Palladium-catalyzed tandem one-pot synthesis of π-expanded imidazoles through a sequential Heck and oxidative amination reaction

Article abstract of DOI:10.1039/c9ob00482c

An efficient palladium-catalyzed route for tandem synthesis of imidazole-fused polyheterocycles from 2-vinyl imidazoles and aryl halides is described. The sequentially accomplished process comprises intermolecular Heck arylation of 2-vinyl imidazoles followed by an intramolecular aerobic oxidative C-H amination reaction promoted by the same Pd catalyst. This Pd-catalyzed tandem approach offers a straightforward protocol for the assembly of benzimidazo/phenanthroimidazo[1,2-a]quinolines in moderate to high yields, serving as a useful tool for the discovery of fluorescent materials.

Full text of DOI:10.1039/c9ob00482c

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Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
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DOI: 10.1039/C9OB00482C
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Palladium-catalyzed Tandem One-pot Synthesis of π-Expanded
Imidazoles through Sequential Heck and Oxidative Amination
Reaction
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a,b
Xue Li,† Xin Chen,† Hui Wang,a Chunxia Chen,*,a,b Peng Sun,a,b Baichuan Mo,a,b and Jinsong
DOI: 10.1039/x0xx00000x
Peng*,a
An efficient palladium-catalyzed route for tandem synthesis of imidazole-fused polyheterocycles from 2-vinyl imidazoles
and aryl halides is described. The sequentially accomplished process comprises intermolecular Heck arylation of 2-vinyl
imidazoles followed by an intramolecular aerobic oxidative C−H amination reaction promoted by the same Pd catalyst.
This Pd-catalyzed tandem approach offers
a straightforward protocol for the assembly of benzimidazo/
phenanthroimidazo[1,2-a]quinolines in moderate to high yields, serving as a useful tool for the discovery of fluorescent
materials.
1. Introduction
H
The last several decades have witnessed the continuous growth in
the discovery of novel (hetero)polycyclic aromatic compounds as
organic electronic and optical materials.1 The ring-fusion extends
the conjugation length of an aromatic molecule, and induces
significant changes in the optical and electrical properties, such as
electron mobility, band gap, and fluorescence. Therefore,
annulative π-extension of (hetero)aromatics has emerged as an
important tool for the assembly of π-extended derivatives with
tunable π-electron distribution and π−π stacking.2 Recently π-
extended aza-fused aromatic polycycles have received significant
attention because of their potential application as organic light-
emitting diodes (OLEDs),3 organic field-effect transistors (OFETs)1b-c
and photovoltaic cells.4 In particular, phenanthroimidazoles (PI), as
electron-transporting and emission functional units, have been
widely utilized in the design, synthesis and applications of organic
materials.3,4 These compounds can be used as efficient deep-blue5
or green6 emitters, bipolar hosts for green and yellow
phosphorescent OLEDs,7 and electron transfer mediators.8 Dye-
sensitized solar cells based on PI chromophores have been found to
exhibit good efficiencies.9 In addition, arene-fused imidazole units
are prevalent in the syntheses of novel functional fluorophores such
as fluorescent probes,10 superradiant laser dye11 and fluorescent
ionic liquid sensor arrays.12
H
H
X
N
N
N
N
(a)
Heck/oxidative N-H arylation
tandem synthesis
in one-pot manner?
-extended aza-fused
polyheterocycles
parent molecules
H
H
H
H
2
X
N
N
(b)
N
N
Heck double arylation
oxidative C-H amination
Scheme 1 Reaction Design.
organic materials; therefore, much effort has been focused on the
synthetic methods leading to imidazole derivatives.13 Fused-
imidazole derivatives have been prepared typically using the
Debus−Radziszewski
method,14
while
various
synthetic
methodologies for direct π-extension of PI or benzimidazole
framework are highly anticipated. In the past decade, direct C−H
functionalization has emerged as an attractive and powerful tool to
construct π-extended imidazole-fused derivatives. For examples,
Satoh and Miura,15 Dong and Chen,16 Hua,17 Li,18 Choudhury,19
Fan,20 Wang,21 and Saá22 reported Rh or Pd-catalyzed oxidative
coupling of aryl-imidazoles and alkynes to build π-extended aza-
fused scaffolds, respectively. More recently, Yu, Gao and You23
Aryl-annulated imidazoles are of great synthetic significance due
to their potential as highly promising building blocks for new
a. Department of Chemistry and Chemical Engineering, College of Science
b. Material Science and Engineering College, Northeast Forestry University, Harbin,
150040, P. R. China. E-mail: ccx1759@163.com, jspeng1998@163.com
† Xue Li and Xin Chen contributed equally to this work.
demonstrated
a
novel synthesis of cationic polycyclic
heteroaromatic compounds through Rh-catalyzed C−H/C−H cross-
coupling reaction between N-(hetero)arylimidazolium salts and
Electronic Supplementary Information (ESI) available: copies of 1H, 13C NMR and
HRMS spectra for new compounds. See DOI: 10.1039/x0xx00000x
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Table 1 Pd-catalyzed tandem annulation reaction condition optimizationa
View Article Online
DOI: 10.1039/C9OB00482C
Ph
Pd/L, base, solvent
N
N
N
+
Ph
2a
I
temperature, air, 72 h
N
H
Ph
1a
3aa
solvent/temp[℃]c
entry
Pd/ligand b
base
yield[%]d
—
1
2
3
4
5
6
7
8
9
10
11
12e
13
14
15
16
17
18
19
20
21
22
23
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
NaOtBu
NaOH
Et3N
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMF/160
DMA/160
DMSO/140
Toluene/160
1,4-Dioxane/140
DMF /100
DMF/120
DMF/140
0
Pd(OAc)2/PPh3
Pd(OAc)2/PCy3
51
78
67
59
79
91
66
20
84
70
75
54
88
7
0
29
0
58
31
0
71
84
Pd(OAc)2/tBu3P·HBF4
Pd(OAc)2/MePhos
Pd(OAc)2/JohnPhos
Pd(OAc)2/Xphos
Pd(OAc)2/DPPE
Pd(OAc)2/DPPF
PdCl2/Xphos
Pd(PPh3)4/Xphos
Pd2(dba)3/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
Pd(OAc)2/Xphos
a Reaction conditions unless otherwise stated: 1a (0.2 mmol), 2a (0.6 mmol), base (0.6 mmol), Pd (10 mol%), ligand (20 mol%) and
solvent (2.0 mL), 72 h, air. b Abbreviations: MePhos = 2-dicyclohexylphosphino-2'-methylbiphenyl, JohnPhos = 2-(di-tert-
butylphosphino)biphenyl, Xphos = 2-dicyclohexylphosphino-2', 4', 6'-triisopropylbiphenyl, dppe = 1,1-bis-
(diphenylphosphino)ethane, dppf =1,1ʹ-bis(diphenylphosphino)ferrocene, dba = dibenzylideneacetone. c 160 ℃ (Oil temperature).
The accurate reaction temperature was the reflux temperature of solvent employed (entries 1-20). d Yield of isolated product. e
mol% of catalyst was used.
