Palladium-catalyzed tandem N-H/C-H arylation: Regioselective synthesis of N-heterocycle-fused phenanthridines as versatile blue-emitting luminophores

Article abstract of DOI:10.1039/c3ob41760c

A general and highly regioselective synthetic protocol for structurally diverse N-heteroaryl-fused phenanthridines has been developed. Varieties of fluorescence molecules comprising imidazole-fused, benzoimidazole-fused, indole-fused and pyrrole-fused phenanthridines were obtained by this modular approach, some of which exhibit excellent blue-emitting performance, high quantum yields, long fluorescence lifetimes, interesting electrochemical properties, and thermal stabilities.

Full text of DOI:10.1039/c3ob41760c

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ARTICLE TYPE
Palladium-catalyzed tandem N–H/C–H arylation: regioselective
synthesis of N-heterocycle-fused phenanthridines as versatile blue-
emitting luminophores
Lipeng Yan, Dongbing Zhao, Jingbo Lan,* Yangyang Cheng, Qiang Guo, Xiaoyu Li, Ningjie Wu and
Jingsong You*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A general and highly regioselective synthetic protocol for structurally diverse Nꢀheteroarylꢀfused
phenanthridines has been developed. Varieties of fluorescence molecules comprising imidazoleꢀfused,
10 benzoimidazoleꢀfused, indoleꢀfused and pyrroleꢀfused phenanthridines were obtained by this modular
approach, some of which exhibit excellent blueꢀemitting performance, high quantum yields, long
fluorescence lifetimes, interesting electrochemical properties, and thermal stabilities.
fused phenanthridines. Recently, Miura et al. reported the
palladiumꢀcatalyzed direct annulation of 2ꢀphenylꢀimidazole, ꢀ
benzoimidazole, and ꢀindole with oꢀdibromobenzene to produce
the corresponding heterocycle fused phenanthridines.10 However,
50 all of three examples, also including those known routes using
2,2'ꢀdiiodobiphenyl or arynes as raw materials, are usually limited
to symmetrically substituted oꢀdihaloarene or aryne substrates.
The highly regioselective transformation of unsymmetric
substrates, which would lead to the structural diversity of the
55 chemical library, remains unsolved so far. In addition, the
incorporation of an unsymmetric struture, particularly
Introduction
The rational design and construction of luminophores for using in
15 organic lightꢀemitting diodes (OLEDs) has recently been the
subject of growing interest owing to their applications in flatꢀ
panel displays and solidꢀstate lighting.1 High performance blueꢀ
emitting materials have been one of the most important
prerequisites to promote the popularization of OLEDs. However,
20 only
a limited number of blueꢀemitting small molecular
luminophores with high efficiency, stability, and color purity
have been reported.2 Nꢀheterocycleꢀfused phenanthridines such as
imidazoleꢀfused, benzoimidazoleꢀfused, indoleꢀfused and pyrroleꢀ
fused phenanthridines contain an extensive πꢀconjugated
25 polycyclic heteroaromatic structure, the optical and
electrochemical properties of which can be easily tuned by
incorporating electronꢀdonors or acceptors and also by simply
altering the position of substituents on chromophores, and may be
potential candidates as blueꢀemitting materials.3 The main
30 methods to prepare these Nꢀheterocycleꢀfused phenanthridines
include the addition reaction of arynes with Nꢀ(oꢀ
halophenyl)indoles (or pyrroles),4 the palladiumꢀcatalyzed
intramolecular direct arylation reaction or electrochemical
cyclization of oꢀhaloaryl substituted phenylpyrroles (imidazoles,
35 benzoimidazoles),5 the copperꢀcatalyzed tandem coupling of 2,2'ꢀ
diiodobiphenyl with imidazole,6 the consecutive Suzuki coupling
of 9ꢀ(2ꢀbromophenyl)purines with 2ꢀbromophenylboronic acid
followed by intramolecular C–H arylation,7 the annulation
reaction of 2ꢀbromoethylꢀphenanthridinium bromide,8 and the
40 intramolecular rearrangement reaction between nitro and carbodiꢀ
imide groups.9 However, these methods generally suffer from
limitations with regard to substrate generality, multistep
syntheses, poor regioselectivity, and sometimes the harsh reaction
conditions. Moreover, most of current synthetic methods are
45 typically restricted to prepare only one type of Nꢀheterocycleꢀ
unsymmetric
electronꢀdonating
or
electronꢀwithdrawing
substituents, has been shown the profound influence on
photoelectric properties of materials.11 Therefore, there is a great
60 demand for methodology detailing the regioselective synthesis of
Nꢀheterocycleꢀfused phenanthridines with various structures.
Development of a simple and efficient access to the Nꢀ
heterocycleꢀfused phenanthridine library bearing the appropriate
functional groups to control optical and electronic properties is
65 highly warranted for exploration and improvement of the
property of such materials. Herein, we report the Pdꢀcatalyzed
tandem N–H/C–H arylation starting from 2ꢀaryl substituted Nꢀ
heteroarenes with generally more available oꢀhaloaryl chlorides
or bromides, which constitutes
a
general and highly
70 regioselective method for the synthesis of the structurally diverse
Nꢀheteroarylꢀfused phenanthridines for screening out high
performance blueꢀemitting luminophores (Scheme 1).
X
R2
X1
D
10 mol% Pd(PPh3)4
10 mol% Xantphos
C
X
R2
R1
N
B
A
+
Cs2CO3, DMF
140 oC, 24 h
X2
N
H
X1, X2 = Br, Cl
X = CH, N
R1
2
1
3
Scheme 1 Pdꢀcatalyzed tandem N–H/C–H arylation of 2ꢀarylꢀNꢀ
75
heteroarenes with 1,2ꢀdihaloarenes.
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1

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DOI: 10.1039/C3OB41760C
benzoimidazo[2,1ꢀa]benzothieno[2,3ꢀc]isoquinoline (3j) in
a
Results and discussion
moderate yield, and none of regioisomer was detected (Table 2,
1
Entry 10). The structure of 3j was confirmed by H NMR, 13C
Optimization of Pd-catalyzed tandem N–H/C–H arylation
NMR, 1Hꢀ1H NOESY spectra, and mass spectrum (see
65 Supporting Information).
The investigation started with the coupling of 2ꢀphenyl
benzoimidazole with oꢀdibromobenzene as a model reaction to
optimize the reaction conditions. We firstly screened various
phosphine ligands in the presence of Pd(OAc)2 using Cs2CO3 as
the base in DMF for 24 h at 140 °C. None of desired products
were detected both in the absence of ligand and with Cy3PꢁHBF4
as ligand (Table 1, entries 1, 2). After screening a series of
Table 1. Optimization of Pdꢀcatalyzed tandem N–H/C–H arylation.a
5
N
Br
N
[Pd], ligand
N
+
base,solvent
N
H
Br
3a
1a
2a
10 phosphine ligands, to our delight, the annulation product 3a was
obtained in 77% yield when employing Xantphos as ligand
(Table 1, entry 9). Other bases were also investigated, and
Cs2CO3 was turned out to be the optimal choice (Table 1, entries
9ꢀ15). Although a slightly higher yield (79%) was obtained when
15 dioxane was employed as the solvent, DMF was still selected as
the solvent for safety and economic considerations (Table 1,
entries 16ꢀ18). It was more gratifying that zeroꢀvalent palladium
species exhibited higher catalytic activity in this reaction (Table 1,
entries 19, 20). Especially, while using Pd(PPh3)4 (10 mol%) as
20 catalyst for 24 h at 140 ºC, 3a was obtained in almost quantitative
yield (96%) (Table 1, entry 22). Thus, the optimal reaction
condition was obtained when 10 mol% of Pd(PPh3)4 was
employed in combination with 10 mol% of Xantphos, Cs2CO3
(3.0 equiv) in DMF under N2 atmosphere at 140 °C for 24 h.
Entry
Pd
Ligand
ꢀ
Base
Solvent
Yieldb
ꢀ
1
2
3
4
5
Pd(OAc)2
Pd(OAc)2
Cs2CO3
Cs2CO3
DMF
DMF
DMF
DMF
DMF
ꢀ
Cy3PꢁHBF4
9%
32%
31%
Pd(OAc)2 tꢀBu3PꢁHBF4 Cs2CO3
Pd(OAc)2
Pd(OAc)2
Sꢀphos
Cs2CO3
Cs2CO3
Davesꢀphos
45%
6
Pd(OAc)2
Xꢀphos
Cs2CO3
DMF
43%
70%
77%
75%
ꢀ
7
8
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Dppf
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
KOtBu
DMF
DMF
DMF
DMF
DMF
BINAP
9
Xantphos
Xantphos
Xantphos
25 Pd-catalyzed tandem N–H/C–H arylation of 2-aryl-N-
heteroarenes with 1,2-dihaloarenes
10c
11
Subsequently, the coupling of 2ꢀphenyl benzoimidazole with the
unsymmetrically substituted substrate (1b, 2ꢀbromoꢀ1ꢀchloroꢀ4ꢀ
methylbenzene) was examined with the optimized condition. It
30 was found that the 1,2ꢀdihaloarene containing two different
halogen atoms worked well under this reaction condition and
affording 2ꢀmethylbenzoimidazo[1,2ꢀf]phenanthridine (3b) in
88% yield (Table 2, Entry 2). The structure identification of 3b
32%
ꢀ
12
13
14
15
16
17
18
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
NaOtBu
LiOtBu
K2CO3
K3PO4
DMF
DMF
DMF
DMF
DMSO
70%
67%
55%
79%
Trace
1
1
was carried out by H NMR, 13C NMR, Hꢀ1H NOESY spectra,
Cs2CO3
35 and mass spectrometry analysis (see Supporting Information).
