A novel approach for the synthesis of imidazo and triazolopyridines from dithioesters

Article abstract of DOI:10.1039/c6nj01038e

T3P-DMSO mediated desulfurative cyclization of in situ generated thioamides serves as an efficient and versatile method for the synthesis of imidazo[1,5-a]pyridines and [1,2,4]-triazolo[4,3-a]pyridines with good to excellent yields. Substrates such as 2-methylaminoquinoline and pyrazin-2-yl-methanamine also undergo the corresponding reactions at room temperature. This efficient protocol has several advantages such as mild conditions, short reaction time, operational simplicity and high yields.

Full text of DOI:10.1039/c6nj01038e

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Novel Approach for the Synthesis of Imidazo and
Triazolopyridines from Dithioesters
Ajjahalli. B. Ramesha,a# Nagarakere. C. Sandhya,b# Chottanahalli. S. Pavan Kumar,a
Mahanthawamy Hiremath,a Kempegowda Mantelingua* and Kanchugarakoppal. S. Rangappa,a*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Abstract: T3P–DMSO mediated desulfurative cyclization of in situ generated thioamides serves as an efficient, and
versatile method for the synthesis of imidazo[1,5-a]pyridines and [1,2,4]-triazolo[4,3-a]pyridines with good to excellent
yields. Substrates such as 2-methylaminoquinoline and pyrazin-2-ylmethanamine also undergo the corresponding
reactions at room temperature. This efficient protocol has several advantages such as mild conditions, short reaction time,
operational simplicity and high yields.
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Introduction
H
CH3COOH
N
R
N
N
N
N
H
o
180 C, ꢀꢁwave
Imidazo and triazolopyridines, which belong to a class of N-
bridged 5,6-bicylic heterocycles are important motifs in
medicinal chemistry.1 Imidazo[1,2-a]pyridine (Figure 1) is the
key structure of anoxiolytic agents (Alpidem),2a comprising of
drugs used for treatment of insomnia (Zolpidem)2b and heart
failure (Olprinone).2c In addition imidazopyridine derivatives
have received considerable attention as core ligands in the
field of electronic devices.3 They have also been identified as
calcium channel blockers,4a phosphodiesterase 10A (PDE-10A)
inhibitors,4b and (GABA) modulators.4c Furthermore, The
N
O
R
Reichelt et al ref (8c)
Burgess reagent
(2.5 equv)
Y
R
N
X
N
X
THF, reflux, 30 min
Y
O
R
Chen et al ref (10)
triazolopyridine scaffold possess
a broad spectrum of
Figure 1 Previous reports
biological and pharmaceutical activities,5a including antiviral,5b
antibacterial,5c and antidepressent.5d Moreover, Pettit et al.6a
the synthesis of triazolopyridines using dehydrative cyclization
reported
imidazo[1,5-a]isoquinolinedione in the tricyclic structure of
cribrostatin , a highly active antimicrobial and antineoplastic
a unique example of a naturally occurring
in acetic acid under microwave irradiation (figure 1).8c
Synthesis of imidazo[1,5-a]pyridines by using Tf2O,9 and Burges
reagent,10 have been reported. Paoletti et al also reported the
synthesis of imidazo[1,5-a]pyridines starting from carboxylic acids
using Propylphosphonic anhydride(T3P).11 Very recently, Schmidt et
al synthesized triazolopyridines from 2-hydroxypyridine and
imidates using acetic acid.12 Bhate et al synthesized
triazolopyridines from hydrazinopyridine and aldehydes.13
However, the most commonly used procedures have the large
excess use of activating reagents, have narrow scope, perform at
elevated temperatures, and use multistep synthesis. There is still
need for a general procedure applicable for the synthesis of N-
bridged 5,6-bicyclic pyridines. To address this issue we decided to
elaborate a T3P-DMSO mediated cyclodehydration/aromatization
strategy under operationally simple and mild conditions applicable
to wide variety of substitution patterns. Several groups have
reported the utility of T3P reagent.14a T3P was initially employed as
6
agent. Many groups reported the total synthesis of cribostatin
analogs.6b-d
Early synthetic methods involve the conventional
cyclodehydrogenation of amides or thioamides to form cyclic
compounds by strong acidic, corrosive reagents such as
POCl3,7a SOCl2,7b etc. Cyclodehydration using Lawesson’s
reagent8a and a modified Mitsunobu reaction8b to prepare
triazolopyridines have been reported. Riechelt et al reported
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peptide coupling agent,14b-c dehydrating agent.14d–e Its utility was
successfully demonstrated in rearrangement reactions,14f-g
heterocyclic synthesis14h-j
and C-C bond formation.14k In
continuation of our work on synthetic applications of T3P,15
dithioesters16 and synthesis of heterocyclic compounds,17-19 we
here in report a new and simple one-pot procedure to access
imidazo[1,5-a]pyridines and [1,2,4]-triazolo[4,3-a]pyridines starting
from dithioesters and 2-methylaminopyridines using T3P in THF
(50% solution in ethylacetate).
