Electrochemical Synthesis of Sulfinic Esters via Aerobic Oxidative Esterification of Thiophenols with Alcohols

Article abstract of DOI:10.1055/s-0040-1707966

A method for the electrochemical synthesis of sulfinic esters by aerobic oxidative coupling of thiophenols and alcohols has been developed. Using electrons as the redox reagent and O ₂in air as the oxygen source, the reactions proceeded smoothly at room temperature, even for a gram-scale preparation. No use of catalyst, clean redox reagent, green and abundant oxygen source, and mild reaction conditions make this strategy eco-friendl.

Full text of DOI:10.1055/s-0040-1707966

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2020, 52, A–H
paper
A
en
H. Zhou et al.
Paper
Synthesis
Electrochemical Synthesis of Sulfinic Esters via Aerobic Oxidative
Esterification of Thiophenols with Alcohols
Hongyan Zhou §a,b
Jiaokui Duan §a
Dongtai Xiea
Jingya Yang*a
Ben Maa
Ganggang Wanga
Chengqi Wua
O
RSH
+
R'OH
S
undivided cell, air (O2), r.t.
R
OR'
0
0
0
0-
0
0
0
2-7
4
1
9-5
1
3
3
• catalyst-free
• air as the sole oxygen source
• mild reaction conditions • 31 examples, up to 98% yield
Xi-Cun Wang*a
a College of Chemistry and Chemical Engineering, Northwest
Normal University, Lanzhou 730070, P. R. of China
yangjy@nwnu.edu.cn
wangxicun@nwnu.edu.cn
b College of Science, Gansu Agricultural University, Lanzhou
730070, P. R. of China
§ These authors contributed equally to this work.
Received: 21.01.2020
Accepted after revision: 18.04.2020
Published online: 14.05.2020
hydrazides16 or -keto sulfones17 has also been reported.
Recently, the decomposition of N-sulfonylhydrazones18 has
been described as a complementary protocol for the prepa-
ration of sulfinic esters. Despite the enormous progress
achieved, most of these transformations suffer from the use
of pre-functionalized starting materials, the need of waste-
generating oxidants and specific catalysts (transition met-
als, strong Brønsted acids or Lewis acids), and the produc-
tion of environmentally harmful byproducts. Thus, the de-
velopment of sustainable and environmentally benign ap-
proaches for the synthesis of sulfinic esters is still highly
desired.
DOI: 10.1055/s-0040-1707966; Art ID: ss-2020-g0043-op
Abstract A method for the electrochemical synthesis of sulfinic esters
by aerobic oxidative coupling of thiophenols and alcohols has been de-
veloped. Using electrons as the redox reagent and O2 in air as the oxy-
gen source, the reactions proceeded smoothly at room temperature,
even for a gram-scale preparation. No use of catalyst, clean redox re-
agent, green and abundant oxygen source, and mild reaction condi-
tions make this strategy eco-friendly.
Key words aerobic oxidation, electrochemical synthesis, radical reac-
tion, sulfinic esters, synthetic method
The aerobic oxidative cross-coupling of thiols and alco-
hols is undoubtedly the most direct and atom-economic
method for the synthesis of sulfinic esters because the pre-
functionalization of raw materials is avoided and fewer by-
products are produced. In this context, a few examples with
molecular O2 as the green oxidant have been reported in re-
cent years (Scheme 1). In 2016, Jang’s group reported the
copper-catalyzed aerobic coupling of thiophenols and alco-
hols in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene
(TBD) at 65 °C, affording the sulfinic esters via sulfinyl radi-
cal intermediates (Scheme 1a).19 In 2018, Zhang and co-
workers developed a new cobalt nanocatalyst supported on
N–SiO2-doped activated carbon (Co/N–SiO2–AC) which en-
abled the oxidative esterification of (hetero)aryl and alkyl
thiols with alcohols at 60–80 °C (Scheme 1b).20 Recently, a
visible-light-induced method was established for the reac-
tion of aromatic thiols and alcohols by Srivastava’s group.
Using eosin Y as the organophotoredox catalyst, sulfinic es-
ters were readily obtained at room temperature (Scheme
1c).21
Sulfinic esters are an important class of organic sulfur-
containing compounds due to their unique biological and
pharmacological activities.1 In particular, they are used as a
type of highly selective thiol probe2 and fluorescence su-
peroxide probe3 for disease diagnosis. More importantly,
sulfinic esters are very valuable synthetic precursors and
intermediates in organic synthesis, for example, for the
preparation of cyclic sulfinates,4 sulfones,5 sulfonamides,6
sulfoxides,7 sulfonylmethyl isonitriles8 and thioethers.9
Considering these essential applications, a series of use-
ful methods has been exploited for the synthesis of sulfinic
esters from various starting materials. The early represen-
tative method for the preparation of sulfinic esters was the
oxidation of diaryl sulfides in alcohols.10 Later, the reactions
of sulfonyl chlorides,11 sulfinyl chlorides,12 sulfinic acids13
or sodium sulfonates14 with alcohols were developed as the
prevailing alternative strategies. In addition, the sulfination
of alcohols with arylsulfonylmethyl isocyanides,15 sulfonyl
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–H
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
H. Zhou et al.
Paper
Synthesis
cathode (Table 1, entries 8–11). It is worth noting that
changing the constant current has a significant impact on
the reaction. Although the yield decreased slightly when
the constant current was increased to 15 mA, only trace
amounts of 3aa were detected when the constant current
was reduced to 5 mA (Table 1, entries 12 and 13). In sharp
contrast, if no electric current was applied, no reaction oc-
curred at all (Table 1, entry 14).