Cs2CO3 Dioxane
The
regioisomeric
product
3ꢀmethylbenzoimidazo[1,2ꢀ
f]phenanthridine was not found in this reaction system, which
indicated that the tandem N–H/C–H arylation reaction underwent
a regiospecific transformation. We assumed that due to higher
40 reactivity of aryl bromide than aryl chloride, the Nꢀarylation of
benzoimidazole with C–Br might always preferentially occur, and
followed by the intramolecular directed aryltion of the CꢀH bond
with C–Cl. Moreover, it was gratifying that no matter whether the
substituent R1 of oꢀdihaloarenes was electronꢀdonating (1c) or
45 electronꢀwithdrawing (1d and 1e), all of them afforded the
regioselectively N–H/C–H arylated products in good to excellent
yields (Table 2, Entries 3ꢀ5). The structure of 3d was confirmed
Cs2CO3
Toluene
83%
85%
73%
96%
19
20
Pd(dba)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Xantphos
Xantphos
Xantphos
Xantphos
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DMF
DMF
DMF
DMF
21d
22e
a Reactions were carried out by using 1a (0.25 mmol), 2a (0.30 mmol),
[Pd] (5 mol%), Ligand (5 mol%), Base (3.0 equiv), in Solvent (2 mL)
70 under N2 for 24 h at 140 ºC. b Yield of isolated product. c PivOH (0.5
equiv) was added. d 16 h. e Reactions were carried out by using 1a (0.25
mmol), 2a (0.30 mmol), Pd(PPh3)4 (10 mol%), Xantphos (10 mol%),
Cs2CO3 (3.0 equiv), in DMF (2 mL) under N2 for 24 h at 140 ºC.
1
by Hꢀ1H NOESY spectra (see Supporting Information). When
the substituent R1 was a chlorine atom, it still remained a high
50 regioselectivity,
and
gave
3ꢀchlorobenzoimidazo[1,2ꢀ
The scope of 2ꢀarylꢀNꢀheteroarene substrates was also
75 extended. As expected, 2ꢀphenylꢀ1Hꢀimidazole was found to be a
competent substrate and could occur regioselective N–H/C–H
f]phenanthridine (3f) in 81% yield, which suggested once again
that the Nꢀarylation reaction of the C–Br bond took precedence
over the reaction of the C–Cl bond (Table 2, Entry 6). The
reaction condition was also compatible with the oꢀ
55 dihaloheteroarene substrates such as 2ꢀbromoꢀ3ꢀchloropyridine,
2,3ꢀdichloropyrazine and 2,3ꢀdichloroquinoxaline, and provided
the corresponding products in good yields (Table 2, Entries 7ꢀ9).
Owing to the higher reactivity of the C–Br bond at the 2ꢀposition
than 3ꢀposition of benzothiophene,12 2,3ꢀdibromobenzothiophene
60 (1j) could occur a regiospecific tandem arylation, affording
tandem
arylation
reaction
with
1b,
affording
6ꢀ
methylimidazo[1,2ꢀf]phenanthridine (3k) in excellent yield
(Table 2, Entry 11). 2ꢀPhenylꢀ1Hꢀindole was also tolerated under
80 the optimized conditions, but gave rise to slightly low yields
(60%). When Cs2CO3 was replaced by K2CO3, the corresponding
2ꢀmethylindolo[1,2ꢀf]phenanthridine (3l) was obtained in a good
yield (Table 2, Entry 12).
2
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DOI: 10.1039/C3OB41760C
Table 2. Pdꢀcatalyzed tandem N–H/C–H arylation of 2ꢀarylꢀNꢀ
heteroarenes with 1,2ꢀdihaloarenes.a
Table 3. Synthesis of other diverse Nꢀheterocycleꢀfused phenanthridines.a
Entry
1
2
Product
N
Yieldb
Entry
1
2
Product
N
Yieldb
96%
N
Br
Br
N
N
Br
Br
1
88%
N
H
N
1
1a
2d
N
H
4a
1a
2a
N
3a
N
OCH3
N
N
OCH3
N
1a
2
3
91%
75%
Br
N
H
2e
4b
2a
2a
2
3
88%
85%
Cl
1b
OCH3
3b
OCH3
N
N
N
N
N
1a
H3CO
Br
Cl
N
H
2f
4c
1c
N
N
N
F
H3CO
N
3c
F
1a
1a
1a
4
5
6
90%
84%
68%
N
H
F3C
Br
2g
N
4d
2a
2a
2a
4
5
6
90%
71%
81%
N
N
Cl
N
Cl
1d
Cl
F3C
N
3d
N
H
2h
2i
4e
4f
Br
N
N
N
CN
EtOOC
Cl
CN
N
1e
N
H
3e
COOEt
N
F3
C
Br
Cl
F3
C
N
N
N
N
1a
1a
7
8
79%
88%
Cl
N
H
1f
2j
3f
Cl
4g
N
N
N
Cl
N
Ph
N
N
Ph
2a
2a
7
8
65%
64%
N
Br
N
H
1g
3g
2k
4h
N
N
N
N
Cl
Cl
N
N
N
1a
1h
9
65%
N
N
N
3h
N
H
N
N
2l
4i
N
Cl
N
N
S
N
S
2a
2a
9
63%
53%
N
Cl
N
1a
1a
1a
10
11
12
13
14
82%
94%
89%
82%
78%
1i
N
H
2m
4j
3i
N
N
N
N
Br
N
Br
10
N
H
S
S
2b
4k
4l
1j
3j
N
N
N
N
N
Br
N
H
N
11
12
90%
2n
N
H
Cl
1b
1b
2b
3k
N
1a
1a
N
H
Br
Cl
N
2c
4m
75%c
N
H
2c
N
3l
N
H
a Reactions were carried out by using 1 (0.25 mmol), 2 (0.3 mmol),
Pd(PPh3)4 (10 mol%), Xantphos (10 mol%), Cs2CO3 (3.0 equiv), in DMF
(2 mL) for 24 h at 140 ºC. b Yield of isolated product. c K2CO3 (3.0 equiv).
2o
4n
a Reaction conditions were described in Experimental Section; b Yield of
isolated product.
5
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Synthesis
phenanthridines
of
other
diverse
N-heterocycle-fused
displays a large Stokes shift in CH3CN (113 nm), which is a very
60 useful factor to avoid imaging interference by excitation and
scattered light in the various fluorescence analyses (Table 4, 3h
versus 3a). Moreover, 3h was found to exhibit excellent quantum
yields of 0.85 for the solution state and 0.32 for the solid state,
respectively. When pyrazine is replaceed by quinoxaline, a more
65 significant redꢀshift was observed (Table 4, 3i versus 3a). That
there is an extension of conjugation in 3a than in 4k is not
reflected in its emission spectrum, and the emission maximum of
3a in CH3CN is consistent with that of 4k (Table 4, 4k versus 3a).
In contrast, the introduction of two methyls into the “D ring”
70 shows more pronounced influence on the emission spectrum. 2,3ꢀ
Dimethylimidazo[1,2ꢀf]phenanthridine (4l, λem = 424 nm) was
found to be around 35 nm redꢀshifted with respect to 4k (Table 4,
4l versus 4k).
To set up combinatorial library of Nꢀheterocycleꢀfused
a
phenanthridines, the coupling of various substituted 2ꢀarylꢀNꢀ
heteroarenes bore the neutral, electronꢀdonating, or electronꢀ
withdrawing substituents with oꢀdibromobenzene were carried
out under the optimized conditions, and the results are
summarized in Table 3. Varieties of imidazoleꢀfused,
5
benzoimidazoleꢀfused,
indoleꢀfused
and
pyrroleꢀfused
10 phenanthridines were obtained in good to excellent yields. The
chemical structures of these compounds were determined by their
1H/13C NMR spectra and mass spectroscopy.
Photophysical, electrochemical and thermal properties
In view of the broad substrate diversity of the Pdꢀcatalyzed N–
15 H/C–H tandem arylation, we were intensely interested in the
potential of Nꢀheterocycleꢀfused phenanthridines as photoelectric
materials. We therefore investigated their photophysical
properties and the results are summarized in Table 4. Fluorescent
spectra and images of selected blueꢀemitting phenanthridines are
20 shown in Figure 1 for solution states and Figure 2 for solid states,
respectively.
