Rose Bengal-photosensitized oxidation of tertiary amines for the synthesis of bis-1,3-dicarbonyl compounds

Article abstract of DOI:10.1016/j.tet.2017.09.050

We report an example of Rose Bengal-photosensitized oxidation of tertiary amines for the synthesis of bis-1,3-dicarbonyl compounds. This protocol employs Rose Bengal as a visible-light absorbing photocatalyst without the need of a transition metal, and air as a green oxidant. Various functional groups were well tolerated to afford products with yields of up to 80% under mild reaction conditions.

Full text of DOI:10.1016/j.tet.2017.09.050

Accepted Manuscript
Rose Bengal-photosensitized oxidation of tertiary amines for the synthesis of bis-1,3-
dicarbonyl compounds
Ling-Ling Wu, Li Tang, Shui-Gen Zhou, Yi-Jie Peng, Xiao-Dong He, Zhi Guan, Yan-
Hong He
PII:
S0040-4020(17)31006-2
10.1016/j.tet.2017.09.050
TET 29001
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 2 July 2017
Revised Date: 19 September 2017
Accepted Date: 29 September 2017
Please cite this article as: Wu L-L, Tang L, Zhou S-G, Peng Y-J, He X-D, Guan Z, He Y-H, Rose
Bengal-photosensitized oxidation of tertiary amines for the synthesis of bis-1,3-dicarbonyl compounds,
Tetrahedron (2017), doi: 10.1016/j.tet.2017.09.050.
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ACCEPTED MANUSCRIPT
Graphical Abstract

ACCEPTED MANUSCRIPT
Rose Bengal-photosensitized oxidation of tertiary amines for the
synthesis of bis-1,3-dicarbonyl compounds
Ling-Ling Wu, Li Tang, Shui-Gen Zhou, Yi-Jie Peng, Xiao-Dong He, Zhi Guan*and Yan-Hong He*
Key Laboratory of Applied Chemistry of Chongqing Municipality, School of Chemistry and Chemical Engineering,
Southwest University, Chongqing 400715, PR China
E-mails: guanzhi@swu.edu.cn (Z. Guan); heyh@swu.edu.cn (Y.-H. He)
Abstract: We report an example of Rose Bengal-photosensitized oxidation of tertiary amines for
the synthesis of bis-1,3-dicarbonyl compounds. This protocol employs Rose Bengal as a
visible-light absorbing photocatalyst without the need of a transition metal, and air as a green
oxidant. Various functional groups were well tolerated to afford products with yields of up to 80%
under mild reaction conditions.
Key words: visible light; Rose Bengal; bis-1,3-dicarbonyl compounds; photocatalysis; tertiary
amines
1. Introduction
Sunlight is an abundant and renewable energy source that can meet the needs of the earth in
the future. Scientific community long ago recognized the potential of photochemistry which plays
a crucial role in the conversion of solar energy into chemical transformations.1 However, most
organic molecules don't tend to absorb photons in the visible light region that greatly limited the
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potential application of photochemical reactions. In order to overcome this drawback, various
photosensitizers have been widely employed in visible light photoredox catalysis.2 Costly
complexes of transition-metal catalysis have been successfully applied in organic synthesis, such
as inorganic ruthenium3 and iridium4 based polypyridyl complexes, or copper-containing
photocatalysts. 5 However, the potential toxicity of the metal catalysts may cause pollution to the
environment when deal with it at the end of the reaction. Recently, cheap metal-free organic dyes
have been applied as effective visible light photosensitizers6 such as eosin Y, 7methylene blue, 8
Rose Bengal (RB), etc. The application of Rose Bengal in organic synthesis has attracted the
attention of chemists. It has been successfully used as a photosensitizer to oxidize amines to
generate highly reactive iminium ion intermediates under visible light irradiation, which can be
attacked by a variety of nucleophiles. Many new visible-light promoted chemical reactions have
been developed utilizing Rose Bengal as a photosensitizer.9
Bis-1,3-dicarbonyl compounds are valuable intermediates or precursors for organic synthesis
and transition metal complexes. 10 Recently, using amine as carbon source to construct C-C bond
for the synthesis of bis-1,3-dicarbonyl compounds has received considerable attention. However,
among these reactions, metals,11 peroxides,12 or inorganic oxidants13 are necessary for promoting
the oxidation. These classic methods are often harmful to our environment. In order to avoid the
use of those toxic reagents, new synthetic methods for this type of reaction under mild conditions
are highly desirable. Currently, visible light-mediated oxidation of amines to iminium ions and the
subsequent addition of nucleophiles are extensively studied as an efficient method for C-H
14
functionalization,3d,
which can provide new reaction protocols for the synthesis of
bis-1,3-dicarbonyl compounds. But, to the best of our knowledge, up to date only two reports have
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been available for the visible-light photocatalyzed reactions of this type (Scheme 1).15 In these
two works, the range of substrates is relatively limited, and only methylene-bridged
bis-1,3-dicarbonyl compounds have been obtained via oxidation of N-methyl amines under the
condition of visible light. Visible-light-induced oxidation of N-ethyl amines for the synthesis of
ethylidene-bridged bis-1,3-dicarbonyl compounds has never been reported. Therefore, it is still
necessary to develop the application of photosensitized oxidation of tertiary amines for synthesis
of bis-1,3-dicarbonyl compounds. Moreover, as far as we know, there are no precedent methods
for the application of Rose Bengal-photosensitized oxidation of tertiary amines with
1,3-dicarbonyl compounds for synthesis of bis-1,3-dicarbonyl compounds. We herein wish to
report our results about this work.
Previous works: 15a, 15b
Scheme 1. Visible-light photocatalyzed synthesis of bis-1,3-dicarbonyl compounds.
