Palladium Catalyzed Direct Carbonylative Thiomethylation of Aryldiazonium Salts and Amines with 4-(Methylthio)-2-Butanone as (Methylthio) Transfer Agent

Article abstract of DOI:10.1021/acs.joc.1c00665

Herein, an interesting palladium-catalyzed procedure for the direct carbonylative thiomethylation of aromatic amine derivatives with 4-methylthio-2-butanone is developed. Using 4-methylthio-2-butanone as (methylthio) transfer agent, a variety of corresponding thioesters are obtained with moderate to good yields under base-free condition. In addition, good functional group tolerance can be observed.

Full text of DOI:10.1021/acs.joc.1c00665

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Article
Palladium Catalyzed Direct Carbonylative Thiomethylation of
Aryldiazonium Salts and Amines with 4‑(Methylthio)-2-Butanone as
(Methylthio) Transfer Agent
Qingqiang Tian,§ Shasha Xu,§ Chiying Zhang, Xinyi Liu, Xiangwei Wu, and Yahui Li*
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ABSTRACT: Herein, an interesting palladium-catalyzed proce-
dure for the direct carbonylative thiomethylation of aromatic amine
derivatives with 4-methylthio-2-butanone is developed. Using 4-
methylthio-2-butanone as (methylthio) transfer agent, a variety of
corresponding thioesters are obtained with moderate to good
yields under base-free condition. In addition, good functional
group tolerance can be observed.
Scheme 1. Previous Reports and the Present Strategy
INTRODUCTION
■
Thioesters are extremely important in biochemistry due to
their expedient biological properties.1 Since they are more
active than esters due to mesomeric effects based on inferior
orbital overlap,2 thioesters are also used as building blocks in
many reactions.3 Consequently, the development of new
catalytic protocols for the preparation of thioesters has
attracted continuous interest in organic synthesis.4
Transition metal-catalyzed carbonylation presents an
efficient and direct way for the synthesis of carbonyl-containing
moieties.5 Using carbonylative reaction for the preparation of
thioesters is attractive. In fact, a lot of metal-catalyzed
thiocarbonylations have been reported in the past decade.6
However, the majority of the reported thiocarbonylations rely
on thiols as the nucleophiles. Therefore, the challenges brought
by the unpleasant odor and poisonous catalyst properties of
thiols still remain.7 In 2016, Jiang et al. described the Pd-
catalyzed thiocarbonylation using sodium sulfinates as the thiol
surrogate (Scheme 1B).8a Later, the same group reported a
practical protocol for the straightforward construction of α-
ketothioesters available to be used as a stable and convenient
1,2-dicarbonyl reagent.8b In 2018, Lee et al. reported a Pd-
catalyzed carbonylation of thioacetates and aryl iodides
(Scheme 1C).9 In 2020, Wu et al. reported a Ni-catalyzed
thiocarbonylation reaction of arylboronic acids with sulfonyl
chlorides as the sulfur precursor.10 Recently, our group has also
reported the palladium-catalyzed intermolecular transthioe-
therification of aryl halides with thioethers using KOtBu as the
base.11 However, most of these protocols require a
stoichiometric amount of bases to promote the thiocarbony-
lation, which leads to not only narrow substrate scopes but also
a stoichiometric amount of waste of the reaction.
Received: March 20, 2021
Published: June 18, 2021
4-Methylthio-2-butanone is used as a food chemical
additive.12 However, the use of 4-methylthio-2-butanone as a
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methylthio transfer reagent rather than additive or solvent in
modern synthetic methodology is still rare. As methyl
mercaptan is a flammable and toxic gas, the direct use of 4-
methylthio-2-butanone as a methylthio source would be an
attractive choice.
With all these considerations in mind, in this paper, we
would like to report the first Pd-catalyzed methylthio-
carbonylation of tetrafluoroaryl diazonium salts or aromatic
amines using 4-methylthio-2-butanone as a reliable methylthio
transfer reagent under base-free condition.
74% (Table 1, Entry 11). Reducing the amount of solvent can
increase the effective collision among molecules, which is
conductive to the reaction. Interestingly, the reaction at 60 °C
produced the highest yield of desired product 3a (Table 1,
Entry 13). And decreasing yields were obtained at low or high
temperature (80 °C, 50 °C; Table 1, Entries 11, 12).
Considering the solubility of the organic salt, different solvents
were tested. When the reaction was carried out in DMSO,
DME, or iPrOH, the yield of the desired product 3a decreased
(Table 1, Entries 14, 15, and 16). Furthermore, in the absence
ligand, only trace amounts of the desired product were
observed (Table 1, Entry 17). This may be due to that the
ligand can make the catalyst more stable and accelerate the
reduction and elimination. Finally, the amount of 4-
methylthio-2-butanone was also studied, and when 1 equiv
of 4-methylthio-2-butanone was used, 3a was observed in 59%
yield (Table 1, Entry 19). Overall, it was found that the use of
5 mol % of Pd(OAc)2 and brettphos under CO atmosphere
(10 bar) at 60 °C gave 3a in 83% yield.
