CuI-catalyzed aerobic oxidative α-aminaton cyclization of ketones to access aryl or alkenyl-substituted imidazoheterocycles

Article abstract of DOI:10.1021/jo402134x

CuI-catalyzed aerobic oxidative synthesis of imidazoheterocycles has been achieved. Four hydrogen atoms were removed in one step. This protocol was compatible with a broad range of functional groups, and it has been also successfully extended to unsaturated ketones, bringing about the formation of alkenyl-substituted imidazoheterocycles, which were difficult to prepare by previous means. Preliminary mechanistic studies indicated that this reaction was most likely to proceed through a catalytic Ortoleva-King reaction. By using this method, the marketed drug Zolimidine could be prepared with 90% yield on a gram scale from commercially available materials.

Full text of DOI:10.1021/jo402134x

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Article
CuI-Catalyzed Aerobic Oxidative alpha-Aminaton Cyclization of
Ketones to Access Aryl or Alkenyl-Substituted Imidazoheterocycles
Yuanfei Zhang, Zhengkai Chen, Wenliang Wu, Yuhong Zhang, and Weiping Su
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 20 Nov 2013
Downloaded from http://pubs.acs.org on November 22, 2013
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CuI-Catalyzed Aerobic Oxidative α-Aminaton Cyclization of Ketones to
Access Aryl or Alkenyl-Substituted Imidazoheterocycles
Yuanfei Zhang,a Zhengkai Chen,b Wenliang Wu,a Yuhong Zhang*,b and Weiping Su*,a
a State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
E-mail: wpsu@fjirsm.ac.cn
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b Department of Chemistry, Zhejiang University, Hangzhou 310027, China
E-mail: yhzhang@zju.edu.cn
ABSTRACT: CuI-catalyzed aerobic oxidative synthesis of imidazoheterocycles has been
achieved. Four hydrogen atoms were removed in one step. This protocol was compatible with a
broad range of functional groups, and has also successfully extended to unsaturated ketones
bringing about the formation of alkenyl-substituted imidazoheterocycles which were difficult to be
prepared by previous means. Preliminary mechanistic studies indicated that this reaction was most
likely to proceed through a catalytic Ortoleva−King reaction. By using this method, marketed drug
Zolimidine could be prepared on gram scale from commercially available materials with 90%
yield obtained.
1. INTRODUCTION
Imidazo[1,2-a]pyridines are prominent among N-fused heterocycles, and are extensively found in
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biologically active molecules.1 Several compounds bearing the core structure of
imidazo[1,2-a]pyridine ring systems have been successfully developed into commercially
available drugs including alpidem, zolpidem, zolimidine, and olprinone, etc (Scheme 1).2 They are
also useful frameworks in material science,3 and abnormal N-heterocyclic carbenes in
organometallic chemistry.4
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Scheme 1. Biologically active compounds sharing imidazo[1,2-a]pyridine rings.
Progresses were made to gain access to substituted imidazo[1,2-a]pyridines.5 Among them, the
reaction of 2-aminopyridines with mono α-halogenocarbonyl compounds remains the most
commonly used means in both laboratory synthesis and industrial manufacture.3d,5e,6 However,
this methodology is still imperfect. Mono halogenation of carbonyl compounds, particularly
unsaturated ones, is still challenging.7 In addition to the difficulties in controlling mono
substituted product, halogenations using cheap X2 (mainly bromide) as halogen source were
ineffective for unsaturated ketones.8 Furthermore, the coupling efficiency were not good enough
with respect to halogenated unsaturated ketones.2h Because of those intrinsic defects, a wide range
of unsaturated ketones cannot be easily incorporated into imidazoheterocycles using this
traditional method, severely limiting the structural diversity of imidazoheterocycles. Herein, we
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describe a CuI-catalyzed aerobic oxidative α-aminaton cyclization of ketones leading to
substituted imidazoheterocycles. Starting from simple and readily available materials, this
transformation is straightforward and of high efficiency, and is also applicable to unsaturated
ketones.
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Towards waste free synthesis, transition-metals catalyzed oxidative functionalization of organic
molecule involving dioxygen activation present one of most powerful means in organic synthesis.9
Special attentions have been paid to copper/O2 system which exhibits broad catalytic activities
over a spectrum of substrates.9e,9h,10 Some biomimetic oxidation systems based on copper as
co-catalysis have been developed as well.11 Using CuI as catalysis under aerobic conditions, the
role of iodine anion has been ignored by most authors.10,11a In this work, iodine anion is crucial to
the current transformation.
2. RESULTS AND DISCUSSION
Initially, we examined the reaction of 2-aminopyridine (1a) and acetophenone (2a) in the presence
of copper salts (5 mol%) in DMF at 100 oC under aerobic conditions. Interestingly, only CuI gave
the desired product 2-phenylimidazo[1,2-a]pyridine in 66% yield (Table 1, entry 1). Other copper
sources, CuCl, CuBr, CuCl2 and CuBr2, etc, though under the otherwise identical conditions,
failed to produce the product in any detectable amount (Table 1 entries 2-12). Next, we checked
the effect of solvents, the yield was not obviously increased in DMA and NMP (Table 1, entries
13 and 14). Taking into account previous reports concerning the synthesis of
imidazo[1,2-a]pyridines,3d,5e,6 we reasoned that this reaction might proceed via an initial
α-iodination of acetophenone and subsequent amination/cyclization sequence, which differs from
the C-H bond functionalization mechanism or SET process.12 Thus, the efficiency of α-iodination
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of acetophenone was decisive for the overall yield. With this hypothesis in mind, we surveyed
various Lewis acid to accelerate the α-iodination step (Table 1, entries 15-22). Gratifyingly, 81%
yield was obtained accompanied with the addition of 1mol% In(CF3SO3)3 in NMP under 1atm O2
(Table 1, entry 17).
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Table 1. Optimization of the reaction conditionsa
Entry
1
catalyst
CuI
Additive (equiv)
Solvent
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMA
Yield (%)b
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-
-
-
-
-
-
-
-
-
-
-
-
-
2
CuCl
NDc
NDc
NDc
NDc
NDc
NDc
NDc
NDc
NDc
NDc
NDc
68
3
CuBr
4
CuCl2
CuBr2
Cu(OAc)2
Cu(CF3SO3)2
CuO
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8
9
Cu2O
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13
CuF2
CuSO4
.
Cu(NO3)2 3H2O
CuI
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CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
-
NMP
DMA
69
In(CF3SO3)3 (2.5%)
70d
82d
81d
50d
71d
46e
71d,e
80d,e
In(CF3SO3)3 (2.5%) NMP
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In(CF3SO3)3 (1%)
NMP
NMP
NMP
NMP
NMP
NMP
.
BF3 Et2O (10%)
TsOH (10%)
TsOH (10%)
CuBr2 (5%)
CuBr2 (5%)
22
a
Reaction Conditions: 1a (0.6 mmol), 2a (0.3 mmol), cat. (5 mol%), solvent (2 mL), O2 (1 atm),
o
b
c
d
100 C, 24 h. Isolated yield. ND = Not Detected (by GC-MS). The reaction was carried out
e
for 30 h. Under 1 atm air. DMF = N,N-dimethylformamide. DMA = N,N-dimethylacetamide.
NMP = N-methyl-2-pyrrolidone.
