Visible-light-promoted aerobic oxidative synthesis of β-ketosulfones under photocatalyst-free conditions

Article abstract of DOI:10.1016/j.tetlet.2019.151335

A simple and convenient visible-light-mediated method has been developed for the construction of β-ketosulfones via aerobic oxidative difunctionalization of alkynes with arylazo sulfones and dioxygen in air under photocatalyst-free conditions. The present photochemical methodology provides a facile and attractive protocol to construct a series of β-ketosulfones in moderate to good yields.

Full text of DOI:10.1016/j.tetlet.2019.151335

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Visible-light-promoted aerobic oxidative synthesis of β-ketosulfones under
photocatalyst-free conditions
Yufen Lv, Qishun Liu, Fei Liu, Huilan Yue, Jiang-Sheng Li, Wei Wei
PII:
S0040-4039(19)31122-0
DOI:
https://doi.org/10.1016/j.tetlet.2019.151335
TETL 151335
Reference:
Tetrahedron Letters
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Revised Date:
Accepted Date:
23 September 2019
25 October 2019
28 October 2019
Please cite this article as: Lv, Y., Liu, Q., Liu, F., Yue, H., Li, J-S., Wei, W., Visible-light-promoted aerobic oxidative
synthesis of β-ketosulfones under photocatalyst-free conditions, Tetrahedron Letters (2019), doi: https://doi.org/
10.1016/j.tetlet.2019.151335
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Visible-light-promoted aerobic oxidative
synthesis of β-ketosulfones under
photocatalyst-free conditions
Yufen Lv, Qishun liu, Fei Liu, Huilan Yue,
Jiang-Sheng Li, Wei Wei
A simple and photocatalyst-free visible-light-induced strategy has been proposed for the construction of β-
ketosulfones via aerobic oxidative difunctionalization of alkynes with arylazo sulfones and dioxygen in air.

1
Tetrahedron Letters
Visible-light-promoted aerobic oxidative synthesis of β-ketosulfones under
photocatalyst-free conditions
Yufen Lv,a,† Qishun Liu,a,† Fei Liu,a Huilan Yue,b* Jiang-Sheng Li,c Wei Weia,b

a School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu 273165, Shandong, China
b Qinghai Provincial Key Laboratory of Tibetan Medicine Research and Key Laboratory of Tibetan Medicine Research, Northwest Institute of Plateau Biology,
Chinese Academy of Sciences, 810008, Qinghai China
c School of Chemistry and food Engineering, Changsha University of Science and Technology, Changsha, 410114, P. R. China
†These authors contributed equally to this work.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A simple and convenient visible-light-mediated method has been developed for the construction
of β-ketosulfones via aerobic oxidative difunctionalization of alkynes with arylazo sulfones and
dioxygen in air under photocatalyst-free conditions. The present photochemical methodology
provides a facile and attractive protocol to construct a series of β-ketosulfones in moderate to
good yields.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
visible-light
β-ketosulfones
alkynes
photocatalyst-free
Organic sulfones have exhibited widespread applications in the
organic synthesis, functionalized materials, and pharmaceutical
industries.[1,2] Especially, β-ketosulfones are a highly valuable
class of organic sulfones with versatile synthetic utility[3] and
unique biological activity,[4] which are frequently presented in
many pharmaceuticals and biologically active molecules. Given
the significance of β-ketosulfones, a number of synthetic
methods have been developed for the construction of β-
ketosulfones during the past several decades.[5-9] Among them,
the oxidative difunctionalization of alkynes with various
sulfonylating agents such as sulfinic acids, sulfinates, and
sulfonylhydrazides have attracted the increasingly synthetic
attention of chemists due to the diversity and commercial
availability of alkynes.[9] For example, in 2013, Lei and co-
NaOAc (Scheme 1d).[9d] Although some significant progress has
been made in this field, the development of more facile, efficient
and catalyst-free synthetic strategy is still highly desirable.
workers
reported
an
elegant
pyridine-mediated
difunctionalization of terminal alkynes with arylsulfinic acids
and dioxygen leading to β-ketosulfones (Scheme 1a).[9a] In 2014,
Lipshutz demonstrated that TPGS-750-M (2 wt.%) could
promote the oxysulfonylation of arylalkynes with arylsulfinate
salts in the presence of dioxygen to yield β-ketosulfones in acid
conditions (Scheme 1b).[9b] The same year, Yadav described an
efficient FeCl3/K2S2O8 (20 mol%) catalyzed aerobic oxidative
difunctionalization of alkynes with arylsulfinate salts in aqueous
media (Scheme 1c).[9c] In 2016, Cai group reported a visible
light-mediated Ru(bpy)3Cl2 catalyzed aerobic oxysulfonylation of
alkynes with sulfonylhydrazides for the preparation of β-
ketosulfones in the presence of 1 equiv. of KI and 4 equiv. of
Scheme 1. The methods for the synthesis of β-ketosulfones from alkynes.
 Corresponding author.
E-mail: weiweiqfnu@163.com (W. Wei); hlyue@nwipb.cas.cn (H. Yue),