previous work
O
S
CuI, TBD, O2
65 °C
a)
b)
c)
RSH
RSH
RSH
+
+
+
R'OH
R'OH
R'OH
R
R
R
OR'
OR'
OR'
O
S
Co/N–SiO2–AC, O2
60–80 °C
O
S
eosin Y, green LEDs, air (O2)
r.t.
this work
d)
Table 1 Optimization of the Reaction Conditionsa
O
S
electricity, air (O2)
r.t., 7–10 h
RSH
+
R'OH
R
OR'
O
undivided cell
SH
Scheme 1 Direct synthesis of sulfinic esters from thiols and alcohols
S
Pt (+) I Pt (–), 10 mA
O
+
MeOH
LiClO4, air (O2), r.t.
1a
2a
3aa
Electrochemical methods provide
a
sustainable,
straightforward and powerful strategy for electron-transfer-
driven reactions, and have been widely used in numerous
bond-dissociation and bond-forming processes, even in the
synthesis of complex molecules.22 From the perspective of
green chemistry, organic electrosynthesis uses electrons as
a traceless and inherently safe reagent, avoiding the genera-
tion of reagent waste, increasing atom economy, and allow-
ing for milder reaction conditions. Based on our previous
work on green organic synthesis methodology,23 here, we
report an electrochemical method for the synthesis of
sulfinic esters by the oxidative esterification of thiophenols
with alcohols in air. It should be noted that during the
preparation of this manuscript, two similar works were re-
ported by the Zhong and Lei groups.24 Therein, alcohols
(could also be water)24a and oxygen24b were considered as
the oxidant and the oxygen source, respectively. Neverthe-
less, the current work still has the following characteristics:
1) oxygen in the air as the only source of oxygen, 2) differ-
ent reaction conditions, 3) a wider range of substrates, and
4) a reasonable reaction mechanism.
Entry
Variation from the standard conditions
Yield (%)b
1
2
none
96
8 h instead of 10 h
83
3
nBu4NBF4 instead of LiClO4
nBu4NClO4 instead of LiClO4
nBu4NI instead of LiClO4
KI instead of LiClO4
90
4
85
5
10
6
trace
44
7
0.25 mmol LiClO4 instead of 0.5 mmol
C (–) instead of Pt (–)
C (+) instead of Pt (+)
Ni (–) instead of Pt (–)
Fe (–) instead of Pt (–)
15 mA instead of 10 mA
5 mA instead of 10 mA
no electric current
8
52
9
77
10
11
12
13
14
62
80
87
trace
N.R.
a Standard reaction conditions: undivided cell, Pt anode (1 cm × 1 cm), Pt
cathode (1 cm × 1 cm), constant current (10 mA), 1a (0.5 mmol), LiClO4
(0.5 mmol), MeOH (8 mL), air, r.t., 10 h.
b Isolated yields. N.R. = no reaction.
At the beginning, we chose 4-methylthiophenol (1a)
and methanol (2a) as the model substrates to optimize the
reaction conditions in an undivided cell at room tempera-
ture (Table 1). Excitedly, using platinum plates as the elec-
trodes and LiClO4 as the electrolyte, the reaction proceeded
smoothly in methanol at a constant current of 10 mA, and
the desired methyl 4-methylbenzenesulfinate (3aa) was
obtained in 96% yield (Table 1, entry 1). When the reaction
time was shortened from 10 to 8 hours, the yield was re-
duced to 83% (Table 1, entry 2). Next, the supporting elec-
trolyte was screened. When nBu4NBF4 or nBu4NClO4 was
used instead of LiClO4, the yield of 3aa was slightly de-
creased, while nBu4NI and KI only gave 10% or trace
amounts of 3aa, respectively (Table 1, entries 3–6). In addi-
tion, when the amount of LiClO4 was halved, the yield of
3aa was reduced to 44% (Table 1, entry 7). Subsequently, in-
vestigation of different electrodes showed that platinum
plate electrodes were the best choice for both anode and
With the optimum reaction conditions in hand, we then
examined the substrate scope to verify the applicability of
the method. First, we tried the reactions of a variety of thio-
phenols with methanol (Scheme 2). The results indicate
that the position of the substituent on the thiophenol has
an obvious influence on the aerobic oxidative esterification
reaction. para-Substituted thiophenols 1a–1g reacted well
with methanol to afford the corresponding sulfinic esters
3aa–3ga in high yields. Differently, ortho- and meta-substi-
tuted thiophenols, whether with an electron-withdrawing
or electron-donating group, provided the desired 3ha–3na
in only moderate yields. However, the 2,4- and 3,4-disubsti-
tuted thiophenols 1o–1q were well tolerated, leading to the
corresponding products 3oa–3qa in high yields. Regretfully,
an alkyl thiol, phenylmethanethiol (1r), was inert under the
standard conditions, probably due to its low reactivity.
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–H

C
H. Zhou et al.
Paper
Synthesis
O
S
O
S
undivided cell
undivided cell
R'
SH
SH
Pt (+) I Pt (–), 10 mA
Pt (+) I Pt (–), 10 mA
O
O
R
R
+
R'OH
+
MeOH
R
R
air (O2), r.t.
LiClO4, air (O2), r.t.
