Orientation of bromination in bay-region of perylene diimides

Article abstract of DOI:10.1016/j.tet.2013.07.035

We found that the entering position of the bromination in the bay-region (e.g., 1,6,7,12-positions) was precisely determined by the orientation director(s), either individually or cooperatively. In particular, a combination of two directors shows precisely positioning for the third entering bromo with an effect of '1+1>2'.

Full text of DOI:10.1016/j.tet.2013.07.035

Tetrahedron 69 (2013) 8155e8160
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Tetrahedron
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Orientation of bromination in bay-region of perylene diimides
*
*
Xin Zhang, Chuanlang Zhan , Xinliang Zhang, Jiannian Yao
Beijing National Laboratory for Molecular Sciences, CAS Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 May 2013
Received in revised form 5 July 2013
Accepted 11 July 2013
Available online 16 July 2013
We found that the entering position of the bromination in the bay-region (e.g., 1,6,7,12-positions) was
precisely determined by the orientation director(s), either individually or cooperatively. In particular,
a combination of two directors shows precisely positioning for the third entering bromo with an effect of
‘1þ1>2’.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Orientation
Bromination
Perylene diimides
1. Introduction
the cooperative effects of the first and second groups on the third
entering group are both not only basically important for the ad-
It is well-known that nature of the first group attached at the
benzene nucleus can significantly influence the substituted posi-
tion and reactivity of the second entering group.1 Perylene diimides
(PDIs) have been paid much attention in the past decades because
of their outstanding optoelectronic and self-assembling properties
and the potential applications in the fields of organic electronics.2e6
Because of the nodes of the HOMO and LUMO at the imide nitrogen
atoms, substitutions at the bay-region, e.g., 1,6,7,12-positions are
the most elaborate synthetic strategy to fine-tune the optoelec-
tronic properties.2 Since the first introduction by Seybold et al. at
BASF in 1987,7 functionalizations at the bay-region have been well
developed. However, the possible orientation of the substitutions at
the 1,6,7,12-positions (Scheme 1) has been submerged by the fast
advances of perylene diimide chemistry. Understanding the ori-
entation of the first group on the second entering group and further
vances of perylene diimide chemistry, but it is also a key approach
to precisely position functions at the 1,6,7,12-positions and further
fine-tune the optoelectronic properties for the utilizations in the
organic electronics.
2. Results and discussion
To demonstrate the orientation of bromination in the bay-
region, we chose 2-methoxyethoxyl (EG) as the electron-donating
group, while bromo (Br) and cyano (CN) as the weak and strong
electron-withdrawing groups (Scheme 2), respectively. Selection of
EG is because the EG-functionalized PDIs are more easily purified
than the alkoxyl-substituted ones.8 The reaction of bromination
was conducted at reflux temperature in dichloromethane (DCM)
and using bromine as the bromination reagent.9
Substitution of monobrominated PDI 2 with EG8 and CN10
yielded 3 (Scheme 2) and mono-CN PDI 4 (Fig. S1) in yields of
95% and 99%, respectively. Bromination of 3 preferably gave 5a in
a yield of over 95%, whereas no 6- or 12-brominated isomer (5b or
5c) was detected. We noted that 5a can be further brominated at its
12-position (vide post), but practically, it can be obtained in a very
high yield by controlling the stoichiometric ratio and carefully
monitoring the reaction using TLC. This is due to the relative de-
crease of the electron density at the ortho-carbon (ꢀ0.210 jej
vs ꢀ0.207 jej) after the para-carbon was brominated (3 vs 5a, Table
S1 vs S2). Structure of 5a was fully determined by using the 1H
NMR, NOESY, and HMBC spectra (Figs. S1eS4). Unique formation of
5a means that the electron-donating EG group is a preferable 1/7
Scheme 1. Definitions of the ortho-, meta-, and para-position at the bay-region of
a modeling 1-substituted PDI compound, with respect to the conventional nomen-
clature in the benzene nucleus.
* Corresponding authors. Tel.: þ86 10 82616517; fax: þ86 10 82617312; e-mail
addresses: clzhan@iccas.ac.cn (C. Zhan), jnyao@iccas.ac.cn (J. Yao).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.035

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X. Zhang et al. / Tetrahedron 69 (2013) 8155e8160
at the para- and ortho-position created after attack of one bromo
can move to the 1-carbon along the conjugated backbone, where it
may be stabilized by the electron-donating EG-oxygen. However,
the positive charge created at the meta-position cannot.