5
(hetero)arenes. π-Expansion of imidazole parent molecule has been arylation followed by aerobic oxidative N−H arylation (Scheme 1).
achieved by Pd-catalyzed C−H functionalization processes in recent Thus, a highly π-extended aza-fused polyheterocyclic system could
years. For instance, palladium-catalyzed intramolecular C−H be rapidly assembled in a tandem one-pot fashion. To realize this
alkenylation24 or arylation25 has become an important strategy for proposed tandem process, two key issues need to be addressed.
the synthesis of π-expanded imidazoles. Pd-catalyzed double First, controlling chemical selectivity to ensure that Heck reaction
arylation has also been developed for the construction of similar occurs before N-arylation32 under same reaction conditions.
skeleton with o-dihaloarenes or aryl halides as arylating reagents by Second, establishing a rational catalytic cycle to accommodate both
Miura,26 Lan and You,27 Liu and Zhuo,28 and our group,29 traditional Heck arylation and oxidative arylation.
respectively. In addition to transition-metal catalysis,
photochemical arylation30 and cycloaddition-dehydogenation31
involving the cleavage of aromatic C−H bond have been successfully
2. Results and discussion
employed to produce imidazole-based heterocyclic fluorescent 2-Vinyl-PI (1a), readily derived from multi-component reaction of
materials. Despite major advancements in this field, tandem multi- 9,10-phenanthraquinone, cinnamaldehyde, and ammonium
arylation of several different C–H bonds will provide a more acetate,17 was selected as the substrate to verify the assumption
efficient and rapid approach to the syntheses of π-expanded mentioned above with iodobenzene (2a) as the coupling partner
imidazole fluorophores. Such synthetic strategy is quite challenging, (Scheme 1a). Extensive condition optimization experiments were
and reported examples remain scarce.29b
With our continuous efforts24, 29 on chemical modifications of ligands, bases, solvents, and temperatures with air as the oxidant
imidazole-based fluorophore through Pd-catalyzed C−H (Table 1). The blank experiment (without the catalyst and ligand)
conducted in the presence of various Pd catalysts, phosphorous
functionalization, we envisioned that 2-vinyl PIs or benzimdazoles was examined in N,N-dimethylforamide (DMF) at 160 ℃ for 72 h
and aryl halides should be suitable substrates for sequential Heck using K2CO3 as the base, and no desired product was obtained
2 | Org. Biomol. Chem., 2019, 00, 1-10
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DOI: 10.1039/C9OB00482C
Table 2 Pd-Catalyzed Annulation of Phenanthroimidazoles with Aryl Iodidesa
Ar2
Ar1
Ar1
HN
N
N
Pd(OAc)2/Xphos
N
Ar2-I
+
1
2
3
K2CO3, DMF, air, 160 ℃, 72 h
Ar1 = C6H5-
1a
1b
1c
Ar1 = p-Me-C6H4-
Ar1 = p-MeO-C6H4-
Ar1 = m-MeO-C6H4-
Ar1 = NO2-C6H4-
1d
1e
entry
s-1
s-2
products 3
yieldb
N
Ph
1a
1a
1a
Ph-I
2a
2a'
2a''
91
63
39
1
2
3
N
Ph-Br
Ph-Cl
3aa
1a
1a
R = Me 2b
R = MeO 2c
R = Ph 2d
3ab
3ac
84
66
52
50
4
5
6
7
R
N
N
1a
1a
R
I
3ad
3ae
3af
R = F
2e
1a
1a
R = Cl
2f
27
0
8
9
R = CN, NO2, -CO2Me
R
R
N
N
1a
1a
R = Me 2g
3ag
3ah
62
40
10
11
I
R = F
2h
R
R
N
N
1a
1a
R =Me
2i
3ai
3aj
12
13
83
72
I
R = MeO 2j
N
N
I
2k
2b
1a
1b
3ak
3bb
34
64
14
15
Me
N
N
Me
I
Me
MeO
N
N
N
MeO
I
2c
1c
3cc
58
46
16
OMe
Ph
17c
18
N
1d
Ph-I
Ph-I
2a
2a
3da
3da'
1
MeO
(3-MeO/1-MeO) = 2:1
3
1e, 1f
0
a Reaction conditions: 1 (0.2 mmol), 2 (0.6 mmol), K2CO3 (0.6 mmol), Pd(OAc)2 (10 mol%), Xphos (20 mol%) and DMF (2.0 mL), 160 ℃
(oil temperature), 72 h, air. b Yield of isolated product. c The ratio of the regioisomers was determined by NMR analysis.
t
(entry 1). We examined the model reaction in the presence of phosphorus ligands (PCy3, Bu3P, MePhos, JohnPhos, Xphos, dppe,
Pd(OAc)2 (10 mol%) and PPh3 (20 mol%), fortunately, the desired and dppf) on the reaction was then investigated using Pd(OAc)2 as
product 3aa was isolated in 51% yield (entry 2). The effect of the catalyst (entries 3−9). Sterically hindered biaryl phosphine
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Xphos33 proved to be a highly efficient ligand for this tandem
annulation, and the yield was improved to 91% (entry 7). A survey
of palladium catalysts showed that Pd(OAc)2 provided better results
(91% yield, entry 7) than PdCl2, Pd(PPh3)4, and Pd2(dba)3 (70-84%
yields, entries 10−12) with Xphos as the ligand. The effect of bases
such as Cs2CO3, NaOtBu, NaOH and Et3N on the reaction was next
examined (entries 13−16), NaOtBu provided similar result to K2CO3
in yield (88% vs 91%, entries 7 and 14). A survey of reaction media
showed that the use of DMF provided better results than those
obtained in DMA, DMSO, toluene, and 1,4-dioxane (entries 7 and
17−20). Finally, a set of experiments were carried out to reveal the
crucial role of the reaction temperature, with increased reaction
temperature, higher yields were obtained (entries 7, 21−23). When
the reaction temperature was reduced to 100 and 120 ℃, the
desired product 3aa was isolated in a trace quantity and 71% yield,
respectively (entries 21 and 22). Reactions carried out at 140 ℃
gave a comparable yield to the reaction at 160 ℃ (84% vs 91%,
entries 7 and 23).
Table 3 Pd-Catalyzed Tandem Reaction of BenzVimiewidAartzicoleleOsnline
DOI: 10.1039/C9OB00482C
with Aryl Iodidesa
Ar
Ar
Pd(OAc)2/Xphos
HN
N
Ar-I
+
N
N
R
K2CO3, DMF, air, 160 ℃, 72 h
4
2
5
R
4a
R = H,
4b
R = Me,
Me
OMe
Me
MeO
N
N
5aa
N
N
N
N
Ph-I, 63%
Ph-Br, 53%
Ph-Cl, trace
5ab
5ac
, 37%
, 52%
Ph
Cl
Having established the feasibility of this domino Heck/aerobic
oxidative N−H double arylation reaction sequence, the reaction of
2-vinyl PIs with aryl halides was then explored to examine the scope
and generality of this annulation process (Table 2). We first
examined the effect of the nature of the halogen on the reaction,
and attempts to extend the substrate scope to less reactive aryl
bromides and chlorides were conducted (entries 1−3). Aryl iodide or
bromide can smoothly be converted to the desired product 3aa in
good to excellent yields (63% and 91% yield), however, aryl chloride
afforded an inferior result (39% yield) than its iodo or bromo
analogue. The observed trend is consistent with the chemical
reactivity of aryl halides. Second, the scope of aryl iodides as
arylating reagents was next investigated under the optimized
conditions (entries 4−13). As shown in Table 2, most of substituents
(such as Me, OMe, Ph, F, and Cl) were tolerant, and the
corresponding products 3ab−3ak can be obtained in moderate to
good yields (27−84%). In addition, α-naphthyl iodide 2k can also be
transformed into the corresponding product 3ak in 34% yield (entry
13). Aryl iodides containing electron-donating groups at the ortho
(entry 10), meta (entries 11 and 12), or para (entries 4−6) position
were generally more reactive than those bearing electron-
withdrawing substituents (entries 7 and 8) and provided higher
yields. Nevertheless, when extending the electron-withdrawing
substituent scope from halide to cyano, nitro and ester groups, the
reactions cannot proceed to give the corresponding products (entry
9). Finally, the scope and limitation of 2-vinyl PIs 1 was examined
(entries 14−17). The reaction outcome was heavily affected by the
electronic nature of styryl moiety. The incorporation of electron-
donating groups (Me, and MeO) on the aryl ring of 2-styryl moiety
did not hamper the reaction, and the corresponding products can
be obtained in good yields (entries 14−16). However, the substrate
1e, bearing electron-withdrawing nitro group, gave no products
under the standard conditions (entry 17). When meta-substituted
2-styryl PI 1d was used, regioselectivity issue surfaced in the
oxidative N−H arylation step, and the reaction preferentially
occurred at the most sterically accessible site to give two
regioisomers 3da and 3da' in a 2:1 ratio (entry 16).
