C-N Coupling via Antiaromatic Endocyclic Nitrenium Ions

Article abstract of DOI:10.1021/acs.joc.9b01921

Herein, we report a C-N coupling reaction via antiaromatic endocyclic nitrenium ions. The nitrenium ion intermediate was generated by a combination of iodine(III) reagent PhI(OCOCF₃)₂ and the N-H center of benzimidazole units at ambient laboratory conditions. Metal-free synthesis of benzimidazole-fused phenanthridine derivatives was achieved in good to excellent yields.

Full text of DOI:10.1021/acs.joc.9b01921

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Article
C-N Coupling via Antiaromatic Endocyclic Nitrenium Ion
Shyamal Kanti Bera, Md Toufique Alam, and Prasenjit Mal
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01921 • Publication Date (Web): 23 Aug 2019
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C-N Coupling via Antiaromatic Endocyclic Nitrenium Ion
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Shyamal Kanti Bera,‡ Md Toufique Alam‡ and Prasenjit Mal *
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School of Chemical Sciences, National Institute of Science Education and Research (NISER),
HBNI, Bhubaneswar, PO Bhimpur-Padanpur, Via Jatni, District Khurda, Odisha 752050, India,
E-mail: pmal@niser.ac.in
‡ Equal Contributing Authors
ABSTRACT:
Herein, we report a C-N coupling reaction via antiaromatic endocyclic nitrenium ion. The
nitrenium ion intermediate was generated by combination of iodine(III) reagent PhI(OCOCF3)2
and N-H center of benzimidazole units at ambient laboratory condition. Metal-free synthesis
of benzimidazole-fused phenanthridine derivatives were achieved in good to excellent yields.
TOC GRAPHIC
O
PhI(OCCF3)2
(2 equiv)
N
N
N
N
H
HFIP, rt
C
N
N
antiaromatic and endocyclic nitrenium ion
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INTRODUCTION
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The nitrenium ion chemistry rose to prominence among synthetic chemists since beginning.1
The combinations of amine or amine derivatives with hypervalent iodine(III) reagents2-8
generally produce nitrenium ion.9,10 The divalent nitrogen-containing species with six electrons
in its valence shell with positive charge on nitrogen is recognized as nitrenium ion (Figure
1a).11,12 Nitrenium ions are isoelectronic with carbene family having two non-bonding
electrons. Nitrenium ion is considered as one of the most important synthetic intermediates in
innumerable chemical transformations.13-18 Depending on the nature and stability of nitrenium
ion, many oxidative transformations are reported for the preparation of functional molecules
of interests using exocyclic nitrenium ions.19,20 Due to the electron spin orientation nitrenium
ions exist in two different forms i.e., singlet state and triplet state (Figure 1a).21 In Figure 1b,
generation of nitrenium ion is shown from the mixtures of amine or amide with iodine(III)
reagents. In general, nitrenium ion is electrophilic and highly reactive intermediate with the
formula of RR’N+.22,23
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The Hückel aromatic and antiaromatic systems consist of [4n + 2] or [4n] delocalized circuits
electrons, respectively and display ring currents around their perimeters.24 The antiaromatic
compounds are highly reactive and unstable. Therefore the existence of antiaromatic
compounds are often found in porphyrinoid systems25,26 or in large ring macrocycles.27
However, in case of small molecules the antiaromaticity is demonstrated in acene systems
having1,4-diazapentalene core.28 The mixture of iodine(III) reagent PhI(OCOCF3)2 (PIFA) and
N-H center of benzimidazole scaffold produced endocyclic nitrenium ion which has 4nπ
system and is considered to be antiaromatic. The antiaromatic transition state is possibly
stabilized via resonance. Interestingly, limited reports are available in which endocyclic and
antiaromatic nitrenium ions are directly used for synthesis.23 Falvey and co-workers
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demonstrated the existence of endocyclic and antiaromatic nitrenium ions through
spectroscopic investigations and theoretical calculations.23,29 The term endocyclic was
documented to demonstrate that nitrenium ions having cationic nitrogen contained inside a ring
and possesses antiaromatic character (Figure 1c).29 Herein, we report the synthesis of
phenanthridine derivatives via C-N coupling reaction. And, demonstrated the use of
antiaromatic and endocyclic nitrenium ions as the intermediate which were directly generated
from benzimidazole system using iodine(III) reagent PhI(OCOCF3)2 (PIFA, Figure 1d).
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a)
b)
The Nitrenium Ion
R
R
R
R
R
R
R
or
N
N
nitrenium ion
carbocation
C
R
N
R
singlet
triplet
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Generation of Nitrenium Ion
OCOCF3
I
Ph
R1
R1
Ph
R1
N
OCOCF3
H
N
I
N
R2
R2
OCOCF3
R2
-PhI
-CF3COO-
CF3COOH
exocyclic nitrenium ion
c)
Endocyclic and Anti-Aromatic Nitrenium Ion by Laser Flash Photolysis
BF4
N
h
N
N
+
CH3CN
BF4
N
2007
J. Org. Chem.
, 72, 8186
endocyclic nitrenium ion
this work
d)
C-N Coupling by Endocyclic and Anti-Aromatic Nitrenium Ion using Iodine(III) Reagent
O
N
PhI(OCCF3)2
(2 equiv)
N
N
N
N
N
H
HFIP, rt
C
antiaromatic and endocyclic nitrenium ion
Figure 1. a) The nitrenium ion. b) Generation of nitrenium ion. c) Using laser flash photolysis
Falvey and co-workers reported the generation and detection of endocyclic and antiaromatic
nitrenium ion.29 d) Our current work on the C-N coupling reaction based on the generation of
endocyclic and antiaromatic nitrenium ion using iodine(III) reagent PIFA.
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RESULTS AND DISCUSSION
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Nitrogen-containing fused heteroaromatic compounds having phenanthridine moiety are
ubiquitous in many pharmaceuticals and natural products.30 Owing to extensive π-conjugation,
these type of compounds are utilized as organic semiconductors and luminescent materials.31
For example, 1,2-disubstituted (hetero)aryl-fused benzimidazoles acts as an electron-
transporting and emission functional units.32,33 Due to the planarity of the system,
phenanthridine moiety shows the ability to bind with human telomere derived g-
quadruplexes.34 Considerable efforts have been paid for developing the methods for synthetic
transformations of (hetero)aryl-fused phenanthridines using metal catalyst.31,35,36 Moreover,
this type of methodology suffers from disadvantages like metal contamination in products,
reusability of metal catalyst, requirements of multistep paths, etc.37 We anticipate that our
current N-H/C-H arylation method (Figure 1c) using PIFA in 1,1,1,3,3,3-hexafluoro-2-
propanol (HFIP) for the preparation of benzimidazole-fused phenanthridines can be considered
as the easiest approach known in literature.
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Towards optimization of the reaction condition, compound 2-([1,1'-biphenyl]-2-yl)-5,6-
dichloro-1H-benzo[d]imidazole (1e) was chosen as a model substrate (Table 1). When 1e was
treated with 2.0 equiv of PIFA in dichloromethane, the product 2e was isolated in 57% yield
after 20 h of stirring at room temperature (entry 1). However, using polar protic solvent such
as ethanol (EtOH) and methanol (MeOH), trace amount of product formation was observed.
However, in water no product was obtained (entry 10). When the reaction was carried out in
solvents DCE (1,2-dichloroethane), TFE (2,2,2-trifluoroethanol), CH3CN (acetonitrile) and
DMF, yield of the products were found to be poor. Contrastingly, in non-polar solvents like
benzene and toluene, 70% and 40% yield of final products were obtained, respectively. In this
reaction, HFIP was found to be the best among the solvents examined (entry 7). The reaction
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did not proceed in absence of any oxidant (entry 16). Upon lowering the equivalence of PIFA,
inferior results were obtained (entries 17-18). Attempts to the use of PhI(OAc)2 (PIDA) instead
of PIFA did not make any appreciable change in yield (entry 19). The oxidizing ability of
PIDA is much less than that of PIFA. In case of PIDA, under the stander condition 44% yield
of final products were obtained and 52% of the starting material was recovered. Use of
molecular iodine was also found to be unsuccessful (entry 20). Finally, the most appropriate
condition was recognized when the reaction was performed using PIFA (2.0 equiv) in HFIP.
Under this optimized condition, the final product 11,12-dichlorobenzo[4,5]imidazo[1,2-
f]phenanthridine (2e) was isolated in near quantitative (98%) yield within 20 h at room
temperature (entry 7). In addition, using PhIO the product 2e was obtained in 48% yield (entry
21).
