Integration of nitrogen into coronene bisimides

Article abstract of DOI:10.1016/j.tet.2012.08.084

N-Decorated PBIs and CBIs have been synthesized by the combination of Pictet-Spengler condensation and subsequent oxidative aromatization based on highly electron-deficient amino-PBIs. A detailed analysis of their photophysical properties and molecular crystals has shown that the lateral aryl groups appended on the N-heterocycle have a negligible effect on their optical absorptions and electrochemical potentials, but the subtle modification leads to significant variations on arrangement in the solid state.

Full text of DOI:10.1016/j.tet.2012.08.084

Tetrahedron 68 (2012) 9234e9239
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Integration of nitrogen into coronene bisimides
,
,
a,
Linxiao Hao a b, Wei Jiang a , Zhaohui Wang
*
*
a Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b Graduate School of the Chinese Academy of Sciences, Beijing 100190, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 May 2012
Received in revised form 18 July 2012
Accepted 28 August 2012
Available online 1 September 2012
N-Decorated PBIs and CBIs have been synthesized by the combination of PicteteSpengler condensation
and subsequent oxidative aromatization based on highly electron-deficient amino-PBIs. A detailed
analysis of their photophysical properties and molecular crystals has shown that the lateral aryl groups
appended on the N-heterocycle have a negligible effect on their optical absorptions and electrochemical
potentials, but the subtle modification leads to significant variations on arrangement in the solid state.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Perylene bisimides
Coronene bisimides
PicteteSpengler
Aromatization
Isomerization
1. Introduction
and also provide access to various new potentially useful molecular
scaffold by affording a reaction site for further transformation.
Derivatives of perylene-3,4:9,10-tetracarboxylic acid bisimides
(PBIs) have received considerable attention as functional materials
because of their outstanding optical and electronic properties,
chemical and thermal stabilities, easily modified which have found
their great potential in the field of photovoltaic devices,1 organic
field effect transistors,2 light emitting diodes,3 near-infrared dyes,4
and constructing of graphene nanoribbons.5
Core-extended PBIs have been sought with the aim of creating
various novel chromophores to improve their performance in
molecular (opto)electronic devices.6 Annulation of PBIs with a va-
riety of cyclic units in the bay regions including diverse heterocy-
cles such as sulfur-, thiophene-, and N-heterocycles has been
actively investigated.7 An S-heterocyclic annulated PBI with tun-
able self-assembly behavior by the inclusion of different guest
molecules has been reported recently by our group.8 Furthermore,
bay-regions annulated S-diPBIs or N-diPBIs that bears two chro-
mophores coupled by triply linkage displays extraordinary doubly
bowl-shaped structures.9
The PicteteSpengler condensation of aromatic amines with al-
dehydes and ketones has been explored extensively for the prep-
aration of tetrahydroisoquinolines and b
-cabolines.11 In general, the
electron-rich aromatic amines used to undergo PicteteSpengler
reaction to achieve N-heterocycles can improve the reaction ef-
fectively.12 In this contribution, we describe our endeavors to de-
velop N-decorated coronene bisimides, a new family of core-
extended PBIs, from the highly electron-deficient PBI amines and
corresponding aldehydes by the combination of PicteteSpengler
reaction and subsequent oxidative aromatization. Accordingly, we
elucidate the crystal structures with different substituents appen-
ded on the N-heterocylces, as well as their influence on photo-
physical properties (Fig. 1).
Recently, we have presented regiospecifically pyridyl annulated
PBIs by a facile synthesis, which realized the light-promoted cy-
clization in high yields.10 The incorporation of electron-rich or
electron-deficient heterocycles directly into the framework of PBIs
can offer the means by which properties of them can be modulated
* Corresponding authors. Tel./fax: þ86 010 6265 3617; e-mail addresses: jiang-
wei@iccas.ac.cn (W. Jiang), wangzhaohui@iccas.ac.cn (Z. Wang).
Fig. 1. The molecular structures of PBIs, CBIs, and N-decorated CBIs.
