Rhodium(II)-Catalyzed Regioselective C3-Alkylation of 2-Arylimidazo[1,2-a]pyridines with Aryl Diazoesters

Article abstract of DOI:10.1002/adsc.201900092

A regioselective C3-alkylation based on the reaction of 2-arylimidazo[1,2-a]pyridines with a wide range of aryl α-diazoesters in the presence of a Rh(II) catalyst in dichloroethane at room temperature was developed. This method could be applied in the synthesis of benzoimidazoquinolizinone and cycloheptaimidazopyridinone, which are novel heterocyclic scaffolds. (Figure presented.).

Full text of DOI:10.1002/adsc.201900092

Title: Rhodium(II)-Catalyzed Regioselective C3-Alkylation of 2-
Arylimidazo[1,2-a]pyridines with Aryl Diazoesters
Authors: Hyunseok Kim, Minhyeon Byeon, Eunchong Jeong,
Yonghyeon Baek, Seung Jin Jung, Kyusik Um, Sang Hoon
Han, Gi Uk Han, Gi Hoon Ko, Chanyoung Maeng, Jeong-Yu
Son, Dongwook Kim, Sung Hong Kim, Kooyeon Lee, and Phil
Ho Lee
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201900092
Link to VoR: http://dx.doi.org/10.1002/adsc.201900092

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Rhodium(II)-Catalyzed Regioselective C3-Alkylation of
2-Arylimidazo[1,2-a]pyridines with Aryl Diazoesters
Hyunseok Kim,a Minhyeon Byeon,a Eunchong Jeong,a Yonghyeon Baek,a Seung Jin
Jeong,a Kyusik Um,a Sang Hoon Han,a Gi Uk Han,a Gi Hoon Ko,a Chanyoung Maeng,a
Jeong-Yu Son,a Dongwook Kim,b,c Sung Hong Kim,d Kooyeon Lee,e and Phil Ho Leea,*
a
Department of Chemistry, Kangwon National University, Chuncheon 24341, Republic of Korea.
E-mail: phlee@kangwon.ac.kr
Center for Catalytic Hydrocarbon Functionalization, Institute for Basic Science (IBS), Daejeon 34141, Republic of
b
Korea.
c
Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of
Korea.
d
Korea Basic Scientific Institute, Daegu Center, Daegu 41566, Republic of Korea.
Department of Bio-Health Technology, Kangwon National University, Chuncheon 24341, Republic of Korea.
e
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. A regioselective C3-alkylation based on the reaction of 2-arylimidazo[1,2-a]pyridines with a wide range of aryl -
diazoesters in the presence of a Rh(II) catalyst in dichloroethane at room temperature was developed. This method could be
applied in the synthesis of benzoimidazoquinolizinone and cycloheptaimidazopyridinone, which are novel heterocyclic
scaffolds.
Keywords: Imidazopyridine; Regioselective; Aryl diazoester; Rhodium; C3-Alkylation
from N-benzyloxycarbonylamino sulfones (eq 1);[4]
Introduction
Friedel-Crafts alkylation of imidazo[1,2-a]pyridines
with β-nitrostyrenes (eq 2);[5] and Yb-catalyzed three-
component reaction of aldehydes, acetamides, and
imidazo[1,2-a]pyridines (eq 3),[6] have been
Imidazo[1,2-a]pyridines are significant privileged
scaffolds in azaheterocycle chemistry,[1] and they are
commonly found in natural products, pharmaceuticals, reported,[7] these methods often suffer from a narrow
and biologically active compounds (Figure 1).[2]
Among azaheterocycles, imidazopyridines and
especially 3-alkyl-2-arylimidazo[1,2-a]pyridines are
not only essential pharmacophores but also practical
synthetic intermediates that can be easily converted
into valuable molecules.[3] Although a variety of
streamlined approaches for synthesizing 3-alkyl-2-
arylimidazo[1,2-a]pyridines, including Cu-catalyzed
nucleophilic addition to N-acyliminium ions derived
substrate scope, requiring harsh reaction conditions,
and poor regioselectivity (Scheme 1). In addition, Li
and coworkers reported that Ir(III) and Rh(III)
complexes could catalyze the carbocyclization
between 2-phenylimidazo[1,2-a]pyridine and -diazo
esters (eqs 4 and 5).[8] The reaction occurs through C–
H activation and monoalkylation or dialkylation of
the arene followed by an intramolecular electrophilic
aromatic substitution. Iridium(III) and rhodium(III)
catalysts showed complementary scopes of the -
diazo substrate. However, since they utilize C–H
activation, only one or two reactive species derived
from the diazo compound can be introduced at the
ortho-positions of the 2-phenyl group of 2-
phenylimidazo[1,2-a]pyridine. Hence, functional
groups could not be introduced at the C3-position of
2-arylimidazo[1,2-a]pyridine. Recently, we attempted
to introduce various functional groups onto 2-
arylimidazo[1,2-a]pyridine to construct a library
based on the imidazo[1,2-a]pyridine skeleton.[9]
Because a highly reactive electrophilic carbene was
generated from the Rh(II) catalysts and diazo
Figure 1. Bioactive Imidazo[1,2-a]pyridines.
1
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10.1002/adsc.201900092
Advanced Synthesis & Catalysis
Table 1. Reaction Optimization [a]
Entry
1
Catalyst
Solvent
DCE
Yield [%][b]
CuCl
0
2
Cu(OAc)2
Cu(OTf)2
Rh2(TPA)4
Rh2(Opiv)4
Rh2(OAc)4
Rh2(oct)4
Rh2(oct)4
Rh2(oct)4
Rh2(oct)4
Rh2(oct)4
Rh2(oct)4
DCE
11
3
DCE
63
4
DCE
72
5
DCE
84
6
DCE
83
98 (97)[c]
7
DCE
8
CH2Cl2
THF
89
9
30
10
11
12
Toluene
DCE
91
85[d]
85[e]
DCE
[a] Reaction conditions: 1a (0.2 mmol, 1.0 equiv) was
reacted with 2a (1.5 equiv) in the presence of catalyst (2.0
mol %) in solvent (2.0 mL) under a N2 atmosphere.
[b] NMR yield using dibromomethane as an internal
standard.
Scheme 1. 3-Alkylation of 2-Arylimidazo[1,2-a]pyridines.
[c] Isolated yield.
[d] 2a (1.2 equiv) was used.
compounds, we were very curious about the
introduction of carbene moieties derived from diazo
compounds in the presence of a transition metal
catalyst into the aryl or the imidazopyridine ring upon
treatment with 2-arylimidazo[1,2-a]pyridine. Herein,
we report a regioselective C3-alkylation based on the
reaction of 2-arylimidazo[1,2-a]pyridines with a wide
range of aryl -diazoesters in the presence of a Rh(II)
catalyst at room temperature (eq 6). No mono- or di-
alkylation of the aryl ring of the 2-arylimidazo[1,2-
a]pyridine was observed. Additional cyclizations
using C3-alkylated 2-arylimidazo[1,2-a]pyridines
[e] DCE (1.0 mL) was used.
number of rhodium(II) catalysts, including
Rh2(TPA)4, Rh2(OPiv)4, Rh2(OAc)4, and Rh2(oct)4
(each at 2.0 mol %), were tested in DCE at room
temperature, and these experiments revealed that
Rh2(oct)4 performed the best, providing 3a in
quantitative yield (entries 4-7). Dichloromethane,
tetrahydrofuran, and toluene gave inferior results
compared to that achieved with DCE (entries 8-10).
The reaction of 2a (1.2 equiv) in DCE at room
temperature for 6 h gave rise to 3a in 85% yield
(entry 11). Concentrations of substrate from 0.1 M to
0.2 M furnished 3a in 85% yield (entry 12). No
alkylation of the aryl ring of 2-arylimidazo[1,2-
a]pyridine was observed.
were
conducted
to
provide
and
benzoimidazoquinolizinone
cycloheptaimidazopyridinone, which are novel
heterocyclic scaffolds.
The solid-state structure of 3a was confirmed by
single-crystal X-ray diffraction (Figure 2 and the
Supporting Information). Importantly, X-ray analyses
revealed that the phenyl rings at the 2- and 3-
positions are distorted with respect to the plane of the
imidazopyridine, and they show dihedral angles of
47.8° and 74.1°, respectively. Although the solid-
state structure suggests that electron delocalization
between each phenyl group and the imidazopyridine
moiety is unfavorable, these moieties can interact
with each other electronically through the free
rotation of the phenyl groups in solution.
Results and Discussion
First, we examined the reaction of 2-
phenylimidazo[1,2-a]pyridine (1a) (0.2 mmol, 1.0
equiv) with methyl 2-phenyl-2-diazoacetate (2a) (0.3
mmol, 1.5 equiv) using a variety of catalysts and
solvents (Table 1). CuCl (2.0 mol %) was not
effective (entry 1). However, when Cu(OAc)2 and
Cu(OTf)2 (each at 2.0 mol %) were used in
dichloroethane (DCE) at room temperature for 6 h,
the desired C3-alkylated 2-phenylimidazo[1,2-
a]pyridine (3a) was gratifyingly produced in yields of
11% and 63%, respectively (entries 2 and 3). Next, a
2
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10.1002/adsc.201900092
Advanced Synthesis & Catalysis
and these substrates provided the desired
imidazo[1,2-a]pyridines (3h, 3i, and 3j) in high yields
(85% to 92%). 4-Ethoxycarbonyl- and 4-cyano-
substituted 2-aryl-2-diazoesters are tolerated in the
present transformation, providing corresponding
products 3k (90%) and 3l (91%). Notably, a
diazoacetate bearing a labile trimethylsilyl group
efficiently underwent C3-alkylation with 1a at 60 °C
in 2 h, producing desired product 3m in 73% yield.
Ethyl 1-naphthyl-2-diazoacetate was C3-alkylated
product (3n) in 50% yield due to steric effects. The
tolerance of a variety of substituents, including chloro,
bromo, ester, cyano, and trimethylsilyl groups, is
important, as these functional groups can be further
Figure 2. Molecular Structure of Imidazo[1,2-a]pyridine
3a.
Inspired by these results, we investigated the
scope of alkyl 2-aryl-2-diazoacetates (2) in the
reaction with 2-phenylimidazo[1,2-a]pyridine (1a)
(Table 2). Electronic variation of the substituents on
the aryl group of 2-aryl-2-diazoacetate (2) slightly
influenced the reaction efficiency. Electron-donating
2-methyl, 3-methyl, and 4-methyl groups afforded the
corresponding C3-alkylated 2-phenylimidazo[1,2-
a]pyridines (3b, 3c, and 3d) in good to excellent
yields (65% to 91%). Strongly electron-donating 3-
and 4-methoxy groups did not affect the efficiency of
transformed.
However,
methyl
2-diazo-3-
oxobutanoate, methyl 2-diazo-4-phenylbutanoate,
ethyl 2-diazo-3-oxo-3-phenylpropanoat, and dimethyl
2-diazomalonate were not effective. In addition, the
present method worked equally well even with
unstable ethyl diazoacetates at room temperature and
afforded the desired compounds (4a-4c) in good
yields.
the
C3-alkylation
reaction.
Methylenedioxy-
substituted ethyl 2-aryl-2-diazoacetate efficiently
underwent the C3-alkylation, producing desired
imidazo[1,2-a]pyridine 3g in 94% yield. The
conditions of the C3-alkylation reaction were
compatible with electron-withdrawing groups,
including 2-chloro, 3-chloro, and 4-bromo groups,
To demonstrate the applicability of the present
method to larger scale processes, 2.0 mmol of 2-
phenylimidazo[1,2-a]pyridine (1a, 0.39 g) was
Table 2. Scope of Alkyl 2-Aryl-2-diazoacetates[a]
treated
with
methyl
2-(2-chlorophenyl)-2-
diazoacetate (2h, 1.5 equiv) with 0.5 mol % catalyst
loading in DCE at room temperature for 6 h, and the
reaction afforded corresponding compound 3h (0.72
g, 95%).
Next, imidazo[1,2-a]pyridine derivatives (1) with
a wide range of substituents on the pyridine moiety
were examined in the C3-alkylation reaction with
methyl 2-phenyl-2-diazoacetate (2a) (Table 3).