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2. Results and Discussion
Our initial study was conducted by investigating the reaction of ethyl
3-oxo-3-phenylpropanoate (1a) with N,N-dimethyl aniline (2a) in the presence of 2 mol% of Rose
Bengal in MeCN at room temperature under air atmosphere. After 24 h of irradiation with a 15 W
compact fluorescent light (CFL) bulb (λ = 405-577 nm), we were delight to find that the reaction
indeed proceeded and the desired methylene-bridged bis-1,3-dicarbonyl compound (3a) was
obtained with 72% yield (Table 1, entry 1). To verify if visible light and Rose Bengal were
necessary in this catalytic process, some control experiments were conducted (Table 1). In the
absence of visible-light irradiation, no desired product was observed (Table 1, entry 2), indicating
that visible light was necessary for the reaction. When the reaction was conducted without Rose
Bengal, a low yield of 22% was obtained (Table 1, entry 3), suggesting that Rose Bengal could
promote the reaction. Additionally, to confirm if air played a role in this process, the reaction was
performed under N2 instead of air, which only gave a very low yield of 8% (Table 1, entry 4). The
result indicated that air was essential for the reaction.
Inspired by the promising result, different solvents, molar ratios of substrates and catalyst
loading were examined to improve the reaction efficiency (Table 1, entries 5-15). The data
confirmed that solvent played an important role in this reaction. The reaction in MeCN gave the
best yield of 72% after 24 h (Table 1, entry 1). No better results were obtained in other tested
solvents such as MeOH, H2O, 1,2-dichloroethane, DMF, DMSO and cyclohexane. A slightly
improved yield of product 3a was achieved when molar ratio ranged from 1:0.5 to 1:2 (1a:2a)
(Table 1, entries 1, 10-12). Next, the catalyst loading was screened. When increasing the loading
of Rose Bengal from 0.5 mol% to 3 mol%, the yield increased slightly (Table 1, entries 1, 13-15).
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Taking into consideration of the yield and the cost of the reaction, MeCN, 1a:2a = 1:1 and catalyst
dosage of 1 mol% were chosen as the suitable conditions for the reaction.
Table 1. Control experiments and optimization studies for the reaction of 1a and 2aa.
Entry
1
Rose Bengal (mol%)
Solvent
MeCN
MeCN
MeCN
MeCN
EtOH
Molar ratio (1a:2a)
Yield (%)b
2
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:0.5
1:1.5
1:2
1:1
1:1
1:1
72
--
2
2 (dark)
none
3
22
8
4
2
(N2 instead of air)
5
2
2
49
10
45
49
5
6
H2O
7
2
EtOAc
CH2Cl2
ClCH2CH2Cl
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
8
2
9
2
10
11
12
13
14
15
2
67
74
76
68
71
72
2
2
0.5
1
3
a Reaction conditions: A mixture of 1a (0.3 mmol), 2a (0.15-0.6 mmol), Rose Bengal (0.5-3 mol %) in solvent (1.0
mL) was irradiated with a 15 W CFL bulb in air for 24 h.
b Yield of the isolated product after silica gel chromatography.
Next, the effect of different solvent volume and sources of light on the reaction was
investigated (For details, please see the Supporting Information Table S1). Based on the
experiment results, 1.0 mL of MeCN and 32 W CFL bulb were chosen as the optimum conditions
for the reaction (0.3 mmol of 1a and 0.3 of mmol 2a). Moreover, time course of the reaction was
also investigated, extending the reaction time led to an increase of the yield (Tables S1, entries
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10-13), but yield did not improve obviously after 24 h.
With the optimized conditions established, the substrate scope of the reaction was explored
using N,N-dimethylaniline (2a) as a model substrate to react with various β-ketoesters,
1,3-diketones and 2-benzoylacetanilide (Table 2). It can be seen that substituted ethyl
benzoylacetate could be proceeded smoothly to give the corresponding products in moderate
yields (Table 2, entries 2-5). Other β-ketoesters such as benzyl benzoylacetate and cyclohexyl
benzoylacetate also performed well (Table 2, entries 6 and 7), and several kinds of 1,3-diketones
were applicable to the reaction (Table 2, entries 8-10). In addition, heteroaromatic β-ketoesters
were also successfully applied in this transformation (Table 2, entries 12 and 13). This is an
efficient method for the synthesis of methylene-bridged bis-1,3-dicarbonyl compounds through
oxidation of N, N-dimethylaniline.
Table 2. Reaction of 1 with N, N-dimethylaniline (2a)a.
Entry
R1
Ph
R2
OEt
Product
3a
Time (h)
24
Yield (%)b
1
2
3
4
5
6
7
76
65
72
63
63
77
56
4-F-C6H4
4-Br-C6H4
4-NO2-C6H4
3-NO2-C6H4
Ph
OEt
29
3b
OEt
26
3c
OEt
24
3d
OEt
24
3e
OCH2-C6H5
24
3f
Ph
29
3g
8
9
Ph
Ph
Ph
Ph
Me
Ph
24
24
24
24
62
45
52
60
3h
3i
10
11
2-OH-C6H4
NH-C6H5
3j
3k
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12
13
OEt
24
24
52
39
3l
OEt
3m
a Reaction conditions: A mixture of 1 (0.3 mmol), 2a (0.3 mmol), Rose Bengal (1 mol %) in MeCN (1.0 mL) was
irradiated with a 32 W CFL bulb in air.
b Yield of the isolated product after silica gel chromatography.
The above data show that, Rose Bengal can oxidize N-methyl amines give methylene-bridged
bis-1,3-dicarbonyl compounds under the irradiation of visible light. We were curious to know
whether Rose Bengal can catalyze N-ethyl amines to give the same type of products. It was nice to
see that the results were consistent with what we expected. 1.5 mmol of Et3N (2b) with 0.3 mmol
of 1a led to a 40% yield of the desired product ethylidene-bridged bis-1,3-dicarbonyl compound
(4a) after 8 h (For details, please see the Supporting Information Table S2). In order to study the
applicability of the substrate, Et3N (2b) as a substrate was used to react with 1 (Table 3). The
reaction with various β-ketoesters could be proceeded smoothly to give the corresponding
products.