RESULTS AND DISCUSSION
■
At the beginning of our study, 4-methoxybenzenediazonium
tetrafluoroborate (1) and 4-methylthio-2-butanone (2) were
selected as a model substrate. First, the effect of palladium salts
was tested (as shown in Table 1). Pd(OAc)2 showed the best
a
Table 1. Optimization of Reaction Conditions
Considering that arenediazoniumtetrafluoroborates are one
of the aromatic amine derivatives,13 we decided to examine
carbonylative thiomethylation reactions with aromatic amine
directly. To our delight, when 1 equiv of HBF4 and 1.5 equiv of
tBuONO were used as additives, 13% of the desired product
could be obtained (Table 2, Entry 1). The yield was improved
b
entry
catalyst
ligand
solvent
yield (%)
1
Pd(MeCN)2Cl2
Pd2(dba)2
Pd(ally)Cl2
Pd(TFA)2
Pd(OAc)2
Pd/C
L1
L1
L1
L1
L1
L1
L2
L3
L4
L5
L1
L1
L1
L1
L1
L1
−
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
DMSO
DME
30
44
46
61
65
2
3
Table 2. Optimization of Reaction Conditions of Aniline
a
4
and 4-Methylthio-2-butanone
5
c
6
43
7
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
−
66
61
58
53
8
9
b
entry
HBF4 (equiv)
temp (°C)
yield (%)
10
11
12
13
14
15
16
17
18
19
c
1
2
3
4
5
6
1
3
3
3
3
5
60
60
25
80
100
60
13
63
20
41
trace
26
74
d
75
e
83
e
25
69
74
e
e
iPrOH
tBuOH
tBuOH
tBuOH
a
e
e
Reaction conditions: 4 (0.2 mmol), 2 (0.6 mmol), HBF4 (0.2−1.0
t
trace
trace
mmol), BuONO (0.3 mmol), Pd(OAc)2 (5 mol %), brettphos (5
mol %), CO (10 bar), BuOH (1 mL), 25−100 °C, 16 h. Yield
determined by GC using n-dodecane as an internal standard.
L1
b
t
f
Pd(OAc)2
L1
59
a
Reaction conditions: 1 (0.2 mmol), 2 (0.6 mmol), Pd salt (5.0 mol
b
%), solvent (2.0 mL), CO (10 bar), 80 °C, 16 h. Yield determined
to 63% when HBF4 was increased to 3 equiv (Table 2, Entry
2). When 5 equiv of HBF4 was applied, the yield decreased to
26% (Table 2, Entry 6). This may be due to the instability of
the thioester under acidic conditions. Next, the effect of
temperature was studied, but no better yield was obtained.
Especially, when the reaction was conducted at 100 °C, only a
trace amount of desired products was obtained (Table 2, Entry
5). It is possible that aryldiazonium salts and the desired
product thioesters are not stable under high-temperature
condition, especially under acid condition.
In order to examine the scope of this method, different aryl
tetrafluoroborate diazonium salts were evaluated for direct
carbonylative thiomethylation (as shown in Scheme 2). First,
electron-donating substrates were tested under the optimized
conditions. Both methyl- and tert-butyl- substituted aryl
tetrafluoroborate diazonium salts reacted smoothly and
provided the corresponding thioesters in 86% and 69% yield,
respectively (Scheme 2, 3b and 3c). Simultaneously, the
c
by GC using n-dodecane as an internal standard. Solvent (1.0 mL).
d
e
f
Solvent (1.0 mL), 50 °C. Solvent (1.0 mL), 60 °C. Solvent (1.0
mL), 2 (0.2 mmol), 60 °C.
result, and gave the desired product 3a with 65% GC yield
(Table 1, Entry 5). Interestingly, heterogeneous catalyst Pd/C
can be also used in this catalytic protocol, which gave the
desired product with a 43% yield (Table 1, Entry 6). Screening
of different phosphine ligands revealed that brettphos is the
most effective ligand for delivering the desired thioester
t
product. Subsequently, the amount of BuOH was studied.
t
When 1 mL of BuOH was used, the yield was increased to
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Scheme 2. Substrate Scope of Diazonium Tetrafluoroborate
and Aromatic Amine
substrates containing heteroatom substituents (S, O) also
reacted well, and gave the desired products with moderate to
good yields (66−84% yield, Scheme 2, 3e−3i). Interestingly,
chloro and bromo groups can also be tolerated by the
employed reaction conditions, with no observable competitive
byproducts detected by GC-MS (Scheme 2, 3j and 3k).
Electron-withdrawing groups can also be tolerated and gave
the corresponding products, such as 3-acetylbenzene-diazo-
nium and 4-acetylbenzene-diazonium (Scheme 2, 3l and 3m).
Furthermore, substrates containing −CN and −SO2Me can
react smoothly (Scheme 2, 3o and 3p). Notably, Alkynes can
also be tolerated in this system (Scheme 2, 3s). In order to
prove the synthetic potential of this methodology, testing of
different 4-(methylthio)-2-butanone derivatives were also
conducted under our standard conditions. As shown in
Scheme 2, good yield of the desired thioester can be produced
by reacting 4-methoxybenzenediazonium tetrafluoroborate
with 1-(pentylthio) hexan-3-one (Scheme 2, 3t). Similarly,
when 4-(benzylthio) pentan-2-one and 4-(phenethylthio)
pentan-2-one substituted 4-(methylthio)-2-butanone were
employed, good yields of the desired thioester can be obtained
from the corresponding diazonium salt, and 3u and 3z were
obtained in 89% and 82% yields, respectively.
Next we turned our attention to evaluating the scope of the
aromatic amines carbonylative thiomethylation. As shown in
Scheme 2, the use of aromatic amines instead of aryldiazonium
salts as precursors affords thioesters. The reaction showed a
good functional group tolerance, for example, −Br (3k), −CN
(3o), −CO2Me (3n), and −SO2Me (3p) can be tolerated,
which provides the possibility for further synthetic trans-
formations.
To demonstrate the practical utility, the reaction of 4-
methoxybenzenediazonium tetrafluoroborate and 4-methyl-
thio-2-butanone was performed at the 5 mmol scale. As
illustrated in Scheme 3, the desired S-methyl-4-methoxy
benzothioate was formed in 65% yield.