Electronic modification of the substituents on the
pyridine ring did not affect the reaction efficiency.
The Rh-catalyzed C3-alkylation with methyl 2-
phenyl-2-diazoacetate occurred regioselectively at the
C3-position of the imidazopyridine ring of 8-, 7-, and
6-methyl-2-phenylimidzo[1,2-a]pyridines
and
provided the desired products (5a 5b, and 5c) in good
to excellent yields (73% to 98%). A substrate having
an electron-donating 7-ethyl group was converted to
the corresponding imidazo[1,2-a]pyridine (5d) in
91% yield. C3-Alkylation product 5e was obtained in
98% yield despite the presence of a strong electron-
donating methoxy group. The conditions of the C3-
alkylation reaction were compatible with 7- and 6-
chloro groups, and 5f and 5g were produced in 90%
and 75% yields, respectively. Encouraged by these
[a] Reaction conditions: 1a (0.2 mmol, 1.0 equiv) was
reacted with 2 (1.5 equiv) and Rh2(oct)4 (2.0 mol %) in
DCE (2.0 mL) under N2 atmosphere.
[b] 60 °C, 2 h.
3
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10.1002/adsc.201900092
Advanced Synthesis & Catalysis
Table 3. Scope of 2-Arylimidazo[1,2-a]pyridines[a]
results, we applied this catalytic system to a number
of 2-arylimidazo[1,2-a]pyridines to demonstrate the
scope of the developed method. Although
imidazo[1,2-a]pyridine with an ortho-tolyl group at
the C2-position was C3-alkylated to produce 5h in
58% yield due to steric effects, para-tolyl-substituted
imidazopyridine smoothly underwent the Rh-
catalyzed C3-alkylation reaction to afford 5i in 92%
yield. Likewise, imidazo[1,2-a]pyridine, with a 4-
methoxyphenyl
group,
efficiently
afforded
corresponding C3-alkylated compound 5j in 98%
yield. The present method worked equally well with
the electron-poor 3-chloro- and 3-bromophenyl-
substituted imidazopyridines, which allowed the
facile
construction
of
C3-alkylimidazo[1,2-
a]pyridines 5k (86%) and 5n (88%). Because the
reactivities of imidazopyridines with 4-chloro- and 4-
bromophenyl moieties were low due to the inductive
and resonance effects, the C3-alkylation was
conducted under slightly modified conditions (DCE,
60 °C, 2 h) but still produced 5l and 5m in
quantitative yields, respectively. 2-Naphthyl-
substituted imidazo[1,2-a]pyridine underwent the Rh-
catalyzed C3-alkylation, affording the desired
compound (5o) in 84% yield. An imidazo[1,2-
a]pyridine bearing a thiophen-2-yl and pyridin-2-yl
moieties
also
provided
the
corresponding
imidazopyridines 5p and 5q in 77% and 66% yields,
respectively. Replacement of phenyl to ethyl group
(5r) expanded diversity of the present method and
increased substrate scope. The substrate having a
methyl group on the pyridine as well as on the phenyl
ring of 2-phenylimidazo[1,2-a]pyridine furnished
desired imidazopyridine 5s in 72% yield. Two
chloro-substituted
2-phenylimidazo[1,2-a]pyridine
was also reacted with 2a to produce 5t in 81% yield.
When 2-(2-chlorophenyl)-2-diazoacetate (2h) was
reacted with imidazopyridines (1) with a wide range
of substituents, including methyl, chloro, and bromo
groups, on the pyridine as well as on the phenyl ring
of 2-phenylimidazo[1,2-a]pyridine, the corresponding
products were obtained in high yields. Thiophen-2-yl-
substituted imidazo[1,2-a]pyridine was easily
converted to the desired product (5b’) in 60% yield.
Next, various methods using C3-alkylated
imidazopyridines have been developed to synthesize
novel heterocyclic scaffolds (Scheme 2). When C3-
alkylated imidazopyridine (3a) was treated again with
methyl 2-phenyl-2-diazoacetate (2a) in the presence
of Rh2(oct)4 (2.0 mol %) in DCE at room temperature
for 6 h, the desired dialkylated compound from the
electrophilic aromatic substitution reaction on the 2-
phenyl ring was not observed (eq 7). This reaction
was carried out with [Cp*RhCl2]2 (4.0 mol %) and
AgSbF6 (16.0 mol %), and it afforded ortho-alkylated
product 6 in 56% yield (dr = 1:1.3) through a C–H
activation (eq 8). C3-Alkylated substrate 3h,
generated from 2-phenylimidazo[1,2-a]pyridine (1a)
and methyl 2-(2-chlorophenyl)-2-diazoacetate (2h),
was treated with Pd(OAc)2 (5.0 mol %), PCy3∙HBF4
(10.0 mol %), and K2CO3 (1.5 equiv) in DMA at
130 °C for 12 h under a nitrogen atmosphere,
[a] Reaction conditions: 1 (0.2 mmol, 1.0 equiv) was
reacted with 2a (1.5 equiv) and Rh2(oct)4 (2.0 mol %) in
DCE (2.0 mL) under a N2 atmosphere.
[b] Reaction time 18 h.
[c] 60 °C, 2 h.
[d] Rh2(oct)4 (4.0 mol %) was used at 100 °C for 4 h.
[e] 100 °C, 4 h.
4
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10.1002/adsc.201900092
Advanced Synthesis & Catalysis
providing benzoimida-zoquinolizinone 7a (76%) and
ortho-chlorobenzoyl imidazopyridine 8 (14%) (eq 9).
The structure of 7a and 8 was unambiguously
determined by X-ray crystallography (see the
Supporting Information). When the reaction was
Scheme 2. Second Alkylation and Application Using C3-
Alkylation Products.
A possible mechanism for the production of the
C3-alkylated imidazopyridines (3 and 5) from the 2-
arylimidazo[1,2-a]pyridines (1) and alkyl 2-aryl-2-
diazoacetates (2) is described in Scheme 3. First, the
diazoester (2) was converted into a rhodium-
carbenoid[10] in the presence of the rhodium(II)
catalyst with the release of N2 as the only byproduct.
The nucleophilic attack[7] of the C3-carbon atom of
the imidazopyridine onto the electrophilic carbene
carbon of I affords rhodium-bound zwitterionic
intermediate II, which is aromatized by deprotonation
to furnish intermediate III. Finally, protoderhodation
of III provides C3-alkylated imidazopyridine (3 and
5) and regenerates the Rh(II) catalyst.
conducted
under
an
oxygen
atmosphere,
imidazopyridine 8 was produced in 98% yield (eq 10).
In addition, when the reaction was carried out without
o
K2CO3 in DMA at 130 C for 12 h under a nitrogen
atmosphere, ortho-chlorobenzyl imidazopyridine (9)
was obtained in 46% yield (eq 11). The structure of 9
was
unambiguously determined
by
X-ray
crystallography (see the Supporting Information). We
were pleased to obtain cyclohepta-imidazopyridinone
(10) in 63% yield from 8 in the presence of Pd(OAc)2
(5.0 mol %), PCy3∙HBF4 (10.0 mol %), and K2CO3
(1.5 equiv) in DMA at 145 °C in 12 h under a
nitrogen atmosphere, indicating that 8 is not an
intermediate
in
the
formation
of
benzoimidazoquinolizinone (7a) (eq 12). The
obtained cyclic compound was confirmed to be
cycloheptaimidazopyridinone
(10)
by
NMR
spectroscopy and single-crystal X-ray analysis (see
the Supporting Information). The C3-alkylated
compounds (3h and 5u) were smoothly converted to
7a (84%) and 7b (75%), respectively, under the same
reaction conditions (eq 13).
Scheme 3. A Possible Mechanism.
Conclusion
In summary, we have developed a regioselective
C3-alkylation of 2-arylimidazo[1,2-a]pyridines with
aryl -diazoesters in the presence of a Rh(II) catalyst
in dichloroethane at room temperature. This method
was applied in the synthesis of benzoimidazoqui-
nolizinone and cycloheptaimidazopyridinone, which
are novel heterocyclic scaffolds.
Experimental Section
General: Commercial available reagents were used
without purification. All reaction mixtures were stirred
magnetically and were monitored by thin-layer
chromatography using silica gel pre-coated glass plates,
which were visualized with UV light and then, developed
using either iodine or a solution of anisaldehyde. Flash
column chromatography was carried out using silica gel
1
(230-400 mesh). H NMR (400 MHz) and 13C{1H} NMR
(100 MHz) spectra were recorded on NMR spectrometer.
Deuterated chloroform was used as the solvent and
chemical shift values () are reported in parts per million
relative to the residual signals of this solvent [δ 7.26 for 1H
5
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10.1002/adsc.201900092
Advanced Synthesis & Catalysis
(chloroform-d) and δ 77.2 for 13C{1H} (chloroform-d)].
Infrared spectra were recorded on FT-IR spectrometer as
either a thin film pressed between two sodium chloride
plates or as a solid suspended in a potassium bromide disk.
High resolution mass spectra (HRMS) were obtained by
electron impact (EI) ionization technique (magnetic sector
- electric sector double focusing mass analyzer) from the
KBSI (Korea Basic Science Institute Daegu Center).
Melting points were determined in open capillary tube.
CCDC-1845635, 1884733, 1885361, 1892633, and
1887335 contains the supplementary crystallographic data
of 3a, 7a, 8, 9 and 10 for this paper. These data can be
obtained free of charge from The Cambridge
1H), 7.49-7.45 (m, 2H), 7.41-7.37 (m, 1H), 7.21-7.16 (m,
2H), 7.08 (dd, J = 7.5 Hz, J = 0.4 Hz, 1H), 6.86 (t, J = 8.6
Hz, 2H), 6.62 (td, J = 10.3 Hz, J = 1.2 Hz, 1H), 5.83 (s,
1H), 4.31-4.19 (m, 2H), 2.27 (s, 3H), 1.26 (t, J = 7.1 Hz,
3H); 13C{1H} NMR (100 MHz, CDCl3)  171.0, 146.2,
145.8, 138.8, 134.5, 134.3, 129.1, 128.9, 128.7, 128.5,
128.2, 126.5, 124.9, 124.5, 117.6, 115.8, 111.7, 61.9, 47.5,
21.6, 14.3; IR (film): 3052, 2979, 1732, 1606, 1383, 1186,
1073, 699 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C24H22N2O2 370.1681; Found 370.1684.
Methyl
2-(2-phenylimidazo[1,2-a]pyridin-3-yl)-2-(p-
tolyl)acetate (3d): Yield: 64.9 mg (91%); Rf = 0.3
(EtOAc: Hexane = 1:1); Ivory solid; Melting point: 137-
139 oC; 1H NMR (400 MHz, CDCl3)  7.99 (dt, J = 7.0 Hz,
J = 1.0 Hz, 1H), 7.78-7.75 (m, 2H), 7.67 (dt, J = 9.0 Hz, J
= 1.1 Hz, 1H), 7.49-7.45 (m, 2H), 7.41-7.37 (m, 1H), 7.21-
7.17 (m, 1H), 7.10 (d, J = 8.1 Hz, 2H), 6.94 (d, J = 7.8 Hz,
2H), 6.63 (td, J = 10.3 Hz, J = 1.0 Hz, 1H), 5.85 (s, 1H),
3.76 (s, 3H), 2.31 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  171.5, 146.2, 145.8, 137.5, 134.3, 131.4, 129.1,
128.8, 128.2, 127.5, 126.4, 124.9, 117.7, 115.7, 111.9, 52.7,
47.0, 21.1; IR (film): 3397, 3051, 2950, 1736, 1605, 1383,
1073, 700 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C23H20N2O2 356.1525; Found 356.1526.
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif.
Procedure of the Rh-Catalyzed C3-Alkylation of
Imidazo[1,2-a]pyridine with Aryl Diazoester: A dried
test tube equipped with a magnetic stirring bar was charged
with imidazo[1,2-a]pyridine 1 (0.2 mmol, 1.0 equiv),
Rh2(oct)4 (3.2 mg, 0.004 mmol, 2.0 mol %), diazoester 2
(0.3 mmol, 1.5 equiv), and DCE (2.0 mL) under a nitrogen
atmosphere. After being stirred at room temperature for 6 h,
the reaction mixture was concentrated under reduced
pressure. The crude product was purified by Silica gel
column chromatography with EtOAc and hexane to give
the corresponding alkylated products 3, and 4.