Scheme 1 Substrate scope for reaction of amines with dithioesters
via cyclodehydration using T3P-DMSO
Results and Discussion
We set out to identify the possible mild conditions under which
the reaction of 2-methylaminopyridine 2a with phenyl dithioester
1a would proceed. Initially, the reaction of 2- methylaminopyridine
2a (1.1 eq), T3P (0.5 eq, 50% in EtOAc), DMSO (1.0 eq) in THF at
room -temperature for 24 h was carried out. The desired product
was obtained in 25% yield (Table 1, entry 1). Upon increasing the
amount of T3P to 1.0 eq, yield of the product was increased to 45%
Table 1 Optimization of conditions for the synthesis of 3a
No.
T3P
DMSO Solvent
Time Temperature Yield
in h
%
1
0.5 eq 1.0 eq THF
1.0 eq 1.0 eq THF
1.5 eq 1.0 eq THF
2.0 eq 1.0 eq THF
1.0 eq 1.5 eq THF
1.0 eq 2.0 eq THF
1.0 eq 2.5 eq THF
24
24
24
24
12
2
RT
RT
25
45
43
42
65
82
78
-
2
3
RT
4
RT
5
RT
6
RT
7
2
RT
8
1.0 eq
-
THF
24
2
RT
9
1.0 eq 2.0 eq THF
1.0 eq 2.0 eq THF
1.0 eq 2.0 eq THF
1.0 eq 2.0 eq THF
1.0 eq 2.0 eq DMF
1.0 eq 2.0 eq EtOAc
1.0 eq 2.0 eq Toluene
1.0 eq 2.0 eq CH3CN
1.0 eq 2.0 eq CHCl3
40 °C
50 °C
60 °C
reflux
RT
80
78
74
74
66
75
46
55
47
43
10
11
12
13
14
15
16
17
18
1.5
1
(Table 1, entry-2). No significant improvement in the yield was
observed when T3P was increased to 1.5 eq and 2.0 eq (Table 1,
entries 3-4). Further, the effect of DMSO was also investigated (Table
1, entries 5-7). Significant improvement in the yield of 3a was
observed when the amount of DMSO was increased (Table 1, entries
5-6). No significant change in the yield was observed when DMSO
was increased to 2.5 eq (Table 1, entry 7). We found that with 2
methylaminopyridine (1.1 eq), dithioester (1.0 eq), T3P (1.0 eq), and
DMSO (2.0 eq), the reaction condition was ideal. The reaction did not
take place at room temperature for 24 h in the absence of DMSO and
this made the point obvious that DMSO was needed
1
2
2
RT
2
RT
2
RT
2
RT
1.0 eq 2.0eq
Dioxane
2
RT
aReactions were performed with T3P (50 % in ethyl acetate) 1.1 mmol of 1a and 1.0 mmol
of 2a. Yields are isolated yields of chromatographically purified compounds.
