Efficient synthesis of 3-Aminoimidazo[1,2-a] pyridines using silica-supported perchloric acid (HClO4-SiO2) as a novel heterogenous catalyst

Article abstract of DOI:10.2174/157017812800167439

One pot three-component reaction of 2-amino pyridines, aldehydes and isocyanides in the presence of silicasupported perchloric acid (HClO ₄-SiO₂), produces 3-aminoimidazo[1,2-a] pyridines in excellent yields. The reaction time is sho

Full text of DOI:10.2174/157017812800167439

Letters in Organic Chemistry, 2012, 9, 155-159
155
Efficient Synthesis of 3-Aminoimidazo[1,2-a] Pyridines Using Silica-
Supported Perchloric Acid (HClO4-SiO2) as a Novel Heterogenous Catalyst
Azizollah Habibi*,1, Zahra Tarameshloo1, Shahnaz Rostamizadeh2 and Ali M. Amani2
1Faculty of Chemistry, Tarbiat Moallem University, No. 43, Mofateh Avenue, Tehran, Iran
2Department of Chemistry, Faculty of Sciences, K.N. Toosi University of Technology, Tehran, Iran
Received September 09, 2011: Revised January 16, 2012: Accepted January 17, 2012
Abstract: One pot three-component reaction of 2-amino pyridines, aldehydes and isocyanides in the presence of silica-
supported perchloric acid (HClO4-SiO2), produces 3-aminoimidazo[1,2-a] pyridines in excellent yields. The reaction time
1
is short and work up of reaction is very easy. New compounds were identified by IR, H NMR, 13C NMR and Mass
spectrum.
Keywords: 3-Aminoimidazo[1,2-a] pyridine, isocyanide, multi-component reaction, silica-supported perchloric acid (HClO4-
SiO2).
INTRODUCTION
and efficient synthesis of a wide variety of organic
molecules. In the usual organic chemistry, only a few MCRs
are known and each reaction produces compounds with
similar skeleton and only different substituent, whereas in
the chemistry of the isocyanides, a much greater variation of
MCRs is known and more different educts and products can
participate than the conventional reactions. Three-component
reaction of 2-amino pyridine, aldehyde and isocyanide was
performed in different situations and their results were
published in the literature. Some of these needs long time
[for instance, reaction in the presence of protic acid (AcOH,
HClO4)] [12] whereas reactions which were performed in the
presence of Lewis acid (Sc(OTf)3) [13] had complicated
work up procedure. Other synthetic routes for three
condensation reaction in the condition of solid acid
(montmorillonite clay K10 [14], (Sc (OTf)3) [13], solid
support {using isonitrile resin [3], resin bound aldehydes
[15] or immobilized acid [16]}; catalyst-free, in water [17];
synthesis in ionic liquid medium [18], application of
TMSCN as a non-classical isonitrile equivalent [19], were
recently reported. Table 1, shows differences in situation and
condition, time of reaction, simplicity of work up and finally
yields of reactions that recently reported. In spite of these
interesting and suitable methods [13-24], there is a need to
develop a facile route that can be easily used as a general and
efficient synthetic approach.
Heterocyclic compounds are particularly interested in all
branches of chemistry especially in medicinal chemistry.
These classes of compounds are widely distributed in nature
and are essential to life. Extensive researches have been done
to discover new heterocyclic compounds and develop novel
methods. The imidazo[1,2-a]annulanes bearing pyridine,
pyrazine and pyrimidine core constitute are an important
heterocycles which they show broadly biologically activities
such as anticytomegalo-zoster and antivaricella-zoster virus
[1], antifungal, antibacterial [2, 3], anti-inflammatory [4],
antiviral, antiulcer [5] and calcium channel blocker activities
[6]. Among new studies in 2007, Gudmundsson described
synthetic approach of novel imidazo[1,2-a] pyridines and
their anti-HSV activity [7, 8].
In recent years, considerable efforts have been devoted to
introduce new routes for the synthesis of imidazo[1,2-
a]pyridines and other analogs. An earlier method for the
synthesis of imidazo[1,2-a]pyridine is coupling of ꢀ-
halocarbonyl compound with 2-amino pyridine. Although,
this reaction has been used for imidazo[1,2-a]annulated
pyrazines and pyrimidines, but has restricted for generation
of a diverse library of this heterocycles. Another one-pot
method is coupling of 2-amino annulated heterocycle,
sodium cyanide and formaldehyde which have limitation for
desired diversification in the molecules. These protocols
because of their restrictions could not be introduced as a
good general method.