Ph
Cl
N
N
N
N
N
N
Me
5ba
, 49%
5ad
5af
, 61%
, 21%
Me
OMe
Ph
Me
MeO
Ph
N
N
N
N
N
N
Me
Me
Me
5bb
5bc
, 40%
5bd
, 44%
, 52%
a
Reaction conditions: 4 (0.2 mmol), 2 (0.6 mmol), K2CO3 (0.6
mmol), Pd(OAc)2 (10 mol%), Xphos (20 mol%) and DMF (2.0
mL), 160 ℃ (oil temperature), 72 h, air. Yield of isolated
product.
b
benzimidazoles 4 and aryl iodides 2 was practicable through one-
pot sequential double Heck arylation and intramolecular aerobic
oxidative C−H amination (Table 3). Similarly, phenyl iodide provided
a better result (5aa, 63% yield) than its bromo or chloro analogue.
para-Substituted aryl iodides containing electron-donating groups
(Me, MeO, and Ph) underwent the reaction smoothly and afforded
the corresponding products (5ab−5ad, and 5bb−5bd) in good yields
(37−61%); however, the presence of weak electron-withdrawing
substituent led to an inferior result (5af, 21% isolated yield), and
aryl iodides having strong electron-withdrawing substituents (such
as cyano, nitro, and ester) provided no products. Regioselectivity
may potentially exist in this cascade process when asymmetrically
substituted 2-vinyl benzimidazoles are used. For the selected case
of 4-methyl-substituted benzimidazole 4b, oxidative N−H arylation
occurred specifically at the sterically accessible N-atom to give
single products 5ba−5bd.
To gain insight into the mechanism of the reaction, some
designed control experiments were conducted under standard
reaction conditions (Scheme 2). First, the reactivity of N-phenyl PI
1g was examined, the reaction cannot proceed to form the target
product 3aa (eq 1, Scheme 2). The result implied that 1g cannot be
an intermediate, and further confirmed that the reaction pathway
was comprised of intermolecular Heck arylation of 2-styryl PIs
Using the same reaction conditions, Pd-catalyzed modular
synthesis of benzimidazole-fused quinolines 5 direct from 2-vinyl
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Ph
Table 4 Photophysical Properties of π-ExteVniedweAdrticlAe zOan-line
DOI: 10.1039/C9OB00482C
polycycles 3 and 5
Ph
N
N
Pd(OAc)2/Xphos
N
N
(1)
a
b
K2CO3, DMF, air, 160 ℃, 72 h
entry compd
λmax (nm)
λem
ΦF
Stokes
shift (cm-1)
4600
4100
4500
4800
4200
4700
4600
3900
4100
4200
4100
4100
4700
5700
5700
4300
3200
5900
6100
5800
4100
5100
1g
3aa
No Reaction
ε (M-1cm-1)
374 [15600]
379 [14300]
379 [10200]
383 [19100]
377 [35200]
374 [20900]
370 [10200]
380 [21600]
377 [58100]
378 [36400]
374 [18300]
376 [20700]
372 [7700]
342 [26800]
343 [20900]
362 [13000]
375 [4100]
340 [10800]
344 [22000]
344 [29100]
365 [17600]
356 [15200]
(nm)
451
449
456
469
447
453
446
447
446
449
442
445
451
425
426
428
427
426
435
430
430
435
1
2
3
4
5
3aa
3ab
3ac
3ad
3ae
3af
0.53
0.70
0.54
0.50
0.25
0.87
0.70
0.62
0.62
0.69
0.80
0.79
0.80
0.82
0.63
0.59
0.57
0.43
0.31
0.27
0.34
0.45
OMe
MeO
Ph
Ph
HN
Pd(OAc)2/Xphos
N
N
MeO
N
(2)
I
+
N
+
N
K2CO3, DMF, air, 160 ℃, 72 h
1d
2a
46% yield
6
7
8
9
3ag
3da
3ai
3da
3da'
OMe
10
11
12
13
14
15
16
17
18
19
20
21
22
3aj
OMe
HN
N
3ak
3bb
3cc
5aa
5ab
5ac
5ad
5af
5ba
5bb
5bc
5bd
Pd(OAc)2/Xphos
N
(3)
N
I
+
K2CO3, DMF, air, 160 ℃, 72 h
1a
2j
3aj
72% yield
Scheme 2 Investigation of the Reaction Mechanism.
followed by an intramolecular oxidative N−H arylation sequence.
Second, the reaction of 1d and iodobenzene 2a gave two
regioisomers 3da and 3da' in 46% yield (eq 2, Scheme 2), however,
the reaction of 1a and meta-methoxyl iodobenzene 2j afforded a
single product 3aj in 72% yield (eq 3, Scheme 2). The above results
showed that intramolecular oxidative N−H arylation step occurred
specifically at the aromatic residue of 2-styryl moiety rather than at
the aromatic ring of aryl iodide substrates.
Concentration: 1.0× 10−5 M in CH2Cl2. Determined by p-
terphenyl (ΦF = 0.87, excited at 265 nm) as a standard.
a
b
On the basis of the above results, a plausible catalytic cycle is
outlined for this tandem reaction. The scheme 3 shows a simplified
sequence of events beginning with the generation of the active
Pd(0) catalyst. Oxidative addition of Pd(0) into the C−I bond of aryl
iodide 2 gave an arylpalladium(II) iodide 6, which reacted with 2-
styryl PI 1 to afford an alkylpalladium(II) intermediate 7 through the
syn migratory insertion into the olefin moiety. An internal C−C bond
rotation in the σ-alkyl-palladium(II) iodide 7 brought β-hydrogen in
a syn position relative to the palladium atom. A syn β-hydride
elimination afforded the arylated PI intermediate
9 and a
hydridopalladium(II) iodide 10, which underwent a reversible
reductive elimination to regenerate the active Pd(0) complex. The
base (K2CO3) shifted the equilibrium towards the Pd(0) species by
quenching the hydrogen iodide. The Pd(0) species was then
oxidized by O2 to form the active Pd(II) complex for an
intramolecular aromatic C−H amination of Heck intermediate 9.
K2CO3-promoted deprotonation of the acidic N−H group of 9 and
subsequent nucleophilic substitution reaction with Pd(II) provided
an amino-palladium intermediate 11. Intramolecular aromatic C−H
palladation of 11 led to the formation of seven-membered
palladacycle 12 through a concerted metalation deprotonation
(CMD) transition state.34 Finally, palladacycle 12 underwent C−N
reductive elimination to afford the desired product 3 and a Pd(0)
species for Heck arylation process.35
Ar-I
2
oxidative
addition
Pd(0)
Ar
PdII
N
Ar
base
Y
reductive
elimination
Ar-PdII-I
HN
PdII
Ar
C-H
H
N
N
6
1
N
N
palladation
N
N
12
migratory
insertion
Ar
CMD TS
Y
PdII
Ar
PdII-I
N
3
Ar
N
Ar
Ar
Ar
N
11
H
HN
substitution
Ar
H
7
N
N
H
base
PdII
Y
C-C bond
rotation
H
Ar
(Y = I or OAc)
Y
Ar
Ar
oxidation
9
PdII-I
Ar
O2
Pd(0)
syn hydride
elimination
reductive
elimination
8
N
H
=
HN
Ar
PdII-
10
H
I
base
note:
Ar
PdII-I
H
HN
N
HN
Ar
N
N
=
H
1
Ar
HN
Figure 1 Absorption (left) and emission (right) spectra of 3aa
(red) and 5aa (blue).
Scheme 3 Proposed Catalytic Pathway.