Quantum chemical calculations (Table S1) revealed that the
electron density at the 1-, 6-, 7-, and 12-carbon of PDI 1, in which
the bay-positions are all free of substitutions, was the same, all
being ꢀ0.204 jej. Hereafter, this value was used as a reference:
higher or lower than this value represents that position may be
activated or deactivated by the director(s). When 1-carbon is bro-
minated, affording 2, the electron density at the para- and meta-
carbon is slightly raised to ꢀ0.205 jej, whereas that at the ortho-
carbon is slightly down to ꢀ0.200 jej, which is consistent with the
para-/meta-orientation results. Similarly, with respect to the ref-
erence value of ꢀ0.204 jej, the electron density at the para-, meta-
and ortho-carbon is either increased or decreased slightly after
1-position is substituted with the EG (3) or CN (4) group, and the
changing tendency is all consistent with the experimental obser-
vations from the corresponding directors, for example, the para-
orientation for the EG group. Noted that the electron density at
the ortho-carbon of 3 is also higher enough for the bromination.
Although no ortho-brominated products were obtained from 3, as
shown from the following-presented experimental results, the EG
group really shows the ortho-orientation, and so it is a preferable
para-director and also an ortho-director.
After realizing the orientation of the EG, Br, and CN groups in-
dividually, we turned to study the cooperation from both of them.
Firstly, we demonstrated the cooperative effect from two same
groups.
Scheme 2. Orientation of bromination at the ortho-, meta-, and para-position of three
typical 1-substituted PDI derivatives.
Scheme 4 displays the cooperative orientation from two EG
groups. From the mixture of 1,7- and 1,6-diBr isomers, 1,7- and
1,6-diEG PDIs (8a and 8b) were got in a total yield of over 92%. Their
molar ratio was estimated as 80%/20% from the 1H NMR spectrum
(Fig. S6), consistent well with the molar ratio of the reactants of
6a and 6b. The 1,12-diEG derivative (8c) was obtained from the
1,12-dichlorinated PDI (7).12
director. Hereafter, we used ortho- (12-), meta- (6-), and para- (7-)
to describe the orientation with respect to that director at the 1-
position, as similarly used for the benzene nucleus (Scheme 1).
Accordingly, EG is a para-director.
Further bromination of 2 yielded a mixture of 6a (1,7-isomer)
and 6b (1,6-isomer) in a total yield of >95%. Because of the very
close polarity at TLC, it is very difficult to isolate 6a and 6b.9,11 The
ratio of 6a/6b was then estimated from 1H NMR spectrum as
70e80% and 20e30%, respectively (Fig. S5). It is well-known that no
1,12-isomer (6c) was formed from this reaction.9,11 Furthermore, as
shown vide post, substitutions of the mixture of 6a and 6b with the
EG and CN groups did not give any clues for the existence of 6c in
the mixture of 6a and 6b, further strongly supporting that no 6c
was formed. This indicates that bromo is a para-/meta-director. In
a striking contrast, CN is a strong electron-withdrawing group, and
it causes deactivation of the PDI nucleus. No further bromination
takes place from 4.
Similar to the bromination in the benzene nucleus, the orien-
tation of bromination in the bay-region of PDI nucleus can be de-
scribed by the resonant structures (Scheme 3). The positive charge
Scheme 4. Cooperative orientation of bromination from the diEG-substituted PDI
derivatives.
Full bromination of the 8a/8b mixture yielded 1,7-diEG-6,12-
diBr (10a) and 1,6-diEG-7,12-diBr (10b) PDIs. These two isomers
were fully isolated by chromatography, both in yields of 79% (10a)
and 18% (10b) (Fig. S7), respectively, which are both very close to
that molar ratio of 6a and 6b (80% vs 20%).
We then carefully monitored the bromination of the 8a/8b mix-
ture with TLC and stopped the reaction when most 8b was likely
converted. From this reaction pure 10a and 10b were isolated.
Scheme 3. Resonant structures along the PDI nucleus after the para-, ortho- and meta-
carbon were attacked by one bromo, respectively.

X. Zhang et al. / Tetrahedron 69 (2013) 8155e8160
8157
Compounds 9a and 9b had very close polarity on TLC, and fortu-
nately, a small part of pure 9a (Fig. S8a) was isolated from the 9a/9b
mixture. Yields of 9a and 9b were calculated from the 1H NMR
spectrum (Fig. S8b) and the total quantity of the 9a/9b mixture.
Together, about 28% and 69% of 8b was converted into 9b and 10b,
respectively, whereas only about 15% and 5% of 8a converted into 9a
and 10a, respectively (Table 1). Un-reacted 8a of 75% was recovered
whereas no un-reacted 8b was isolated. Structures of 8a, 9a, and 10a
were further determined by using the 1H NMR and HMBC spectra
(Figs. S9eS12) as well as the relatively much higher quantity of the
isolated product 8a, 9a, and 10a than that of 8b, 9b, and 10b. These
reaction results indicate that cooperation of the orthoþpara orien-
tation from the 1,6-EG groups promotes the bromination, with re-
spect to the orthoþmeta combination from 1,7-EG groups.