1
2
3
1a–r
2a
3aa–3qa
O
O
O
S
O
O
S
O
S
S
S
O
S
S
O
O
O
O
O
O
O
O
Cl
Cl
3ab, 9 h, 90%a
3db, 8 h, 76%a
3fb, 10 h, 83%a
O
3aa, 10 h, 96%
3ba, 8 h, 95%
3ca, 10 h, 85%
3da, 10 h, 81%
O
Cl
O
S
O
O
O
S
O
S
O
S
S
S
O
O
O
S
O
O
O
O
Br
F
F
Cl
Br
3gb, 10 h, 84%a
3ob, 8 h, 81%a
3pb, 9 h, 89%a
3ea, 9 h, 90%
3fa, 9 h, 94%
3ga, 10 h, 92%
3ha, 7 h, 50%
O
O
O
O
O
S
O
S
F
O
S
S
S
S
O
O
O
S
Cl
Br
O
O
O
O
3ac, 8 h, 95%b
3ad, 8 h, 90%b
3ae, 8 h, 93%b
3ia, 12 h, 43%
3ja, 9 h, 45%
3ka, 10 h, 54%
3la, 9 h, 42%
O
O
O
Cl
O
S
Cl
O
S
Br
O
O
S
S
S
S
S
O
O
O
O
O
O
O
Cl
3af, 9 h, 78%b
3ag, 9 h, 56%b
3ah, 15 h, 52%b
3ma, 9 h, 46%
3na, 7 h, 52%
3oa, 9 h, 89%
3pa, 10 h, 92%
O
O
O
S
S
O
S
O
O
O
S
O
O
3ai, 9 h, 91%b
3aj, 8 h, 98%b
3qa, 10 h, 80%
3ra, 10 h, 0%
Scheme 3 Substrate scope of alcohols. a Reagents and conditions A:
undivided cell, Pt anode (1 cm × 1 cm), Pt cathode (1 cm × 1 cm),
constant current (10 mA), current density (10 mA/cm2), 1 (0.5 mmol),
LiClO4 (0.5 mmol), EtOH (8 mL), air, r.t. b Reagents and conditions B:
undivided cell, Pt anode (1 cm × 1 cm), Pt cathode (1 cm × 1 cm),
constant current (10 mA), current density (10 mA/cm2), 1 (0.5 mmol),
nBu4NClO4 (0.75 mmol), 2 (2 mL), MeCN (6 mL), air, r.t. Isolated yields.
Scheme 2 Substrate scope of thiophenols. Reagents and conditions:
undivided cell, Pt anode (1 cm × 1 cm), Pt cathode (1 cm × 1 cm),
constant current (10 mA), 1 (0.5 mmol), LiClO4 (0.5 mmol), MeOH
(8 mL), air, r.t. Isolated yields.
Next, the scope of alcohols was investigated with reac-
tions of thiophenols and various alcohols (Scheme 3). De-
lightedly, when ethanol (2b) served as the reaction partner
and solvent, the reactions with para-substituted and 2,4-
disubstituted thiophenols proceeded smoothly, and the de-
sired products (3ab, 3db, 3fb, 3gb, 3ob and 3pb) were ob-
tained in 76–90% yield (reaction conditions A). When pro-
panol (2c), isopropyl alcohol (2d), butanol (2e), isobutyl al-
cohol (2f), cyclopentanol (2g), cyclohexanol (2h), octanol
(2i) and 2-ethoxyethanol (2j) were subjected to the reac-
tion, acetonitrile was selected as the solvent due to the poor
solubility of LiClO4 in these alcohols. Meanwhile, nBu4NClO4
was found to be the best supporting electrolyte for these re-
action systems. Fortunately, the products 3ac–3aj were ob-
tained in moderate to excellent yields under the modified
conditions (reaction conditions B). For other higher aliphat-
ic alcohols, although the reactions occurred, the pure prod-
ucts were not successfully isolated.
O
undivided cell
SH
S
Pt (+) I Pt (–), 60 mA
O
+
MeOH
air (O2), r.t., 20 h
1a (10 mmol)
2a (100 mL)
3aa (1.43 g, 84%)
Scheme 4 Gram-scale synthesis of 3aa [Pt anode (1.5 cm × 1.5 cm), Pt
cathode (1.5 cm × 1.5 cm)]
In order to explore the reaction mechanism, a series of
control experiments was conducted (Scheme 5). These con-
trol reactions were essentially carried out under conditions
in which only one reaction parameter was changed based
on the standard reaction conditions. First, when the reac-
tion of 1a was carried out under argon in degassed metha-
nol, no reaction occurred at all (Scheme 5, eq 1). Further-
more, 3aa was obtained in anhydrous methanol in 91%
yield (Scheme 5, eq 2). In addition, the reaction with air
bubbling was completed within 7 hours, which is shorter
than the time required for the standard reaction, and 3aa
was obtained in 91% yield (Scheme 5, eq 3). These results
indicate that the O2 in air is the sole oxygen source. Then,
when the radical scavenger TEMPO or BHT was added, the
reaction was remarkably inhibited (Scheme 5, eqs 4 and 5),
To identify the practicability of the established method,
a gram-scale experiment was conducted (Scheme 4). Thus,
10 mmol of 4-methylthiophenol (1a) reacted smoothly in
methanol (2a) at a constant current of 60 mA (current den-
sity about 26.7 mA/cm2), and the desired 3aa was isolated
in 84% yield (1.43 g) after 20 hours.