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Organic & Biomolecular Chemistry
The absorption and fluorescence spectra of π-extended 150 MHz. Unless otherwise stated, deuterochloroform (CDCl3) was
View Article Online
imidazole-fused aromatic polycycles 3 and 5 were measured in used as a solvent. Chemical shifts (δ) are gDivOeIn: 1i0n.1p03a9rt/sC9pOeBr0m04il8li2oCn
CH2Cl2, as shown in Table 4 and Figure 1. In comparison with downfield relative to tetramethylsilane (TMS). Chemical shifts for
benzimidazole or PI substrates,
a longer wavelength of the carbon resonances are reported in parts per million and are
maximum absorption peak (λmax) was obtained as a result of the referenced to the carbon resonance of the solvent CHCl3 (δ = 77.16
formation of π-extended framework. A change of less than 43 nm ppm). The splitting patterns are reported as s (singlet), d (doublet),
for λmax was observed among these compounds by a simple dd (double doublet), td (triplet of doublet), t (triplet), q (quartet), br
modification of aryl substituent on the backbone (entries 1−22), (broad), and m (multiplet). Coupling constants are given in hertz.
and all of these compounds showed blue fluorescent emissions in High-resolution mass spectra were recorded on a BIO TOF Q mass
CH2Cl2. Emission maxima of PIs 3 and benzimidazoles 5 were spectrometer equipped with an electrospray ion source (ESI),
significantly bathochromically shifted. Increasing the number of operated in the positive mode.
conjugated aromatic ring and planarity, benzimidazoles 5 resulted
4.2. General Procedure for Synthesis of (E)-2-styryl-1H-
phenanthro[9,10-d]imidazoles 1
in larger change range in the optical properties as compared to PIs
3. 5 exhibited a larger Stokes shift range from 6100 to 3200 cm-1
To a 50 mL round bottom flask equipped with a magnetic stirrer
and reflux condenser were added 9,10-phenanthraquinone (416.4
mg, 2.0 mmol), NH4OAc (925.0 mg, 12 mmol), (E)-3-
arylacrylaldehyde (2.0 mmol), and acetic acid (20.0 mL). The flask
was immersed in an oil bath (80 ℃) for 22 h. The mixture was then
cooled to room temperature and poured into ice-water, and the
yellow precipitate was collected by filtration. The precipitate was
finally recrystallized from ethanol to give a product.
(entries 14−22) than PIs 3 (3900−4800 cm-1, entries 1−13). In these
conjugated systems, the fluorescence quantum yield (ΦF) remained
in the range of 0.25−0.87, and the introduction of naphthyl, and
methoxyl group into phenanthro[9',10':4,5]imidazo[1,2-a]quinoline
core showed a good fluorescence quantum yield (entries 11 and
13).
3. Conclusions
(E)-2-Styryl-1H-phenanthro[9,10-d]imidazole (1a). Yield, 54% (0.35
In conclusion, we have developed a novel and modular approach g); yellow solid, mp 172-174 ℃; 1H NMR (600 MHz, DMSO-d6) δ
for rapid syntheses of ring-fused phenanthroimidazoles and 13.51 (s, 1H), 8.87 – 8.83 (m, 2H), 8.65 (d, J = 6.4 Hz, 1H), 8.51 (d, J =
benzimidazoles. This tandem reaction sequence is comprised of 6.5 Hz, 1H), 7.84 – 7.78 (m, 5H), 7.66 (t, J = 6.7 Hz, 2H), 7.50 – 7.46
palladium-catalyzed
intermolecular
Heck
arylation
and (m, 3H), 7.39 (t, J = 7.1 Hz, 1H). 13C NMR (150 MHz, DMSO-d6) δ
intramolecular aerobic oxidative C−H amination, involving the 149.3, 137.7, 136.6, 132.9, 129.5 (2xC), 129.0, 128.2, 128.0, 127.8,
rupture of two or three C−H bonds, one C−X bond, and one N−H 127.7, 127.6, 127.4, 127.3 (2xC), 125.8, 125.6, 124.6, 124.2, 122.7,
bond in a one-pot manner. The Pd0−PdII−Pd0 catalytic cycle is 122.4, 122.3, 118.2. HRMS-ESI: [M+H]+ calcd for C23H17N2 m/z
proposed to generate π-extended PIs or benzimidazoles with 321.1392, found m/z 321.1387.
diverse substituents from 2-styryl PIs or 2-vinyl benzimidazoles and (E)-2-(4-Methylstyryl)-1H-phenanthro[9,10-d]imidazole (1b). Yield,
aryl halides, respectively. Because of the interesting and important 53% (0.354 g); yellow solid, mp 201-203 ℃; 1H NMR (600 MHz,
optical properties of fused multi-core imidazoles, these DMSO-d6) δ 13.39 (s, 1H), 8.84 (d, J = 8.7 Hz, 2H), 8.54 (s, 1H), 8.44
fluorophores are good candidates for purposes such as emitters in (s, 1H), 7.73 – 7.70 (m, 3H), 7.62 – 7.60 (m, 4H), 7.32 (d, J = 16.5 Hz,
OLEDs, OFETs, and photovoltaic cells. Therefore, this Pd-catalyzed 1H), 7.25 (d, J = 7.7 Hz, 2H), 2.34 (s, 3H). 13C NMR (150 MHz, DMSO-
tandem multi-arylation will provide a useful tool for the discovery d6) δ 149.4, 138.6, 137.6, 133.8, 132.9, 130.1 (2xC), 128.1 (2xC,
of fluorescent materials.
overlap), 128.0, 127.6, 127.4 (2xC, overlap), 127.3 (2xC), 125.8 (2xC,
overlap), 125.6, 124.6, 124.2, 122.7, 122.3, 117.2, 21.4. HRMS-ESI:
[M+H]+ calcd for C24H19N2 m/z 335.1548, found m/z 335.1545.
4. Experimental section
(E)-2-(4-Methoxystyryl)-1H-phenanthro[9,10-d]imidazole
(1c).
4.1. General information
Yield, 49% (0.343 g); yellow solid, mp 220-222 ℃; 1H NMR (600
MHz, DMSO-d6) δ 13.36 (s, 1H), 8.81 (d, J = 5.7 Hz, 2H), 8.55 – 8.47
(m, 2H), 7.73 – 7.70 (m, 3H), 7.66 (d, J = 7.7 Hz, 2H), 7.61 (t, J = 6.6
Hz, 2H), 7.26 (d, J = 16.4 Hz, 1H), 6.99 (d, J = 7.7 Hz, 2H), 3.77 (s, 3H).
13C NMR (150 MHz, DMSO) δ 160.1, 149.7, 132.7, 129.2, 128.8 (2xC),
128.0, 127.6, 125.6, 124.6, 124.5 (3xC, overlap), 124.4 (4xC,
overlap), 124.3 (2xC, overlap), 122.3, 115.9, 114.9 (2xC), 55.6.
HRMS-ESI: [M+H]+ calcd for C24H19N2O m/z 351.1497, found m/z
351.1494.
Chemicals were all purchased from commercial supplies and used
without further purification unless otherwise stated. Solvents were
dried and purified according to the standard procedures before use.
Reactions were monitored by analytical thin-layer chromatography
(TLC). All reactions were conducted in dried glassware. Purification
of reaction products was done by flash chromatography with
230−400 mesh silica gel. Phenanthroimidazoles (1)17 and
benzimidazoles (4)36 were prepared according to the literature
methods. Melting points were determined on a melting point
apparatus in open capillaries and are uncorrected. Infrared spectra
of samples were recorded from 4,000 to 500 cm−1 in ATR
(E)-2-(3-Methoxystyryl)-1H-phenanthro[9,10-d]imidazole
(1d).
Yield, 46% (0.322 g); yellow solid, mp 197-198 ℃; 1H NMR (600
MHz, DMSO-d6) δ 13.46 (s, 1H), 8.83 – 8.79 (m, 2H), 8.59 (d, J = 7.2
Hz, 1H), 8.45 (d, J = 7.1 Hz, 1H), 7.77 – 7.73 (m, 3H), 7.61 (br, 2H),
7.44 (d, J = 16.5 Hz, 1H), 7.35 (t, J = 7.6 Hz, 1H), 7.30 (s, 2H), 6.92
(br, 1H), 3.83 (s, 3H). 13C NMR (150 MHz, DMSO-d6) δ 160.2, 149.2,
138.1, 137.7, 132.9, 130.5, 128.2, 128.0, 127.8, 127.7, 127.6, 127.4,
1
(attenuated total reflectance) mode using an FT-IR instrument. H
NMR spectra were recorded on
spectrometer, and 13C NMR spectra were recorded at 100, 125 or
a 400, 500 or 600 MHz
6 | Org. Biomol. Chem., 2019, 00, 1-10
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(3ab).
125.9, 125.6, 124.6, 124.2, 122.7, 122.3, 122.3, 120.0, 118.6, 115.0, 5-(p-Tolyl)phenanthro[9',10':4,5]imidazo[1,2-a]quinoline
112.0, 55.6. HRMS-ESI: [M+H]+ calcd for C24H19N2O m/z 351.1497, Yield, 84% (68.5 mg); yellow solid, mp 167-168 ℃; IR (KBr, cm ):
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-1
DOI: 10.1039/C9OB00482C
found m/z 351.1496.
