Temperature-dependent synthesis of vinyl sulfones and β-hydroxy sulfones from: t -butylsulfinamide and alkenes under aerobic conditions

Article abstract of DOI:10.1039/c9nj04457d

A novel temperature-dependent synthesis of organic sulfones from t-butylsulfinamide and alkenes under aerobic CuSO₄-phosphorous acid catalyzed conditions was developed. Via this newly developed method, a series of vinyl sulfones and β-hydroxy s

Full text of DOI:10.1039/c9nj04457d

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Temperature-dependent synthesis of vinyl
sulfones and b-hydroxy sulfones from
t-butylsulfinamide and alkenes under aerobic
conditions†
Cite this: New J. Chem., 2019,
43, 17941
Received 29th August 2019,
Accepted 31st October 2019
Wen-Zhu Bi, *a Wen-Jie Zhang,a Su-Xiang Feng,*abc Zi-Jie Li,a Hui-Li Ma,d
DOI: 10.1039/c9nj04457d
d
de
Shao-Hua Zhu,d Xiao-Lan Chen,
Ling-Bo Qud and Yu-Fen Zhao
rsc.li/njc
A novel temperature-dependent synthesis of organic sulfones from significantly to the synthetic methodology of organic chemistry,
t-butylsulfinamide and alkenes under aerobic CuSO4-phosphorous the pursuit of novel strategies for the synthesis of sulfone-
acid catalyzed conditions was developed. Via this newly developed containing molecules is still tireless.22
method, a series of vinyl sulfones and b-hydroxy sulfones were
synthesized at 120 8C and 40 8C, respectively.
t-Butylsulfinamide, known as a chiral source due to its low
cost and easy preparation properties, has been widely used to
synthesize various chiral amines and chiral ligands in metal-
Sulfone-containing molecules, such as vinyl sulfones and catalyzed asymmetric reactions.23 In our previously reported
b-hydroxysulfones, are pharmaceutically significant compounds,1 studies related to the construction of C–S bonds,24 we disclosed
which exhibit a wide range of biological activities including an efficient method for the synthesis of organic sulfones
protease inhibition,2 anticancer,3 anti-HIV4, anti-Parkinson’s through CuSO4-phosphorous acid catalyzed N–S bond cleavage
disease5, etc. Besides, they are also widely used as synthetic of t-butylsulfinamide.24a It is worth mentioning here that
building blocks for numerous transformations.6 Traditional t-butylsulfinamide was used as a sulfur source for the first time
synthetic methods for the synthesis of vinyl sulfones7–9 and concerning the construction of C–S bonds. Encouraged by this
b-hydroxy sulfones10,11 suffer from obvious limitations such as interesting transformation, we continuously committed our
unavailable starting materials, harsh reaction conditions, poor efforts to exploring the diverse reactivity of t-butylsulfinamide
selectivity, requirement of noble transition-metal catalysts, etc. in the challenging C–S bond construction. Herein, we would
During the last decade, the construction of C–S bonds through like to disclose a temperature-dependent synthesis of vinyl
radical-initiated cross-coupling reactions12 of alkenes/alkynes sulfones and b-hydroxy sulfones from t-butylsulfinamide and
and their derivatives with commonly used sulfonyl chlorides,13 alkenes under aerobic CuSO4-phosphorous acid catalyzed con-
sulfonyl hydrazides,14 sodium sulfinates15 and sulfinic acids16 ditions (Scheme 1). This newly developed synthetic method
has been well explored and continuously reported. Besides, broadens the reaction scope of t-butylsulfinamide and provides an
uncommonly used sulfur sources, such as thiols/thiophenols,17 alternative for the synthesis of pharmaceutically and biologically
disulfides,18 DMSO,19 tosylmethyl isocyanide (TosMIC)20 and important vinyl sulfones and b-hydroxy sulfones.
DABCOꢀ(SO2)2,21 were also frequently employed for the synthesis
Initially, the optimization reaction conditions for the sulfo-
of organic sulfones. Even though these strategies greatly enrich nylation of alkenes were investigated using styrene 1a and
the diversity of the construction of C–S bonds and contribute t-butylsulfinamide 2 as model substrates (Table 1). We were
glad to observe that styrene 1a was successfully converted in the
presence of 20 mol% of CuSO4ꢀ5H2O, 2 equiv. of H3PO3 and 2
a College of Pharmacy, Henan University of Chinese Medicine, Zhengzhou, 450046,
equiv. of trifluoroacetic acid (TFA) at 80 1C for 5 h under
China. E-mail: biwenzhu2018@hactcm.edu.cn; Fax: +86 371 65962746;
Tel: +86 371 65962746
b Collaborative Innovation Center for Respiratory Disease Diagnosis and Treatment
& Chinese Medicine Development of Henan Province, Zhengzhou, 450046, China
c Zhengzhou Key Laboratory of Chinese Medicine Quality Control and Evaluation,
Zhengzhou, 450046, China
d College of Chemistry and Molecular Engineering, Zhengzhou University,
Zhengzhou, 450052, China
e Department of Chemistry, Xiamen University, Xiamen, 361005, China
Scheme 1 Strategies for the synthesis of vinyl sulfones and b-hydroxy
† Electronic supplementary information (ESI) available: Detailed experimental
sulfones.
procedures and analytical data. See DOI: 10.1039/c9nj04457d
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Table 1 Optimization of the reaction conditionsa
Entry
Cat. (mol%)
Add. (equiv.)