2 | J. Name., 2012, 00, 1-3
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. Effect of the temperature was also tested, as the temperature final product 3a.
increase no significant improvement in the yield was observed (Table
1, entries 9-12). The solvents screened included THF, DMF, EtOAc,
toluene, CH3CN, CHCl3, and dioxane, among which THF was found to
be the preferred solvent (Table 1, entries 6, 13-17).
Reactions of 2-methylaminopyridine with a range of dithioesters
were evaluated under optimized conditions (Scheme 2). In all cases,
products were obtained in good yields at room temperature. The
presence of electron withdrawing and electron donating
substituents on the aromatic rings of the dithioesters did not affect
the efficiency of reaction. Dithioesters bearing halogens such as –F,
–Cl was employed and the desired products were obtained in
excellent yields
and 3m) benzothiophene (3n) and pyridine (3o) were compatible in
this reaction to give the desired products without polymerization
. The hetero-cyclic dithioesters like thiophene (3l
.
The reaction was successfully carried out with various aliphatic
dithioesters like isopropyl (3p) and isobutyl (3q). Importantly other
amines including 2-methylaminoquinoline and pyrazin-2-
ylmethanamine (3j and 3k) also underwent the reaction under
Scheme 3 Plausible mechanism for the formation of imidazo
[1,5-a]pyridine
equally mild conditions (scheme 1)
.
The scope of the reaction was further enhanced with the
different amine substrate like 2-hydrazinylpyridine. Surprisingly, all
reactions took place at room temperature (scheme 2).
Conclusion
In conclusion,
a mild, an efficient substitution and
intramolecular cyclization of the pyridine 2-methylamine and
dithioester leading to imidazo[1,5-a]pyridines and [1,2,4]-
triazolo[4,3-a]pyridines have been developed. The transformation
affords the products under mild conditions in good to excellent
yields at room temperature. The key step is intramolecular
cyclization of in situ generated thioamides. The overall process is
facilitated by the combined action of T3P and DMSO.
Experimental section:
(3a): 3-phenylimidazo[1,5-a]pyridine
Pale yellow solid (164mg, 82%); MP 101–103 oC; 1H NMR (400 MHz
DMSO-d6): δ 6.70–6.66 (m, 1H), 6.82–6.79 (m, 1H), 7.45 (t, J = 7.2
Hz,1H), 7.54–7.50 (m, 3H), 7.62 (d, J = 8.8 Hz, 1H), 7.81–7.79 (m, 2H),
8.42 (d, J = 6.8 Hz, 1H); 13C NMR (100 MHz, DMSO-d6): δ 137.7, 131.8,
130.6, 128.5, 128.1, 127.8, 122.4, 122.1, 121.4, 119.1, 118.9, 113.9,
113.8; HRMS (ESI-MS): m/z [M+H]+ Calcd for C13H10N2: 195.2319
found: 195.2321.
Scheme 2 Substrate scope for reaction of 2-hydrazinylpyridine with
dithioesters via cyclodehydration using T3P-DMSO
(3b): 8-methyl-3-phenylimidazo[1,5-a]pyrazine
Pale yellow solid; yield: 160mg (80%); MP 85–87 oC; 1H NMR (400
MHz DMSO-d6): δ 8.32 (d, J = 7.2 Hz, 1H), 7.78 (d, J = 7.6 Hz, 2H),
7.54–7.47 (m, 3H), 7.40 (d, J = 7.2 Hz, 1H), 6.69 (t, J = 6.8 Hz, 1H), 6.60
(t, J = 7.2 Hz, 1H), 2.43 (s, 3H); 13C NMR (100 MHz, DMSO-d6): δ
135.9, 130.6, 129.3, 128.6, 128.4, 128.2, 127.7, 121.9, 118.5, 117.8,
113.6, 12.8; HRMS (ESI-MS) m/z: Calcd for C14H12N2 [M + H]+
209.2585 found: 209.2574.