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Table 1. Condition Optimization.a
Cl
Cl
Cl
Cl
N
N
N
PIFA
HFIP, rt, 20 h
N
H
1e
2e
Entry
Reagent (equiv)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
Solvent
DCM
Yield (%)b
1
57
28
38
70
40
25
98
60
35
2
DCE
3
CH3CN
Benzene
Toluene
TFE
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HFIP
8
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DMF
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-
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PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
PIFA (2)
EtOH
07
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05
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MeOH
Acetone
EtOAc
HFIP:DCM (1:1)
HFIP
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d
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-
-
PIFA (1)
PIFA (1.5)
PIDA (2)
I2 (2)
HFIP
67
80
44
HFIP
HFIP
c
HFIP
-
PhIO (2)
HFIP
48
aReaction conditions: 0.176 mmol of 1e and 0.353 mmol of PIFA (2 equiv) in 1.0 mL HFIP at
b
room temperature for 20 h. Yield of isolated product after purification through silica-gel
column chromatography. cNo reaction. dWithout any reagent.
Under standard conditions, the substrate scope was explored for the synthesis of highly
substituted fused heterocycles via C-N bond formation reaction. Symmetrically substituted or
disubstituted benzimidazoles having various neutral, electron rich and electron poor functional
groups could be efficiently converted into benzimidazole-fused phenanthridine derivatives
(Figure 2). Benzimidazoles bearing ethyl, fluoro, acetyl groups of the 2-aryl moiety afforded
2b, 2c and 2d with 96%, 95% and 94%, respectively. Similarly, the unsubstituted aryl skeleton
at the 2-position of benzimidazole produced 2a with 91% yield of product. Again the
substitutions in 2-aryl moiety by electron withdrawing (fluoro, chloro, acetyl, trifluoromethyl),
as well as electron donating groups (such as ethyl, tbutyl) of the 5,6-dichloro benzimidazoles,
could be successfully converted to corresponding products (2f- 2k) in good to excellent yields.
t
However, 5,6-dimethyl benzimidazoles with a variety of substituents (ethyl, butyl, fluoro,
chloro and acetyl) at the 2-aryl group also afforded the respective product (2m-2q) in good
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yields. The unsubstituted aryl group at 2-position of 5,6-dichloro and 5,6-dimethyl
benzimidazoles gave 2e and 2I with 98% and 96% yield, respectively. The incorporation of
the electron withdrawing fluoro group in the meta-position of the 2-aryl moiety of 5,6-dichloro
and 5,6-dimethyl benzimidazoles correspondingly provided 2r and 2s with 95% and 94% yield,
respectively. Overall, electron deficient functional group containing substrates took longer time
than that of electron rich substrates. Notably, substrate 1e was prepared by the reaction of
commercially available o-phenylene diamines and formylbiphenyl derivatives in presence of
dimethyl formamide (DMF) as a solvent at 80 ºC (supporting information).
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Ar2
Ar3
N
N
N
NH2
NH2
80 oC
Ar2
Ar1
Ar2
Ar1
OHC
PIFA (2 equiv)
HFIP, rt
Ar1
+
N
DMF, 8 h
H
7
Ar3
Ar3
1
2
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N
N
N
N
N
N
N
N
F
H3COC
Et
2a
, 91%, 28 h
2d
, 94%, 48 h
2c
, 95%, 24 h
2b,
96%, 22 h
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
N
N
N
N
N
N
N
N
tBu
Cl
Et
2e
, 98%, 20 h
2f
, 93%, 19 h
2g
, 94%, 20 h
2h
, 92%, 42 h
Cl
Me
Me
Cl
Cl
Cl
N
N
N
N
N
N
N
N
Cl
Cl
H3COC
F
F3C
2j
, 93%, 36 h
2k
2l
, 96%, 19 h
2i
, 92%, 24 h
, 94 %, 42 h
Me
Me
Me
Me
Me
Me
N
N
N
N
N
N
tBu
Et
F
2m
, 94%, 21 h
2n
, 82%, 22 h
2o
, 92%, 24 h
CCDC 1910734
F
F
Me
Me
Me
Me
Me
Me
Cl
Cl
N
N
N
N
N
N
N
N
Cl
H3COC
2r
, 95%, 23 h
2p
, 89%, 22 h
2q
, 82%, 28 h
2s
, 94%, 22 h
Figure 2. Functional-group tolerance in synthesis of benzimidazole-fused phenanthridines.
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N
N
N
Ar
PIFA (2 equiv)
HFIP, rt
Ar
N
H
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Me
O2N
+
N
N
N
N
N
N
N
N
Me
O2N
+
2b'
2a'
, 91%, 32 h, ratio 2:1
, 96%, 20 h, ratio 5:3
Me
N
O2N
N
N
N
N
N
N
N
O2N
+
Me
+
Et
Et
Et
Et
2d',
93%, 24 h, ratio 5:2
2c',
92%, 20 h, ratio 5:2
F
F
Me
N
N
N
N
Me
N
N
Me
+
N
N
Me
+
F
F
2f',
82%. 18h, ratio 10:1
2e',
94%, 21 h, ratio 2:1
Me
N
N
N
N
Me
+
H3COC
H3COC
87%, 28 h, ratio 5:2
2g',
Figure 3. Inseparable mixture of regioisomers.
The substrates scope for this methodology was further extended to unsymmetrically substituted
or mono substituted benzimidazoles, which furnished the mixture of regioisomers under
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standard reaction condition (Figure 3). Thus, for the mono substituted benzimidazoles, there
are two possibilities for the formation of products. One is 11-substituted and another is 12-
substituted (hetero)aryl-fused phenanthridines. The aryl group at 2-position of 3-methyl and 3-
nitro benzimidazoles led to 5:3 and 2:1 mixture of regioisomers 2a' and 2b' with 96% and 91%
yield, respectively. Similarly, 3-methyl and 3-nitro benzimidazoles bearing ethyl group in the
2-aryl moiety also afforded 5:2 mixture of regioisomers 2c' and 2d' with excellent yield of
products. Nevertheless, the electron withdrawing fluoro group in the meta-position of 2-aryl
moiety of 3-methyl benzimidazole gave 10:1 mixture of regioisomers 2f'. Again, 3-methyl
benzimidazoles bearing fluoro and acetyl group in the 2-aryl moiety also produced 2:1 and 5:2
mixture of regioisomers 2e' and 2g' with 94% and 87% yield of products.
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To establish the mechanism of the reaction, control experiments were performed which are
shown in (Figure 4). In presence of TEMPO19 at standard condition, reaction proceeded
smoothly and giving 98% of the product as isolated (based on recovery yield, Figure 4a). This
fact clearly indicates that radical pathway for the reaction was not operative. For the generation
of nitrenium ion the presence of N-H group in the benzimidazole core was one of the essential
criteria. After the removal of N-H bond in presence of iodine(III) reagent the antiaromatic
transition state was created. This hypothesis was further proved when N-Me substituted
benzimidazole moiety (2ab) was found to be unreactive under standard condition (Figure 4b).
Based on control experiments and literature precedence38 a plausible mechanism is proposed
in Figure 4c. Initially, substrate 1a was reacted with PIFA to form ammonium ion intermediate
3,39 which could undergo proton abstraction by trifluoroacetate ion and followed by elimination
of trifluoroacetic acid and iodobenzene to produce nitrenium ion intermediate 4. Following,
the nitrenium ion 4 underwent C-N bond formation via cyclization to form the Wheland
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intermediate 5 or 6.40,41 Finally, the product 2a was formed after elimination of one hydrogen
by trifluoroacetate anion. Trifluoroacetic acid is generated in the reaction mixture as a by-
product, which can also protonate the N-H proton that’s why higher concentration (2 equiv) of
oxidant PIFA was required for the conversion.
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a)
Cl
Cl
Cl
Cl
N
N
N
TEMPO (1 equiv)
PIFA (2 equiv)
N
H
HFIP, rt, 20 h
a
1e
2e
, 98%
b)
Cl
Cl
N
PIFA (2 equiv)
HFIP, rt, 20 h
N
No Reaction
Me
2ab
c)
F3COCO
O
I
N
N
N
PhI(OCCF3)2
N
N
H
N
H
CF3COO
CF3COOH
PhI
nitrenium ion
4
1a
3
N
N
N
N
N
N
H
CF3COO
5
2a
6
Figure 4. a) and b) Control experiments. c) Plausible mechanism.