Table 1
Scheme 5. Cooperative orientation of bromination from the diBr-, diCl- or diCN-
substituted PDI derivatives.
Isolated yields of 9a and 9b as well as 10a and 10b, resulted from the cooperative
orientation of two EG groups
8a/8b Initial
8a/8b Recovered
9a/9b (mmol)
10a/10b (mmol)
(mmol)
(mmol)
0.4:0.1
Yield (%)
0.3a:0
0.059:0.028
14.8:28.0
0.020:0.069
5.0:69.0
75b:0
a
Recovered.
Percentage of recovered versus initial.
b
These cooperative orientations are originated from the re-
distributions of the -electrons when the EG and Br groups are lo-
p
calized at different positions (Table S2). The 1,6-EG groups generate
more electron density at the ortho- and para-position (ꢀ0.212 jej,
8b) than the 1,7-EG groups do on the ortho- and meta-carbon
(ꢀ0.207 jej, 8a), indicating that the ortho- and para-position of 8b
are more active than the ortho- and meta-position of 8a. After one
bromo is attached at the ortho-carbon, affording 1,6-diEG-12-Br
isomer (9b) and 1,7-diEG-12-Br isomer (9a), respectively, the elec-
tron density at the para-carbon of 9b is almost retained (ꢀ0.211 jej),
whereas that at the meta-carbon of 9a is obviously decreased down
to ꢀ0.203 jej, strongly supporting the enhanced reactivity for the
further bromination at the fourth position of 9b with respect to 9a,
and this is in accord with the experimental result that the yield of
10b is very much higher than that of 10a (69% vs 5%, Table 1).
As mentioned above, bromination at the fourth bay-position of
9a is deactivated. Similarly, bromination of 8c only yielded mono-
brominated product of 9c, while no dibrominated product (10c)
was detected, meaning that bromination at the fourth bay-position
of 9c is also deactivated. This is in line with the calculation results.
The electron density at the para- and meta-carbon of 8c is
ꢀ0.209 jej (Table S2), being activated for bromination. After 8c is
monobrominated, the electron density at the fourth bay-carbon is
decreased down to ꢀ0.202 jej, becoming deactivated.
Scheme 6. Cooperative orientation of bromination from the EG/Br (Cl), EG/CN and CN/
Br combinations.
Structure of 14a was assigned from the HMBC spectrum (Fig. S13).
Bromination at the 12-position agrees with the cooperative effect
from both the ortho-orientation of 1-EG and from the meta-orien-
tation of 7-Br, showing ‘1þ1>2’.
Further bromination of the 6a/6b mixture only yielded trace of
1,6,7-tribrominated derivative (typically, much less than 1%) and no
1,6,7,12-tetrabrominated PDI (11b) was formed (Scheme 5),
meaning the ortho-carbon of the Br group is strongly deactivated
(Table S3). Bromination of 1,12-dichlorinated isomer (7) uniquely
yielded 1,12-dichloro-7-brominated product (12), which is consis-
tent with the para- and meta-orientation of Cl (similar to Br). In
contrasts, dicyano substituted 1,7 and 1,6-isomers, 13a and 13b,
strongly deactivated the PDI nucleus, no further bromination took
place. Quantum chemical calculations indicated that only the meta-
and para-carbon of 7 among these diBr (Cl, CN) PDIs showed
a higher electron density (ꢀ0.205 jej) than ꢀ0.204 jej (Table S3).
Secondly, cooperation from two different groups was studied
(Scheme 6). From 1-EG-7-brominated isomer (5a), only 1-EG-7,12-
dibrominated isomer (14a) was uniquely formed in a yield of 95%,
whereas no 1-EG-6,7-dibrominated isomer (14b) was found.
From the 6a/6b mixture, a mixture of 1-EG-7-Br and 1-EG-6-Br
isomers (5a and 5b) was obtained.8 Full bromination of the 5a/5b
mixture, both 14a and 14c were, respectively, separated in yields of
68% and 21%, respectively, agreeing well with the molar ratio of 5a
and 5b (75% vs 25%) (Fig. S14). No 1-EG-6,7-diBr isomer (14b) was
detected. Structure of 14c was also determined from the HMBC
spectrum (Fig. S15). Clearly, 14a was from 5a, and 14c was from 5b.
Formation of the isomer 14a agrees with the cooperative
orthoþmeta orientation of the EGþBr groups, and formation of 14c
is consistent with the orthoþpara orientation of the EGþBr groups,
both showing an effect of ‘1þ1>2’.
Because it was difficult to get the 1-EG-12-Br isomer, we turned
to selectively substitute one of the two Cl groups at the 1,12-
dichlorinated derivative (7) using DMF as the reaction medium

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X. Zhang et al. / Tetrahedron 69 (2013) 8155e8160
and K2CO3 as the weak base, affording 1-EG-12-Cl isomer (15).