It is worth mentioning that the expected product wasn’t achieved when using
1-(2-hydroxyphenyl)-3-phenyl-1,3-propanedione
(1j)
as
a
substrate,
but
3-benzoyl-2-methylchroman-4-one (5a) and 3-benzoyl-2-methyl-4H-chromen-4-one (5b) were
obtained instead (Scheme 2). And we further found that 5a could be converted into the 5b by an
oxidation process under the standard conditions (Scheme 3).
Table 3. Reaction of 1 with Et3N (2b)a
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Entry
R1
R2
Product
4a
Time (h)
Yield (%)b
1
2
3
4
5
6
Ph
OEt
OEt
OEt
OEt
OEt
OEt
8
4
5
8
8
8
40
60
80
40
33
55
4-F-C6H4
4-Br-C6H4
4-NO2-C6H4
3-NO2-C6H4
4b
4c
4d
4e
4f
7
OEt
4
65
4g
a Reaction conditions: A mixture of 1 (0.3 mmol), 2b (1.5 mmol), Rose Bengal (1 mol %) in MeCN (1.0 mL) was
irradiated with a 32 W CFL bulb in air.
b Yield of the isolated product after silica gel chromatography.
Scheme 2. Reaction of 1j with Et3N (2b).
Scheme 3. Conversion of 5a to 5b.
Encouraged by the above experimental results, other tertiary amines were also investigated. In
the case of N-ethyl-N-methylethanamine (2c), methylene-bridged bis-1,3-dicarbonyl product 3a
was obtained as a major product in a yield of 45%, along with a 12% yield of 4a after 11 h
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(Scheme 4). The N-ethyl-N-isopropylpropan-2-amine (2d) reacted with 1a only led to a 25% yield
of 4a after 24 h, but no reaction was observed when using tripropylamine as a substrate.
In total, 21 bis-1,3-dicarbonyl compounds were prepared, and 11 of them are new compounds
and their structures were confirmed by HRMS, 1HNMR and 13CNMR.
O
O
O
O
O
O
Ph
Ph
OEt
OEt
Ph
Ph
OEt
OEt
Rose Bengal (1 mol %)
Et2NꢀMe
Ph
OEt
MeCN, 32 W CFL
air, 11 h
1a
0.3 mmol
2c
O
3a
45 %
O
O
O
4a
12 %
1.5 mmol
O
O
O
O
O
O
Ph
Ph
OEt
OEt
Ph
Ph
OEt
OEt
Rose Bengal (1 mol %)
N
Ph
OEt
MeCN, 32 W CFL
air, 24 h
O
O
O
O
1a
0.3 mmol
2d
4a
6a
1.5 mmol
25 %
0 %
Scheme 4. Reaction of 1a with tertiary amines 2c and 2d.
Finally, in order to understand the mechanism of the Rose Bengal-photosensitized oxidation of
tertiary amines, a number of control experiments were conducted. The UV-visible absorption
spectra of Rose Bengal was performed (the spectrum was shown in the Supporting information).
Rose Bengal exhibited a strong absorption in the visible light region at λmax = 563 nm (ε = 33290
L mol⁻1 cm⁻1). On the other hand, under N2 instead of air conditions, the reaction only gave a low
yield of 8% (Table 1, entry 4), indicating that O2 is involved in the reaction. It has been revealed
1
that in polar aprotic solvents, molecular oxygen could form singlet oxygen O2 through energy
3
1
transfer from the RB* to ground-state O2 under visible light irradiation,16 and O2 is able to
oxidize tertiary amines. 17 In order to understand the role of molecular oxygen in the reaction, we
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determined the rate of product formation in the absence and presence of
1,4-diazabicyclo[2.2.2]octane (DABCO) which is known as a quencher of singlet oxygen18 (Table
4). The data showed that DABCO (1 equiv) indeed has inhibitive effect on the reaction, especially
at the early stage of the reaction, indicating that singlet oxygen may be involved in the reaction
process. However after 24 h, nearly the same yield could be obtained as the reaction under
standard conditions suggesting that even in the presence of DABCO the reaction still can proceed.
Recently, we reported
a
chlorophyll-catalyzed visible-light-mediated synthesis of
tetrahydroquinolines from N,N ‑ dimethylanilines and maleimides.19 Like Rose Bengal,
chlorophyll is also a well-known singlet oxygen photosensitizer. In that chlorophyll-mediated
photocatalysis, the addition of 1 equiv of DABCO almost completely suppressed the reaction
which ruled out the possibility that N,N-dimethyl aniline might be more reactive to singlet oxygen
than DABCO, Thus, in consideration of the fact that the present reaction still can proceed at a
lower rate with the presence of 1 equiv of DABCO, we speculate that besides singlet oxygen
(energy transfer), a photoredox catalysis mechanism may also be involved in the reaction.
Furthermore, a test experiment with the presence of (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl
(TEMPO), a free radical scavenger,20 was performed. No desired product 3a was obtained
(Scheme 5) but some complicated by-products were observed, and starting materials did not
consumed completely. This result suggested that a radical process must be involved in this
reaction. The reduction potential of excited state of Rose Bengal [E*red (RB*/ RB•−) = 0.99 V vs.
