Visible-light-induced deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acids for the synthesis of 2-sulfonylquinoline via radical reactions

Article abstract of DOI:10.1016/S1872-2067(19)63420-0

A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acid induced by visible light is presented. This protocol shows a broad substrate scope, and desired products wi

Full text of DOI:10.1016/S1872-2067(19)63420-0

Chinese Journal of Catalysis 40 (2019) 1494–1498
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Communication
Visible-light-induced deoxygenative C2-sulfonylation of quinoline
N-oxides with sulfinic acids for the synthesis of 2-sulfonylquinoline
via radical reactions
Dao-Qing Dong a,†, Li-Xia Li a,†, Guang-Hui Li a,†, Qi Deng b, Zu-Li Wang a,*, Shu Long c
a College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, Shandong, China
b School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, Hunan, China
c Hunan Provincial Key Laboratory of Materials Protection for Electric Power and Transportation, Changsha University of Science and Technology,
Changsha 410114, Hunan, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenative
C2-sulfonylation of quinoline N-oxides with sulfinic acid induced by visible light is presented. This
protocol shows a broad substrate scope, and desired products with various substituents can be
formed in moderate to high yields at room temperature.
Received 28 June 2019
Accepted 25 July 2019
Published 5 October 2019
© 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Keywords:
Quinoline N-oxides
Sulfinic acid
2-Sulfonylquinoline
Visible light
Radical reaction
Compared with traditional, heat-promoted organic reac-
tions, visible-light-induced organic reactions are milder, envi-
ronmentally benign and operationally simpler. Moreover, visi-
ble light is a readily available source, so it has promising appli-
cations in science and industry [1–5]. In recent years, great
progress has been achieved in visible-light-induced reactions.
For example, various C–C and C-hetero bond-formation reac-
tions induced by visible light have been successfully achieved
[6–21] Among these, visible-light-induced sulfonylation reac-
tions with sulfinic acids have become a hot topic. In 2015, a
visible-light-induced reaction for the synthesis of sulfonated
oxindoles [22] and coumarin derivatives [23] using arylsulfinic
acids was developed by Wang’s group. Jiang’s group [24] de-
veloped a visible-light photocatalytic arylsulfonylation and
bicyclization reaction of C(sp3)-tethered 1,7-enynes with sul-
finic acid which afforded sulfone-containing ben-
zo[a]-fluorene-5-ones in generally good yields [24]. The reac-
tion of terminal alkynes and sulfinic acids mediated by visible
light for the synthesis of α-substituted vinyl sulfones with ex-
clusive Markovnikov regioselectivity was reported by Lei and
coworkers [25]. Mechanistic investigations showed that radi-
cal/radical cross-coupling might be the key step in this trans-
formation. In the absence of additional photocatalyst,
three-component reactions of isocyanides, alkynes, and sulfinic
† These authors contributed equally to this work.
* Corresponding author. E-mail: wangzulichem@163.com, wangzuli09@tsinghua.org.cn
This work was supported by the National Natural Science Foundation of China (21402103, 21772107), the China Postdoctoral Science Foundation
(150030), the Research Fund of Qingdao Agricultural University’s Highlevel Person (631303), and Shandong province key research and development
plan(GG201809130228). We also thank Cai-Zhen Ding, Yan-Li Wang and Hong-Di Yang for their useful help.
DOI: S1872-2067(19)63420-0 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 40, No. 10, October 2019