1623, 1448, 1383, 755, 727; 1H NMR (500 MHz, CDCl3) δ 8.85 (d, J =
7.8 Hz, 1H), 8.76 (d, J = 7.9 Hz, 1H), 8.69 (d, J = 8.2 Hz, 1H), 8.51 –
8.44 (m, 2H), 7.90 (d, J = 8.1 Hz, 1H), 7.74 (t, J = 7.4 Hz, 1H), 7.72 –
7.65 (m, 2H), 7.61 – 7.53 (m, 3H), 7.49 (d, J = 7.8 Hz, 2H), 7.39 (t, J =
7.6 Hz, 1H), 7.35 (d, J = 7.8 Hz, 2H), 2.46 (s, 3H). 13C NMR (125 MHz,
CDCl3) δ 148.0, 142.3, 141.4, 138.2, 135.0, 134.7, 129.8, 129.4 (2xC),
129.3 (2xC), 128.7, 128.0, 127.4, 127.1, 127.0, 126.6, 125.4, 125.0,
124.7, 124.5, 124.3, 123.7, 123.3, 123.0, 122.8, 122.7, 118.9, 116.8,
21.3. HRMS-ESI: [M+H]+ calcd for C30H21N2 m/z 409.1705, found m/z
409.1679.
4.3. General Procedure for Synthesis of 2-vinyl-1H-
benzo[d]imidazoles 4
A mixture of benzene-1,2-diamine or 3-methylbenzene-1,2-diamine
(10 mmol), 3-bromopropionic acid (10 mmol) in PPA (5 mL) was
heated with stirring for 4 hours at 120 ℃. The mixture was then
poured onto ice and neutralized with concentrated ammonia
solution and kept over 8 hours at 5-10 ℃. The yellow residue was
recrystallized from ethanol to give a product.
2-Vinyl-1H-benzo[d]imidazole (4a).36 Yield, 40% (0.576 g); yellow 5-(4-Methoxyphenyl)phenanthro[9',10':4,5]imidazo[1,2-a]
solid, mp 159-161 ℃; 1H NMR (600 MHz, DMSO-d6) δ 11.18 (br, quinoline (3ac). Yield, 66% (55.8 mg); yellow solid, mp 197-199 ℃;
1H), 7.54 (d, J = 1.8 Hz, 2H), 7.18 (d, J = 1.8 Hz, 2H), 6.79 (dd, J = IR (KBr, cm-1): 1605, 1507, 1449, 1381, 1249, 1182, 1029, 759, 749,
17.6, 11.3 Hz, 1H), 6.29 (d, J = 17.8 Hz, 1H), 5.68 (d, J = 11.1 Hz, 1H). 727; 1H NMR (400 MHz, CDCl3) δ 8.88 (d, J = 7.5 Hz, 1H), 8.82 (d, J =
13C NMR (150 MHz, DMSO-d6) δ 151.0, 139.1 (2xC), 127.3, 122.7 7.8 Hz, 1H), 8.75 (d, J = 8.2 Hz, 1H), 8.60 – 8.50 (m, 2H), 7.96 (d, J =
(2xC), 121.4, 115.5 (2xC). HRMS-ESI: [M+H]+ calcd for C9H9N2 m/z 7.8 Hz, 1H), 7.82 – 7.69 (m, 3H), 7.67 – 7.54 (m, 5H), 7.46 (t, J = 7.5
145.0766, found m/z 145.0764.
Hz, 1H), 7.10 (d, J = 8.5 Hz, 2H), 3.92 (s, 3H). 13C NMR (150 MHz,
7-Methyl-2-vinyl-1H-benzo[d]imidazole (4b). Yield, 34% (0.537 g); CDCl3) δ 159.8, 147.9, 142.0, 141.4, 134.8, 130.7 (2xC), 130.2, 129.9,
1
yellow solid, mp 182-183 ℃; H NMR (600 MHz, DMSO-d6) δ 7.58 128.8, 128.1, 127.5, 127.3, 126.8, 126.7, 125.5, 125.1, 124.9, 124.6,
(d, J = 8.2 Hz, 1H), 7.41 (t, J = 7.8 Hz, 1H), 7.31 (d, J = 7.4 Hz, 1H), 124.4, 123.7, 123.4, 123.1, 122.8, 122.7, 119.0, 116.5, 114.2 (2xC),
6.97 (dd, J = 17.7, 11.4 Hz, 1H), 6.82 (d, J = 17.7 Hz, 1H), 6.24 (d, J = 55.4. HRMS-ESI: [M+H]+ calcd for C30H21N2O m/z 425.1654, found
11.4 Hz, 1H), 2.60 (s, 3H). 13C NMR (150 MHz, DMSO-d6) δ 148.0, m/z 425.1621.
131.9, 131.8, 130.2, 126.6, 126.5, 125.0, 120.9, 111.7, 17.2. HRMS- 5-([1,1'-Biphenyl]-4-yl)phenanthro[9',10':4,5]imidazo[1,2-a]
ESI: [M+H]+ calcd for C10H11N2 m/z 159.0922, found m/z 159.0912.
quinoline (3ad). Yield, 52% (48.9 mg); yellow solid, mp 189-190 ℃;
IR (KBr, cm-1): 3056, 1621, 1602, 1486, 1449, 1420, 1382, 751, 726,
697; 1H NMR (600 MHz, CDCl3) δ 8.90 (d, J = 7.6 Hz, 1H), 8.86 – 8.80
(m, 1H), 8.76 (d, J = 8.1 Hz, 1H), 8.59 (d, J = 8.1 Hz, 2H), 8.03 (d, J =
8.0 Hz, 1H), 7.86 – 7.77 (m, 4H), 7.76 – 7.70 (m, 4H), 7.69 – 7.58 (m,
4H), 7.56 – 7.45 (m, 3H), 7.43– 7.40 (m, 1H). 13C NMR (150 MHz,
CDCl3) δ 141.4, 140.5, 136.8, 134.8, 129.9 (2xC), 129.5, 129.2, 129.0
(2xC), 128.9, 128.8, 128.1, 127.7, 127.6 (2xC), 127.5, 127.4, 127.3,
127.2 (2xC), 126.9, 125.6, 125.5, 125.3, 125.0, 124.7, 124.3, 123.7,
123.5, 123.2, 122.9, 119.1, 117.2, 116.8. HRMS-ESI: [M+H]+ calcd for
C35H23N2 m/z 471.1861, found m/z 471.1857.
4.4.
General
Procedure
for
Synthesis
3
of
phenanthro[9',10':4,5]imidazo[1,2-a]quinolines
benzo[4,5]imidazo[1,2-a]quinolines 5
and
A 10 mL schlenk tube equipped with a magnetic stirring bar was
charged with phenanthroimidazoles 1 or benzimidazoles 4 (0.2
mmol, 1.0 equiv), aryl iodides 2 (0.6 mmol, 3.0 equiv), and K2CO3
(82.8 mg, 0.6 mmol, 3.0 equiv), and then Pd(OAc)2 (0.02 mmol, 4.5
mg) and Xphos (0.04 mmol, 19 mg) were added. Finally, DMF (2.0
mL) was added to the mixture via syringe at room temperature
under air. The schlenk tube was sealed and put into a preheated oil
bath at 160 ℃ for 72 h. The mixture was cooled to room
temperature, quenched with water (5 mL), and diluted with ethyl
acetate (5 mL). The layers were separated, and the aqueous layer
was extracted with 2 × 5 mL of ethyl acetate. The combined organic
extracts were dried over anhydrous magnesium sulfate, filtered,
and concentrated in vacuo. The crude product was then purified by
flash chromatography on silica gel (H), eluting with the mixture of
ethyl acetate and petroleum ether (1:5).
