A facile synthesis and application of ethyl 6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate

Article abstract of DOI:10.1007/s11164-014-1581-1

Visible-light-induced radical bromination of ethyl 6-methyl-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (1) was effectively conducted with N-bromosuccinimide using a 150-W tungsten bulb as an initiator, leading to the desired monobromo product ethyl 6-(bro

Full text of DOI:10.1007/s11164-014-1581-1

Res Chem Intermed
DOI 10.1007/s11164-014-1581-1
A facile synthesis and application of ethyl
6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-
carboxylate
Yang Li
Received: 18 December 2013 / Accepted: 27 February 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract Visible-light-induced radical bromination of ethyl 6-methyl-[1,3]diox-
olo[4,5-g]quinoline-7-carboxylate (1) was effectively conducted with N-bromo-
succinimide using a 150-W tungsten bulb as an initiator, leading to the desired
monobromo product ethyl 6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-car-
boxylate (2) in good yield of 76 %. Using the present procedure, a 46 %
improvement in yield of 2 was achieved when compared with the previous method
used by us. In addition, the trace amount of byproduct was isolated and identified as
ethyl 9-bromo-6-methyl-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (3) based on
1H nuclear magnetic resonance (NMR) spectral analysis. As an extended application
of 2, a new synthesis of symmetrical 2-quinolylmethoxyphenyl-containing diethers
11a–c was achieved via Williamson reaction with some dihydroxy arenes (10a–c).
Keywords Radical bromination ꢀ Quinoline ꢀ N-Bromosuccinimide ꢀ
Tungsten bulb ꢀ Williamson reaction ꢀ Diether
Introduction
Bromomethylquinolines as useful building blocks have proven to be valuable tools
to participate in a wide array of chemical transformations, and much effort directed
towards the application of the compounds has been paid to reveal the synthetic
potential of these platforms in accessing important quinoline scaffold derivatives
[1–3]; For example, Yang’s group reported the synthesis and application of ethyl
2-bromomethylquinoline-3-carboxylate as a key intermediate for synthesis of
Y. Li (&)
Institute of Superfine Chemicals, Bohai University, Jinzhou 121000, China
e-mail: bhuzh@163.com
123

Y. Li
quinoline ethers through Williamson reaction [4, 5]. In this context, we reported the
application of ethyl 6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate
(2) for synthesis of fused quinoline [6] or bisquinoline systems [7]. Because we
needed larger amounts of this monobromo product 2, we now needed an efficient
preparation to further extend its application in synthetic organic chemistry.
A literature survey reveals that preparation of 2-bromomethylquinolines could be
achieved generally via radical bromination of corresponding 2-methylquinolines
with N-bromosuccinimide (NBS) [8–10]. The reaction with NBS is well known to
proceed via a radical process promoted by initiators such as azobisisobutyronitrile
(AIBN) and dibenzoyl peroxide (BPO) in refluxing CCl4. The major advantage of
the use of NBS is that the reaction byproduct, succinimide, and solvent can be
recovered effortlessly. However, the reaction has suffered from both low yield and
byproduct excess, because the desired monobromo product is always accompanied
by the gem-dibromo byproduct, which has very close polarity to the monobromo
product and cannot be easily separated by recrystallization or column chromatog-
raphy. Therefore, development of a more efficient strategy for synthesis of
bromomethylquinoline derivatives is highly desirable.
In view of these facts, we report herein a facile and practical visible-light-
induced NBS-mediated radical bromination reaction for synthesis of ethyl
6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate and its application
for further functional group manipulations.
Results and discussion
Scheme 1 outlines the visible-light-induced NBS-mediated radical bromination
reaction developed in our laboratories for preparation of 6-(bromomethyl)-
[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (2).
Previously, we carried out the radical bromination reaction of ethyl 6-methyl-
[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (1) according to the reaction condition
described in literature [4] using NBS as brominating agent in refluxing CCl4.
However, the method was not practical and yielded only 30 % monobromo product
2 (Table 1, entry 1). Our attempt to use azobisisobutyronitrile (AIBN) as radical
initiator instead of dibenzoyl peroxide (BPO) was frustrated by very low yield as
well (Table 1, entry 2). In addition, we also attempted to obtain the desired product
2 by halting the reaction at the point where the byproduct formation was minimal
and did not significantly affect the monobromination of 1. Although significant
amounts of starting material could be recovered, chromatographic separation of the
resulting mixture was unavoidable. Clearly, this approach was very cumbersome
and not one that could be useful for synthesis of 2.
Recently, Jereb et al. described visible-light-induced transformation of toluenes
with NBS [11]. Thus, we felt that this approach could be judiciously extended for
preparation of 2. Based on the report, a solution of 1 in CCl4 was heated at reflux
with 1.5 equiv. of NBS using a 40-W tungsten bulb, but this resulted in only a
slightly improved yield of 35 % (Table 1, entry 3) after 36 h. Interestingly, further
increasing the tungsten bulb power resulted in a significant increase in the yield of
123