A plausible mechanism for the cyclization reaction leading to
imidazo[1,5-a]pyridine is displayed in Scheme 3. In the reaction, 2-
methylaminopyridine 2a reacts with phenyl dithioester 1a to give N-
1-phenylimidazo[1,5-a]quinoline (3c)
o
1
2-pyridylmethyl thioamide A. Thioamide A reacts with T3P20-21 to Yellow solid; yield: 162mg (81%); MP 102–104 C; H NMR (400 MHz
give an intermediate C, which undergoes intramolecular cyclization
to give cyclic compound D. Deprotonation of the cyclic product D
by DMSO gives E, which on further deprotonation generates the
DMSO-d6): δ 7.78–7.76 (m, 1H), 7.60–7.53 (m, 6H), 7.51 (d, J = 9.2 Hz,
1H), 7.37–7.33 (m, 2H), 7.25–7.20 (m, 1H), 7.19 (d, J = 9.2 Hz, 1H); 13
C
NMR (100 MHz, DMSO-d6): δ 142.0, 134.1, 132.0, 130.5, 129.8, 129.8,
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129.3, 129.2, 127.9, 125.7, 125.6, 122.74, 122.70, 121.7, 117.6; HRMS
Journal Name
(ESI-MS) m/z: Calcd for C17H12N2 [M + H]+ 245.2906 found: 245.2907. (3j): 1-(4-fiurophenyl)imidazo[1,5-a]quinoline
1
Oily Compound (176mg, 88%); H NMR (400 MHz DMSO-d6): δ 7.77
(3d): 3-(4-methoxyphenyl)imidazo[1,5-a]pyridine
(d, J = 7.6 Hz, 1H), 7.66–7.62 (m, 2H), 7.53 (s, 1H), 7.50 (d, J = 9.6 Hz,
Brown solid; yield: 136mg (68%); MP 122–124 C; H NMR (400 MHz 1H), 7.41 (m, 5H), 7.19 (d, J = 9.6 Hz, 1H); 13C NMR (100 MHz,
DMSO-d6): δ 9.08 (d, J = 0.8 Hz, 1H), 8.32 (d, J = 5.2 Hz, 1H), 7.94 (s, DMSO-d6): δ 164.0, 161.6, 146.9, 143.7, 143.6, 143.5, 138.0, 130.7,
1H), ), 7.83 (d, J = 8.8 Hz, 2H), 7.53 (d, J = 5.2 Hz, 1H), 7.14 (d, J = 8.4 130.6, 130.5, 129.4, 127.6, 126.6, 126.0, 125.6, 116.6, 116.4; HRMS
Hz, 2H), 3.84 (s, 3H); 13C NMR (100 MHz, DMSO-d6): δ 160.3, 146.8, (ESI-MS) m/z: Calcd for C17H11FN2 [M + H]+ 263.2810 found:
139.2, 129.7, 129.2, 127.4, 125.4, 121.8, 115.1, 114.9, 55.8; HRMS 263.2818.
o
1
(ESI-MS) m/z: Calcd for C14H12N2O [M + H]+ 225.2579 found:
225.2576.
(3k): 3-(4-fiurophenyl)imidazo[1,5-a]pyrazine
Oily Compound; yield: 178mg (89%); 1H NMR (400 MHz DMSO-d6): δ
(3e): 3-(4-methoxyphenyl)-8-methylimidazo[1,5-a]pyridine
9.12 (s, 1H), 8.37 (d, J = 5.2 Hz, 1H), 7.98–7.92 (m, 3H), 7.58 (d, J =
Oily Compound; yield: 144mg (72%); 1H NMR (400 MHz DMSO-d6) δ 5.2 Hz, 1H), 7.43 (t, J = 8.0 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ
8.16 (d, J = 6.0 Hz, 1H), 7.70 (d, J = 8.8 Hz, 2H), 7.48 (s, 1H), 7.07 (d, J = 164.0, 161.6, 146.9, 149.7, 143.7, 143.6, 138.3, 130.7, 130.5, 129.4,
8.4 Hz, 2H), 6.56–6.59 (m, 2H), 3.79 (s, 3H), 2.46 (s, 3H); 13C NMR (100 127.6, 126.6, 126.0, 125.6, 116.6, 116.4; HRMS (ESI-MS) m/z: Calcd
MHz, DMSO-d6): δ 159.8, 138.3, 132.4, 17.6, 129.7, 128.2, 122.8, for C12H8FN3 [M + H]+ 213.2104 found: 213.2102.