Towards exploring the synthetic utility of the method, we have carried out the same
transformation using PhI (iodobenzene, 1.0 equiv)-mCPBA (1.5 equiv) in HFIP as the
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organocatalytic condition42 and the product 2e was isolated in 94% (based on recovered starting
materials, Figure 5a). It is established in literature that PhIO is the reactive intermediate from
PhI-mCPBA combination,42 however, HFIP stabilizes the iodinium intermediates.43,44 Similar
observation we have also made when PhI was treated with mCPBA in presence of HFIP
(supporting information, Figure S107). Furthermore, the efficiency of the method was verified
by scaling up the reaction up to ~4.0 mmol of substrate 1c (gram scale, Figure 5b). Under
optimized condition when the reaction was performed with 2-(4'-fluoro-[1,1'-biphenyl]-2-yl)-
1H-benzo[d]imidazole 1c, fluorobenzo[4,5]imidazo[1,2-f]phenanthridine 2c was isolated in
96% of yield after 20 h of reaction time.
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a)
PhI (1.0 equiv)
mCPBA (1.5 equiv)
Cl
Cl
Cl
Cl
N
N
N
N
H
HFIP, rt, 20 h
a
1e
(80 mg, 0.24 mmol)
2e,
94%
b)
N
N
N
PIFA (2 equiv)
N
H
rt, 20 h
HFIP (12 mL)
F
F
1c
2c
, 96% (1.12 gm)
(1.16 gm, 4.03 mmol)
Figure 5. a) Synthesis of benzimidazole-fused phenanthridines in organocatalytic condition.
a
b) Gram scale synthesis of 2-fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2c). Based on
recovered starting material.
Due to extended π-conjugation nitrogen-containing fused heteroaromatic compounds become
potential fluorophores and shown to have strong luminescence behavior. For selected
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benzimidazole-fused phenanthridines (2f, 2d, 2o, 2r, 2a) absorption and emission properties
are shown in Figure 6. For the acetyl containing benzimidazole-fused phenanthridine 2d, high
bathochromically shifted emission behavior was observed.
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a)
b)
2f
2d
2o
2r
1.2
0.8
0.4
0.0
2a
250
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400
400
500
600
Wavelenth (nm)
Figure 6. a) Absorption and b) emission spectra for selected compounds. Concentration: 3 ×
10-5 M in dichloromethane.
CONCLUSION
In summary, we have shown here that direct C-N coupling reaction could be done via
antiaromatic endocyclic nitrenium ion and subsequently synthesis of fused heterocycles like
benzimidazole-fused phenanthridines were achieved under metal free condition. During the
synthesis we have avoided the use of any expensive catalyst (mainly metal based), harsh
condition and the reactions were performed using PIFA as a sole reagent. Additionally, ambient
condition, commercial viability of iodide reagent, made the methodology more synthetically
attractive towards construction of heterocycles. We anticipate that this approach can provide
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direct access to various heteroaromatic compounds which might be useful in the synthesis of
complex structural motifs.
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EXPERIMENTAL SECTION
General Information. Commercially available reagents and solvents were used as received.
Column chromatographic purifications of the compounds were performed using silica gel
(mesh 230–400) and hexane – ethyl acetate solvent mixtures. NMR spectra were recorded on
a 400 MHz or 700 MHz instrument at 25 °C. The chemical shift values are reported in parts
per million (ppm) with respect to residual trichloromethane (7.26 ppm for 1H and 77.16 ppm
for 13C). The peak patterns are designated as follows: s: singlet; d: doublet; t: triplet; q: quartet;
m: multiplet; dd: doublet of doublets; td: triplet of doublets; br s: broad singlet. The coupling
constants (J) are reported in hertz (Hz). High-resolution mass spectra (HR-MS) were recorded
on an ESI-TOF (time of flight) mass spectrometer. Infrared spectral data are reported in wave
number (cm-1). FT-IR spectra were recorded after making thin layer of the compounds on the
surface of NaCl crystal using dichloromethane. Melting points of the compounds were
determined using a digital melting point apparatus and uncorrected.
Representative Procedure for Preparation of 2-([1,1'-biphenyl]-2-yl)-5,6-dichloro-1H-
benzo[d]imidazole 1e.45 A solution of [1,1'-biphenyl]-2-carbaldehyde (500 mg, 2.82 mmol)
and the appropriate o-phenylenediamine (2.82 mmol) in DMF (5 mL) was heated at 80 °C. The
reaction mixture was allowed to stir for 8 h and resulting solution was brought to room
temperature and then extracted with ethyl acetate (EtOAc). The organic layer washed with
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brine, dried over anhydrous Na2SO4 and concentrated under reduced pressure. The crude
product was purified by silica gel column chromatography with n-Hexane-EtOAc. The
compound 1e was obtained as white solid. (914 mg, 95% yield), Rf = 0.45 (hexane/ethyl acetate
4:1).
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Representative Procedure for Preparation of 11,12-Dichlorobenzo[4,5]imidazo[1,2-
f]phenanthridine (2e). To a stirred solution of 2-([1,1'-Biphenyl]-2-yl)-5,6-dichloro-1H-
benzo[d]imidazole 1e (60 mg, 0.176 mmol), in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) (2.0
mL), PIFA (152 mg, 0.35 mmol) was added slowly at room temperature. The reaction mixture
was allowed to stir until completion. Progress of reaction was monitored by TLC using ethyl
acetate and hexane as eluent. After the completion of reaction (20 h) resulting solution was
evaporated to dryness. The crude residue was purified on silica gel column chromatography
(20% EtOAc in hexane) to get the pure product 11, 12-dichlorobenzo[4,5]imidazo[1,2-
f]phenanthridine 2e (59 mg, yield 98%).
2-([1,1'-Biphenyl]-2-yl)-1H-benzo[d]imidazole (1a). Rf = 0.70 (hexane/ethyl acetate 7:3);
white solid; yield 71% (440 mg); mp 214−216 °C (lit.46 mp 212-213 °C); 1H NMR (700 MHz,
DMSO-d6) δ 12.08 (s, 1H), 7.72 (d, J = 7.7 Hz, 1H), 7.61 (t, J = 7.0 Hz, 1H), 7.59 – 7.55 (m,
1H), 7.53 (t, J = 8.4 Hz, 2H), 7.35 – 7.31 (m, 1H), 7.25 (d, J = 7.7 Hz, 3H), 7.19 (d, J = 6.3 Hz,
2H), 7.16 – 7.11 (m, 2H); 13C{1H} NMR (175 MHz, DMSO-d6) δ 152.1, 143.5, 141.0, 140.2,
134.5, 131.1, 130.5, 130.2, 129.9, 128.8, 128.1, 127.4, 127.1, 122.1, 121.2, 118.9, 111.3; IR
(KBr)
= 3431, 3061, 2981, 2929, 2882, 2733, 1469, 1446, 1432, 1275 cm-1; HR-MS (ESI-
TOF) m/z calcd for C19H15N2 [M + H]+ 271.1230, found 271.1247.
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2-(4'-Ethyl-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole (1b). Rf = 0.45 (hexane/ethyl
acetate 4:1 ); white solid; yield 72% (138 mg); mp 230 °C; 1H NMR (700 MHz, DMSO-d6) δ
12.07 (s, 1H), 7.68 (d, J = 7.0 Hz, 1H), 7.62 – 7.56 (m, 2H), 7.50 (t, J = 7.0 Hz, 2H), 7.35 –
7.32 (m, 1H), 7.15 – 7.12 (m, 2H), 7.11-7.08 (m, 4H), 2.55 (q, J = 7.7 Hz, 2H), 1.13 (t, J = 7.7
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Hz, 3H); C{1H} NMR (175 MHz, DMSO-d6) δ 152.3, 143.5, 142.5, 140.9, 137.5, 134.5,
131.2, 130.5, 130.1, 129.9, 128.7, 127.6, 127.1, 122.1, 121.2, 118.9, 111.3, 27.7, 15.3; IR (KBr)
= 3425, 3058, 2969, 2924, 2857, 1450, 1410, 1282, 1098 cm-1; HR-MS (ESI-TOF) m/z
calcd for C21H19N2 [M + H]+ 299.1543, found 299.1530.
2-(4'-Fluoro-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole (1c). Rf = 0.60 (hexane/ethyl
acetate 7:3 ); white solid; yield 97% (387 mg); mp 254 °C; 1H NMR (700 MHz, DMSO-d6) δ
12.14 (s, 1H), 7.73 (d, J = 7.0 Hz, 1H), 7.60 (t, J = 7.7, Hz, 1H), 7.49 – 7.58 (m, 3H), 7.36 (s,
1H), 7.21-7.19 (m, 2H), 7.14 (d, J = 4.2 Hz, 2H), 7.09 (t, J = 8.4 Hz, 2H); 13C{1H} NMR (175
1
4
MHz, DMSO-d6) δ 161.9 (d, JC, F = 243.9 Hz), 152.3, 143.9, 140.4, 137.0 (d, JC, F = 3.1
Hz), 135.0, 131.5, 131.2 (d, 3JC, F = 8.2 Hz), 131.0, 130.6, 130.4, 128.0, 122.6, 121.8, 119.3,
115.4 (d, 2JC, F = 21.4 Hz), 111.8; IR (KBr)
= 3440, 3060, 2922, 1445, 1423, 1279, 1227,
1163 cm-1; HR-MS (ESI-TOF) m/z calcd for C19H14FN2 [M + H]+ 289.1136, found 289.1149.