SCE in MeCN] 6c, 21 is sufficient enough for the oxidation of N,N-dimethyl aniline (2a) [Half-peak
oxidation potential (E1/2(ox)) = 0.71 V vs. SCE in MeCN]22 and Et3N (2b) [Half-peak oxidation
potential (E1/2(ox)) = 0.96 V vs. SCE in MeCN].22
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Table 4 The rate of product formation in the absence and presence of DABCOa
Entry
Time (h)
Yield (%)b
With DABCO (0.3 mmol)
Standard conditions
1
2
3
4
6
27
51
55
75
43
51
70
76
12
18
24
a Standard conditions: A mixture of 1a (0.3 mmol), 2a (0.3 mmol), and Rose Bengal (1 mol %) in MeCN (1.0 mL)
was irradiated with a 32 W CFL bulb in air.
b Yield of the isolated product after silica gel chromatography.
O
O
O
O
O
O
Ph
Ph
OEt
OEt
N
Rose Bengal (1 mol%), air
MeCN, 32 W CFL, 24 h
Ph
OEt
N
O
1a
0.3 mmol
2a
0.3 mmol
TEMPO
3a
0%
0.3 mmol
Scheme 5. Control experiment.
On the basis of our results and the commonly accepted mechanism from the literature, 11a, 15a a
plausible mechanism was depicted (Scheme 6). On absorption of visible light, the ground state of
RB is induced to its excited state RB*. In path A (energy transfer), RB* transfers its energy to the
ground-state oxygen (3O2) forming the singlet oxygen (1O2). A single-electron transfer (SET) from
1
1
the tertiary amine 2 to O2 leads to the amine cation radical 2'. At the same time, O2 accepts an
electron to form superoxide anion radical (O2•−). Meanwhile, in path B (photoredox catalysis), a
single electron transfer (SET) from the tertiary amine 2 to RB* leads to the amine cation radical
2',9c, 14b, 14e, 14h, 23 and at the same time, RB* is reduced to the RB•−. Upon transfer of an electron to
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•−
O2 to form the superoxide radical anion O2 with the concurrent regeneration of RB, the
photocycle completes. Next, the radical cation 2' generated from the both paths gave up a
hydrogen atom, presumably to the superoxide radical anion to afford hydrogen peroxide anion
(HOO-) and iminium ion 2". Subsequently, the nucleophilic addition of iminium ion 2" with
deprotonated nucleophile 1' (HOO- abstracts the proton of 1 to form H2O2 and 1') affords the
intermediate a. The product 3 or 4 can be formed through an elimination/Michael addition
pathway via an intermediate b in the presence of 1.24 Additionally, the generation of H2O2 was
indirectly proved by the evidence that Ph3P could be oxidized to Ph3PO25 by the reaction mixture
of 1a and 2a (After completion of the model reaction, Ph3P was added to the reaction mixture and
stirred in the dark for 12 h. The formation of Ph3PO could be detected by both HPLC and TLC
through comparison with the authentic sample).
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Scheme 6. Proposed reaction mechanism for the formation of 3 and 4.
From the proposed mechanism as shown in Scheme 6, it can be seen that when 1j reacts with
N,N-dimethylaniline, R3 in the intermediate b is H. While 1j reacts with Et3N, R3 is Me. The latter
is more sterically hindered, which is not easy to react with bulky diketone 1j to form the normal
bis-1,3-dicarbonyl compound, but instead to form 5a by intramolecular Michael addition. Thus,
we also tried to propose the possible reaction mechanism for the formation of 5a and 5b (Scheme
7). By the same process as described in Scheme 6, intermediate a' can be obtained. Product 5a
could be formed through elimination/intramolecular Michael addition of a'. And product 5b could
be formed by oxidation of 5a under the standard conditions.
By the same process as described in Scheme 6
O
O
O
O
O
O
H
n
atio
min
eli
Et3N
+
N
HO
HO
Et
HO
Et
b'
1j
2b
a'
O
O
O
O
O
O
intramolecular
Michael addition
[O]
5a
5b
Scheme 7. Proposed reaction mechanism for the formation of 5.
3. Conclusion
In conclusion, cheap and readily available Rose Bengal was used as a photosensitizer to
oxidize tertiary amines for the synthesis of bis-1,3-dicarbonyl compounds under the irradiation of
visible light. This work avoids the use of metal catalyst and peroxides as terminal oxidant, and
instead air was used as a clean oxidant. The applicability of the substrate is good. Various
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methylene- and ethylidene- bridged bis-1,3-dicarbonyl compounds were obtained with yields of
up
to
80%.
Meanwhile,
the
3-benzoyl-2-methylchroman-4-one
and
3-benzoyl-2-methyl-4H-chromen-4-one were obtained under the standard conditions.
4. Experimental Section
4.1.General experimental details
Rose bengal was purchased from aladdin industrial corporation Shanghai, China.
R104993-1g, 95%. Unless otherwise noted, all reagents were purchased from commercial
suppliers and used without further purification. Reactions were monitored by thin-layer
chromatography (TLC) with Haiyang GF 254 silica gel plates (Qingdao Haiyang chemical
industry Co Ltd, Qingdao, China) using UV light and vanillic aldehyde as visualizing agents.
Flash column chromatography was performed using 200-300 mesh silica gel at increased pressure.
1H NMR spectra and 13C NMR spectra were respectively recorded on 600 MHz and 150 MHz
NMR spectrometers. Chemical shifts (δ) were expressed in ppm with TMS as the internal standard,
and coupling constants (J) were reported in Hz. High-resolution mass spectra were obtained by
using ESI ionization sources (Varian 7.0 T FTICR-MS). Melting points were taken on a WPX-4
apparatus and were uncorrected (Yice instrument equipment Co Ltd, Shanghai).
4.2. General procedure for the synthesis of products
A mixture of 1 (0.3 mmol), 2a (0.3 mmol) or 2b-d (1.5 mmol) and Rose Bengal (1.0 mol%) in
MeCN (1.0 mL) was stirred under irradiation of a 32 W compact fluorescent light bulb (The
parallel distance between the bulb and the reaction flask was about 2 cm) for the specified reaction
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time, and monitored by thin layer chromatography (TLC). The MeCN was removed under reduced
pressure. The crude products were purified by column chromatography on silica gel (petroleum
ether/EtOAc: 20/1~4/1) to give the desired products.