Acid (equiv.)
T (1C)
t (h)
3a/4ab
Yield (%)
1
2
3
4
5
6
7
8
CuSO4ꢀ5H2O (20)
CuI (20)
CuBr (20)
Cu(OAc)2 (20)
CuSO4 (20)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
DMPH (2)
DEPH (2)
DIPPH (2)
DPPH (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
H3PO3 (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
H2SO4 (2)
TMA (2)
AcOH (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
TFA (2)
80
80
80
80
80
80
80
80
80
80
80
80
100
120
140
60
40
RT
40
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
3/1
4/1
4/1
3/1
2/1
4/1
ND
ND
2/1
4/1
3/1
3/1
5/1
20/1
10/1
1/5
1/10
1/10
1/20
1/30
1/50
53c
21c
20c
24c
30c
37c
NR
NR
38c
32c
33c
29c
61c
76c
75c
39d
35d
32d
48d
69d
68d
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
CuSO4ꢀ5H2O (20)
9
10
11
12
13
14
15
16
17
18
19
20
21
5
9
12
15
40
40
a
Reaction conditions: 1a (1.0 mmol), 2 (1.2 mmol), Cat. (20 mol%), Add. (2 equiv.) and acid (2 equiv.) were mixed and stirred at RT-140 1C for
5–15 h under open-air conditions. The mol-ratio of 3a/4a was detected by diagnostic peak integration in 1H-NMR of the crude reaction mixture.
b
c
d
Isolated yields for 3a. Isolated yields for 4a. TMA = trimethylacetic acid. ND = not detected. NR = no reaction. DMPH = dimethyl H-phosphonate.
DEPH = diethyl H-phosphonate. DPPH = diphenyl H-phosphonate. DIPPH = diisopropyl H-phosphonate. RT = room temperature.
open-air conditions. However, two sulfonylated compounds,
Then, the substrate scope of alkenes and t-butylsulfinamide
(E)-vinyl sulfones and b-hydroxy sulfones (3a and 4a), were under the optimized reaction conditions was explored. As demon-
found in the crude reaction mixture with a mol-ratio of 3/1 strated in Scheme 2, various aromatic alkenes were smoothly
and an isolated yield of 53% of 3a was obtained (entry 1). In
order to improve the mol-ratio and isolated yield of 3a, the
catalyst, acid and additive employed in this transformation
were carefully screened. However, as can be seen in entries 2–5,
20 mol% of CuI, CuBr, Cu(OAc)2 and CuSO4 could catalyze the
reaction, but the efficiency (21–30%) was not better than that of
CuSO4ꢀ5H2O (53%). The use of other acids, such as H2SO4,
trimethylacetic acid (TMA) and AcOH, as well as other additive
H-phosphonate esters, such as dimethyl H-phosphonate
(DMPH), diethyl H-phosphonate (DEPH), diisopropyl H-phos-
phonate (DIPPH) and diphenyl H-phosphonate (DPPH), all failed
to provide a satisfactory isolated yield of 3a (entries 6–12).
Surprisingly, when the reaction temperature increased from
80 1C to 120 1C, the mol-ratio of 3a/4a and isolated yield of 3a
were all significantly increased (entries 1, 13 and 14). However,
when a higher temperature (140 1C) was used, the isolated
yield of 3a was slightly decreased in spite of a higher mol-ratio
of 3a/4a (entry 15). Therefore, the optimal reaction condition
for the synthesis of 3a was 120 1C. On the contrary, when the
reaction mixture was stirred at low temperatures for 5 h, the
mol-ratio of 3a/4a decreased and the isolated yield of the main
product 4a ranged from 32–39% (entries 16–18). In order to get
a satisfactory isolated yield of 4a, the reaction was carried out at
Scheme 2 Scope of vinyl sulfones. Reaction conditions: 1 (1.0 mmol), 2
40 1C for prolonged reaction times (9–15 h). As can be seen in
(1.2 mmol), H3PO3 (2 equiv.), CuSO4ꢀ5H2O (20 mol%), and TFA (2 equiv.)
entries 19–21, at least 12 h was necessary for the synthesis of
were mixed and stirred at 120 1C for 5 h. Isolated yields were provided.
a Under O2 atmosphere.
compound 4a.
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converted to the corresponding (E)-vinyl sulfone derivatives via
direct sulfonylation with t-butylsulfinamide at 120 1C under
aerobic conditions. Both electron-withdrawing groups (–Br, –Cl,
or –F) and electron-donating groups (–CH3, –CH2Cl, –OCH3, or
–C(CH3)3) on the phenyl ring of the aromatic alkenes were
suitable for this protocol, and the corresponding (E)-vinyl
sulfones were obtained in moderate to good yields (3b–m).