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.08.084

L. Hao et al. / Tetrahedron 68 (2012) 9234e9239
9235
2. Results and discussion
2.1. Synthesis
(
d
¼8.84) and Hd
(
d
¼8.96) and carbonyl carbons (
d
¼161.96, 162.86)
determined the assignments of Ha (
ence of JCH coupling from protons both Hb and Hd to the same
carbon (Cc,
the case of 1,6-isomer because of their different symmetry (see
Supplementary data).
d
¼8.44), Hb, and Hd. The pres-
3
d¼129.74) could be observed for 1,7-isomer but not in
The key starting materials are nitrated PBIs (Scheme 1). Previous
synthetic reports of regiospecific nitration of PBI utilizing N2O4 or
Recent research results show that many protocols have been
employed for the reducing nitroarenes to arylamines,14 the catalytic
hydrogenation of hydrazine and Pd/C in 1,2-dimethoxyethane
(DME) was found to be the most effective for achieving both
monoamino-PBI (4) and diamino-PBI (7) quantitatively. Sub-
sequently, we applied a PicteteSpengler reaction of 4 with benz-
aldehyde or 2-pyridinecarboxaldehyde using triflic acid as the
catalyst, and DMF as the solvent to directly afford the corre-
sponding N-decorated PBIs, accompanied by oxidative aromatiza-
tion in one pot (Scheme 2).
We then envisaged that the reaction of regioisomerically 1,7-
diamino-PBIs with aldehyde under the same conditions could
produce the definite N-decorated coronene bisimides (CBIs). Un-
expectedly, when we use benzaldehyde as the reactant, there were
two isomers of N-decorated CBIs produced in the reaction simul-
taneously, and the molar ratio of 8 to 80 was 2:1, which was dem-
onstrated by 1H NMR and HMBC spectroscopy (see Supplementary
data). However, when 2-pyridinecarboxaldehyde was selected to
prove the presence of the isomers is not a case. We just find the
trace amount of the normal N-decorated CBIs (9), but its isomeri-
zation compound 90 existed in the resulting mixture as a main
product, which was proved by 1H NMR and HMBC spectroscopy and
X-ray single-crystal analysis as a definite structure (Scheme 3). This
phenomenon may be explained by the occurrence of CeN trans-
formation in the process of the reaction with highly electron-
deficient PBI amines that leads to the presence of isomers in the
resulting mixture. The mixture of N-decorated products (8 and 80)
could not be separated by column chromatography. Regioisomeri-
cally pure N-decorated CBI 8 was obtained by recrystallization from
CH2Cl2 and hexane, which structure is unambiguously character-
ized by mass spectrometry, NMR spectroscopy, and X-ray single-
crystal analysis. A full assignment of the signals of compound 8
Scheme 1. Nitration of perylene bisanhydride and subsequent imidization.
HNO3 were unsatisfactory because of the harsh conditions needed
and low yield of both mono- and dinitro-PBI products.7a,13 We have
found the practical and reproducible synthesis of mono- and
dinitroperylene bisanhydride in one pot through dropping fuming
nitric acid to a solution of perylene bisanhydride (1) in chloroform
and 90 has been achieved using
a HMBC experiment (see
Supplementary data).
Scheme 2. The synthetic route toward N-decorated PBIs.
2.2. X-ray single-crystal structure analysis
X-ray structures of 8 and 90 have been performed for single
crystals grown by slow evaporation of a solution of N-decorated
CBIs. They both show almost planar conformation of the perylene
core, and the lateral aryl groups appended on the N-heterocycles
have a significant effect on the crystal structure in the solid state. As
shown in Fig. 2, the molecules of 8 regularly stack along the b-axis
of the unit cell that form a unique columnar structure without
at room temperature. After imidization, the dark red mixture was
separated by column chromatograph to produce well-soluble di-
nitro-PBI (first fraction, yield 46.3%) and mononitro-PBI as the
second fraction (yield 25.2%) easily. There was no 1,6-substituted
isomer obtained in the dinitration product as evidenced by 1H NMR
and HMBC spectroscopy. The 3JCH correlations between protons Hb
Scheme 3. The synthetic route toward N-decorated CBIs.