Methyl 2-(3-methoxyphenyl)-2-(2-phenylimidazo[1,2-
a]pyridin-3-yl)acetate (3e): Yield: 67.0 mg (90%); Rf =
0.3 (EtOAc:Hexane = 1:1); Colorless oil; H NMR (400
1
Methyl 2-phenyl-2-(2-phenylimidazo[1,2-a]pyridin-3-
yl)acetate (3a): Yield: 66.4 mg (97%); Rf = 0.3 (EtOAc:
MHz, CDCl3)  8.00 (dt, J = 7.0 Hz, J = 1.0 Hz, 1H), 7.78-
7.75 (m, 2H), 7.67 (d, J = 9.1 Hz, 1H), 7.47 (t, J = 7.5 Hz,
2H), 7.39 (t, J = 7.3 Hz, 1H), 7.26-7.17 (m, 2H), 6.81 (dd,
J = 8.2 Hz, J = 1.9 Hz, 1H), 6.67-6.62 (m, 3H), 5.86 (s,
1H), 3.77 (s, 3H), 3.71 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  171.2, 160.2, 146.3, 145.8, 136.1, 134.3, 130.1,
129.1, 128.8, 128.2, 126.4, 125.0, 119.8, 117.7, 115.5,
113.9, 112.7, 111.9, 55.4, 52.8, 47.3; IR (film): 3366, 3053,
2951, 1736, 1600, 1383, 1073, 700 cm-1; HRMS (EI) m/z:
[M]+ Calcd for C23H20N2O3 372.1474; Found 372.1470.
o
1
Hexane = 1:1); Ivory solid; Melting point: 129-131 C; H
NMR (400 MHz, CDCl3)  7.98 (dt, J = 6.9 Hz, J = 1.1 Hz,
1H), 7.79-7.76 (m, 2H), 7.68 (d, J = 9.1 Hz, 1H), 7.48 (t, J
= 7.4 Hz, 2H), 7.42-7.37 (m, 1H), 7.33-7.27 (m, 3H), 7.20
(ddd, J = 9.0 Hz, J = 6.8 Hz, J = 1.2 Hz 1H), 7.08-7.05 (m,
2H), 6.63 (td, J = 10.3 Hz, J = 1.1 Hz, 1H), 5.90 (s, 1H),
3.79 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3)  171.3,
146.3, 145.8, 134.5, 134.2, 129.1, 129.0, 128.8, 128.2,
127.7, 127.5, 126.3, 124.9, 117.7, 115.5, 111.9, 52.8, 47.3;
IR (film): 3366, 3059, 2951, 1736, 1602, 1384, 1073, 699
cm-1; HRMS (EI) m/z: [M]+ Calcd for C22H18N2O2
342.1368; Found 342.1366.
Methyl 2-(4-methoxyphenyl)-2-(2-phenylimidazo[1,2-
a]pyridin-3-yl)acetate (3f): Yield: 68.5 mg (92%); Rf =
0.3 (EtOAc:Hexane = 1:1); Ivory solid; Melting point: 70-
o
1
Ethyl
2-(2-phenylimidazo[1,2-a]pyridin-3-yl)-2-(o-
72 C; H NMR (400 MHz, CDCl3)  7.99 (d, J = 7.0 Hz,
1H), 7.78-7.75 (m, 2H), 7.68 (d, J = 9.1 Hz, 1H), 7.47 (t, J
= 7.4 Hz, 2H), 7.41-7.37 (m, 1H), 7.22-7.13 (m, 1H), 6.98
(d, J = 8.3 Hz, 2H), 6.84-6.80 (m, 2H), 6.64 (t, J = 10.3 Hz,
J = 1.0 Hz, 1H), 5.83 (s, 1H), 3.77 (s, 3H), 3.76 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3)  171.6, 159.1, 146.1,
145.7, 134.3, 129.1, 128.8, 128.7, 128.2, 126.31, 126.29,
125.0, 117.7, 115.8, 114.4, 112.0, 55.4, 52.8, 46.6; IR
(film): 3375, 2952, 2928, 1736, 1610, 1383, 1074, 700 cm-
1; HRMS (EI) m/z: [M]+ Calcd for C23H20N2O3 372.1474;
Found 372.1476.
tolyl)acetate (3b): Yield: 48.2 mg (65%); Rf = 0.3
1
(EtOAc: Hexane = 1:1); Colorless oil; H NMR (400 MHz,
CDCl3)  8.09 (d, J = 7.0 Hz, 1H), 7.68 (d, J = 7.5 Hz, 3H),
7.47-7.43 (m, 2H), 7.40-7.36 (m, 1H), 7.23-7.12 (m, 4H),
7.03 (d, J = 7.6 Hz, 1H), 6.68 (td, J = 10.3 Hz, J = 1.0 Hz,
1H), 5.73 (s, 1H), 4.25-4.10 (m, 2H), 2.03 (s, 3H), 1.20 (t,
J = 7.6 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3)  170.6,
145.9, 145.5, 137.2, 134.4, 133.4, 131.5, 129.0, 128.7,
128.13, 128.08, 127.6, 126.4, 125.5, 124.7, 117.8, 115.7,
112.2, 61.9, 46.6, 19.7, 14.2; IR (film): 3397, 3063, 2978,
1731, 1604, 1383, 1073, 700 cm-1; HRMS (EI) m/z: [M]+
Calcd for C24H22N2O2 370.1681; Found 370.1684.
Ethyl 2-(benzo[d][1,3]dioxol-5-yl)-2-(2-phenylimidazo-
[1,2-a]pyridin-3-yl)acetate (3g): Yield: 75.3 mg (94%); Rf
= 0.3 (EtOAc:Hexane = 1:1); Pink oil; 1H NMR (400 MHz,
CDCl3)  8.05 (d, J = 6.8 Hz, 1H), 7.77 (d, J = 7.4 Hz, 2H),
7.67 (d, J = 9.0 Hz, 1H), 7.47 (t, J = 7.5 Hz, 2H), 7.39 (t, J
= 7.2 Hz, 1H), 7.19 (t, J = 7.8 Hz, 1H), 6.71 (d, J = 8.0 Hz,
1H), 6.66 (t, J = 6.7 Hz, 1H), 6.55-6.52 (m, 2H), 5.91 (s,
Ethyl
2-(2-phenylimidazo[1,2-a]pyridin-3-yl)-2-(m-
tolyl)acetate (3c): Yield: 51.9 mg (70%); Rf = 0.3 (EtOAc:
o
1
Hexane = 1:1); Ivory solid; Melting point: 75-77 C; H
NMR (400 MHz, CDCl3)  8.01 (dt, J = 7.0 Hz, J = 1.1 Hz,
1H), 7.81-7.78 (m, 2H), 7.67 (dt, J = 9.1 Hz, J = 1.1 Hz,
6
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
2H), 5.74 (s, 1H), 4.28-4.15 (m, 2H), 1.24 (t, J = 7.1 Hz,
3H); 13C{1H} NMR (100 MHz, CDCl3)  170.8, 148.3,
147.1, 146.1, 145.7, 134.2, 129.1, 128.7, 128.21, 128.18,
126.3, 125.0, 120.7, 117.6, 115.8, 111.9, 108.5, 108.2,
101.3, 61.9, 47.1, 14.2; IR (film): 3566, 2979, 1730, 1501,
1488, 1235, 1037, 700 cm-1; HRMS (EI) m/z: [M]+ Calcd
for C24H20N2O4 400.1420; Found 400.1423.
(td, J = 10.3 Hz, J = 1.2 Hz, 1H), 5.88 (s, 1H), 4.35 (q, J =
7.6 Hz, 3H), 1.37 (t, J = 7.1 Hz, 3H), 1.27 (t, J = 7.1 Hz,
3H); 13C{1H} NMR (100 MHz, CDCl3)  170.4, 166.2,
146.9, 139.7, 134.1, 130.2, 130.1, 129.1, 128.8, 128.4,
127.7, 126.1, 125.1, 117.8, 115.1, 112.1, 62.2, 61.2, 47.6,
14.4, 14.3; IR (film): 3412, 3055, 2981, 1730, 1610, 1384,
1074, 700 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C26H24N2O4 428.1736; Found 428.1738.
Methyl
2-(2-chlorophenyl)-2-(2-phenylimidazo[1,2-
a]pyridin-3-yl)acetate (3h): Yield: 65.6 mg (87%); Rf =
Ethyl
2-(4-cyanophenyl)-2-(2-phenylimidazo[1,2-
0.3 (EtOAc:Hexane = 1:1); Ivory solid; Melting point: 64-
a]pyridin-3-yl)acetate (3l): Yield: 69.4 mg (91%); Rf =
0.3 (EtOAc:Hexane = 1:1); Pink oil; H NMR (400 MHz,
1
1
66 oC; H NMR (400 MHz, CDCl3)  8.07 (dt, J = 6.8 Hz,
J = 1.0 Hz, 1H), 7.73 (dt, J = 9.1 Hz, J = 1.0 Hz, 1H),
7.66-7.63 (m, 2H), 7.49-7.42 (m, 3H), 7.40-7.35 (m, 1H),
7.31-7.24 (m, 2H), 7.18-7.14 (m, 1H), 6.87 (dd, J = 7.7 Hz,
J = 0.9 Hz, 1H), 6.78 (td, J = 10.3 Hz, J = 1.0 Hz, 1H),
5.95 (s, 1H), 3.61 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  169.8, 146.4, 145.7, 134.7, 134.2, 133.3, 130.4,
129.6, 129.3, 129.0, 128.7, 128.3, 127.3, 125.1, 124.9,
118.1, 114.6, 112.8, 53.0, 46.4; IR (film): 3398, 3061,
2950, 1736, 1383, 1072, 751, 700 cm-1; HRMS (EI) m/z:
[M]+ Calcd for C22H17ClN2O2 376.0979; Found 376.0981.
CDCl3)  7.89 (dt, J = 7.0 Hz, J = 1.0 Hz, 1H), 7.78-7.75
(m, 2H), 7.71 (dt, J = 9.1 Hz, J = 1.0 Hz, 1H), 7.61-7.58
(m, 2H), 7.50-7.46 (m, 2H), 7.43-7.39 (m, 1H), 7.24 (ddd,
J = 9.1 Hz, J = 6.8 Hz, J = 1.2 Hz, 1H), 7.21-7.18 (m, 1H),
6.68 (td, J = 10.3 Hz, J = 1.2 Hz, 1H), 5.86 (s, 1H), 4.33-
4.20 (m, 2H), 1.26 (t, J = 7.1 Hz, 3H); 13C{1H} NMR (100
MHz, CDCl3)  169.9, 146.8, 145.9, 140.0, 133.9, 132.7,
129.0, 128.9, 128.6, 128.5, 125.6, 125.3, 118.4, 118.0,
114.3, 112.4, 111.9, 62.4, 47.4, 14.2; IR (film): 3054, 2981,
2229, 1732, 1607, 1383, 1073, 700 cm-1; HRMS (EI) m/z:
[M]+ Calcd for C24H19N3O2 381.1479; Found 381.1477.
Methyl
2-(3-chlorophenyl)-2-(2-phenylimidazo[1,2-
a]pyridin-3-yl)acetate (3i): Yield: 69.3 mg (92%); Rf =
0.3 (EtOAc:Hexane = 1:1); Ivory solid; Melting point:
127-129 oC; 1H NMR (400 MHz, CDCl3)  7.96 (d, J = 7.0
Hz, 1H), 7.77-7.74 (m, 2H), 7.69 (d, J = 9.1 Hz, 1H), 7.48
(t, J = 7.5 Hz, 2H), 7.41 (t, J = 7.4 Hz, 1H), 7.28-7.20 (m,
3H), 7.10 (s, 1H), 6.92 (dd, J = 7.5 Hz, J = 0.7 Hz, 1H),
6.69 (t, J = 6.8 Hz, 1H), 5.85 (s, 1H), 3.78 (s, 3H); 13C{1H}
NMR (100 MHz, CDCl3)  170.8, 146.6, 145.9, 136.6,
135.1, 134.1, 130.3, 129.1, 128.9, 128.4, 128.2, 127.9,
126.0, 125.8, 125.2, 117.9, 114.8, 112.3, 53.0, 47.0; IR
(film): 3397, 3055, 2951, 1737, 1595, 1383, 1074, 700 cm-
1; HRMS (EI) m/z: [M]+ Calcd for C22H17ClN2O2
376.0979; Found 376.0977.