1-(2'-(1H-Benzo[d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)ethan-1-one (1d). Rf
=
0.50
(hexane/ethyl acetate 7:3 ); white solid; yield 72% (311 mg); mp 276 °C; 1H NMR (700 MHz,
DMSO-d6) δ 12.26 (s, 1H), 7.84 (d, J = 8.4 Hz, 2H), 7.77 (dd, J = 7.7, 0.7 Hz, 1H), 7.65 (td, J
= 7.7, 1.4 Hz, 1H), 7.59 (td, J = 7.7, 1.4 Hz, 1H), 7.56 (d, J = 7.7 Hz, 2H), 7.36 (d, J = 7.0 Hz,
1H), 7.33 (d, J = 8.4 Hz, 2H), 7.11 – 7.16 (m, 2H), 2.53 (s, 3H); 13C{1H} NMR (175 MHz,
DMSO-d6) δ 197.6, 151.7, 145.1, 143.5, 139.9, 135.3, 134.6, 131.2, 130.6, 130.2, 130.0, 129.2,
128.1, 128.1, 122.3, 121.4, 118.9, 111.4, 26.7; IR (KBr)
= 3418, 2924, 2847, 1678, 1651,
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1381, 1269, 1098 cm-1; HR-MS (ESI-TOF) m/z calcd for C21H17N2O [M + H]+ : 313.1335,
found 313.1325.
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2-([1,1'-Biphenyl]-2-yl)-5,6-dichloro-1H-benzo[d]imidazole (1e). Rf = 0.45 (hexane/ethyl
acetate 4:1); white solid; yield 95% (914 mg); mp 249-251 °C; 1H NMR (700 MHz, DMSO-
d6) δ 12.47 (s, 1H), 7.85 (s, 1H), 7.72 (d, J = 7.0 Hz, 1H), 7.66 – 7.63 (m, 1H), 7.59 (s, 1H),
7.55 (t, J = 7.0 Hz, 2H), 7.26 (d, J = 7.0 Hz, 3H), 7.14 – 7.17 (m, 2H); 13C{1H} NMR (175
MHz, DMSO-d6) δ 154.8, 143.1, 141.1, 139.8, 134.0, 131.0, 130.6, 130.4, 129.2, 128.7, 128.3,
127.5, 127.3, 124.5, 123.9, 120.0, 112.7 ; IR (KBr)
= 3095, 2922, 2842, 2364, 2337, 1448,
1428, 1388, 1296, 1101 cm-1; HR-MS (ESI-TOF) m/z calcd for C19H13Cl2N2 [M + H]+
339.0450, found 339.0463.
5,6-Dichloro-2-(4'-ethyl-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole (1f). Rf = 0.60
(hexane/ethyl acetate 4:1); white solid; yield 97% (307 mg); mp 285 °C; 1H NMR (700 MHz,
DMSO-d6) δ 12.46 (s, 1H), 7.87 (s, 1H), 7.69 (d, J = 7.7 Hz, 1H), 7.64 – 7.61 (m, 1H), 7.60 (s,
1H), 7.52 (t, J = 7.7 Hz, 2H), 7.07 – 7.12 (m, 4H), 2.55 (q, J = 7.7 Hz, 2H), 1.14 (t, J = 7.7 Hz,
3H); 13C{1H} NMR (175 MHz, DMSO-d6) δ 154.9, 143.1, 142.7, 140.9, 137.1, 134.0, 131.1,
130.5, 130.4, 129.1, 128.6, 127.7, 127.2, 124.5, 123.9, 120.0, 112.7, 27.7, 15.3; IR (KBr)
=
3420, 2966, 2929, 1445, 1428, 1386, 1296, 1096 cm-1; HR-MS (ESI-TOF) m/z calcd for
C21H17Cl2N2 [M + H]+ 367.0763, found 367.0764.
2-(4'-(Tert-butyl)-[1,1'-biphenyl]-2-yl)-5,6-dichloro-1H-benzo[d]imidazole (1g). Rf = 0.45
(hexane/ethyl acetate 4:1); white solid; yield 79% (315 mg); mp 215 °C; 1H NMR (700 MHz,
DMSO-d6) δ 12.49 (s, 1H), 7.87 (s, 1H), 7.68 (d, J = 7.7 Hz, 1H), 7.63 – 7.58 (m, 2H), 7.54 –
7.50 (m, 2H), 7.28 (d, J = 8.4 Hz, 2H), 7.11 (d, J = 7.7 Hz, 2H), 1.23 (s, 9H); 13C{1H} NMR
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(175 MHz, DMSO-d6) δ 155.0, 149.6, 143.2, 140.8, 136.9, 134.1, 131.2, 130.7, 130.4, 129.1,
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128.4, 127.3, 125.1, 124.5, 124.0, 120.1, 112.7, 34.3, 31.1; IR (KBr)
= 3417, 2969, 1650,
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1445, 1383, 1097 cm-1; HR-MS (ESI-TOF) m/z calcd for C23H20Cl2N2 [M + H]+ 395.1076,
found 395.1084.
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5,6-Dichloro-2-(3'-chloro-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole (1h). Rf = 0.60
(hexane/ethyl acetate 4:1); pale yellow solid; yield 96% (205 mg); mp 226 °C; 1H NMR (700
MHz, DMSO-d6) δ 12.60 (s, 1H), 7.86 (s, 1H), 7.76 (d, J = 7.0 Hz, 1H), 7.67 – 7.62 (m, 2H),
7.60 – 7.55 (m, 2H), 7.32 (dd, J = 8.4, 1.4 Hz, 1H), 7.29 (s, 1H), 7.24 (t, J = 7.7 Hz, 1H), 7.00
(d, J = 7.7 Hz, 1H); 13C{1H} NMR (175 MHz, DMSO-d6) δ 154.4, 143.1, 142.0, 139.6, 134.1,
132.9, 131.1, 130.7, 130.6, 130.0, 129.2, 128.6, 128.2, 127.6, 127.2, 124.7, 124.1, 120.1, 112.8;
IR (KBr)
= 3418, 3065, 2924, 2857, 1594, 1382, 1296, 1096 cm-1; HR-MS (ESI-TOF) m/z
calcd for C19H12Cl3N2 [M + H]+ 373.0061, found 373.0048.
5,6-Dichloro-2-(4'-fluoro-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole (1i). Rf = 0.40
(hexane/ethyl acetate 4:1); white solid; yield 93% (280 mg); mp 224 °C; 1H NMR (400 MHz,
DMSO-d6) δ 12.53 (brs, 1H), 7.73 (d, J = 7.2 Hz, 3H), 7.67 – 7.59 (m, 2H), 7.54 (dd, J = 12.4,
7.2 Hz, 3H), 7.21 – 7.15 (m, 3H), 7.12 – 7.05 (m, 3H); 13C{1H} NMR (100 MHz, DMSO-d6)
δ 161.6 (d, 1JC,F = 244.3 Hz), 154.6 (×2), 142.9, 140.0, 136.2 (d, 4JC,F = 3.2 Hz), 134.1, 131.0,
130.8 (d, 3JC,F = 8.3 Hz), 130.6, 130.4, 129.2, 127.7, 124.3, 120.0, 115.1 (d, 2JC,F = 21.5 Hz),
112.7; IR (KBr)
= 3437, 2947, 2855, 1522, 1485, 1455, 1425, 1396, 1304, 1222, 1158,
1106 cm-1; HR-MS (ESI-TOF) m/z calcd for C19H12Cl2FN2 [M + H]+ 357.0356, found
357.0372.
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1-(2'-(5,6-Dichloro-1H-benzo[d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)ethan-1-one (1j). Rf =
0.40 (hexane/ethyl acetate 4:1); white solid; yield 92% (296 mg); mp 285 °C; 1H NMR (700
MHz, DMSO-d6) δ 12.63 (s, 1H), 7.85 (d, J = 8.4 Hz, 3H), 7.77 (d, J = 7.0 Hz, 1H), 7.70 –
7.65 (m, 1H), 7.64 – 7.55 (m, 3H), 7.30 (d, J = 8.4 Hz, 2H), 2.53 (s, 3H); 13C{1H} NMR (175
MHz, DMSO-d6) δ 197.6, 154.4, 144.7, 143.1, 140.1, 135.4, 134.1, 131.1, 130.7, 130.5, 129.2,
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129.1, 128.3, 128.1, 124.7, 124.1, 120.1, 112.8, 26.7; IR (KBr)
= 3417, 2924, 2855, 1685,
1653, 1443, 1262, 1096 cm-1; HR-MS (ESI-TOF): m/z calcd for C21H15Cl2N2O [M + H]+ :
381.0556, found: 381.0570.