9236
L. Hao et al. / Tetrahedron 68 (2012) 9234e9239
Fig. 2. Space-filling diagram of N-decorated CBI 8 sandwiched by two toluene mole-
cules (carbon in dark green, oxygen in red, nitrogen in blue, and hydrogen in white
color).
strong
pep interactions. In the structure, each molecule is sand-
wiched by two toluene molecules which from the solvent. The
perylene core and additive toluene molecule packed through weak
ꢀ
ꢀ
CeC interactions (3.31 A) and CeH interactions (2.66e2.86 A). The
weak hydrogen bonds are observed between the molecules of
neighboring stacks, and the lateral phenyl groups are twisted by
49.3ꢀ in relative to the perylene backbone. In contrast, the lateral
pyridyl groups are less twisted by just 23.4ꢀ in compound 90, and
the molecules pack along the a-axis. The repeated unit in crystal 90
contains six molecules (Fig. 3), in which the main contacts are
CeH/O contacts (2.44e2.69 A) between the lateral pyridyl hy-
drogen and the oxygen atoms of carbonyl. Together with short
distances between the phenyl group on the imide position and
Fig. 4. UVevis absorption spectra: N-decorated PBIs 5 (black) and 6 (green), N-deco-
rated CBIs 8 (blue) and 90 (red) in chloroform.
rise to the yellow color. The longest absorbance maxima of
N-decorated CBIs (8 and 90) are hypsochromically shifted com-
pared to all-carbon parent CBI (511 nm, εmax¼71,500 Mꢁ1 cmꢁ1 in
CHCl3)16 as a result of incorporation of electronegative nitrogen
atoms. In the region of shorter wavelengths, up to 400 nm, the
spectra of 8 and 90 disclose a small red-shift and sharp band with
a defined structure at 352 nm, 354 nm to that of parent CBI
(338 nm). Furthermore, the longest absorbance maxima of phenyl
substituted products both for PBIs and CBIs are just slightly
bathochromically shifted to their pyridyl counterpart. The fluo-
rescence quantum yields of these N-decorated PBIs and CBIs are
largely decreased, and they all possess small Stokes shifts of about
8e17 nm.
ꢀ
lateral pyridyl hydrogen with C/H distances in the range of
ꢀ
2.84e2.89 A that is indicative of the CeH/
p
interactions, and close
ꢀ
CeH/O contacts (2.51 A) between phenyl hydrogen and the oxy-
gen atoms of carbonyl, this network structure for promising ab-
sorbing materials can be expected.
Cyclic voltammentry of compounds 5, 6, 8, and 90 in CH2Cl2 has
been investigated, and electrochemical data are summarized in
Table 1. They all show two reversible reduction waves (Fig. 5).
Compared with PBI,17 the first half-wave reduction potentials ver-
sus Fc/Fcþ are ꢁ1.00, ꢁ1.01, ꢁ1.04, and ꢁ1.05 V for 5, 6, 8, and 90,
respectively, indicating that the incorporation of nitrogen as well as
their substituents does not induce a significant shift on electro-
chemical behavior. LUMO levels estimated by the onset of re-
duction peaks are ꢁ3.88 eV for 5, ꢁ3.86 eV for 6, ꢁ3.87 eV for 8, and
ꢁ3.82 eV for 90, respectively. According to the optical gap that were
determined from the onset absorption of UVevis spectra, HOMO
levels of these N-decorated PBIs and CBIs are deeper than that of
parent PBI, indicating effective tunability of energy levels for
promising electronic applications.
3. Conclusion
Fig. 3. Crystal structure of N-decorated CBI 90.
In conclusion, we have presented the facile synthesis of novel
N-decorated perylene bisimides (PBI) and coronene bisimides
(CBI) derivatives by the combination of PicteteSpengler conden-
sation and subsequent oxidative aromatization from highly
electron-deficient amino-PBIs with different aldehydes. A detailed
analysis of their photophysical properties and molecular crystals
has shown that the lateral aryl groups appended on the N-het-
erocycle have a negligible effect on their optical absorptions and
electrochemical potentials, but the subtle modification leads to
significant variations on the packing arrangement. Extension of
this synthetic strategy to highly ordered heterocoronene bisi-
mides as well as detailed investigation to clearly understand the
reaction mechanism for the occurrence of different isomers is
currently underway.