On the basis of information of Table 1, our procedure is a
fast, simple and has easily worked up procedure that we can
suggest as a general and efficient method for the synthesis of
imidazo[1,2-a]pyridines derivatives.
RESULTS AND DISCUSSION
Here, we wish to report a three component condensation
of aldehyde 1, 2-aminopyridine 2 and isocyanide 3 in the
presence of silica-supported perchloric acid as catalyst
(Scheme 1).
In recent years, significant isocyanide-based multi-
component reactions (ISMCRs) have been reported [9-11].
Multi-component reactions are important tools for the rapid
This reaction was carried out at 70-90 ºC in a short time
and excellent yield (Table 2). New products (4d, 4f, 4g, 4h,
*Address correspondence to this author at the Faculty of Chemistry, Tarbiat
Moallem University, No. 43, Mofateh Avenue, Tehran, Iran; Tel/Fax: +98-
21-88848949; E-mail: habibi@tmu.ac.ir
1
4i, 4j, 4l, 4n, 4o) were identified by IR, H NMR, 13C NMR
and Mass spectrum. The melting point and spectral data of
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

156 Letters in Organic Chemistry, 2012, Vol. 9, No. 3
Habibi et al.
Table 1. Comparable Situation and Condition of Reported Procedures
Entry
solvent
catalyst
time
yield
Work up
conditions
Reference
1
2
-
Montmorillonite clay k10
3 min
10 min
7 h
56-86
65-93
85-97
14-78
9-75
easy
difficult
easy
microwave
microwave
70°c
14
21
18
22
22
22
20
19
23
24
25
MeOH
Sc(OTf)3
3
water
-
4
1,4-dioxane
1,4-dioxane
1,4- dioxane
1,4-dioxane
Ionic liquid
MeOH
ZnCl2
ZnCl2
1h
difficult
difficult
difficult
difficult
easy
microwave
Reflux
microwave
Reflux
r.t
5
5h
6
Montmorillonite clay k10
Montmorillonite clay k10
b[mim]Br
1h
20-59
26-73
70-98
86-97
77-99
7
5h
8
3h
9
PTSA
2h
easy
r.t
10
11
MeOH
SSA
3h
easy
r.t
CH2Cl2-MeOH
Sc(OTf)3
72h
difficult
r.t
R1
N
R2
NH2
O
R3
HClO4-SiO2
70-90°C
R3
N
C
N
N
N
R1
H
H
R2
2
3
1
4a-4o
Scheme 1. Three component reaction of isocyanide, 2-amino pyridine and aldehyde.
Table 2. Different Products and Yields of Reaction
Time(min)
Yield(%)
R3
R2
R1
Product
80
165
190
40
80
70
81
80
67
78
79
65
74
75
86
85
83
77
78
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
tert-butyl
H
H
Ph
4a
4b
4c
4d
4e
4f
4-CH3C 6H4
4-CH 3OC 6H 4
4-FC 6H 4
H
H
240
45
H
4-ClC 6H 4
4-FC 6H 4
Me
H
30
4-BrC 6H 4
4-CH3C 6H4
ph
4g
4h
4i
60
Me
Me
Me
H
60
60
4-CH 3OC 6H 4
ph
4j
300
225
220
290
60
4k
4l
tert-butyl
H
4-ClC 6H 4
4-CH 3OC 6H 4
4-CH3C 6H4
4-F-C 6H 4
tert-butyl
H
4m
4n
4o
tert-butyl
H
tert-butyl
H
other known products were consistent with characterization
reported earlier.
of silica-supported perchloric acid as a catalyst, in good to
execllent yield and in a short time.
CONCLUSIONS
ACKNOWLEDGEMENTS
In conclusion, we have introduced simple, efficient and
environmentally friendly method for the synthesis of 3-
amino imidazo[1,2-a]pyridines via condensation of an
aldehyde, 2-amino pyridine and isocyanide in the presence
The authors would like to express their thanks to
Research Vice-Chancellor of Tarbiat Moallem University for
financial assistance.