It was found that emission maxima of most of the synthesized
Nꢀheterocycleꢀfused phenanthridines appear in the blue light
region. Very little overlap in the absorption and fluorescence
25 spectra are observed, which suggest that these Nꢀheterocycleꢀ
fused phenanthridine structures may be advantageous for
suppressing Förster resonance energy transfer. The emission
maxima in solid generally redꢀshift compared with those in
acetonitrile solution, maybe due to the formation of a physical
30 dimmer.
Table 4. Absorption and emission spectroscopic data for Nꢀheterocycleꢀ
75 fused phenanthridines
Solution
Solid
Compd
c
c
λabs nma
λem nm (λex nm)b ΦF λem nm (λex nm)d ΦF
3a
3b
3c
3d
3e
3f
269, 306, 328, 345
389 (329)
374 (309)
389 (359)
401 (328)
448 (352)
392 (331)
413 (330)
466 (354)
507 (396)
410 (325)
388 (300)
445 (363)
388 (329)
398 (308)
377 (337)
404 (305)
398 (308)
411 (320)
391 (341)
389 (338)
435 (373)
392 (341)
389 (306)
424 (318)
445 (359)
433 (329)
0.71
0.89
0.22
0.36
0.46
0.34
0.62
0.85
0.51
0.07
0.54
0.28
0.87
0.80
0.54
0.49
0.30
0.91
0.37
0.92
0.79
0.46
0.89
0.58
0.21
0.42
399 (356) <0.01
399 (368) <0.01
262, 270, 306, 349
262, 270, 310, 358
270, 306, 326
281, 310, 354
272, 308, 330, 346
265, 308, 328
265, 311, 353
266, 394
421 (384)
390 (362)
428 (390)
410 (374)
462 (378)
491 (418)
509 (448)
452 (393)
458 (342)
470 (410)
387 (361)
399 (371)
411 (369)
434 (368)
424 (376)
467 (391)
417 (372)
0.04
0.23
0.14
0.11
0.08
0.32
0.18
0.01
0.07
0.22
0.16
0.06
0.07
0.08
0.06
0.04
0.05
3g
3h
3i
3j
273, 297, 324, 355
258, 289, 305
276, 325, 365
270, 306, 328, 344
269, 307
Upon excitation at 329 nm, the acetonitrile solution of
benzoimidazo[1,2ꢀf]phenanthridine (3a) exhibits
a
purple
3k
3l
emission (λem = 389 nm, ΦF = 0.71). The introduction of the
electronꢀwithdrawing ethoxycarbonyl into the “A ring” of the
35 phenanthridine skeleton (3e) causes a 59 nm redꢀshift of emission
maximum with respect to 3a (Table 4, 3e versus 3a, and the “A,
B, C and D ring” are designated in Scheme 1). The introduction
of trifluoromethyl into the “A ring” (3d) also results in a slight
redꢀshift relative to 3a. The incorporation of the electronꢀ
40 donating methoxy substituent onto the parent nucleus does not
bring significant change of fluorescesce emission (Table 4, 3c
versus 3a). A blueꢀshifted emission is observed while the methyl
group is located at the 2ꢀposition of the “A ring” (Table 4, 3b
versus 3a).
The substituent on the “C ring” of phenanthridines, whether it
is electronꢀdonating, neutral or electronꢀwithdrawing, shows a
slighter affection on the emission spectra for the solution states
than those positioned on the “A ring” (Table 4, 4aꢀ4h versus 3a).
The emission maximum of 4h in solid remarkably redꢀshifts
50 compared with that in solution. The redꢀshifted emission is
presumably attributed to the formation of a extensive πꢀ
conjugated system when the rotation of the benzene ring
substituent is suppressed in solid. In CH3CN, the emission
spectrum of 4i shows a band centered at 435 nm (ΦF = 0.79) and
55 a 46 nm redꢀshift relative to 3a with increasing degree of
conjugation from 3a to 4i (Table 4, 4i versus 3a).
4a
4b
4c
4d
4e
4f
275, 314, 337, 353
268, 291, 305
271, 309
267, 319
4g
4h
4i
271, 316, 340, 358
278, 314, 338
294, 306, 371
263, 341, 360
257, 287, 303
262, 295, 319
284, 324, 359
258, 281, 300, 330
503 (395) <0.01
503 (419)
473 (379)
421 (360)
0.03
0.04
0.06
45
4j
4k
4l
452 (372) <0.01
505 (465) 0.15
480 (384) <0.01
4m
4n
a Absorption maximum in acetonitrile solution (~ 10−5 M). b Emission
maximum in acetonitrile solution (~ 10−5 M) with the corresponding
wavelength of excitation in parentheses. c Absolute fluorescence quantum
yields were measured in CH3CN at ~ 10−5 M with an integrating sphere
80 (excited with λex). d Emission maximum in solid with the corresponding
wavelength of excitation in parentheses.
In addition, indolo[1,2ꢀf]phenanthridine (4m) and pyrrolo[1,2ꢀ
f]phenanthridine (4n) were also found to be excellent blueꢀ
emitting luminophores, which exhibit intense blue emissions at
Noteworthily, the replacement of the “A ring” of 3a by
pyrazine triggers a notable bathochromic shift (77 nm, 3h) and
4
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35 HOMOs, whereas benzoimidazoleꢀfused phenanthridines (3e and
3h) show lowꢀlying HOMOs, which are in accordance with their
electronic properties. Their HOMO values vary in the range
−5.18 and −5.14 eV to −5.94 and −5.93, indicating that these Nꢀ
heterocycleꢀfused phenanthridines are potential pꢀtype or nꢀtype
40 blueꢀemitting luminophores for applications in OLEDs.
The thermal properties of 3e, 3h, 3l and 4m were studied by
thermogravimetry/differential thermal analysis (TG/DTA, Table
5, and see Supporting Information, Figure S2). Thermal
decomposition temperatures (Td, the temperature at which the
45 compounds lose 5% of their weight) of 3e, 3h, 3l and 4m ranges
from 292 °C to 316 °C, which indicate that all four compounds
are thermally stable and suitable for vacuum thermal sublimation
for OLED fabrication.
λem = 445 nm and 433 nm with remarkable quantum yields. The
introduction of a methyl into the “A ring” of indolo[1,2ꢀ
f]phenanthridine (4m, λem = 445 nm) does not significantly
change the emission of its solution state (3l, λem = 445 nm), but
leads to a blueꢀshifted emission maximum of its solid state from
λem = 505 nm to 470 nm (Table 4, 3l versus 4m), indicating that
the presence of the methyl group suppresses the intermolecular
π–π* stacking of phenanthridines in the solid state.
5
10 Fig. 1 Fluorescent spectra of selected blueꢀemitting phenanthridines in
CH3CN (signal intensities have been normalized). Insert: Fluorescence
images of phenanthridines in CH3CN, λex = 365 nm. From left to right:
4n, 4i, 3e, 3l, 4m, and 3h.
50
Fig. 3 UVꢀvis absorption spectra of compounds 3e, 3h, 3l and 4m in
CH3CN (signal intensities have been normalized).
Table 5. Fluorescence lifetimes, electrochemical and thermal properties
of compounds 3e, 3h, 3l and 4m.
a
opt
ox
τF
ns
λonset Eg
nmb eVc
Eonset
HOMO LUMO Td
Compd
Vd
eVe
eVf
°Cg
3e
3h
3l
16.38 380 3.26 1.14
18.35 395 3.14 1.13
14.78 400 3.10 0.34
14.26 397 3.12 0.38
ꢀ5.94
ꢀ5.93
ꢀ5.14
ꢀ5.18
ꢀ2.68 316
ꢀ2.79 296
ꢀ2.04 311
ꢀ2.06 292
4m
a Measured in acetonitrile solution, excitation at λex = 352 nm for 3e, λex
=
55 354 nm for 3h, λex = 363 nm for 3l, and λex = 359 nm for 4m. b Estimated
15 Fig. 2 Fluorescent spectra of selected blueꢀemitting phenanthridines in
solid (signal intensities have been normalized). Insert: Fluorescence
images of phenanthridines in solid, λex = 365 nm. From left to right: 3e,
4d, 4l, 3k, 3l, and 4n.
from the absorption cut off of the UVꢀvis spectrum (in acetonitrile); c Eg
opt
= 1240/λonset eV. d Measured from the oxidation onset of the CV (in
opt
acetonitrile). e HOMO = – (4.8 + Eonsetox) eV. f LUMO = (HOMO + Eg
eV. g Detected by TG/DTA analysis and heating rate = 10 °C/min under a
60 nitrogen atmosphere.
)
Fluorescence lifetimes (τF) of compounds 3e, 3h, 3l and 4m
20 were determined in CH3CN upon excitation at the selected
wavelengths, and the results are given in Table 5. The
fluorescence decay of 3e is fitted with the monoexponential
function, whereas those of 3h, 3l and 4m are biexponential (see
Supporting Information, Table S1). All four compounds in
25 acetonitrile exhibit long fluorescence lifetimes in range of 14.26ꢀ
18.35.