2.3. Optical and electrochemical properties
Room temperature absorption spectra of these compounds are
shown in Fig. 4, and optical data are listed in Table 1. The UVevis
absorption spectra showed that they all exhibit well-defined
vibronic
pep* transition absorption bands with high extinction
coefficients. As a result of the extended perylene core along the
short molecular axis, the N-decorated PBIs and CBIs are blue-
shifted relative to the corresponding parent compound (PBI).15 In
the spectra of N-decorated PBIs (5 and 6), the typical perylene
vibronic structure can be seen at a shorter wavelength with an
absorbance maximum at 476 nm, 474 nm, respectively, that give

L. Hao et al. / Tetrahedron 68 (2012) 9234e9239
9237
Table 1
Photophysical properties of the N-decorated PBIs and CBIs
εmax [Mꢁ1 cmꢁ1
]
Fluomaxb [nm]
Vfl
E1r [V]
E2rd [V]
Eonset [V]
ELUMO [eV]
Egf [eV]
EHOMOg [eV]
a
a
c
d
d
e
Compound
Absmax [nm]
PBI
5
6
8
90
527
476
474
488
480
80,900
68,662
68,376
27,092
8326
534
493
485
502
488
1.00
0.74
0.36
0.25
0.10
ꢁ0.96
ꢁ1.00
ꢁ1.01
ꢁ1.04
ꢁ1.05
ꢁ1.22
ꢁ1.30
ꢁ1.29
ꢁ1.36
ꢁ1.34
ꢁ0.89
ꢁ0.92
ꢁ0.94
ꢁ0.93
ꢁ0.98
ꢁ3.91
ꢁ3.88
ꢁ3.86
ꢁ3.87
ꢁ3.82
2.30
2.52
2.55
2.47
2.49
ꢁ6.21
ꢁ6.40
ꢁ6.41
ꢁ6.34
ꢁ6.31
a
Measured in dilute CHCl3 solution (1.0ꢂ10ꢁ5 M).
b
c
d
e
f
Measured in dilute CHCl3 solution (1.0ꢂ10ꢁ6 M).
Average deviation for Vfl, ꢃ0.04, determined with PBI (N,N0-di(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboxylic acid bisimide, Vfl¼1.00 in CHCl3) as the standard.
Half-wave potential in CH2Cl2 solution versus Fc/Fcþ
.
Estimated by the onset of reduction peaks and calculated according to ELUMO¼ꢁ(4.8þEonset) eV.
Calculated by the onset of absorption according to Eg¼1240/lonset
.
g
Calculated according to EHOMO¼(ELUMOꢁEg) eV.
acid bisimide (PBI) in CHCl3 as reference (Vfl¼1.0).15 Cyclic vol-
tammograms (CVs) were recorded on a Zahner IM6e electro-
chemical workstation at a scan rate of 50 mV sꢁ1, with using glassy
carbon discs as the working electrode, Pt wire as the counter
electrode, Ag/AgCl electrode as the reference electrode, and ferro-
cene/ferrocenium as an internal potential marker for the calibra-
tion of potential. 0.1 M tetrabutylammonium hexafluorophosphate
(Bu4NPF6) dissolved in CH2Cl2 (HPLC grade) was employed as the
supporting electrolyte.
4.2. Nitration of perylene bisanhydride and subsequent
imidization (2 and 3)
A mixture of perylene-3,4:9,10-tetracarboxylic acid bisanhy-
dride 1 (5.0 g, 12.74 mmol) in CHCl3 (150 mL) was stirred at room
temperature, and then fuming nitric acid (50 mL) was added
dropwise over a time period of 2 h and the mixture was stirred for
an additional 3 h at room temperature. Then the dark red mixture
was poured into water (500 mL) slowly. The resultant precipitate
was filtered through a funnel, washed with a large amount of water
until the filtrate became neutral. The residue was dried at 110 ꢀC for
5 h to give crude dark red powder (5.8 g). The crude product was
used directly for the next step without further purification.
Next, A suspension of nitrated perylene bisanhydrides (5.8 g)
obtained in the above reaction, and excess 2,6-diisopropylaniline
(7.05 g, 39.76 mmol) in 100 mL of n-propionic acid under N2 at-
mosphere, the reaction mixture was stirred and heated at 140 ꢀC for
12 h. After being cooled to room temperature, the resulting solution
was poured into 500 mL of water. The red solid was collected,
washed with water and brine until neutral and dried in a vacuum.
The crude product was purified by silica gel column chromatogra-
phy (CH2Cl2/PE¼1:3 to 1:1 in v/v) to afford 1,7-dinitro-PBI (3, first
fraction: 4.73 g, 46.3%) and 1-nitro-PBI (2, second fraction: 2.43 g,
25.2%) as dark red solids.