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–H

D
H. Zhou et al.
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Synthesis
and the TEMPO-trapped thiol radical 4a was detected by
HRMS (see the Supporting Information, Figure S1). This im-
plies that the reaction might proceed with the involvement
of a radical process. However, the possibility of oxidation of
TEMPO and BHT cannot be ruled out because they are easi-
ly oxidized at the anode. When the reaction was terminated
after 5 hours, the desired 3aa and disulfide 5a were ob-
tained in yields of 31% and 49%, respectively (Scheme 5, eq
6). Using 5a instead of 1a afforded 3aa in 74% yield (Scheme
5, eq 7). Furthermore, although no thiosulfinate 6a was de-
tected during the standard reaction, subjecting 6a25 to the
standard conditions gave the desired 3aa in 77% yield after
only 5 hours (Scheme 5, eq 8). These results suggest that
the disulfide and thiosulfinate are possible reaction inter-
mediates. In addition, the oxidant peak potentials of 1a
(1.45 V vs Ag/AgCl in MeOH) and 5a (1.68 V vs Ag/AgCl in
MeOH) were obtained by cyclic voltammetry experiments
(see the Supporting Information, Figure S2). This demon-
strates that the oxidation of thiophenol occurs preferential-
ly during the reaction, and then the disulfide is oxidized.
Finally, when the superoxide radical anion (O2•–) inhibitor
N-tert-butyl--phenyl nitrone26 was added to the system,
only trace amounts of 3aa were detected, indicating that
standard conditions
Ar
1a
1a
1a
+
+
+
2a
2a
2a
3aa
(1)
0%
standard conditions
anhydrous MeOH
3aa
(2)
(3)
91%
standard conditions
air (bubbled)
3aa
7 h, 91%
standard conditions
2 equiv TEMPO
O
1a
+
2a
3aa
trace
+
(4)
S
N
4a
detected by HRMS
standard conditions
2 equiv BHT
1a
1a
5a
+
+
+
2a
2a
2a
3aa
(5)
(6)
(7)
18%
standard conditions
5 h
S
S
3aa
+
31%
5a, 49%
standard conditions
3aa
74%
O
standard conditions
5 h
S
+
2a
3aa
(8)
(9)
S
77%
6a
standard conditions
1a
+
2a
3aa
trace
•–
oxygen might participate in the reaction by forming an O2
O
N
intermediate (Scheme 5, eq 9). Furthermore, the reduction
peak potential of O2 was measured by cyclic voltammetry
(–0.86 V vs Ag/AgCl in MeOH) (see the Supporting Informa-
tion, Figure S3). As with literature reports,24b,27 it was found
that O2 is easily reduced to O2•– at the cathode. However, the
reduction of methanol to give evolution of hydrogen at the
cathode should not be ruled out since H2 was detected by
GC analysis (see the Supporting Information, Figure S4).
Based on the above results, a possible reaction mecha-
nism is proposed (Scheme 6). First, thiophenol 1 undergoes
anode oxidation and deprotonation to afford thiol radical A,
followed by dimerization of A, leading to the formation of
disulfide B. Subsequently, disulfide B loses an electron at
the anode and is oxidized to disulfide radical cation C. On
the other hand, O2 is easily reduced at the cathode to pro-
vide superoxide radical anion (O2•–). Then, radical cation C
reacts with O2•– to give species D, which combines a proton
to generate intermediate E. Next, intermediate E gains an
electron at the cathode to give thiosulfinate F and hydrox-
ide radical. Finally, nucleophilic substitution of thiosulfi-
nate F by alcohol 2 affords the final product 3. Meanwhile,
hydroxide radical is reduced to hydroxide anion, which
then combines a proton to produce the byproduct H2O.
In summary, we have developed an electrochemical
method for the direct synthesis of sulfinic esters from read-
ily available thiophenols and alcohols. The reactions were
performed at room temperature in an undivided cell under
air atmosphere, affording a variety of sulfinic esters in up to
98% yield. Oxygen in air proved to be the sole oxygen
source. Compared with the literature methods for the syn-
(2 equiv)
Scheme 5 Control experiments
·
–
2 RSH
O2
1
– 2 H+
e–
2 e–
·
O2
2 RS
A
H+
–OH
H2O
RS SR
e–
B
·OH
e–
RS SR
R'OH
2
O
O
C
RS SR
S
R
OR'
F
·
–
O2
3
e–
O–
OH
O
O
H+
RS SR
RS SR
D
E
Scheme 6 Proposed mechanism
thesis of sulfinic esters, this electrochemical method avoids
the use of waste-generating oxidants and catalyst, uses air
as the green oxygen source, does not produce harmful by-
products, and allows for milder reaction conditions. These
features, plus the simple experimental setup, make this
protocol eco-friendly and practicable.
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–H

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H. Zhou et al.
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Synthesis
Methyl 4-tert-Butylbenzenesulfinate (3ca)16
1H NMR and 13C NMR spectra were recorded on a Varian Mercury-400
Plus or an Agilent Technologies DD2 (600 MHz) spectrometer. High-
resolution mass spectra (HRMS) were performed on a Thermo Or-
bitrap Elite instrument with an ESI source. Electrolysis reactions were
conducted using a dual display potentiostat (DJS-292B) (made in Chi-
na). Both the anode and cathode were all Pt plate electrodes (1.0 cm ×
1.0 cm) and were purchased from Beijing Yidian Technology Co., Ltd.