119.9, 119.1, 119.0, 118.4, 118.2, 114.7, 55.7; HRMS (ESI-MS)
m/z: Calcd for C15H14N2O[M + H]+ 239.2845 found: 239.2847.
(3l): 3-(thiophen-3-yl)imidazo[1,5-a]pyridine
Pale brown solid (160mg, 80%); MP 106–108 oC; 1H NMR (400 MHz
DMSO-d6): δ 8.49 (d, J = 6.4 Hz, 1H), 7.66– 7.58 (m, 3H), 7.50 (s, 1H),
7.19–7.17 (m, 1H), 6.82–6.74 (m, 2H); 13C NMR (100 MHz, DMSO-
d6): δ 133.1, 132.7, 131.9, 128.5, 126.7, 126.6, 124.28, 124.23,
122.6, 121.08, 121.03, 119.6, 118.9, 114.5; HRMS (ESI-MS) m/z:
Calcd for C11H8N2S [M + H]+ 201.2596 found: 201.2593.
(3f): 3-(p-tolyl)imidazo[1,5-a]pyridine
Pale green solid; yield: 138mg (69%); MP 90–92 oC; 1H NMR (400MHz
DMSO-d6): δ 8.20 (d, J = 7.6 Hz, 1H), 7.67 (d, J = 7.6 Hz, 2H), 7.52 (s,
1H), 7.45 (d, J = 8.8 Hz, 1H), 7.31 (d, J = 7.6 Hz, 2H), 6.69–6.65 (m, 1H),
6.53–6.49 (m, 1H), 2.40 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ
138.6, 132.6, 131.3, 129.7, 129.5, 127.9, 127.7, 127.3, 121.43, 121.41.
120.1, 119.3, 119.2, 118.9, 113.0, 112.9, 21.4; HRMS (ESI-MS) m/z:
Calcd for C14H12N2 [M + H]+ 209.2585 found: 209.2587.
(3m): 8-methyl-3-(thiophen-2-yl)imidazo[1,5-a]pyridine
Pale yellow solid; yield: 148mg (74%); MP 110–112 oC; 1H NMR (400
MHz DMSO-d6): δ 8.39 (d, J = 6.8 Hz, 1H), 7.67 (d, J = 3.2 Hz, 1H),
7.61 (d, J = 4.8 Hz, 1H), 7.50 (s, 1H), 7.20 (t, J = 4.0 Hz, 1H), 6.74 (t, J
= 6.8 Hz, 1H), 6.63 (d, J = 6.4 Hz, 1H), 2.37 (s, 3H); 13C NMR (100
MHz, DMSO-d6): δ 133.3, 133.2, 132.9, 128.5, 128.7, 126.7, 124.3,
124.2, 120.5, 120.0, 119.9, 118.5, 114.6, 17.6; HRMS (ESI-MS) m/z:
Calcd for C12H10N2S [M + H]+ 215.2862 found: 215.2868.
(3g):8-methyl-3-(p-tolyl)imidazo[1,5-a]pyridine
Pale yellow solid (140mg, 70%); MP 90–92 oC; 1H NMR (400M Hz
DMSO-d6): δ 2.30 (s, 3H), 2.32 (s, 3H), 6.38–6.37 (m, 2H), 7.21 (d, J =
7.6 Hz, 2H), 7.41 (d, J = 0.8 Hz, 1H), 7.57 (d, J = 7.6 Hz, 2H), 8.00–
7.98 (m, 1H); 13C NMR (100 MHz, DMSO-d6): δ 138.7, 138.6, 132.6,
129.7, 129.5, 128.6, 128.0, 127.8, 127.4, 119.3, 119.2, 118.9, 118.7,
117.7, 117.6, 117.5, 113.3, 113.2, 113.1, 21.4, 17.8; HRMS (ESI-MS):
m/z [M+H]+ Calcd for C15H14N2: 222.2851 found: 222.2864.