Fig. 5. Reductive cyclic voltammograms of 5, 6, 8, and 90 in CH2Cl2 (electrolyte, 0.1 M
Bu4NPF6) with a scan rate of 100 mV/s versus Fc/Fcþ
.
4. Experimental section
4.1. General materials and methods
All chemicals and solvents were purchased from commercial
suppliers and used without further purification unless otherwise
specified.
N,N0-di(2,6-diisopropylphenyl)perylene-3,4:9,10-
tetracarboxylic acid bisimide (PBI) was synthesized according to
the literature.18 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra
were recorded in deuterated solvents on a Bruker ADVANCE 400
NMR Spectrometer. J values are expressed in hertz and quoted
chemical shifts are in parts per million downfield from tetrame-
thylsilane (TMS) reference using the residual protonated solvent as
an internal standard. The signals have been designated as follows: s
(singlet), d (doublet), t (triplet), q (quartet), dd (doublet of dou-
blets), and m (multiplets). Mass spectra (MALDI-TOF-MS) were
determined on a Bruker BIFLEX III Mass Spectrometer.
UVevis spectra were measured with Hitachi (Model U-3010)
UVevis spectrophotometer in a 1-cm quartz cell. Fluorescence
excitation and emission spectra were recorded with a Hitachi FP-
6600 FL fluorimeter at room temperature. And fluorescence
quantum yields were determined by optical dilute method with
N,N0-di(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboxylic
4.2.1. N,N0-Di(2,6-diisopropylphenyl)-1-nitroperylene-3,4:9,10-
tetracarboxylic acid bisimide (2). 1H NMR (CDCl3, 400 MHz, ppm)
d
¼8.92 (d, J¼8.0 Hz, 1H), 8.80e8.87 (m, 4H), 8.73 (d, J¼8.0 Hz, 1H),
8.36 (d, J¼8.0 Hz, 1H), 7.50e7.55 (m, 2H), 7.35e7.38 (m, 4H),
2.68e2.78 (m, 4H), 1.18e1.20 (m, 24H). 13C NMR (CDCl3, 100 MHz,
ppm)
d
¼163.51, 163.19, 163.12, 162.30, 148.27, 145.95, 145.88,
136.36, 133.88, 133.81, 132.40, 132.13, 130.50, 130.38, 130.27, 130.20,
129.99, 128.58, 128.27, 127.64, 127.22, 127.17, 125.25, 125.17, 124.69,
124.63, 124.53, 124.27, 123.79, 123.44, 29.67, 29.61, 24.35. MS
(MALDI-TOF): calcd for Mꢁ, 755.3; found, 755.1.
4.2.2. N,N0-Di(2,6-diisopropylphenyl)-1,7-dinitroperylene-3,4:9,10-
tetracarboxylic acid bisimide (3). 1H NMR (CDCl3, 400 MHz, ppm)
d
¼8.96 (s, 2H), 8.84 (dd, 2H), 8.40e8.44 (m, 2H), 7.51e7.58 (m, 2H),
7.36e7.40 (m, 4H), 2.65e2.77 (m, 4H), 1.19e1.20 (m, 24H). 13C NMR

9238
L. Hao et al. / Tetrahedron 68 (2012) 9234e9239
(CDCl3, 100 MHz, ppm)
d
¼162.86, 162.47, 161.96, 161.59, 149.25,
triflic acid (0.25 mL) was stirred at 110 ꢀC until the starting material
could not be detected by TLC. Then the reaction mixture was cooled
to room temperature and diluted with water, alkalized with 15%
aqueous NaOH solution and extracted with CH2Cl2 (20 mL). The
organic phase was washed with brine and water, and dried with
Na2SO4. The crude product was purified by silica gel column
chromatography (CH2Cl2/PE¼1:1 in v/v) to afford 8 and 80 (150 mg,
30%, the ratio of 8 to 80 is 2:1) as yellow solids. Then the mixture
isomers were recrystallized with CH2Cl2 and hexane and the
regioisomerically pure 8 was obtained.
148.88, 145.90, 145.82, 145.75, 133.58, 132.05, 131.11, 130.69, 130.52,
130.34, 130.16, 130.07, 129.84, 129.74, 129.54, 129.48, 129.38, 128.60,
128.36, 128.24, 127.22, 127.07, 126.33, 125.85, 124.95, 124.76, 124.67,
124.58, 123.96, 29.75, 29.68, 29.61, 24.36. MS (MALDI-TOF): calcd
for Mꢁ, 800.3; found, 800.4.