Efficient Heterogenous Synthesis of 3-aminoimidazo[1,2-a]pyridines
Letters in Organic Chemistry, 2012, Vol. 9, No. 3
157
EXPERIMENTAL
General
2-(4-bromophenyl)-N-cyclohexylH-imidazo[1,2-a] pyridine-
3-amine (4g)
˚
Yield: 79%; m.p. 175-177 C; Anal.calcd for C19H20BrN3
Melting points were measured on an Electrothermal 9200
apparatus. IR spectra were recorded on a FT-IR 102MB
BOMEM apparatus. Mass spectra were recorded on a
AGILENT TECHNOLOGY(HP)-5973 mass spectrometer
operating at an ionization potential of 70 eV(EI). 1H and 13C
NMR spectra were recorded on a BRUKER DRX-300
(370.11): C, 61.63; H, 5.44; N, 11.35. Found: C, 61.42; H,
5.37; N, 11.36; IR (KBr, cm-1): 3230 (N-H), 1659, 1631
(Ar); 1H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.14-1.26 (10H,
m, 5CH2 of cyclohexyl), 2.94 (1H, m, CH-NH), 3.05 (1H, d,
J = 4.5 Hz, NH), 6.80 (1H, t, J = 6.8 Hz , CH of pyridine)
7.15 (1H, dd, J = 6.8 and J = 8.2 Hz, CH of pyridine), 7.53
(1H, d, J = 8.2, CH of pyridine), 7.57 (2H, d, J = 8.5 Hz ,
2CH of ph), 7.97 (2H, d, J = 8.5 Hz , 2CH of ph), 8.08 (1H,
d, J = 6.8 Hz, CH of pyridine). 13C NMR (75.5 MHz, CDCl3,
ꢀ/ppm): 24.80, 25.68, 34.21 (CH2 of cyclohexyl), 56.87 (CH-
NH), 111.80, 117.42 (2CH-Ar), 121.27 (C-Ar), 122.67,
124.26 (2 CH-Ar), 125.31 (C-Ar), 128.58, 131.5 (2CH-Ar),
133.38, 141.60, 146.12 (3C-Ar); MS (m/z, (relative
abundance, %)): 371 (M+, 42), 369 (M+, 40), 289 (24), 288
(73), 287 (24), 286 (68), 261 (53), 259 (51), 79 (20), 78
(100).
1
AVANCE spectrometer at 300.13 and 75.47MHz. H and
13C NMR spectra were obtained on solutions in CDCl3. All
starting materials were purchased from Fluka and Merck and
used without purification. Silica-supported perchloric acid
was prepared on the basis of procedure was used by Khan’s
group [25].
Typical Procedure for Preparation of N-Cyclohexyl -2-(4-
fluorophenyl)H-imidazo[1,2-a]pyridine-3-amine ( 4d)
A mixture of p-fluoro benzaldehyde 1 (1 mmol), 2-amino
pyridine 2 (1 mmol), cyclohexyl isocyanide 3 (1 mmol) and
0.2 g silica-supported perchloric acid was stirred in a tube at
70-90°C. Completion of reaction was monitored by TLC.
Time needed for completion was about 45 minutes. At the
end of the reaction time, mixture was cooled to room
temperature. Then dichloromethane was added to reaction
mixture and silica was filtered off. Finally, the solvent was
removed under reduced pressure and the curde product was
purified by crystallization in n-hexane to give 4d as a
colorless crystal. Yield: 80%; m.p. 166-171˚C; Anal. calcd
for C19H20FN3 (309.37): C, 73.76; H, 6.52; N, 13.58. Found:
C, 73.65; H, 6.50; N, 13.67; IR (KBr, cm-1): 3231 (N-H),
N-cyclohexyl-7-methyl-2-p-tolyl H-imidazo[1,2-a]pyridine-
3-amine (4h)
˚
Yield: 65%; m.p. 186-187 C; Anal. calcd for C21H25N3:
C, 78.96; H, 7.89; N, 13.55%. Found: C, 78.99; H, 7.67;
N, 13.78%; IR (KBr, cm-1): 3227 (N-H), 1673, 1642 (Ar);
1H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.13-1.57 (10H, m,
5CH2 of cyclohexyl), 2.39 (6H, s, 2CH3), 2.93 (1H, m, CH-
NH), 3.16 (1H, d, J = 4.7 Hz, NH), 6.65 (1H, d, J = 7.0 Hz,
CH of pyridine) ,7.24 (2H, d, J = 8.4 Hz, 2CH of ph), 7.35
(1H, s, CH of pyridine), 7.90 (2H, d, J = 8.4 Hz , 2CH of
ph), 8.02 (1 H, d, J = 7.0 Hz ,CH of pyridine). 13C NMR
(75.5 MHz, CDCl3, ꢀ/ppm): 21.29 (2CH3), 24.40, 25.04,
34.11 (5CH2 of cyclohexyl), 56.37 (CH-NH), 112.03 (C-Ar),
114.28, 117.6 (2CH-Ar), 122.0 (C-Ar), 124.4, 127.4, 130.2
(3CH-Ar), 135.1, 138.4, 144.4, 146.8, 151.1 (5C-Ar); MS
(m/z, (relative abundance, %)): 319 (M+,35), 236 (65), 209
(100), 92 (30), 78 (52).