4.2.1. Compound 3a11a
o
Yellow solid; 76% yield (45 mg); m.p. 80.4-81.0 C; Rf = 0.30 (PE/EtOAc, 6:1); The ratio of
1
two diastereomers is 1.4:1. Two diastereomers: H NMR (600 MHz, CDCl3): δ = 8.05-8.03 (m,
4H), 7.61-7.56 (m, 2H), 7.51-7.45 (m, 4H), 4.62 (t, J = 7.3 Hz, 1.17H), 4.55 (t, J = 7.3 Hz, 0.85H),
4.25-4.18 (m, 2.40H), 4.12-4.08 (m, 1.76H), 2.76-56 (m, 2H), 1.21 (t, J = 7.1 Hz, 3.46 H), 1.11 (t,
J = 7.1 Hz, 2.57 H); 13C NMR (150 MHz, CDCl3): δ = 196.1, 194.8, 169.60, 169.3, 136.1, 135.6,
133.7, 128.9, 128.81, 61.6, 61.5, 51.6, 51.4, 28.2, 27.7, 14.0, 13.8.
4.2.2. Compound 3b12a
o
Yellow solid; 65% yield (42 mg); m.p. 61.6-62.1 C; Rf = 0.30 (PE/EtOAc, 5:1); The ratio of
1
two diastereomers is 1.6:1. Two diastereomers: H NMR (600 MHz, CDCl3): δ = 8.14-8.04 (m,
4H), 7.27-7.14 (m, 4H), 4.59 (t, J = 7.2 Hz, 1.21 H), 4.50 (t, J = 7.2 Hz, 0.78 H), 4.26-4.19 (m,
2.52 H), 4.12-4.10 (m, 1.59 H), 2.73-2.53 (m, 2H), 1.22 (t, J = 7.1 Hz, 3.65 H), 1.13 (t, J = 7.1 Hz,
2.39 H); 13C NMR (150 MHz, CDCl3): δ193.5, 193.2, 169.5, 169.1,167.0, 165.3, 132.4, 131.9,
131.7, 131.6, 131.6, 131.5, 116.0, 61.7, 61.7, 51.5, 51.3, 28.1, 27.5, 14.0, 13.9.
4.2.3. Compound 3c26
Yellow oil; 72% yield (60 mg); Rf = 0.30 (PE/EtOAc, 15:1); The ratio of two diastereomers is
1.4:1. Two diastereomers: 1H NMR (600 MHz, CDCl3): δ = 7.92-7.9(m, 4H), 7.65-7.61 (m, 4H),
4.56 (t, J = 7.2 Hz, 1.20 H), 4.48 (t, J = 7.2 Hz, 0.83 H), 4.25-4.18 (m, 2.50 H), 4.12-4.09 (m, 1.71
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H), 2.73-2.51 (m, 4H), 1.22 (t, J = 7.1 Hz, 3.75 H), 1.13 (t, J = 7.1 Hz, 2.66 H); 13C NMR (150
MHz, CDCl3): δ = 194.1, 193.7, 169.3, 169.0, 134.7, 134.3, 132.1, 130.3, 130.2, 129.2, 129.1,
61.8, 51.4, 51.3, 28.0, 27.4, 14.0, 13.9.
4.2.4. Compound 3d11a
Yellow oil; 63% yield (46 mg); Rf = 0.30 (PE/EtOAc, 4:1);The ratio of two diastereomers is
1:1. Two diastereomers: 1H NMR (600 MHz, CDCl3): δ = 8.37-8.34 (m, 4H), 8.24-8.21 (m, 4H),
4.68 (t, J = 7.0 Hz, 1H), 4.58 (t, J = 7.0 Hz, 1H), 4.27-4.20 (m, 2H), 4.16-4.10 (m, 2H), 2.78-2.56
(m, 2H), 1.22 (t, J = 7.1 Hz, 3H), 1.13 (t, J = 7.1 Hz, 3H); 13C NMR (150 MHz, CDCl3): δ = 193.7,
193.4, 168.9, 168.5, 150.7, 150.7, 140.4, 140.0, 129.9, 129.8, 124.0,123.9, 62.17, 51.70, 27.47,
26.9, 13.9, 13.8.
4.2.5. Compound 3e
Yellow oil; 63% yield (46 mg); Rf = 0.30 (PE/EtOAc, 6:1); The ratio of two diastereomers is
1
1:1. Two diastereomers: H NMR (600 MHz, CDCl3): δ = 8.87 (d, J = 5.6 Hz, 2H), 8.47 (t, J =
8.4 Hz, 2H), 8.40 (t, J = 7.5 Hz, 2H), 7.76-7.72 (m, 2H), 4.69 (t, J = 7.0 Hz, 1H), 4.59 (t, J = 7.0
Hz, 1H), 4.28-4.21 (m, 2H), 4.18-4.11 (m, 2H), 2.81-2.61 (m, 2H), 1.22 (t, J = 7.1 Hz, 3H), 1.15 (t,
J = 7.1 Hz, 3H); 13C NMR (150 MHz, CDCl3): δ = 193.0, 192.7, 168.8, 168.5, 148.7, 137.3, 137.0,
134.3, 130.1, 130.1, 127.9, 123.7, 123.6, 62.2, 62.1, 51.5, 51.4, 27.4, 27.0, 13.9,13.8. HRMS (ESI)
calc. for C31H24O6 (M-H)-: 485.1190, found: 485.1198.