Ethyl
2-(2-phenylimidazo[1,2-a]pyridin-3-yl)-2-(4-
(trimethylsilyl)phenyl)acetate (3m): Yield: 62.6 mg
(73%); Rf = 0.3 (EtOAc:Hexane = 2:1); Ivory solid;
o
1
Melting point: 67-69 C; H NMR (400 MHz, CDCl3) 
8.02 (dt, J = 7.0 Hz, J = 1.1 Hz, 1H), 7.79-7.76 (m, 2H),
7.68 (dt, J = 9.0 Hz, J = 1.1 Hz, 1H), 7.48-7.43 (m, 4H),
7.40-7.36 (m, 1H), 7.19 (ddd, J = 9.1 Hz, J = 6.7 Hz, J =
1.2 Hz, 1H), 7.05 (dd, J = 8.2 Hz, J = 0.9 Hz, 2H), 6.64 (td,
J = 10.3 Hz, J = 1.2 Hz, 1H), 5.85 (s, 1H), 4.31-4.18 (m,
2H), 1.26 (t, J = 7.1 Hz, 3H), 0.23 (s, 9H); 13C{1H} NMR
(100 MHz, CDCl3)  172.2, 147.7, 147.0, 141.3, 136.4,
135.6, 135.3, 130.4, 130.0, 129.4, 128.1, 127.8, 126.2,
118.9, 116.9, 113.1, 63.2, 48.7, 15.5, 0.2; IR (film): 3446,
3055, 2955, 1731, 1382, 1248, 1073, 700 cm-1; HRMS (EI)
m/z: [M]+ Calcd for C26H28N2O2Si 428.1924; Found
428.1920.
Ethyl
2-(4-bromophenyl)-2-(2-phenylimidazo[1,2-
a]pyridin-3-yl)acetate (3j): Yield: 74.0 mg (85%); Rf =
0.3 (EtOAc:Hexane = 1:1); Ivory solid; Melting point:
o
1
Ethyl
2-(naphthalen-1-yl)-2-(2-phenylimidazo[1,2-
147-149 C; H NMR (400 MHz, CDCl3)  7.95 (dt, J =
7.0 Hz, J = 1.2 Hz, 1H), 7.78-7.75 (m, 2H), 7.69 (dt, J =
9.1 Hz, J = 1.2 Hz, 1H), 7.49-7.46 (m, 2H), 7.44-7.38 (m,
3H), 7.23-7.19 (m, 1H), 6.96-6.93 (m, 2H), 6.69-6.65 (m,
1H), 5.77 (s, 1H), 4.30-4.17 (m, 2H), 1.25 (t, J = 7.1 Hz,
3H); 13C{1H} NMR (100 MHz, CDCl3)  170.4, 146.5,
145.8, 134.1, 133.6, 132.1, 129.4, 129.1, 128.8, 128.3,
126.1, 125.1, 121.8, 117.8, 115.1, 112.1, 62.1, 47.0, 14.2;
IR (film): 3366, 3052, 1732, 1605, 1382, 1074, 700, 604
cm-1; HRMS (EI) m/z: [M]+ Calcd for C23H1979BrN2O2
434.0630, C23H1981BrN2O2 436.0612; Found 434.0632,
436.0617.
a]pyridin-3-yl)acetate (3n): Yield: 40.6 mg (50%); Rf =
0.3 (EtOAc:Hexane = 1:1); Ivory solid; Melting point:
187-189 oC; 1H NMR (400 MHz, CDCl3)  8.17 (d, J = 7.0
Hz, 1H), 7.84 (q, J = 8.2 Hz, 2H), 7.74-7.71 (m, 2H), 7.66
(t, J = 9.0 Hz, 2H), 7.47-7.42 (m, 3H), 7.38 (t, J = 7.8 Hz,
3H), 7.25 (s, 1H), 7.19-7.15 (m, 1H), 6.66 (t, J = 6.9 Hz,
1H), 6.33 (s, 1H), 4.26-4.10 (m, 2H), 1.19 (t, J = 7.1 Hz,
3H); 13C{1H} NMR (100 MHz, CDCl3)  170.7,145.9,
145.8, 134.4, 134.3, 131.7, 130.7, 129.22, 129.17, 129.1,
128.8, 128.3, 126.8, 126.1, 125.8, 125.7, 125.2, 124.7,
123.1, 117.8, 116.0, 112.2, 62.1, 46.2, 14.2; IR (film):
3052, 2979, 1732, 1598, 1385, 1186, 1072, 700 cm-1;
HRMS (EI) m/z: [M]+ Calcd for C24H22N2O2 370.1681;
Found 370.1684.
Ethyl
4-(2-ethoxy-2-oxo-1-(2-phenylimidazo[1,2-
a]pyridin-3-yl)ethyl)benzoate (3k): Yield: 77.1 mg
(90%); Rf = 0.3 (EtOAc:Hexane = 1:1); Ivory solid;
o
1
Methyl 2-(8-methyl-2-phenylimidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5a): Yield: 69.6 mg (98%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 58-60
oC; 1H NMR (400 MHz, CDCl3)  7.83 (d, J = 7.0 Hz, 1H),
7.77-7.75 (m, 2H), 7.48-7.44 (m, 2H), 7.40-7.35 (m, 1H),
Melting point: 62-64 C; H NMR (400 MHz, CDCl3) 
7.97 (dt, J = 8.4 Hz, J = 1.9 Hz, 2H), 7.93 (dt, J = 7.0 Hz, J
= 1.1 Hz, 1H), 7.80-7.77 (m, 2H), 7.69 (dt, J = 9.1 Hz, J =
1.0 Hz, 1H), 7.51-7.46 (m, 2H), 7.43-7.39 (m, 1H), 7.21
(ddd, J = 9.0 Hz, J = 6.8 Hz, 2H), 7.16-7.13 (m, 2H), 6.63
7
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
7.31-7.24 (m, 3H), 7.07-7.05 (m, 2H), 6.98 (dt, J = 6.8 Hz,
J = 1.0 Hz, 1H), 6.55 (t, 1H), 5.84 (s, 1H), 3.76 (s, 3H),
2.68 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3 )  171.4,
146.2, 145.9, 134.7, 134.5, 129.3, 129.0, 128.8, 128.1,
127.7, 127.5, 124.0, 123.7, 115.9, 112.0, 52.7, 47.4, 17.3;
IR (film): 3387, 3058, 2951, 1736, 1603, 1380, 1073, 699
cm-1; HRMS (EI) m/z: [M]+ Calcd for C23H20N2O2
356.1525; Found 356.1521.
52.8, 47.3; IR (film): 3366, 3060, 2953, 1736, 1604, 1214,
1071, 699 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C23H20N2O3 372.1474; Found 372.1476.
Methyl
2-(7-chloro-2-phenylimidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5f): Yield: 67.8 mg (90%); Rf = 0.3
1
(EtOAc:Hexane = 1:3); Colorless oil; H NMR (400 MHz,
CDCl3)  7.92 (dd, J = 7.4 Hz, J = 0.4 Hz, 1H), 7.77-7.75
(m, 2H), 7.66 (dd, J = 2.0 Hz, J = 0.5 Hz, 1H), 7.48 (t, J =
7.4 Hz, 2H), 7.42-7.38 (m, 1H), 7.32-7.27 (m, 3H), 7.04
(dd, J = 7.1 Hz, J = 1.4 Hz, 2H), 6.60 (dd, J = 7.4 Hz, J =
2.1 Hz, 1H), 5.89 (s, 1H), 3.80 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3)  171.2, 147.1, 145.6, 134.1, 133.7, 131.6,
129.1, 129.0, 128.8, 128.4, 127.9, 127.3, 126.7, 116.4,
115.9, 113.5, 52.8, 47.2; IR (film): 3366, 3061, 2951, 1736,
1383, 1155, 1070, 698 cm-1; HRMS (EI) m/z: [M]+ Calcd
for C22H17N2O2 376.0978; Found 376.0979.
Methyl 2-(7-methyl-2-phenylimidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5b): Yield: 63.4 mg (89%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 90-92
oC; 1H NMR (400 MHz, CDCl3)  7.85 (d, J = 7.1 Hz, 1H),
7.77-7.75 (m, 2H), 7.48-7.44 (m, 2H), 7.42 (t, J = 0.8 Hz,
1H), 7.39-7.36 (m, 1H), 7.32-7.26 (m, 3H), 7.07-7.04 (m,
2H), 6.46 (dd, J = 7.1 Hz, J = 1.7 Hz, 1H), 5.86 (s, 1H),
3.78 (s, 3H), 5.37 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  171.5, 146.3, 146.0, 136.0, 134.7, 134.4, 129.0,
128.8, 128.1, 127.7, 127.6, 125.5, 116.0, 114.9, 114.6, 52.8,
21.4; IR (film): 3058, 2950, 1736, 1604, 1381, 1156, 1073,
698 cm-1; HRMS (EI) m/z: [M]+ Calcd for C23H20N2O2
356.1523; Found 356.1525.
Methyl
2-(6-chloro-2-phenylimidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5g): Yield: 56.5 mg (75%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 120-
122 oC; 1H NMR (400 MHz, CDCl3)  8.04 (dd, J = 1.9 Hz,
J = 0.7 Hz, 1H), 7.75-7.73 (m, 2H), 7.61 (dd, J = 9.5 Hz, J
= 0.6 Hz, 1H), 7.50-7.46 (m, 2H), 7.35-7.28 (m, 3H), 7.16
(dd, J = 9.5 Hz, J = 1.9 Hz, 1H), 7.06-7.04 (m, 2H), 5.87 (s,
1H), 3.81 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) 
171.1, 147.2, 144.2, 133.9, 133.8, 129.3, 129.0, 128.9,
128.5, 128.0, 127.4, 126.4, 124.1, 120.1, 118.0, 116.4, 52.9,
47.3; IR (film): 3060, 2951, 1736, 1603, 1382, 1197, 1075,
Methyl 2-(6-methyl-2-phenylimidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5c): Yield: 52.0 mg (73%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 148-
1
150 oC; H NMR (400 MHz, CDCl3)  7.85 (d, J = 7.1 Hz,
1H), 7.77-7.74 (m, 2H), 7.48-7.44 (m, 2H), 7.85 (t, J = 7.1
Hz, 1H), 7.40-7.36 (m, 1H), 7.32-7.27 (m, 3H), 7.07-7.04
(m, 2H), 6.47 (dd, J = 7.1 Hz, J = 1.7 Hz, 1H), 5.86 (s, 1H), 698 cm-1; HRMS (EI) m/z: [M]+ Calcd for C22H17ClN2O2
3.78 (s, 3H), 2.37 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  171.5, 146.3, 146.1, 136.0, 134.7, 134.4, 129.0,
128.8, 128.1, 127.7, 127.6, 125.5, 116.1, 114.9, 114.6, 52.8,
47.3, 21.4; IR (film): 3367, 3059, 2951, 1736, 1604, 1381,
1073, 699 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C23H20N2O2 356.1525; Found 356.1527.
376.0978; Found 376.0979.