1
1633, 1605 (Ar); H NMR (300.1 MHz, CDCl3, ꢀ/ppm):
1.14-1.83 (10H, m, 5CH2 of cyclohexyl), 2.93 (1H, m, CH-
NH), 3.09 (1H, d, J = 4.5 Hz, NH), 6.80 (1H, t, J = 6.8 Hz,
CH of pyridine), 7.11 (1H, dd, J = 6.8, J = 9.0 Hz, CH of
pyridine), 7.17 (2H, dd, J = 5.7 and J = 8.5 Hz, 2CH of ph),
7.56 (1H, d, J = 9.0 , CH of pyridine), 8.05 (2H, dd, J = 5.7
and J = 8.5 Hz, 2CH of ph), 8.10 (1H, d, J = 6.8, CH of
pyridine); 13C NMR (75.5 MHz, CDCl3, ꢀ/ppm): 24.79,
25.69, 34.19 (5CH2 of cyclohexyl), 56.82 (CH-NH), 111.84,
115.28, 115.57 (3CH-Ar), 117.23, 122.72, 124.30 (3C-Ar),
128.78, 128.88 (3CH-Ar), 160.63, 163.92 (2C-Ar); MS (m/z,
(relative abundance, %)): 309 (M+, 52), 227 (33), 226 (100),
200 (15), 199 (97), 78 (59.
N-Cyclohexyl-7-methyl-2-phenylH-imidazo[1,2-a]pyridine-
3-amine (4i)
˚
Yield: 74%; m.p. 168-171 C; Anal.calcd for C20H23N3
(305.24): C, 78.65; H, 7.59; N, 13.76. Found: C, 78.67; H,
7.76; N, 13.58; IR (KBr, cm-1): 3240 (N-H), 1643, 1604
(Ar); 1H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.14-1.83 (10H,
m, 5CH2 of cyclohexyl), 2.40 (3H, s, CH3), 2.95 (1H, m, CH-
NH), 3.13 (1H, d, J = 4.7 Hz, NH), 6.63 (1H, d, J = 7.0 Hz,
CH of pyridine), 7.31 (2H, m, 2CH of ph), 7.42 (1H, s, CH
of pyridine), 7.45 (1H, m, CH of ph), 8.01 (2H, m, 2CH of
ph), 8.04 (1H, d, J = 7.0, CH of pyridine). 13C NMR (75.5
MHz, CDCl3, ꢀ/ppm): 21.32 (CH3), 24.8, 25.7, 34.1 (CH2 of
cyclohexyl), 57.0 (CH-NH), 114.4 (CH-Ar), 115.6 (C-Ar),
117.6, 122.0 (2CH-Ar), 122.3 (C-Ar), 124.3, 127.2, 128.5
(3CH-Ar), 144.4, 147.5, 151.1 (3C-Ar). MS (m/z, (relative
abundance, %)): 305 (M+, 60), 223 (29), 222 (100), 196 (16),
195 (90), 92 (60), 65 (21).