4.2.6. Compound 3f
Yellow oil; 77% yield (60 mg); Rf = 0.30 (PE/EtOAc, 10:1); The ratio of two diastereomers is
1
1.3:1. Two diastereomers: H NMR (600 MHz, CDCl3): δ = 7.95-7.94 (m, 4H), 7.57-7.52 (m,
2H), 7.43-7.38 (m, 4H), 7.28-7.22 (m, 10H), 5.19-5.06 (m, 4H), 4.65 (t, J = 7.3 Hz, 1.10 H), 4.56
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ACCEPTED MANUSCRIPT
(t, J = 7.3 Hz, 0.87 H), 2.82-2.59 (m, 2H); 13C NMR (150 MHz, CDCl3): δ = 194.7, 194.5, 169.4,
169.1, 135.9, 135.5, 135.3, 135.2, 133.7, 128.9, 128.8, 128.7, 128.6, 128.5, 128.4, 128.3, 128.2,
128.1, 67.4, 67.3, 51.63 (s), 51.6, 51.4, 28.2, 27.6, 27.0. HRMS (ESI) calc. for C33H28O6 (M+Na)+:
543.1778, found: 543.1783.
4.2.7. Compound 3g
Yellow oil; 56% yield (42 mg); Rf = 0.25 (PE/EtOAc, 20:1); The ratio of two diastereomers is
1
1.4:1. Two diastereomers: H NMR (600 MHz, CDCl3): δ = 8.05-8.01 (m, 4H), 7.59-7.55 (m,
2H), 7.50-7.44 (m, 4H), 4.86 (br, 1.11 H), 4.75 (br, 0.82 H), 4.59-4.50 (m, 2H), 2.78-2.57 (m, 2H),
1.48-1.21 (m, 20H); 13C NMR (150 MHz, CDCl3): δ = 195.1, 194.9, 169.0, 168.8, 136.2, 135.8,
133.6, 128.8, 128.7, 128.6, 51.9, 51.7, 31.3, 31.1, 31.0, 27.9, 27.5, 25.2, 25.1, 23.4, 23.3, 23.2.
HRMS (ESI) calc. for C31H36O6 (M+Na)+: 527.2404, found: 527.2411.
4.2.8. Compound 3h11a
Yellow oil; 62% yield (31 mg); Rf = 0.30 (PE/EtOAc, 6:1); The ratio of two diastereomers is
1:1. Two diastereomers: 1H NMR (600 MHz, CDCl3): δ = 8.06-8.02 (m, 4H), 7.64-7.59 (m, 2H),
7.53-7.44 (m, 4H), 4.71 (t, J = 6.9 Hz, 1.08 H), 4.64 (t, J = 6.9 Hz, 0.91 H), 2.60-2.15 (m, 2H),
2.19 (s, 3H), 2.15 (s, 3H); 13C NMR (150 MHz, CDCl3): δ = 203.8, 203.3, 196.6, 196.4, 136.0,
135.8, 134.0, 129.0, 128.9, 128.9, 128.8, 59.4, 59.3, 29.3, 29.0, 27.4, 27.1.
4.2.9. Compound 3i11a
Yellow oil; 45% yield (31 mg); Rf = 0.25 (PE/EtOAc, 15:1);1H NMR (600 MHz, CDCl3): δ =
8.13 (d, J = 7.7 Hz, 8H), 7.58 (t, J = 7.2 Hz, 4H), 7.48 (t, J = 7.4 Hz, 8H), 5.74 (t, J = 6.8 Hz, 2H),
2.78-2.75 (m, 2H); 13C NMR (150 MHz, CDCl3): δ = 196.6, 135.6, 133.9, 129.0, 128.8, 54.1,
29.0.
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4.2.10. Compound 3j
1
Yellow oil; 52% yield (41 mg); Rf = 0.30 (PE/EtOAc, 6:1); H NMR (600 MHz, CDCl3): δ =
11.91 (s, 1H), 11.87 (s, 1H), 8.19 (d, J = 7.9 Hz, 1H), 8.14 (d, J = 7.6 Hz, 2H), 8.06 (d, J = 7.6 Hz,
2H), 7.98 (d, J = 7.9 Hz, 1H), 7.62-7.57 (m, 2H), 7.52-7.46 (m, 7H), 7.02-6.99 (m, 3H), 6.94-6.91
(m, 1H), 5.72-5.70 (m, 2H), 2.80-2.79 (m, 2H); 13C NMR (150 MHz, CDCl3): δ = 202.4, 202.3,
195.7, 195.7, 163.5, 163.4, 137.4, 130.4, 130.1, 129.2, 129.2, 128.8, 128.6, 119.9, 119.0, 118.9,
118.4, 118.2, 53.8, 29.2, 29.0. HRMS (ESI) calc. for C31H24O6 (M+Na)+: 515.1465, found:
515.1472.
4.2.11. Compound 3k11a
Yellow oil; 60% yield (44 mg); Rf = 0.25 (PE/EtOAc, 5:1); 1H NMR (600 MHz, DMSO-d6): δ
= 10.41 (s, 1H), 10.36 (s, 1H), 8.14 (m, 4H), 7.68-7.50 (m, 10H), 7.35-7.27 (m, 4H), 7.10-7.04 (m,
2H), 4.74-4.72 (m, 2H), 2.49-2.37 (m, 2H); 13C NMR (150 MHz, DMSO-d6): δ = 196.4, 195.6,
167.4, 139.4, 139.1, 136.5, 135.9, 134.1, 129.7, 129.3, 129.2, 129.2, 129.2, 128.9, 124.2, 124.1,
120.1, 120.0, 53.9, 53.7, 29.1, 29.0.