Scheme 3. Gram Scale Experiment
To prove the synthetic practicability of this method, three
reactions have been exemplified to build C−N, C−C, C−O
bonds (see the Supporting Information). Related amides,
ketones, and carboxylic acids were efficiently obtained using
thioesters as the starting substrates under relatively mild
reaction conditions.
To gain insight into the reaction mechanism, control
experiments were conducted under different reaction con-
ditions (see the Supporting Information). When 4-methylthio-
2-butanone was under the catalyst-free condition, no methyl
vinyl ketone was observed. However, when 4-methylthio-2-
butanone was applied under the standard reaction conditions,
methyl vinyl ketone was observed with the NMR yield of 8%.
Furthermore, increasing the loading of Pd(OAc)2 to 50 mol %,
the yield of the expected methyl vinyl ketone was improved to
a
Reaction conditions: 1 (0.2 mmol), 2 (0.6 mmol), Pd(OAc)2 (5 mol
%), Brettphos (5 mol %), tBuOH (1 mL), CO (10 bar), 60 °C, 16 h.
Yields refer to the isolated products. Reaction conditions: 4 (0.2
b
t
mmol), 2 (0.6 mmol), HBF4 (0.6 mmol), BuONO (0.3 mmol),
Pd(OAc)2 (5 mol %), brettphos (5 mol %), CO (10 bar), tBuOH (1
c
mL), 60 °C, 16 h, isolated yield. Reaction conditions: 1 (0.2 mmol),
1-(pentylthio)hexan-3-one (0.6 mmol), Pd(OAc)2 (5 mol %),
t
Brettphos (5 mol %), BuOH (1 mL), CO (10 bar), 60 °C, 16 h.
d
Reaction conditions: 1 (0.2 mmol), 4-(benzylthio) pentan-2-one
t
(0.6 mmol), Pd(OAc)2 (5 mol %), Brettphos (5 mol %), BuOH (1
mL), CO (10 bar), 60 °C, 16 h. Reaction conditions: 1 (0.2 mmol),
4-(phenethylthio) pentan-2-one (0.6 mmol), Pd(OAc)2 (5 mol %),
e
t
Brettphos (5 mol %), BuOH (1 mL), CO (10 bar), 60 °C, 16 h.
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General Procedure of Diazonium Salt Carbonylative
Thiomethylation. A 4 mL screw-cap vial was charged with
ArN2BF4 (0.2 mmol), Brettphos (5.36 mg, 5 mol %), Pd(OAc)2
(2.24 mg, 5 mol %), and an oven-dried stirring bar. Then 2 (0.6
50%. The results indicated that the palladium salt plays an
important role in this C−S bond cleavage process.
On the basis of the above investigations and references, a
tentative mechanism for this carbonylative thiomethylation
chemistry is depicted in Scheme 4.14 We propose that the
t
mmol) and BuOH (1 mL) were injected by syringe. The vial was
closed by a Teflon septum and a phenolic cap and connected to the
atmosphere through a needle. Then the vial was fixed in an alloy plate
and put into a Parr 4560 series autoclave (300 mL). At room
temperature, the autoclave was flushed with carbon monoxide for
three times and 10 bar of carbon monoxide was charged. The
autoclave was placed on a heating plate equipped with magnetic
stirring and an aluminum block. The reaction was heated at 60 °C for
16 h. Afterward, the autoclave was cooled to room temperature and
the pressure was carefully released. After removal of solvent under
reduced pressure, pure product was obtained by column chromatog-
raphy on silica gel (eluent: pentane/EA = 500−30:1).
Scheme 4. Possible Mechanism for the Carbonylative
Thiomethylation
General Procedure of Aromatic Amine Carbonylative
Thiomethylation. A 4 mL screw-cap vial was charged with aromatic
amine (0.2 mmol), Brettphos (5.36 mg, 5 mol %), Pd(OAc)2 (2.24
mg, 5 mol %), and an oven-dried stirring bar. Then HBF4 (50 wt %,
t
0.6 mmol), 4-(methylthio)-2-butanone (70.8 mg, 0.6 mmol), BuOH
t
(1 mL), and BuONO (0.3 mmol) were injected by syringe. The vial
mechanism involves two catalytic cycles. Initially, the catalyst
precursor could be reduced to Pd(0) species in the presence of
CO and brettphos ligand. Then, Pd(0)L insert into the carbon
diazonium bond to give the intermediate 2, which is followed
by CO insertion for the formation of acyl intermediate 3. In
addition, the organometallic nucleophile 8 is formed via the β-
elimination of 4-methylthio-2-butanone. Next, intermediate 4
could be formed through the transmetalation between
intermediate 3 and the organometallic nucleophile 8. Finally,
the desired thioester product 5 could be formed by classic
reductive elimination of intermediate 4 and regenerate Pd(0)L.
was closed by a Teflon septum and a phenolic cap and connected to
the atmosphere through a needle. Then the vial was fixed in an alloy
plate and put into a Parr 4560 series autoclave (300 mL). At room
temperature, the autoclave was flushed with carbon monoxide for
three times and 10 bar of carbon monoxide was charged. The
autoclave was placed on a heating plate equipped with magnetic
stirring and an aluminum block. The reaction was heated at 60 °C for
16 h. Afterward, the autoclave was cooled to room temperature and
the pressure was carefully released. After removal of solvent under
reduced pressure, pure product was obtained by column chromatog-
raphy on silica gel (eluent pentane/EA = 500−30:1).
General Procedure of Gram Scale Experiment. A 25 mL
screw-cap vial was charged with 4-methoxybenzene-diazonium
tetrafluoroborate (1.1 g, 5.0 mmol), Brettphos (134.0 mg, 5 mol
%), Pd(OAc)2 (56.0 mg, 5 mol %), and an oven-dried stirring bar.