The HOMO energy levels of 3e, 3h, 3l and 4m were obtained
with cyclic voltammetry (CV) and the results are also
summarized in Table 5 (and see Supporting Information, Figure
30 S1). The energy gap between the HOMOs and LUMOs were
calculated from the absorption edge of their UVꢀvis spectra
(Figure 3), and the energy levels of the LUMOs were estimated
from the HOMO–LUMO gaps and HOMO energies. Indoleꢀfused
phenanthridines (4m and 3l) exhibit high energy levels of
Conclusions
In summary, we have developed
a general and highly
regioselective method for the synthesis of the structurally diverse
Nꢀheteroarylꢀfused phenanthridines through the Pdꢀcatalyzed
65 tandem N–H/C–H arylation starting from 2ꢀaryl substituted
imidazoles, benzoimidazoles, pyrroles and indoles with 1,2ꢀ
dihaloarenes. A library of fluorescence molecules comprising
imidazoleꢀfused, benzoimidazoleꢀfused, indoleꢀfused and pyrroleꢀ
fused phenanthridines have been obtained by this modular
70 approach. Some of the synthesized Nꢀheterocycleꢀfused
phenanthridines
exhibit
interesting
photophysical
and
electrochemical properties, moderate to excellent quantum yields,
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long fluorescence lifetimes, and thermal stabilities, which makes
silica gel to provide the desired product.
them potential candidates for several important applications in
optoelectronic devices, such as blueꢀemitting luminophores in
OLEDs, or as models for further developing other
phenanthridineꢀbased organic materials.
General procedure for tandem N–H/C–H arylation of 2-aryl-
N-heteroarenes with 1,2-dihaloarenes
60 A flameꢀdried Schlenk tube with a magnetic stir bar was charged
with Pd(PPh3)4 (28.8 mg, 25.0 ꢂmol, 10 mol%), Xantphos (14.6
mg, 25.0 ꢂmol, 10 mol%), Cs2CO3 (243 mg, 0.75 mmol) and 2ꢀ
arylꢀNꢀheteroarenes (0.30 mmol, 1.2 equiv). Then, 1,2ꢀ
dihaloarenes (0.25 mmol) and DMF (2.0 mL) were added to the
65 reaction mixture under an N2 atmosphere. The reaction mixture
was stirred for 10 min at room temperature, and then heated at
140 °C in preꢀheated oil bath for 24 h. After that, the reaction
mixture was cooled to room temperature, diluted with CH2Cl2 (10
mL), filtered through a celite pad, and washed with CH2Cl2 (10ꢀ
70 20 mL). The combined organic extracts were concentrated and
the resulting residue was purified by column chromatography on
silica gel to provide the desired product.
5
Experimental
General
NMR spectra were obtained on a Bruker AV IIꢀ400 MHz or a
Varian Inova 400 spectrometer. The 1H NMR (400 MHz)
10 chemical shifts were measured relative to CDCl3 as the internal
reference (CDCl3: δ = 7.26 ppm). The 13C NMR (100 MHz)
chemical shifts were given using CDCl3 as the internal standard
(CDCl3: δ = 77.16 ppm). High resolution mass spectra (HRMS)
were recorded by ESIꢀTOF. Melting points were determined with
15 XRCꢀ1 and are uncorrected. Absorption spectra were obtained on
a HITACHI Uꢀ2910 spectrometer. Fluorescence spectra were
Synthesis of benzo[4,5]imidazo[1,2-f]phenanthridine (3a).
Purification via silica gel column chromatography (petroleum
75 ether/ethyl acetate = 5/1, v/v) afforded the desired product as a
white solid (64 mg, 96% yield). M.p.: 144ꢀ146 °C. 1H NMR (400
MHz, CDCl3): δ = 7.45ꢀ7.54 (m, 3H), 7.66ꢀ7.74 (m, 3H), 8.05 (d,
J = 8.0 Hz, 1H), 8.30ꢀ8.38 (m, 2H), 8.42ꢀ8.45 (m, 1H), 8.51ꢀ8.56
(m, 1H), 8.85ꢀ8.88 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ
80 = 114.1, 116.1, 120.5, 121.9, 122.4, 123.1, 123.6, 124.3, 124.4,
124.6, 126.2, 128.8, 129.3, 129.7, 130.6, 132.0, 134.6, 144.7,
147.7 ppm. HRMS (ESI+): calcd for C19H13N2 [M+H]+ 269.1079,
found 269.1081.
collected on
a Horiba Jobin YvonꢀEdison Fluoromaxꢀ4
fluorescence spectrometer with a slit width of 3.0 nm for solution
and 5.0 nm in the solid state, and absolute quantum yields were
20 collected with a calibrated integrating sphere system. The
fluorescence lifetimes were determined on a HORIBA TEMPROꢀ
01 instrument. Cyclic voltammetry (CV) measurements were
performed on LK2005A using an Ag/Ag+ (0.01 M of AgNO3 in
acetonitrile) reference electrode,
a platinum wire counter
25 electrode, and platinum plate working electrode. CV
a
measurements were carried out in dry acetonitrile using Fc/Fc+ as
reference at a scan rate of 100 mVꢁsꢀ1 with tetrabutylammonium
hexafluorophosphate (NBu4PF6, 0.1 M) as supporting electrolyte.
Thermal decomposition temperatures were detected by
30 thermogravimetry/differential thermal analysis (TG/DTA) on a
NETZSCHꢀLeading Thermal Analysis in the temperature range
of 30ꢀ500 °C at a heating rate of 10 °C/min under a nitrogen
atmosphere.
Synthesis
85 f]phenanthridine (3b). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate 5/1, v/v)
of
2-methylbenzo[4,5]imidazo[1,2-
=
afforded the desired product as a pale yellow solid (62 mg, 88%
yield). M.p.: 187ꢀ189 °C. 1H NMR (400 MHz, CDCl3): δ = 2.44
(s, 3H), 7.33 (d, J = 8.4 Hz, 1H), 7.42 (t, J = 7.6 Hz, 1H), 7.49 (t,
90 J = 7.6 Hz, 1H), 7.58ꢀ7.66 (m, 2H), 8.02 (d, J = 8.0 Hz, 1H), 8.07
(s, 1H), 8.19ꢀ8.27 (m, 3H), 8.79 (d, J = 7.6 Hz, 1H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 21.3, 113.9, 115.7, 120.3, 121.5,
122.2, 122.8, 123.5, 124.0, 124.3, 126.0, 128.5, 129.5, 130.0,
130.3, 131.9, 132.3, 134.0, 144.5, 147.4 ppm. HRMS (ESI+):
95 calcd for C20H15N2 [M+H]+ 283.1235, found 283.1228.
Unless otherwise noted, all reagents were obtained from
35 commercial suppliers and used without further purification. 2ꢀ
Phenylꢀ1Hꢀbenzo[d]imidazole and various substituted 2ꢀarylꢀ1Hꢀ
benzo[d]imidazoles13,
2ꢀphenylꢀ1Hꢀindole14,
2ꢀphenylꢀ1Hꢀ
pyrrole15, 4,5ꢀdimethylꢀ2ꢀphenylꢀ1Hꢀimidazole16, ethyl 4ꢀbromoꢀ
3ꢀchlorobenzoate17, 2,3ꢀdichloroquinoxaline18,
and 2,3ꢀ
40 dibromobenzo[b]thiophene19 were prepared according to the
literature procedures. Solvents were dried by refluxing for at least
24 hours over CaH2 (DMF or DMSO), sodium (dioxane or
toluene), and freshly distilled prior to use.
Synthesis
of
2-methoxybenzo[4,5]imidazo[1,2-
f]phenanthridine (3c). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate/triethylamine =
5/1/0.01, v/v/v) afforded the desired product as a white solid (63
100 mg, 85% yield). M.p.: 219ꢀ221 °C. 1H NMR (400 MHz, CDCl3):
δ = 3.94 (s, 3H), 7.19 (dd, J = 9.2 Hz, 2.8 Hz, 1H), 7.44 (t, J = 7.6
Hz, 1H), 7.50 (t, J = 7.6 Hz, 1H), 7.63ꢀ7.70 (m, 2H), 7.81 (d, J =
2.4 Hz, 1H), 8.04 (d, J = 8.0 Hz, 1H), 8.23 (d, J = 8.0 Hz, 2H),
8.39 (d, J = 9.2 Hz, 1H), 8.85 (d, J = 7.6 Hz, 1H) ppm. 13C NMR
105 (100 MHz, CDCl3): δ = 55.7, 108.1, 113.7, 115.8, 117.1, 120.4,
122.4, 122.8, 123.1, 123.7, 124.0, 126.2, 128.77, 128.79, 129.3,
130.3, 131.8, 144.5, 147.1, 156.2 ppm. HRMS (ESI+): calcd for
C20H15N2O [M+H]+ 299.1184, found 299.1186.