With the optimized reaction conditions in hand, we evaluated the scope of the reaction. As
depicted in (Table 2), the nature of substituents on the benzene ring of (hetero)aryl methyl ketones
did not affect the reaction much, good to excellent yields were obtained. Notably, cyano group
was also compatible with the current reaction condition (Table 2, 3c).10f Propiophenone and
butyrophenone were transformed into the corresponding products in synthetically useful yields
with some variations from the standard conditions (Table 2, 3t and 3u). With regards to
2-aminopyridine counterparts, to those with electron-withdrawing group, higher temperature was
required to achieve satisfying yields (Table 2, 3n-3q), and vice versa (Table 2, 3m).
2-aminopyrimidine and 2-aminothiazole which were ineffective in prior work could be applicable
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to our system as well (Table 2, 3q and 3r).5h
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Table 2. CuI-catalyzed aerobic oxidative reaction of 2-aminopyridines with Arylketonesa
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a
Reaction Conditions: 1a (0.6 mmol), 2a (0.3 mmol), CuI (5 mol%), In(CF3SO3)3 (1 mol%) ,
NMP (2 mL), O2 (1 atm), 100 oC , 30 h. Isolated yields. b The reaction was carried out at 90 oC. c
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The reaction was carried out at 120 oC for 48 h. d Without In(CF3SO3)3. e 1a (0.9 mmol), 5 mol%
CuBr2 was used instead of In(CF3SO3)3.
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Surprisingly, the reaction was also amenable to unsaturated ketones bringing about the
formation of alkenyl-substituted imidazoheterocycles (Table 3). Those obtained compounds were
rarely investigated due to the difficulties imposed in their preparations.13 Though α,β-unsaturated
ketones are well recognized as Michael acceptors, the Michael addition cyclization products were
not observed.5i Extending the conjugated system between carboxyl group and benzene ring had no
distinct impact on the yields (Table 3, 4d, 4g, 4j, 4m and 4p). However, the absence of conjugated
system was fatal to the reaction (Table 3, 4q). It is noteworthy that alkenyl group can be easily
transformed making the structural diversity of imidazoheterocycles abundant.
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Table 3. CuI-catalyzed aerobic oxidative reaction of 2-aminopyridines with unsaturated ketonesa
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a
Reaction Conditions: 1a (0.6 mmol), 2b (0.3 mmol), CuI (5 mol%), In(CF3SO3)3 (1 mol%) ,
o
b
o
NMP (2 mL), O2 (1 atm), 100 C , 30 h. Isolated yields. The reaction was carried out at 120 C
for 48 h. c The reaction was carried out at 90 oC.
Application of this method to the synthesis of zolimidine (3v) on gram scale from commercially
available materials was successful with 90% isolated yield (Scheme 2). Interestingly, with the
protection of 2', 3' hydroxyl groups, adenosine which is an important fragment in biochemistry
could be converted to imidazo[1,2-i]purineheterocycle in 36% yield (Scheme 3). Although this
process ran at 120 oC under oxygen atmosphere, the rest hydroxyl group was still intact.14
Scheme 2. Gram scale synthesis of zolimidine.
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Scheme 3. Reaction of 2', 3'-O-isopropylideneadenosine with acetophenone.a
a
Conditions: 2',3'-O-Isopropylideneadenosine (0.6 mmol), acetophenone (0.3 mmol), CuI (5
mol%), In(CF3SO3)3 (1 mol%) , NMP (2 mL), O2 (1 atm), 120 oC , 48 h. Isolated yield.
To gain some insights into the reaction mechanism, an intramolecular reaction was carried out,
3a was produced in only 19% yield (Scheme 4, Eq. (1)), which indicates that both
copper-catalyzed tandem condensation-oxidative C-N bond formation cyclization and SET
process are in some degree impossible.9h,10b,12,15 When quantitative CuI was used, iodinated
product 3x was introduced in good yield (Scheme 4, Eq. (3)), which shows that the release of
iodine is possible in the reaction.16,17 The generation of dehydrogenative product 5a further
confirmed the possibility (Scheme 4, Eq. (4)). 3a was not formed when AgOAc was used to
quench the iodine anion (Scheme 4, Eq. (5)). Cu(CF3SO3)2, CuSO4, and Cu(NO3).3H2O, etc,
which were unreactive could work well when TBAI or NaI was used as additive (Table 4).
Recently, the boom of hypervalent iodine chemistry, especially issues concerning catalytic
iodination cascade substitution reactions convince us to believe that this transformation proceeds
through a similar passway.18
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Scheme 4. Mechanistic studies.
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Table 4. Evaluating the effect of iodine aniona
Entry
catalyst
CuCl
Additive (equiv)
TBAI (5%)
Solvent
NMP
Yield (%)b
1
2
3
16
0
CuBr
TBAI (5%)
NMP
CuCl2
TBAI (5%)
NMP
0
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4
CuBr2
TBAI (5%)
TBAI (5%)
TBAI (5%)
TBAI (5%)
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
0
5
Cu(OAc)2
Cu(CF3SO3)2
0
6
52 (55)
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7
CuSO4
33
40
9
.
8
Cu(NO3)2 3H2O TBAI (5%)
9
CuCl
NaI (5%)
NaI (5%)
NaI (5%)
NaI (5%)
NaI (5%)
NaI (5%)
NaI (5%)
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CuBr
<5
<5
0
CuCl2
CuBr2
Cu(OAc)2
Cu(CF3SO3)2
0
89 (76)
56
57
CuSO4
.
16
Cu(NO3)2 3H2O NaI (5%)
a
Reaction Conditions: 1a (0.6 mmol), 2a (0.3 mmol), cat. (5 mol%), solvent (2 mL), O2 (1 atm),
100 oC, 24 h. b GC yield; isolated yield in parentheses. TBAI = Tetrabutylammonium Iodide.
Based on the observations and considerations above, a plausible mechanism was postulated in
Scheme 5. CuI initially coordinates with 2-aminopyridine to form LnCuI complex, which is
oxidized to LnCuII species by O2.19 The LnCuII species with higher oxidation potential cannot
coexist with iodine anion.16 Subsequently, the release of iodine takes place, iodine may further
transformed to HOI under the reaction conditions.18e,19 When iodine or HOI appears in the system,
the staring materials are smoothly converted to the products via Ortoleva−King reaction promoted
by Lewis acid (Scheme 4, Eq. (2)). Ortoleva-King reaction as key step in another method for
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imidazo[1,2-a]pyridine synthesis has been proposed recently.3d,20 The reasons for the
transformation available to unsaturated ketones are that only a catalytic amount of iodine or HOI
exists in the system and the Ortoleva−King reaction dominates over Michael addition.
Scheme 5. Proposed reaction mechanism.
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3. SUMMARY
In this work, we have developed an efficient and straightforward method for the synthesis of
substituted imidazoheterocycles. Compared with the established protocols, this approach presents
advantages in the formation of alkenyl-substituted imidazoheterocycles, in which the extended
π-conjugated systems are potential optical materials.3e By employing dioxygen (1atm) as the
oxidant under approximately neutral condition, this transformation proved to be reliable at gram
scale reaches the goal of waste free synthesis, which, we suppose, may be applicable to
pharmaceutical industrial manufacture. Further studies to fully clarify the role of iodine anion and
the application of CuI/O2 system in other transformations are in progress.
4. EXPERIMENTAL SECTION
General Methods. All reactions were carried out under dry O2 with dry solvents under anhydrous
conditions. The reagents for experiments were purchased and used as received. DMF, DMA and
NMP were distilled from CaH2 under nitrogen and stored under nitrogen.