CONCLUSIONS
■
In conclusion, an interesting palladium-catalyzed procedure for
the direct carbonylative thiomethylation of various arenedia-
zonium tetrafluoroborates has been developed with a good
functional group compatibility. A variety of desired thioesters
can be produced with moderate to excellent yields using 4-
methylthio-2-butanone as methylthio transfer agent. In
addition, the use of aromatic amines instead of aryldiazonium
salts as precursors also affords thioesters in moderate to good
yields.
t
Then 4-(methylthio)-2-butanone (1.44 mg, 2.4 mmol) and BuOH
(15 mL) were injected by syringe. The vial was closed by a Teflon
septum and a phenolic cap and connected to the atmosphere through
a needle. Then the vial was fixed in an alloy plate and put into a Parr
4560 series autoclave (300 mL). At room temperature, the autoclave
was flushed with carbon monoxide for three times and 10 bar of
carbon monoxide was charged. The autoclave was placed on a heating
plate equipped with magnetic stirring and an aluminum block. The
reaction was heated at 60 °C for 16 h. Afterward, the autoclave was
cooled to room temperature and the pressure was carefully released.
After removal of solvent under reduced pressure, pure product was
obtained by column chromatography on silica gel (eluent: pentane/
EA = 100−30:1) to obtain the product 3aa as colorless liquid (600.0
mg, yield 65%).
Synthesis of N-Benzyl-4-methoxybenzamide (3ab). A mixture of
S-methyl 4-methoxybenzothioate (58.0 mg, 0.31 mmol), phenyl-
methanamine (100 mg, 0.9 mmol), K2CO3 (171.0 mg, 1.2 mmol),
and DMF (4 mL) was stirred in a 100 mL round-bottom flask at 120
°C under reflux for 12 h. Afterward, the autoclave was cooled to room
temperature, and then a saturated solution of NaCl (25 mL) was
added. The aqueous phase was extracted with EA (4 × 10 mL) and
dried over anhydrous Na2SO4 and concentrated in a vacuum with
silica gel added. The residue was purified by flash chromatography
(PE/EA = 20:1) to obtain the product as a white solid (42.0 mg, yield
53%).
EXPERIMENTAL SECTION
■
General Information. Most of the chemicals were purchased
from Aladdin, TCI, Alfa Aesar, Energy-Chemical and used as such
unless stated otherwise. Solvents (anhydrous and under inert
atmosphere) were collected from the solvent purification system by
MBRAUN and used under standard Schlenk technique. NMR spectra
were recorded on Bruker Avance 600 and Bruker ARX 400
spectrometers. Chemical shifts (ppm) are given relative to solvent:
references for CDCl3 were 7.26 ppm (1H NMR) and 77.00 ppm (13C
NMR). Multiplets were assigned as s (singlet), d (doublet), t (triplet),
q (quartet), p (pentet), dd (doublet of doublet), m (multiplet), and
br. s (broad singlet). GC-yields were calculated using isooctane as
internal standard. All measurements were carried out at room
temperature unless otherwise stated. GC-MS analysis was performed
on a Shimadzu 2010 instrument and Rtx-5 capillary column. High
resolution mass spectra (HRMS) were recorded on Agilent 6210. The
data are given as mass units per charge (m/z). Gas chromatography
analysis was performed on a Shimadzu 2010 instrument with an FID
detector and Rtx-5 capillary column. The products were isolated from
the reaction mixture by column chromatography on silica gel 60,
0.063−0.2 mm, 70−230 mesh (Merck). The arenediazonium salts
and 4-methylthio-2-butanone derivative were all synthesized as
described preciously.
Synthesis of Benzophenone (3ac). A mixture of S-methyl
benzothioate (45.6 mg, 0.3 mmol), trimethoxy(phenyl)silane (89.1
mg, 0.45 mmol), Pd(PPh3)4 (17.0 mg, 5 mol %), CuI (57.0 mg, 0.3
mmol), TBAF (15.7 mg, 20 mol %), and THF (4 mL) was stirred in a
25 mL tube at 60 °C under reflux for 0.5 h. Afterward, the autoclave
was cooled to room temperature, and then the residue was purified by
flash chromatography (PE/EA = 20:1) to obtain the product as a
white solid (26.0 mg, yield 49%)
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Synthesis of 4-(Benzyloxy)benzoic acid (3ad). A mixture of S-
methyl 4-(benzyloxy)benzothioate (77.4 mg, 0.3 mmol), KOH (672.0
mg, 12.0 mmol), and EtOH (10 mL) was stirred in a 100 mL round-
bottom flask at 80 °C under reflux for 30 h. Afterward, the autoclave
was cooled to room temperature, and then a solution of HCl (1 mol/
L, 25 mL) was added. The aqueous phase was extracted with EA (4 ×
10 mL) and dried over anhydrous Na2SO4 and concentrated in a
vacuum with silica gel added. The residue was purified by flash
chromatography (PE/EA = 10:1) to obtain the product as a white
solid (38.0 mg, yield 56%).
123.10, 107.96, 107.13, 101.86, 11.70. GC-MS (EI, 70 ev) m/z (%) =
196 (M+, 14), 149 (100), 121 (37), 91 (9), 65 (30), 53 (5).
S-Methyl 4-chlorobenzothioate (3j).15 Purified by column
1
chromatography (PE). Yield = 28.6 mg (77%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ 7.96−7.82 (m, 2H), 7.44−7.36 (m, 2H),
2.47 (d, J = 1.2 Hz, 3H). 13C NMR (151 MHz, CDCl3) δ 191.15,
139.61, 135.38, 128.86, 128.43, 11.73. GC-MS (EI, 70 ev) m/z (%) =
186 (M+, 8), 141 (30), 139 (100), 111 (47), 75 (32), 50 (15).