Optimization of tandem N–H/C–H arylation of 2-phenyl
45 benzoimidazole with o-dibromobenzene
A flameꢀdried Schlenk tube with a magnetic stir bar was charged
with palladium source (5ꢀ10 mol%), ligand (5ꢀ10 mol%), base
(0.75 mmol) and 2a (58.4 mg, 0.30 mmol, 1.2 equiv). Then, 1a
(30 ꢂL, 0.25 mmol) and solvent (2.0 mL) were added to the
50 reaction mixture under an N2 atmosphere. The reaction mixture
was stirred for 10 min at room temperature, and then heated at
140 °C in preꢀheated oil bath for 24 h. After that, the reaction
mixture was cooled to room temperature, diluted with CH2Cl2 (10
mL), filtered through a celite pad, and washed with CH2Cl2 (10ꢀ
55 20 mL). The combined organic extracts were concentrated and
the resulting residue was purified by column chromatography on
Synthesis
110 f]phenanthridine (3d). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate 5/1, v/v)
of
2-trifluoromethylbenzo[4,5]imidazo[1,2-
=
afforded the desired product as a white solid (76 mg, 90% yield).
M.p.: 204ꢀ207 °C. 1H NMR (400 MHz, CDCl3): δ = 7.44ꢀ7.53 (m,
6
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2H), 7.64ꢀ7.73 (m, 2H), 7.84 (d, J = 8.8 Hz, 1H), 8.00 (d, J = 7.6
131.3, 131.7, 135.7, 140.6, 142.0, 142.5, 144.3, 147.1 ppm.
Hz, 1H), 8.19 (d, J = 8.0 Hz, 1H), 8.28 (d, J = 8.0 Hz, 1H), 8.50 60 HRMS (ESI+): calcd for C17H11N4 [M+H]+ 271.0984, found
(d, J = 8.4 Hz, 1H), 8.60 (s, 1H), 8.76 (d, J = 7.6 Hz, 1H) ppm.
13C NMR (100 MHz, CDCl3): δ = 113.8, 116.4, 120.8, 121.58,
121.62, 121.66, 121.70, 122.0, 122.4, 122.8, 123.6, 123.8, 124.8,
125.46, 125.48, 125.67, 125.71, 125.74, 126.0, 126.3, 126.4,
271.0985.
Synthesis
of
benzo[4,5]imidazo[2,1-
5
a]benzo[5,6]pyrazino[2,3-c]isoquinoline (3i). Purification via
silica gel column chromatography (petroleum ether/ethyl acetate
126.7, 127.0, 128.5, 129.6, 130.9, 131.8, 136.4, 144.7, 147.5 ppm. 65 = 5/1, v/v) afforded the desired product as a yellowꢀgreen solid
HRMS (ESI+): calcd for C20H12F3N2 [M+H]+ 337.0953, found
337.0953.
Synthesis of ethyl benzo[4,5]imidazo[1,2-f]phenanthridine-
3-carboxylate (3e). Following the general procedure, Pd(PPh3)4
(50 mg, 63% yield). M.p.: 250ꢀ253 °C. 1H NMR (400 MHz,
CDCl3): δ = 7.53ꢀ7.55 (m, 2H), 7.78ꢀ7.87 (m, 4H), 8.00 (d, J =
6.8 Hz, 1H), 8.23 (t, J = 8.4 Hz, 2H), 8.77ꢀ8.79 (m, 1H), 9.04ꢀ
9.06 (m, 1H), 9.18 (d, J = 8.0 Hz, 1H) ppm. 13C NMR (100 MHz,
10
(28.8 mg, 0.025 mmol), Xantphos (14.6 mg, 0.025 mmol), 70 CDCl3): δ = 116.8, 120.1, 124.5, 125.2, 125.5, 125.6, 125.8,
Cs2CO3 (243 mg, 0.75 mmol), 2a (48.5 mg, 0.25 mmol) and ethyl
4ꢀbromoꢀ3ꢀchlorobenzoate (72.6 mg, 0.275 mmol) in DMF (2.0
15 mL). Purification via silica gel column chromatography
(petroleum ether/ethyl acetate = 5/1, v/v) afforded the desired
128.2, 129.1, 129.5, 129.8, 130.9, 131.0, 131.7, 132.2, 137.2,
140.2, 140.4, 141.1, 144.3, 147.3 ppm. HRMS (ESI+): calcd for
C21H13N4 [M+H]+ 321.1140, found 321.1148.
Synthesis of benzo[4,5]imidazo[2,1-a]benzo[4,5]thieno[2,3-
product as a white solid (60 mg, 71% yield). M.p.: 168ꢀ170 °C. 75 c]isoquinoline (3j). Purification via silica gel column
1H NMR (400 MHz, CDCl3): δ = 1.51 (t, J = 7.2 Hz, 3H), 4.50 (q,
J = 7.2 Hz, 2H), 7.48ꢀ7.55 (m, 2H), 7.66ꢀ7.70 (m, 2H), 8.02ꢀ8.04
20 (m, 2H), 8.27ꢀ8.32 (m, 2H), 8.37 (d, J = 8.4 Hz, 1H), 8.84 (d, J =
6.4 Hz, 1H), 9.10 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ =
chromatography (petroleum ether/ethyl acetate = 5/1, v/v)
afforded the desired product as a offꢀwhite solid (43 mg, 53%
1
yield). M.p.: 241ꢀ244 °C. H NMR (400 MHz, CDCl3): δ = 7.42ꢀ
7.47 (m, 1H), 7.51ꢀ7.59 (m, 3H), 7.68ꢀ7.76 (m, 2H), 7.93ꢀ7.95 (m,
14.5, 61.8, 114.1, 117.4, 120.2, 123.0, 123.9, 124.3, 124.9, 125.2, 80 1H), 7.99ꢀ8.02 (m, 1H), 8.09 (d, J = 8.0 Hz, 1H), 8.46 (d, J = 8.4
125.3, 126.5, 128.8, 129.9, 130.9, 131.1, 131.5, 133.8, 136.4,
146.7, 165.7 ppm. HRMS (ESI+): calcd for C22H17N2O2 [M+H]+
25 341.1290, found 341.1291.
Hz, 1H), 8.76 (d, J = 8.0 Hz, 1H), 8.90ꢀ8.92 (m, 1H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 114.7, 120.5, 121.4, 122.6, 123.6,
123.7, 123.8, 124.4, 124.5, 124.9, 126.1, 126.2, 128.3, 128.6,
128.8, 130.7, 131.0, 131.4, 138.2, 144.3, 148.7 ppm. HRMS
Synthesis
of
3-chlorobenzo[4,5]imidazo[1,2-
f]phenanthridine (3f). Purification via silica gel column 85 (ESI+): calcd for C21H13N2S [M+H]+ 325.0799, found 325.0795.
chromatography (petroleum ether/ethyl acetate
=
5/1, v/v)
Synthesis of 6-methylimidazo[1,2-f]phenanthridine (3k).
Following the general procedure, Pd(PPh3)4 (28.8 mg, 0.025
mmol), Xantphos (14.6 mg, 0.025 mmol), Cs2CO3 (243 mg, 0.75
mmol), 2b (36 mg, 0.25 mmol) and 1b (46 ꢂL, 0.30 mmol) in
afforded the desired product as a white solid (61 mg, 81% yield).
30 M.p.: 144ꢀ148 °C. 1H NMR (400 MHz, CDCl3): δ = 7.42ꢀ7.46 (m,
1H), 7.48ꢀ7.56 (m, 2H), 7.65ꢀ7.74 (m, 2H), 8.04 (d, J = 7.6 Hz,
1H), 8.24ꢀ8.29 (m, 2H), 8.34 (t, J = 8.0 Hz, 1H), 8.48ꢀ8.50 (m, 90 DMF (2.0 mL). Purification via silica gel column
1H), 8.82ꢀ8.84 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ =
113.8, 116.1, 120.3, 120.7, 122.2, 123.3, 123.4, 124.6, 124.7,
35 125.4, 126.2, 128.8, 129.0, 130.7, 131.6, 135.0, 135.1, 144.6,
147.5 ppm. HRMS (ESI+): calcd for C19H12ClN2 [M+H]+
303.0689, found 303.0694.
chromatography (petroleum ether/ethyl acetate = 8/1, v/v)
afforded the desired product as a yellow solid (52 mg, 90% yield).
M.p.: 134ꢀ138 °C. 1H NMR (400 MHz, CDCl3): δ = 2.51 (s, 3H),
7.36 (d, J = 8.4 Hz, 1H), 7.57 (s, 1H), 7.61 (t, J = 4.0 Hz, 2H),
95 7.67 (d, 1H), 7.90 (s, 1H), 8.16 (s, 1H), 8.29ꢀ8.31 (m, 1H), 8.61ꢀ
8.63 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.8, 112.2,
115.9, 121.9, 122.6, 124.0, 124.4, 127.7, 128.7, 128.8, 130.0,
130.2, 131.6, 135.0, 142.6 ppm. HRMS (ESI+): calcd for
C16H13N2 [M+H]+ 233.1079, found 233.1079.