(China). Reactions were monitored by TLC on silica gel plates (GF254).
Reagents and solvents are commercially available, and were used
without further purification. Reaction mixtures were purified by col-
umn chromatography over silica gel (PE/EtOAc).
Pale-yellow oil; yield: 90.2 mg (85%).
1H NMR (600 MHz, CDCl3):  = 7.62 (d, J = 8.4 Hz, 2 H), 7.54 (d, J = 8.4
Hz, 2 H), 3.48 (s, 3 H), 1.33 (s, 9 H).
13C NMR (150 MHz, CDCl3):  = 155.9, 140.9, 126.0, 125.2, 49.6, 35.1,
31.2.
Methyl 4-Methoxybenzenesulfinate (3da)16
Pale-yellow oil; yield: 75.4 mg (81%).
1H NMR (400 MHz, CDCl3):  = 7.63 (d, J = 9.2 Hz, 2 H), 7.03 (d, J = 8.8
Hz, 2 H), 3.87 (s, 3 H), 3.46 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 162.7, 135.4, 127.2, 114.4, 55.5, 49.2.
Electrochemical Synthesis of Sulfinic Esters 3 (Standard Condi-
tions, Reaction Conditions A); General Procedure
Thiophenol 1 (0.5 mmol), LiClO4 (53.2 mg, 0.5 mmol) and alcohol 2 (8
mL) were sequentially added into a 25-mL three-necked flask
equipped with a platinum anode and cathode (plate, 1.0 cm × 1.0 cm).
The reaction mixture was stirred at a constant current of 10 mA un-
der air at ambient temperature. After completion of the reaction
(monitored by TLC), the reaction mixture was purified by column
chromatography on silica gel (PE/EtOAc) to afford pure product 3.
Methyl 4-Fluorobenzenesulfinate (3ea)16
Colorless oil; yield: 78.3 mg (90%).
1H NMR (400 MHz, CDCl3):  = 7.76–7.67 (m, 2 H), 7.27–7.20 (m, 2 H),
3.48 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 165.0 (d, J = 252.0 Hz), 139.8 (d, J =
2.85 Hz), 127.8 (d, J = 9.1 Hz), 116.3 (d, J = 22.4 Hz), 49.6.
Methyl 4-Chlorobenzenesulfinate (3fa)16
Electrochemical Synthesis of Sulfinic Esters 3 (Reaction Condi-
tions B); General Procedure
Colorless oil; yield: 90.0 mg (94%).
Thiophenol 1 (0.5 mmol), nBu4NClO4 (256.3 mg, 0.75 mmol), alcohol 2
(2 mL) and MeCN (6 mL) were sequentially added into a 25-mL three-
necked flask equipped with a platinum anode and cathode (plate, 1.0
cm × 1.0 cm). The reaction mixture was stirred at a constant current
of 10 mA under air at ambient temperature. After completion of the
reaction (monitored by TLC), the reaction mixture was purified by
column chromatography on silica gel (PE/EtOAc) to afford pure prod-
uct 3.
1H NMR (600 MHz, CDCl3):  = 7.66–7.60 (m, 2 H), 7.53–7.48 (m, 2 H),
3.47 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 142.4, 138.6, 129.4, 126.9, 49.7.
Methyl 4-Bromobenzenesulfinate (3ga)16
Colorless oil; yield: 108.1 mg (92%).
1H NMR (600 MHz, CDCl3):  = 7.69–7.66 (m, 2 H), 7.58–7.54 (m, 2 H),
3.47 (s, 3 H).
Gram-Scale Synthesis of 3aa
13C NMR (150 MHz, CDCl3):  = 143.0, 132.3, 127.1, 127.0, 49.7.
Thiophenol 1a (1.24 g, 10 mmol), LiClO4 (1.04 g, 10 mmol) and MeOH
(100 mL) were sequentially added into a 250-mL beaker equipped
with a platinum anode and cathode (plate, 1.5 cm × 1.5 cm). The reac-
tion mixture was stirred at a constant current of 60 mA under air at
ambient temperature for 20 h. After completion of the reaction (mon-
itored by TLC), the reaction mixture was purified by column chroma-
tography on silica gel (PE/EtOAc, 15:1) to afford pure product 3aa
(1.43 g, 84%).
Methyl 3-Methylbenzenesulfinate (3ha)20
Pale-yellow oil; yield: 42.2 mg (50%).
1H NMR (600 MHz, CDCl3):  = 7.51 (s, 1 H), 7.49 (d, J = 7.8 Hz, 1 H),
7.42 (t, J = 7.2 Hz, 1 H), 7.35 (d, J = 7.8 Hz, 1 H), 3.48 (s, 3 H), 2.43 (s,
3 H).
13C NMR (150 MHz, CDCl3):  = 143.8, 139.2, 133.0, 128.9, 125.6,
122.5, 49.6, 21.4.
Methyl 4-Methylbenzenesulfinate (3aa)
Pale-yellow oil; yield: 82.0 mg (96%).
1H NMR (600 MHz, CDCl3):  = 7.57 (d, J = 8.4 Hz, 2 H), 7.33 (d, J = 8.4
Methyl 3-Fluorobenzenesulfinate (3ia)
Colorless oil; yield: 37.5 mg (43%).
Hz, 2 H), 3.45 (s, 3 H), 2.41 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 142.8, 140.9, 129.6, 125.3, 49.3, 21.5.