(3n):
3-(benzo[b]thiophen-3-yl)-8-fluoro-1-isobutylimidazo[1,5-
a]pyridine
1
Oily compound; yield: 152mg (76%); H NMR (400 MHz DMSO-d6): δ
8,32 (s, 1H), 8.26–8.22 (m, 1H), 8.16 (d, J = 6.8 Hz, 1H), 8.09–8.05 (m,
1H), 7.47–7.42 (m, 2H), 6.63–6.54 (m, 2H), 2.83 (d, J = 6.4 Hz, 2H),
2.10–2.03 (m, 1H), 0.94 (s, 6H); 13C NMR (100 MHz, DMSO-d6): δ
155.6, 153.1, 139.6, 137.9, 133.6, 131.77, 131.71, 127.3, 125.5, 125.2,
124.8, 124.4, 123.2, 120.4, 120.0, 119.4, 112.9, 112.8, 101.3, 37.4,
29.7, 22.7; HRMS (ESI-MS) m/z: Calcd for C19H17FN2S [M + H]+
325.4151 found: 325.4150.
(3h): 3-(4-chlorophenyl)imidazo[1,5-a]pyridine
Pale yellow solid; yield: 172mg (86%); MP 105–107 oC; 1H NMR
(400MHz DMSO-d6): δ 8.35–8.33 (m, 1H), 7.78–7.74 (m, 2H), 7.60–
7.57 (m, 1H), 7.54–7.49 (m, 3H), 6.83–6.78 (m, 1H), 6.71–6.67 (m,
1H); 13C NMR (100 MHz, DMSO-d6): δ 136.4, 133.4, 132.0, 129.5,
129.4, 128.9, 122.0, 120.8, 120.1, 118.9, 114.3; HRMS (ESI-MS) m/z:
Calcd for C13H9ClN2 [M + H]+ 229.6770 found: 229.6774.
(3o): 3-(pyridine-4-yl)imidazo[1,5-a]pyridine
Pale yellow solid; yield: 166mg (83%); MP 96–98 oC; 1H NMR (400
MHz DMSO-d6): δ 9.08 (s, 1H), 8.67 (d, J = 4.0 Hz, 1H), 8.25 (d, J = 7.2
Hz, 1H), 8.14 (d, J = 8.0 Hz, 1H), 7.60–7.44 (m, 1H), 6.80–6.76 (m, 1H),
6.65 (t, J = 6.4 Hz, 1H); 13C NMR (100 MHz, DMSO-d6) δ 149.3, 148.4,
135.2, 132.1, 126.8, 123.7, 121.45, 121.41, 120.9, 113.7; HRMS (ESI-
MS) m/z: Calcd for C12H9N3 [M + H]+ 195.2200 found: 195.2201.
(3i): 3-(4-Fluorophenyl)-8-methylimidazo[1,5-a]pyridine
Oily compound (168mg, 84%); 1H NMR (400 MHz DMSO-d6): δ 8.23–
8.21 (m, 1H), 7.84–7.80 (m, 2H), 7.51 (s, 1H), 7.36–7.31 (m, 2H),
6.60 (d, J = 5.6 Hz, 2H), 2.34 (s, 3H); 13C NMR (100 MHz, DMSO-d6): δ
163.3, 161.1, 137.9, 132.8, 130.3, 130.2, 128.2, 127.3, 127.2, 119.9,
119.76, 119.71, 118.3, 116.4, 116.2, 114.0, 17.6; HRMS (ESI-MS)
m/z: Calcd for C14H11FN2 [M + H]+ 227.2489 found: 227.2488.
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(3p): 3-isopropylimidazo[1,5-a]pyridine
HRMS (ESI-MS) m/z Calcd for C12H9N3 [M + H]+ 196.2080 found:
1
Oily Compound; yield: 134mg (67%); H NMR (400 MHz DMSO-d6): δ 196.2079.