Synthesis
of
benzo[4,5]imidazo[1,2-
a]benzo[c][1,8]naphthyridine (3g). Purification via silica gel
40 column chromatography (petroleum ether/ethyl acetate = 5/1, v/v)
afforded the desired product as a pale yellow solid (44 mg, 65%
1
yield). M.p.: 158ꢀ161 °C. H NMR (400 MHz, CDCl3): δ = 7.49ꢀ 100 Synthesis of 2-methylindolo[1,2-f]phenanthridine (3l).
7.58 (m, 3H), 7.74ꢀ7.81 (m, 2H), 8.05ꢀ8.07 (m, 1H), 8.35ꢀ8.37
Following the general procedure, Pd(PPh3)4 (28.8 mg, 0.025
mmol), Xantphos (14.6 mg, 0.025 mmol), K2CO3 (104 mg, 0.75
mmol), 2c (48 mg, 0.25 mmol) and 1b (46 ꢂL, 0.30 mmol) in
DMF (2.0 mL). Purification via silica gel column
(m, 1H), 8.74 (dd, J = 8.0 Hz, 1.6 Hz, 1H), 8.79 (dd, J = 4.4 Hz,
45 1.6 Hz, 1H), 8.97 (d, J = 6.8 Hz, 1H), 9.17ꢀ9.19 (m, 1H) ppm. 13
C
NMR (100 MHz, CDCl3): δ = 116.7, 117.3, 119.5, 120.2, 122.6,
123.7, 124.8, 126.2, 128.6, 129.5, 130.6, 131.8, 132.0, 146.2, 105 chromatography (petroleum ether/dichloromethane/ethyl acetate
147.56, 147.64, 148.5 ppm. HRMS (ESI+): calcd for C18H12N3
[M+H]+ 270.1031, found 270.1032.
= 40/5/1, v/v/v) afforded the desired product as a white solid (53
mg, 75% yield). M.p.: 152ꢀ156 °C. H NMR (400 MHz, CDCl3):
1
50
Synthesis
c]isoquinoline (3h). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate
of
benzo[4,5]imidazo[2,1-a]pyrazino[2,3-
δ = 2.53 (s, 3H), 7.28 (s, 1H), 7.33ꢀ7.41 (m, 3H), 7.49ꢀ7.51 (m,
2H), 7.85 (d, J = 7.6 Hz, 1H), 8.15ꢀ8.17 (m, 2H), 8.24ꢀ8.27 (m,
=
5/1, v/v) 110 1H), 8.38 (d, J = 8.4 Hz, 1H), 8.46 (d, J = 8.4 Hz, 1H) ppm. 13C
afforded the desired product as a pale yellow solid (43 mg, 64%
yield). M.p.: 178ꢀ181 °C. H NMR (400 MHz, CDCl3): δ = 7.49ꢀ
NMR (100 MHz, CDCl3): δ = 21.3, 96.0, 114.3, 116.4, 121.2,
121.8, 122.0, 122.1, 122.6, 124.4, 124.5, 126.4, 127.0, 127.9,
128.3, 129.8, 130.4, 132.6, 134.0, 134.1, 135.3 ppm. HRMS
(ESI+): calcd for C21H16N [M+H]+ 282.1283, found 282.1285.
1
55 7.56 (m, 2H), 7.80ꢀ7.84 (m, 2H), 8.02 (d, J = 7.6 Hz, 1H), 8.70 (s,
1H), 8.76 (s, 1H), 8.85 (t, J = 3.2 Hz, 1H), 8.89ꢀ8.91 (m, 1H),
8.96 (d, J = 8.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 115 Synthesis
of
6-tert-butyl-benzo[4,5]imidazo[1,2-
116.5, 120.1, 124.1, 124.8, 125.1, 125.2, 125.5, 129.7, 130.9,
f]phenanthridine (4a). Purification via silica gel column
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DOI: 10.1039/C3OB41760C
chromatography (petroleum ether/ethyl acetate
=
5/1, v/v)
7.54 (m, 3H), 7.60 (dd, J = 8.4 Hz, 2.0 Hz, 1H), 7.67ꢀ7.71 (m,
afforded the desired product as a pale yellow solid (71 mg, 88% 60 1H), 8.01ꢀ8.03 (m, 1H), 8.26ꢀ8.28 (m, 1H), 8.30ꢀ8.34 (m, 2H),
1
yield). M.p.: 131ꢀ134 °C. H NMR (400 MHz, CDCl3): δ = 1.50
(s, 9H), 7.46ꢀ7.58 (m, 3H), 7.71ꢀ7.75 (m, 1H), 7.79 (dd, J = 8.4
Hz, 1.2 Hz, 1H), 8.08 (d, J = 8.0 Hz, 1H), 8.37 (d, J = 8.0 Hz,
1H), 8.42 (d, J = 1.2 Hz, 1H), 8.55ꢀ8.61 (m, 2H), 8.86 (d, J = 8.4
8.49 (d, J = 8.4 Hz, 1H), 8.77 (d, J = 8.8 Hz, 1H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 114.0, 116.2, 120.6, 120.7, 122.0, 122.4,
123.3, 124.5, 124.7, 127.8, 129.2, 130.0, 131.1, 131.9, 134.9,
137.0, 144.6, 146.9 ppm. HRMS (ESI+): calcd for C19H12ClN2
5
Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 31.5, 35.6, 114.0, 65 [M+H]+ 303.0689, found 303.0691.
116.1, 118.5, 120.3, 121.2, 122.1, 122.8, 124.1, 124.2, 124.4,
126.0, 126.8, 129.0, 129.3, 132.0, 134.7, 144.8, 147.8, 153.8 ppm.
Synthesis
of
6-cyano-benzo[4,5]imidazo[1,2-
f]phenanthridine (4f). Following the general procedure,
Pd(PPh3)4 (28.8 mg, 0.025 mmol), Xantphos (14.6 mg, 0.025
mmol), Cs2CO3 (243 mg, 0.75 mmol), 4ꢀ(1Hꢀbenzo[d]imidazolꢀ
10 HRMS (ESI+): calcd for C23H21N2 [M+H]+ 325.1705, found
325.1706.
Synthesis
of
6-methoxy-benzo[4,5]imidazo[1,2- 70 2ꢀyl)benzonitrile (55 mg, 0.275 mmol) and 1a (32 ꢂL, 0.265
f]phenanthridine (4b). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate/triethylamine =
15 5/1/0.01, v/v/v) afforded the desired product as a pale yellow
solid (68 mg, 91% yield). M.p.: 172ꢀ174 °C. 1H NMR (400 MHz,
mmol) in DMF (2.0 mL). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate 5/1, v/v)
=
afforded the desired product as a yellow solid (53 mg, 68% yield).
M.p.: 258ꢀ260 °C. 1H NMR (400 MHz, CDCl3): δ = 7.61ꢀ7.66 (m,
CDCl3): δ = 4.00 (s, 3H), 7.23ꢀ7.26 (m, 1H), 7.41ꢀ7.51 (m, 3H), 75 3H), 7.82ꢀ7.86 (m, 1H), 7.92 (d, J = 8.0 Hz, 1H), 8.16 (d, J = 7.2
7.66 (t, J = 7.6 Hz, 1H), 7.72 (d, J = 2.0 Hz, 1H), 8.00 (d, J = 8.0
Hz, 1H), 8.29 (d, J = 8.0 Hz, 1H), 8.35 (d, J = 8.4 Hz, 1H), 8.51
20 (d, J = 8.4 Hz, 1H), 8.77 (d, J = 8.8 Hz, 1H) ppm. 13C NMR (100
MHz, CDCl3): δ = 55.6, 105.4, 113.8, 115.9, 116.6, 117.0, 120.0,
Hz, 1H), 8.40 (d, J = 7.2 Hz, 1H), 8.47 (d, J = 8.0 Hz, 1H), 8.63
(d, J = 8.0 Hz, 1H), 8.68 (s, 1H), 9.16 (d, J = 7.2 Hz, 1H) ppm.
13C NMR (100 MHz, CDCl3): δ = 113.9, 114.2, 116.4, 118.7,
120.2, 121.1, 124.2, 124.6, 124.9, 125.2, 126.7, 127.1, 127.3,
121.4, 122.4, 124.0, 124.10, 124.14, 127.9, 129.2, 131.3, 131.9, 80 129.9, 130.7, 130.8, 132.0, 135.0, 144.7 ppm. HRMS (ESI+):
134.7, 144.7, 147.8, 161.5 ppm. HRMS (ESI+): calcd for
calcd for C20H12N3 [M+H]+ 294.1031, found 294.1028.