1H NMR (600 MHz, CDCl3):  = 7.56–7.50 (m, 1 H), 7.50–7.46 (m, 1 H),
7.46–7.41 (m, 1 H), 7.27–7.22 (m, 1 H), 3.49 (s, 3 H).
HRMS (ESI): m/z [M + H]+ calcd for C8H11O2S+: 171.0474; found:
171.0477.
13C NMR (150 MHz, CDCl3):  = 162.9 (d, J = 250.5 Hz), 146.4 (d, J = 5.1
Hz), 130.8 (d, J = 7.4 Hz), 121.2 (d, J = 3.2 Hz), 119.3 (d, J = 21.3 Hz),
112.6 (d, J = 23.4 Hz), 49.8.
HRMS (ESI): m/z [M + H]+ calcd for C7H8FO2S+: 175.0224; found:
Methyl 4-Isopropylbenzenesulfinate (3ba)
Pale-yellow oil; yield: 94.7 mg (95%).
175.0225.
1H NMR (400 MHz, CDCl3):  = 7.62 (d, J = 8.0 Hz, 2 H), 7.39 (d, J = 8.0
Hz, 2 H), 3.48 (s, 3 H), 3.04–2.92 (m, 1 H), 1.27 (d, J = 6.8 Hz, 6 H).
Methyl 3-Chlorobenzenesulfinate (3ja)16
13C NMR (150 MHz, CDCl3):  = 153.6, 141.3, 127.2, 125.4, 49.6, 34.2,
Colorless oil; yield: 42.8 mg (45%).
1H NMR (600 MHz, CDCl3):  = 7.69 (s, 1 H), 7.57 (d, J = 7.2 Hz, 1 H),
7.52 (d, J = 7.8 Hz, 1 H), 7.50–7.45 (m, 1 H), 3.49 (s, 3 H).
23.7.
HRMS (ESI): m/z [M + H]+ calcd for C10H15O2S+: 199.0787; found:
199.0788.
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–H

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13C NMR (150 MHz, CDCl3):  = 145.9, 135.59, 132.3, 130.4, 125.6,
HRMS (ESI): m/z [M + H]+ calcd for C7H7Cl2O2S+: 224.9538; found:
123.6, 49.9.
224.9538.
Methyl 3-Bromobenzenesulfinate (3ka)
Methyl 3,4-Dimethylbenzenesulfinate (3qa)
Pale-yellow oil; yield: 63.4 mg (54%).
Colorless oil; yield: 73.2 mg (80%).
1H NMR (600 MHz, CDCl3):  = 7.84 (s, 1 H), 7.68 (d, J = 7.8 Hz, 1 H),
7.61 (d, J = 7.8 Hz, 1 H), 7.45–7.35 (m, 1 H), 3.49 (s, 3 H).
1H NMR (400 MHz, CDCl3):  = 7.47 (s, 1 H), 7.43 (d, J = 7.8 Hz, 1 H),
7.30 (d, J = 7.8 Hz, 1 H), 3.48 (s, 3 H), 2.34 (s, 3 H), 2.33 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 146.1, 135.3, 130.6, 128.4, 124.1,
13C NMR (150 MHz, CDCl3):  = 141.5, 141.1, 137.8, 130.2, 126.1,
123.4, 49.9.
122.8, 49.4, 19.9, 19.8.
HRMS (ESI): m/z [M + H]+ calcd for C7H8BrO2S+: 234.9423; found:
HRMS (ESI): m/z [M + H]+ calcd for C9H13O2S+: 185.0631; found:
234.9422.
185.0634.
Methyl 2-Fluorobenzenesulfinate (3la)
Ethyl 4-Methylbenzenesulfinate (3ab)20
Colorless oil; yield: 36.2 mg (42%).
Colorless oil; yield: 82.6 mg (90%).
1H NMR (600 MHz, CDCl3):  = 7.87–7.81 (m, 1 H), 7.58–7.51 (m, 1 H),
7.34 (t, J = 7.8 Hz, 1 H), 7.15 (t, J = 8.4 Hz, 1 H), 3.57 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 159.8 (d, J = 250.8 Hz), 134.4 (d, J = 7.9
Hz), 131.1 (d, J = 15.6 Hz), 126.7 (d, J = 2.0 Hz), 124.5 (d, J = 3.6 Hz),
116.2 (d, J = 20.3 Hz), 50.8.
1H NMR (400 MHz, CDCl3):  = 7.60 (d, J = 8.4 Hz, 2 H), 7.33 (d, J = 8.4
Hz, 2 H), 4.16–4.04 (m, 1 H), 3.77–3.67 (m, 1 H), 2.42 (s, 3 H), 1.27 (t, J
= 6.8 Hz, 3 H).
13C NMR (150 MHz, CDCl3):  = 142.6, 141.8, 129.6, 125.2, 60.7, 21.5,
15.5.
HRMS (ESI): m/z [M + H]+ calcd for C7H8FO2S+: 175.0224; found:
175.0225.
Ethyl 4-Methoxybenzenesulfinate (3db)20
Pale-yellow oil; yield: 76.1 mg (76%).
Methyl 2-Chlorobenzenesulfinate (3ma)16
1H NMR (600 MHz, CDCl3):  = 7.64 (d, J = 9.0 Hz, 2 H), 7.01 (d, J = 9.0
Hz, 2 H), 4.15–4.03 (m, 1 H), 3.86 (s, 3 H), 3.77–3.67 (m, 1 H), 1.27 (t,
J = 7.2 Hz, 3 H).