Bromination of 15 uniquely yielded 1-EG-7-Br-12-Cl PDI (16), also
due to the cooperative paraþmeta orientation of the 1-EG and the
12-Cl, further supporting the ‘1þ1>2’ effect. Structure of 16 was
also determined from the HMBC spectrum (Fig. S16).
according to the literature method.10 PDI 7 was obtained according
to the literature procedure.12
4.2. Synthesis of compound 5a
Calculations revealed that, for 5a and 5b, the electron density at
the ortho-carbon was ꢀ0.207 jej and ꢀ0.206 jej, respectively, both
higher than that on the meta-carbon of 5a (ꢀ0.198 jej) and that on
the para-carbon of 5b (ꢀ0.204 jej) (Table S4), so the ortho-position
is activated with respect to the other position. Also, the electron
density at the para-carbon of 15 reaches to ꢀ0.210 jej, being much
higher than that on the meta-carbon (ꢀ0.203 jej), also supporting
the cooperative paraþmeta orientation of 1-EG and 12-Cl in 15.
We should note that no further brominated product was
detected from 14a, 14c, and 16. Substitutions of the 7- and 6-bromo
of 5a and 5b with CuCN yielded 17a and 17b, respectively. Mono-CN
substitution of 6a and 6b produced 18a and 18b, respectively. These
mono-CN substituted and diCN-substituted derivatives were all
deactivated and no further bromination were observed from de-
rivatives (Scheme 6).
A mixture of 3 (68.8 mg, 0.1 mmol) and 1 mL of bromine in 20 mL
dichloromethane (DCM) was allowed to react under reflux. The re-
action was monitored by using TLC for 4 h. The excess of bromine
was removed by flow of N2, and the solvent was removed under
vacuum and the residue was purified by column chromatography on
silica gel (DCM/ethanol, 100:1 v/v) to afford compound 5a as a dark-
red solid (73.7 mg, 0.096 mmol, yield¼96%). 1H NMR (CDCl3,
400 MHz)
d
ppm: 9.54 (d, J¼8.00 Hz,1H), 9.52 (d, J¼8.00 Hz,1H), 8.89
(s, 1H), 8.64 (d, J¼8.00 Hz, 1H), 8.56 (d, J¼8.00 Hz, 1H), 8.44 (s, 1H),
4.61 (m, 2H), 4.16 (m, 4H), 3.97 (m, 2H), 3.58 (s, 3H),1.95 (m, 2H),1.41
(m, 8H), 1.33 (m, 8H), 0.96 (m, 6H), 0.91 (m, 6H). 13C NMR (100 MHz,
CDCl3)
d ppm: 163.23, 163.18, 162.51, 156.63, 137.50, 132.94, 132.64,
131.94, 130.79, 128.65, 128.41, 128.16, 127.40, 126.71, 123.69, 122.94,
122.74,121.70,121.04,119.66,119.16,117.20, 70.63, 69.19, 59.41, 44.39,
38.03, 30.81, 28.74, 24.08, 23.12, 14.14, 10.62. MS (MALDI-TOF):
m/z¼767.8 [MþH]þ. Elemental analysis: calcd (%) for C43H47BrN2O6:
C 67.27, H 6.17, N 3.65; found C 66.93, H 6.20, N 3.65.
3. Conclusion
In conclusions, we have found the precise orientation of bromi-
nation in the bay-region (e.g., 1,6,7,12-positions) of the PDI nucleus.
The electron-donating EG group shows para-/ortho-orientation. The
weak electron-withdrawing bromo shows the para-/meta-orienta-
tion. However, the strong electron-withdrawing CN group de-
activates the PDI nucleus, and no bromination takes place.
Cooperation of the EG and EG groups exhibits a ‘1þ1>2’ effect. For
example, the combined orthoþpara orientation of 1,6-diEG groups
accelerates the bromination reaction, with respect to the orthoþmeta
combination of the 1,7-diEG groups. Similarly, combination of the
orthoþmeta, or orthoþpara, or paraþmeta orientation of the EGþBr
groups yields precise position for the third entering Br group. The
orientation presented herein extends our understandings from the
traditional orientation at the aromatic nucleus to the toady’s per-
ylene diimide chemistry and this will open opportunities to fine-
tune the optoelectronic and self-assembling properties of PDI de-
rivatives through precisely positioning the functional groups at the
targeted bay-carbons, and thus pushing further advances for the
applications of PDI derivatives in the relative fields.