Methyl 2-phenyl-2-(2-(o-tolyl)imidazo[1,2-a]pyridin-3-
yl)acetate (5h): Yield: 41.3 mg (58%); Rf = 0.3 (EtOAc:
o
1
Hexane = 1:3); Ivory solid; Melting point: 114-116 C; H
NMR (400 MHz, CDCl3)  7.97 (d, J = 6.9 Hz, 1H), 7.64
(d, J = 9.0 Hz, 1H), 7.34-7.28 (m, 6H), 7.25-7.18 (m, 2H),
7.05 (d, J = 6.7 Hz, 2H), 6.66 (t, J = 6.8 Hz, 1H), 5.46 (s,
1H), 3.72 (s, 3H), 2.30 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  171.4, 146.7, 145.5, 138.3, 134.6, 133.5, 130.7,
Methyl 2-(7-ethyl-2-phenylimidazo[1,2-a]pyridin-3-yl)-
2-phenylacetate (5d): Yield: 67.4 mg (91%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 108-
110 oC; 1H NMR (400 MHz, CDCl3)  7.87 (dd, J = 7.1 Hz, 130.4, 129.0, 128.6, 127.7, 127.6, 126.1, 125.6, 124.7,
J = 0.7 Hz, 1H), 7.78-7.75 (m, 2H), 7.48-7.44 (m, 3H),
7.40-7.36 (m, 1H), 7.32-7.27 (m, 3H), 7.08-7.05 (m, 2H),
6.50 (dd, J = 7.1 Hz, J = 1.7 Hz, 1H), 5.87 (s, 1H), 3.78 (s,
3H), 2.67 (q, J = 7.5 Hz, 2H), 1.26 (t, J = 7.6 Hz, 3H);
13C{1H} NMR (100 MHz, CDCl3)  171.5, 146.4, 146.1,
142.1, 134.7, 134.4, 129.0, 128.8, 128.1, 127.7, 127.6,
125.7, 114.9, 114.6, 113.6, 52.8, 47.3, 28.5, 14.4; IR
(film): 3375, 3059, 2965, 1737, 1604, 1382, 1073, 699 cm-
1; HRMS (EI) m/z: [M]+ Calcd for C24H22N2O2 370.1681;
Found 370.1678.
117.9, 116.7, 111.9, 52.6, 47.3, 20.3; IR (film): 3059, 3028,
2951, 1736, 1602, 1381, 734, 698 cm-1; HRMS (EI) m/z:
[M]+ Calcd for C23H20N2O2 356.1527; Found 356.1525.
Methyl 2-phenyl-2-(2-(p-tolyl)imidazo[1,2-a]pyridin-3-
yl)acetate (5i): Yield: 65.6 mg (92%); Rf = 0.3 (EtOAc:
o
1
Hexane = 1:3); Ivory solid; Melting point: 160-162 C; H
NMR (400 MHz, CDCl3)  7.97 (d, J = 7.0 Hz, 1H), 7.67
(d, J = 8.0 Hz, 3H), 7.32-7.27 (m, 5H), 7.18 (ddd, J = 8.9
Hz, J = 6.7 Hz, J = 1.1 Hz, 1H), 7.07-7.05 (m, 2H), 7.97
(td, J = 7.0 Hz, J = 1.1 Hz, 1H), 5.89 (s, 1H), 3.78 (s, 3H),
2.40 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3)  171.5,
146.4, 145.8, 138.1, 134.6, 131.3, 129.5, 129.1, 129.0,
127.7, 127.6, 126.3, 124.9, 117.6, 115.3, 111.9, 52.8, 47.4,
21.4; IR (film): 2950, 1736, 1601, 1380, 1361, 1067, 731,
697 cm-1; HRMS (EI) m/z: [M]+ Calcd for C23H20N2O2
356.1525; Found 356.1524.
Methyl 2-(7-methoxy-2-phenylimidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5e): Yield: 73.0 mg (98%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 120-
1
122 oC; H NMR (400 MHz, CDCl3)  7.81 (d, J = 7.6 Hz,
1H), 7.78-7.75 (m, 2H), 7.48-7.45 (m, 2H), 7.40-7.36 (m,
1H), 7.32-7.27 (m, 3H), 7.07-7.05 (m, 2H), 6.97 (s, 1H),
6.35 (dd, J = 7.6 Hz, J = 2.6 Hz, 1H), 5.84 (s, 1H), 3.85 (s,
3H), 3.80 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) 
171.6, 158.3, 147.3, 145.7, 134.8, 134.2, 129.1, 128.9,
128.8, 128.1, 127.7, 127.5, 126.9, 114.4, 106.9, 94.8, 55.6,
Methyl 2-(2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-
3-yl)-2-phenylacetate (5j): Yield: 73.0 mg (98%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 189-
8
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
1
191 oC; H NMR (400 MHz, CDCl3)  7.96 (d, J = 3.5 Hz,
J = 1.0 Hz, 1H), 7.35-7.27 (m, 4H), 7.21 (ddd, J = 9.1 Hz,
J = 6.8 Hz, J = 1.2 Hz, 1H), 7.06-7.04 (m, 2H), 6.65 (td, J
= 10.3 Hz, J = 1.1 Hz, 1H), 5.85 (s, 1H), 3.81 (s, 3H);
1H), 7.73-7.70 (m, 2H), 7.67-7.64 (m, 1H), 7.31-7.27 (m,
3H), 7.16 (ddd, J = 9.0 Hz, J = 6.8 Hz, J = 1.2 Hz, 1H),
7.07-7.05 (m, 2H), 7.03-6.99 (m, 2H), 6.60 (td, J = 10.3 Hz, 13C{1H} NMR (100 MHz, CDCl3)  171.2. 145.8. 144.8.
J = 1.2 Hz, 1H), 5.87 (s, 1H), 3.84 (s, 3H), 3.78 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3)  171.4, 159.7, 146.2,
145.7, 134.5, 130.2, 129.0, 127.7, 127.5, 126.7, 126.2,
124.8, 117.5, 115.0, 114.2, 111.8, 55.4, 52.7, 47.3; IR
(film): 3367, 2951, 1736, 1499, 1384, 1249, 1175, 698 cm-
1; HRMS (EI) m/z: [M]+ Calcd for C23H20N2O3 372.1474;
Found 372.1474.
136.3. 134.2. 132.2. 131.3. 130.3. 129.1. 127.9. 127.51.
127.47. 126.4. 125.3. 123.0. 117.8. 115.9. 112.2. 52.9.
47.3; IR (film): 3060, 2950, 1737, 1362, 1198, 996, 696,
607 cm-1; HRMS (EI) m/z: [M]+ Calcd for C22H1779BrN2O2
420.0473 C22H1781BrN2O2 422.0456; Found 420.0475,
422.0453.
Methyl 2-(2-(naphthalen-2-yl)imidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5o): Yield: 65.9 mg (84%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 147-
Methyl 2-(2-(3-chlorophenyl)imidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5k): Yield: 64.8mg (86%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 128-
o
1
149 C; H NMR (400 MHz, CDCl3)  8.25 (s, 1H), 8.02
(d, J = 7.0 Hz, 1H), 7.97-7.92 (m, 2H), 7.91-7.85 (m, 2H),
7.91-7.85 (m, 2H), 7.71 (d, J = 9.0 Hz, 1H), 7.52-7.47 (m,
2H), 7.33-7.27 (m, 3H), 7.21 (ddd, J = 9.0 Hz, J = 6.8 Hz,
J = 0.9 Hz, 1H), 7.10-7.08 (m, 2H), 6.65 (td, J = 6.9 Hz, J
= 0.8 Hz, 1H) 6.01 (s, 1H), 3.80 (s, 3H); 13C{1H} NMR
(100 MHz, CDCl3)  171.4, 146.3, 145.9, 134.5, 133.5,
133.1, 131.7, 129.1, 128.5, 128.2, 127.84, 127.79, 127.6,
126.9, 126.4, 126.3, 125.1, 117.7, 115.9, 112.0, 52.8, 47.5;
IR (film): 3057, 2950, 1736, 1602, 1359, 1159, 732, 698
cm-1; HRMS (EI) m/z: [M]+ Calcd for C26H20N2O2
392.1525; Found 392.1521.
1
130 oC; H NMR (400 MHz, CDCl3)  7.98 (d, J = 7.0 Hz,
1H), 7.83 (s, 1H), 7.67 (d, J = 9.0 Hz, 1H), 7.63 (td, J = 6.8
Hz, J = 1.8 Hz, 1H), 7.42-7.35 (m, 2H), 7.34-7.28 (m, 3H),
7.22 (ddd, J = 9.1 Hz, J = 6.8 Hz, J = 1.2 Hz, 1H), 7.06-
7.04 (m, 2H), 6.65 (td, J = 10.3 Hz, J = 1.1 Hz, 1H), 5.85
(s, 1H), 3.81 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) 
171.2, 145.8, 144.9, 136.1, 134.8, 134.2, 130.0, 129.2,
129.1, 128.3, 127.9, 127.5, 127.0, 126.3, 125.3, 117.7,
115.9, 112.2, 52.9, 47.3; IR (film): 2951, 1736, 1600, 1362,
1197, 1078, 739, 696 cm-1; HRMS (EI) m/z: [M]+ Calcd
for C22H17ClN2O2 376.0976; Found 376.0979.
Methyl
2-phenyl-2-(2-(thiophen-2-yl)imidazo[1,2-
Methyl 2-(2-(4-chlorophenyl)imidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5l): Yield: 73.9 mg (98%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 127-
a]pyridin-3-yl)acetate (5p): Yield: 53.7 mg (77%); Rf =
0.3 (EtOAc:Hexane = 1:3); Ivory solid; Melting point:
148-150 oC; 1H NMR (400 MHz, CDCl3)  7.92 (d, J = 7.0
Hz, 1H), 7.65 (d, J = 9.0 Hz, 1H), 7.46 (dd, J = 3.5 Hz, J =
0.7 Hz, 1H), 7.42 (dd, J = 5.1 Hz, J = 0.7 Hz, 1H), 7.34-
7.28 (m, 3H), 7.18 (ddd, J = 8.8 Hz, J = 7.1 Hz, J = 0.8 Hz,
1H), 7.15-7.13 (m, 1H), 7.10-7.08 (m, 2H), 6.60 (td, J =
10.2 Hz, J = 0.7 Hz, 1H), 6.06 (s, 1H), 3.81 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3)  171.1, 145.8, 140.2,
137.0, 134.1, 129.1, 127.9, 127.8, 127.5, 126.6, 126.2,
125.8, 125.3, 117.5, 115.2, 112.1, 52.8, 47.3; IR (film):
3063, 2950, 1736, 1601, 1360, 1079, 735, 698 cm-1;
HRMS (EI) m/z: [M]+ Calcd for C20H16N2O2S 348.0930;
Found 348.0932.
1
129 oC; H NMR (400 MHz, CDCl3)  7.97 (d, J = 7.0 Hz,
1H), 7.71 (d, J = 8.4 Hz, 2H), 7.67 (d, J = 9.1 Hz, 1H),
7.45 (d, J = 8.5 Hz, 2H), 7.33-7.29 (m, 3H), 7.21 (ddd, J =
8.8 Hz, J = 6.9 Hz, J = 0.8 Hz, 1H), 7.06-7.04 (m, 2H),
6.65 (td, J = 6.8 Hz, J = 0.7 Hz, 1H), 5.83 (s, 1H), 3.79 (s,
3H); 13C{1H} NMR (100 MHz, CDCl3)  171.2, 145.9,
145.2, 134.3, 134.2, 132.8, 130.3, 129.1, 129.0, 127.9,
127.5, 126.3, 125.3, 117.7, 115.7, 112.1, 52.9, 47.3; IR
(film): 3060, 2951, 1736, 1599, 1380, 1092, 698, 604 cm-1;
HRMS (EI) m/z: [M]+ Calcd for C22H17ClN2O2 376.0978;
Found 376.0979.
Methyl 2-(2-(4-bromophenyl)imidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5m): Yield: 81.7 mg (97%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 157-
159 oC; 1H NMR (400 MHz, CDCl3)  7.97 (dt, J = 7.0 Hz,
J = 1.1 Hz, 1H), 7.68-7.64 (m, 3H), 7.62-7.58 (m, 2H),
7.33-7.28 (m, 3H), 7.20 (ddd, J = 9.1 Hz, J = 6.8 Hz, J =
1.2 Hz, 1H), 7.06-7.03 (m, 2H), 6.64 (td, J = 10.3 Hz, J =
1.2 Hz, 1H), 5.83 (s, 1H), 3.79 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3)  171.2, 145.9, 145.1, 134.2, 133.2, 132.0,
130.7, 129.1, 127.9, 127.5, 126.3, 125.3, 122.6, 117.7,
115.7, 112.1, 52.9, 47.3; IR (film): 3060, 2951, 1736, 1599,
1361, 1072, 1010, 700 cm-1; HRMS (EI) m/z: [M]+ Calcd
for C22H1779BrN2O2 420.0475, C22H1781BrN2O2 422.0466;
Found 420.0473, 420.0456.