Colorless oil; yield: 44.1 mg (46%).
1H NMR (600 MHz, CDCl3):  = 7.94–7.91 (m, 1 H), 7.50–7.45 (m, 2 H),
7.44–7.41 (m, 1 H), 3.57 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 162.6, 136.5, 127.0, 114.4, 60.5, 55.5,
15.6.
13C NMR (150 MHz, CDCl3):  = 141.0, 133.4, 132.7, 130.3, 127.1,
126.6, 51.2.
Ethyl 4-Chlorobenzenesulfinate (3fb)15b
Pale-yellow oil; yield: 84.8 mg (83%).
Methyl 2-Bromobenzenesulfinate (3na)
Pale-yellow oil; yield: 61.0 mg (52%).
1H NMR (400 MHz, CDCl3):  = 7.66 (d, J = 8.4 Hz, 2 H), 7.52 (d, J = 8.4
Hz, 2 H), 4.18–4.05 (m, 1 H), 3.80–3.67 (m, 1 H), 1.29 (t, J = 7.2 Hz,
3 H).
1H NMR (600 MHz, CDCl3):  = 7.90 (dd, J = 7.8, 1.2 Hz, 1 H), 7.59 (dd,
J = 7.8, 0.6 Hz, 1 H), 7.50 (dd, J = 7.2, 1.2 Hz, 1 H), 7.39 (dd, J = 7.2, 1.2
Hz, 1 H), 3.56 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 143.3, 138.4, 129.3, 126.7, 61.2, 15.5.
13C NMR (150 MHz, CDCl3):  = 142.7, 133.6, 133.5, 127.7, 126.9,
121.0, 51.4.
Ethyl 4-Bromobenzenesulfinate (3gb)15b
HRMS (ESI): m/z [M + H]+ calcd for C7H8BrO2S+: 234.9423; found:
Pale-yellow oil; yield: 104.5 mg (84%).
1H NMR (600 MHz, CDCl3):  = 7.66 (d, J = 8.4 Hz, 2 H), 7.57 (d, J = 8.4
Hz, 2 H), 4.15–4.05 (m, 1 H), 3.77–3.68 (m, 1 H), 1.27 (t, J = 7.1 Hz,
3 H).
234.9422.
Methyl 2,4-Dimethylbenzenesulfinate (3oa)
Pale-yellow oil; yield: 82.4 mg (89%).
13C NMR (150 MHz, CDCl3):  = 143.9, 132.2, 126.9, 126.8, 61.2, 15.5.
1H NMR (600 MHz, CDCl3):  = 7.77 (d, J = 7.8 Hz, 1 H), 7.18 (d, J = 7.8
Hz, 1 H), 7.05 (s, 1 H), 3.45 (s, 3 H), 2.43 (s, 3 H), 2.36 (s, 3 H).
Ethyl 2,4-Dimethylbenzenesulfinate (3ob)
13C NMR (150 MHz, CDCl3):  = 142.7, 138.2, 136.4, 132.0, 126.9,
Pale-yellow oil; yield: 80.5 mg (81%).
1H NMR (400 MHz, CDCl3):  = 7.80 (d, J = 8.0 Hz, 1 H), 7.19 (d, J = 8.0
Hz, 1 H), 7.05 (s, 1 H), 4.15–4.00 (m, 1 H), 3.75–3.65 (m, 1 H), 2.45 (s,
3 H), 2.37 (s, 3 H), 1.26 (t, J = 7.2 Hz, 3 H).
124.8, 49.6, 21.3, 17.9.
HRMS (ESI): m/z [M + H]+ calcd for C9H13O2S+: 185.0631; found:
185.0631.
13C NMR (100 MHz, CDCl3):  = 142.5, 139.2, 136.2, 131.8, 127.0,
124.4, 60.7, 21.3, 17.9, 15.5.
Methyl 2,4-Dichlorobenzenesulfinate (3pa)
Pale-yellow oil; yield: 103.5 mg (92%).
HRMS (ESI): m/z [M + H]+ calcd for C10H15O2S+: 199.0787; found:
199.0788.
1H NMR (600 MHz, CDCl3):  = 7.86 (d, J = 9.0 Hz, 1 H), 7.47–7.43 (m,
2 H), 3.57 (s, 3 H).
13C NMR (150 MHz, CDCl3):  = 139.8, 139.2, 133.5, 130.2, 127.8,
127.6, 51.3.
Ethyl 2,4-Dichlorobenzenesulfinate (3pb)
Pale-yellow oil; yield: 106.7 mg (89%).
© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–H

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H. Zhou et al.
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1H NMR (400 MHz, CDCl3):  = 7.88 (d, J = 8.8 Hz, 1 H), 7.49–7.43 (m,
2 H), 4.25–4.10 (m, 1 H), 3.92–3.80 (m, 1 H), 1.31 (t, J = 6.8 Hz, 3 H).
13C NMR (150 MHz, CDCl3):  = 140.7, 139.0, 133.3, 130.1, 127.6,
Octyl 4-Methylbenzenesulfinate (3ai)15c
Colorless oil; yield: 122.3 mg (91%).
1H NMR (600 MHz, CDCl3):  = 7.57 (d, J = 7.8 Hz, 2 H), 7.31 (d, J = 7.8
Hz, 2 H), 4.04–3.96 (m, 1 H), 3.62–3.55 (m, 1 H), 2.41 (s, 3 H), 1.63–
1.57 (m, 2 H), 1.30–1.20 (m, 10 H), 0.85 (t, J = 7.0 Hz, 3 H).