4.3. Synthesis of compounds 9a, 9b, 10a, and 10b
A mixture of 8a and 8b (381.2 mg, 0.5 mmol, 8a/8b¼80%:20%)
was dissolved into 100 mL of CH2Cl2, to which 3 mL bromine was
dropwise added. The mixture was allowed to react under reflux. The
reaction was monitored by using TLC for 2 h. The excess of bromine
was removed by flow of N2, and the solvent was removed under
vacuum. It was purified by column chromatography on silica gel
(DCM/ethanol, 100:1 to 50:1 v/v). The first fraction was collected to
afford 10b as a dark-red solid (63.3 mg, 0.069 mmol). The second
fraction afforded 10a as a dark-red solid (18.4 mg, 0.020 mmol). The
third fraction afforded a mixture of 9a and 9b as a dark-red solid
(72.9 mg, 0.087 mmol, 9a/9b¼68%:32%), from which a small part of
pure 9a was fortunately isolated. The last fraction was the un-reacted
reactant, being pure 8a (228.1 mg, 0.3 mmol).
4.3.1. Compound 10b. 1H NMR (CDCl3, 400 MHz)
d ppm: 8.81
(s, 2H), 8.31 (s, 2H), 4.64 (m, 4H), 4.13 (m, 4H), 3.99 (m, 2H), 3.88
(m, 2H), 3.33 (s, 6H), 1.96 (m, 2H), 1.40 (m, 8H), 1.34 (m, 8H), 0.95
(m, 6H), 0.92 (m, 6H). 13C NMR (100 MHz, CDCl3)
d ppm: 163.92,
4. Experimental section
4.1. General information
163.26, 156.90, 136.05, 132.53, 131.54, 124.71, 124.37, 122.72, 120.69,
118.08, 114.90, 70.70, 68.43, 59.42, 44.58, 38.27, 30.86, 28.86, 24.16,
23.17, 14.25,10.77. MS (MALDI-TOF): m/z¼920.3 [MþH]þ. Elemental
analysis: calcd (%) for C46H52Br2N2O8: C 60.01, H 5.69, N 3.04; found
C 59.56, H 5.72, N 3.04.
All reagents and chemicals were purchased from commercial
sources (TCI, Acros, Sigma, or Alfa) and used without further puri-
fication except statements. Solvents (toluene and tetrahydrofuran)
were distilled by standard procedures before used for organic
synthesis. Starting materials are all commercially available reagents
and solvents used as received except for statements. Reactions
were monitored by thin-layer chromatography (TLC) on pre-coated
silica gel plates (Yantai Shi Huaxue Gongye Yanjiusuo) and visual-
ized using UV irradiation (254 nm). Flash chromatography was
performed on silica gel H60 (Qingdao Haiyang Huagongchang). 1H,
13C, NOESY, and HMBC NMR spectra were recorded on a Bruker
AVANCE 400 or AVANCE 600 spectrometer with CDCl3 as a solvent
and tetramethylsilane as an internal reference. MALDI-TOF mass
spectra were recorded by a Bruker BIFLEXIII. Elemental analysis was
performed on a flash EA1112 analyzer. The mixture of 6a and 6b
was synthesized following the literature method.9 The mixture of
5a and 5b and the mixture of 8a and 8b were synthesized following
our reported procedure.8 The mixture of 13a and 13b, the mixture
of 17a and 17b, and the mixture of 18a and 18b were prepared
4.3.2. Compound 10a. 1H NMR (CDCl3, 400 MHz)
d ppm: 8.72
(s, 2H), 8.41 (s, 2H), 4.60 (m, 4H), 4.16 (m, 4H), 3.99 (m, 2H), 3.88
(m, 2H), 3.33 (s, 6H), 1.96 (m, 2H), 1.40 (m, 8H), 1.34 (m, 8H), 0.95
(m, 6H), 0.92 (m, 6H). 13C NMR (100 MHz, CDCl3)
d ppm: 163.77,
163.39, 156.86, 134.45, 132.26, 131.49, 123.94, 123.76, 121.23, 121.07,
119.28, 116.55, 70.70, 68.50, 59.41, 44.55, 38.15, 30.87, 28.85, 24.16,
23.18, 14.26, 10.77. MS (MALDI-TOF): m/z¼920.3 [MþH]þ. Elemen-
tal analysis: calcd (%) for C46H52Br2N2O8: C 60.01, H 5.69, N 3.04;
found C 59.78, H 5.60, N 3.02.