Synthesis of 8-trifluoromethyl-benzo[4,5]imidazo[1,2-
f]phenanthridine (4g). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate 5/1, v/v)
Pd(PPh3)4 (14.4 mg, 0.0125 mmol), Xantphos (7.3 mg, 0.0125 85 afforded the desired product as a pale yellow solid (66 mg, 79%
C20H15N2O [M+H]+ 299.1184, found 299.1185.
25 Synthesis
of
7-methoxy-benzo[4,5]imidazo[1,2-
f]phenanthridine (4c). Following the general procedure,
=
1
mmol), Cs2CO3 (122 mg, 0.375 mmol), 2ꢀ(3ꢀmethoxyphenyl)ꢀ
1Hꢀbenzo[d]imidazole (28 mg, 0.125 mmol) and 1a (15 ꢂL,
30 0.125 mmol) in DMF (1.0 mL). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate/triethylamine =
yield). M.p.: 187ꢀ189 °C. H NMR (400 MHz, CDCl3): δ = 7.43
(t, J = 7.6 Hz, 1H), 7.47ꢀ7.54 (m, 2H), 7.66 (t, J = 8.0 Hz, 1H),
7.73 (t, J = 8.0 Hz, 1H), 8.09ꢀ8.12 (m, 2H), 8.30 (d, J = 8.0 Hz,
1H), 8.38 (d, J = 8.0 Hz, 1H), 8.49 (d, J = 8.4 Hz, 1H), 8.56 (d, J
5/1/0.01, v/v/v) afforded the desired product as a pale yellow 90 = 8.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 113.8,
solid (28 mg, 75% yield). M.p.: 163ꢀ165 °C. 1H NMR (400 MHz,
CDCl3): δ = 4.06 (s, 3H), 7.32 (dd, J = 8.8 Hz, 2.4 Hz, 1H), 7.47ꢀ
35 7.56 (m, 3H), 7.62ꢀ7.66 (m, 1H), 8.09 (d, J = 7.6 Hz, 1H), 8.26 (d,
J = 9.2 Hz, 1H), 8.34ꢀ8.38 (m, 3H), 8.54 (d, J = 8.4 Hz, 1H) ppm.
115.9, 121.0, 121.7, 121.9, 123.9, 124.3, 124.6, 124.7, 125.6,
126.4, 128.0, 128.2, 128.3, 128.37, 128.44, 129.0, 130.0, 131.2,
131.9, 134.5, 143.9, 144.5 ppm. HRMS (ESI+): calcd for
C20H12F3N2 [M+H]+ 337.0953, found 337.0954.
13C NMR (100 MHz, CDCl3): δ = 56.2, 106.9, 114.3, 116.2, 95 Synthesis
of
6-phenyl-benzo[4,5]imidazo[1,2-
120.0, 121.3, 122.1, 123.40, 123.44, 123.8, 124.2, 124.7, 124.9,
128.3, 131.8, 133.3, 147.0, 151.9, 152.2, 160.2 ppm. HRMS
40 (ESI+): calcd for C20H15N2O [M+H]+ 299.1184, found 299.1187.
f]phenanthridine (4h). Following the general procedure,
Pd(PPh3)4 (14.4 mg, 0.0125 mmol), Xantphos (7.3 mg, 0.0125
mmol), Cs2CO3 (122 mg, 0.375 mmol), 2ꢀ(biphenylꢀ4ꢀyl)ꢀ1Hꢀ
benzo[d]imidazole (34 mg, 0.125 mmol) and 1a (18 ꢂL, 0.15
Synthesis
of
6-fluoro-benzo[4,5]imidazo[1,2-
f]phenanthridine (4d). Purification via silica gel column 100 mmol) in DMF (1.0 mL). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate 5/1, v/v) chromatography (petroleum ether/ethyl acetate 5/1, v/v)
=
=
afforded the desired product as a yellow solid (64 mg, 90% yield).
45 M.p.: 151ꢀ154 °C. H NMR (400 MHz, CDCl3): δ = 7.36 (td, J =
8.4 Hz, 2.0 Hz, 1H), 7.44ꢀ7.53 (m, 3H), 7.69 (t, J = 8.0 Hz, 1H),
afforded the desired product as a yellow solid (38 mg, 88% yield).
M.p.: 207ꢀ209 °C. 1H NMR (400 MHz, CDCl3): δ = 7.43ꢀ7.55 (m,
6H), 7.65 (t, J = 8.0 Hz, 1H), 7.74 (d, J = 7.6 Hz, 2H), 7.88 (dd, J
1
7.94 (dd, J = 10.4 Hz, 2.4 Hz, 1H), 8.01 (d, J = 8.0 Hz, 1H), 8.28ꢀ 105 = 8.4 Hz, 1.2 Hz, 1H), 8.05 (d, J = 8.0 Hz, 1H), 8.28 (d, J = 8.4
8.30 (m, 2H), 8.50 (d, J = 8.4 Hz, 1H), 8.83 (dd, J = 8.8 Hz, 2.0
Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 108.4, 108.6,
50 114.0, 116.2, 117.0, 117.2, 120.1, 120.5, 121.0, 123.1, 124.4,
124.55, 124.62, 128.8, 128.9, 130.0, 131.9, 132.0, 134.9, 144.6,
Hz, 1H), 8.48ꢀ8.49 (m, 3H), 8.90 (d, J = 8.0 Hz, 1H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 114.1, 116.2, 120.2, 120.8, 121.8,
122.0, 123.2, 124.3, 124.5, 124.7, 126.8, 127.6, 128.0, 128.3,
129.2, 129.4, 130.0, 131.8, 134.5, 140.5, 143.5, 144.1, 147.2 ppm.
147.1, 163.1, 165.6 ppm. HRMS (ESI+): calcd for C19H12FN2 110 HRMS (ESI+): calcd for C25H17N2 [M+H]+ 345.1392, found
[M+H]+ 287.0985, found 287.0985.
Synthesis of 6-chloro-benzo[4,5]imidazo[1,2-
55 f]phenanthridine (4e). Purification via silica gel column
chromatography (petroleum ether/ethyl acetate 5/1, v/v)
345.1394.
Synthesis
of
dibenzo[i,k]-benzo[4,5]imidazo[1,2-
f]phenanthridine (4i). Following the general procedure,
Pd(PPh3)4 (14.4 mg, 0.0125 mmol), Xantphos (7.3 mg, 0.0125
=
afforded the desired product as a pale yellow solid (64 mg, 84% 115 mmol), Cs2CO3 (122 mg, 0.375 mmol), 2ꢀ(phenanthrenꢀ9ꢀyl)ꢀ1Hꢀ
1
yield). M.p.: 198ꢀ200 °C. H NMR (400 MHz, CDCl3): δ = 7.46ꢀ
benzo[d]imidazole (38 mg, 0.125 mmol) and 1a (18 ꢂL, 0.15
8
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DOI: 10.1039/C3OB41760C
mmol) in DMF (1.0 mL). Purification via silica gel column
general procedure, Pd(PPh3)4 (28.8 mg, 0.025 mmol), Xantphos
chromatography (petroleum ether/ethyl acetate 5/1, v/v) 60 (14.6 mg, 0.025 mmol), K2CO3 (104 mg, 0.75 mmol), 2c (48 mg,
=
afforded the desired product as a yellow solid (30 mg, 65% yield).
M.p.: 219ꢀ222 °C. 1H NMR (400 MHz, CDCl3): δ = 7.50ꢀ7.60 (m,
3H), 7.65 (t, J = 7.6 Hz, 1H), 7.72ꢀ7.82 (m, 3H), 7.88ꢀ7.92 (m,
1H), 8.22 (d, J = 7.6 Hz, 1H), 8.42 (d, J = 8.0 Hz, 1H), 8.61ꢀ8.64
0.25 mmol) and 1a (36 ꢂL, 0.30 mmol) in DMF (2.0 mL).
Purification via silica gel column chromatography (petroleum
ether/dichloromethane/ethyl acetate = 40/5/1, v/v/v) afforded the
desired product as a yellow solid (55 mg, 82% yield). M.p.: 145ꢀ
5
(m, 2H), 8.68 (d, J = 8.0 Hz, 1H), 8.74 (t, J = 8.0 Hz, 2H), 10.55 65 147 °C. 1H NMR (400 MHz, CDCl3): δ = 7.30 (s, 1H), 7.34ꢀ7.42
(d, J = 8.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 113.7,
116.0, 119.3, 120.8, 122.0, 122.6, 123.2, 123.8, 124.0, 124.4,
(m, 3H), 7.50ꢀ7.53 (m, 2H), 7.60 (t, J = 8.0 Hz, 1H), 7.86 (d, J =
7.2 Hz, 1H), 8.16ꢀ8.18 (m, 1H), 8.25ꢀ8.27 (m, 1H), 8.36 (d, J =
7.6 Hz, 1H), 8.41 (d, J = 8.4 Hz, 1H), 8.58 (d, J = 8.4Hz, 1H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 96.4, 114.4, 116.5, 121.2,
10 126.5, 127.6, 127.9, 128.0, 128.3, 128.5, 128.98, 129.05, 129.6,
129.7, 130.3, 130.56, 130.65, 132.5, 133.9, 144.8, 147.2 ppm.