Facile synthesis and application
150 W light bulb
O
C
r
B
O
O
O
O
O
Et
r
O
O
O
Et
O
Et
O
NBS
reflux
CCl4,
N
H B
O
2
N
N
1
2 (76%)
3 (17%)
Scheme 1 Visible-light-induced radical bromination reaction of 1 with NBS
Table 1 Radical bromination of 2-methylquinoline 1 in different reaction conditions
Entry
Reaction conditions
Yield (%)a
1
2
3
4
5
6
7
8
9
a
NBS (1.5 equiv.), BPOb
NBS (1.5 equiv.), AIBNc
30
28
35
66
71
68
76
70
72
NBS (1.5 equiv.), 40-W light bulb
NBS (1.5 equiv.), 100-W light bulb
NBS (1.5 equiv.), 150-W light bulb
NBS (1.5 equiv.), 200-W light bulb
NBS (1.5 equiv.) added in batches, 150-W light bulb
NBS (1.2 equiv.) added in batches, 150-W light bulb
NBS (1.8 equiv.) added in batches, 150-W light bulb
c
b
Isolated yield; BPO (5 mol%); AIBN (5 mol%)
the product, and the yield plateaued to 71 % when we placed a 150-W tungsten bulb
10 cm from the flask (Table 1, entries 4–6). Thus, we can conclude that visible-
light-induced radical bromination did afford a significant improvement versus the
previous method [4], which was effective at suppressing the formation of side
products. In addition, we found that the bromination reaction could be further
improved by adding NBS in batches (Table 1, entry 7); NBS was added in the
amount of 1/5 portions of 1.5 equiv. every 1.0 h. Thus, the desired product 2 was
obtained in 76 % yield, along with a trace amount of byproduct 3, which could be
separated by careful column chromatography over silica gel. In addition, in this
bromination reaction, the use of 1.5 equiv. of NBS was found optimal to complete
the reaction. Lower conversion of 1 to 2 was observed when a lesser equivalent of
NBS was used, whereas use of excess NBS also resulted in lower yield of 2
(Table 1, entries 8, 9). After cooling the reaction mixture to room temperature,
almost all succinimide crystallizes from the reaction mixture and can be recycled
into NBS. The solvent was distilled off under reduced pressure and could be used in
new bromination reactions.
The main advantage of the visible-light-induced method is the significant
improvement of yield. Presumably, it may be considered that the radical
bromination reaction using visible light from a 150-W tungsten bulb as the radical
chain process initiator was milder compared with those using AIBN or BPO, and the
irradiation resulted in relatively slow conversion of NBS to succinimide.
Accordingly, the resulting Br2 might remain in a low concentration throughout
the course of the reaction, thereby restraining the side reaction and leading to the
123