Methyl
2-phenyl-2-(2-(pyridin-2-yl)imidazo[1,2-a]
pyridin-3-yl)acetate (5q): Yield: 45.3 mg (66%); Rf = 0.3
(EtOAc:Hexane = 1:1); Red oil; 1H NMR (400 MHz,
CDCl3)  8.61 (dq, J = 4.8 Hz, J = 0.8 Hz, 1H), 8.34 (d, J
= 8.0 Hz, 1H), 7.97 (d, J = 7.0 Hz, 1H), 7.78 (td, J = 11.6
Hz, J = 1.9 Hz, 1H), 7.67 (s, 1H), 7.64 (dt, J = 9.1 Hz, J =
1.1 Hz, 1H), 7.32-7.15 (m, 8H), 6.62 (td, J = 10.3 Hz, J =
1.2 Hz, 1H), 3.76 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  171.9, 154.4, 148.8, 145.3, 141.9, 136.6, 135.4,
128.8, 127.7, 127.3, 126.0, 125.1, 122.3, 122.2, 119.2,
117.7, 112.0, 52.4, 46.4; IR (film): 3042, 1621, 1488, 1427,
1226, 1201, 1011, 988, 751 cm-1; HRMS (EI) m/z: [M]+
Calcd for C21H17N3O2 343.1321; Found 343.1325.
Methyl 2-(2-ethylimidazo[1,2-a]pyridin-3-yl)-2-phenyl
Methyl 2-(2-(3-bromophenyl)imidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5n): Yield: 74.1 mg (88%); Rf = 0.3
(EtOAc:Hexane = 1:3); White solid; Melting point: 146-
148 C; H NMR (400 MHz, CDCl3)  8.00-7.97 (m, 2H),
7.67 (d, J = 9.0 Hz, 2H), 7.53 (ddd, J = 8.0 Hz, J = 1.9 Hz,
acetate (5r): Yield: 57.1 mg (97%); Rf
= 0.3
1
(EtOAc:Hexane = 3:1); Colorless oil; H NMR (400 MHz,
CDCl3)  7.87 (d, J = 7.0 Hz, 1H), 7.57 (d, J = 9.0 Hz, 1H),
7.37-7.26 (m, 3H), 7.13-7.09 (m, 3H), 6.56 (td, J = 10.3 Hz,
o
1
9
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
J = 1.1 Hz, 1H), 5.59 (s, 1H), 3.78 (s, 3H), 2.85 (q, J = 7.5
Hz, 2H), 1.37 (t, J = 7.6 Hz, 3H); 13C{1H} NMR (100
MHz, CDCl3)  171.3, 148.3, 145.3, 134.5, 128.9, 127.6,
127.5, 125.4, 124.1, 117.0, 114.7, 111.4, 52.6, 46.7, 21.2,
14.5; IR (film): 3072, 2898, 1718, 1647, 1426, 1321, 1226,
978, 751 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C18H18N2O2 294.1368; Found 294.1370.
114.8, 114.3, 53.1, 46.3; IR (film): 3062, 2951, 1738, 1445,
1382, 1201, 1066, 700 cm-1; HRMS (EI) m/z: [M]+ Calcd
for C22H16Cl2N2O2 410.5087; Found 410.0589.
Methyl
2-(2-chlorophenyl)-2-(2-(p-tolyl)imidazo[1,2-
a]pyridin-3-yl)acetate (5w): Yield: 76.6 mg (98%); Rf =
0.3 (EtOAc:Hexane = 1:10); White solid; Melting point:
o
1
147-149 C; H NMR (400 MHz, CDCl3)  8.07 (dt, J =
7.0 Hz, J = 1.0 Hz, 1H), 7.72 (dt, J = 9.1 Hz, J = 0.6 Hz,
1H), 7.55-7.52 (m, 2H), 7.48 (dd, J = 8.0 Hz, J = 1.2 Hz,
1H), 7.30-7.22 (m, 4H), 7.14 (td, J = 11.4 Hz, J = 1.2 Hz,
1H), 6.86 (dd, J = 7.8 Hz, J = 0.9 Hz, 1H), 6.76 (td, J =
10.3 Hz, J = 1.2 Hz, 1H), 5.95 (s, 1H), 3.62 (s, 3H), 2.39 (s,
3H); 13C{1H} NMR (100 MHz, CDCl3)  169.9, 146.5,
145.6, 138.1, 134.7, 133.3, 131.2, 130.4, 129.51, 129.45,
129.3, 128.8, 127.3, 125.0, 124.8, 118.0, 114.3, 112.7, 53.0,
46.4, 21.4; IR (film): 3389, 2950, 1737, 1502, 1360, 1200,
909, 732 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C23H19ClN2O2 390.1131; Found 390.1135.
Methyl 2-(6-methyl-2-(p-tolyl)imidazo[1,2-a]pyridin-3-
yl)-2-phenylacetate (5s): Yield: 53.3 mg (72%); Rf = 0.3
(EtOAc:Hexane = 1:3); Ivory solid; Melting point: 129-
o
1
131 C; H NMR (400 MHz, CDCl3)  7.73 (s, 1H), 7.63
(d, J = 7.9 Hz, 2H), 7.57 (d, J = 7.9 Hz, 1H), 7.32-7.25 (m,
5H), 7.07-7.02 (m, 3H), 5.85 (s, 1H), 3.76 (s, 3H), 2.39 (s,
3H), 2.18 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) 
171.5, 146.1, 144.8, 137.9, 134.7, 131.5, 129.5, 129.0,
128.9, 128.0, 127.7, 123.7, 121.5, 116.9, 115.0, 52.7, 47.3,
21.4, 18.6; IR (film): 3367, 2950, 1736, 1603, 1496, 1382,
1164, 697 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C24H22N2O2 370.1681; Found 370.1679.
Methyl
2-(2-chlorophenyl)-2-(2-(4-chlorophenyl)
imidazo[1,2-a]pyridin-3-yl)acetate (5x): Yield: 75.7 mg
(92%); Rf = 0.3 (EtOAc:Hexane = 1:3); Purple solid;
Methyl
2-(6-chloro-2-(4-chlorophenyl)imidazo[1,2-
a]pyridin-3-yl)-2-phenylacetate (5t): Yield: 66.6 mg
(81%); Rf = 0.3 (EtOAc:Hexane = 1:3); Ivory solid;
o
1
Melting point: 163-165 C; H NMR (400 MHz, CDCl3) 
8.06 (dt, J = 7.0 Hz, J = 1.1 Hz, 1H), 7.69 (dt, J = 9.1 Hz, J
= 1.1 Hz, 1H), 7.60-7.57 (m, 2H), 7.45 (dd, J = 8.0 Hz, J =
1.2 Hz, 1H), 7.41-7.37 (m, 2H), 7.27-7.20 (m, 2H), 7.13
(td, J = 11.4 Hz, J = 1.2 Hz, 1H), 6.89 (dd, J = 7.8 Hz, J =
1.1 Hz, 1H), 6.75 (td, J = 10.3 Hz, J = 1.2 Hz, 1H), 5.89 (s,
1H), 3.63 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) 
169.6, 145.7, 145.3, 134.7, 134.4, 133.1, 132.8, 130.4,
130.2, 129.6, 129.2, 128.8, 127.3, 125.0, 124.9, 118.1,
114.9, 112.8, 52.9, 46.4; IR (film): 3388, 3054, 2950, 1738,
1380, 1361, 1201, 703 cm-1; HRMS (EI) m/z: [M]+ Calcd
for C22H16Cl2N2O2 410.0586; Found 410.0589.
o
1
Melting point: 127-129 C; H NMR (400 MHz, CDCl3) 
8.03 (d, J = 1.2 Hz, 1H), 7.70-7.67 (m, 2H), 7.60 (dd, J =
9.5 Hz, J = 0.4 Hz, 1H), 7.47-7.43 (m, 2H), 7.36-7.30 (m,
3H), 7.17 (dd, J = 9.5 Hz, J = 2.0 Hz, 1H), 7.05-7.03 (m,
2H), 5.80 (s, 1H), 3.81 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  170.9, 146.0, 144.2, 134.6, 132.3, 130.3, 129.3,
129.1, 128.1, 127.4, 126.7, 124.1, 120.3, 118.0, 116.5, 53.0,
47.3; IR (film): 3061, 2952, 1736, 1602, 1484, 1380, 1102,
698 cm-1; HRMS (EI) m/z: [M]+ Calcd for C22H16Cl2N2O2
410.0586; Found 410.0589.
Methyl
2-(2-chlorophenyl)-2-(7-methyl-2-phenyl
Methyl
2-(2-chlorophenyl)-2-(2-(3-chlorophenyl)-
imidazo[1,2-a]pyridin-3-yl)acetate (5u): Yield: 75.0 mg
(96%); Rf = 0.3 (EtOAc:Hexane = 1:1); Ivory solid;
imidazo[1,2-a]pyridin-3-yl)acetate (5y): Yield: 79.8 mg
(97%); Rf = 0.3 (EtOAc:Hexane = 1:3); Ivory solid;
o
1
Melting point: 166-168 C; H NMR (400 MHz, CDCl3) 
7.95 (d, J = 7.1Hz, 1H), 7.48-7.46 (m, 2H), 7.45-7.41 (m,
2H), 7.38-7.34 (m, 1H), 7.30-7.26 (m, 1H), 6.86 (dd, J =
7.8 Hz, J = 1.0 Hz, 1H), 6.61 (dd, J = 7.1 Hz, J = 1.7 Hz,
1H), 5.92 (s, 1H), 3.61 (s, 3H), 2.42 (s, 3H); 13C{1H} NMR
(100 MHz, CDCl3)  169.9, 146.1, 135.9, 134.7, 134.3,
133.5, 130.4, 129.5, 129.3, 128.9, 128.7, 128.2, 127.3,
124.3, 116.4, 115.4, 113.9, 52.9, 46.4, 21.4; IR (film):
3397, 3061, 2950, 1738, 1380, 1200, 1072, 700 cm-1;
HRMS (EI) m/z: [M]+ Calcd for C23H19ClN2O2 390.1136;
Found 390.1135.
o
1
Melting point: 138-140 C; H NMR (400 MHz, CDCl3) 
8.07 (d, J = 7.0 Hz, 1H), 7.74-7.70 (m, 2H), 7.49-7.46 (m,
2H), 7.37-7.32 (m, 2H), 7.31-7.25 (m, 2H), 7.16 (td, J =
7.6 Hz, J = 0.9 Hz, 1H), 6.88 (d, J = 7.0 Hz, 1H), 6.80 (td,
J = 10.3 Hz, J = 0.9 Hz, 1H), 5.91 (s, 1H), 3.65 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3)  169.6, 145.6, 144.9,
135.9, 134.68, 134.65, 132.9, 130.4, 129.9, 129.7, 129.2,
128.4, 127.3, 126.9, 125.2, 125.0, 118.1, 115.03, 115.02,
113.0, 53.1, 46.2; IR (film): 3397, 3063, 2951, 1739, 1601,
1201, 1078, 700 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C22H16Cl2N2O2 410.0591; Found 410.0589.