Dao-Qing Dong et al. / Chinese Journal of Catalysis 40 (2019) 1494–1498
1495
acids
were
described
by
Wang’s
group
[26].
Initially, to optimize the reaction conditions, the reaction
between quinoline 1-oxide and benzenesulfinic acid was ex-
amined. As can be seen in Table 1, solvents play an important
role in the reaction. The desired product can be obtained with
an 83% yield when acetone is used as the solvent (Table 1,
entry 1). The use of DMSO and CH3CN as solvents led to lower
yields (Table 1, entries 3 and 4, respectively). To our disap-
pointment, no product was obtained when DMF, H2O,
1,2-dimethoxyethane (DME), or EtOAc were used as solvents
(Table 1, entries 2 and 5–7, respectively). Dichloroethane
(DCE) was found to be an excellent solvent for this reaction,
providing the highest yield (88%) of the desired products (Ta-
ble 1, entry 8). Several different catalysts for this reaction were
also investigated. Methylene blue was found to be effective in
this reaction, yielding moderate product isolation (62%, Table
1, entry 10). Other catalysts, such as Acid Red 94, Acridine Red,
Eosin Y, and Ru(bpy)3Cl2, were less effective for this reaction
(Table 1, entries 9 and 11–13, respectively). An examination of
the effects of the oxidant on the reaction was then performed.
tert-Butyl peroxybenzoate (TBPB), dibutylperoxide (DTBP),
and K2S2O8 were less effective than tert-butyl hydroperoxide
(TBHP) (Table 1, entries 14–16, respectively). Next, different
visible-light sources such as green, UV, white, and blue were
tested. Blue light showed the best result (Table 1, entries 8 and
17–19, respectively). When the reaction was conducted in the
absence of light, catalyst, or oxidant, it was completely inhibited
(Table 1, entries 20–22, respectively). Increasing the loading of
the catalyst to 5 mol% also did not improve the efficiency of the
reaction (Table 1, entry 23).
C6-polyfunctionalized phenanthridines with high selectivity
were formed. It is interesting that the novel electron do-
nor-acceptor (EDA) complex generated from the reaction of
arylsulfinic acid and biaryl isocyanide drives the reaction. Alt-
hough various sulfonylated compounds have been synthesized
via visible-light-induced sulfonylation reactions using sulfinic
acids, it is highly desirable to expand the substrate scope of the
sulfonylation reaction.
2-Sulfonylquinoline derivatives are important nitro-
gen-containing heterocyclic compounds in agricultural and
pharmaceutical chemistry [27–41]. Therefore, significant ef-
forts have been focused on the development of efficient and
economically feasible protocols for their preparation [42–49].
At present, sodium benzenesulfinate [50–53], sulfonyl chlo-
rides [54–56], and sulfonyl hydrazides [57,58], have been
shown to be efficient sulfonylation reagents for the preparation
of deoxygenative 2-sulfonylquinolines. However, to the best of
our knowledge, there is no example of visible-light-induced
C2-sulfonylation of quinoline N-oxides with sulfinic acids. Con-
sistent with our interest in green chemistry [59–66], we de-
scribe visible-light-induced reactions for the synthesis of
2-sulfonylquinolines using sulfinic acids via a radical mecha-
nism.
Table 1
Optimization of reaction conditions a.
To survey the versatility of the deoxygenative sulfonylation
Entry
1
2
3
4
Cat. (2 mol%)
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Acid Red 94
Methylene blue
Acridine Red
Eosin Y
Ru(bpy)3Cl2
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
Na2.eosinY
—
[O] (2 equiv.)
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBPB
DTBP
K2S2O8
TBHP
TBHP
TBHP
TBHP
TBHP
—
Solvent
acetone
DMF
DMSO
CH3CN
H2O
DME
EtOAc
DCE
Yield (%)
83
Table 2
Reaction scope a.
NR
65
45
5
6
7
8
NR
NR
NR
88
27
62
3a, 88%
3d, 77%
3g, 72%
3c, 80%
3b, 82%
3e, 80%
3f, 72%
3i, 85%
9
DCE
DCE
10
11
12
13
14
15
16
17b
18c
19d
20e
21
22
23 f
DCE
DCE
DCE
DCE
DCE
DCE
35
24
22
27
NR
11
3h, 76%
3k, 75%
3l, 79%
3o, 81%
3r, 77%
3j, 93%
DCE
DCE
DCE
DCE
DCE
DCE
52
15
27
NR
NR
NR
89
3n, 82%
3q, 80%
3m, 75%
Na2.eosinY
Na2.eosinY
TBHP
DCE
a Reaction conditions: quinoline 1-oxide (1a) (0.2 mmol), benzenesul-
finic acid (2a) (0.4 mmol), 8 W blue LED, catalyst (2 mol%), solvent (1
mL), rt, 24 h, isolated yields. b 8 W green LED. c 8 W UV. d 8 W white LED.
e No light.f Catalyst loading 5 mol%.
3p, 96%
a Reaction conditions: quinoline 1-oxide (0.2 mmol), sulfinic acid (0.4
mmol), tert-butyl hydroperoxide (TBHP, 0.4 mmol), 8 W blue LED, Na2‧
eosinY (2 mol%), dichloroethane (DCE, 1 mL), rt, 24 h, isolated yields.