Y. Li
formation of the desired product in higher yield. Additionally, we also attempted the
bromination reaction by using a 180- or 200-W tungsten bulb under similar reaction
conditions. Although the higher intensity of visible light shortened the reaction time
to 3 h, the amounts of byproducts were also further increased, which significantly
reduced the yield of the desired product.
Encouraged by the achievement of the suitable radical bromination reaction
conditions for synthesis of the title compound, we also attempted the similar
reaction of ethyl 2-methylquinoline-3-carboxylate under similar reaction conditions.
We were delighted to find that the reaction also proceeded well and the yield of
ethyl 2-bromomethylquinoline-3-carboxylate was increased to 74 from the 58 %
value in the literature [5]. In addition, we also attempted the bromination of toluene.
As expected, toluene was equally amenable to the reaction conditions, and the
corresponding (bromomethyl)benzene was obtained in good yield of 78 %, albeit
with no further improvement compared with literature [12, 13].
The structure of the monobrominated product 2 was easily identified based on the
1
consistency of its H NMR spectral data and melting point with literature [4].
However, concerning the possible structure of the trace amount of byproduct 3,
there was no further elucidation in the literature [4]. We initially presumed that the
gem-dibromo product (4) was the byproduct in this reaction, since one might
reasonably expect 4 to be produced based on some closely analogous reports; For
example, in the radical bromination of ethyl 2-methylquinoline-3-carboxylate, the
desired monobromo product is always accompanied by the dibromo-substituted
byproduct 5 (Scheme 2) [5]. Similarly, Xu et al. also described that the dibromo-
substituted 8-bromo-6-(dibromomethyl)quinoline (6) was formed during the radical
bromination of 8-bromo-6-methylquinoline with NBS [14] (Fig. 1).
However, to our surprise, its 1H NMR spectrum showed the presence of a three-
hydrogen singlet due to methyl protons, along with the presence of two quinoline
ring proton singlets at 7.04 and 8.53 ppm, which clearly indicated the occurrence of
aromatic bromination on quinoline ring, instead of the expected gem-dibromo
byproduct (4). Moreover, its 13C NMR spectrum also showed the presence of
methyl carbon at 23.81 ppm. Further, the electrospray ionization mass spectroscopy
(ESI-MS) (positive-ion mode) spectrum of the byproduct exhibited a characteristic
quasi-molecular ion peak cluster [M ? H]? at m/z of 339.1, 341.1 with a ratio of
1:1, suggesting the presence of one Br atom in its structure. We anticipate that the
main reason is the presence of 1,3-benzodioxole system, which could activate the
quinoline ring, thereby leading to quinoline ring becoming the important reaction
site for bromination. However, as for the exact structure of the byproduct, one can
easily imagine that the aromatic bromination might occur at 4-position, 5-position
or 8-position of the quinoline ring, resulting in three possible structural isomers as
shown in Fig. 2.
1
Further careful analysis of its H NMR spectrum and comparison with starting
compound 1 and product 2 found that there were significant aspects of the spectral
data that were quite helpful for identification of the substitution position of bromine
atom. The presence of the singlet at 8.53 ppm and a notable downfield chemical
shift due to the deshielding effect of the proximate ester carbonyl clearly indicated
the presence of H-4 proton, thereby ruling out the possibility of formation of 30. In
123

Facile synthesis and application
O
O
O
O
N
O
H
O
H
O
O
O
N
O
10a
O
O
11a (Yield: 91%)
N
N
O
O
O
O
O
O
2
O
O
K
MeCN
2CO3/
H
O
H
O
O
O
10b
11b(Yield: 86%)
O
O
O
O
H
O
N
O
O
N
O
O
O
H
O
10c
O
11c(Yield: 89%)
Scheme 2 Synthesis of symmetrical 2-quinolylmethoxyphenyl-containing diethers 11a–c
Ο
Ο
r
HB
C
2
Ο
Ο
Ο
Et
O
N
r
N
HB
C
2
r
N
4
HB
C
r
B
2
5
6
Lit. [5]
not observed
Fig. 1 Structures of compounds 4–6
Lit. [14]
Ο
Ο
r
B
Ο
Br
Ο
Ο
OEt
Ο
Ο
Ο
Ο
OEt
OEt
N
N
N
r
B
3
3'
3''
Fig. 2 Possible isomer structures of the byproduct
1
the H NMR spectra of substrate 1 and product 2, the quinoline ring H-8 and H-5
protons appear as two singlets at 7.0–7.1 and 7.2–7.3 ppm, respectively. However,
1
in the H NMR spectrum of the byproduct, the corresponding signal from H-5
proton at the region 7.2–7.3 ppm was not observed, only indicating a singlet at 7.04
attributable to H-8 proton, which indicated that the H-5 proton was substituted by a
123

