Visible-Light-Mediated Additive-Free Decarboxylative Ketonization Reaction of Acrylic Acids: An Access to α-Thiocyanate Ketones

Article abstract of DOI:10.1021/acs.joc.0c02471

Visible-light-mediated additive-free decarboxylative functionalization of acrylic acids has been developed. The reaction uses inexpensive organic dye 9,10-dicyanoanthracene as a photocatalyst and uses the ubiquitous dioxygen as both an oxygen source and an oxidant. Through this mild and environmentally friendly method, a series of important α-thiocyanate ketones can be generated from easily available acrylic acids and ammonium thiocyanate. In addition, the facile transformation of product α-thiocyanate ketones makes this method have great potential for application in organic and pharmaceutical chemistry.

Full text of DOI:10.1021/acs.joc.0c02471

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Article
Visible-Light-Mediated Additive-Free Decarboxylative Ketonization
Reaction of Acrylic Acids: An Access to α‑Thiocyanate Ketones
Zhi-Lv Wang, Jie Chen, Yan-Hong He,* and Zhi Guan*
Cite This: J. Org. Chem. 2021, 86, 3741−3749
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ABSTRACT: Visible-light-mediated additive-free decarboxylative
functionalization of acrylic acids has been developed. The reaction
uses inexpensive organic dye 9,10-dicyanoanthracene as a photo-
catalyst and uses the ubiquitous dioxygen as both an oxygen source
and an oxidant. Through this mild and environmentally friendly
method, a series of important α-thiocyanate ketones can be
generated from easily available acrylic acids and ammonium
thiocyanate. In addition, the facile transformation of product α-
thiocyanate ketones makes this method have great potential for
application in organic and pharmaceutical chemistry.
organosulfur compounds are an important class of compounds
in biological and pharmaceutical fields, naturally, as a
continuation of our work, we wonder whether there exists a
more economical and greener approach to simplify the C−S
bond-forming conditions and minimize the waste formation,
likewise through a visible-light-mediated decarboxylative
strategy.
INTRODUCTION
■
Carboxylic acids are one of the most abundant and inexpensive
chemicals, so they are usually used as raw materials for organic
synthesis. The decarboxylative functionalization reaction of
carboxylic acids has long been regarded as a general platform
to access many high-value chemical products.1 Traditionally,
metal catalysis is an effective strategy for decarboxylative
functionalization of carboxylic acids.2 For instance, Wang’s
group developed a CuBr2-catalyzed decarboxylative acylation
of acyl C−H of formamides with α-oxocarboxylic acids, leading
to α-ketoamides (Scheme 1A).2c Qu’s group reported a silver-
catalyzed decarboxylative acylarylation of acrylamides with α-
oxocarboxylic acids, producing 3-acyl-4-arylquinolin-2(1H)-
ones (Scheme 1B).2d However, metal-catalyzed decarboxyla-
tive reactions usually require harsh conditions, such as (over)
stoichiometric dangerous oxidants and elevated reaction
temperatures. Recently, the visible-light-mediated radical
strategy has opened a new window for realizing decarboxylative
functionalization reactions, owing to its mild, environmentally
friendly, and sustainable conditions.3 As such, visible-light-
mediated decarboxylative functionalization reactions have
received extensive attention, and various relevant trans-
formations including the formation of a novel C−C bond
and a C−heteroatom bond have been reported.4
Very recently, our group reported a mild photomediated
decarboxylative ketonization reaction of atropic acids with
sulfonyl hydrazides for the synthesis of α-ketosulfones
(Scheme 1C).4The reaction has great advantages of metal-
free conditions, readily available materials, and use of dioxygen
as both an oxygen source and an oxidant. Nevertheless, this
reaction requires a stoichiometric amount of potassium iodide