1496
Dao-Qing Dong et al. / Chinese Journal of Catalysis 40 (2019) 1494–1498
reaction, a variety of quinoline N-oxides and arylsulfinic acids
were tested, with the results summarized in Table 2. Quinoline
N-oxides with electron-neutral, electron-poor, and elec-
tron-rich groups all reacted efficiently with benzenesulfic acid
to generate the corresponding products in moderate to high
yields (Table 2, 3a–3h). For substituted sulfinic acids, various
groups such as F, Cl, Br, CH3, and tBu were all suitable for this
reaction (Table 2, 3i–3p). Steric hindrance did not have any
obvious impact on this reaction, as compounds 3f, 3m, and 3n
were obtained in 72%–82% yields. It is interesting to note that
naphthalene-2-sulfinic acid also reacted well with quinoline
N-oxides, affording the desired products in 77%–80% yields
(Table 2, 3q and 3r). Br and CH3OCO are active groups which
render the corresponding products ready for further function-
alization.
To investigate the mechanism of this transformation, radi-
cal-trapping reagents, 2,2,6,6-tetramethyl-1-piperidinyloxy
(TEMPO) and 2,6-di-tert-butyl-4-methylphenol (BHT), were
introduced to the reaction, with no desired product being
formed (Scheme 1). This suggests that free-radical intermedi-
ates may be involved in the presented transformation. Visible
light, photocatalyst, and oxidant also play important roles in the
sulfonylation reaction, because the reaction will not proceed if
any of these are absent (Table 1, entries 20–22, respectively).
Based on our initial mechanistic studies and previous work
Scheme 2. Proposed reaction mechanism.
underway in our lab.
References
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a
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1497
Graphical Abstract
Chin. J. Catal., 2019, 40: 1494–1498 doi: S1872-2067(19)63420-0
Visible-light-induced deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acids for the synthesis of
2-sulfonylquinoline via radical reactions
Dao-Qing Dong, Li-Xia Li, Guang-Hui Li, Qi Deng, Zu-Li Wang *, Shu Long
Qingdao Agricultural University; Hunan University of Science and Technology; Changsha University of Science and Technology
SO2H
Na2 EosinY, rt
+
TBHP, 8w Blue LED
N
O
N
S
O
O
A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenative C2-sulfonylation of quinoline N-oxides with
sulfinic acid induced by visible light is presented. This protocol shows a broad substrate scope, and desired products with various sub-
stituents can be formed in moderate to high yields at room temperature.
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可见光诱导喹啉-N-氧化物与亚磺酸的脱氧C2-磺酰化通过自由基反应
合成2-磺酰喹啉
董道青a,†, 李丽霞a,†, 李光辉a, 邓 企b, 王祖利a,*, 龙 姝c
a青岛农业大学化学与药学院, 山东青岛266109
b湖南科技大学化学化工学院, 湖南湘潭411201
c长沙理工大学化学与食品工程学院电力与交通材料保护湖南省重点实验室, 湖南长沙410114
摘要: 喹啉类衍生物在有机合成、药物化学以及材料化学等领域一直具有重要作用, 通过喹啉-N-氧化物合成喹啉类衍生物
目前已有许多报道, 其中采用金属催化剂实现反应占有很大比例, 但这些方法存在催化剂对空气敏感及环境不友好等问
题. 因此, 发展无金属催化反应受到越来越多的重视. 近年来, 光催化反应在有机合成中得到广泛应用. 基于我们在光催
化相关反应方面的研究, 本文报道了一种可见光诱导喹啉-N-氧化物与亚磺酸脱氧C2-磺酰化合成2-磺酰喹啉衍生物的合成
方法.
我们选用喹啉-N-氧化物与苯亚磺酸为底物进行条件筛选实验, 发现Na2‧eosinY (2 mol%)为催化剂, 二氯乙烷为溶剂,
TBHP (0.4 mmol)为氧化剂, 在蓝光照射下为最优化的实验条件, 目标产物2-磺酰喹啉最高产率为88%. 在该优化反应条件
下, 带有供电子或吸电子基团的喹啉-N-氧化物都能与苯亚磺酸反应得到中等至以上产率的目标物, 另外带有不同官能团
(F, Cl, Br, CH3和t-Bu等)的亚磺酸与喹啉-N-氧化物也都能得到中等以上产率. 当使用萘亚磺酸作为反应底物时也能以较
高产率得到相应目标产物. 对照实验显示, 在反应体系中加入自由基捕获剂TEMPO或BHT时反应不能发生, 表明自由基中
间体可能参与本反应的转化. 另外在黑暗条件、无氧化剂或者无催化剂下反应也不能发生, 证明这些反应条件是必须的.
基于上述实验结果, 提出了可能的反应机理. 首先光催化剂在可见光照射下形成激发态, 然后与TBHP反应生成叔丁氧基
自由基, 再作用于苯亚磺酸使其生成磺酰基并与喹啉氮氧化物反应, 其中通过两步的磺酰基反应, 最后通过芳构化得到目
标产物, 光催化剂可以通过TBHP氧化再生完成催化循环.
在此, 我们发展了一种简单高效的合成2-磺酰喹啉衍生物的反应方法, 该方法无需金属催化剂, 可在温和条件下通过
可见光诱导实现反应发生.
关键词: 喹啉-N-氧化物; 亚磺酸; 2-磺酰喹啉; 可见光; 自由基反应
收稿日期: 2019-06-28. 接受日期: 2019-07-25. 出版日期: 2019-10-05.
*通讯联系人. 电子信箱: wangzulichem@163.com
基金来源: 国家自然科学基金(21402103, 21772107); 中国博士后基金(150030); 青岛农业大学人才基金(631303); 山东省重点研
发计划(GG201809130228).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).