(E)-N-(1-phenylethylidene)pyridin-2-amine21 and (3E,5E)-6-phenylhexa-3,5-dien-2-one22 were
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prepared according to the reported procedures. 1H and 13C NMR spectra were measured at 298 K
on 400 MHz spectrometer in CDCl3 solutions unless otherwise noted. Chemical shifts were
reported in δ (ppm), relative to the internal standard of TMS.
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General Procedure: In a glove box, a 25 mL of the Schlenk tube equipped with a stir bar was
charged with CuI (5 mol%), In(CF3SO3)3 (1 mol%), 2-aminopyridine (2 equiv), and NMP (2mL).
The tube was fitted with a rubber septum and removed out of the glove box. Then, the tube was
evacuated and refilled with O2 for three times. Subsequently, acetophenone (0.3 mmol) were
added to the Schlenk tube through the rubber septum using syringes, and then the septum was
replaced by a Teflon screwcap under an oxygen flow (if the acetophenone was solid, it was added
to the tube in glove box). The reaction mixture was stirred at 100 C for 30 h. Upon completion,
the reaction mixture was diluted with 10 mL of ethyl acetate, filtered through a pad of silica gel,
followed by washing the pad of the silica gel with the ethyl acetate (20 mL). The filtrate was
washed with water (3×15 mL). The organic phase was dried over Na2SO4, filtered, concentrated
under reduced pressure. The residue was then purified by chromatography on silica gel (petroleum
ether/EtOAc: 1/6 to 1/2) to provide the corresponding product 3 or 4.
Mechanistic studies
Intramolecular experiment: In a glove box, a 25 mL of the Schlenk tube equipped with a stir bar
was
charged
with
CuI
(5
mol%),
In(CF3SO3)3
(1
mol%),
(E)-N-(1-phenylethylidene)pyridin-2-amine (0.3 mmol), and NMP (2mL). The tube was fitted
with a rubber septum and removed out of the glove box. The tube was evacuated and refilled with
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O2 for three times. Subsequently, the septum was replaced by a Teflon screwcap under an oxygen
flow. The reaction mixture was stirred at 100 C for 30 h. Upon completion, the reaction mixture
was diluted with 10 mL of ethyl acetate, filtered through a pad of silica gel, followed by washing
the pad of the silica gel with the ethyl acetate (20 mL). The filtrate was washed with water (3×15
mL). The organic phase was dried over Na2SO4, filtered, concentrated under reduced pressure.
The residue was then purified by chromatography on silica gel (petroleum ether/EtOAc: 1/6 to 1/2)
to provide the corresponding product 3a in 19% yield.
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Following the procedure above without adding In(CF3SO3)3, 3a was obtained in 15% yield.
Following the procedure above with CuI (1equiv), 3x was obtained in 72% yield.
Under the standard conditions, 3y was obtained in 32% yield with 0.17mmol 5a obtained.
Under the standard conditions, using AgOAc (5%) instead of In(CF3SO3)3, 3a was not obtained.
Analytical data for compounds 3 and 4
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2-Phenylimidazo[1,2-a]pyridine (3a): The title compound was prepared according to the general
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procedure. White solid (47.3 mg, 81%). H NMR (400 MHz, CDCl3) δ: 8.11 (d, J=6.7 Hz, 1H),
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Hz, 1H), 7.16 (t, J=7.9 Hz, 1H), 6.77 (t, J=6.7 Hz, 1H). 13C NMR (100 MHz, CDCl3): 145.9,
145.7, 133.8, 128.7, 127.9, 126.0, 125.5, 124.6, 117.6, 112.4, 108.1. This compound is known.
The 1H and 13C NMR spectral data are in agreement with the literature data.5f
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2-(Naphthalen-2-yl)imidazo[1,2-a]pyridine (3b): The title compound was prepared according to
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the general procedure. White solid (62.5 mg, 85%). H NMR (400 MHz, CDCl3) δ: 8.50 (s, 1H),
7.99-7.95 (m, 2H), 7.92-7.90 (m, 1H), 7.86-7.81 (m, 3H), 7.64 (d, J=9.1 Hz, 1H), 7.50-7.43 (m,
2H), 7.12 (ddd, J=9.0, 6.8, 1.1 Hz, 1H), 6.68 (td, J=6.8, 0.9 Hz, 1H). 13C NMR (100 MHz, CDCl3):
145.7, 145.6, 133.7, 133.1, 131.1, 128.2, 128.2, 127.6, 126.2, 125.8, 125.5, 124.7, 124.6, 124.1,
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117.3, 112.3, 108.5. This compound is known. The H and 13C NMR spectral data are in
agreement with the literature data.23
4-(Imidazo[1,2-a]pyridin-2-yl)benzonitrile (3c): The title compound was prepared according to
the general procedure. White solid (54.7 mg, 83%). 1H NMR (400 MHz, DMSO) δ : 8.54-8.52 (m,
2H), 8.13 (d, J=7.8 Hz, 3H), 7.86 (d, J=7.9 Hz, 2H), 7.59 (d, J=9.1 Hz, 1H), 7.27 (t, J=7.8 Hz,
1H), 6.91 (t, J=6.7 Hz, 1H). 13C NMR (100 MHz, DMSO): 145.1, 142.4, 138.4, 132.6, 127.1,
1
126.0, 125.6, 119.0, 116.9, 112.7, 111.0, 109.7. This compound is known. The H and 13C NMR
spectral data are in agreement with the literature data.24
2-(4-Iodophenyl)imidazo[1,2-a]pyridine (3d): The title compound was prepared according to the
general procedure. White solid (81.7 mg, 85%). 1H NMR (400 MHz, CDCl3) δ: 8.07 (d, J=6.6 Hz,
1H), 7.82 (s, 1H), 7.71 (dd, J=26.4, 8.1 Hz, 4H), 7.60 (d, J=9.0 Hz, 1H), 7.16 (t, J=7.8 Hz, 1H),
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6.76 (t, J=6.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): 145.7, 144.7, 137.7, 133.3, 127.7, 125.6,
124.9, 117.6, 112.6, 108.2, 93.4. This compound is known. The 1H and 13C NMR spectral data are
in agreement with the literature data.24
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2-(4-(Trifluoromethyl)phenyl)imidazo[1,2-a]pyridine (3e): The title compound was prepared
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according to the general procedure. White solid (73.5 mg, 93%). H NMR (400 MHz, CDCl3) δ:
8.09 (d, J=6.7 Hz, 1H), 8.04 (d, J=8.0 Hz, 2H), 7.88 (s, 1H), 7.67-7.61 (m, 3H), 7.20-7.16 (m, 1H),
6.78 (t, J=6.5 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ = 145.8, 144.2, 137.3, 129.7 (q, J=32 Hz),
126.1, 125.7 (d, J=2.3 Hz), 125.6, 125.2, 124.3 (q, J=271 Hz), 117.7, 112.8, 109.0. 19F NMR
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(377MHz, CDCl3) δ = -62.5. This compound is known. The H and 13C NMR spectral data are in
agreement with the literature data.25
Methyl-4-(imidazo[1,2-a]pyridin-2-yl)benzoate (3f): The title compound was prepared
o
1
according to the general procedure. White solid (61.7 mg, 81%). Mp 209-211 C. H NMR (400
MHz, CDCl3) δ: 8.08-8.06 (m, 3H), 7.99 (d, J=8.5 Hz, 2H), 7.88 (s, 1H), 7.60 (d, J=9.1 Hz, 1H),
7.17-7.13 (m, 1H), 6.75 (td, J=6.8, 0.8 Hz, 1H), 3.90 (s, 3H). 13C NMR (100 MHz, CDCl3): 166.9,
145.8, 144.5, 138.1, 130.0, 129.2, 125.7, 125.6, 125.04, 117.6, 112.7, 109.2, 52.0. Anal. Calcd.
For C15H12N2O2: C, 71.42; H, 4.79; N, 11.10. Found: C, 71.41; H, 4.79; N, 11.12.
2-(2-Methoxyphenyl)imidazo[1,2-a]pyridine (3g): The title compound was prepared according
to the general procedure. White solid to colorless oil (61.0 mg, 91%). 1H NMR (400 MHz, CDCl3)
δ: 8.44 (d, J=7.7 Hz, 1H), 8.18 (s, 1H), 8.09 (d, J=6.7 Hz, 1H), 7.62 (d, J=9.1 Hz, 1H), 7.31 (t,
J=7.7 Hz, 1H), 7.12 (t, J=7.6 Hz, 2H), 7.00 (d, J=8.2 Hz, 1H), 6.71 (t, J=6.7 Hz, 1H), 3.98 (s, 3H).
13C NMR (100 MHz, CDCl3): 156.6, 144.3, 141.1, 128.7, 128.5, 125.5, 124.3, 122.3, 120.9, 117.1,
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112.4, 111.8, 110.7, 55.3. This compound is known. The H and 13C NMR spectral data are in
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2-(Benzofuran-2-yl)imidazo[1,2-a]pyridine (3h): The title compound was prepared according to
the general procedure. White solid (58.3 mg, 83%). 1H NMR (400 MHz, CDCl3) δ: 8.13 (d, J=6.8
Hz, 1H), 7.99 (s, 1H), 7.66-7.61 (m, 2H), 7.53 (d, J=7.7 Hz, 1H), 7.26-7.19 (m, 4H), 6.81 (td,
J=6.8, 0.9 Hz, 1H). 13C NMR (100 MHz, CDCl3): 154.8, 151.5, 145.9, 137.5, 129.0, 125.7, 125.3,
124.3, 122.9, 121.1, 117.6, 112.7, 111.09, 109.5, 102.8. This compound is known. The 1H and 13C
NMR spectral data are in agreement with the literature data.26
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2-(Imidazo[1,2-a]pyridin-2-yl)thiazole (3i): The title compound was prepared according to the
1
general procedure. White solid (44.9 mg, 74%). Mp 159-161 oC. H NMR (400 MHz, CDCl3) δ:
8.12 (s, 1H), 8.09 (d, J=6.8 Hz, 1H), 7.83 (d, J=3.2 Hz, 1H), 7.60 (d, J=9.1 Hz, 1H), 7.33 (d,
J=3.2 Hz, 1H), 7.19-7.14 (m, 1H), 6.79-6.75 (m, 1H). 13C NMR (101 MHz, CDCl3): 163.4, 145.3,
143.5, 140.3, 125.9, 125.4, 119.1, 117.7, 113.1, 109.4. Anal. Calcd. For C10H7N3S: C, 59.68; H,
3.51; N, 20.88. Found: C, 59.59; H, 3.63; N, 20.76.
2-(Thiophen-2-yl)imidazo[1,2-a]pyridine (3j): The title compound was prepared according to
the general procedure. White solid (50.4 mg, 84%). 1H NMR (400 MHz, CDCl3) δ: 8.02 (d, J=6.8
Hz, 1H), 7.71 (s, 1H), 7.58 (d, J=9.1 Hz, 1H), 7.45 (dd, J=3.6, 1.0 Hz, 1H), 7.28 (dd, J=5.0, 1.0
Hz, 1H), 7.14-7.10 (m, 1H), 7.07 (dd, J=5.0, 3.6 Hz, 1H), 6.72 (td, J=6.8, 0.9 Hz, 1H). 13C NMR
(100 MHz, CDCl3): 145.4, 140.8, 137.5, 127.8, 125.4, 125.0, 124.7, 123.6, 117.2, 112.5, 107.4.
1
This compound is known. The H and 13C NMR spectral data are in agreement with the literature
data.5f
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6-Methyl-2-p-tolylimidazo[1,2-a]pyridine (3k): The title compound was prepared according to
the general procedure. White solid (55.2 mg, 83%). 1H NMR (400 MHz, CDCl3) δ: 7.82-7.78 (m,
3H), 7.65 (s, 1H), 7.49 (d, J=9.1 Hz, 1H), 7.21 (d, J=7.7 Hz, 2H), 6.95 (d, J=9.1 Hz, 1H), 2.37 (s,
3H), 2.25 (s, 3H). 13C NMR (100 MHz, CDCl3): 145.5, 144.6, 137.4, 131.1, 129.3, 127.5, 125.7,
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123.2, 121.7, 116.6, 107.4, 21.2, 18.0. This compound is known. The H and 13C NMR spectral
data are in agreement with the literature data.5f
8-Methyl-2-phenylimidazo[1,2-a]pyridine (3l): The title compound was prepared according to
the general procedure. White solid (48.7 mg, 78%). 1H NMR (400 MHz, CDCl3) δ: 7.98 (d, J=7.7
Hz, 2H), 7.94 (d, J=6.7 Hz, 1H), 7.80 (s, 1H), 7.44 (t, J=7.6 Hz, 2H), 7.33 (t, J=7.4 Hz, 1H), 6.93
(d, J=6.8 Hz, 1H), 6.65 (t, J=6.8 Hz, 1H), 2.67 (s, 3H). 13C NMR (100 MHz, CDCl3): 146.2, 145.2,
134.1, 128.6, 127.7, 127.5, 126.1, 123.3, 123.2, 112.2, 108.5, 17.0. This compound is known. The
1H and 13C NMR spectral data are in agreement with the literature data.27
7-Methoxy-2-phenylimidazo[1,2-a]pyridine (3m): The title compound was prepared according
to the general procedure. The reaction mixture was stirred at 90 oC for 30 h. White solid (49.7 mg,
74%). Mp 93-95 oC .1H NMR (400 MHz, CDCl3) δ: 7.93-7.88 (m, 3H), 7.67 (s, 1H), 7.42 (t, J=7.8
Hz, 2H), 7.30 (t, J=7.4 Hz, 1H), 6.90 (d, J=2.4 Hz, 1H), 6.48 (dd, J=7.4, 2.5 Hz, 1H), 3.85 (s, 3H).
13C NMR (100 MHz, CDCl3): 157.9, 147.1, 145.5, 133.9, 128.6, 127.6, 125.9, 125.7, 107.4, 106.8,
94.7, 55.4. Anal. Calcd. For C14H12N2O: C, 74.98; H, 5.39; N, 12.49. Found: C, 75.15; H, 5.52; N,
12.30.