(KI) as an essential additive for reducing the peroxyl radical in
intermediate D to the peroxy anion (E), which generates
additional waste and deteriorates the atom efficiency. Since
Thiocyanates are highly versatile building blocks in synthetic
chemistry because they can be easily transformed into thiols,5
disulfides,6 phosphonothioates,7 isothicyanats,8 tri- and di-
fluoromethyl thioethers,9 and a variety of heterocyclic
scaffolds.10 In addition, thiocyanate can work as a safe cyanide
reagent to avoid the toxic cyanide source11 and be treated as a
pseudohalide to function as a leaving group.12 Consequently,
the introduction of a thiocyanate group into organic molecules
has very important synthetic significance. Recently, some
excellent thiocyanate functionalization reactions have been
developed.13 For instance, N-thiocyano-dibenzenesulfonimide
(NTSI) was used as a thiocyanation reagent to realize the
electrophilic thiocyano semipinacol rearrangement of allylic
alcohols13c and the electrophilic thiocyano oxyfunctionaliza-
tion of alkenes,13d providing various SCN-containing com-
pounds. In all kinds of thiocyanative reagents, ammonium
thiocyanate (NH4SCN), featuring low cost, commercially
availability, good solubility in organic solvents, and traceless
byproducts, has attracted considerable attention.13 In
Received: October 18, 2020
Published: February 17, 2021
https://dx.doi.org/10.1021/acs.joc.0c02471
© 2021 American Chemical Society
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Scheme 1. Decarboxylative Functionalization Reactions
particular, the potential of ammonium thiocyanate
[Eox(•SCN/−SCN) = +0.61 V in MeCN vs SCE]14 is close
to that of KI [Eox(I•/I−) = +0.627 V vs SCE],4g so we
speculate that it may also be a good single-electron reductant.
Inspired by these investigations, we envisaged whether
NH4SCN could act as both a sulfur source and a reductant
to achieve a visible-light-mediated additive-free decarboxylative
functionalization reaction (Scheme 1D), which would be more
environmentally friendly and atom-economic.
Herein, we present our work on a visible-light-mediated
additive-free decarboxylative ketonization reaction using
NH4SCN as both a sulfur source and a reductant and cheap
organic dye 9,10-dicyanoanthracene (DCA) as a green
photocatalyst at ambient temperature. In terms of applicability,
this reaction is not only feasible for various substituted atropic
acids but also can be expanded to alkyl-, heteroaryl-substituted
acrylic acids and disubstituted acrylic acids.
First, in an oxygen atmosphere, using acetonitrile (MeCN) as a
solvent and a 23 W compact fluorescent lamp (CFL) as a light
source, a series of photocatalysts were screened. It was a
delight to find that the proposed reaction was indeed feasible
with some photocatalysts (Table 1, entries 1−4). Among the
tested photocatalysts, common organic dye 9,10-dicyanoan-
thracene (DCA) exhibited the best efficiency to afford product
3a in 71% yield (Table 1, entry 3). Under these conditions,
replacing MeCN with other solvents and changes in the
molecular ratio of starting materials did not lead to a higher
yield of product 3a (Table 1, entries 5−8). Additionally, it was
found that the addition of a small amount of water had no
obvious effect on the reaction yield (Table 1, entries 9 and 10).
Subsequently, the effects of solvent volume and photocatalyst
loading were investigated. Experiments showed that when 1
mL of MeCN was used as a solvent, the reaction yield could be
increased to 79% (Table 1, entries 3, and 11−13), and the
photocatalyst loading could be decreased to 1.0 mol % without
loss in yield (Table 1, entries 12, 14 and 15). Ultimately,
control experiments were also conducted (Table 1, entries 16−
19). The results demonstrated that the photocatalyst, light
RESULTS AND DISCUSSION
■
Our initial effort to develop a new photomediated decarbox-
ylative C−S bond-forming protocol started with atropic acid
(1a) and ammonium thiocyanate (2) as model substrates.