Aromatic alkenes with electron-donating groups (3h–m) gave
slightly higher yields than those with electron-withdrawing
groups (3b–g). In addition, polycyclic aromatic alkenes, 2-vinyl-
naphthalene, could also be converted in this reaction to afford
(E)-2-(2-(t-butylsulfonyl)vinyl)naphthalene in a yield of 77% (3n).
Furthermore, several disubstituted alkenes, including prop-1-
en-2-ylbenzene, 1-methyl-4-(prop-1-en-2-yl)benzene, ethene-1,1-
diyldibenzene and (E)-1-methoxy-4-(prop-1-en-1-yl)benzene,
were employed to react with t-butylsulfinamide in this reaction.
As can be seen, the 1,1-disubstituted terminal alkenes were
successfully converted to the corresponding vinyl sulfones
with relatively high yields (3o–q, 68–74%). Meanwhile, the
1,2-disubstituted non-terminal alkene was converted with
relatively low yields (3r, 36%).
Scheme 4 Control experiments.
To gain further insight into the reaction mechanism, a series
of control experiments were performed as shown in Scheme 4.
Firstly, when the reaction was carried out at 120 1C under a
Furthermore, the synthesis of b-hydroxy sulfones was also
carried out at 40 1C for 12 h under open-air conditions as shown N2 atmosphere, only 9% of the corresponding vinyl sulfone was
in Scheme 3. Aromatic alkenes with both electron-withdrawing obtained (Scheme 4a), which indicated that the oxygen was
groups (–Br, –Cl, or –F) and electron-donating groups (–CH3, necessary in this transformation. However, when the reaction
–CH2Cl, or –C(CH3)3) were smoothly converted to the corres- was performed under O2 atmosphere, the corresponding vinyl
ponding b-hydroxy sulfone derivatives with moderate to good sulfone was obtained with a yield of 79% (Scheme 4b), which
yield (4b–k, 57–73%). Contrary to the synthesis of vinyl sulfones, was only slightly higher than that under open-air conditions
aromatic alkenes with electron-withdrawing groups (4b–g) gave (76%). When the reaction was carried out in the absence of
slightly higher yields than those with electron-donating groups CuSO4ꢀ5H2O or in the presence of 2.0 equiv. of TEMPO (2,2,6,6-
(4h–k). Aromatic alkenes with strong electron-donating groups tetramethyl-1-piperidinyloxy), only a trace of 4a was found
(–OCH3) as well as disubstituted alkenes failed to be converted to (Scheme 4c and d), indicating that a Cu(II)-promoted radical
the corresponding b-hydroxy sulfone (4l–o).
pathway was possibly involved in this reaction process. An
isotopic labelling experiment clearly demonstrated that the
additional oxygen atom of the sulfone groups in 3a and 4a
originated from H2O instead of O2 in the air (Scheme 4e).
Finally, an intermolecular transformation from b-hydroxy
sulfone 4a to vinyl sulfone 3a was performed at 120 1C for 5 h
(Scheme 4f). However, no corresponding vinyl sulfone was
obtained, which suggested that vinyl sulfones were not synthe-
sized via the simple dehydration of b-hydroxy sulfones under
high temperatures.
Referring to the literature14c and our previous work,24a
a
plausible mechanism for the reaction is proposed in Scheme 5.
Initially, the tricoordinated phosphorous acid 6 and t-butyl-
sulfinamide 2 coordinate with Cu2+ to form complex 7. In this
case, a six-membered ring is generated inside 7 as a result of the
formation of an intramolecular hydrogen bond (O–Hꢀ ꢀ ꢀOQS).
Subsequently, a proton transfers from the OH group of 6 to the
oxygen of the SQO group, giving the copper complex 8, which
can resonate with 80. The two positively charged sulfur atoms in
80 imply the highly electrophilic ability of the protonated sulfonyl
group. Meanwhile, one molecule of water attacks the protonated
sulfonyl group of 8, affording the pentavalent intermediate 9.
Then, intermediate 9 loses an ammonium and a proton, yielding
the key intermediate copper complex 10 (Scheme 5I). When the
Scheme 3 Scope of b-hydroxy sulfones. Reaction conditions: 1 (1.0 mmol),
2 (1.2 mmol), H3PO3 (2 equiv.), CuSO4ꢀ5H2O (20 mol%), and TFA (2 equiv.)
were mixed and stirred at 40 1C for 12 h. Isolated yields were provided.
aUnder O2 atmosphere.
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Notes and references
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Scheme 5 Plausible mechanism.
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In conclusion, we developed a novel temperature-dependent
methodology for the synthesis of organic sulfones using t-butyl-
sulfinamide as a sulfur source under aerobic CuSO4-phosphorous
acid catalyzed reaction conditions. Two different kinds of
organic sulfones, vinyl sulfones and b-hydroxy sulfones were
synthesized through the cleavage of the N–S bond of
t-butylsulfinamide and the formation of C–S bonds with
alkenes at 120 1C and 40 1C, respectively. The newly developed
synthetic method broadens the reaction scope of t-butylsulfin-
amide and provides an alternative for the synthesis of pharma-
ceutically and biologically important vinyl sulfones and
b-hydroxy sulfones.
Conflicts of interest
There are no conflicts to declare.
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