5-(4-Fluorophenyl)phenanthro[9',10':4,5]imidazo[1,2-a]quinoline
(3ae). Yield, 50% (41.2 mg); yellow solid, mp 195-197 ℃; IR (KBr,
1
cm-1): 1604, 1507, 1450, 1381, 1233, 1219, 839, 753, 726; H NMR
(400 MHz, CDCl3) δ 8.88 – 8.83 (m, 2H), 8.77 (d, J = 7.7 Hz, 1H), 8.58
(d, J = 8.2 Hz, 2H), 7.88 (d, J = 8.2 Hz, 1H), 7.80 – 7.73 (m, 3H), 7.69 –
7.60 (m, 5H), 7.48 (t, J = 7.5 Hz, 1H), 7.33 – 7.24 (m, 2H). 13C NMR
1
(125 MHz, CDCl3) δ 162.9 (163.9, 161.9, d, JC-F = 246 Hz), 147.7,
4
142.3, 140.2, 134.7, 134.0 (134.0, 133.9, d, JC-F = 4 Hz), 131.2
(131.2, 131.1, d, 3JC-F = 9 Hz, 2xC), 129.9, 128.9, 127.7, 127.5, 127.3,
5-Phenylphenanthro[9',10':4,5]imidazo[1,2-a]quinoline
(3aa). 127.0, 126.8, 125.5, 125.2, 124.9, 124.6, 124.1, 123.7, 123.4, 123.1,
Yield, 91% (71.7 mg); yellow solid, mp 130-132 ℃; IR (KBr, cm-1): 122.8, 122.7, 119.0, 117.2, 115.9 (116.0, 115.8, d, 2JC-F = 21 Hz, 2xC).
1622, 1449, 1421, 1382, 750, 726; 1H NMR (400 MHz, CDCl3) δ 8.86 HRMS-ESI: [M+H]+ calcd for C29H18FN2 m/z 413.1454, found m/z
(d, J = 7.6 Hz, 1H), 8.77 (d, J = 7.8 Hz, 1H), 8.71 (d, J = 8.1 Hz, 1H), 413.1479.
8.51 (t, J = 7.4 Hz, 2H), 7.89 (d, J = 8.0 Hz, 1H), 7.78 – 7.66 (m, 3H), 5-(4-Chlorophenyl)phenanthro[9',10':4,5]imidazo[1,2-a]quinoline
7.62 – 7.48 (m, 8H), 7.41 (t, J = 7.5 Hz, 1H). 13C NMR (150 MHz, (3af). Yield, 27% (23.1 mg); yellow solid, mp 175-178 ℃; IR (KBr, cm-
CDCl3) δ 147.9, 142.3, 141.4, 138.0, 134.8, 129.9, 129.5 (2xC), 128.9, 1): 1623, 1488, 1449, 1383, 1090, 1014, 750, 726; 1H NMR (400
128.8 (2xC), 128.4, 128.0, 127.5, 127.3, 127.0, 126.7, 125.5, 125.1, MHz, CDCl3) δ 8.86 (dd, J = 7.8, 1.2 Hz, 1H), 8.82 (d, J = 7.8 Hz, 1H),
124.8, 124.6, 124.2, 123.8, 123.4, 123.1, 122.8, 122.8, 118.9, 117.1. 8.75 (d, J = 8.0 Hz, 1H), 8.56 (d, J = 8.8 Hz, 2H), 7.88 – 7.82 (m, 1H),
HRMS-ESI: [M+H]+ calcd for C29H19N2 m/z 395.1548, found m/z 7.80 – 7.70 (m, 3H), 7.68 – 7.59 (m, 3H), 7.58 – 7.53 (m, 4H), 7.46 (t,
395.1519.
J = 7.3 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 147.8, 142.5, 140.1,
136.5, 134.8, 134.6, 130.8 (2xC), 130.0, 129.1 (2xC), 129.0, 127.7,
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Organic & Biomolecular Chemistry
127.6, 127.5, 127.0, 126.9, 125.6, 125.3, 125.0, 124.7, 124.0, 123.8, Hz, 1H), 2.53 (s, 3H), 2.47 (s, 3H). 13C NMR (150 MHz, CDCl3) δ
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123.5, 123.2, 123.0, 122.9, 119.1, 117.3. HRMS-ESI: [M+H]+ calcd for 148.3, 142.3, 141.4, 138.2, 137.9, 135.2, 134.8, 129.9, 129.4 (2xC),
DOI: 10.1039/C9OB00482C
C29H18ClN2 m/z 429.1159, found m/z 429.1132.
129.3 (2xC), 128.7, 127.8, 127.4, 127.0, 126.6, 126.1, 125.2, 124.9,
5-(o-Tolyl)phenanthro[9',10':4,5]imidazo[1,2-a]quinoline
(3ag). 124.6, 123.9, 123.4, 123.1, 122.8, 122.6, 122.0, 119.2, 115.9, 21.7,
Yield, 62% (50.6 mg); yellow solid, mp 180-182 ℃; IR (KBr, cm-1): 21.3. HRMS-ESI: [M+H]+ calcd for C31H23N2 m/z 423.1861, found m/z
1
1654, 1618, 1450, 1380, 777, 749, 723; H NMR (600 MHz, CDCl3) δ 423.1859.
8.92 – 8.88 (m, 1H), 8.86 (d, J = 7.9 Hz, 1H), 8.79 (d, J = 8.2 Hz, 1H), 2-Methoxy-5-(4-methoxyphenyl)phenanthro[9',10':4,5]imidazo
8.65 – 8.62 (m, 1H), 8.61 (d, J = 8.4 Hz, 1H), 7.81 – 7.79 (m, 1H), 7.77 [1,2-a]quinoline (3cc). Yield, 58% (52.3 mg); yellow solid, mp 215-
1
– 7.73 (m, 1H), 7.71 – 7.62 (m, 4H), 7.51 (dd, J = 8.0, 1.1 Hz, 1H), 217 ℃; IR (KBr, cm-1): 1609, 1508, 1459, 1449, 1249, 1191, 758; H
7.48 – 7.41 (m, 3H), 7.40 (d, J = 3.7 Hz, 2H), 2.24 (s, 3H). 13C NMR NMR (600 MHz, CDCl3) δ 8.87 (dd, J = 7.9, 1.0 Hz, 1H), 8.84 – 8.80
(150 MHz, CDCl3) δ 148.0, 142.2, 141.3, 137.5, 136.6, 134.5, 130.3, (m, 1H), 8.75 (d, J = 8.2 Hz, 1H), 8.54 – 8.49 (m, 1H), 7.90 (d, J = 2.4
130.0, 129.9, 128.9, 128.5, 127.8, 127.5, 127.2, 127.0, 126.7, 126.1, Hz, 1H), 7.84 (d, J = 9.0 Hz, 1H), 7.78– 7.76 (m, 1H), 7.73 – 7.69 (m,
125.5, 125.2, 124.9, 124.7, 124.6, 123.8, 123.4, 123.1, 123.0, 122.8, 1H), 7.64 – 7.60 (m, 2H), 7.60 (s, 1H), 7.57 – 7.52 (m, 2H), 7.11 –
118.8, 117.5, 20.2. HRMS-ESI: [M+H]+ calcd for C30H21N2 m/z 7.07 (m, 2H), 7.03 (dd, J = 9.0, 2.5 Hz, 1H), 3.91 (s, 3H), 3.87 (s, 3H).
409.1705, found m/z 409.1669.
13C NMR (150 MHz, CDCl3) δ 159.7, 158.8, 148.7, 142.5, 141.2,
5-(m-Tolyl)phenanthro[9',10':4,5]imidazo[1,2-a]quinoline
(3ai). 136.2, 130.6 (2xC), 130.5, 129.9, 129.4, 128.7, 127.5, 127.0, 126.7,
Yield, 83% (67.7 mg); yellow solid, mp 187-190 ℃; IR (KBr, cm-1): 125.1, 124.9, 124.6, 123.7, 123.5, 123.4, 123.1, 122.2, 118.1, 114.2
1625, 1600, 1449, 1419, 1376, 750, 728; 1H NMR (600 MHz, CDCl3) δ (2xC), 114.1, 113.8, 102.6, 55.8, 55.4. HRMS-ESI: [M+H]+ calcd for
8.88 (d, J = 7.7 Hz, 1H), 8.81 (d, J = 7.9 Hz, 1H), 8.75 (d, J = 8.2 Hz, C31H23N2O2 m/z 455.1760, found m/z 455.1759.