Methyl
2-(7-chloro-2-phenylimidazo[1,2-a]pyridin-3-
Methyl 2-(2-(4-bromophenyl)imidazo[1,2-a]pyridin-3-
yl)-2-(2-chlorophenyl)acetate (5z): Yield: 82.0 mg
(90%); Rf = 0.3 (EtOAc:Hexane = 1:3); Purple solid;
yl)-2-(2-chlorophenyl)acetate (5v): Yield: 80.6 mg
(98%); Rf = 0.3 (EtOAc:Hexane = 1:3); Ivory solid;
o
1
Melting point: 147-149 C; H NMR (400 MHz, CDCl3) 
8.03 (dd, J = 7.4 Hz, J = 0.7 Hz, 1H), 7.71 (dd, J = 2.1 Hz,
J = 0.8 Hz, 1H), 7.65-7.62 (m, 2H), 7.48-7.42 (m, 3H),
7.41-7.37 (m, 1H), 7.29 (td, J = 7.7 Hz, J = 1.6 Hz, 1H),
7.16 (td, J = 11.4 Hz, J = 1.3 Hz, 2H), 6.85 (dd, J = 7.8 Hz,
J = 0.8 Hz, 1H), 6.76 (dd, J = 7.4 Hz, J = 2.1 Hz, 1H), 5.92
(s, 1H), 3.64 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) 
169.7, 147.3, 145.5, 134.7, 133.7, 132.9, 131.6, 130.6,
129.7, 129.1, 128.9, 128.8, 128.5, 127.4, 125.6, 116.8,
o
1
Melting point: 174-176 C; H NMR (400 MHz, CDCl3) 
8.06 (d, J = 7.0 Hz, 1H), 7.70 (d, J = 9.1 Hz, 1H), 7.56-
7.20 (m, 4H), 7.45 (dd, J = 8.0 Hz, J = 1.1 Hz, 1H), 7.28-
7.21 (m, 2H), 7.13 (td, J = 11.4 Hz, J = 1.1 Hz, 1H), 6.89
(dd, J = 7.7 Hz, J = 0.8 Hz, 1H), 6.76 (td, J = 10.3 Hz, J =
1.1 Hz, 1H), 5.89 (s, 1H), 3.63 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3)  169.6, 145.7, 145.3, 134.7, 133.3, 133.1,
131.8, 130.5, 130.4, 129.6, 129.2, 127.36, 125.02, 124.96,
10
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
122.6, 118.1, 114.9, 112.8, 52.9, 46.4; IR (film): 3053,
2950, 1737, 1361, 1201, 1073, 752, 703 cm-1; HRMS (EI)
m/z: [M]+ Calcd for C22H1679BrClN2O2 454.0084
C22H1681BrClN2O2 456.0063; Found 454.0084, 456.0063.
were added. After being stirred at room temperature for 3 h,
the reaction mixture was concentrated under reduced
pressure. The crude product was purified by silica gel
column chromatography with EtOAc and hexane to give
the corresponding drug precursors.
Methyl 2-(2-(3-bromophenyl)imidazo[1,2-a]pyridin-3-
yl)-2-(2-chlorophenyl)acetate (5a‘): Yield: 88.4 mg
(97%); Rf = 0.3 (EtOAc:Hexane = 1:3); Brown solid;
Ethyl
2-(2-phenylimidazo[1,2-a]pyridin-3-yl)acetate
(4a)[7h]: Yield: 38.1 mg (68%); Rf = 0.3 (EtOAc:Hexane =
1:2); Yellow solid 1H NMR (400 MHz, CDCl3)  8.13 (d, J
= 6.9 Hz, 1H), 7.86-7.84 (m, 2H), 7.67 (d, J = 6.9 Hz, 1H),
7.50-7.47 (m, 2H), 7.41-7.37 (m, 1H), 7.23 (ddd, J = 9.1
Hz, J = 6.7 Hz, J = 1.2 Hz, 1H), 6.86 (td, J = 10.2 Hz, J =
1.0 Hz, 1H), 4.23 (q, J = 7.1 Hz, 2H), 4.05 (s, 2H), 1.28 (t,
J = 7.1 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3)  169.6,
145.2, 144.8, 134.2, 128.8, 128.7, 128.0, 124.6, 123.8,
117.8, 113.1, 112.5, 61.8, 31.0, 14.3.
o
1
Melting point: 139-141 C; H NMR (400 MHz, CDCl3) 
8.06 (d, J = 7.0 Hz, 1H), 7.86 (t, J = 1.7 Hz, 1H), 7.72 (d, J
= 9.1 Hz, 1H), 7.53-7.46 (m, 3H), 7.30-7.24 (m, 3H), 7.14
(td, J = 11.4 Hz, J = 1.0 Hz, 1H), 6.88 (dd, J = 7.7 Hz, J =
0.7 Hz, 1H), 6.80 (td, J = 6.9 Hz, J = 0.9 Hz, 1H), 5.91 (s,
1H), 3.65 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) 
169.6, 145.6, 144.7, 136.2, 134.6, 132.9, 132.0, 131.2,
130.4, 130.1, 129.6, 129.1, 127.29, 127.26, 125.2, 124.9,
122.8, 118.1, 115.1, 113.0, 53.0, 46.2; IR (film): 3389,
3058, 2951, 1737, 1599, 1470, 1201, 700 cm-1; HRMS (EI)
m/z: [M]+ Calcd for C22H1679BrClN2O2 454.0081
C22H1681BrClN2O2 456.0070; Found 454.0084, 456.0063.
Ethyl 2-(6-methyl-2-(p-tolyl)imidazo[1,2-a]pyridin-3-
yl)acetate (4b)[7h]: Yield: 31.5 mg (51%); Rf = 0.3 (EtOAc:
1
Hexane = 1:2); Ivory solid; H NMR (400 MHz, CDCl3) 
7.88 (s, 1H), 7.72 (d, J = 8.1 Hz, 2H), 7.55 (d, J = 9.2 Hz,
1H), 7.29-7.26 (m, 2H), 7.06 (dd, J = 9.2 Hz, J = 1.5 Hz,
1H), 4.22 (dd, J = 7.1 Hz, 2H), 4.01 (s, 2H), 2.40 (s, 3H),
2.36 (s, 3H), 1.28 (t, J = 7.1 Hz,, 3H); 13C{1H} NMR (100
MHz, CDCl3)  169.7, 144.6, 144.2, 137.6, 131.5, 129.4,
128.5, 127.6, 122.0, 121.4, 116.9, 112.5, 61.6, 31.0, 21.4.
Methyl 2-(2-chlorophenyl)-2-(2-(thiophen-2-yl)imidazo
[1,2-a]pyridin-3-yl)acetate (5b‘): Yield: 45.9 mg (60%);
Rf = 0.3 (EtOAc:Hexane = 1:3); White solid; Melting
o
1
point: 151-153 C; H NMR (400 MHz, CDCl3)  8.05 (d,
J = 7.0 Hz, 1H), 7.70 (d, J = 9.1 Hz, 1H), 7.47 (dd, J = 8.0
Hz, J = 0.8 Hz, 2H), 7.39 (dd, J = 5.1 Hz, J = 0.6 Hz, 1H),
7.29-7.21 (m, 3H), 7.14 (td, J = 7.6 Hz, J = 0.7 Hz, 1H),
7.09 (dd, J = 5.0 Hz, J = 3.7 Hz, 1H), 6.87 (dd, J = 7.7 Hz,
J = 0.5 Hz, 1H), 6.75 (td, J = 10.2 Hz, J = 0.8 Hz, 1H),
6.11 (s, 1H), 3.68 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3)  169.7, 145.6, 140.3, 136.7, 134.7, 132.8, 130.4,
129.6, 129.1, 127.8, 127.3, 126.7, 125.8, 125.2, 124.8,
117.9, 114.2, 112.9, 53.0, 46.2; IR (film): 3069, 2950,
1737, 1380, 1213, 1081, 751, 702 cm-1; HRMS (EI) m/z:
[M]+ Calcd for C20H15ClN2O2S 382.0545; Found 382.0543.
Ethyl
2-(6-chloro-2-(4-chlorophenyl)imidazo[1,2-
a]pyridin-3-yl)acetate (4c)[7h]: Yield: 39.8 mg (57%); Rf =
0.3 (EtOAc:Hexane = 1:2); Ivory solid; 1H NMR (400
MHz, CDCl3)  8.20 (dd, J = 1.9 Hz, J = 0.7 Hz, 1H),
7.79-7.75 (m, 2H), 7.59 (dd, J = 9.5 Hz, J = 0.6 Hz, 1H),
7.47-7.44 (m, 2H), 7.21 (dd, J = 9.5 Hz, J = 1.9 Hz, 1H),
4.25 (q, J = 7.1 Hz, 2H), 3.99 (s, 2H), 1.31 (t, J = 7.1 Hz,
3H); 13C{1H} NMR (100 MHz, CDCl3)  169.0, 144.6,
143.6, 134.4, 132.3, 129.9, 129.1, 126.3, 121.9, 121.0,
118.1, 113.8, 62.0, 30.9, 14.3.
Methyl
2-(2-chlorophenyl)-2-(6-methyl-2-(p-tolyl)
imidazo[1,2-a]pyridin-3-yl)acetate (5c'): Yield: 51.0 mg
Procedure of Rh (III)-Catalyzed Alkylation of C3-
Alkylated Imidazopyridine: A dried test tube equipped
with a magnetic stirring bar was charged with C3-alkylated
imidazo[1,2-a]pyridine 3a (0.2 mmol, 1.0 equiv),
[RhCp*Cl2]2 (4.9 mg, 0.008 mmol, 4.0 mol %), AgSbF6 (11
mg, 0.032 mmol, 16.0 mol %), PivOH (46 μL, 0.4 mmol,
2.0 equiv), diazoester 2a (0.4 mmol, 2.0 equiv), and DCE
(2.0 mL) under a nitrogen atmosphere. After being stirred
(63%); Rf = 0.3 (EtOAc:Hexane = 1:3); Purple solid;
o
1
Melting point: 69-71 C; H NMR (400 MHz, CDCl3) 
7.82 (s, 1H), 7.63 (d, J = 9.2 Hz, 1H), 7.52-7.47 (m, 3H),
7.28 (td, J = 11.5 Hz, J = 1.3 Hz, 1H), 7.24 (t, J = 7.9 Hz,
2H), 7.15 (td, J = 11.4 Hz, J = 1.2 Hz, 1H), 7.10 (dd, J =
9.2 Hz, J = 1.6 Hz, 1H), 6.85 (dd, J = 7.8 Hz, J = 0.9 Hz,
1H), 5.91 (s, 1H), 3.61 (s, 3H), 2.38 (s, 3H), 2.27 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3)  169.9, 146.2, 144.7,
138.0, 134.7, 133.5, 131.3, 130.3, 129.5, 129.4, 128.7,
128.0, 127.3, 122.5, 122.4, 117.3, 114.0, 52.9, 46.4, 21.4,
18.6; IR (film): 3025, 2950, 1738, 1442, 1382, 1168, 1042,
702 cm-1; HRMS (EI) m/z: [M]+ Calcd for C24H21ClN2O2
404.1294; Found 404.1292.
o
at 80 C for 12 h, the reaction mixture was concentrated
under reduced pressure. The crude product was purified by
silica gel column chromatography with EtOAc and hexane
to give 6 (1:1.3 ratio).
Methyl
2-(2-(3-(2-methoxy-2-oxo-1-phenylethyl)
imidazo[1,2-a]pyridin-2-yl)phenyl)-2-phenylacetate (6):
Yield: 54.9 mg (56%); Rf = 0.3 (EtOAc:Hexane = 1:2);
Orange oil; inseparable mixture of diasteromers (1:1.3
Procedure for the Preparation of Alpidem and
Zolpidem Precursors: A dried test tube equipped with a
magnetic stirring bar was charged with imidazo[1,2-
a]pyridine 1 (0.2 mmol, 1.0 equiv), Rh2(oct)4 (2.3 mg,
0.004 mmol, 2.0 mol %), ethyl diazoacetate (15% in
toluene, 0.3 mmol, 1.5 equiv), and DCE (2.0 mL). The
resulting mixture was stirred at room temperature for 3 h
under a nitrogen atmosphere, and then another batch of
Rh2(oct)4 (2.0 mol %) and ethyldiazoacetate (1.5 equiv)
1
ratio); H NMR (400 MHz, CDCl3)  7.97 (d, J = 7.0 Hz,
0.6H), 7.96 (d, J = 7.0 Hz, 0.4H), 7.67 (d, J = 9.1 Hz, 1H),
7.45 (d, J = 7.8 Hz, 1H), 7.41-7.34 (m, 2H), 7.33-7.25 (m,
6H), 7.23-7.16 (m, 4H), 7.11-7.06 (m, 2H), 6.65 (td, J =
10.3 Hz, J = 1.1 Hz, 0.6H), 6.60 (td, J = 10.3 Hz, J = 1.1
Hz, 0.4H), 6.02 (s, 0.3H), 5.75 (s, 0.6H), 5.52 (s, 0.6H),
5.45 (s, 0.3H), 3.77 (s, 1H), 3.667 (s, 1.7H) 3.666 (s, 1H),
11
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
3.52 (s, 1.7H); 13C{1H} NMR (100 MHz, CDCl3)  173.7,
173.4, 171.5, 171.3, 145.9, 145.6, 145.5, 139.3, 139.1,
139.0. 138.8. 134.6. 134.4. 133.5. 133.4. 131.1. 130.9.