5,6-Dichloro-2-(4'-(trifluoromethyl)-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole (1k). Rf
= 0.40 (hexane/ethyl acetate 4:1); white solid; yield 93% (320 mg); mp 286 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.66 (s, 1H), 7.84 (s, 1H), 7.79 (d, J = 7.6 Hz, 1H), 7.71 – 7.67 (m, 1H),
7.66 – 7.60 (m, 4H), 7.59 (d, J = 7.6 Hz, 1H), 7.38 (d, J = 8.0 Hz, 2H); 13C{1H} NMR (100
MHz, DMSO-d6) δ 154.2, 144.2, 143.1, 139.6, 134.0, 131.1, 130.8, 130.5, 129.6, 129.2, 128.4,
127.8, 127.4, 125.6, 125.0 (q, 3JC,F = 3.9 Hz), 124.7, 124.1, 120.1, 112.8; IR (KBr)
= 3440,
2922, 2850, 1653, 1324, 1128, 1078 cm-1; HR-MS (ESI-TOF): m/z calcd for C20H12N2Cl2F3
[M + H]+ : 407.0324, found: 407.0324.
2-([1,1'-Biphenyl]-2-yl)-5,6-dimethyl-1H-benzo[d]imidazole (1l). Rf = 0.40 (hexane/ethyl
1
acetate 4:1); orange-red solid; yield 98% (538 mg); mp 248-250 °C; H NMR (700 MHz,
DMSO-d6) δ 11.81 (s, 1H), 7.68 (dd, J = 7.7, 1.4 Hz, 1H), 7.62 – 7.57 (m, 1H), 7.51 (t, J = 7.0
Hz, 2H), 7.31 (s, 1H), 7.24 (d, J = 7.0 Hz, 3H), 7.18 – 7.14 (m, 2H), 7.08 (s, 1H), 2.27 (s, 6H);
13C{1H} NMR (175 MHz, DMSO-d6) δ 151.1, 142.2, 140.9, 140.2, 133.1, 131.0, 130.6, 130.5,
130.4, 129.7, 129.4, 128.7, 128.1, 127.3, 127.0, 118.9, 111.30, 19.9 (×2); IR (KBr)
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3057, 2974, 2921, 2696, 1455, 1431, 1402, 1311, 1267, 1165, 1108 cm-1; HR-MS (ESI-TOF)
m/z calcd for C21H19N2 [M + H]+ 299.1543, found 299.1548.
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2-(4'-Ethyl-[1,1'-biphenyl]-2-yl)-5,6-dimethyl-1H-benzo[d]imidazole (1m). Rf = 0.50
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(hexane/ethyl acetate 4:1); white solid; yield 88% (306 mg); mp 218-220 °C; H NMR (700
MHz, DMSO-d6) δ 11.80 (s, 1H), 7.65 (d, J = 7.0 Hz, 1H), 7.57 (t, J = 7.7 Hz, 1H), 7.48 (t, J
= 7.7 Hz, 2H), 7.33 (s, 1H), 7.08 (s, 5H), 2.55 (q, J = 7.0 Hz, 2H), 2.27 (s, 6H), 1.14 (t, J = 7.7
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Hz, 3H); C{1H} NMR (175 MHz, DMSO-d6) δ 151.3, 142.4, 142.2, 140.8, 137.5, 133.1,
131.1, 130.5, 130.4, 130.4, 129.6, 129.4, 128.6, 127.5, 127.0, 118.9, 111.3, 27.7, 19.9 (×2),
15.3; IR (KBr)
= 3438, 2964, 2925, 1633, 1455, 1407, 1312, 1264 cm-1; HR-MS (ESI-
TOF) m/z calcd for C23H23N2 [M + H]+ 327.1856, found 327.1861.
2-(4'-(Tert-butyl)-[1,1'-biphenyl]-2-yl)-5,6-dimethyl-1H-benzo[d]imidazole (1n). Rf = 0.40
(hexane/ethyl acetate 4:1); white solid; yield 82% (320 mg); mp 205 °C. 1H NMR (700 MHz,
DMSO-d6) δ 11.87 (s, 1H), 7.62 (d, J = 7.5 Hz, 1H), 7.57 (dd, J = 10.8, 4.2 Hz, 1H), 7.48 (dd,
J = 15.6, 7.8 Hz, 2H), 7.32 (s, 1H), 7.26 (d, J = 8.4 Hz, 2H), 7.12 (d, J = 8.4 Hz, 2H), 7.08 (s,
1H), 2.27 (s, 6H), 1.22 (s, 9H). 13C{1H} NMR (175 MHz, DMSO-d6) δ 151.4, 149.4, 142.2,
140.6, 137.3, 133.2, 131.3, 130.7, 130.6, 130.3, 129.7, 129.5, 128.5, 127.1, 125.0, 118.9, 111.3,
34.2, 31.1, 20.0 (×2); IR (KBr)
= 3439, 2962, 2924, 2860, 1457, 1405, 1316, 1269, 1111,
1002 cm-1; HR-MS (ESI-TOF) m/z calcd for C25H27N2 [M + H]+ 356.2202, found 356.2214.
2-(4'-Fluoro-[1,1'-biphenyl]-2-yl)-5,6-dimethyl-1H-benzo[d]imidazole (1o). Rf = 0.40
(hexane/ethyl acetate 4:1); white solid; yield 96% (337 mg); mp 230 °C; 1H NMR (700 MHz,
DMSO-d6) δ 11.85 (s, 1H), 7.71 – 7.67 (m, 1H), 7.58 (td, J = 7.7, 1.4 Hz, 1H), 7.53 – 7.47 (m,
2H), 7.32 (s, 1H), 7.18 (dd, J = 8.4, 5.6 Hz, 2H), 7.08 (dd, J = 16.8, 7.7 Hz, 3H), 2.27 (s, 6H);
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13C{1H} NMR (175 MHz, DMSO-d6) δ 161.4 (d, 1JC,F = 243.7 Hz), 150.9, 142.2, 139.8, 136.6,
133.1, 131.0, 130.8, 130.7, 130.4, 130.4, 129.7, 129.5, 127.5, 119.0, 114.9 (d, 2JC,F = 21.4 Hz),
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111.3, 20.0, 19.9 (×2); IR (KBr)
= 3048, 2971, 2921, 2857, 2689, 1514, 1462, 1405, 1316,
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1227, 1160 cm-1; HR-MS (ESI-TOF) m/z calcd for C21H18FN2 [M + H]+ 317.1448, found
317.1422.
2-(3'-Chloro-[1,1'-biphenyl]-2-yl)-5,6-dimethyl-1H-benzo[d]imidazole (1p). Rf = 0.40
(hexane/ethyl acetate 4:1); white solid; yield 93% (340 mg); mp 232 °C; 1H NMR (700 MHz,
DMSO-d6) δ 11.95 (s, 1H), 7.72 (dd, J = 7.7, 1.4 Hz, 1H), 7.60 (td, J = 7.7, 1.4 Hz, 1H), 7.56
– 7.49 (m, 2H), 7.34 – 7.25 (m, 3H), 7.22 (t, J = 8.4 Hz, 2H), 7.00 (d, J = 7.7 Hz, 1H), 2.27 (s,
6H); 13C{1H} NMR (175 MHz, DMSO-d6) δ 150.6, 142.5, 142.2, 139.3, 133.0, 132.7, 131.0,
130.5, 130.4, 129.8, 129.7, 128.7, 128.6, 128.1, 128.0, 127.5, 126.9, 118.9, 111.4, 20.0 (×2);
IR (KBr)
= 3440, 3058, 2969, 2917, 2867, 1601, 1457, 1408, 1319, 1262, 1081 cm-1; HR-
MS (ESI-TOF) m/z calcd for C21H18ClN2 [M + H]+ 333.1153, found 333.1164.