6-Chloro-2-(4-chlorophenyl)imidazo[1,2-a]pyridine (3n): The title compound was prepared
o
according to the general procedure. The reaction mixture was stirred at 120 C for 48 h. White
solid (55.4 mg, 70%). 1H NMR (400 MHz, CDCl3) δ: 8.13 (s, 1H), 7.85 (d, J=8.3 Hz, 2H), 7.78 (s,
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1H), 7.55 (d, J=9.5 Hz, 1H), 7.39 (d, J=8.3 Hz, 2H), 7.14 (d, J=8.8 Hz, 1H). 13C NMR (100 MHz,
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CDCl3) : 145.7, 144.1, 134.0, 131.8, 129.0, 127.3, 126.3, 123.4, 120.7, 117.8, 108.5. This
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compound is known. The H and 13C NMR spectral data are in agreement with the literature
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6-Bromo-2-phenylimidazo[1,2-a]pyridine (3o): The title compound was prepared according to
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the general procedure. The reaction mixture was stirred at 120 C for 48 h. White solid (55.7 mg,
68%). 1H NMR (400 MHz, CDCl3) δ: 8.24 (s, 1H), 7.93 (d, J=7.4 Hz, 2H), 7.80 (s, 1H), 7.52 (d,
J=9.5 Hz, 1H), 7.44 (t, J=7.6 Hz, 2H), 7.35 (t, J=7.3 Hz, 1H), 7.22 (dd, J=9.5, 1.7 Hz, 1H). 13C
NMR (100 MHz, CDCl3): 146.7, 144.1, 133.2, 1288, 128.3, 128.0, 126.1, 125.5, 118.1, 108.2,
106.9. This compound is known. The H and 13C NMR spectral data are in agreement with the
1
literature data.5f
7-Methyl-6-nitro-2-phenylimidazo[1,2-a]pyridine (3p): The title compound was prepared
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according to the general procedure. The reaction mixture was stirred at 120 C for 48 h. Yellow
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solid (50.7 mg, 67%). H NMR (400 MHz, CDCl3) δ: 9.09 (s, 1H), 7.93-7.89 (m, 3H), 7.44-7.37
(m, 4H), 2.67 (s, 3H). 13C NMR (100 MHz, CDCl3): 149.2, 145.4, 138.7, 132.5, 130.2, 128.9,
128.9, 126.3, 126.2, 117.9, 109.0, 21.1. This compound is known. The H and 13C NMR spectral
1
data are in agreement with the literature data.29
2-(4-(Methylsulfonyl)phenyl)imidazo[1,2-a]pyrimidine (3q): The title compound was prepared
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according to the general procedure. The reaction mixture was stirred at 120 C for 48 h. Light
yellow solid (64.2 mg, 78%). Mp 261-263 oC . 1H NMR (400 MHz, DMSO) δ: 9.00 (dd, J=6.7, 1.8
Hz, 1H), 8.59-8.56 (m, 1H), 8.56 (s, 1H), 8.26 (d, J=8.3 Hz, 2H), 8.01 (d, J=8.4 Hz, 2H),
7.11-7.08 (m, 1H), 3.26 (s, 3H). 13C NMR (100 MHz, DMSO): 151.3, 148.2, 143.2, 139.9, 138.3,
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135.4, 127.6, 126.2, 109.4, 109.3, 43.5. Anal. Calcd. For C13H11N3O2S: C, 57.13; H, 4.06; N,
15.37. Found: C, 57.41; H, 4.28; N, 15.13.
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procedure without adding 1 mol% In(CF3SO3)3. Yellow to white solid (30.6 mg, 50%). H NMR
(400 MHz, CDCl3) δ: 7.82 (d, J=7.4 Hz, 2H), 7.71 (s, 1H), 7.42-7.38 (m, 3H), 7.28 (t, J=7.4 Hz,
1H), 6.79 (d, J=4.5 Hz, 1H). 13C NMR (100 MHz, CDCl3): 150.2, 147.8, 134.0, 128.6, 127.3,
125.2, 118.4, 112.4, 107.9. This compound is known. The H and 13C NMR spectral data are in
1
agreement with the literature data.30
2-Phenylimidazo[2,1-a]isoquinoline (3s): The title compound was prepared according to the
general procedure. White solid (67.6 mg, 92%). 1H NMR (400 MHz, CDCl3) δ: 8.75 (d, J=7.9 Hz,
1H), 8.01 (d, J=7.4 Hz, 2H), 7.79 (d, J=7.2 Hz, 1H), 7.74 (s, 1H), 7.64 (dd, J=11.3, 7.8 Hz, 2H),
7.54 (t, J=7.3 Hz, 1H), 7.46 (t, J=7.6 Hz, 2H), 7.34 (t, J=7.3 Hz, 1H), 6.95 (d, J=7.2 Hz, 1H). 13
C
NMR (100 MHz, CDCl3): 143.9, 143.2, 134.0, 129.4, 128.6, 128.0, 128.0, 127.5, 126.8, 125.8,
123.8, 123.4, 122.8, 112.9, 109.8. This compound is known. The H and 13C NMR spectral data
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are in agreement with the literature data.5f
3-Methyl-2-phenylimidazo[1,2-a]pyridine (3t): The title compound was prepared according to
the general procedure using 1a (3equiv) and 5 mol% CuBr2 instead of 1 mol% In(CF3SO3)3. White
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solid (47.1 mg, 75%). H NMR (400 MHz, CDCl3) δ: 7.87 (d, J=6.9 Hz, 1H), 7.81-7.78 (m, 2H),
7.64 (d, J=9.1 Hz, 1H), 7.48-7.44 (m, 2H), 7.36-3.32 (m, 1H), 7.18-7.14 (m, 1H), 6.82 (td, J=6.8,
1.0 Hz, 1H), 2.62 (s, 3H). 13C NMR (100 MHz, CDCl3): 144.2, 142.3, 134.7, 128.4, 128.3, 127.3,
123.4, 122.8, 117.3, 115.8, 112.0, 9.5. This compound is known. The H and 13C NMR spectral
1
data are in agreement with the literature data.31
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3-Ethyl-2-phenylimidazo[1,2-a]pyridine(3u): The title compound was prepared according to the
general procedure using 1a (3equiv) and 5 mol% CuBr2 instead of 1 mol% In(CF3SO3)3. Colorless
oil (41.1 mg, 62%). 1H NMR (400 MHz, CDCl3) δ: 7.96 (d, J=6.9 Hz, 1H), 7.79 (d, J=7.5 Hz, 2H),
7.64 (d, J=9.1 Hz, 1H), 7.47 (t, J=7.6 Hz, 2H), 7.35 (t, J=7.4 Hz, 1H), 7.16 (t, J=7.2 Hz, 1H), 6.83
(t, J=6.7 Hz, 1H), 3.12 (q, J=7.5 Hz, 2H), 1.37 (t, J=7.5 Hz, 3H). 13C NMR (100 MHz, CDCl3):
144.4, 142.0, 135.0, 128.5, 128.2, 127.4, 123.5, 122.8, 121.8, 117.7, 112.0, 17.1, 12.2. This
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compound is known. The H and 13C NMR spectral data are in agreement with the literature
data.31
2-(4-(Methylsulfonyl)phenyl)imidazo[1,2-a]pyridine (3v): The title compound was prepared
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according to the general procedure at 6mmol scale. Light yellow solid (1.47 g, 90%). H NMR
(400 MHz, CDCl3) δ: 8.15-8.13 (m, 3H), 7.99-7.97 (m, 3H), 7.64 (d, J=9.1 Hz, 1H), 7.24-7.20 (m,
1H), 6.84-6.81 (m, 1H), 3.08 (s, 3H). 13C NMR (100 MHz, CDCl3): 145.9, 143.6, 139.3, 127.8,
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126.6, 125.8, 125.4, 117.8, 113.0, 109.6, 44.6. This compound is known. The H and 13C NMR
spectral data are in agreement with the literature data.5f
((3aR,4R,6R,6aR)-2,2-dimethyl-6-(8-phenyl-3H-imidazo[1,2-i]purin-3-yl)tetrahydrofuro[3,4-
d][1,3]dioxol-4-yl)methanol (3w): The title compound was prepared according to the general
o
procedure. The reaction mixture was stirred at 120 C for 48 h. White solid (43.6 mg, 36%). Mp
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257-259 C. H NMR (400 MHz, CDCl3) δ: 8.78 (s, 1H), 8.17 (s, 1H), 8.00 (d, J=7.3 Hz, 2H),
7.89 (s, 1H), 7.42 (t, J=7.5 Hz, 2H), 7.34 (t, J=7.3 Hz, 1H), 6.06 (d, J=4.2 Hz, 1H), 5.26-5.23 (m,
1H), 5.14 (dd, J=6.0, 1.5 Hz, 1H), 4.55 (d, J=1.7 Hz, 1H), 4.03 (dd, J=12.4, 1.9 Hz, 1H), 3.88 (dd,
J=12.4, 2.4 Hz, 1H), 1.66 (s, 3H), 1.39 (s, 3H). 13C NMR (100 MHz, CDCl3): 146.5, 141.2, 140.5,
137.7, 135.2, 132.6, 128.7, 128.5, 126.3, 124.8, 114.24 105.9, 93.3, 86.3, 83.9, 81.5, 63.0, 27.5,
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25.3. Anal. Calcd. For C21H21N5O4: C, 61.91; H, 5.20; N, 17.19. Found: C, 62.19; H, 5.26; N,
17.23.