130.0, 129.5, 129.05, 129.03, 128.98, 128.91, 128.87,
128.8, 128.6, 128.5, 127.7, 127.6, 127.5, 127.3, 127.10,
127.07, 127.02, 126.96, 126.4, 126.3, 124.89, 124.86,
117.9, 117.8, 117.4, 117.2, 111.9, 111.8, 53.1, 52.9, 52.7,
52.3, 52.1, 47.30, 47.27; IR (film): 3366, 3059, 2951, 1736,
1602, 1384, 1073, 699 cm-1; HRMS (EI) m/z: [M]+ Calcd
for C31H26N2O4 490.1895; Found 490.1893.
with C3-alkylated imidazo[1,2-a]pyridine 3h or 5u (0.2
mmol, 1.0 equiv), Pd(OAc)2 (2.2 mg, 0.01 mmol, 5.0
mol %), PCy3·HBF4 (7.4 mg, 0.02 mmol, 10.0 mol %),
K2CO3 (41.5 mg, 0.3 mmol, 1.5 equiv), and DMA (1.0
mL) under a nitrogen atmosphere. After being stirred at
o
145 C for 12 h, the reaction mixture was concentrated
under reduced pressure. The crude product was purified by
silica gel column chromatography with EtOAc and hexane
to give the corresponding Cyclization products 7a or 7b.
5-Phenyl-6H-benzo[a]imidazo[5,1,2-de]quinolizin-6-one
(7a): Yield: 49.8 mg (84%); Rf = 0.3 (EtOAc:Hexane =
Application of C3-Alkylated Imidazopyridine
o
1
1:1); Yellow solid; Melting point: 197-199 C; H NMR
(400 MHz, CDCl3)  8.74-8.69 (m, 3H), 8.43 (d, J = 7.4
Hz, 1H), 8.15 (d, J = 7.2 Hz, 1H), 8.06 (d, J = 8.6 Hz, 1H),
7.86 (q, J = 8.0 Hz, 2H), 7.79 (t, J = 7.3 Hz, 1H), 7.61-7.57
(m, 2H), 7.55-7.50 (m, 1H); 13C{1H} NMR (100 MHz,
CDCl3)  170.8, 155.5, 145.0, 134.0, 132.9, 132.5, 130.91,
130.88, 130.4, 130.1, 128.5, 128.4, 128.3, 127.6, 123.5,
119.6, 116.7, 110.9; IR (film): 3069, 1630, 1478, 1331,
1235, 921, 754, 691 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C20H12N2O 296.0947; Found 296.0950.
1) Synthetic procedure for 7a and 8 (eq 11): A dried test
tube equipped with a magnetic stirring bar was charged
with C3-alkylated imidazo[1,2-a]pyridine 3h (0.2 mmol,
1.0 equiv), Pd(OAc)2 (2.2 mg, 0.01 mmol, 5.0 mol %),
PCy3·HBF4 (7.4 mg, 0.02 mmol, 10.0 mol %), K2CO3
(41.5 mg, 0.3 mmol, 1.5 equiv), and DMA (1.0 mL) under
o
a nitrogen atmosphere. After being stirred at 130 C for 12
h, the reaction mixture was concentrated under reduced
pressure. The crude product was purified by silica gel
column chromatography with EtOAc and hexane to give
the corresponding Cyclization products 7a and 8.
5-(p-tolyl)-6H-benzo[a]imidazo[5,1,2-de]quinolizin-6-
one (7b): Yield: 46.6 mg (75%); Rf = 0.3 (EtOAc:Hexane
1
= 1:1); Yellow solid; Melting point: 187-189 oC; H NMR
2) Synthetic procedure for 8 (eq 12): A dried test tube
equipped with a magnetic stirring bar was charged with
C3-alkylated imidazo[1,2-a]pyridine 3h (0.2 mmol, 1.0
equiv), Pd(OAc)2 (2.2 mg, 0.01 mmol, 5.0 mol %),
PCy3·HBF4 (7.4 mg, 0.02 mmol, 10.0 mol %), K2CO3
(41.5 mg, 0.3 mmol, 1.5 equiv), and DMA (1.0 mL) under
(400 MHz, CDCl3)  8.73 (dd, J = 7.9 Hz, J = 1.3 Hz, 1H),
8.62 (d, J = 8.2 Hz, 2H), 8.42 (d, J = 7.8 Hz, 1H), 8.14 (d,
J = 7.6 Hz, 1H), 8.04 (dd, J = 8.7 Hz, J = 0.6 Hz, 1H),
7.88-7.82 (m, 2H), 7.78 (td, J = 7.5 Hz, J = 1.1 Hz, 1H),
7.39 (d, J = 8.0 Hz, 2H), 2.47 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3)  170.7, 155.7, 145.1, 140.7, 134.1, 132.5,
130.9, 130.1, 130.0, 129.2, 128.5, 128.3, 127.6, 123.5,
119.6, 116.5, 110.7, 21.8; IR (film): 3073, 2918, 1631,
1599, 1480, 1332, 1232, 757 cm-1; HRMS (EI) m/z: [M]+
Calcd for C21H14N2O 310.1102; Found 310.1106.
o
an oxygen atmosphere. After being stirred at 130 C for 12
h, the reaction mixture was concentrated under reduced
pressure. The crude product was purified by silica gel
column chromatography with EtOAc and hexane to give
the corresponding products 8.
3) Synthetic procedure for 9 (eq 13): A dried test tube
equipped with a magnetic stirring bar was charged with
C3-alkylated imidazo[1,2-a]pyridine 3h (0.2 mmol, 1.0
equiv), Pd(OAc)2 (2.2 mg, 0.01 mmol, 5.0 mol %),
PCy3·HBF4 (7.4 mg, 0.02 mmol, 10.0 mol %), and DMA
(1.0 mL) under a nitrogen atmosphere. After being stirred
(2-Chlorophenyl)(2-phenylimidazo[1,2-a]pyridin-3-
yl)methanone (8): Yield: 65.2 mg (98%); Rf = 0.3
(EtOAc: Hexane = 1:4); Yellow solid; Melting point: 136-
138 oC; 1H NMR (400 MHz, CDCl3)  9.89 (dt, J = 6.9 Hz,
J = 1.1 Hz, 1H), 7.82 (dt, J = 8.9 Hz, J = 1.0 Hz, 1H),
7.63-7.58 (m, 1H), 7.28-7.25 (m, 2H), 7.18 (td, J = 10.4 Hz,
J = 1.2 Hz, 1H), 7.13-7.03 (m, 6H), 6.90 (td, J = 11.1 Hz, J
= 1.4 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3)  184.6,
157.5, 147.9, 139.0, 133.8, 131.9, 131.0, 130.3, 130.0,
129.8, 129.7, 129.3, 128.3, 127.5, 126.2, 120.7, 117.6,
115.4; IR (film): 3062, 1612, 1393, 1327, 1221, 898, 753,
645 cm-1; HRMS (EI) m/z: [M]+ Calcd for C20H13ClN2O
332.0718; Found 332.0716.
o
at 130 C for 12 h, the reaction mixture was concentrated
under reduced pressure. The crude product was purified by
silica gel column chromatography with EtOAc and hexane
to give the corresponding products 9.
4) Synthetic procedure for 10 (eq 14): A dried test tube
equipped with a magnetic stirring bar was charged with 3-
Acylated imidazo[1,2-a]pyridine 8 (0.2 mmol, 1.0 equiv),
Pd(OAc)2 (2.2 mg, 0.01 mmol, 5.0 mol %), PCy3·HBF4
(7.4 mg, 0.02 mmol, 10.0 mol %), K2CO3 (41.5 mg, 0.3
mmol, 1.5 equiv), and DMA (1.0 mL) under a nitrogen
3-(2-Chlorobenzyl)-2-phenylimidazo[1,2-a]pyridine (9):
Yield: 29.3 mg (46%); Rf = 0.3 (EtOAc:Hexane = 1:4);
Yellow solid; Melting point: 66-68 oC; 1H NMR (400 MHz,
CDCl3)  7.74-7.69 (m, 3H), 7.61 (d, J = 6.9 Hz, 1H), 7.47
(dd, J = 8.0 Hz, J = 1.1 Hz, 1H), 7.43-7.39 (m, 2H), 7.35-
7.31 (m, 1H), 7.21-7.16 (m, 2H), 7.05 (td, J = 11.5 Hz, J =
1.1 Hz, 1H), 6.73-6.70 (m, 2H), 4.52 (s, 2H); 13C{1H}
NMR (100 MHz, CDCl3)  145.1, 144.7, 134.4, 134.3,
134.2, 129.8, 128.7, 128.5, 128.4, 128.1, 127.9, 127.4,
124.4, 123.3, 117.7, 116.6, 112.4, 27.8; IR (film): 3059,
1678, 1504, 1444, 1359, 1073, 749, 699 cm-1; HRMS (EI)
o
atmosphere. After being stirred at 130 C for 12 h, the
reaction mixture was concentrated under reduced pressure.
The crude product was purified by silica gel column
chromatography with EtOAc and hexane to give the
corresponding Cyclization products 10.
5) Synthetic procedure for 7a, and 7b (eq 15): A dried
test tube equipped with a magnetic stirring bar was charged
12
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900092
Advanced Synthesis & Catalysis
m/z: [M]+ Calcd for C20H15ClN2 318.0921; Found
318.0924.
484-495; d) Y. Uemura, S. Tanaka, S. Ida, T. Yuzuriha,
J. Pharm. Pharmacol. 1993, 45, 1077-1081; e) L.
Almirante, L. Polo, A. Mugnaini, E. Provinciali, P.
Rugarli, A. Biancotti, A. Gamba, W. Murmann, J. Med.
Chem. 1965, 8, 305-312; f) K. Mizushige, T. Ueda, K.
Yukiiri, H. Suzuki, Cardiovasc. Drug Rev. 2002, 20,
163-174.
9H-Dibenzo[4',5':6',7']cyclohepta[1',2':4,5]imidazo[1,2-
a]pyridin-9-one (10): Yield: 37.3 mg (63%); Rf = 0.3
(EtOAc:Hexane = 1:5); Ivory solid; Melting point: 180-
1
182 oC; H NMR (400 MHz, CDCl3)  9.61 (d, J = 7.0 Hz,
1H), 8.72 (dd, J = 7.8 Hz, J = 1.6 Hz, 1H), 8.38 (dd, J =
7.8 Hz, J = 1.6 Hz, 2H), 7.95 (dd, J = 7.9 Hz, J = 0.6 Hz,
1H), 7.89 (dd, J = 7.9 Hz, J = 1.0 Hz, 1H), 7.77 (d, J = 9.0
Hz, 1H), 7.63 (td, J = 11.1 Hz, J = 1.5 Hz, 1H), 7.60-7.52
(m, 3H), 7.51-7.47 (m, 1H), 7.02 (td, J = 10.4 Hz, J = 1.1
Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3)  181.1, 149.3,
147.6, 138.9, 136.9, 136.2, 131.8, 131.7, 131.4, 130.4,
129.7, 129.4, 129.23, 129.17, 128.54, 128.45, 128.1, 124.2,
117.2, 114.2; IR (film): 3073, 2918, 1631, 1599, 1480,
1332, 1232, 757 cm-1; HRMS (EI) m/z: [M]+ Calcd for
C20H12N2O 296.0954; Found 296.0950.
[4] H. J. Park, J.-G. Jun, Bull. Korean Chem. Soc. 2017, 38,
1123-1128.
[5] K. Li, X. Zhu, S. Lu, X.-Y. Zhou, Y. Xu, X.-Q. Hao,
M.-P. Song, Synlett 2016, 27, 387-390.
[6] K. Pericherla, B. Khungar, A. Kumar, Tetrahedron Lett.
2012, 53, 1253-1257.
[7] a) J. Koubachi, S. El Kazzouli, S. Berteina-Raboin, A.
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Acknowledgements
This paper is dedicated to Professor Sang-gi Lee (Ewha Womans
University) for his honorable retirement. This work was
supported by a grant from the National Research Foundation of
Korea (NRF), funded by the Korean government (2011-0018355)
and BRL (2017R1A4A1015405).
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10.1002/adsc.201900092
Advanced Synthesis & Catalysis
FULL PAPER
Rhodium(II)-Catalyzed
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14
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