2
Tetrahedron Letters
Arylazo sulfones are stable colored solid compounds that can
product 3aa could be isolated in 23% yield (Table 1, entry 1).
Encouraged by this result, we further examined a variety of
solvents (Table 1, entries 2-9). Among a number of solvents
tested, 1,4-dioxane was found to be the best reaction medium for
this oxysulfonylation reaction, and the desired product was
obtained in 51% yield (Table 1, entry 7). Only a trace amount of
product was obtained in DMF (Table 1, entry 8). When reaction
was conducted in H2O, the product 3aa was only isolated in 12%
yield (Table 1, entry 9). Further investigation found that the yield
of 3aa was not increased obviously by the addition of a series of
photocatalysts such as Na2-eosin Y, Eosin B, Rhodamine B and
Eosin Y (Table 1, entries 10-14). Pleasingly, the product 3aa
could be isolated in 73% yield when the reaction was conducted
at 50oC under the irradiation of 3 W blue LED lamps (Table 1,
entry 15). The low reaction efficiency was observed by replacing
of 3 W blue LEDs with 3 W green LEDs or 3 W white LEDs
(Table 1, entries 16 and 17). Only a trace amount of product was
detected when the model reaction was performed in the absence
of light irradiation (Table 1, entry 18).
be readily prepared from aryldiazonium salts.[10] It is known that
arylazo sulfones can undergo the photodissociation process to
afford aryl radical/aryl cation and sulfonyl radical/sulfonyl anion
under the irradiation of visible light.[10,11] In recent years, arylazo
sulfones have been widely utilized as arylation reagents to
construct various aromatic compounds in photochemical
reactions in the absence of any photocatalyst (Scheme 1e).[11]
Visible light as a clean and sustainable energy has been
increasingly used to promote various synthetic transformations in
the field of synthetic chemistry.[12] As part of our interest in
developing new visible-light-mediated reactions[13] and
sulfonylations,[14] herein, we report a simple and photocatalyst-
free strategy for the synthesis of β-ketosulfones via visible-light-
promoted oxysulfonylation of alkynes with arylazo sulfones in
the presence of dioxygen in air (Scheme 1e). This reaction
provides a convenient and highly attractive approach to access
various β-ketosulfones in moderate to good yields under metal-
and additive-free conditions.
Moreover, when 4-methoxyphenylazo mesylate was
replaced by other aryldiazosulfones such as 4-fluorophenylazo
mesylate, 4-chlorophenylazo mesylate or 4-methylphenylazo
mesylate, the present oxysulfonylation reaction would also
undergo smoothly under the standard conditions, but leading to
the corresponding β-ketosulfone 3aa in a relatively lower yield
(Scheme 2). This result indicated that electron rich 4-methoxy
group might more efficiently promote the homolytic cleavage of
C-N and N−S bonds of arylazo sulfones.
Table 1
Screening of the reaction conditionsa
Entry
Photocatalyst
Solvent
Yield(%)b
(2 mol%)
--
-
CH3CN
DCE
23
41
1
2
--
--
DMSO
EtOH
14
44
3
4
--
DME
46
5
--
THF
42
6
--
--
--
1,4-dioxane
DMF
H2O
51
trace
12
7
8
9
Scheme 2. The reaction of phenylacetylene (1a) with other aryldiazosulfones.
Na2-eosin Y (2)
Eosin B (2)
Rhodamine B (2) 1,4-dioxane
Eosin Y (2)
Rose Bengal (2)
--
--
--
--
1,4-dioxane
1,4-dioxane
51
46
50
51
10
11
12
13
14
15
16
17
18
With the optimal conditions in hand, we moved on to
examine the scope of various alkynes and arylazo sulfones
(Table 2). Firstly, various aromatic alkynes bearing different
substitutions were tested. In general, phenylacetylene with a
series of substituents at the ortho-, meta- or para-position,
regardless of the electron-donating (tBu and Me) or electron-
withdrawing (F, Cl, Br and CF3) groups, afforded the
corresponding β-ketosulfones 3ba–3ka in moderate to good
yields. It is noteworthy that heteroaromatic alkyne such as 3-
ethynylthiophene showed favorable compatibility providing
the corresponding product 3la in 43% yield. When internal
alkyne such as prop-1-ynylbenzene was used in the present
reaction system, only a trace amount of desired product 3ma
was detected. Unfortunately, when alkyl alkynes were
employed in the present reaction system, none of desired
product 3na was detected. Next, the scope of arylazo sulfones
was evaluated. Arylazo alkylsulfone such as 4-
methoxyphenylazo ethyl sulfone was also suitable substrates
to give the desired product 3ab in 63% yield. In addition, a
number of arylazo arylsulfones that possessed an electron-
donating or an electron-withdrawing group on the aryl rings
were all well tolerated in this chemistry and thus amenable to
this process to afford the corresponding products (3ac-3ah)
with moderate to good yields.
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
48
73c
12d
9e
tracef
a Reaction conditions: 1a (0.1 mmol), 2a (0.25 mmol), solvent (3 mL), room
temperature, 3 W blue LED lamps (460-485 nm), 12h, air.
b Isolated yields based on 1a.
c 3 W blue LED lamps, 50oC.
d 3 W green LED lamps, 50oC.
e 3 W white LED lamps, 50oC
Without visible-light irradiation, 50oC.
f
Initially, phenylacetylene (1a) and 4-methoxyphenylazo
mesylate (2a) were chosen as model substrates to optimize the
reaction conditions under the irradiation of 3 W blue LED lamps
in air. When the model reaction was conducted in CH3CN at
room temperature in the absence of photocatalyst, the desired