S-Methyl 4-bromobenzothioate (3k).16 Purified by column
1
chromatography (PE). Yield = 27.8 mg (60%). Colorless liquid. H
S-Methyl 4-methoxybenzothioate (3a).11 Purified by column
NMR (600 MHz, CDCl3) δ 7.94−7.65 (m, 2H), 7.65−7.50 (m, 2H),
2.47 (s, 3H). 13C NMR (151 MHz, CDCl3) δ 191.33, 135.80, 131.85,
128.54, 128.24, 11.73. GC-MS (EI, 70 ev) m/z (%) = 232 (M+, 10),
183 (100), 155 (38), 75 (45), 50 (40).
1
chromatography (PE). Yield = 29.5 mg (81%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ = 7.93 (dd, J = 9.3, 2.4, 2H), 6.90 (t, J =
5.9, 2H), 3.84 (s, 3H), 2.44 (s, 3H). 13C NMR (151 MHz, CDCl3) δ
= 190.89, 163.64, 130.00, 129.21, 113.71, 55.43, 11.52. GC-MS (EI,
70 ev) m/z (%) = 182 (M+, 5), 135 (100), 92 (17), 77 (25), 50 (7).
S-Methyl 4-methylbenzothioate (3b).14 Purified by column
S-Methyl 3-acetylbenzothioate (3l). Purified by column chroma-
tography (PE). Yield = 21.7 mg (56%). White solid, mp 30−33 °C.
1H NMR (600 MHz, CDCl3) δ = 8.68−8.35 (m, 1H), 8.24−8.04 (m,
2H), 7.54 (m, 1H), 2.73−2.59 (m, 3H), 2.54−2.43 (m, 3H). 13C
NMR (151 MHz, CDCl3) δ = 196.92, 191.71, 137.47, 132.47, 131.29,
129.02, 126.89, 26.60, 11.78. GC-MS (EI, 70 ev) m/z (%) = 194 (M+,
4), 147 (100), 119 (18), 91 (35), 76 (19), 50 (12). HRMS (ESI)
calcd for C10H11O2S [M + H]+: 195.0480, found 195.0475.
S-Methyl 4-acetylbenzothioate (3m). Purified by column
chromatography (PE). Yield = 19.8 mg (51%). White solid, mp 27
°C. 1H NMR (600 MHz, CDCl3) δ = 8.02 (q, J = 8.2, 4H), 2.63 (d, J
= 0.9, 3H), 2.50 (d, J = 1.0, 3H). 13C NMR (151 MHz, CDCl3) δ =
197.21, 191.75, 140.36, 140.24, 128.47, 127.30, 26.79, 11.85. GC-MS
(EI, 70 ev) m/z (%) = 194 (M+, 6), 147 (100), 119 (19), 91 (26), 76
(17), 50(12). HRMS (ESI) calcd for C10H11O2S [M + H]+: 195.0474,
found 195.0480.
1
chromatography (PE). Yield = 28.6 mg (86%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ = 7.86 (d, J = 8.2, 2H), 7.28−7.18 (m,
2H), 2.45 (s, 3H), 2.40 (s, 3H). 13C NMR (151 MHz, CDCl3) δ =
191.97, 144.01, 134.59, 129.19, 127.15, 21.58, 11.55. GC-MS (EI, 70
ev) m/z (%) = 166 (M+, 8), 119 (100), 91 (55), 65 (21), 51 (4).
S-Methyl 4-(tert-butyl)benzothioate (3c).11 Purified by column
chromatography (PE). Yield = 28.7 mg (69%). White solid, mp 64−
1
66 °C. H NMR (600 MHz, CDCl3) δ = 7.90 (d, J = 8.4, 2H), 7.45
(d, J = 8.4, 2H), 2.46 (s, 3H), 1.33 (s, 9H). 13C NMR (151 MHz,
CDCl3) δ = 191.98, 157.00, 134.48, 126.99, 125.49, 35.10, 31.04,
11.55. GC-MS (EI, 70 ev) m/z (%) = 208 (M+, 3), 161 (100), 146
(15), 118 (16), 91 (16), 77 (9), 51 (6).
S-Methyl benzothioate (3d).11 Purified by column chromatog-
1
raphy (PE). Yield = 21.3 mg (70%). Colorless liquid. H NMR (600
Methyl 4-((methylthio)carbonyl)benzoate (3n). Purified by
column chromatography (PE). Yield = 35.7 mg (85%). White solid,
mp 59−62 °C. 1H NMR (600 MHz, CDCl3) δ = 8.14−8.05 (m, 2H),
8.05−7.90 (m, 2H), 3.93 (d, J = 4.3, 3H), 2.50 (d, J = 4.9, 3H). 13C
NMR (151 MHz, CDCl3) δ = 191.79, 166.06, 140.31, 134.09, 129.80,
127.00, 52.38, 11.81. GC-MS (EI, 70 ev) m/z (%) = 210 (M+, 3), 163
(100), 135 (25), 120 (8), 103 (18), 76 (20), 50 (14). HRMS (ESI)
calcd for C10H11O3S [M + H]+: 211.0423, found 211.0425.
S-Methyl 4-cyanobenzothioate (3o). Purified by column
chromatography (PE). Yield = 18.1 mg (51%). White solid, mp
MHz, CDCl3) δ 7.99−7.93 (m, 2H), 7.56 (m, 1H), 7.48−7.41 (m,
2H), 2.47 (s, 3H). 13C NMR (151 MHz, CDCl3) δ 192.38, 137.08,
133.20, 128.55, 127.09, 11.66. GC-MS (EI, 70 ev) m/z (%) = 152
(M+, 7), 105 (100), 77 (68), 51 (30).