4.3.3. Compound 9a. 1H NMR (CDCl3, 400 MHz)
d ppm: 9.43 (d,
J¼8.00 Hz,1H), 8.73 (s,1H), 8.55 (d, J¼8.00 Hz,1H), 8.44 (s, 2H), 4.66
(m, 2H), 4.57 (m, 1H), 4.50 (m, 1H), 4.15 (m, 4H), 4.03 (m, 1H), 3.95
(m, 2H), 3.90 (m, 1H), 3.56 (s, 3H), 3.38 (s, 3H), 1.95 (m, 2H), 1.40 (m,
8H), 1.32 (m, 8H), 0.96 (m, 6H), 0.90 (m, 6H). 13C NMR (100 MHz,
CDCl3)
d ppm: 164.19, 163.71, 163.42, 156.58, 156.60, 135.00, 133.27,
132.10, 131.91, 129.94, 128.99, 128.85, 124.12, 123.00, 121.31, 121.12,

X. Zhang et al. / Tetrahedron 69 (2013) 8155e8160
8159
120.94, 120.51, 117.11, 116.74, 70.70, 68.50, 59.41, 44.55, 38.15, 30.87,
28.85, 24.16, 23.18, 14.26, 10.77. MS (MALDI-TOF): m/z¼841.8
[MþH]þ. Elemental analysis: calcd (%) for C46H53BrN2O8: C 65.64, H
6.32, N 3.35; found C 65.29, H 6.31, N 3.32.
mixture was allowed to react under reflux. The reaction was
monitored by TLC for 4 h. The excess of bromine was removed by
flow of N2, and the solvent was removed under vacuum. It was
purified by column chromatography on silica gel (DCM/ethanol,
50:1 v/v) to afford compound 9c as a dark-red solid (79.8 mg,
4.3.4. Compounds 9a and 9b. 1H NMR (CDCl3, 400 MHz)
d
ppm:
0.095 mmol, yield¼95%). 1H NMR (CDCl3, 400 MHz)
d ppm: 9.38
9.43 (d, J¼8.00 Hz, 0.68H), 9.37 (d, J¼8.00 Hz, 0.32H), 8.82 (s,
0.32H), 8.73 (s, 0.68H), 8.64 (d, J¼8.00 Hz, 0.32H), 8.56 (d,
J¼8.00 Hz, 0.68H), 8.42 (s, 1.36H), 8.33 (s, 0.64H), 4.66 (m, 2H), 4.57
(m, 1H), 4.50 (m, 1H), 4.15 (m, 4H), 4.03 (m, 1H), 3.95 (m, 2H), 3.90
(m, 1H), 3.56 (s, 3H), 3.38 (s, 3H), 1.95 (m, 2H), 1.40 (m, 8H), 1.32 (m,
8H), 0.96 (m, 6H), 0.90 (m, 6H). MS (MALDI-TOF): m/z¼841.8
[MþH]þ. Elemental analysis: calcd (%) for C46H53BrN2O8: C 65.63, H
6.35, N 3.33; found C 65.29, H 6.31, N 3.32.
(d, J¼8.00 Hz, 1H), 8.78 (s, 1H), 8.55 (d, J¼8.00 Hz, 1H), 8.43 (s,
2H), 4.54 (m, 2H), 4.44 (m, 2H), 4.17 (m, 4H), 3.75 (m, 4H), 3.36 (s,
6H), 1.96 (m, 2H), 1.42 (m, 8H), 1.33 (m, 8H), 0.96 (m, 6H), 0.90
(m, 6H). 13C NMR (100 MHz, CDCl3)
d ppm: 164.21, 163.87, 163.84,
163.01, 156.50, 156.46, 135.39, 132.16, 131.99, 130.95, 129.98,
127.44, 127.27, 122.92, 122.89, 122.52, 122.18, 121.93, 121.73,
120.34, 119.63, 119.07, 117.55, 117.31, 71.17, 68.91, 59.32, 59.28,
44.51, 44.41, 38.14, 38.11, 30.90, 28.88, 24.20, 23.21, 23.18, 14.25,
10.78, 10.77. MS (MALDI-TOF): m/z¼842.9 [MþH]þ. Elemental
analysis: calcd (%) for C46H53BrN2O8: C 65.63, H 6.35, N 3.33;
found C 65.85, H 6.29, N 3.31.
4.3.5. Compound 8a. 1H NMR (CDCl3, 400 MHz)
d ppm: 9.46
(d, J¼8.00 Hz, 2H), 8.41 (d, J¼8.00 Hz, 2H), 8.14 (s, 2H), 4.53 (m, 4H),
4.18 (m, 4H), 3.67 (m, 4H), 3.39 (s, 6H),1.98 (m, 2H),1.44 (m, 8H),1.38
(m, 8H),1.01 (m, 6H), 0.95 (m, 6H). 13C NMR (100 MHz, CDCl3)
d
ppm:
4.6. Synthesis of compound 12
163.96, 163.60, 156.11, 133.33, 129.12, 128.90, 128.57, 123.15, 122.89,
121.08, 120.98, 116.51, 70.93, 69.04, 59.54, 44.45, 38.15, 31.00, 28.94,
24.28, 23.26, 14.30, 10.79. MS (MALDI-TOF): m/z¼763.5 [MþH]þ.
Elemental analysis: calcd (%) for C46H54N2O8: C 72.42, H 7.13, N 3.67;
found C 72.27, H 7.17, N 3.65.