4.2.12. Compound 3l12a
Yellow oil; 52% yield (32 mg); Rf = 0.30 (PE/EtOAc, 6:1);The ratio of two diastereomers is
1.1:1. Two diastereomers: 1H NMR (600 MHz, CDCl3): δ = 7.92 (dd, J = 16.0, 3.2 Hz, 2H), 7.71
(dd, J = 21.2, 4.9 Hz, 2H), 7.18-7.12 (m, 2H), 4.43 (t, J = 7.3 Hz, 1.06 H), 4.38 (t, J = 7.3 Hz, 0.94
H), 4.23-4.21 (m, 2.28 H), 4.15-4.13 (m, 1.84 H), 2.74-2.60 (m, 2H), 1.24 (t, J = 7.1 Hz, 3.44 H),
1.16 (t, J = 7.1 Hz, 2.66 H); 13C NMR (150 MHz, CDCl3): δ = 187.5, 187.3, 169.1, 168.8, 143.1,
142.8, 135.2, 135.1, 133.9, 133.7, 128.4, 61.8, 61.7, 52.6, 28.6, 28.0, 14.0, 13.9. HRMS (ESI) calc.
for C19H20O6S2 (M+Na)+: 431.0594, found: 431.0598.
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4.2.13. Compound 3m
Yellow oil; 39% yield (23 mg); Rf = 0.30 (PE/EtOAc, 4:1); The ratio of two diastereomers is
1:1. Two diastereomers: 1H NMR (600 MHz, CDCl3): δ = 8.59 (d, J = 4.4 Hz, 1H), 8.51 (d, J =
4.4 Hz, 1H), 8.06 (d, J = 7.8 Hz, 2H), 7.84-7.81 (m, 2H), 7.45-7.40 (m, 2H), 4.92 (t, J = 7.3 Hz,
1H), 4.85 (t, J = 7.3 Hz, 1H), 4.14-4.08 (m, 4H), 2.76-2.67 (m, 2H), 1.14 (t, J = 7.1 Hz, 3H), 1.10
(t, J = 7.1 Hz, 3H); 13C NMR (150 MHz, CDCl3): δ = 196.2, 195.9, 170.2, 170.1, 152.3, 148.8,
136.9, 127.2, 122.4, 61.1, 50.7, 50.5, 26.9, 26.5, 13.9, 13.8. HRMS (ESI) calc. for C21H22N2O6
(M+Na)+: 421.1370, found: 421.1378.
4.2.14. Compound 4a27
Yellow oil; 40% yield (25 mg); Rf = 0.25 (PE/EtOAc, 10:1); 1H NMR (600 MHz, CDCl3) δ =
8.08-7.98 (m, 4H), 7.62-7.56 (m, 2H), 7.52-7.44 (m, 4H), 4.88-4.71 (m, 2H), 4.21-4.05 (m, 2H),
4.09-4.03 (m, 2H), 3.40-3.29 (m, 1H), 1.26-1.18 (m, 5H), 1.09-1.06 (m, 4H); 13C NMR (150 MHz,
CDCl3): δ = 195.1, 194.9, 169.2, 168.7, 137.1, 136.2, 133.7, 128.8, 128.7, 128.7, 61.6, 61.4, 61.3,
61.2, 56.5, 56.0, 55.7, 33.7, 32.9, 14.0, 13.9, 13.8, 13.7, 13.4.
4.2.15. Compound 4b
1
Yellow oil; 60% yield (40 mg); Rf = 0.3 (PE/EtOAc, 10:1); H NMR (600 MHz, CDCl3) δ =
8.13-8.02 (m, 4H), 7.20-7.12 (m, 4H), 4.84-4.66 (m, 1H), 4.67-4.66 (m, 1H), 4.21-4.18 (m, 2H),
4.09-4.07 (m, 4H), 3.37-3.24 (m, 1H), 1.24-1.05 (m, 9H); 13C NMR (150 MHz, CDCl3): δ = 193.5,
193.3, 169.1, 168.9, 168.5, 167.0, 165.3, 133.4, 132.5, 132.2, 131.6, 131.5, 131.4, 131.2, 131.1,
116.1, 116.0, 115.9, 115.8, 61.7, 61.6, 61.4, 56.4, 55.8, 55.5, 54.9, 33.6, 32.8, 14.0, 13.9, 13.8,
13.7, 13.4. HRMS (ESI) calc. for C24H24F2O6 (M+Na)+: 469.1433, found: 469.1431.
4.2.16. Compound 4c
19

ACCEPTED MANUSCRIPT
1
Yellow oil; 80% yield (68 mg); Rf = 0.3 (PE/EtOAc, 10:1); H NMR (600 MHz, CDCl3) δ =
7.94-7.83 (m, 4H), 7.66-7.59 (m, 4H), 4.79-4.74 (m, 1H), 4.63-4.62 (d, 1H), 4.22-4.16 (m, 2H),
4.11-4.05 (m, 2H), 3.36-3.22 (m, 1H), 1.23-1.15 (m, 5H), 1.12-1.04 (m, 4H); 13C NMR (150 MHz,
CDCl3): δ = 194.1, 194.0, 193.8, 168.9, 168.8, 168.4, 135.7, 134.8, 134.6, 132.2, 132.2, 132.1,
130.2, 130.2, 130.2, 129.9, 129.2, 129.1, 61.7, 61.6, 61.5, 61.4, 56.4, 55.8, 55.5, 54.9, 33.5, 32.6,
14.0, 14.0, 13.9, 13.8, 13.5. HRMS (ESI) calc. for C24H24Br2O6 (M+Na)+: 588.9832, found:
588.9831.
4.2.17. Compound 4d
1
Yellow oil; 40% yield (30 mg); Rf = 0.3 (PE/EtOAc, 5:1); H NMR (600 MHz, CDCl3) δ =
8.35-8.15 (m, 8H), 4.90-4.69 (m, 2H), 4.20-4.04 (m, 4H), 3.34-3.30 (m, 1H), 1.26-1.02 (m, 9H);
13C NMR (150 MHz, CDCl3): δ = 193.9, 193.5, 193.2, 168.5, 168.3, 167.9, 150.7, 150.7, 150.6,
141.5, 141.2, 140.6, 140.4, 138.3, 130.3, 129.7, 129.4, 128.0, 124.0, 123.8, 62.1, 62.0, 61.9, 61.7,
60.0, 56.5, 55.7, 33.2, 33.2, 14.3, 14.0, 13.9, 13.7. HRMS (ESI) calc. for C24H24N2O10 (M+Na)+:
523.1323, found: 523.1320.