Y. Li
N
HN
H
O
N
O
O
N
N
N
O
RG5901 (8)
RG12525 (7)
H
COO
O
O
N
N
bis(4-(2-quinolylmethoxy)phenyl)pentanoic acid (9)
Fig. 3 Structures of 2-quinolylmethoxyphenyl-containing compounds 7–9
Br atom. From these observations, the byproduct was characterized as ethyl
9-bromo-6-methyl-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (3).
Having established the best reaction conditions for the preparation of 2, we
decided to further extend its application for building more novel and interesting
quinoline systems. It has been proven that the 2-quinolylmethoxyphenyl structural
motif is useful in the design of several leukotriene biosynthesis inhibitors or
leukotriene receptor antagonists [15–17]; For example, (2-quinolinylmethoxy)phen-
oxy-containing compound RG12525 (7) was used in clinical studies as an
antiasthmatic agent [18], and compound REV-591 (8) showed potent inhibition of
5-lipoxygenase (5-LO) activity and slow reacting substance of anaphylaxis (SRS-
A)-mediated bronchospasm [19]. In particular, in 2000, Kolasa et al. [20] reported
that the symmetrical 4,4-bis(4-(2-quinolylmethoxy)phenyl)pentanoic acid (9)
showed high selectivity for inhibition of ionophore-stimulated LTB4 formation
and promise for use as a new leukotriene inhibitor drug (Fig. 3).
Given the importance of the (2-quinolinylmethoxy)phenyl moiety as a pharma-
cophore, we conceived that synthesis of new types of symmetrical 2-quinolyl-
methoxyphenyl-containing compounds as possible drug-like candidates would be of
synthetic importance. Accordingly, in continuation of our studies concerning
preparation of potentially biologically active quinolines [6, 7], our present work
focused on extension of 2 to the reaction with hydroquinone (10a), naphthalene-1,5-
diol (10b), and naphthalene-2,7-diol (10c), expecting to achieve some meaningful
symmetrical 2-quinolylmethoxyphenyl-containing diether derivatives.
As shown in Scheme 2, reaction between 2 and respective 10a–c was performed
in 2:1 molar ratio of the substrates in refluxing MeCN in the presence of K2CO3 as
base. These conditions are the same as those used previously in the preparation of
bisquinoline derivatives [7]. The reactions were followed by thin-layer chromatog-
raphy (TLC) and found to be complete after 5 h in high yields. In the initial stages
123

Facile synthesis and application
of the reaction, TLC exhibited a spot probably due to the formation of a monoether
product, which gradually disappeared with the appearance of a new dark spot
arising from the formation of symmetrical diether quinolines 11a–c. After usual
workup followed by purification of the crude products by recrystallization from
ethanol, the symmetrical 11a–c were obtained in 91, 86, and 89 % yields,
respectively. In addition, it is worth mentioning that, if the molar ratio was 1:1, a
mixture of 2, 11a–c, and the corresponding monoether was obtained as observed
from TLC.
Conclusions
We have established an effective and practical procedure for synthesis of ethyl
6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (2) via visible-light-
induced NBS-mediated radical bromination reaction. Using the present procedure,
the desired monobromo product 2 was obtained in 76 % yield, a 46 % improvement
compared with previous studies. Further application of 2 to synthesis of symmetrical
2-quinolylmethoxyphenyl-containing diether derivatives was accomplished via
Williamson reaction with dihydroxy arenes. These newly synthesized quinoline
derivatives could be good candidates for development of lead compounds.
Experimental
The chemicals used in this work were obtained from Fluka and were used without
purification. The melting points were determined by using a WRS-1B melting point
apparatus and were uncorrected. The infrared (IR) spectrum was obtained in the
1
range of 400–4,000 cm-1 on a Shimadzu FTIR-8400S spectrophotometer. The H
(400 MHz) and 13C (100 MHz) NMR spectra were recorded on a Bruker BRX 400
spectrometer. The reported chemical shifts are against tetramethylsilane (TMS). The
mass spectra were determined using a MSD VL ESI1 spectrometer. The elemental
analyses were performed for C, H, N using an Elementar Vario EL III element
analyzer. Progress of reactions was monitored by TLC on silica gel GF254 using
hexane/ethyl acetate mixture as eluent (5:1, v/v). Ethyl 6-methyl-[1,3]dioxolo[4,5-
g]quinoline-7-carboxylate (1) was prepared according to literature [4].
Reaction procedure for visible-light-induced NBS-mediated radical bromination
reaction of ethyl 6-methyl-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (1)
A solution of 1 (2.6 g, 10 mmol) in CCl4 (45 mL) was heated with vigorous
stirring until the solution boiled gently, and then was exposed to illumination with a
150-W tungsten lamp. Maintaining the reaction temperature, 0.534 g portions of
2.67 g (15 mmol) NBS were added to the mixture every 1.0 h. After the addition of
NBS was complete, the resulting reaction mixture continued to reflux with
illumination until practically full conversion was achieved (6 h) (TLC). On
completion, the reaction was cooled to 10 °C, and the precipitated succinimide was
filtered. The filtrate was evaporated under vacuum to dryness. The residue was
subjected to column chromatography over silica gel (200–400 mesh) using hexane/
123