1H), 8.55 (t, J = 8.5 Hz, 2H), 7.93 (d, J = 8.0 Hz, 1H), 7.78– 7.71 (m, Mixture of 3-methoxy-5-phenylphenanthro[9',10':4,5]imidazo[1,2-
3H), 7.69 – 7.51 (m, 4H), 7.49 – 7.40 (m, 3H), 7.33 (d, J = 7.4 Hz, 1H), a]quinoline (3da) and 1-methoxy-5-phenylphenanthro[9',10':4,5]
2.49 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 147.9, 141.7, 138.5, 137.9, imidazo[1,2-a]quinoline (3daʹ). Yield, 46% (39.0 mg); yellow solid,
1
134.7, 130.1, 129.9, 129.5, 129.1, 128.8, 128.7, 128.6, 128.1, 127.5, the ratio (3da:3daʹ = 2:1) is determined by H NMR; IR (KBr, cm-1):
1
127.2, 126.9, 126.7, 126.6, 125.5, 125.1, 124.8, 124.6, 124.3, 123.8, 1617, 1553, 1450, 1420, 1382, 1229, 1038, 752, 726; H NMR (600
123.4, 123.1, 122.8, 118.9, 116.8, 21.6. HRMS-ESI: [M+H]+ calcd for MHz, CDCl3) δ 8.88 – 8.86 (m, 1.43Hoverlap), 8.82 – 8.79 (m,
C30H21N2 m/z 409.1705, found m/z 409.1674.
1.44Hoverlap), 8.75
– 8.72 (m, 1.59Hoverlap), 8.56 – 8.54 (m,
5-(3-Methoxyphenyl)phenanthro[9',10':4,5]imidazo[1,2-a]
1.86Hoverlap), 8.47 (d, J = 9.1 Hz, 1H3ad), 7.97 – 7.95 (m, 0.49H3ad’),
quinoline (3aj). Yield, 72% (61.1 mg); yellow solid, mp 210-213 ℃; 7.78 – 7.75 (m, 2.75Hoverlap), 7.73 – 7.69 (m, 1.62Hoverlap), 7.65 – 7.60
IR (KBr, cm-1): 1621, 1604, 1506, 1448, 1248, 1181, 1027, 846, 759, (m, 5Hoverlap), 7.57 (t, J = 7.5Hz, 2H3ad), 7.52 (d, J = 7.4 Hz, 1H3ad),
1
748, 726; H NMR (400 MHz, CDCl3) δ 8.88 (d, J = 7.7 Hz, 1H), 8.81 7.50 – 7.45 (m, 1.49Hoverlap), 7.34 (d, J = 2.8 Hz, 1H3ad), 7.22 – 7.20
(d, J = 7.8 Hz, 1H), 8.75 (d, J = 8.1 Hz, 1H), 8.59 – 8.52 (m, 2H), 7.97 (m, 1.49Hoverlap), 7.17 (t, J = 2.1Hz, 0.53H3ad’), 7.06 (d, J = 8.2, 2.1 Hz,
(d, J = 8.0 Hz, 1H), 7.81 – 7.69 (m, 3H), 7.67 – 7.57 (m, 3H), 7.51 – 0.51H3ad’), 3.90 (s, 1.31H3adʹ), 3.82 (s, 3H3ad). HRMS-ESI: [M+H]+ calcd
7.44 (m, 2H), 7.25 – 7.16 (m, 2H), 7.07 (dd, J = 8.3, 2.1 Hz, 1H), 3.91 for C30H21N2O m/z 425.1654, found m/z 425.1635.
(s, 3H). 13C NMR (125 MHz, CDCl3) δ 159.8, 147.9, 142.4, 141.3, 5-Phenylbenzo[4,5]imidazo[1,2-a]quinoline (5aa). Yield, 63% (37.1
139.4, 134.8, 129.9, 129.8, 128.9, 128.0, 127.5, 127.3, 127.0, 126.7, mg); yellow solid, mp 170-171 ℃; IR (KBr, cm-1): 1730, 1634, 1453,
1
125.5, 125.2, 124.9, 124.6, 124.2, 123.8, 123.4, 123.1, 122.9, 122.8, 1384, 1278, 1172, 1121, 1073, 749, 734, 703; H NMR (400 MHz,
121.9, 118.9, 117.0, 115.1, 114.0, 55.4. HRMS-ESI: [M+H]+ calcd for CDCl3) δ 8.67 (d, J = 8.4 Hz, 1H), 8.44 (d, J = 8.2 Hz, 1H), 8.04 (d, J =
C30H21N2O m/z 425.1654, found m/z 425.1624.
5-(Naphthalen-1-yl)phenanthro[9',10':4,5]imidazo[1,2-a]quinoline
7.9 Hz, 1H), 7.86 (d, J = 8.1 Hz, 1H), 7.78 (t, J = 7.8 Hz, 1H), 7.62 –
7.47 (m, 8H), 7.43 (t, J = 7.6 Hz, 1H). 13C NMR (150 MHz, CDCl3) δ
(3ak). Yield, 34% (30.2 mg); yellow solid, mp 252-253 ℃; IR (KBr, 147.9, 145.0, 143.4, 138.0, 135.9, 130.8, 129.7, 129.5 (2xC), 128.7
1
cm-1): 1654, 1636, 1617, 1507, 1449, 779, 750, 723; H NMR (600 (2xC), 128.5, 128.4, 124.5, 124.0, 123.2, 122.7, 120.4, 117.5, 115.5,
MHz, CDCl3) δ 8.93 (br, 1H), 8.87 (d, J = 7.5 Hz, 1H), 8.79 (d, J = 7.5 114.1. HRMS-ESI: [M+H]+ calcd for C21H15N2 m/z 295.1235, found
Hz, 1H), 8.68 – 8.64 (m, 2H), 8.05 (d, J = 7.4 Hz, 1H), 8.00 (d, J = 7.8 m/z 295.1249.
Hz, 1H), 7.92 (br, 1H), 7.81 – 7.77 (m, 2H), 7.71 – 7.65 (m, 5H), 7.57 2-Methyl-5-(p-tolyl)benzo[4,5]imidazo[1,2-a]quinoline (5ab). Yield,
– 7.48 (m, 1H), 7.47 – 7.32 (m, 3H), 7.26 (s, 1H). 13C NMR (125 MHz, 52% (33.5 mg); yellow solid, mp 241-243 ℃; IR (KBr, cm-1): 1731,
CDCl3) δ 148.0, 142.4, 140.1, 135.7, 134.5, 133.7, 132.3, 130.0, 1635, 1616, 1510, 1449, 1380, 1336, 1279, 1255, 1125, 1073, 816,
129.0, 128.9, 128.5, 128.4, 127.8, 127.6, 127.3, 127.1, 126.8, 126.5, 737; 1H NMR (400 MHz, CDCl3) δ 8.47 (s, 1H), 8.45 (d, J = 8.2 Hz, 1H),
126.3, 126.2, 125.6, 125.5, 125.3, 125.2, 124.9, 124.7, 123.9, 123.5, 8.03 (d, J = 8.0 Hz, 1H), 7.76 (d, J = 8.3 Hz, 1H), 7.58 – 7.47 (m, 3H),
123.2, 123.1, 122.9, 118.8, 118.7. HRMS-ESI: [M+H]+ calcd for 7.39 (dd, J = 32.0, 7.8 Hz, 4H), 7.25 (d, J = 10.0 Hz, 1H), 2.67 (s, 3H),
C33H21N2 m/z 445.1705, found m/z 445.1701.
2.48 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 148.3, 144.9, 143.5, 140.4,
2-Methyl-5-(p-tolyl)phenanthro[9',10':4,5]imidazo[1,2-a]quinoline 138.4, 136.0, 135.3, 130.8, 129.4 (2xC), 129.3 (2xC), 128.3, 125.3,
(3bb). Yield, 64% (54.0 mg); yellow solid, mp 256-257 ℃; IR (KBr, 124.5, 122.4, 121.0, 120.2, 116.2, 115.7, 114.1, 22.2, 21.3. HRMS-
cm-1): 1654, 1637, 1617, 1560, 755; 1H NMR (600 MHz, CDCl3) δ ESI: [M+H]+ calcd for C23H19N2 m/z 323.1548, found m/z 323.1566.