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a
Table 1. Selected Optimization Experiments
b
entry
photocatalyst (x mol %)
solvent (v mL)
MeCN (2)
MeCN (2)
MeCN (2)
MeCN (2)
EtOH (2)
THF (2)
acetone (2)
MeCN (2)
MeCN (1.9) + H2O (0.1)
MeCN (1.7) + H2O (0.3)
MeCN (0.5)
MeCN (1.0)
MeCN (3.0)
MeCN (1.0)
MeCN (1.0)
MeCN (1.0)
MeCN (1.0)
MeCN (1.0)
MeCN (1.0)
xs (equiv)
yield (%)
1
2
3
4
5
6
7
8
rose bengal (2)
anthraquinone (2)
DCA (2)
Ru(bpy)3Cl2 (2)
DCA (2)
DCA (2)
DCA (2)
DCA (2)
DCA (2)
DCA (2)
DCA (2)
DCA (2)
DCA (2)
DCA (1)
DCA (4)
2
2
2
2
2
2
2
3
2
2
2
2
2
2
2
2
2
2
2
26
55
71
27
9
42
44
69
72
70
32
79
46
79
76
<10
trace
42
<10
9
10
11
12
13
14
15
16
c
17
DCA (1)
DCA (1)
DCA (1)
d
18
e
19
a
Reaction conditions: a mixture of 1a (0.2 mmol), NH4SCN (xs equiv), and a photocatalyst (x mol %) in a solvent (v mL) was irradiated by a 23
b
c
d
W CFL under a O2 balloon at rt for 10 h. Isolated yield after silica gel column chromatography. Without light irradiation. Air balloon instead of
an O2 balloon. Argon balloon instead of an O2 balloon.
e
irradiation, and O2 are all necessary in this reaction (for
detailed reaction condition screening, please see SI).
compatible to alkyl-substituted acrylic acids (3o). Further
investigations demonstrated that some acrylic acids of internal
olefins could also successfully participate in this decarbox-
ylative transformation to produce the desired products, albeit
in low yields (3p and 3q). However, when using 2,3-diaryl-
substituted acrylic acids (1s and 1t), no obvious reaction was
observed, possibly due to the high steric hindrance. Finally, 2-
heteroaryl-substituted acrylic acid could also participate in the
reaction smoothly, giving the desired product in moderate
yield (3r).
Next, we explored the utility of the products. The carbonyl
and thiocyanide in the products are both versatile building
blocks. As can be seen in Scheme 3, under simple alkaline
conditions, product 3a could be conveniently converted into
disulfide 4 (reaction a) or heteroaromatic compound 5
(reaction b). Under acidic conditions, product 3a could be
easily transformed into heterocyclic compound 6 in a high
yield within a short reaction time (reaction c). The facile
transformation of α-thiocyanate ketone provides great
potential for its application in organic and medicinal chemistry.
In order to get some insight into the reaction mechanism of
this visible-light-mediated decarboxylative ketonization reac-
tion, a series of experiments were carried out. The addition of
radical scavenger 2,2,6,6-tetramethyl-1-piperidinyloxy
(TEMPO) to the reaction system completely inhibited the
desired reaction, indicating that a radical pathway may be
involved in this transformation. Simultaneously, the detection
of TEMPO-adduct 7 by high-resolution mass spectrometry
(HRMS) suggested that radical intermediate II may be formed
during the reaction (Scheme 4a). When 2,6-di-tert-butyl-4-
methyl-phenol (BHT) and 1,1-diphenylethylene (DE) were,
With the optimized conditions in the hand (Table 1, entry
14), we continued our efforts toward exploring the reactivity of
various substituted acrylic acids with NH4SCN (Scheme 2).
First, it was found that the electronic nature of the substituents
of atropic acid had a great influence on the reaction. Atropic
acids with an electron-withdrawing substituent (such as
fluoro-, chloro-, bromo-, or trifluoromethyl-) at the para
position of the aromatic ring could provide the corresponding
products (3b−3e). However, para- cyano-, nitro-, carbonyl-,
carboxyl-, and ortho-fluoro-substituted atropic acids (1u and
1w−1z) could not undergo this transformation. After
extending the reaction time to 24 h, no obvious reaction was
observed, and a large amount of raw materials still remained,
which may be attributed to the strong electron-withdrawing
effect of the substituents. The presence of electron-donating
groups, such as para- n-Bu, t-Bu, and Me- groups, on the
aromatic ring of atropic acid could facilitate the reaction and
gave the desired products in good yields (3f−3h). However,
para-MeO- and MeS-substituted atropic acids were only
converted to the desired products in moderate yields (3i and
3j), and some complicated byproducts were formed. Second,
the steric hindrance also exhibited some effect on this reaction.
For instance, 2,4,6-trimethyl-substituted atropic acid 1v could
not be decarboxylated in this way, probably because of the high
steric hindrance. Pleasingly, some di- and trisubstituted atropic
acids with a lower steric hindrance could smoothly react with
NH4SCN under the optimized conditions (3k−3m and 3n).
Different from a previous visible-light-mediated decarboxyla-
tive reaction reported by our group,4 this reaction is
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a
Scheme 2. Scope of Substrates
a
Reaction conditions: a mixture of 1 (0.2 mmol), NH4SCN (0.4 mmol), and DCA (1.0 mol %) in MeCN (1.0 mL) was irradiated by a 23 W CFL
b
under an O2 balloon at rt for 10 h. Isolated yields were provided.
Scheme 3. Transformation of Products
respectively, added to the model reaction, BHT-adduct 8 and
DE-adduct 9 could be detected by HRMS, indicating that both
a superoxide radical and a thiocyanate radical may be involved
in the reaction (Scheme 4b,c). Subsequently, to find out where
the oxygen atom of the carbonyl group in the desired product
comes from, we performed an isotope-labeling experiment in
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Scheme 4. Mechanistic Studies
the presence of 18O2 (Scheme 4d). The result showed that the
oxygen atom of the carbonyl group comes from O2. Besides,
on/off visible-light irradiation experiments were carried out to
verify whether there is a radical chain propagation process
(Figure 1). It was found that in the absence of light, the
acid could not (SI, Figures S8−S10). This luminescence
quenching is most likely due to the photoinduced electron
transfer process, as NH4SCN [Eox(•SCN/−SCN) = +0.61 V in
MeCN vs SCE]14 can be easily oxidized by the excited
photocatalyst DCA*, which is reported to have potential
among 1.9−2.1 V vs SCE.15
Based on the above experiments, we proposed a possible
reaction mechanism (Scheme 5), which includes two possible
pathways. The photocatalyst DCA is excited by the visible light
to the excited state DCA*, which undergoes single-electron
transfer with the thiocyanate anion (liberated from ammonium
thiocyanate) to afford the thiocyanate radical I along with the
formation of reduced DCA•−. Then, DCA•− is single-electron-
oxidized back to DCA by O2, and at the same time, a
superoxide anion radical (O2•−) is formed, thus completing the
photoredox catalytic cycle. Subsequently, the radical addition
between the thiocyanate radical I and the acrylic acid 1 forms
the alkyl radical II. In path A, intermediate II can be added to
O2 to form intermediate III. The thiocyanate anion may work
as an internal reductant to reduce intermediate III to generate
intermediate IV, while the thiocyanate anion is single-electron-
oxidized to the thiocyanate radical I, contributing to the radical
chain process. Intermediate IV undergoes intramolecular
proton transfer, protonation, decarboxylation, and dehydration
processes, and is finally transformed into the target product 3.
Figure 1. Light on/off experiments.
reaction still continued (the yield was determined by 1H
NMR), so we speculate that there may be a radical chain
propagation process. UV−visible absorption spectroscopy
demonstrated that except for the photocatalyst, other reactants
in this reaction could not absorb the visible light (SI, Figure
S2). The fluorescence quenching experiments (Stern−Volmer
studies) showed that NH4SCN could readily quench the
luminescence of the excited photocatalyst DCA*, while atropic
•
In path B, the alkyl radical II is captured by HO2 , which is
•−
produced by a combination of O2 and the proton from 2,
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Scheme 5. Possible Mechanism
Deuterated chloroform with TMS as an internal standard was used as
a solvent for NMR analyses. In the evaluation of H NMR spectra,
providing the intermediate VII. After successive intramolecular
proton transfer, decarboxylation, and dehydration, the
intermediate VII is finally converted to the desired product 3.
1
chemical shifts (δ) were expressed in parts per million (ppm),
wherein “s” stands for singlet, “d” for doublet, “t” for triplet, “q” for
quartet, “dd” for doublet of doublets, and “m” for multiplet. The
coupling constants (J) were reported in Hz. High-resolution mass
spectra were obtained using ESI ionization sources (Varian 7.0 T
FTICR-MS) and ESI-TOF. Melting points were taken on a WPX-4
apparatus and were uncorrected (Yice Instrument Equipment Co.
Ltd., Shanghai).
The starting materials 1b−m and 1o−1p are known compounds,
which were all prepared according to the reported procedures.16,17
General Procedure for the Preparation of α-Thiocyanate
Ketones 3. A round bottom flask (10 mL) equipped with a magnetic
stir bar was charged with acrylic acid 1 (0.2 mmol, 1.0 equiv),
ammonium thiocyanate 2 (0.4 mmol, 2.0 equiv), 9,10-dicyanoan-
thracene (DCA, 0.002 mmol, 1 mol %), and MeCN (1.0 mL). The
mixture was irradiated by a 23 W CFL (Philips, 220 V, 50 Hz, 400−
780 nm, without any filters, placed approximately 2.5 cm from the
flask) under an O2 balloon at room temperature. After completion of
the reaction (monitored by TLC), the reaction mixture was
concentrated under reduced pressure and the resulting residue was
treated with water and extracted with EtOAc. The combined organic
layers were washed with brine, dried over anhydrous Na2SO4, and
concentrated under reduced pressure. The crude product was purified
by silica gel column chromatography using petroleum ether/ethyl
acetate as an eluent to give the desired product α-thiocyanate ketones
3 (20−89% yields).
CONCLUSIONS
■
In summary, using NH4SCN as both a sulfur source and a
reductant and using inexpensive organic dye DCA as a green
photocatalyst, we have successfully developed a visible-light-
mediated additive-free decarboxylative reaction for simulta-
neous construction of C−S and CO bonds. The reaction has
advantages of simple operation and environmental friendliness.
Moreover, since the produced α-thiocyanate ketones are
important synthons in organic and pharmaceutical fields, this
reaction can be used for the further preparation of other
important complex molecules, thereby contributing to the
progress of organic synthesis.
EXPERIMENTAL SECTION
■
General Information. All reactions were performed in round
bottom flasks made of borosilicate glass. The optimized light source
was a 23 W CFL (Philips, 220 V, 50 Hz, 400−780 nm) without any
filters, and the spectral distribution and intensity of the lamp are
shown in Figure S1. Commercially available reagents were purchased
at the highest commercial quality and used without further
purifications. Thin-layer chromatography (TLC) plates (Qingdao
Haiyang Chemical Industry Co. Ltd., Qingdao, China) were
visualized by exposure to UV light and/or staining with the solution
of vanillic aldehyde. Flash column chromatography (ethyl acetate/
petroleum ether) was carried out using 200−300 mesh silica gel at
increased pressure. 1H NMR spectra and 13C{1H} NMR spectra were,
respectively, recorded on 600 and 151 MHz NMR spectrometers.
Procedure for the Preparation of 4. A 10 mL vial equipped
with a magnetic stir bar was charged with 3a (0.17 mmol) and MeCN
(1 mL) and then isopropylamine (3.6 mmol) was added. The reaction
was allowed to proceed overnight. The reaction mixture was
concentrated under reduced pressure and the resulting residue was
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2
2
treated with water and extracted with EtOAc. The organic extracts
were combined, dried with sodium sulfate, and the solvent was
subsequently removed under reduced pressure to afford the crude
product, which then further purified by silica gel column
chromatography using 5% EtOAc/hexane as an eluent to give the
desired product 4 in 63% yields.
Procedure for the Preparation of 5. To a round bottom flask
(10 mL) equipped with a magnetic stir bar, 3a (0.17 mmol), aniline
(0.32 mmol), and methanol (0.30 mL) were added. The mixture was
refluxed overnight after which the solvent was removed under reduced
pressure and the residue was purified by silica gel column
chromatography using petroleum ether/ethyl acetate in a 10:1 ratio
to afford the product 5 in 64% yields.
Procedure for the Preparation of 6. 3a (2.5 mmol) was added
to acetic acid (20 mL) in a round bottom flask (50 mL), and the
mixture was heated until 3a completely dissolved. Sulfuric acid (50%
v/v, 4 mL) was added and the solution was brought to reflux for 30
min. The reaction mixture was then cooled to ambient temperature
and poured into cold water, resulting in precipitation. The precipitate
was separated by filtration and washed with hexane to give product 6
in 96% yields.
Enlarged-Scale Synthesis of 3a. A round bottom flask (25 mL)
equipped with a magnetic stir bar was charged with 2-phenylacrylic
acid 1a (148.2 mg, 1.0 mmol, 1.0 equiv), ammonium thiocyanate 2
(152.2 mg, 2.0 mmol, 2.0 equiv), 9,10-dicyanoanthracene (DCA, 11.4
mg, 0.01 mmol, 1 mol %), and MeCN (5.0 mL). The mixture was
irradiated by a 23 W CFL (Philips, 220 V, 50 Hz, 400−780 nm,
without any filters, placed approximately 2.5 cm from the flask) under
an O2 balloon at room temperature. After completion of the reaction
(monitored by TLC), the reaction mixture was concentrated under
reduced pressure and the resulting residue was treated with water and
extracted with EtOAc. The combined organic layers were washed with
brine, dried over anhydrous Na2SO4, and concentrated under reduced
pressure. The crude product was purified by silica gel column
chromatography using petroleum ether/ethyl acetate (10:1 ratio) as
an eluent to give the desired product 1-phenyl-2-thiocyanatoethan-1-
one 3a (108 mg, 61%).
136.7, 136.3 (C-F, JC‑F = 30.0 Hz), 136.1(C-F, JC‑F = 30.0 Hz),
2
2
135.9 (C-F, JC‑F = 30.0 Hz), 135.7 (C-F, JC‑F = 30.0 Hz), 128.9,
126.3, 125.9 (C-F, JC‑F = 270.0 Hz), 124.1 (C-F, JC‑F = 270.0 Hz),
1
1
1
1
122.3 (C-F, JC‑F = 270.0 Hz), 120.5 (C-F, JC‑F = 270.0 Hz), 111.2,
42.5; 19F NMR (565 MHz, CDCl3): δ −63.4; HRMS (ESI-TOF) m/
z: [M + H]+ calcd for C10H7F3NOS 246.0195; found: 246.0192.
1-(4-Butylphenyl)-2-thiocyanatoethan-1-one (3f). Isolated yield
(39.2 mg, 84%), yellow solid, Rf value = 0.2 [EtOAc/petroleum ether
= 1:10 (v/v)], FTIR νmax (neat): 3414, 2928, 2152, 1673, 1601, 1381,
1296, 1179, 996, 821, 610, 564 cm−1, melting: 83 °C; 1H NMR (600
MHz, CDCl3): δ 7.85 (d, J = 8.1 Hz, 2H), 7.33 (d, J = 8.1 Hz, 2H),
4.72 (s, 2H), 2.70 (t, J = 7.7 Hz, 2H), 1.64−1.61 (m, 2H), 1.38−1.34
(m, 2H), 0.94 (t, J = 7.4 Hz, 3H); 13C{1H} NMR (151 MHz,
CDCl3): δ 190.4, 151.0, 129.2, 128.6, 126.2, 111.9, 43.0, 35.8, 33.1.
HRMS (ESI-TOF) m/z: [M + H]+ calcd for C13H16NOS 234.0947;
found: 234.0944.
1-(4-(tert-Butyl)phenyl)-2-thiocyanatoethan-1-one (3g).18 Iso-
lated yield (41.5 mg, 89%), yellow solid, Rf value = 0.2 [EtOAc/
1
petroleum ether = 1:10 (v/v)], melting range: 79−81 °C; H NMR
(600 MHz, CDCl3): δ 7.88 (d, J = 8.5 Hz, 2H), 7.54 (d, J = 8.5 Hz,
2H), 4.73 (s, 2H), 1.35 (s, 9H); 13C{1H} NMR (151 MHz, CDCl3):
δ 190.4, 159.0, 131.5, 128.5, 126.2, 111.9, 43.0, 35.4, 31.0.
2-Thiocyanato-1-(p-tolyl)ethan-1-one (3h).19 Isolated yield (32.9
mg, 86%), yellow solid, Rf value = 0.2 [EtOAc/petroleum ether =
1:10 (v/v)], melting range: 99−101 °C; 1H NMR (600 MHz,
CDCl3): δ 7.83 (d, J = 8.2 Hz, 2H), 7.32 (d, J = 8.1 Hz, 2H), 4.72 (s,
2H), 2.45 (s, 3H); 13C{1H} NMR (151 MHz, CDCl3): δ 190.4,
146.1, 131.6, 129.9, 128.6, 111.9, 43.0, 21.8.
1-(4-Methoxyphenyl)-2-thiocyanatoethan-1-one (3i). Isolated
yield (17.4 mg, 42%), yellow solid, Rf value = 0.1 [EtOAc/petroleum
ether = 1:10 (v/v)]; H NMR (600 MHz, DMSO-d6) δ 7.99 (d, J =
8.8 Hz, 2H), 7.09 (d, J = 8.8 Hz, 2H), 5.05 (s, 2H), 3.86 (s, 3H);
13C{1H} NMR (151 MHz, DMSO-d6) δ 191.0, 164.5, 131.5, 127.6,
114.7, 113.4, 56.2, 42.0.
1-(4-(Methylthio)phenyl)-2-thiocyanatoethan-1-one (3j). Iso-
lated yield (17.9 mg, 40%), yellow solid, Rf value = 0.1 [EtOAc/
1
1
petroleum ether = 1:10 (v/v)]; H NMR (600 MHz, CDCl3) δ 7.83
Characterization of Products. 1-Phenyl-2-thiocyanatoethan-
1-one (3a).18 Isolated yield (28.0 mg, 79%), yellow solid, Rf value =
0.2 [EtOAc/petroleum ether = 1:10 (v/v)], melting range: 68−69
°C; 1H NMR (600 MHz, CDCl3): δ 7.97−7.93 (m, 2H), 7.67 (t, J =
7.5 Hz, 1H), 7.54 (t, J = 7.8 Hz, 2H), 4.74 (s, 2H); 13C{1H} NMR
(151 MHz, CDCl3): δ 190.8, 134.8, 134.0, 129.2, 128.5, 111.7, 42.9.
1-(4-Fluorophenyl)-2-thiocyanatoethan-1-one (3b).19 Isolated
yield (23.4 mg, 60%), yellow solid, Rf value = 0.3 [EtOAc/petroleum
(d, J = 8.2 Hz, 1H), 7.30 (d, J = 8.2 Hz, 1H), 4.69 (s, 1H), 2.54 (s,
2H); 13C{1H} NMR (151 MHz, CDCl3) δ 189.8, 148.9, 130.2, 128.9,
125.3, 112.0, 42.9, 14.8.
1-(3,4-Dimethylphenyl)-2-thiocyanatoethan-1-one (3k). Isolated
yield (34.5 mg, 84%), yellow solid, Rf value = 0.2 [EtOAc/petroleum
ether = 1:10 (v/v)], FTIR νmax (neat): 3422, 2974, 2151, 1672, 1601,
1304, 1228, 1129, 828, 600 cm−1, melting range: 87−88 °C; 1H NMR
(600 MHz, CDCl3): δ 7.70 (s, 1H), 7.66 (d, J = 7.9 Hz, 1H), 7.28 (s,
1H), 4.72 (s, 2H), 2.35 (s, 3H), 2.34 (s, 3H). 13C{1H} NMR (151
MHz, CDCl3): δ 190.6, 144.8, 137.7, 131.9, 130.3, 129.5, 126.2,
112.0, 43.1, 20.2, 19.8; HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C11H12NOS 206.0634; found: 206.0633.
1-(2,5-Dimethylphenyl)-2-thiocyanatoethan-1-one (3l). Isolated
yield (8.1 mg, 20%), yellow solid, Rf value = 0.2 [EtOAc/petroleum
ether = 1:10 (v/v)], FTIR νmax (neat): 3432, 2941, 2151, 1667, 1387,
1274, 1135, 818, 651 cm−1; 1H NMR (600 MHz, CDCl3): δ 7.49 (s,
1H), 7.30 (d, J = 7.7 Hz, 1H), 7.20 (d, J = 7.7 Hz, 1H), 4.71 (s, 2H),
2.51 (s, 3H), 2.39 (s, 3H); 13C{1H} NMR (151 MHz, CDCl3): δ
193.2, 137.3, 135.9, 134.2, 133.4, 132.7, 130.1, 112.0, 45.0, 21.3, 20.9;
HRMS (ESI-TOF) m/z: [M + H]+ calcd for C11H12NOS 206.0634;
found: 206.0635.