1-(2'-(5,6-Dimethyl-1H-benzo[d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)ethan-1-one (1q). Rf
= 0.40 (hexane/ethyl acetate 7:3); white solid; yield 73% (272 mg); mp 278 °C; 1H NMR (700
MHz, DMSO-d6) δ 12.00 (s, 1H), 7.82 (d, J = 8.4 Hz, 2H), 7.72 (d, J = 7.0 Hz, 1H), 7.62 (td,
J = 7.7, 1.4 Hz, 1H), 7.57 (dd, J = 7.7, 1.4 Hz, 1H), 7.54 (d, J = 7.7 Hz, 1H), 7.29 (d, J = 8.4
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Hz, 3H), 7.10 (s, 1H), 2.52 (s, 3H), 2.26 (s, 6H); C{1H} NMR (175 MHz, DMSO-d6) δ
197.6, 150.8, 145.2, 142.2, 139.9, 135.2, 133.1, 131.1, 130.8, 130.5, 130.4, 129.8, 129.6, 129.1,
128.1, 128.0, 119.0, 111.4, 26.7, 19.9 (×2); IR (KBr)
= 3440, 2966, 2924, 2862, 2681,
1681, 1651, 1605, 1403, 1353, 1267, 1009 cm-1; HR-MS (ESI-TOF) m/z calcd for C23H21N2O
[M + H]+ 341.1648, found 341.1660.
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5,6-Dichloro-2-(4-fluoro-[1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole (1r). Rf = 0.50
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6
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(hexane/ethyl acetate 4:1); white solid; yield 84% (255 mg); mp 258-260 °C; H NMR (700
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MHz, DMSO-d6) δ 12.57 (s, 1H), 7.86 (s, 1H), 7.62 (s, 1H), 7.60 – 7.55 (m, 2H), 7.49 (td, J =
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8.4, 2.8 Hz, 1H), 7.28 – 7.23 (m, 3H), 7.14 (dd, J = 6.4, 2.8 Hz, 2H). C{1H} NMR (175
MHz, DMSO-d6) δ 161.1 (d, 1JC,F = 245.5 Hz), 153.4, 142.9, 138.9, 137.6 (d, 4JC,F = 3.0 Hz),
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133.9, 132.8 (d, JC,F = 8.2 Hz), 131.0 (d, JC,F = 8.3 Hz), 128.8, 128.3, 127.3, 124.9, 124.2,
120.2, 117.6 (d, 2JC,F = 23.0 Hz), 117.3 (d, 2JC,F = 21.0 Hz), 112.8; IR (KBr)
= 3417, 2927,
2845, 1655, 1477, 1448, 1383, 1200, 1093 cm-1; HR-MS (ESI-TOF) m/z calcd for
C19H12Cl2FN2 [M + H]+ 357.0356, found 357.0368.
2-(4-Fluoro-[1,1'-biphenyl]-2-yl)-5,6-dimethyl-1H-benzo[d]imidazole (1s). Rf = 0.60
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(hexane/ethyl acetate 4:1); white solid; yield 91% (320 mg); mp 220-222 °C; H NMR (400
MHz, DMSO-d6) δ 11.90 (s, 1H), 7.57 – 7.49 (m, 2H), 7.43 (td, J = 8.4, 2.8 Hz, 1H), 7.32 (s,
1H), 7.24 – 7.21 (m, 3H), 7.16 – 7.04 (m, 3H), 2.26 (s, 6H). 13C{1H} NMR (100 MHz, DMSO-
d6) δ 161.1 (d, 1JC,F = 245.2 Hz), 149.8, 142.0, 139.3, 137.5 (d, 4JC,F = 3.1 Hz), 133.1, 132.7 (d,
3JC,F = 8.3 Hz), 132.3 (d, JC,F = 8.3 Hz), 131.1, 129.8, 128.8, 128.2, 127.2, 119.1, 117.4 (d,
3
2JC,F = 22.6 Hz), 116.6 (d, 2JC,F = 20.9 Hz), 111.5, 19.98 (×2); IR (KBr)
= 3438, 2969, 2919,
2857, 1610, 1586, 1460, 1417, 1314, 1200, 1006 cm-1; HR-MS (ESI-TOF) m/z calcd for
C21H18FN2 [M + H]+ 317.1449, found 317.1451.
Mixture of 2-([1,1'-Biphenyl]-2-yl)-5-methyl-1H-benzo[d]imidazole and 2-([1,1'-
Biphenyl]-2-yl)-6-methyl-1H-benzo[d]imidazole (1a'). Rf = 0.60 (hexane/ethyl acetate 7:3);
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inseparable white solid (1:1); yield 85% (590 mg); mp 220-222 °C; H NMR (700 MHz,
DMSO-d6) δ 11.97 (s, 1H), 11.92 (s, 1H), 7.69 (d, J = 7.0 Hz, 2H), 7.62 – 7.56 (m, 2H), 7.52
(t, J = 7.0 Hz, 4H), 7.43 (s, 1H), 7.34 (s, 1H), 7.21 – 7.25 (m, 6H), 7.18 (dd, J = 7.0, 1.4 Hz,
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5H), 7.10 (s, 1H), 6.95 (d, J = 8.4 Hz, 2H), 2.37 (s, 6H); 13C{1H} NMR (175 MHz, DMSO-
d6) δ 152.0, 151.6, 144.8, 141.6, 140.9, 140.2, 134.8, 132.6, 131.4, 131.1, 130.5, 130.3, 130.1,
129.8, 128.8, 128.1, 127.4, 127.1, 123.5, 122.8, 118.5, 118.4, 111.0, 110.8, 21.3; IR (KBr)
= 3440, 3057, 2922, 2867, 2664, 2362, 2337, 1455, 1434, 1403, 1311, 1289, 1232, 1148 cm-1;
HR-MS (ESI-TOF) m/z calcd for C20H17N2 [M + H]+ 285.1386, found 285.1361.
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2-([1,1'-Biphenyl]-2-yl)-5-nitro-1H-benzo[d]imidazole (1b'). Rf = 0.40 (hexane/ethyl
acetate 4:1); white solid; yield 81% (332 mg); mp 234-236 °C; 1H NMR (400 MHz, DMSO-
d6) δ 12.84 (s, 1H), 8.41 (s, 1H), 8.07 (dd, J = 8.8, 2.0 Hz, 1H), 7.78 (d, J = 7.2 Hz, 1H), 7.68
(t, J = 7.6 Hz, 1H), 7.58 (t, J = 7.2 Hz, 3H), 7.32 – 7.23 (m, 3H), 7.22 – 7.14 (m, 2H); 13C{1H}
NMR (175 MHz, DMSO-d6) δ 156.8, 142.6, 141.2, 139.7, 131.1, 130.7(×2), 129.0, 128.8(×2),
128.3(×2), 127.6, 127.4, 117.7, 114.9, 111.9; IR (KBr)
= 3418, 3063, 2922, 2850, 2714,
1636, 1519, 1477, 1430, 1338, 1286, 1068 cm-1; HR-MS (ESI-TOF) m/z calcd for C19H14N3O2
[M + H]+ 316.1081, found 316.1052.
Mixture of 2-(4'-Ethyl-[1,1'-biphenyl]-2-yl)-5-methyl-1H-benzo[d]imidazole and 2-(4'-
Ethyl-[1,1'-biphenyl]-2-yl)-6-methyl-1H-benzo[d]imidazole (1c'). Rf = 0.45 (hexane/ethyl
acetate 4:1); Inseparable white solid (1:1.2); yield 92% (355 mg); mp 222 °C; 1H NMR (700
MHz, DMSO-d6) δ 11.96 (s, 1H), 11.92 (s, 1H), 7.66 (d, J = 7.7 Hz, 2.2H), 7.61 – 7.56 (m,
2.2H), 7.51 – 7.47 (m 4.8H), 7.44 (d, J = 8.4 Hz, 1.2H), 7.35 (s, 1H), 7.21 (d, J = 7.7 Hz, 1H),
7.11 – 7.07 (m 9.6H), 6.95 (d, J = 8.4 Hz, 2.2H), 2.55 (q, J = 7.7 Hz, 4.4H), 2.37 (s, 6.6H),
1.13 (t, J = 7.7 Hz, 6.6H); 13C{1H} NMR (175 MHz, DMSO-d6) δ 152.2, 151.7, 143.8, 142.5,
141.6, 140.8, 137.5, 134.8, 132.6, 131.3, 131.1, 130.4, 130.3, 130.1, 129.8, 128.7, 127.6, 127.1,
123.5, 122.7, 118.6, 118.4, 111.0, 110.8, 27.7, 21.3, 15.3; IR (KBr)
= 3430, 3057, 2964,
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2921, 2872, 2662, 1633, 1446, 1407, 1314, 1282, 1267, 1150, 1054, 1007 cm-1; HR-MS (ESI-
TOF) m/z calcd for C22H21N2 [M + H]+ 313.1699, found 313.1710.