8.86 (d, J = 7.8 Hz, 1H), 8.80 (d, J = 8.0 Hz, 1H), 8.73 (d, J = 8.2 Hz, 2-Methoxy-5-(4-methoxyphenyl)benzo[4,5]imidazo[1,2-a]
1H), 8.55 (d, J = 8.0 Hz, 1H), 8.36 (s, 1H), 7.80 (d, J = 8.2 Hz, 1H), 7.76 quinoline (5ac). Yield, 37% (26.2 mg); yellow solid, mp 186-188 ℃;
(t, J = 7.4 Hz, 1H), 7.71– 7.69 (m, 1H), 7.66 (s, 1H), 7.64 – 7.55 (m, IR (KBr, cm-1): 1731, 1635, 1610, 1527, 1511, 1453, 1382, 1281,
1
2H), 7.50 (d, J = 7.9 Hz, 2H), 7.36 (d, J = 7.8 Hz, 2H), 7.23 (d, J = 8.3 1258, 1249, 1228, 1177, 1125, 1030, 840, 734; H NMR (400 MHz,
8 | Org. Biomol. Chem., 2019, 00, 1-10
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CDCl3) δ 8.38 (d, J = 8.2 Hz, 1H), 8.13 (d, J = 2.1 Hz, 1H), 8.03 (d, J = 100.3, 100.0, 55.8, 55.4, 17.3. HRMS-ESI: [M+H]+ calcd
View Article Onflioner
DOI: 10.1039/C9OB00482C
8.0 Hz, 1H), 7.83 (d, J = 9.0 Hz, 1H), 7.56 (t, J = 7.6 Hz, 1H), 7.53 – C24H21N2O2 m/z 369.1603, found m/z 369.1562.
7.41 (m, 4H), 7.13 – 6.96 (m, 3H), 4.06 (s, 3H), 3.91 (s, 3H). 13C NMR 5-([1,1'-Biphenyl]-4-yl)-8-methyl-2-phenylbenzo[4,5]imidazo[1,2-
(125 MHz, CDCl3) δ 160.9, 159.8, 148.7, 145.3, 143.0, 137.2, 130.7, a]quinoline (5bd). Yield, 44% (40.5 mg); yellow solid, mp 290-291
130.7 (2xC), 130.6, 129.8, 124.4, 122.2, 120.3, 117.2, 114.6, 114.1 ℃; IR (KBr, cm-1): 1734, 1653, 1647, 1636, 1559, 1540, 1384, 1261,
1
(2xC), 113.8, 111.0, 100.4, 55.8, 55.4. HRMS-ESI: [M+H]+ calcd for 1096, 801; H NMR (400 MHz, CDCl3) δ 8.88 (s, 1H), 8.33 (d, J = 8.1
C23H19N2O2 m/z 355.1447, found m/z 355.1464.
Hz, 1H), 8.01 (d, J = 8.4 Hz, 1H), 7.81 – 7.78 (m, 4H), 7.74 – 7.63 (m,
5-([1,1'-Biphenyl]-4-yl)-2-phenylbenzo[4,5]imidazo[1,2-a]quinoline 6H), 7.58 (t, J = 7.6 Hz, 2H), 7.54 – 7.48 (m, 3H), 7.47 – 7.36 (m, 3H),
(5ad). Yield, 61% (54.4 mg); yellow solid, mp 211-213 ℃; IR (KBr, 2.86 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 147.5, 142.8, 142.3, 141.4,
1
cm-1): 1735, 1637, 1611, 1450, 1285, 1191, 769, 754, 734; H NMR 140.4, 140.2, 137.0, 136.4, 130.5, 130.4, 130.0 (2xC), 129.3 (2xC),
(400 MHz, CDCl3) δ 8.89 (s, 1H), 8.50 (d, J = 8.0 Hz, 1H), 8.07 (d, J = 128.9 (2xC), 128.8, 128.7, 128.3, 127.7, 127.6 (2xC), 127.4 (2xC),
7.5 Hz, 1H), 8.02 (d, J = 8.4 Hz, 1H), 7.81 – 7.79 (m, 4H), 7.72 – 7.65 127.2 (2xC), 124.9, 123.0, 122.7, 122.1, 117.5, 114.0, 111.6, 17.3.
(m, 6H), 7.62 – 7.46 (m, 7H), 7.42 (t, J = 7.2 Hz, 1H). 13C NMR (150 HRMS-ESI: [M+H]+ calcd for C34H25N2 m/z 461.2018, found m/z
MHz, CDCl3) δ 148.1, 143.0, 142.9, 141.5, 140.4, 140.2, 136.9, 136.4, 461.2017.
130.9, 130.0 (2xC), 129.3 (2xC), 129.0 (2xC), 128.9, 128.4, 127.7,
127.6 (2xC), 127.5 (2xC), 127.2 (2xC), 124.7, 123.2, 122.8, 122.1,
120.5, 117.24, 117.23, 114.1, 114.0. HRMS-ESI: [M+H]+ calcd for
C33H23N2 m/z 447.1861, found m/z 447.1880.
Conflicts of interest
There are no conflicts to declare.
2-Chloro-5-(4-chlorophenyl)benzo[4,5]imidazo[1,2-a]quinoline
(5af). Yield, 21% (15.2 mg); yellow solid, mp 264-266 ℃; IR (KBr, cm-
1): 1735, 1636, 1629, 1491, 1451, 1174, 1090, 816, 751; 1H NMR
(400 MHz, CDCl3) δ 8.62 (d, J = 1.8 Hz, 1H), 8.34 (d, J = 7.6 Hz, 1H),
8.05 – 7.99 (m, 1H), 7.71 (d, J = 8.7 Hz, 1H), 7.58 – 7.51 (m, 5H), 7.46
– 7.44 (m, 2H), 7.39 (dd, J = 8.7, 1.8 Hz, 1H). 13C NMR (125 MHz,
CDCl3) δ 147.8, 145.1, 142.0, 136.5, 135.9, 134.7, 130.9, 130.8 (2xC),
129.9, 129.0 (2xC), 128.2, 124.6, 124.1, 122.9, 122.8, 120.6, 117.8,
115.7, 114.1. HRMS-ESI: [M+H]+ calcd for C21H13Cl2N2 m/z 363.0456,
found m/z 363.0454.
Acknowledgements
We are grateful for financial support from the Fundamental
Research Funds for the Central Universities (2572017DB07,
2572017AB25), Natural Science Foundation of Heilongjiang
Province (LC2018003), and Heilongjiang Postdoctoral Grant
(LBH-Q17005).
8-Methyl-5-phenylbenzo[4,5]imidazo[1,2-a]quinoline (5ba). Yield,
49% (30.2 mg); yellow solid, mp 198-199 ℃; IR (KBr, cm-1): 1752,
1629, 1608, 1450, 1388, 1327, 776, 751, 707; H NMR (400 MHz,
CDCl3) δ 8.65 (d, J = 8.4 Hz, 1H), 8.25 (d, J = 8.1 Hz, 1H), 7.85 (d, J =
8.1 Hz, 1H), 7.77 – 7.73 (m, 1H), 7.64 (s, 1H), 7.58 – 7.47 (m, 5H),
7.44 – 7.32 (m, 3H), 2.84 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 147.3,
144.3, 142.8, 138.2, 135.9, 130.4, 130.3, 129.6, 129.5 (2xC), 128.7
(2xC), 128.4, 128.3, 124.7, 123.9, 123.1, 122.5, 117.7, 115.5, 111.6,
17.3. HRMS-ESI: [M+H]+ calcd for C22H17N2 m/z 309.1392, found m/z
309.1409.
Notes and references
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1735, 1631, 1613, 1452, 1378, 1330, 1263, 814, 826, 735; H NMR
(400 MHz, CDCl3) δ 8.46 (s, 1H), 8.27 (d, J = 8.1 Hz, 1H), 7.75 (d, J =
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a]quinoline (5bc). Yield, 40% (29.5 mg); yellow solid, mp 202-204
℃; IR (KBr, cm-1): 1734, 1613, 1512, 1458, 1382, 1251, 1164, 1122,
1028, 825, 734, 668; 1H NMR (400 MHz, CDCl3) δ 8.20 (d, J = 7.5 Hz,
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3H), 7.40 – 7.34 (m, 2H), 7.06 (d, J = 8.6 Hz, 2H), 7.00 (dd, J = 9.0, 2.3
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130.1, 129.7, 124.7, 122.1, 117.2, 114.7, 114.1 (2xC), 111.3, 111.0,
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Organic & Biomolecular Chemistry
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