7-Chloro-2-oxo-2H-chromen-4-ylmethyl)-1H-[1,2,3]tri-
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1721 (lactone C¼¼O), 1754 (ester C¼¼O); H NMR (300 MHz,
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5.81 (s, 1H, C3AH), 6.06 (s, 2H, C4ACH2), 7.72–7.64 (m,
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