Y. Li
ethyl acetate mixture as eluent (10:1, v/v) to give 2.53 g of 2 along with 0.58 g of
byproduct 3 as white solid.
Ethyl 6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (2)
1
White solid, m.p. 162–163 °C (lit. [4]: 166–168 °C). H NMR (400 MHz, CDCl3),
d: 1.46 (t, J = 7.2 Hz, 3H, COOCH2CH3), 4.39 (q, J = 7.2 Hz, 2H, COOCH2CH3),
4.96 (s, 2H, CH2Br), 6.13 (s, 2H, OCH2O), 7.09 (s, 1H, quinoline H-8), 7.32 (s, 1H,
quinoline H-5), 8.52 (s, 1H, quinoline H-4). MS (ESI, m/z): 339.0, 341.1 [M ? H]?.
Ethyl 9-bromo-6-methyl-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate (3)
White solid, m.p. 144–145 °C. IR (KBr, m, cm-1): 1,710 (C=O), 1,573, 1,481,
1,455, 1,379, 1,251, 1,231, 1,068, 948; 1H NMR (CDCl3, 400 MHz) (d, ppm): 1.45
(t, J = 7.2 Hz, 3H, COOCH2CH3), 2.99 (s, 3H, CH3), 4.42 (q, J = 7.2 Hz, 2H,
COOCH2CH3), 6.22 (s, 2H, OCH2O), 7.04 (s, 1H, quinoline H-8), 8.53 (s, 1H,
quinoline H-4); 13C NMR (CDCl3, 100 MHz) d: 14.18, 23.81, 61.79, 102.68,
117.56, 123.72, 126.33, 127.72, 128.69, 130.89, 139.19, 145.88, 153.94, 165.35. MS
(ESI, m/z): 339.1, 341.1 [M ? H]?. Anal. Calcd. for C14H12BrNO4: C, 49.73; H,
3.58; N, 4.14. Found: C, 49.88; H, 3.54; N, 3.94.
General procedure for synthesis of symmetrical 2-quinolylmethoxyphenyl-
containing diethers 11a–c
To a solution of ethyl 6-(bromomethyl)-[1,3]dioxolo[4,5-g]quinoline-7-carbox-
ylate (2, 0.68 g, 2 mmol) in 25 mL MeCN was added respective dihydroxy arene
10a–c (1 mmol) and anhydrous K2CO3 (1.1 g, 8 mmol). The resulting mixture was
heated at reflux for 5 h. The conversion was monitored by TLC. After completion,
MeCN was evaporated to dryness and 20 mL water was added slowly to the
mixture. The resulting precipitate was collected by filtration and purified by
recrystallization from ethanol to give products 11a–c.
Diethyl 6,60-((1,4-phenylenebis(oxy))bis(methylene))bis([1,3]dioxolo[4,5-g]quino-
line-7-carboxylate) (11a)
White solid, m.p. 209–210 °C. IR (KBr, m, cm-1): 1,720 (C=O), 1,594, 1,556,
1
1,501, 1,380, 1,267, 1,236, 1,149, 1,085; H NMR (CDCl3, 600 MHz) (d, ppm):
0.87 (t, J = 7.2 Hz, 6H, COOCH2CH3), 3.96 (q, J = 7.2 Hz, 4H, COOCH2CH3),
5.45 (s, 4H, OCH2Ar), 6.14 (s, 4H, OCH2O), 6.93 (s, 4H, Ph-H), 7.31 (s, 2H,
quinoline-H), 7.35 (s, 2H, quinoline-H), 8.69 (s, 2H, quinoline-H); 13C NMR
(CDCl3, 150 MHz) d: 14.24, 61.24, 73.69, 102.08, 105.74, 115.50, 123.63, 124.41,
134.31, 148.11, 152.82, 153.06, 154.44, 156.87, 158.24, 167.63. MS (ESI, m/z):
625.3 [M ? H]?. Anal. Calcd. for C34H28N2O10: C, 65.38; H, 4.52; N, 4.49. Found:
C, 65.62; H, 4.78; N, 4.21.
Diethyl 6,60-((naphthalene-2,7-diylbis(oxy))bis(methylene))bis([1,3]dioxolo[4,5-g]
quinoline-7-carboxylate) (11b)
White solid, m.p. 215–216 °C. IR (KBr, m, cm-1): 1,722 (C=O), 1,629, 1,568,
1
1,512, 1,390, 1,298, 1,211, 1,172, 1,070; H NMR (CDCl3, 600 MHz) (d, ppm):
1.30 (t, J = 7.2 Hz, 6H, COOCH2CH3), 4.36 (q, J = 7.2 Hz, 4H, COOCH2CH3),
5.79 (s, 4H, OCH2Ar), 6.18 (s, 4H, OCH2O), 7.10 (d, J = 8.4 Hz, 2H, Ph-H), 7.38
(s, 2H, quinoline-H), 7.41 (s, 2H, quinoline-H), 7.95 (d, J = 8.4 Hz, 2H, Ph-H),
8.74 (s, 2H, quinoline-H); 13C NMR (CDCl3, 150 MHz) d: 14.18, 61.28, 73.56,
102.16, 107.64, 114.36, 124.67, 126.43, 127.15, 128.39, 129.30, 130.54, 135.64,
135.93, 147.57, 153.70, 156.44, 156.93, 158.43, 168.03. MS (ESI, m/z): 675.6
123