S-Methyl 4-(methylthio)benzothioate (3e).11 Purified by column
1
chromatography (PE). Yield = 33.3 mg (84%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ = 7.86 (d, J = 8.6, 2H), 7.26−7.21 (m,
2H), 2.50 (s, 3H), 2.45 (s, 3H). 13C NMR (151 MHz, CDCl3) δ =
191.28, 146.03, 133.37, 127.43, 125.05, 14.81, 11.55. GC-MS (EI, 70
ev) m/z (%) = 198 (M+, 14), 151 (100), 123 (14), 108 (13), 79 (12),
50 (8).
1
54−56 °C. H NMR (600 MHz, CDCl3) δ = 8.04 (d, J = 8.3, 2H),
7.75 (d, J = 8.3, 2H), 2.51 (s, 3H). 13C NMR (151 MHz, CDCl3) δ =
191.01, 140.09, 132.45, 127.54, 117.74, 116.56, 11.91. GC-MS (EI, 70
ev) m/z (%) = 177 (M+, 7), 130 (100), 102 (45), 75 (18), 50 (9).
HRMS (ESI) calcd for C9H8NOS [M + H]+: 178.0321, found
178.0327.
S-Methyl 3,4,5-trimethoxybenzothioate (3f). Purified by column
chromatography (PE). Yield = 37.8 mg (78%). White solid, mp 53−
1
56 °C. H NMR (600 MHz, CDCl3) δ = 7.22 (s, 2H), 3.89 (dd, J =
10.6, 4.7, 9H), 2.46 (s, 3H). 13C NMR (151 MHz, CDCl3) δ =
191.41, 153.09, 142.66, 132.29, 104.57, 60.94, 56.14, 11.81. GC-MS
(EI, 70 ev) m/z (%) = 242 (M+, 18), 195 (100), 152 (9), 122 (8),
109 (9), 66 (12). HRMS (ESI) calcd for C11H15O4S [M + H]+:
243.0686, found 243.0691.
S-Methyl 4-(methylsulfonyl)benzothioate (3p). Purified by
column chromatography (PE/EtOAc 30:1). Yield = 41.4 mg (90%).
1
White solid, mp 142−144 °C. H NMR (600 MHz, CDCl3) δ =
S-Methyl 4-(benzyloxy)benzothioate (3g).11 Purified by column
chromatography (PE). Yield = 41.3 mg (80%). White solid, mp 65−
8.21−8.08 (m, 2H), 8.03 (d, J = 8.5, 2H), 3.07 (s, 3H), 2.52 (s, 3H).
13C NMR (151 MHz, CDCl3) δ = 191.11, 144.38, 141.09, 127.96,
127.78, 44.30, 11.96. GC-MS (EI, 70 ev) m/z (%) = 230 (M+, 4), 183
(100), 121 (55), 104 (18), 76 (35), 50 (20). HRMS (ESI) calcd for
C9H11O3S2 [M + H]+: 231.0144, found 231.0150.
1
68 °C. H NMR (600 MHz, CDCl3) δ = 8.07−7.79 (m, 2H), 7.38
(m, 5H), 7.04−6.83 (m, 2H), 5.12 (s, 2H), 2.45 (s, 3H). 13C NMR
(151 MHz, CDCl3) δ = 190.84, 162.81, 136.15, 130.22, 129.25,
128.65, 128.19, 127.41, 114.61, 70.18, 11.54. GC-MS (EI, 70 ev) m/z
(%) = 258 (M+, 2), 211 (40), 91 (100), 65 (14).
S-Methyl [1,1′-biphenyl]-4-carbothioate (3q).11 Purified by
column chromatography (PE). Yield = 32.8 mg (72%). White solid,
1
S-Methyl 4-phenoxybenzothioate (3h).11 Purified by column
chromatography (PE). Yield = 32.2 mg (66%). White solid, mp 35−
mp 100−101 °C. H NMR (600 MHz, CDCl3) δ = 8.04 (d, J = 8.3,
2H), 7.67 (d, J = 8.3, 2H), 7.62 (d, J = 7.8, 2H), 7.47 (t, J = 7.6, 2H),
7.40 (t, J = 7.4, 1H), 2.50 (s, 3H). 13C NMR (151 MHz, CDCl3) δ =
191.88, 146.01, 139.81, 135.79, 128.92, 128.20, 127.65, 127.21,
127.20, 11.68. GC-MS (EI, 70 ev) m/z (%) = 228 (M+, 7), 182 (15),
181 (100), 152 (48), 127 (6), 76 (13).
1
37 °C. H NMR (600 MHz, CDCl3) δ 8.02−7.85 (m, 2H), 7.45−
7.34 (m, 2H), 7.19 (m, 1H), 7.09−7.03 (m, 2H), 7.01−6.92 (m, 2H),
2.46 (s, 3H). 13C NMR (151 MHz, CDCl3) δ 190.91, 162.12, 155.48,
131.64, 130.01, 129.25, 124.58, 120.11, 117.33, 11.62. GC-MS (EI, 70
ev) m/z (%) = 244 (M+, 6), 197 (100), 141 (18), 115 (21), 77 (17),
51 (9).
S-Methyl 3,5-dimethoxybenzothioate (3r).11 Purified by column
chromatography (PE). Yield = 20.8 mg (49%). White solid, mp 50−
54 °C. 1H NMR (600 MHz, CDCl3) δ 7.10 (d, J = 2.3 Hz, 2H), 6.64
(d, J = 2.2 Hz, 1H), 3.82 (s, 6H), 2.46 (s, 3H). 13C NMR (151 MHz,
CDCl3) δ 192.27, 160.81, 139.00, 105.65, 104.88, 55.57, 11.82. GC-
MS (EI, 70 ev) m/z (%) = 212 (M+, 35), 165 (100), 137 (48), 122
(43), 107 (25), 73 (29), 51 (15).