3
Table 2
Furthermore, only a trace amount of product 3aa was detected
when the reaction was carried out under N2, suggesting that
dioxygen in air is essential for this reaction (Scheme 3b).
Moreover, 18O labeling experiment using H218O showed that the
carbonyl oxygen atom of product 3aa came from dioxygen in air
(Scheme 3c). Further investigations on the reaction mechanism
of this protocol are currently under way in our laboratory.
Substrate scope.a,b
In conclusion, a simple and photocatalyst-free visible-light-
mediated strategy has been successfully developed for the
preparation of β-ketosulfones from alkynes, arylazo sulfones and
dioxygen in air. The present oxysulfonylation reaction of alkynes
offers a facile and attractive approach to synthesize various β-
ketosulfones without metal catalysts and additives.
Acknowledgements
This work was supported by the Natural Science Foundation of
Shandong Province (ZR2018MB009), Youth Innovation and
Technology Project of Shandong Province (2019KJC021), the
International Cooperation Project of Qinghai Province (2018-HZ-
806), the Special Project for the Transformation of Scientific and
Technological Achievements (2019-SF-122) and the Qinghai
Key Laboratory of Tibetan Medicine Research (2017-ZJ-Y11).
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5

Visible-light-promoted oxidative synthesis
of β-ketosulfones



Photocatalyst-free
Air as the green oxidant and oxygen source
A radical process

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Tetrahedron Letters
Declaration of interests
☒ The authors declare that they have no known
competing financial interests or personal
relationships that could have appeared to influence
the work reported in this paper.
☐The authors declare the following financial
interests/personal relationships which may be
considered as potential competing interests: