Synthesis of β-Keto Sulfones by a Catalyst-Free Reaction of Aryldiazonium Tetrafluoroborates, Sulfur Dioxide, and Silyl Enol Ethers

Article abstract of DOI:10.1002/asia.201601617

A green approach for the generation of β-keto sulfones through a reaction of aryldiazonium tetrafluoroborates and sulfur dioxide with silyl enol ether under catalyst- and additive-free conditions has been realized. This reaction proceeds efficiently at room temperature and goes to completion in half an hour. During the reaction process, aryldiazonium tetrafluoroborate is treated with DABCO?(SO₂)₂ (DABCO=1,4-diazabicyclo[2.2.2]octane) to provide a sulfonyl radical as the key intermediate, which then initiates the transformation. Oxidants or metal catalysts are avoided, and the presence of DABCO also plays an important role in the reaction.

Full text of DOI:10.1002/asia.201601617

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AN ASIAN JOURNAL
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Accepted Article
Title: Synthesis of β-Keto Sulfones via A Catalyst-Free Reaction of
Aryldiazonium Tetrafluoroborates, Sulfur Dioxide, and Silyl Enol
Ethers
Authors: Tianshuo Liu, Danqing Zheng, Yechun Ding, Xiaona Fan, and
Jie Wu
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Synthesis of β-Keto Sulfones via A Catalyst-Free Reaction of
Aryldiazonium Tetrafluoroborates, Sulfur Dioxide, and Silyl Enol
Ethers
Tianshuo Liu,[a,b] Danqing Zheng,[b] Yechun Ding,[a] Xiaona Fan,*[a] and Jie Wu*[b,c]
Dedication ((optional))
DABCO.(SO2)2 was crucial for the outcome, since the presence
Abstract: A green approach for the generation of β-keto sulfones
through a reaction of aryldiazonium tetrafluoroborates, sulfur dioxide,
with silyl enol ether under catalyst-free and additive-free conditions
is realized. This reaction proceeds efficiently at room temperature,
and goes to completion in half an hour. During the reaction process,
aryldiazonium tetrafluoroborate would react with DABCO.(SO2)2 to
provide sulfonyl radical as the key intermediate, which would initiate
the transformation. Oxidants or metal catalysts are avoided, and the
presence of DABCO plays an important role in the reaction as well.
of DABCO was also essential during the transformation. This
strategy is attractive, which provides an efficient route to sulfonyl
compounds through the fixation of sulfur dioxide under
extremely mild conditions. For example, the sulfonyl radical
intermediate was usually produced in the reaction process
through reductive or oxidative approaches starting from sulfonyl
halides, sulfonyl selenides, sulfonyl azides, sulfonyl cyanides,
sulfinates, sulfinic acids, and sulfonyl hydrazides.[5,6] The
alternative pathway for the generation of sulfonyl radical via the
combination
of
DABCO.(SO2)2
with
aryldiazonium
Introduction
tetrafluoroborate would provide a straight forward route to
sulfonyl compounds. The application of this method for the
synthesis of 3-sulfonyl coumarins has been demonstrated.[3a]
Among the family of sulfones, β-keto sulfones have attracted
much attention, due to their applications in organic synthesis as
useful synthons[7,8] and their remarkable biological activities.[9]
The synthetic applications of β-keto sulfones have been
widespreadly demonstrated.[7,8] Thus, generation of β-keto
sulfones is highly demanded. So far, several classic methods for
the synthesis of β-keto sulfones have been reported.[10,11] For
example, β-keto sulfones could be accessible via oxidation of β-
keto sulfides or through the reaction of sodium sulfonates with α-
halo ketones. Preparation of β-keto sulfones through radical
sulfonylation of enol acetates was reported as well.[12] For
instance, sulfonyl hydrazide was used as the source of sulfonly
radical in the iron-catalyzed reaction of aryl enol acetates,
leading to β-keto sulfones in good yields.[12a] As mentioned
above, the sulfonyl radical could be also generated from the
reaction of aryldiazonium salts with DABCO.(SO2)2. Encouraged
by this result, we postulated that the approach through insertion
of sulfur dioxide could be utilized in the formation of β-keto
sulfones as well. A possible synthetic route is shown in Scheme
1. We envisioned that silyl enol ether might be a good partner in
the reaction. We have demonstrated that the treatment of
aryldiazonium salt 1 with DABCO.(SO2)2 would result in a
complex A,[3a] which would produce aryl radical, nitrogen, sulfur
dioxide, and cation radical intermediate B. The addition of aryl
radical to sulfur dioxide would provide the key intermediate of
sulfonyl radical C. Subsequently, silyl enol ether 2 would be
involved, leading to the formation of radical D. This intermediate
D would undergo a single electron transfer with cation radical
intermediate B, delivering the corresponding cation E with the
release of DABCO. The presence of DABCO would facilitate the
following desilylation, which would result in the formation of β-
keto sulfone 3. It is noteworthy that the role of DABCO is
In the past few years, continuous interest has been paid to the
incorporation of sulfur dioxide into small molecules, since the
sulfur dioxide surrogate of DABCO.(SO2)2 (DABSO) was
introduced by Willis and co-workers.[1] The utilization of sulfur
dioxide in the form of toxic gas is therefore avoided, which
stimulates the rapid progress in this filed.[2,3] Diverse sulfonyl
compounds could be conveniently synthesized by using DABSO
or inorganic sulfite as the source of sulfur dioxide. Due to the
importance of sulfonyl compounds in pharmaceuticals,
agrochemicals, materials, and organic synthesis,[4] methods
involving the insertion of sulfur dioxide for the preparation of
sulfonyl compounds have been explored extensively.[2,3] So far,
the transformations proceeded under transition metal catalysis
or through radical process have been reported.
Recently, we focused on the radical process via insertion of
sulfur dioxide. We discovered that sulfonyl radical could be
easily produced via the reaction of sulfur dioxide with
aryldiazonium
tetrafluoroborate
under
catalyst-free
conditions.[3a,3b] It was found that the sulfur dioxide surrogate of
[a]
[b]
[c]
T. Liu, Y. Ding, Dr. X. Fan
Gannan Medical University Collaborative Innovation Center for
Gannan Oil-tea Camellia Industrial Development
1 Yixueyuan Road, Ganzhou, Jiangxi 341000, China
Email: fxn918@126.com
T. Liu, D. Zheng, Prof. Dr. J. Wu
Department of Chemistry
Fudan University
220 Handan Road, Shanghai 200433, China
E-mail: jie_wu@fudan.edu.cn
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, 345 Lingling Road, Shanghai 200032, China
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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1
2
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
1.1
1.5
2.0
MeCN
DCE
60
60
60
60
60
60
25
40
80
25
25
25
41
49
39
9
28
18
35
38
37
31
18
15
19
21
20
22
important if this proposed route is feasible: (1) release from
complex A to form cation radical B, which subsequently proceed
through a single electron transfer to provide cation E; (2)
facilitate the desilylation of cation E to produce the final product.
From this route, it seemed that the reaction might occur under
catalyst- and additive-free conditions and no oxidants were
needed. With these considerations in mind, we therefore started
to explore the synthesis of β-keto sulfones through insertion of
sulfur dioxide via radical process.
3
1,4-dioxane
toluene
DMF
4
5
17
21
62
64
42
70
78
76
6
DMSO
DCE
7
8
DCE
9
DCE
10
11
12
DCE
O
OSiMe3
O
O
+
+
DABCO (SO2)2
Ar N2
S
DCE
Ar
R
R
2
1
3
DCE
O
[a] Isolated yield based on silyl enolate 2a. [b] GC yield.
N
B
R'
Ar
S
R'
Ar
O
OSiMe3
SO2Ar
R'
C
N
R'
DABCO
R'
R'
B
R2
SO2
Under the above optimized conditions, we next explored the
scope of the reaction of aryldiazonium tetrafluoroborates 1,
DABCO.(SO2)2 and silyl enol ethers 2 (Table 2). At the outset,
various aryldiazonium tetrafluoroborates with different functional
groups attached on the aromatic ring were examined. It was
found that the yields were lower when aryldiazonium
tetrafluoroborates substituted with electron-withdrawing groups
were employed in the reaction. Reactions of ortho-substituted
aryldiazonium tetrafluoroborates proceeded smoothly as well.
D
N2
OSiMe3
SiMe3
SO2Ar
O
N
2
R2
N
R2
Ar
A
O
O
O
E
O
O
O
S
S
O
S
Ar
R
N
N
R'
R'
3
Ar N2
1
R'
R'
R'
R'
DABCO (SO2)2
Scheme 1. A proposed synthetic route to β-keto sulfones
Various silyl enolates
2
were then examined in the
transformation. In most cases, the reactions worked well to
provide the corresponding β-keto sulfones in good yields.
Moreover, both heterocyclic and alkyl-substituted silyl enolate
could be tolerated the reaction condition. For example, reaction
of thiophenyl-substituted silyl enolate could deliver the desired
product 3r in 45% yield. It is noteworthy that all conversions are
fast, and usually go to completion in 30 min at room temperature.
The efficiency of this transformation with the insertion of sulfur
dioxide would make this approach attractive with great potential
for further applications.
Results and Discussion
Initially, reaction of phenyldiazonium tetrafluoroborate 1a,
DABCO.(SO2)2, and silyl enolate 2a was selected as the model.
At the beginning, the reaction took place in MeCN at 60 oC.
Gratifyingly, the corresponding product 3a was afforded in 41%
yield (Table 1, entry 1). In the meantime, the hydrodediazonation
occurred to give benzene as the byproduct with 28% yield. The
result encouraged us to further screen different solvents. The
reaction worked efficiently in dichloroethane (DCE), which
provided the desired β-keto sulfone 3a in 49% yield with the
minimal amount of benzene produced (Table 1, entry 2). The
yield was improved significantly when the reaction was
performed at 25 oC or 40 oC (Table 1, entries 7 and 8).
Interestingly, better results could be obtained when the amount
of DABCO.(SO2)2 was increased (Table 1, entries 10-12). For
example, the expected β-keto sulfone 3a was delivered in 78%
yield in half an hour in the presence of 1.5 equivalent of
DABCO.(SO2)2 (Table 1, entry 11).
As mentioned in Scheme 1, we reasoned that the three-
component catalyst- and additive-free reaction of aryldiazonium
tetrafluoroborates 1, DABCO.(SO2)2, and silyl enol ethers 2
proceeded through
a radical process. Therefore, 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO) was added into the
reaction of phenyldiazonium tetrafluoroborate 1a, DABCO.(SO2)2,
and silyl enolate 2a (Scheme 2). As expected, the reaction was
hampered in the presence of 1.2 equivalent of TEMPO, which
confirmed the proposed radical process. Furthermore,
compound 4 was employed as the substrate in the reaction of
DABCO.(SO2)2 with silyl enolate 2a. The corresponding product
5 was afforded in 81% yield under the standard conditions. This
experimental observation indicated that the transformation
underwent through the radical intermediate F with the insertion
of sulfur dioxide.
Table 1. Initial studies for the reaction of phenyldiazonium tetrafluoroborate 1a,
DABSO, and silyl enol ether 2a
O
O
O
N2BF4
OSiMe3
S
Ph
+ DABCO (SO2)2
+
Ph
solvent
2a
3a
1a
Table 2. Scope investigation for the reaction of aryldiazonium
tetrafluoroborates 1, DABCO.(SO2)2, and silyl enol ethers 2. [a]
Entry DABSO
(equiv.)
Solvent
T (oC)
Yield (%)[a]
Yield of
benzene (%)[b]
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OSiMe3
O
DCE
initiate the transformation. Oxidants or metal catalysts are
avoided, and the presence of DABCO plays an important role in
the reaction as well. The experimental operation is easy, which
simply combines three components in one pot. The efficiency of
this transformation with the insertion of sulfur dioxide would
make this approach attractive with great potential for further
applications.
O
O
+
DABCO (SO2)2
+
Ar N2BF4
S
R
rt, 30 min
Ar
R
1
2
3
O
O
O
O
O
O
O
O
O
S
S
S
Ph
Ph
Ph
Cl
Cl
MeO
3c, 46% yield
3a, 78% yield
3b, 78% yield
O
O
O
O
O
O
O
O
O
S
S
S
Ph
O
Ph
Ph
Experimental Section
F
General procedure for the synthesis ofβ-keto sulfones 3 via the reaction
of phenyldiazonium tetrafluoroborate 1 with silyl enol ethers 2: Silyl
3d, 55% yield
3e, 75% yield
3f, 38% yield
O
O
O
O
O
O
O
O
enolate
2 (0.2 mmol) was added to a solution of aryldiazonium
MeO
S
S
S
Ph
Ph
Ph
tetrafluoroborate 1 (0.24 mmol), and DABCO•(SO2)2 (0.3 mmol) in DCE
(2.0 mL). The mixture was stirred at room temperature for 30 minutes.
After completion of reaction as indicated by TLC, the mixature was
purified directly by flash column chromatograph (EtOAc/n-hexane, 1:4) to
give the desired product 3.
3g, 58% yield
3h, 67% yield
3i, 66% yield
O
O
O
O
O
O
O
O
O
S
S
S
Ph
Ph
Ph
1-Phenyl-2-(phenylsulfonyl)ethan-1-one (3a).[13a] 1H NMR (400 MHz,
CDCl3): δ 7.90-7.95 (m, 4H), 7.60-7.69(m, 2H), 7.55 (t, J = 7.9 Hz, 2H),
7.48 (t, J = 7.8 Hz, 2H), 4.76 (s, 2H). 13C NMR (100 MHz, CDCl3): δ
187.9, 138.7, 135.7, 134.2, 129.2, 128.8, 128.5, 63.4.
F
Cl
Br
3j, 85% yield
3k, 78% yield
3l, 74% yield
O
O
O
O
O
O
O
O
O
S
S
S
Ph
Ph
Ph
CF3
Cl
2-((4-Methoxyphenyl)sulfonyl)-1-phenylethan-1-one (3b).[8a] 1H NMR
(400 MHz, CDCl3): δ 7.94 (d, J = 7.4 Hz, 2H), 7.81 (d, J = 8.9 Hz, 2H),
7.62 (t, J = 7.4 Hz, 1H), 7.48 (t, J = 7.8 Hz, 2H), 6.99 (d, J = 8.9 Hz, 2H),
4.73 (s, 2H), 3.87 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 188.3, 164.1,
135.7, 134.3, 130.8, 130.1, 129.3, 128.8, 114.3, 63.7, 55.7.
3m, 65% yield
3o, 73% yield
3n, 80% yield
O
O
O
O
O
O
S
O
S
O
O
Ph
Ph
S
Ph
3q, 28% yield
S
3r, 45% yield
2-((4-Chlorophenyl)sulfonyl)-1-phenylethan-1-one (3c).[10k] 1H NMR
(400 MHz, CDCl3): δ 7.95 (d, J = 7.4 Hz, 2H), 7.85 (d, J = 8.6 Hz, 2H),
7.65 (t, J = 7.4 Hz, 1H), 7.49-7.54 (m, 4H), 4.76 (s, 2H). 13C NMR (100
MHz, CDCl3): δ 188.0, 141.1, 137.0, 135.5, 134.5, 130.1, 129.5, 129.2,
128.9, 63.3.
3p, 64% yield
[a] Isolated yield based on silyl enolate 2.
O
O
TEMPO
(1.2 equiv.)
O
N2BF4
OSiMe3
S
+ DABCO (SO2)2
+
Ph
2-((4-Fluorophenyl)sulfonyl)-1-phenylethan-1-one (3d).[8a] 1H NMR
(400 MHz, CDCl3): δ 7.91-7.96 (m, 4H), 7.65 (t, J = 7.4 Hz, 1H), 7.50 (t, J
= 7.8 Hz, 2H), 7.23 (t, J = 8.6 Hz, 2H), 4.76 (s, 2H). 13C NMR (100 MHz,
Ph
DCE
2a
1a
3a, n.d.
O
1
4
DABCO (SO2)2
OSiMe3
CDCl3): δ 188.0, 166.1 (d, JCF = 256.0 Hz), 135.6, 134.8 (d, JCF = 3.0
N2BF4
O
O
S
3
2
Hz), 134.6, 131.7 (d, JCF = 9.8 Hz), 129.2, 128.9, 116.5 (d, JCF = 22.6
Hz), 63.4.
+
DCE
O
Ph
O
Ph
4
2a
5, 81% yield
1-Phenyl-2-tosylethan-1-one (3e).[13a] 1H NMR (400 MHz, CDCl3): δ
7.95 (d, J = 7.5 Hz, 2H), 7.77 (d, J = 8.2 Hz, 2H), 7.63 (t, J = 7.4 Hz, 1H),
7.49 (t, J = 7.8 Hz, 2H), 7.34 (d, J = 8.1 Hz, 2H), 4.73 (s, 2H), 2.45 (s,
3H). 13C NMR (100 MHz, CDCl3): δ 188.1, 145.3, 135.7, 134.3, 129.8,
129.3, 128.8, 128.6, 63.5, 21.7.
O
F
Scheme 2. Mechanism investigation
2-((3-Chlorophenyl)sulfonyl)-1-phenylethan-1-one (3f).[13a] 1H NMR
(400 MHz, CDCl3): δ 7.90-7.95 (m, 3H), 7.80 (d, J = 7.8 Hz, 1H), 7.65 (t,
J = 7.4 Hz, 2H), 7.51 (t, J = 7.8 Hz, 3H), 4.77 (s, 2H). 13C NMR (100 MHz,
CDCl3): δ 187.7, 140.3, 135.5, 135.4, 134.5, 134.3, 130.4, 129.2, 128.9,
128.6, 126.8, 63.2.
Conclusions
In summary, we have developed a green approach for the
efficient synthesis of β-keto sulfones through a reaction of
aryldiazonium tetrafluoroborates, sulfur dioxide, and silyl enol
ether under catalyst- and additive-free conditions. This
transformation proceeds efficiently at room temperature, and
goes to completion in half an hour. During the reaction process,
aryldiazonium tetrafluoroborate would react with DABCO.(SO2)2
to provide sulfonyl radical as the key intermediate, which would
2-((3-Methoxyphenyl)sulfonyl)-1-phenylethan-1-one (3g).[13b] 1H NMR
(400 MHz, CDCl3): δ 7.94 (d, J = 7.4 Hz, 2H), 7.63 (t, J = 7.4 Hz, 1H),
7.43-7.50 (m, 4H), 7.37 (s, 1H), 7.17 (d, J = 6.8 Hz, 1H), 4.75 (s, 2H),
3.83 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 187.8, 159.9, 139.8, 135.7,
134.3, 130.2, 129.2, 128.8, 120.9, 120.6, 112.8, 63.4, 55.7.
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1-Phenyl-2-(o-tolylsulfonyl)ethan-1-one (3h).[13b] 1H NMR (400 MHz,
CDCl3): δ 7.96 (d, J = 7.4 Hz, 2H), 7.89 (d, J = 7.8 Hz, 1H), 7.62 (t, J =
7.4 Hz, 1H), 7.46-7.55 (m, 3H), 7.31-7.36 (m, 2H), 4.77 (s, 2H), 2.74 (s,
3H). 13C NMR (100 MHz, CDCl3): δ 187.9, 138.3, 136.9, 135.8, 134.3,
134.2, 132.7, 130.5, 129.3, 128.8, 126.6, 62.9, 20.5.
(100 MHz, CDCl3): δ 181.4, 141.1, 138.5, 135.5, 134.3, 129.2, 128.5,
127.2, 127.0, 65.1.
2-(((2,3-Dihydrobenzofuran-3-yl)methyl)sulfonyl)-1-phenylethan-1-
one (5). 1H NMR (400 MHz, CDCl3): δ 8.01 (d, J = 7.8 Hz, 2H), 7.68 (t, J
= 7.4 Hz, 1H), 7.54 (t, J = 7.5 Hz, 2H), 7.28 (d, J = 7.2 Hz, 1H), 7.20 (t, J
= 7.7 Hz, 1H), 6.92 (t, J = 7.4 Hz, 1H), 6.84 (d, J = 8.0 Hz, 1H), 4.56-
2-(Phenylsulfonyl)-1-(p-tolyl)ethan-1-one (3i).[13c] 1H NMR (400 MHz,
CDCl3): δ 7.90 (d, J = 7.6 Hz, 2H), 7.84 (d, J = 8.2 Hz, 2H), 7.67 (t, J = 7.4
Hz, 1H), 7.56 (t, J = 7.8 Hz, 2H), 7.28 (d, J = 6.9 Hz), 4.73 (s, 2H), 2.43 (s,
3H). 13C NMR (100 MHz, CDCl3): δ 187.4, 145.6, 138.7, 134.1, 133.3,
129.5, 129.4, 129.1, 128.5, 63.4, 21.7.
4.78(m, 4H), 4.14-4.18 (m, 1H), 3.77-3.81 (m, 1H), 3.47-3.54 (m, 2H). 13
C
NMR (100 MHz, CDCl3): δ 189.1, 159.7, 135.5, 134.8, 129.4, 129.2,
126.7, 124.5, 121.0, 110.1, 60.4, 57.5, 36.0.
1-(4-Fluorophenyl)-2-(phenylsulfonyl)ethan-1-one (3j).[10j] 1H NMR
(400 MHz, CDCl3): δ 7.99-8.02 (m, 2H), 7.90 (d, J = 7.5 Hz, 2H), 7.69 (t,
J = 7.4 Hz, 1H), 7.57 (t, J = 7.9 Hz, 2H), 7.17 (t, J = 8.5 Hz, 2H), 4.73 (s,
Acknowledgements
1
2H). 13C NMR (100 MHz, CDCl3): δ 186.4, 166.4 (d, JCF = 256.5 Hz),
Financial support from National Natural Science Foundation of
China (Nos. 21372046, 21532001, 21672037) and the Opening
Project of Gannan Medical University Collaborative Innovation
Center for Gannan Oil-tea Camellia Industrial Development
(YP201607) is gratefully acknowledged.
138.5, 134.3, 132.2, 132.1, 129.2, 128.8, 116.1 (d, 2JCF = 22.0 Hz), 63.7.
1-(4-Chlorophenyl)-2-(phenylsulfonyl)ethan-1-one (3k).[8a] 1H NMR
(400 MHz, CDCl3): δ 7.88-7.92 (m, 4H), 7.70 (t, J = 7.5 Hz, 1H), 7.57 (t, J
= 7.8 Hz, 2H), 7.47 (t, J = 8.6 Hz, 2H), 4.72 (s, 2H). 13C NMR (100 MHz,
CDCl3): δ 186.8, 141.1, 134.3, 134.0, 130.7, 129.2, 128.8, 128.5, 63.5.
Keywords: aryldiazonium tetrafluoroborate • silyl enol ether • β-
keto sulfone • sulfur dioxide • catalyst-free
1-(4-Bromophenyl)-2-(phenylsulfonyl)ethan-1-one (3l).[13a] 1H NMR
(400 MHz, CDCl3): δ 7.89 (d, J = 7.6 Hz, 2H), 7.82 (d, J = 8.5 Hz, 2H),
7.69 (t, J = 7.4 Hz, 1H) , 7.57 (d, J = 8.5 Hz, 2H), 7.57 (t, J = 7.8 Hz, 2H),
4.72 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 186.8, 141.1, 134.3, 134.0,
130.7, 129.2, 128.8, 128.5, 63.5.
[1]
a) B. Nguyen, E. J. Emmet, M. C. Willis, J. Am. Chem. Soc. 2010, 132,
16372. b) E. J. Emmet, C. S. Richards-Taylor, B. Nguyen, A. Garcia-
Rubia, R. Hayter, M. C. Willis, Org. Biomol. Chem. 2012, 10, 4007. For
reviews: c) G. Liu, C. Fan, J. Wu, Org. Biomol. Chem. 2015, 13, 1592.
d) P. Bisseret, N. Blanchard, Org. Biomol. Chem. 2013, 11, 5393. e) A.
S. Deeming, E. J. Emmett, C. S. Richards-Taylor, M. C. Willis,
Synthesis, 2014, 46, 2701.
2-(Phenylsulfonyl)-1-(4-(trifluoromethyl)phenyl)ethan-1-one (3m).[13b]
1H NMR (400 MHz, CDCl3): δ 8.09 (d, J = 8.2 Hz, 2H), 7.90 (d, J = 7.4 Hz,
2H), 7.77 (d, J = 8.3 Hz, 2H), 7.71 (t, J = 7.4 Hz, 1H), 7.58 (t, J = 7.8 Hz,
2H), 4.78 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 187.2, 138.4, 138.2,
135.6 (q, 2JCF = 31.4 Hz), 134.4, 129.6, 129.3, 128.5, 125.9 (q, 3JCF = 3.7
Hz), 123.5(q, 1JCF = 274.0 Hz), 63.7.
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CDCl3): δ 7.88 (d, J = 7.7 Hz, 2H), 7.64-7.71 (m, 2H), 7.54 (t, J = 7.8 Hz,
2H), 7.42 (t, J = 7.4 Hz, 1H), 7.24-7.29 (m, 2H), 4.73 (s, 2H), 2.44 (s, 3H).
13C NMR (100 MHz, CDCl3): δ 190.3, 140.0, 138.9, 135.6, 134.1, 132.8,
130.3, 129.2, 128.5, 125.9, 65.4, 21.5.
2-(Phenylsulfonyl)-1-(m-tolyl)ethan-1-one (3o).[13d] 1H NMR (400 MHz,
CDCl3): δ 7.91 (d, J = 7.5 Hz, 2H), 7.65- 7.75 (m, 3H), 7.56 (t, J = 7.8 Hz,
2H), 7.43 (d, J = 7.4 Hz, 1H), 7.36 (t, J = 7.5 Hz, 1H),4.75 (s, 2H), 2.40 (s,
3H). 13C NMR (100 MHz, CDCl3): δ 188.1, 138.7, 135.7, 135.2, 134.2,
129.6, 129.1, 128.7, 128.5, 126.5, 63.4, 21.2.
1-(3-Chlorophenyl)-2-(phenylsulfonyl)ethan-1-one (3p).[10j] 1H NMR
(400 MHz, CDCl3): δ 7.83-7.91 (m, 4H), 7.68 (t, J = 7.4 Hz, 1H), 7.54-7.59
(m, 3H), 7.43 (t, = 7.9 Hz, 1H), 4.73 (s, 2H). 13C NMR (100 MHz,
J
CDCl3): δ 186.9, 138.5, 137.1, 135.2, 134.4, 134.2, 130.2, 129.3, 129.0,
128.5, 127.5, 63.4.
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2-(Phenylsulfonyl)-1-(thiophen-3-yl)ethan-1-one (3r). [8a] 1H NMR (400
MHz, CDCl3): δ 8.20-8.21 (m, 1H), 7.90 (d, J = 7.5 Hz, 2H), 7.68 (t, J =
7.4 Hz, 1H), 7.52-7.58 (m, 3H), 7.33-7.35 (m, 1H), 4.63 (s, 2H). 13C NMR
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Synthesis of β-Keto Sulfones via A
Catalyst-Free Reaction of
Aryldiazonium Tetrafluoroborates,
Sulfur Dioxide, and Silyl Enol Ethers
OSiMe3
O
DCE
O
O
+ DABCO (SO2)2
Ar N2BF4
+
S
R
rt, 30 min
Ar
R
catalyst-free, additive-free
insertion of sulfur dioxide
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