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3-Iodo-2-phenylimidazo[1,2-a]pyridine (3x): White solid (68.8 mg, 72%). H NMR (400 MHz,
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CDCl3) δ: 8.23 (d, J=6.9 Hz, 1H), 8.10 (d, J=7.3 Hz, 2H), 7.63 (d, J=9.0 Hz, 1H), 7.51 (t, J=7.5
Hz, 2H), 7.42 (t, J=7.4 Hz, 1H), 7.28-7.24 (m, 1H), 6.92 (t, J=6.6 Hz, 1H). 13C NMR (100 MHz,
CDCl3): 148.1, 148.0, 133.6, 128.5, 128.3, 128.3, 126.5, 125.5, 117.5, 113.1, 59.4. This compound
is known. The 1H and 13C NMR spectral data are in agreement with the literature data.3e
1-(2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-yl)butan-2-one (3y): Light yellow oil (30.0 mg,
1
32%). H NMR (400 MHz, CDCl3) δ: 9.06 (d, J=7.0 Hz, 1H), 7.79 (d, J=9.1 Hz, 1H), 7.71 (d,
J=8.5 Hz, 2H), 7.50-7.46 (m, 1H), 7.41 (d, J=8.5 Hz, 2H), 7.08 (t, J=6.7 Hz, 1H), 3.97 (q, J=7.1
Hz, 2H), 1.01 (t, J=7.1 Hz, 3H). 13C NMR (100 MHz, CDCl3): 185.2, 162.7, 146.4, 142.5, 139.2,
138.0, 130.2, 129.2, 128.7, 127.4, 122.3, 118.6, 115.7, 61.8, 13.6. This compound is known. The
1H and 13C NMR spectral data are in agreement with the literature data.5h
1
(E)-ethyl 4-(4-chlorophenyl)-4-oxobut-2-enoate (5a): White solid (40.4 mg, 0.17mmol). H
NMR (400 MHz, CDCl3) δ: 7.93 (d, J=8.5 Hz, 2H), 7.84 (d, J=15.5 Hz, 1H), 7.47 (d, J=8.5 Hz,
2H), 6.87 (d, J=15.5 Hz, 1H), 4.29 (q, J=7.1 Hz, 2H), 1.34 (t, J=7.1 Hz, 3H). 13C NMR (100 MHz,
CDCl3): 188.2, 165.4, 140.4, 135.8, 134.9, 133.0, 130.2, 129.2, 61.4, 14.1. This compound is
known. The 1H and 13C NMR spectral data are in agreement with the literature data.32
(E)-2-styrylimidazo[1,2-a]pyridine (4a): The title compound was prepared according to the
general procedure. White solid (51.3 mg, 78%). 1H NMR (400 MHz, CDCl3) δ: 8.00 (d, J=6.8 Hz,
1H), 7.58-7.55 (m, 5H), 7.36 (t, J=7.5 Hz, 2H), 7.28-7.25 (m, 1H), 7.17-7.12 (m, 2H), 6.71 (t,
J=6.7 Hz, 1H). 13C NMR (100 MHz, CDCl3): 145.6, 144.0, 137.1, 130.4, 128.6, 127.6, 126.5,
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125.4, 124.9, 119.9, 117.0, 112.1, 110.5. This compound is known. The 1H and 13C NMR spectral
data are in agreement with the literature data.14b
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(E)-2-(4-chlorostyryl)imidazo[1,2-a]pyridine (4b): The title compound was prepared according
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to the general procedure. White solid (63.3 mg, 83%). H NMR (400 MHz, CDCl3) δ: 8.02 (d,
J=6.6 Hz, 1H), 7.57-7.55 (m, 2H), 7.50-7.44 (m, 3H), 7.30 (d, J=8.2 Hz, 2H), 7.17-7.07 (m, 2H),
6.73 (t, J=6.6 Hz, 1H). 13C NMR (100 MHz, CDCl3): 145.7, 143.7, 135.7, 133.2, 129.1, 128.8,
127.7, 125.5, 125.2, 120.4, 117.2, 112.3, 110.8. This compound is known. The H and 13C NMR
1
spectral data are in agreement with the literature data.14b
(E)-2-(2-(thiophen-2-yl)vinyl)imidazo[1,2-a]pyridine (4c): The title compound was prepared
o
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according to the general procedure. White solid (53.6 mg, 79%). Mp 165-167 C. H NMR (400
MHz, CDCl3) δ: 7.99 (d, J=6.8 Hz, 1H), 7.66 (d, J=15.8 Hz, 1H), 7.53 (dd, J=9.1, 0.5 Hz, 1H),
7.49 (s, 1H), 7.17 (d, J=5.1 Hz, 1H), 7.14-7.08 (m, 2H), 6.98 (dd, J=5.0, 3.6 Hz, 1H), 6.92 (d,
J=15.8 Hz, 1H), 6.69 (td, J=6.8, 1.0 Hz, 1H). 13C NMR (100 MHz, CDCl3): 145.6, 143.6, 142.6,
127.6, 126.4, 125.4, 125.0, 124.4, 123.6, 119.4, 117.0, 112.1, 110.5. Anal. Calcd. For C13H10N2S:
C, 69.00; H, 4.45; N, 12.38. Found: C, 68.72; H, 4.43; N, 12.34.
2-((1E,3E)-4-phenylbuta-1,3-dienyl)imidazo[1,2-a]pyridine (4d): The title compound was
prepared according to the general procedure. White solid (53.8 mg, 73%). Mp 191-193 C.1H
o
NMR (400 MHz, CDCl3) δ: 8.00 (d, J=6.8 Hz, 1H), 7.54 (d, J=9.1 Hz, 1H), 7.51 (s, 1H), 7.44 (d,
J=7.4 Hz, 2H), 7.37-7.30 (m, 3H), 7.22 (t, J=7.3 Hz, 1H), 7.13 (ddd, J=9.0, 6.8, 1.2 Hz, 1H), 6.97
(dd, J=15.5, 10.8 Hz, 1H), 6.73-6.68 (m, 3H). 13C NMR (100 MHz, CDCl3): 145.7, 144.1, 137.3,
133.3, 131.2, 128.9, 128.6, 127.5, 126.4, 125.4, 124.9, 123.9, 117.08, 112.2, 110.4. Anal. Calcd.
For C17H14N2: C, 82.90; H, 5.73; N, 11.37. Found: C, 82.94; H, 5.76; N, 11.41.
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(E)-2-(4-chlorostyryl)-6-methylimidazo[1,2-a]pyridine (4e): The title compound was prepared
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according to the general procedure. White solid (61.9 mg, 77%). Mp 233-235 oC. H NMR (400
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MHz, CDCl3) δ: 7.83 (s, 1H), 7.50-7.46 (m, 5H), 7.32 (d, J=7.0 Hz, 2H), 7.12-7.06 (m, 2H), 2.31
(s, 3H). 13C NMR (100 MHz, CDCl3): 144.8, 143.4, 135.8, 133.1, 128.8, 128.4, 127.7, 123.0,
121.9, 120.6, 116.5, 110.5, 18.1. Anal. Calcd. For C16H13N2Cl: C, 71.51; H, 4.88; N, 10.42. Found:
C, 71.66; H, 4.92; N, 10.52.
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(E)-6-methyl-2-(2-(thiophen-2-yl)vinyl)imidazo[1,2-a]pyridine (4f): The title compound was
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prepared according to the general procedure. White solid (52.8 mg, 73%). Mp 167-169 C. H
NMR (400 MHz, CDCl3) δ: 7.78 (s, 1H), 7.63 (d, J=15.8 Hz, 1H), 7.43 (d, J=9.9 Hz, 2H), 7.17 (d,
J=5.1 Hz, 1H), 7.08 (d, J=3.4 Hz, 1H), 6.99-6.96 (m, 2H), 6.91 (d, J=15.8 Hz, 1H), 2.26 (s, 3H).
13C NMR (100 MHz, CDCl3) δ: 144.8, 143.3, 142.8, 128.20 127.6, 126.3, 124.2, 123.2, 121.7,
119.6, 116.3, 110.3, 18.0. Anal. Calcd. For C14H12N2S: C, 69.97; H, 5.03; N, 11.66. Found: C,
69.89; H, 5.23; N, 11.68.
6-Methyl-2-((1E,3E)-4-phenylbuta-1,3-dienyl)imidazo[1,2-a]pyridine
(4g):
The
title
compound was prepared according to the general procedure. White solid (52.9 mg, 68%). Mp
o
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216-218 C. H NMR (400 MHz, CDCl3) δ: 7.78 (s, 1H), 7.45-7.42 (m, 4H), 7.34-7.28 (m, 3H),
7.21 (t, J=7.3 Hz, 1H), 6.96 (dd, J=15.1, 10.7 Hz, 2H), 6.69 (dd, J=15.4, 7.2 Hz, 2H), 2.27 (s, 3H).
13C NMR (100 MHz, CDCl3): 144.8, 143.9, 137.4, 133.0, 130.7, 129.0, 128.6, 128.1, 127.4, 126.4,
124.2, 123.1, 121.8, 116.4, 110.2, 18.0. Anal. Calcd. For C18H16N2: C, 83.04; H, 6.19; N, 10.76.
Found: C, 82.79; H, 6.19; N, 10.64.
(E)-6-chloro-2-(4-chlorostyryl)imidazo[1,2-a]pyridine (4h): The title compound was prepared
o
according to the general procedure. The reaction mixture was stirred at 120 C for 48 h. White
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solid (50.8 mg, 58%). Mp 251-253 C. H NMR (400 MHz, CDCl3) δ:8.10 (s, 1H), 7.55 (s, 1H),
7.52-7.45 (m, 4H), 7.32 (d, J=8.4 Hz, 2H), 7.14 (dd, J=9.6, 1.7 Hz, 1H), 7.08 (d, J=16.1 Hz, 1H).
13C NMR (100 MHz, CDCl3): 144.8, 144.1, 135.5, 133.5, 129.8, 128.9, 127.8, 126.6, 123.3, 120.4,
120.0, 117.5, 111.0. Anal. Calcd. For C15H10N2Cl2: C, 62.30; H, 3.49 N, 9.69. Found: C, 62.28; H,
3.66; N, 9.45.
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(E)-6-chloro-2-(2-(thiophen-2-yl)vinyl)imidazo[1,2-a]pyridine (4i): The title compound was
prepared according to the general procedure. The reaction mixture was stirred at 120 oC for 48 h.
o
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White solid (41.6 mg, 53%). Mp 194-196 C. H NMR (400 MHz, CDCl3) δ: 8.05 (d, J=1.3 Hz,
1H), 7.64 (d, J=15.8 Hz, 1H), 7.47 (d, J=9.0 Hz, 2H), 7.19 (d, J=5.0 Hz, 1H), 7.11-7.08 (m, 2H),
6.99 (dd, J=5.0, 3.6 Hz, 1H), 6.89 (d, J=15.8 Hz, 1H). 13C NMR (100 MHz, CDCl3): 144.7, 144.0,
142.4, 127.6, 126.8, 126.4, 124.7, 124.3, 123.2, 120.2, 118.9, 117.26, 110.7. Anal. Calcd. For
C13H9N2SCl: C, 59.88; H, 3.48; N, 10.74. Found: C, 59.83; H, 3.67; N, 10.78.
6-Chloro-2-((1E,3E)-4-phenylbuta-1,3-dienyl)imidazo[1,2-a]pyridine (4j): The title compound
o
was prepared according to the general procedure. The reaction mixture was stirred at 120 C for
48 h. White solid (31.6 mg, 38%). Mp 210-212 oC . 1H NMR (400 MHz, CDCl3) δ: 8.08-8.07 (m,
1H), 7.50-7.44 (m, 4H), 7.36-7.29 (m, 3H), 7.23 (t, J=7.3 Hz, 1H), 7.11 (dd, J=9.7, 2.0 Hz, 1H),
6.96 (dd, J=15.3, 10.9 Hz, 1H), 6.70 (dd, J=20.8, 15.5 Hz, 2H).13C NMR (100 MHz, CDCl3):
145.2, 144.1, 137.2, 133.9, 131.8, 128.7, 128.6, 127.7, 126.5, 126.3, 123.4, 123.2, 120.3, 117.4,
110.6. Anal. Calcd. For C17H13N2Cl: C, 72.73; H, 4.67; N, 9.98. Found: C, 72.91; H, 4.66; N,
9.98.
(E)-2-(4-chlorostyryl)-7-methoxyimidazo[1,2-a]pyridine (4k): The title compound was
o
prepared according to the general procedure. The reaction mixture was stirred at 90 C for 30 h.
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White solid (60.2 mg, 70%). Mp 222-224 C . H NMR (400 MHz, CDCl3) δ: 7.81 (d, J=7.4 Hz,
1H), 7.43 (dd, J=12.1, 3.6 Hz, 3H), 7.37 (s, 1H), 7.28 (d, J=8.4 Hz, 2H), 7.02 (d, J=16.1 Hz, 1H),
6.82 (d, J=2.2 Hz, 1H), 6.45 (dd, J=7.4, 2.4 Hz, 1H), 3.83 (s, 3H). 13C NMR (100 MHz, CDCl3):
158.3, 147.3, 143.4, 135.9, 132.9, 128.7, 128.3, 127.6, 125.8, 120.5, 109.8, 107.3, 94.2, 55.4. Anal.
Calcd. For C16H13N2OCl: C, 67.49; H, 4.60; N, 9.84. Found: C, 67.32; H, 4.67; N, 9.59.
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(E)-7-methoxy-2-(2-(thiophen-2-yl)vinyl)imidazo[1,2-a]pyridine (4l): The title compound was
o
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o
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Brown solid (42.0 mg, 55%). Mp 144-146 C. H NMR (400 MHz, CDCl3) δ: 7.79 (d, J=7.4 Hz,
1H), 7.61 (d, J=15.8 Hz, 1H), 7.33 (s, 1H), 7.16 (d, J=5.1 Hz, 1H), 7.06 (d, J=3.4 Hz, 1H), 6.97
(dd, J=5.0, 3.6 Hz, 1H), 6.86 (d, J=15.8 Hz, 1H), 6.80 (d, J=2.4 Hz, 1H), 6.42 (dd, J=7.4, 2.5 Hz,
1H), 3.82 (s, 3H). 13C NMR (100 MHz, CDCl3): 158.2, 147.2, 143.3, 142.9, 127.5, 126.2, 125.8,
124.1, 122.9, 119.5, 109.5, 107.2, 94.2, 55.4. Anal. Calcd. For C14H12N2OS: C, 65.60; H, 4.72; N,
10.93. Found: C, 65.88; H, 4.93; N, 11.05.
7-Methoxy-2-((1E,3E)-4-phenylbuta-1,3-dienyl)imidazo[1,2-a]pyridine (4m): The title
compound was prepared according to the general procedure. The reaction mixture was stirred at
90 oC for 30 h. Light yellow solid (40.2 mg, 48%). Mp 160-162 oC. 1H NMR (400 MHz, CDCl3) δ:
7.77 (d, J=7.4 Hz, 1H), 7.43 (d, J=7.5 Hz, 2H), 7.32-7.29 (m, 4H), 7.20 (t, J=7.3 Hz, 1H), 6.95 (dd,
J=15.5 Hz, 10.9, 1H), 6.81 (d, J=2.3 Hz, 1H), 6.65 (dd, J=20.3, 15.4 Hz, 2H), 6.42 (dd, J=7.4, 2.4
Hz, 1H), 3.82 (s, 3H). 13C NMR (100 MHz, CDCl3) δ = 158.1, 147.2, 143.8, 137.4, 132.8, 130.4,
129.0, 128.5, 127.4, 126.3, 125.7, 124.0, 109.4, 107.2, 94.2, 55.4. Anal. Calcd. For C18H16N2O: C,
78.24; H, 5.84; N, 10.14. Found: C, 78.05; H, 6.06; N, 10.35.
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(E)-2-(4-chlorostyryl)imidazo[2,1-a]isoquinoline (4n): The title compound was prepared
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o
according to the general procedure. Light yellow solid (73.9 mg, 81%). Mp 192-194 C. 1H NMR
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9
(400 MHz, CDCl3) δ: 8.68 (d, J=7.9 Hz, 1H), 7.77 (d, J=7.2 Hz, 1H), 7.64 (dd, J=16.5, 7.9 Hz,
2H), 7.57-7.45 (m, 5H), 7.31 (d, J=8.3 Hz, 2H), 7.13 (d, J=16.1 Hz, 1H), 6.97 (d, J=7.2 Hz, 1H).
13C NMR (100 MHz, CDCl3): 143.4, 142.1, 135.9, 132.9, 129.6, 128.7, 128.3, 128.2, 128.1, 127.6,
126.9, 123.5, 123.4, 122.7, 120.7, 113.0, 112.3. Anal. Calcd. For C19H13N2Cl: C, 74.88; H, 4.30;
N, 9.19. Found: C, 74.92; H, 4.35; N, 9.20.
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(E)-2-(2-(thiophen-2-yl)vinyl)imidazo[2,1-a]isoquinoline (4o): The title compound was
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prepared according to the general procedure. White solid (60.3 mg, 73%). Mp 168-170 C. H
NMR (400 MHz, CDCl3) δ: 8.69 (d, J=8.0 Hz, 1H), 7.76 (d, J=7.2 Hz, 1H), 7.71 (d, J=15.8 Hz,
1H), 7.64 (dd, J=12.4, 7.8 Hz, 2H), 7.58-7.54 (m, 1H), 7.47 (s, 1H), 7.21 (d, J=5.0 Hz, 1H), 7.14
(d, J=3.4 Hz, 1H), 7.07-7.95 (m, 3H). 13C NMR (100 MHz, CDCl3): 143.3, 142.9, 141.9, 129.5,
128.2, 128.0, 127.6, 126.9, 126.0, 124.1, 123.4, 123.3, 122.7, 122.7, 119.8, 112.8, 112.0. Anal.
Calcd. For C17H12N2S: C, 73.88; H, 4.38; N, 10.14. Found: C, 74.04; H, 4.38; N, 10.18.
2-((1E,3E)-4-phenylbuta-1,3-dienyl)imidazo[2,1-a]isoquinoline (4p): The title compound was
prepared according to the general procedure. Light yellow solid (61.8 mg, 70%). Mp 197-199 oC.
1H NMR (400 MHz, CDCl3) δ: 8.68 (d, J=7.9 Hz, 1H), 7.77 (d, J=7.2 Hz, 1H), 7.67-7.61 (m, 2H),
7.55 (td, J=7.6, 1.2 Hz, 1H), 7.48-7.45 (m, 3H), 7.41-7.32 (m, 3H), 7.23 (t, J=7.3 Hz, 1H),
7.03-6.95 (m, 2H), 6.74 (dd, J=15.4, 4.3 Hz, 2H). 13C NMR (100 MHz, CDCl3): 143.4, 142.5,
137.5, 132.8, 130.3, 129.5, 129.1, 128.6, 128.2, 128.0, 127.4, 126.9, 126.36, 124.2, 123.5, 123.4,
122.7, 112.9, 112.1. Anal. Calcd. For C21H16N2: C, 85.11; H, 5.44; N, 9.45. Found: C, 84.85; H,
5.25; N, 9.25.
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■ ASSOCIATED CONTENT
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Supporting Information
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1H and 13C NMR spectral data of all compounds reported. This material is available free of charge
via the Internet at http://pubs.acs.org.
■ AUTHOR INFORMATION
Corresponding Author
*E-mail: wpsu@fjirsm.ac.cn
*E-mail: yhzhang@zju.edu.cn
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
Financial support from the 973 Program (2009CB939803), NSFC (21201164) is greatly
appreciated. We thank one of our reviewers to recommend us to conduct control experiments to
confirm the reaction mechanism.
■ REFERENCES
(1) (a) Katritzky, A. R.; Ramsden, C. A.; Scriven, E. F. V.; Taylor, R. J. K. Comprehensive
Heterocyclic Chemistry III, Elsevier; Oxford, 2008. (b) Katritzky, A. R.; Xu, Y. J.; Tu, H. J. Org.
Chem. 2003, 68, 4935, and references therein.
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51,7243. (e) Ueda, T.; Mizusgige, K.; Yukiiri, K.; Takahashi, T. Cerebrovasc. Dis. 2003, 16, 396.
(f) Almirante, L.; Polo, L.; Mugnaini, A.; Provinciali, E.; Rugarli, P.; Biancotti, A.; Gamba, A.;
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