S-Methyl benzo[d][1,3]dioxole-5-carbothioate (3i).15 Purified by
column chromatography (PE). Yield = 27.0 mg (69%). White solid,
1
mp 70−72 °C. H NMR (600 MHz, CDCl3) δ = 7.59 (d, J = 8.2,
1H), 7.40 (s, 1H), 6.82 (d, J = 8.2, 1H), 6.03 (s, 2H), 2.44 (s, 3H).
13C NMR (151 MHz, CDCl3) δ = 190.58, 151.86, 148.00, 131.66,
8801
https://doi.org/10.1021/acs.joc.1c00665
J. Org. Chem. 2021, 86, 8797−8804

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
S-Methyl 3-ethynylbenzothioate (3s).17 Purified by column
chromatography (PE). Yield = 19.0 mg (54%). Colorless liquid. H
Benzophenone (3ac).24 Purified by flash chromatography (PE).
1
1
Yield = 26.0 mg (49%). White solid, mp 46−48 °C. H NMR (600
NMR (600 MHz, CDCl3) δ 8.07 (d, J = 1.7 Hz, 1H), 7.92 (ddd, J =
7.9, 1.9, 1.1 Hz, 1H), 7.66 (dt, J = 7.8, 1.4 Hz, 1H), 7.41 (t, J = 7.7
Hz, 1H), 3.13 (s, 1H), 2.48 (d, J = 0.9 Hz, 3H). 13C NMR (151 MHz,
CDCl3) δ 191.57, 137.21, 136.43, 130.72, 128.64, 127.21, 122.83,
82.38, 78.39, 11.74. GC-MS (EI, 70 ev) m/z (%) = 176 (M+, 9), 129
(100), 101 (55), 75 (37), 51 (13).
MHz, CDCl3) δ 7.84−7.76 (m, 4H), 7.58 (dd, J = 10.6, 4.2 Hz, 2H),
7.48 (t, J = 7.7 Hz, 4H).
4-(Benzyloxy)benzoic acid. (3ad).25 Purified by flash chromatog-
raphy (PE/EA = 10:1). Yield = 38.0 mg (56%). White solid, mp 173−
175 °C. 1H NMR (600 MHz, DMSO-d6) δ 7.76−7.66 (m, 2H), 7.42
(d, J = 7.4 Hz, 2H), 7.36 (t, J = 7.5 Hz, 2H), 7.29 (t, J = 7.4 Hz, 1H),
6.85−6.76 (m, 2H), 5.05 (s, 2H).
S-Pentyl 4-methoxybenzothioate (3t).18 Purified by column
1
chromatography (PE). Yield = 33.3 mg (70%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ 8.05−7.84 (m, 2H), 6.99−6.84 (m, 2H),
3.86 (d, J = 1.3 Hz, 3H), 3.04 (t, J = 7.3 Hz, 2H), 1.66 (p, J = 7.4 Hz,
2H), 1.44−1.31 (m, 4H), 0.90 (t, J = 7.3 Hz, 3H). 13C NMR (151
MHz, CDCl3) δ 190.65, 163.61, 130.23, 129.27, 113.67, 55.44, 31.06,
29.35, 28.86, 22.20, 13.88. GC-MS (EI, 70 ev) m/z (%) = 238 (M+,
3), 135 (10), 92 (8), 77 (14).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.joc.1c00665.
■
sı
1H and 13C NMR spectra for all new compounds (PDF)
FAIR data, including the primary NMR FID files, for
compounds 3a−3z, 3ab, 3ac, and 3ad (ZIP)
S-Benzyl 4-methoxybenzothioate (3u).19 Purified by column
1
chromatography (PE). Yield = 46.0 mg (89%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ 7.95 (d, J = 8.9 Hz, 2H), 7.40−7.34 (m,
2H), 7.34−7.28 (m, 2H), 7.27−7.21 (m, 1H), 6.94−6.88 (m, 2H),
4.30 (s, 2H), 3.84 (s, 3H). 13C NMR (151 MHz, CDCl3) δ 189.69,
163.81, 137.74, 129.70, 129.45, 128.93, 128.58, 127.19, 113.78, 55.46,
33.20. GC-MS (EI, 70 ev) m/z (%) = 258 (M+, 4), 135 (100), 77
(16).
AUTHOR INFORMATION
Corresponding Author
■
Yahui Li − Key Laboratory of Agri-Food Safety of Anhui
Province, School of Resources and Environment, Anhui
Agricultural University, Hefei 230036, China; State Key
Laboratory Breeding Base of Green Pesticide and Agricultural
Bioengineering, Key Laboratory of Green Pesticide and
Agricultural Bio-engineering, Ministry of Education, Guizhou
University, Guiyang 550025, China; orcid.org/0000-
0002-1980-1751; Email: yahui.li@ahau.edu.cn
S-Benzyl 4-fluorobenzothioate (3v).19 Purified by column
1
chromatography (PE). Yield = 40.0 mg (81%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ 8.03−7.95 (m, 2H), 7.37 (d, J = 7.0 Hz,
2H), 7.32 (t, J = 7.7 Hz, 2H), 7.29−7.20 (m, 1H), 7.11 (t, J = 8.6 Hz,
2H), 4.32 (s, 2H). 13C NMR (151 MHz, CDCl3,) δ 189.70, 165.93
(JC−F = 255.2 Hz), 137.29, 133.19, 129.81 (JC−F = 9.0 Hz), 128.93,
128.64, 127.36, 115.73 (JC−F = 21.1 Hz), 33.45. 19F NMR (564 MHz,
CDCl3) δ −104.61. GC-MS (EI, 70 ev) m/z (%) = 246 (M+, 10), 123
(100), 95 (25).