N-cyclohexyl-2-(4-fluorophenyl)-7-methyl H-imidazo[1,2-
a]pyridine-3-amine (4f)
˚
Yield: 78%; m.p. 156-158 C; Anal. calcd for C20H22FN3
(323.41): C, 74.28; H, 6.86; N, 12.99. Found: C, 74.15; H,
6.80; N, 13.18; IR (KBr, cm-1): 3227 (N-H), 1645, 1606
(Ar); 1H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.13-1.70 (10H,
m, 5CH2 of cyclohexyl), 2.40 (3H, s, CH3), 2.92 (1H, m,
CH-NH), 3.05 (1H, d, J = 4.4 Hz, NH), 6.64 (1H, d, J = 7.0
Hz, CH of pyridine), 7.13 (2H, d, J = 8.8 Hz, 2CH of ph),
7.32 (1H, s, CH of pyridine), 7.98 (1H, d, J = 7.0 Hz, CH of
pyridine), 8.06 (2H, d, J = 8.8, 2CH of ph); 13C NMR (75.5
MHz, CDCl3, ꢀ/ppm): 21.32 (CH3), 23.9, 24.9, 34.0 (5 CH2
of cyclohexyl), 55.4 (CH-NH), 116, 117.1 (2CH-Ar), 122.3
(C-Ar), 124, 124.3, 129.2 (3 CH-Ar), 128.7, 135.1, 144.4,
151.1, 162 (5C-Ar); MS (m/z, (relative abundance, %)): 323
(M+, 50), 241 (26), 240 (100), 213 (90), 78 (45).
N-Cyclohexyl-2-(4-methoxyphenyl)-7-methylHimidazo[1,
2a]pyridine-3-amin (4j)
˚
Yield: 75%; m.p. 190-192 C; Anal.calcd for C21H25N3O
(335.23): C, 75.19; H, 7.51; N, 12.53. Found: C, 75.05; H,
7.28; N, 12.50; IR (KBr, cm-1): 3227 (N-H), 1673, 1642
(Ar); 1H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.14-1.83 (10H,

158 Letters in Organic Chemistry, 2012, Vol. 9, No. 3
Habibi et al.
m, 5CH2 of cyclohexyl), 2.40 (6H, s, 2CH3), 2.94 (1H, m,
CH-NH), 3.09 (1H, d, J = 4.6 Hz, NH), 6.62 (1H, d, J = 7.0
Hz , CH of pyridine), 7.25 (2H, d, J = 8.0 Hz, 2CH of ph),
7.33 (1H, s, CH of pyridine), 7.93 (2H, d, J = 8.0 Hz , 2CH
of ph), 8.0 (1H, d, J = 7.0 Hz, CH of pyridine). 13C NMR
(75.5 MHz, CDCl3, ꢀ/ppm): 21.29 (2CH3), 24.80, 25.74,
34.13 (5CH2 of cyclohexyl), 56.97 (CH-NH), 112.03 (C-Ar),
114.28 (CH-Ar), 114.68, 115.52, 119.60 (3C-Ar), 122.0
(CH-Ar), 124.1 (C-Ar), 124.9, 126.82, 129.23 (3CH-Ar),
136.9 (C-Ar); MS (m/z, (relative abundance, %)): 335 (M+,
1), 319 (97), 252 (10), 237 (24), 236 (100), 225 (16), 209
(82), 117 (98), 92 (36).
(4CH-Ar), 123.20, 123.42, 124.42 (3C-Ar), 129.75, 129.86
(2CH-Ar), 160.63, 163.89 (2C-Ar). ); MS (m/z, (relative
abundance, %)): 283 (M+, 37), 227 (74), 226 (78), 199 (100),
79 (28), 78 (94).
REFERENCES
[1]
a) Gueiffier, A.; Lhassani, M.; Elhakmaoui, A.; Snoeck, R.; Andrei,
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N-tert-butyl-2-(4-chlorophenyl) H-imidazo[1,2-a]pyridine-
3-amine (4l)
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a Novel Class of Inhibitors of Human
Rhinovirus: Stereospecific Synthesis and Antiviral Activity. J.
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˚
Yield: 85%; m.p. 146-148 C; Anal.calcd for C17H18ClN3
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a) Fisher, M.H.; Lusi, A. Imidazo[1,2-a]pyridine anthelmintic and
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(299.78): C, 68.11; H, 6.05; N, 14.02. Found: C, 67.87; H,
5.93; N, 14.08; IR (KBr, cm-1): 3284 (N-H), 1654, 1632
1
(Ar); H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.04 (9H, s,
C(CH3)3), 3.07 (1H, s, NH), 6.80 (1H, t, J = 6.7 Hz, CH of
pyridine), 7.17 (1H, dd, J = 6.7 and J = 9.0 Hz, CH of
pyridine), 7.40 (2H, d, J = 8.4 Hz, 2CH of ph), 7.55 (1H, d, J
= 9.0, CH of pyridine), 7.92 (2H, d, J = 8.4 Hz, 2CH of ph),
8.21 (1H, d, J = 6.7 Hz, CH of pyridine); 13C NMR (75.5
MHz, CDCl3, ꢀ/ppm): 30.33 (C(CH3)3), 56.53 (C(CH3)3),
111.82, 116.9, 122.45, 123.48 (4CH–Ar), 124.86 (C-Ar),
128.48 (CH-Ar), 128.93 (C-Ar), 129.30 (CH-Ar), 130.13,
133.28, 140.01 (3C-Ar). ); MS (m/z, (relative abundance,
%)): 301 (M+, 14), 299 (M+, 42), 245 (34), 244 (46), 243
(90), 242 (87), 217 (37), 215 (100), 149 (38), 78 (94).
[3]
[4]
[5]
[6]
N-tert-butyl-2-p-tolyl
(4n)
H-imidazo[1,2-a]pyridine-3-amine
˚
Yield: 77%; m.p. 149-150 C; Anal.calcd for C18H21N3
(279.37): C, 77.38; H, 7.57; N, 15.04. Found: C, 77.32; H,
7.75; N, 15.17; IR (KBr, cm-1): 3316 (N-H), 1656, 1632
[7]
[8]
1
(Ar); H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.04 (9 H, s,
C(CH3)3), 2.39 (3H, s, CH3), 3.12 (1H, s, NH) , 6.77 (1 H, t,
J = 6.8 Hz, CH of pyridine), 7.13 (1H, dd, J = 6.8 and J =
9.0 Hz, CH of pyridine), 7.24 (2H, d, J = 8.1 Hz, 2CH of
ph), 7.55 (1H, d, J = 9.0 Hz, CH of pyridine), 7.81 (2H, d, J
= 8.1 Hz, 2CH of ph) , 8.23 (1H, d, J = 6.8 Hz, CH of
pyridine). 13C NMR (75.5 MHz, CDCl3, ꢀ/ppm): 21.30
(CH3), 30.27 (C(CH3)3), 56.43 (C(CH3)3), 111.25, 117.11
(2CH–Ar), 123.22 (C-Ar), 123.43, 123.98, 127.94, 128.99
(4CH-Ar), 132.11, 137.06, 139.33, 141.82 (4C-Ar); MS
(m/z, (relative abundance, %)): 279 (M+, 39), 223 (54), 222
(81), 196 (20), 195 (100), 78 (49).
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3-amine (4o)
[13]
[14]
˚
Yield: 78%; m.p. 158-160 C; Anal. calcd for C17H18FN3
(283.33): C, 72.06; H, 6.40; N, 14.83. Found: C, 71.66; H,
6.45; N, 14.63; IR (KBr, cm-1): 3286 (N-H), 1632, 1605
1
(Ar); H NMR (300.1 MHz, CDCl3, ꢀ/ppm): 1.05 (9H, s,
[15]
[16]
[17]
C(CH3)3), 3.05 (1H, s, NH), 6.80 (1H, t, J = 6.8 Hz, CH of
pyridine), 7.13 (1H, dd, J = 6.8 and J = 9.0 Hz, CH of
pyridine), 7.17(2H, dd, J = 5.7 and J = 8.5 Hz, 2CH of ph),
7.55 (1H, d, J = 9.1 Hz, CH of pyridine), 7.92 (2H, dd, J =
5.7 and J = 8.5 Hz, 2CH of ph), 8.22 (1H, d, J = 6.8 Hz, CH
of pyridine); 13C NMR (75.5 MHz, CDCl3, ꢀ/ppm): 30.32
(C(CH3)3), 56.42 (C(CH3)3), 111.58, 115.09, 115.38, 117.14
Adib, M.; Mahdavi, M.; Alizadeh Noghani, M.; Mirzaei, P.
Catalyst-free three-component reaction between 2-aminopyridines
(or 2-aminothiazoles), aldehydes, and isosyanides in water.
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Efficient Heterogenous Synthesis of 3-aminoimidazo[1,2-a]pyridines
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Parallel Synthesis of 3-Aminoimidazo[1,2-a]pyridines and
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