Facile synthesis and application
[M ? H]?. Anal. Calcd. for C38H30N2O10: C, 67.65; H, 4.48; N, 4.15. Found: C,
67.78; H, 4.30; N, 4.01.
Diethyl 6,60-((naphthalene-1,5-diylbis(oxy))bis(methylene))bis([1,3]dioxolo[4,5-g]
quinoline-7-carboxylate) (11c)
White solid, m.p. 231–232 °C. IR (KBr, m, cm-1): 1,722 (C=O), 1,618, 1,543,
1
1,476, 1,390, 1,269, 1,209, 1,170, 1,089; H NMR (CDCl3, 600 MHz) (d, ppm):
0.76 (t, J = 7.2 Hz, 6H, COOCH2CH3), 3.86 (q, J = 7.2 Hz, 4H, COOCH2CH3),
5.82 (s, 4H, OCH2Ar), 6.28 (s, 4H, OCH2O), 7.08 (d, J = 7.8 Hz, 2H, naphthalene-
H), 7.32 (s, 2H, quinoline-H), 7.39 (s, 2H, quinoline-H), 7.53 (t, J = 7.8 Hz, 2H,
naphthalene-H), 7.79 (d, J = 7.8 Hz, 2H, naphthalene-H), 8.61 (s, 2H, quinoline-
H); 13C NMR (CDCl3, 150 MHz) d: 14.21, 61.39, 73.44, 102.08, 105.96, 112.23,
112.56, 118.79, 121.12, 124.66, 126.78, 128.63, 137.88, 146.53, 152.27, 152.86,
154.75, 158.30, 167.93. MS (ESI, m/z): 675.7 [M ? H]?. Anal. Calcd. for
C38H30N2O10: C, 67.65; H, 4.48; N, 4.15. Found: C, 67.86; H, 4.54; N, 4.29.
Acknowledgments The authors would like to thank the Scientific Research Foundation of the
Education Department of Liaoning Province (grant no. L2013428) for financial support.
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