HRMS (ESI+): calcd for C27H17N2 [M+H]+ 369.1392, found 70 122.0, 122.2, 122.3, 122.6, 123.2, 124.2, 124.3, 126.3, 127.0,
369.1394.
128.0, 128.4, 128.9, 130.5, 134.1, 135.4, 136.2 ppm. HRMS
(ESI+): calcd for C20H14N [M+H]+ 268.1126, found 268.1124.
Synthesis of pyrrolo[1,2-f]phenanthridine (4n). Following the
general procedure, Pd(PPh3)4 (28.8 mg, 0.025 mmol), Xantphos
Synthesis of benzo[4,5]imidazo[1,2-a]thieno[2,3-c]quinoline
15 (4j). Following the general procedure, Pd(PPh3)4 (14.4 mg,
0.0125 mmol), Xantphos (7.3 mg, 0.0125 mmol), Cs2CO3 (122
mg, 0.375 mmol), 2ꢀ(thiophenꢀ2ꢀyl)ꢀ1Hꢀbenzo[d]imidazole (25 75 (14.6 mg, 0.025 mmol), K2CO3 (104 mg, 0.75 mmol), 2ꢀphenylꢀ
mg, 0.125 mmol) and 1a (18 ꢂL, 0.15 mmol) in DMF (1.0 mL).
Purification via silica gel column chromatography (petroleum
20 ether/ethyl acetate = 15/1, v/v) afforded the desired product as a
pale yellow solid (28 mg, 82% yield). M.p.: 190ꢀ194 °C. 1H
1Hꢀpyrrole (39 mg, 0.275 mmol) and 1a (32 ꢂL, 0.265 mmol) in
DMF (2.0 mL). Purification via silica gel column
chromatography (petroleum ether/dichloromethane/ethyl acetate
= 60/5/1, v/v/v) afforded the desired product as a yellow solid (45
1
NMR (400 MHz, CDCl3): δ = 7.38ꢀ7.45 (m, 2H), 7.48ꢀ7.52 (m, 80 mg, 78% yield). M.p.: 113ꢀ117 °C. H NMR (400 MHz, CDCl3):
1H), 7.56ꢀ7.61 (m, 1H), 7.67 (d, J = 5.2 Hz, 1H), 7.71 (d, J = 5.2
Hz, 1H), 8.00 (dd, J = 8.4 Hz, 0.8 Hz, 1H), 8.07 (dd, J = 8.0 Hz,
25 1.6 Hz, 1H), 8.27 (d, J = 8.4 Hz, 1H), 8.47 (d, J = 8.4 Hz, 1H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 113.9, 115.9, 120.2,
δ = 6.74 (t, J = 3.2 Hz, 1H), 6.97 (dd, J = 3.6 Hz, 1.2 Hz, 1H),
7.37ꢀ7.44 (m, 2H), 7.46ꢀ7.55 (m, 2H), 7.78ꢀ7.79 (m, 1H), 7.87 (d,
J = 8.4 Hz, 1H), 8.02 (d, J = 8.0 Hz, 1H), 8.26 (d, J = 8.0 Hz, 1H),
8.35 (d, J = 8.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ =
120.6, 122.6, 122.9, 124.47, 124.50, 125.2, 126.4, 128.5, 130.3, 85 102.2, 112.3, 113.2, 115.1, 121.9, 122.6, 122.9, 124.0, 124.1,
131.4, 134.2, 137.5, 144.4, 144.8 ppm. HRMS (ESI+): calcd for
C17H11N2S [M+H]+ 275.0643, found 275.0646.
125.0, 126.1, 126.5, 128.3, 128.7, 129.5, 133.4 ppm. HRMS
(ESI+): calcd for C16H12N [M+H]+ 218.0970, found 218.0965.
30 Synthesis of imidazo[1,2-f]phenanthridine (4k). Following
the general procedure, Pd(PPh3)4 (28.8 mg, 0.025 mmol),
Xantphos (14.6 mg, 0.025 mmol), Cs2CO3 (243 mg, 0.75 mmol),
2ꢀphenylꢀ1Hꢀimidazole (36 mg, 0.25 mmol) and 1a (36 ꢂL, 0.30
mmol) in DMF (2.0 mL). Purification via silica gel column
Acknowledgements
This work was supported by grants from 863 Program
90 (2013AA031901), the National NSF of China (Nos 21372164,
21172155, 21025205, 21021001, and J1103315/J0104), and
Sichuan Provincial Foundation (2012JQ0002).
35 chromatography (petroleum ether/ethyl acetate
= 8/1, v/v)
afforded the desired product as a yellow solid (51 mg, 94% yield).
M.p.: 119ꢀ123 °C. 1H NMR (400 MHz, CDCl3): δ = 7.49ꢀ7.53 (m,
1H), 7.59ꢀ7.66 (m, 4H), 7.86 (dd, J = 8.4 Hz, 0.8 Hz, 1H), 7.98 (d,
J = 1.2 Hz, 1H), 8.35ꢀ8.39 (m, 1H), 8.45 (dd, J = 8.0 Hz, 1.2 Hz,
40 1H), 8.64ꢀ8.68 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ =
112.1, 115.9, 121.8, 122.4, 123.8, 124.19, 124.21, 125.1, 127.5,
128.6, 128.7, 128.8, 131.6, 131.8, 142.6 ppm. HRMS (ESI+):
calcd for C15H11N2 [M+H]+ 219.0922, found 219.0918.
Notes and references
Key Laboratory of Green Chemistry and Technology of Ministry of
95 Education, College of Chemistry, and State Key Laboratory of
Biotherapy, West China Medical School, Sichuan University, 29
Wangjiang Road, Chengdu 610064, PR China. Fax: (+86) 28ꢀ85412203;
Eꢀmail: jingbolan@scu.edu.cn; jsyou@scu.edu.cn
†Electronic Supplementary Information (ESI) available: Detailed
100 experimental procedures, analytical data. See DOI: 10.1039/b000000x/
Synthesis of 2,3-dimethylimidazo[1,2-f]phenanthridine (4l).
45 Following the general procedure, Pd(PPh3)4 (28.8 mg, 0.025
mmol), Xantphos (14.6 mg, 0.025 mmol), Cs2CO3 (243 mg, 0.75
mmol), 4,5ꢀdimethylꢀ2ꢀphenylꢀ1Hꢀimidazole (43 mg, 0.25 mmol)
and 1a (36 ꢂL, 0.30 mmol) in DMF (2.0 mL). Purification via
silica gel column chromatography (petroleum ether/ethyl acetate
50 = 8/1, v/v) afforded the desired product as a yellow solid (55 mg,
1
(a) G. Méhes, H. Nomura, Q. Zhang, T. Nakagawa and C. Adachi,
Angew. Chem. Int. Ed., 2012, 51, 11311; (b) M. Shimizu, R. Kaki, Y.
Takeda, T. Hiyama, N. Nagai, H. Yamagishi and H. Furutani,
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M. G. Helander, Z.ꢀH. Lu and S. Wang, Adv. Mater., 2012, 24, 2922;
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Rudati, H. Frohne, O. Nuyken, H. Becker and K. Meerholz, Nature,
2003, 421, 829.
105
110
115
1
89% yield). M.p.: 141ꢀ144 °C. H NMR (400 MHz, CDCl3): δ =
2.43 (s, 3H), 2.77 (s, 3H), 7.37ꢀ7.40 (m, 1H), 7.45ꢀ7.48 (m, 1H),
7.52ꢀ7.59 (m, 2H), 8.21ꢀ8.24 (m, 2H), 8.37ꢀ8.38 (m, 1H), 8.61 (d,
J = 7.6 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ = 13.4,
55 14.4, 116.2, 120.7, 122.1, 122.5, 123.8, 123.9, 124.1, 124.2,
127.0, 128.0, 128.1, 128.4, 134.2, 137.9, 141.4 ppm. HRMS
(ESI+): calcd for C17H15N2 [M+H]+ 247.1235, found 247.1236.
Synthesis of indolo[1,2-f]phenanthridine (4m). Following the
2
3
M. Zhu and C. Yang, Chem. Soc. Rev., 2013, 42, 4963.
(a) H. Yamamoto, J. Brooks, M. S. Weaver, J. J. Brown, T.
Murakami and H. Murata, Appl. Phys. Lett., 2011, 99, 033301; (b)
C. Ritchie, G. J. T. Cooper, Y.ꢀF. Song, C. Streb, H. Yin, A. D. C.
Parenty, D. A. MacLaren and L. Cronin, Nature Chem., 2009, 1, 47;
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Page 10 of 10
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DOI: 10.1039/C3OB41760C
(c) C. Baik, D. Kim, M.ꢀS. Kang, K. Song, S. O. Kang and J. Ko,
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