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Mixture of 2-(4'-Ethyl-[1,1'-biphenyl]-2-yl)-5-nitro-1H-benzo[d]imidazole and 2-(4'-
Ethyl-[1,1'-biphenyl]-2-yl)-6-nitro-1H-benzo[d]imidazole (1d'). Rf = 0.55 (hexane/ethyl
acetate 4:1); Inseparable pale yellow solid(1:1); yield 84% (283 mg); mp 228-230 °C; 1H NMR
(700 MHz, DMSO-d6) δ 12.81 (s, 1H), 8.49 (s, 1H), 8.22 (s, 1H), 8.10 – 8.05 (m, 2H), 7.79 –
7.72 (m, 3H), 7.65 (t, J = 7.0 Hz, 2H), 7.56 – 7.53 (m, 5H), 7.11 (s, 8H), 2.55 (q, J = 7.7 Hz,
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4H), 1.13 (t, J = 7.7 Hz, 6H); C{1H} NMR (175 MHz, DMSO-d6) δ 158.1, 156.9, 148.5,
143.3, 143.1, 143.0, 141.5, 139.7, 137.5, 134.2, 131.6, 131.1, 129.4, 129.2, 128.2, 127.8, 119.5,
118.5, 117.7, 115.5, 112.2, 108.3, 28.1, 15.7 ; IR (KBr)
= 3403, 2966, 2929, 2850, 2364,
2342, 1625, 1521, 1476, 1339, 1066 cm-1; HR-MS (ESI-TOF) m/z calcd for C21H18N3O2 [M +
H]+ 344.1394, found 344.1410.
Mixture of 2-(4'-Fluoro-[1,1'-biphenyl]-2-yl)-5-methyl-1H-benzo[d]imidazole and 2-(4'-
Fluoro-[1,1'-biphenyl]-2-yl)-6-methyl-1H-benzo[d]imidazole (1e'). Rf = 0.50 (hexane/ethyl
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acetate 7:3); Inseparable white solid (1:1.2); yield 86% (319 mg); mp 226-228 °C; H NMR
(700 MHz, DMSO-d6) δ 12.01 (s, 1H), 11.96 (s, 1H), 7.71 (d, J = 7.0 Hz, 2.2H), 7.59 (td, J =
7.7, 1.4 Hz, 2.2H), 7.53 (dd, J = 7.7, 1.4 Hz, 2.2H), 7.52 – 7.49 (m, 2.2H), 7.43 (s, 1.2H), 7.35
(s, 1H), 7.23 (s, 1H), 7.22 – 7.18 (m, 4.4H), 7.13 (s, 1.2H), 7.09 (t, J = 9.1 Hz, 4.4H), 6.96 (d,
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J = 7.0 Hz, 2.2H), 2.38 (s, 6.6H); C{1H} NMR (100 MHz, DMSO-d6) δ 161.5 (d, JC,F
=
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243.9 Hz), 151.8, 151.4, 143.9, 141.6, 139.9, 136.6 (d, JC,F = 3.0 Hz), 134.8, 132.6, 131.5,
131.0, 130.8 (d, 3JC,F = 8.2 Hz), 130.5, 130.3, 129.8, 127.5, 123.6, 122.9, 118.7, 118.5, 115.0
(d, 2JC,F = 21.4 Hz), 111.1, 110.9, 21.3; IR (KBr)
= 3444, 3057, 2971, 2919, 2855, 2669,
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1633, 1605, 1511, 1494, 1446, 1463, 1403, 1309, 1280, 1222, 1158, 1094 cm-1; HR-MS (ESI-
TOF) m/z calcd for C20H16FN2 [M + H]+ 303.1292, found 303.1272.
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Mixture of 2-(4-Fluoro-[1,1'-biphenyl]-2-yl)-5-methyl-1H-benzo[d]imidazole and 2-(4-
Fluoro-[1,1'-biphenyl]-2-yl)-6-methyl-1H-benzo[d]imidazole (1f'). Rf = 0.60 (hexane/ethyl
acetate 4:1); Inseparable white solid (1:1.2); yield 85% (154 mg); mp 185 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.04 (s, 1H), 11.98 (s, 1H), 7.56 – 7.50 (m, 4.8), 7.48 – 7.40 (m, 3.6H),
7.35 (s, 1H), 7.27 – 7.21 (m, 7.2H), 7.18 – 7.09 (m, 5.8H), 6.96 (t, J = 7.2 Hz, 2.2H), 2.37 (s,
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6.6H); C{1H} NMR (100 MHz, DMSO-d6) δ 161.1 (d, JC,F = 245.6 Hz), 150.62, 150.18,
143.7, 141.5, 139.26, 137.5, 134.8, 132.7 (d, 3JC,F = 8.2 Hz), 132.6, 132.1 (d, 3JC,F = 8.9 Hz),
131.8, 130.4, 128.8, 128.2, 127.2, 123.9, 123.0, 118.8, 118.6, 117.5 (d, 2JC,F = 22.5 Hz), 116.7
(d, 2JC,F = 21.2 Hz), 111.2, 111.0, 21.30; IR (KBr)
= 3437, 3070, 3023, 2918, 2862, 2778,
1611, 1589, 1509, 1446, 1418, 1284, 1201, 1073 cm-1; HR-MS (ESI-TOF) m/z calcd for
C20H16FN2 [M + H]+ 303.1292, found 303.1273.
Mixture of 1-(2'-(5-Methyl-1H-benzo[d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)ethan-1-one
and 1-(2'-(6-Methyl-1H-benzo[d]imidazol-2-yl)-[1,1'-biphenyl]-4-yl)ethan-1-one (1g'). Rf
= 0.60 (hexane/ethyl acetate 7:3); Inseparable pale yellow solid (1:1.2); yield 88% (351 mg);
mp 265−267 °C; 1H NMR (700 MHz, DMSO-d6) δ 12.15 (s, 1H), 12.10 (s, 1.2H), 7.82 (d, J =
7.7 Hz, 4.4H), 7.74 (d, J = 7.7 Hz, 2.2H), 7.63 (td, J = 7.7, 1.4 Hz, 2.2H), 7.57 (td, J = 7.7, 1.4
Hz, 2.2H), 7.54 (d, J = 7.7 Hz, 2.2H), 7.42 (d, J = 8.4 Hz, 1.2H), 7.35 – 7.29 (m, 5.6H), 7.23
(d, J = 7.7 Hz, 1H), 7.12 (s, 1H), 6.99 – 6.91 (m, 2.2H), 2.52 (s, 6.6H), 2.36 (s, 6.6H); 13C{1H}
NMR (175 MHz, DMSO-d6) δ 197.7, 151.7, 151.2, 145.2, 143.9, 141.7, 139.9, 135.3, 134.9,
132.6, 131.7, 131.2, 130.6, 130.4, 130.3, 130.0, 129.2, 128.2, 128.1, 123.8, 123.0, 118.7, 118.6,
111.2, 111.0, 26.8, 21.4, 21.3; IR (KBr)
= 3351, 3060, 2919, 2857, 1682, 1606, 1405, 1361,
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1314, 1269, 1185 cm-1; HR-MS (ESI-TOF) m/z calcd for C22H19N2O [M + H]+ 327.1492,
found 327.1475.
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Benzo[4,5]imidazo[1,2-f]phenanthridine (2a). Rf = 0.40 (hexane/ethyl acetate 9:1 ); pale yellow
solid; yield 91% (58 mg); mp 144 °C (lit.36 mp 144−146 °C); 1H NMR (700 MHz, CDCl3) δ
8.87 (d, J = 8.4 Hz, 1H), 8.56 (d, J = 7.7 Hz, 1H), 8.47 (d, J = 7.0 Hz, 1H), 8.37 (d, J = 8.4 Hz,
1H), 8.34 (d, J = 7.7 Hz, 1H), 8.06 (d, J = 7.7 Hz, 1H), 7.73 (t, J = 7.0 Hz, 1H), 7.71 – 7.66 (m,
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2H), 7.55 – 7.45 (m, 3H); C{1H} NMR (175 MHz, CDCl3) δ 147.7, 144.7, 134.6, 132.0,
130.6, 129.7, 129.3, 128.8, 126.2, 124.6, 124.4, 124.3, 123.6, 123.1, 122.4, 121.9, 120.5, 116.2,
114.1; IR (KBr)
= 3351, 2364, 2332, 1532, 1453, 1440, 1373 cm-1; HR-MS (ESI-TOF) m/z
calcd for C19H13N2 [M + H]+ 269.1073, found 269.1058.