4.3. Synthesis of amino-PBIs (4 or 7)
To a solution of 1-nitro-PBI 2 or 1,7-dinitro-PBI 3 (0.25 mmol) in
1,2-dimethoxyethane (10 mL) was added about 10% palladium on
charcoal (20 mg), then 0.2 mL of 85% hydrazine wad added into the
reaction. The mixture was stirred at 83 ꢀC for 15 min, and then
cooled to room temperature. The catalyst was removed and the
solvent was distilled to leave a blue solid. The crude product either
monoamino-PBI 4 or diamino-PBI 7 was used directly for the next
step without further purification because of the instability of the
amino in the air.
Compound 8: 1H NMR (CDCl3, 400 MHz, ppm)
d
¼10.41 (s, 2H),
10.30 (s, 2H), 8.27 (d, J¼8.0 Hz, 4H), 7.75e7.85 (m, 6H), 7.56e7.59
(m, 2H), 7.43e7.45 (m, 4H), 2.95e2.97 (m, 4H), 1.24e1.26 (m, 24H).
13C NMR (C2D2Cl4, 100 MHz, ppm)
d
¼163.90, 163.75, 162.72, 145.43,
143.14, 138.13, 134.36, 131.13, 130.88, 130.58, 130.30, 129.68, 129.25,
127.51, 125.15, 124.47, 124.22, 123.23, 122.47, 120.09, 118.37, 31.48,
29.26, 24.14, 22.60. MS (MALDI-TOF): calcd for Mꢁ, 912.4; found,
912.7. HRMS calcd for C62H49N4Oþ4 [MHþ], 913.37483; found,
913.37329.
4.4. Synthesis of N-decorated PBIs and CBIs
Compound 80: 1H NMR (CDCl3, 400 MHz, ppm)
d
¼10.39 (s, 2H),
10.35 (s, 2H), 8.25 (s, 2H), 8.26 (s, 2H), 7.75e7.85 (m, 6H), 7.54e7.60
(m, 2H), 7.41e7.46 (m, 4H), 2.87e3.04 (m, 4H), 1.21e1.27 (m, 24H).
MS (MALDI-TOF): calcd for Mꢁ, 912.4; found, 912.7.
4.4.1. Compound (5). A mixture of monoamino-PBI 4 (200 mg) and
benzaldehyde (175 mg, 1.65 mmol) in DMF (10 mL) containing
triflic acid (0.1 mL) was stirred at 110 ꢀC until the starting material
could not be detected by TLC. Then the reaction mixture was cooled
to room temperature and diluted with water, alkalized with 15%
aqueous NaOH solution and extracted with CH2Cl2 (20 mL). The
organic phase was washed with brine and water, and dried with
Na2SO4. The crude product was purified by silica gel column
chromatography (CH2Cl2/PE¼1:1 in v/v) to afford 5 (94 mg, 42.1%)
4.4.4. Compound (90). A mixture of diamino-PBI 7 (300 mg) and 2-
pyridinecarboxaldehyde (520 mg, 4.86 mmol) in DMF (15 mL)
containing triflic acid (0.15 mL) was stirred at 110 ꢀC until the
starting material could not be detected by TLC. Then the reaction
mixture was cooled to room temperature and diluted with water,
alkalized with 15% aqueous NaOH solution and extracted with
CH2Cl2 (20 mL). The organic phase was washed with brine and
water, and dried with Na2SO4. The crude product was purified by
silica gel column chromatography (CH2Cl2/THF¼150:1 in v/v) to
afford 90 (102 mg, 27.7%) as yellow solid. 1H NMR (CDCl3, 400 MHz,
as an orange-yellow solid. 1H NMR (CDCl3, 400 MHz, ppm)
d¼9.81
(s, 1H), 9.75 (s, 1H), 9.51 (d, J¼8.0 Hz, 2H), 9.31 (d, J¼8.0 Hz, 1H),
9.26 (d, J¼8.0 Hz, 1H), 8.05 (d, J¼8.0 Hz, 2H), 7.66e7.75 (m, 3H),
7.51e7.56 (m, 2H), 7.37e7.41 (m, 4H), 2.79e2.91 (m, 4H), 1.20e1.24
(m, 24H). 13C NMR (THF-d8, 100 MHz, ppm)
d¼164.42, 164.12,
ppm)
d
¼11.12 (s, 2H), 10.36 (s, 2H), 9.11e9.12 (m, 2H), 8.79e8.81 (d,
164.00, 162.01, 146.91, 146.83, 145.41, 139.58, 135.63, 135.54, 134.20,
133.13, 132.20, 132.11, 132.03, 131.65, 130.49, 130.33, 130.05, 129.61,
129.49, 127.96, 127.21, 125.82, 125.02, 124.93, 124.58, 124.53, 124.36,
124.30, 124.20, 123.30, 122.69, 119.56, 30.16, 30.09, 24.50, 24.40. MS
(MALDI-TOF): calcd for Mꢁ, 811.3; found, 811.3. HRMS calcd for
C55H46N3Oþ4 [MHþ], 812.34828; found, 812.34618.