Authors
S-Benzyl 4-chlorobenzothioate (3w).20 Purified by column
1
Qingqiang Tian − Key Laboratory of Agri-Food Safety of
Anhui Province, School of Resources and Environment, Anhui
Agricultural University, Hefei 230036, China
Shasha Xu − Key Laboratory of Agri-Food Safety of Anhui
Province, School of Resources and Environment, Anhui
Agricultural University, Hefei 230036, China
Chiying Zhang − Key Laboratory of Agri-Food Safety of
Anhui Province, School of Resources and Environment, Anhui
Agricultural University, Hefei 230036, China
Xinyi Liu − Key Laboratory of Agri-Food Safety of Anhui
Province, School of Resources and Environment, Anhui
Agricultural University, Hefei 230036, China
chromatography (PE). Yield = 45.0 mg (86%). Colorless liquid. H
NMR (600 MHz, CDCl3) δ 7.90 (d, J = 8.7 Hz, 2H), 7.41 (d, J = 8.6
Hz, 2H), 7.39−7.35 (m, 2H), 7.31 (t, J = 7.6 Hz, 2H), 7.25 (d, J = 2.7
Hz, 1H), 4.32 (s, 2H). 13C NMR (151 MHz, CDCl3) δ 190.05,
139.80, 137.16, 135.16, 128.93, 128.91, 128.65, 128.60, 127.39, 33.47.
GC-MS (EI, 70 ev) m/z (%) = 262 (M+, 14), 139 (100), 111 (25), 91
(20).
S-Benzyl benzothioate (3x).21 Purified by column chromatography
1
(PE). Yield = 32.4 mg (71%). Colorless liquid. H NMR (600 MHz,
CDCl3) δ 7.96 (m, 2H), 7.58−7.53 (m, 1H), 7.44 (t, J = 7.8 Hz, 2H),
7.37 (d, J = 7.1 Hz, 2H), 7.31 (m, 2H), 7.25 (s, 1H), 4.32 (s, 2H). 13C
NMR (151 MHz, CDCl3) δ 191.75, 140.04, 137.17, 133.26, 128.60,
128.54, 128.49, 127.18, 126.49, 35.90, 30.39. GC-MS (EI, 70 ev) m/z
(%) = 228 (M+, 12), 105 (100), 77 (36), 51 (14).
Xiangwei Wu − Key Laboratory of Agri-Food Safety of Anhui
Province, School of Resources and Environment, Anhui
Agricultural University, Hefei 230036, China; orcid.org/
0000-0003-3589-4051
S-Phenethyl benzothioate (3y).22 Purified by column chromatog-
1
raphy (PE). Yield = 38.7 mg (80%). Colorless liquid. H NMR (600
MHz, CDCl3) δ 7.99−7.93 (m, 2H), 7.59−7.54 (m, 1H), 7.44 (t, J =
7.7 Hz, 2H), 7.32 (t, J = 7.5 Hz, 2H), 7.29−7.26 (m, 2H), 7.23 (d, J =
7.1 Hz, 1H), 3.32 (m, 2H), 2.97 (m, 2H). 13C NMR (151 MHz,
CDCl3) δ 191.75, 140.04, 137.17, 133.26, 128.60, 128.54, 128.49,
127.18, 126.49, 35.90, 30.39. GC-MS (EI, 70 ev) m/z (%) = 242 (M+,
5), 105 (100), 77 (50), 51 (18).
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.joc.1c00665
Author Contributions
S-Phenethyl 4-methoxybenzothioate (3z).19 Purified by column
§TQ and SX contributed equally to this paper.
1
chromatography (PE). Yield = 45.0 mg (82%). Colorless liquid. H
Notes
NMR (600 MHz, CDCl3) δ 7.95 (d, J = 8.9 Hz, 2H), 7.32 (t, J = 7.5
Hz, 2H), 7.30−7.26 (m, 2H), 7.23 (m, 1H), 6.97−6.89 (m, 2H), 3.85
(s, 3H), 3.34−3.26 (m, 2H), 2.97 (m, 2H). 13C NMR (151 MHz,
CDCl3) δ 190.24, 163.74, 140.19, 130.08, 129.34, 128.60, 128.47,
126.45, 113.74, 55.46, 36.07, 30.27. GC-MS (EI, 70 ev) m/z (%) =
272 (M+, 3), 168 (22), 135 (100), 77 (18).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are thankful for the financial support from the
Anhui Natural Science Foundation (1908085MC71), National
Key Research and Development Program of China
(2016YFD0200201), Program of Introducing Talents to
Chinese Universities (111 Program, D20023), Innovation
Project for Returned Students in Hefei, and Program of Young
Wanjiang Scholars in Anhui Province.
N-Benzyl-4-methoxybenzamide (3ab).23 Purified by flash chro-
matography (PE/EA = 20:1). Yield = 42.0 mg (53%). White solid, mp
128−131 °C. 1H NMR (600 MHz, CDCl3) δ 7.75 (m, 2H), 7.34 (d, J
= 3.8 Hz, 3H), 7.29 (q, J = 4.2 Hz, 1H), 7.25 (d, J = 3.4 Hz, 1H),
6.94−6.87 (m, 2H), 6.35 (s, 1H), 4.62 (m, 2H), 3.83 (d, J = 3.2 Hz,
3H).
8802
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Article
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