A mixture of 7 (68.2 mg, 0.1 mmol) and 1 mL bromine in 20 mL
DCM was allowed to react under reflux. The reaction was moni-
tored by using TLC for 12h. The excess of bromine was removed by
flow of N2, and the solvent was removed under vacuum. It was
purified by column chromatography on silica gel (petroleum ether/
DCM, 2:1 v/v) to afford compound 12 as an orange solid (25.1 mg,
0.033 mmol, yield¼33%), while 60% of 7 was recovered unchanged.
4.4. Synthesis of compounds 15 and 8c
A mixture of 7 (136.4 mg, 0.2 mmol), 2-methoxyethanol
(76.1 mg, 1.0 mmol), and potassium carbonate (K2CO3, 140 mg,
1.0 mmol) in 10 mL dimmethylformamide (DMF) was heated at
80 ꢁC. The reaction was monitored by using TLC for 2 days. Then, the
reaction mixture was poured into 30 mL water and the red solid
was re-dissolved in 20 mL DCM and washed with 1 N hydrochloric
acid and then water each for three times. Then, DCM layer was
dried over Na2SO4. After removal of DCM, the residue was purified
by column chromatography on silica gel (DCM/ethanol, 100:1 to
50:1 v/v). The first fraction was collected to afford 15 as a dark-red
solid (86.7 mg, 0.12 mmol, yield¼60%). The second fraction afforded
8c as a dark-red solid (30.5 mg, 0.04 mmol, yield¼20%).
1H NMR (CDCl3, 400 MHz)
d
ppm: 9.46 (d, J¼8.00 Hz, 1H), 8.92 (s,
1H), 8.71 (d, J¼8.00 Hz, 1H), 8.69 (s, 2H), 4.16 (m, 4H), 1.95 (m, 2H),
1.40 (m, 8H), 1.32 (m, 8H), 0.95 (m, 6H), 0.91 (m, 6H). MS (MALDI-
TOF): m/z¼762.5 [MþH]þ.
4.7. Synthesis of compounds 14a and 14c
A mixture of 5a and 5b (76.7 mg, 0.1 mmol, 5a/5b¼75%:25%)
was dissolved into 20 mL of CH2Cl2, to which 1 mL bromine was
dropwise added. The mixture was allowed to react under reflux.
The reaction was monitored by using TLC for 3 h. The excess of
bromine was removed by flow of N2, and the solvent was removed
under vacuum. It was purified by column chromatography on silica
gel (DCM/ethanol, 200:1 v/v) to afford compounds 14a and 14c as
a dark-red solid. The regioisomeric 14a and 14c can be separated in
yields of 68% (57.4 mg) and 21% (17.7 mg).
4.4.1. Compound 15. 1H NMR (CDCl3, 400 MHz)
d ppm: 8.63 (s, 1H),
8.57 (d, J¼8.00 Hz, 1H), 8.52 (d, J¼8.00 Hz, 1H), 8.45 (s, 1H), 8.44 (d,
J¼8.00 Hz, 1H), 8.41 (d, J¼8.00 Hz, 1H), 4.66 (m, 2H), 4.16 (m, 4H),
4.03 (m, 1H), 4.02 (m, 1H), 3.42 (s, 3H), 1.97 (m, 2H), 1.39 (m, 8H),
1.31 (m, 8H), 0.95 (m, 6H), 0.90 (m, 6H). 13C NMR (100 MHz, CDCl3)
4.7.1. Compound 14a. 1H NMR (CDCl3, 400 MHz)
d ppm: 9.40 (d,
d
ppm: 163.31, 163.23, 163.14, 162.84, 156.09, 133.92, 133.92, 133.71,
J¼8.00 Hz,1H), 8.86 (s, 1H), 8.82 (s, 1H), 8.54 (d, J¼8.00 Hz, 1H), 8.45
(s, 1H), 4.69 (m, 1H), 4.63 (m, 1H), 4.17 (m, 4H), 4.02 (m, 1H), 3.91
(m,1H), 3.41 (s, 3H),1.97 (m, 2H),1.43 (m, 8H),1.36 (m, 8H), 0.99 (m,
132.75, 131.68, 131.15, 129.53, 128.50, 128.00, 126.17, 124.28, 123.13,
122.77, 122.11, 121.95, 121.58, 121.46, 118.06, 117.40, 70.77, 68.27,
59.40, 44.30, 37.99, 30.78, 28.71, 24.03, 23.13, 14.17, 10.62. MS
(MALDI-TOF): m/z¼723.5 [MþH]þ. Elemental analysis: calcd (%) for
6H), 0.94 (m, 6H). 13C NMR (100 MHz, CDCl3)
d ppm: 163.75, 163.61,
162.85, 162.61, 156.18, 138.28, 138.68, 133.17, 132.42, 131.34, 131.24,
129.72, 128.27, 127.47, 125.39, 124.62, 123.87, 122.78, 122.66, 121.84,
121.13,120.30, 119.14,117.23, 70.60, 68.36, 59.32, 44.50, 38.10, 30.77,
28.74, 24.08, 23.11, 14.14, 10.65. MS (MALDI-TOF): m/z¼846.8
[MþH]þ. Elemental analysis: calcd (%) for C43H46Br2N2O6: C 61.00,
H 5.48, N 3.31; found C 60.75, H 5.53, N 3.33.