J¼8.0 Hz, 2H), 8.25e8.29 (m, 2H), 7.71e7.74 (m, 2H), 7.55e7.62 (m,
2H), 7.42e7.48 (m, 4H), 2.92e3.06 (m, 4H), 1.23e1.28 (m, 24H). 13C
NMR (CDCl3, 100 MHz, ppm)
d
¼164.12, 164.02, 163.93, 157.95,
157.49, 149.52, 146.03, 144.49, 138.17, 136.01, 135.10, 134.98, 133.90,
131.83, 130.88, 130.85, 130.60, 130.48, 130.21, 130.09, 129.36, 129.15,
128.55,127.73,126.59,126.30,125.62,124.69,124.59, 124.50, 124.27,
124.10, 123.94, 123.63, 123.47, 122.80, 122.70, 120.17, 29.70, 29.62,
24.50, 24.41. MS (MALDI-TOF): calcd for Mꢁ, 914.4; found, 914.2.
HRMS calcd for C60H47N6Oþ4 [MHþ], 915.36533; found, 915.36287.
4.4.2. Compound (6). A mixture of monoamino-PBI 4 (200 mg) and
2-pyridinecarboxaldehyde (180 mg, 1.68 mmol) in DMF (10 mL)
containing triflic acid (0.15 mL) was stirred at 110 ꢀC until the
starting material could not be detected by TLC. Then the reaction
mixture was cooled to room temperature and diluted with water,
alkalized with 15% aqueous NaOH solution and extracted with
CH2Cl2 (20 mL). The organic phase was washed with brine and
water, and dried with Na2SO4. The crude product was purified by
silica gel column chromatography (CH2Cl2/PE¼1:1 in v/v) to afford
6 (83 mg, 37.4%) as an orange-yellow solid. 1H NMR (CDCl3,
Acknowledgements
For financial support of this research, we thank the National
Natural Science Foundation of China (91027043, 21190032), 973
Program (Grant 2011CB932301), Chinese Academy of Sciences. We
are grateful to Prof. J. Pei (Peking University) for his profound
discussions.
400 MHz, ppm)
d
¼10.47 (s, 1H), 9.79 (s, 1H), 9.51 (dd, 2H), 9.31 (dd,
2H), 8.99 (d, J¼8.0 Hz, 1H), 8.58 (d, J¼8.0 Hz, 1H), 8.12e8.16 (m, 1H),
7.57e7.62 (m, 1H), 7.51e7.55 (m, 2H), 7.38e7.42 (m, 4H), 2.81e2.92
(m, 4H), 1.20e1.24 (m, 24H). 13C NMR (CDCl3, 100 MHz, ppm)
Supplementary data
1H and 13C spectra for all the new compounds. Supplementary
data related to this article can be found at http://dx.doi.org/10.1016/
j.tet.2012.08.084.
d
¼164.13, 164.04, 164.01, 163.95, 157.89, 157.44, 149.48, 146.04,
144.52, 138.23, 136.03, 135.13, 134.95, 133.93, 131.86, 130.88, 130.62,
130.51, 130.21, 130.09, 129.17, 127.76, 126.61, 126.32, 124.72, 124.59,
124.50, 124.30, 124.13, 123.97, 123.66, 123.49, 122.82, 122.72, 120.21,
29.70, 29.63, 24.49, 24.41. MS (MALDI-TOF): calcd for Mꢁ, 812.3;
found, 812.4. HRMS calcd for C54H45N4Oþ4 [MHþ], 813.34353; found,
813.34306.
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