127.4, 62.9, 15.5.
HRMS (ESI): m/z [M + H]+ calcd for C8H9Cl2O2S+: 238.9695; found:
13C NMR (150 MHz, CDCl3):  = 142.5, 141.9, 129.6, 125.2, 64.6, 31.7,
238.9695.
29.7, 29.1, 29.0, 25.7, 22.6, 21.5, 14.0.
Propyl 4-Methylbenzenesulfinate (3ac)20
Colorless oil; yield: 94.5 mg (95%).
2-Ethoxyethyl 4-Methylbenzenesulfinate (3aj)24b
1H NMR (600 MHz, CDCl3):  = 7.58 (d, J = 7.8 Hz, 2 H), 7.32 (d, J = 7.8
Hz, 2 H), 4.01–3.94 (m, 1 H), 3.60–3.52 (m, 1 H), 2.41 (s, 3 H), 1.68–
1.60 (m, 2 H), 0.90 (t, J = 7.2 Hz, 3 H).
Colorless oil; yield: 111.9 mg (98%).
1H NMR (600 MHz, CDCl3):  = 7.58 (dd, J = 9.6, 2.4 Hz, 2 H), 7.30–7.28
(m, 2 H), 4.15–4.10 (m, 1 H), 3.70–3.65 (m, 1 H), 3.57–3.54 (m, 2 H),
3.44–3.42 (m, 2 H), 2.38 (s, 3 H), 1.15 (t, J = 10.8 Hz, 3 H).
13C NMR (150 MHz, CDCl3):  = 142.5, 141.9, 129.6, 125.2, 66.1, 23.1,
13C NMR (150 MHz, CDCl3):  = 142.6, 141.5, 129.5, 125.2, 68.9, 66.4,
21.5, 10.3.
63.0, 21.3, 14.9.
Isopropyl 4-Methylbenzenesulfinate (3ad)20
Colorless oil; yield: 89.2 mg (90%).
S-p-Tolyl 4-Methylbenzenesulfinothioate (6a)24a
1H NMR (600 MHz, CDCl3):  = 7.57 (d, J = 8.4 Hz, 2 H), 7.43 (d, J = 7.8
Hz, 2 H), 7.30 (d, J = 7.8 Hz, 2 H), 7.19 (d, J = 8.4 Hz, 2 H), 2.42 (s, 3 H),
2.38 (s, 3 H).
1H NMR (600 MHz, CDCl3):  = 7.58 (d, J = 8.4 Hz, 2 H), 7.31 (d, J = 7.8
Hz, 2 H), 4.58 (dt, J = 12.6, 6.0 Hz, 1 H), 2.40 (s, 3 H), 1.36 (d, J = 6.0 Hz,
3 H), 1.23 (d, J = 6.6 Hz, 3 H).
13C NMR (150 MHz, CDCl3):  = 142.1, 140.8, 136.5, 135.4, 130.1,
13C NMR (150 MHz, CDCl3):  = 142.7, 142.4, 129.6, 125.0, 72.6, 23.9,
129.6, 126.2, 124.3, 21.5, 21.4.
23.7, 21.4.
Butyl 4-Methylbenzenesulfinate (3ae)20
Funding Information
Colorless oil; yield: 98.7 mg (93%).
1H NMR (600 MHz, CDCl3):  = 7.57 (d, J = 8.4 Hz, 2 H), 7.31 (d, J = 8.4
Hz, 2 H), 4.04–3.98 (m, 1 H), 3.63–3.56 (m, 1 H), 2.41 (s, 3 H), 1.63–
1.56 (m, 2 H), 1.38–1.30 (m, 2 H), 0.86 (t, J = 7.2 Hz, 3 H).
13C NMR (150 MHz, CDCl3):  = 142.5, 141.8, 129.6, 125.2, 64.3, 31.7,
21.4, 18.9, 13.5.
This work was supported by the National Natural Science Foundation
of China (21961035 and 21901213), the Program for Improving Sci-
entific Research Ability of Young Teachers of Northwest Normal Uni-
versity (NWNU-LKQN-17-3 and NWNU-LKQN-18-22), and the Gansu
International Scientific and Technological Cooperation Base of Water-
Retention Chemical Functional Materials.
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Isobutyl 4-Methylbenzenesulfinate (3af)13a
Colorless oil; yield: 83.2 mg (78%).
Supporting Information
1H NMR (600 MHz, CDCl3):  = 7.58 (d, J = 8.4 Hz, 2 H), 7.32 (d, J = 8.4
Hz, 2 H), 3.78 (dd, J = 9.6, 6.6 Hz, 1 H), 3.33 (dd, J = 9.6, 6.6 Hz, 1 H),
2.41 (s, 3 H), 1.94–1.82 (m, 1 H), 0.89 (d, J = 7.2 Hz, 3 H), 0.88 (d, J = 6.6
Hz, 3 H).
Supporting information for this article is available online at
https://doi.org/10.1055/s-0040-1707966
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13C NMR (150 MHz, CDCl3):  = 142.5, 141.8, 129.6, 125.2, 70.3, 28.6,
21.5, 19.0.
References
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Colorless oil; yield: 62.7 mg (56%).
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© 2020. Thieme. All rights reserved. Synthesis 2020, 52, A–H