7.75 (d, J = 7.2 Hz, 1H), 7.41 (d, J = 9.2 Hz 1H), 6.65–6.61(m, 1H), 6.53
Acknowledgements:
Financial support from the DST-Fastrack, New Delhi (grant No.
SERB/F/5061/2013-14 dated 31-10-2013) is gratefully
acknowledged. We also thank NMR Facility, Institute of
(t, J = 6.4 Hz 1H), 3.35–3.28 (m, 1H), 1.45 (s, 6H); 13C NMR (100 MHz,
DMSO-d6) δ 143.4, 130.3, 120.4, 118.7, 117.4, 111.9, 26.0, 20.4;
HRMS (ESI-MS) m/z: Calcd for C10H12N2 [M + H]+ 160.2157 found: 160
2154.
Excellence, University of Mysore, Manasagangotri, Mysuru-
570006, India for spectral data.
(3q): 3-(tert-butyl)imidazo[1,5-a]pyridine
1
Oily Compound; yield: 138mg (69%); H NMR (400 MHz DMSO-d6): δ
8.34 (d, J = 7.6 Hz, 1H), 7.50 (d, J = 9.6 Hz, 1H), 7.22 (s, 1H), 6.70–6.65
(m, 1H), 6.58 (t, J = 6.8 Hz, 1H), 1.45 (s, 9H); 13C NMR (100 MHz,
DMSO-d6): δ 145.0, 131.6, 123.8, 118.9, 117.89, 117.83, 112.0, 28.2,
27.4; HRMS (ESI-MS) m/z: Calcd for C11H14N2 [M + H]+ 174.2423
found: 174.2427.
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o
1
Pale brown solid; yield: 178mg (89%); MP 172–174 C; H NMR (400
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Hz, 1H), 8.13 (d, J = 8 Hz, 1H), 7.54 (s, 1H), 7.51-7.47 (m, 1H), 7.45 (t, J
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195.0796 found: 195.0793.
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o
1
Pale yellow solid; yield: 170mg (85%); MP 118–120 C; H NMR (400
MHz DMSO-d6): δ 8.19 (t, J = 6.8 Hz, 1H), 7.70 (t, J = 9.2 Hz, 1H), 7.64-
7.60 (m, 2H), 7.30 (d, J = 7.6 Hz, 2H), 7.20-7.18 (m, 1H), 6.78 (t, J = 6.4
Hz, 1H), 2.37 (s, 3H); 13C NMR (100 MHz, DMSO-d6): δ 150.3, 146.7,
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(5c): 3-(4-methoxyphenyl)-[1,2,4]triazolo[4,3-a]pyridine
Pale yellow solid; yield: 168mg (84%); MP 121–123 oC; 1H NMR (400
MHz DMSO-d6): δ 8.20 (d, J = 6.8 Hz, 1H), 7.77-7.71 (m, 3H), 7.22 (t,
J = 7.2 Hz, 1H), 7.06 (d, J = 8 Hz, 2H), 6.81 (t, J = 6.4 Hz, 1H), 3.86 (s,
3H); 13C NMR (100 MHz, DMSO-d6) δ 161.0, 129.7, 126.6, 122.5,
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[M + H]+ 225.2459 found: 225.2458.
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Hz, 1H), 8.14 (d, J = 8.0 Hz, 1H), 7.60–7.44 (m, 1H), 6.80–6.76 (m,
1H), 6.65 (t, J = 6.4 Hz, 1H); 13C NMR (100 MHz, DMSO-d6): δ 149.3,
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This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C6NJ01038E
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DOI: 10.1039/C6NJ01038E
Novel Approach for the Synthesis of Imidazo and Triazolopyridines from Dithioesters
Ajjahalli. B. Ramesha,a Nagarakere. C. Sandhya,b Chottanahalli. S. Pavan Kumar,a Mahanthawamy Hiremath,a Kempegowda
Mantelingua* and Kanchugarakoppal. S. Rangappa,a*
Various Imidazo and Triazolopyridines were synthesised by the intramolecular cyclization of pyridine 2-methylamine
and dithioesters under mild conditions.