2-Ethylbenzo[4,5]imidazo[1,2-f]phenanthridine (2b). Rf = 0.55 (hexane/ethyl acetate 4:1);
pale yellow solid; yield 96% (57 mg); mp 162 °C; 1H NMR (700 MHz, CDCl3) δ 8.85 (d, J =
7.7 Hz, 1H), 8.38 – 8.26 (m, 4H), 8.05 (d, J = 7.7 Hz, 1H), 7.71 (t, J = 7.0 Hz, 1H), 7.64 (t, J
= 7.0 Hz, 1H), 7.52 (t, J = 7.0 Hz, 1H), 7.48 (t, J = 7.7 Hz, 1H), 7.34 (d, J = 7.7 Hz, 1H), 2.92
(q, J = 7.7 Hz, 2H), 1.42 (t, J = 7.7 Hz, 3H); 13C{1H} NMR (175 MHz, CDCl3) δ 147.7, 146.1,
144.3, 134.6, 131.9, 130.7, 129.9, 128.4, 126.2, 124.7, 124.3(×2), 123.0, 122.9, 122.2, 120.3,
119.6, 115.3, 114.2, 29.29, 15.64; IR (KBr)
= 3416, 2961, 2923, 2855, 1614, 1537, 1449,
1428, 1665 cm-1; HR-MS (ESI-TOF) m/z calcd for C21H17N2 [M + H]+ 297.1386, found
297.1372.
2-Fluorobenzo[4,5]imidazo[1,2-f]phenanthridine (2c). Rf = 0.55 (hexane/ethyl acetate (4:1);
white solid; yield 95% (55 mg); mp 190 °C; 1H NMR (700 MHz, CDCl3) δ 8.77 (d, J = 7.7 Hz,
1H), 8.37 – 8.30 (m, 1H), 8.18 (dd, J = 12.6, 7.7 Hz, 2H), 8.13 (d, J = 9.8 Hz, 1H), 8.01 (d, J
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= 7.7 Hz, 1H), 7.67 (t, J = 7.7 Hz, 1H), 7.62 (t, J = 7.0 Hz, 1H), 7.51 (t, J = 7.7 Hz, 1H), 7.47
(t, J = 7.7 Hz, 1H), 7.15 (t, J = 7.0 Hz, 1H); 13C{1H} NMR (175 MHz, CDCl3) δ 162.87 (d,
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1JC,F = 249.0 Hz), 147.6, 144.6, 135.3 (d, J = 10.6 Hz), 131.7, 130.7, 129.1, 128.5, 126.2,
126.1 (d, 4JC,F = 9.7 Hz), 124.6, 123.3, 122.9, 122.1, 120.6, 118.2, 113.6, 112.1 (d, 3JC,F = 22.0
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Hz), 103.32 (d, JC,F = 26.9 Hz); IR (KBr)
= 3422, 2927, 2857, 1618, 1540, 1450, 1432,
1350, 1169 cm-1; HR-MS (ESI-TOF) m/z calcd for C19H12FN2 [M + H]+ 287.0979, found
287.0971.
1-(Benzo[4,5]imidazo[1,2-f]phenanthridin-2-yl)ethan-1-one (2d). Rf = 0.70 (hexane/ethyl
acetate 7:3); white solid; yield 94% (56 mg); mp 222 °C; 1H NMR (700 MHz, CDCl3) δ 8.95
(s, 1H), 8.80 – 8.73 (m, 1H), 8.31 (d, J = 8.4 Hz, 1H), 8.27 (d, J = 8.4 Hz, 1H), 8.22 – 8.18 (m,
1H), 8.01 (d, J = 7.7 Hz, 1H), 7.85 (d, J = 7.7 Hz, 1H), 7.67 (dd, J = 5.6, 2.8 Hz, 2H), 7.53 (t,
J = 7.7 Hz, 1H), 7.49 (t, J = 7.7 Hz, 1H), 2.71 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ
196.7, 147.1, 144.2, 136.7, 134.1, 131.7, 130.7, 129.9, 128.4, 126.2, 125.4, 124.7, 124.3, 124.1,
124.0, 123.8, 123.0, 120.5, 115.5, 114.1, 26.9; IR (KBr)
= 3439, 3048, 1682, 1620, 1534,
1450, 1427, 1653, 1264 cm-1; HR-MS (ESI-TOF) m/z calcd for C21H15N2O [M + H]+
311.1179, found 311.1168.
11,12-Dichlorobenzo[4,5]imidazo[1,2-f]phenanthridine (2e). Rf = 0.55 (hexane/ethyl
1
acetate 4:1 ); white solid; yield 98% (59 mg); mp 234 °C (lit.35 mp 231-232 ℃); H NMR (700
MHz, CDCl3) δ 8.65 (d, J = 7.7 Hz, 1H), 8.36 (d, J = 7.7 Hz, 1H), 8.26 (d, J = 7.7 Hz, 1H),
8.21 (s, 1H), 8.14 (d, J = 8.4 Hz, 1H), 7.93 (s, 1H), 7.71 (t, J = 7.0 Hz, 1H), 7.62 (s, 2H), 7.46
13
(t, J = 7.0 Hz, 1H); C{1H} NMR (175 MHz, CDCl3) δ 149.1, 143.9, 133.6, 131.1, 130.7,
129.7, 129.5, 128.9, 128.2, 126.5, 126.3, 125.1, 124.4, 122.8, 122.4, 121.8, 121.1, 115.7, 115.1;
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IR (KBr)
= 3444, 2919, 2852, 1651, 1537, 1438, 1364 cm-1; HR-MS (ESI-TOF) m/z calcd
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for C19H11Cl2N2 [M + H]+ 337.0294, found 337.0270.
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11,12-Dichloro-2-ethylbenzo[4,5]imidazo[1,2-f]phenanthridine
(2f).
Rf
=
0.60
(hexane/ethyl acetate 4:1); white solid; yield 93% (55.5 mg); mp 241 °C; 1H NMR (700 MHz,
CDCl3) δ 8.69 (d, J = 7.7 Hz, 1H), 8.29 (d, J = 8.4 Hz, 1H), 8.26 (t, J = 7.7 Hz, 2H), 7.99 (d, J
= 11.9 Hz, 2H), 7.71 (t, J = 7.7 Hz, 1H), 7.62 (t, J = 7.7 Hz, 1H), 7.34 (d, J = 8.4 Hz, 1H), 2.90
(q, J = 7.7 Hz, 2H), 1.41 (t, J = 7.7 Hz, 3H); 13C{1H} NMR (175 MHz, CDCl3) δ 149.3, 146.4,
143.9, 133.8, 131.1, 130.8, 129.9, 128.5, 128.2, 126.3, 126.3, 125.1, 124.5, 122.4, 122.2, 121.0,
119.5, 115.2, 114.8, 29.3, 15.6; IR (KBr)
= 3442, 2969, 2924, 2364, 2335, 1440, 1311,
1116 cm-1; HR-MS (ESI-TOF) m/z calcd for C21H15Cl2N2 [M + H]+ 365.0607, found
365.0594.
2-(Tert-butyl)-11,12-dichlorobenzo[4,5]imidazo[1,2-f]phenanthridine (2g). Rf = 0.60
(hexane/ethyl acetate 4:1); white solid; yield 94% (56 mg); mp 234 °C; 1H NMR (700 MHz,
CDCl3) δ 8.75 (d, J = 7.0 Hz, 1H), 8.39 (t, J = 6.6 Hz, 1H), 8.32 – 8.34 (m, 3H), 8.03 (dd, J =
11.9, 5.6 Hz, 1H), 7.72 – 7.76 (m, 1H), 7.65 (t, J = 7.0 Hz, 1H), 7.62 – 7.58 (m, 1H), 1.54 (s,
13
9H); C{1H} NMR (175 MHz, CDCl3) δ 153.4, 149.5, 144.2, 133.8, 131.2, 130.9, 129.9,
128.6, 128.2, 126.4, 126.3, 124.3, 122.9, 122.7, 122.3, 121.2, 119.4, 115.3, 112.5, 35.6, 31.5;
IR (KBr)
= 3439, 2959, 2867, 2359, 2339, 1615, 1439 cm-1; HR-MS (ESI-TOF) m/z calcd
for C23H19Cl2N2 [M + H]+ 393.0920, found 393.0932.
3,11,12-Trichlorobenzo[4,5]imidazo[1,2-f]phenanthridine (2h). Rf = 0.70 (hexane/ethyl
acetate 4:1); white solid; yield 92% (55 mg); mp 260 °C; 1H NMR (400 MHz, CDCl3 + TFA-
D) δ 8.85 (d, J = 8.0 Hz, 1H), 8.63 (d, J = 1.6 Hz, 1H), 8.61 (s, 1H), 8.54 (t, J = 9.2 Hz, 2H),
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