C
43H47ClN2O6: C 71.40, H 6.55, N 3.87; found C 71.13, H 6.48, N 3.85.
4.4.2. Compound 8c. 1H NMR (CDCl3, 400 MHz)
J¼8.00 Hz, 2H), 8.41 (s, 2H), 8.37 (d, J¼8.00 Hz, 2H), 4.50 (m, 4H),
4.15 (m, 4H), 3.79 (m, 4H), 3.39 (s, 6H), 1.96 (m, 2H), 1.40 (m, 8H),
1.33 (m, 8H), 0.95 (m, 6H), 0.90 (m, 6H). 13C NMR (100 MHz, CDCl3)
d ppm: 8.46 (d,
d
ppm: 163.98, 163.89, 156.19, 133.09, 128.55, 128.21, 123.41, 122.74,
4.7.2. Compound 14c. 1H NMR (CDCl3, 400 MHz)
d ppm: 9.38 (d,
122.38,121.66,119.78,117.97, 71.33, 68.80, 59.35, 44.37, 38.10, 30.93,
28.89, 24.20, 23.21, 14.25, 10.78. MS (MALDI-TOF): m/z¼763.5
[MþH]þ. Elemental analysis: calcd (%) for C46H54N2O8: C 72.42, H
7.13, N 3.67; found C 72.31, H 7.09, N 3.68.
J¼8.00 Hz, 1H), 8.84 (s, 1H), 8.81 (s, 1H), 8.68 (d, J¼8.00 Hz, 1H),
8.45 (s, 1H), 4.68 (m, 1H), 4.61 (m, 1H), 4.16 (m, 4H), 4.04 (m, 1H),
3.88 (m, 1H), 3.37 (s, 3H), 1.96 (m, 2H), 1.42 (m, 8H), 1.36 (m, 8H),
0.96 (m, 6H), 0.91 (m, 6H). 13C NMR (100 MHz, CDCl3)
d ppm:
163.73, 163.59, 163.45, 163.01, 156.40, 138.84, 136.67, 136.45,
135.78, 131.54, 130.90, 129.56, 128.69, 127.43, 125.60, 124.45,
124.38, 123.63, 122.44, 122.29, 121.91, 121.67, 119.78, 117.37, 70.69,
68.61, 59.50, 44.67, 38.13, 30.90, 28.86, 24.20, 23.22, 14.28, 10.78.
MS (MALDI-TOF): m/z¼846.8 [MþH]þ. Elemental analysis: calcd
4.5. Synthesis of compound 9c
Compound 8c (76.3 mg, 0.1 mmol) was dissolved into 20 mL
of CH2Cl2, to which 1 mL bromine was dropwise added. The

8160
X. Zhang et al. / Tetrahedron 69 (2013) 8155e8160
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5.53, N 3.32.
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4.8. Synthesis of compound 16
A mixture of 15 (68.8 mg, 0.1 mmol) and 1 mL bromine in 20 mL
DCM was heated under reflux. The reaction was monitored by using
TLC. The excess of bromine was removed by flow of N2, and the
solvent was removed under vacuum. It was purified by column
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compound 16 as
a dark-red solid (75.2 mg, 0.094 mmol,
yield¼94%). 1H NMR (CDCl3, 400 MHz)
d
ppm: 9.25 (d, J¼8.00 Hz,
1H), 8.74 (s, 1H), 8.55 (s, 1H), 8.41 (s, 1H), 8.37 (d, J¼8.00 Hz, 1H),
4.61 (m, 2H), 4.12 (m, 4H), 3.97 (m, 1H), 3.88 (m, 1H), 3.40 (s, 3H),
1.95 (m, 2H), 1.41 (m, 8H), 1.35 (m, 8H), 0.97 (m, 6H), 0.92 (m, 6H).
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Acknowledgements
€
€
This work is financially supported by NSFC (nos. 91227112 and
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Supplementary data
Quantum chemical calculations and copies of 1H NMR, 13C NMR,
NOESY and HMBC spectra. Supplementary data associated with this
article can be found in the online version, at http://dx.doi.org/
10.1016/j.tet.2013.07.035. These data include MOL files and InChi-
Keys of the most important compounds described in this article.
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