4.2.18. Compound 4e
1
Yellow oil; 33% yield (25 mg); Rf = 0.3 (PE/EtOAc, 5:1); H NMR (600 MHz, CDCl3) δ =
8.89-8.81 (m, 2H), 8.48-8.32 (m, 4H), 7.77-7.72 (m, 2H), 4.91-4.86 (m, 1H), 4.70-4.69 (m, 1H),
4.23-4.22 (m, 2H), 4.21-4.12 (m, 2H), 3.42-3.32 (m, 1H), 1.26-1.20 (m, 5H), 1.16-1.12 (m, 4H);
13C NMR (150 MHz, CDCl3): δ = 193.2, 193.1, 192.8, 192.5, 168.5, 168.4, 168.3, 168.0, 148.7,
138.1, 137.4, 134.1, 130.2, 130.1, 127.9, 127.9, 127.8, 123.5, 123.4, 123.2, 62.2, 62.0, 62.0, 56.7,
56.3, 55.6, 33.2, 32.2, 14.3, 14.0, 13.9, 13.9, 13.8, 13.7. HRMS (ESI) calc. for C24H24N2O10
(M+Na)+: 523.1323, found: 523.1322.
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4.2.19. Compound 4f
1
Yellow oil; 55% yield (35 mg); Rf = 0.3 (PE/EtOAc, 6:1); H NMR (600 MHz, CDCl3) δ =
7.97-7.67 (m, 4H), 7.21-7.10 (m, 2H), 4.68-4.59 (m, 2H), 4.23-4.17 (m, 2H), 4.13-4.09 (m, 2H),
3.31-3.27 (m, 1H), 1.26-1.20 (m, 5H), 1.19-1.12 (m, 4H); 13C NMR (150 MHz, CDCl3): δ = 187.6,
187.4, 187.3, 168.9, 168.6, 168.3, 144.4, 143.3, 143.2, 135.3, 135.2, 134.9, 133.8, 133.6, 128.5,
128.3, 61.7, 61.4, 61.3, 57.4, 57.2, 56.7, 34.3, 33.8, 14.1, 14.0, 13.9, 13.7, 13.2. HRMS (ESI) calc.
for C20H22O6S2 (M+K)+: 461.0489, found: 461.0483.
4.2.20. Compound 4g
1
Yellow oil; 55% yield (34 mg); Rf = 0.3 (PE/EtOAc, 3:1); H NMR (600 MHz, CDCl3) δ =
8.62-8.36 (m, 2H), 8.10-8.04 (m, 2H), 7.84-7.80 (m, 2H), 7.46-7.37 (m, 2H), 5.25-5.20 (m, 1H),
5.05 (d, J = 6.06 Hz, 0.49H), 4.90 (d, J = 6.72 Hz, 0.52H), 4.19-4.00 (m, 4H), 3.52-3.37 (m, 1H),
1.21-1.18 (m, 3H), 1.13-1.02 (m, 6H); 13C NMR (150 MHz, CDCl3): δ = 196.7, 196.1, 195.5,
195.3, 169.9, 169.7, 169.3, 169.2, 152.7, 148.8, 148.7, 148.6, 136.8, 136.8, 127.2, 127.1, 127.1,
127.0, 122.2, 122.1, 122.0, 61.0, 60.9, 60.9, 56.0, 55.4, 54.4, 54.3, 33.3, 32.0, 30.2, 15.1, 14.8,
14.5, 14.0, 13.9, 13.8, 13.7. HRMS (ESI) calc. for C22H24N2O6 (M+Na)+: 435.1527, found:
435.1524.
4.2.21. Compound 5a
Yellow solid; 35% yield (14 mg); m.p. 105.6.1-106.0 oC; Rf = 0.3 (PE/EtOAc, 15:1); 1H NMR
(600 MHz, CDCl3) δ = 7.98-7.97 (m, 2H), 7.88-7.87 (m, 1H), 7.63-7.60 (m, 1H), 7.53-7.49 (m,
3H), 7.04-7.01 (m, 2H), 5.10-5.07 (m , 1H), 4.64 (d, J = 11.5 Hz, 1H), 1.49 (d, J = 6.2 Hz, 3H);
13C NMR (150 MHz, CDCl3): δ = 196.5, 190.0, 161.3, 137.8, 136.4, 133.7, 128.8, 128.7, 127.3,
121.5, 120.6, 117.9, 76.3, 60.0, 19.9. HRMS (ESI) calc. for C17H14O3 (M+Na)+:289.0835, found:
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ACCEPTED MANUSCRIPT
289.0832.
4.2.22. Compound 5b28
Yellow solid; 31% yield (12 mg); m.p. 76.4-76.9 oC; Rf = 0.3 (PE/EtOAc, 5:1); 1H NMR (600
MHz, CDCl3) δ = 8.18 (d, J = 7.9 Hz, 1H), 7.92 (d, J = 8.2 Hz, 2H), 7.72-7.69 (m, 1H), 7.60-7.57
(m, 1H), 7.49-7.41 (m, 4H), 2.38 (s, 3H); 13C NMR (150 MHz, CDCl3): δ = 193.8, 175.8, 165.4,
156.0, 137.1, 134.0, 133.8, 129.4, 128.7, 126.1, 125.5, 123.5, 123.2, 117.9, 19.1.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (No.
21672174 and No. 21472152), the Basic and Frontier Research Project of Chongqing
(cstc2015jcyjBX0106), and the Program of Science and Technology Innovation for
Undergraduates of Southwest University (No. 20162003008).
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