1
ether = 1:10 (v/v)], melting range: 95−97 °C; H NMR (600 MHz,
CDCl3): δ 7.99 (dd, J = 8.6, 5.3 Hz, 2H), 7.21 (t, J = 8.4 Hz, 2H),
4.70 (s, 2H); 13C{1H} NMR (151 MHz, CDCl3): δ 189.2, 167.5 (C-
F, 1JC‑F = 256.5 Hz), 165.8 (C-F, 1JC‑F = 256.5 Hz), 131.3 (C-F, 3JC‑F
3
2
= 10.5 Hz), 131.2 (C-F, JC‑F = 10.5 Hz), 130.6, 116.6 (C-F, JC‑F
=
22.5 Hz), 116.4 (C-F, JC‑F = 22.5 Hz), 111.5, 42.6; 19F NMR (565
2
MHz, CDCl3): δ −101.3.
1-(4-Chlorophenyl)-2-thiocyanatoethan-1-one (3c).19 Isolated
yield (27.1 mg, 64%), yellow solid, Rf value = 0.3 [EtOAc/petroleum
1
ether = 1:10 (v/v)], melting range: 122−124 °C; H NMR (600
MHz, CDCl3): δ 7.89 (d, J = 8.2 Hz, 2H), 7.52 (d, J = 8.2 Hz, 2H),
4.69 (s, 2H); 13C{1H} NMR (151 MHz, CDCl3): δ 189.7, 141.6,
132.4, 129.9, 129.6, 111.5, 42.6.
1-(4-Bromophenyl)-2-thiocyanatoethan-1-one (3d).19 Isolated
yield (37.7 mg, 74%), yellow solid, Rf value = 0.3 [EtOAc/petroleum
1-(3,4-Dichlorophenyl)-2-thiocyanatoethan-1-one (3m). Isolated
yield (20.9 mg, 43%), yellow solid, Rf value = 0.3 [EtOAc/petroleum
ether = 1:10 (v/v)], FTIR νmax (neat): 3428, 2926, 2159, 1670. 1465,
1
ether = 1:10 (v/v)], melting range: 114−116 °C; H NMR (600
1
1383, 1202, 1008, 799 cm−1, melting range: 95−97 °C; H NMR
MHz, CDCl3): δ 7.81 (d, J = 8.6 Hz, 2H), 7.69 (d, J = 8.6 Hz, 2H),
4.68 (s, 2H); 13C{1H} NMR (151 MHz, CDCl3): δ 189.8, 132.7,
132.6, 130.3, 129.8, 111.4, 42.5.
(600 MHz, CDCl3): δ 8.03 (d, J = 1.9 Hz, 1H), 7.77 (dd, J = 8.4, 1.9
Hz, 1H), 7.63 (d, J = 8.4 Hz, 1H), 4.65 (s, 2H); 13C{1H} NMR (151
MHz, CDCl3): δ 188.8, 139.7, 134.2, 133.5, 131.4, 130.4, 127.3,
111.1, 42.2; HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C9H6Cl2NOS 245.9542; found: 245.9538.
2-Thiocyanato-1-(4-(trifluoromethyl)phenyl)ethan-1-one (3e).
Isolated yield (11.7 mg, 24%), yellow solid, Rf value = 0.3 [EtOAc/
petroleum ether = 1:10 (v/v)], FTIR νmax (neat): 3416, 2156, 1675,
1
1261, 1100, 1068, 1019, 801 cm−1, melting range: 110−111 °C; H
1-(4-Methoxy-3,5-dimethylphenyl)-2-thiocyanatoethan-1-one
(3n). Isolated yield (39.1 mg, 83%), pale yellow solid, Rf value = 0.1
[EtOAc/petroleum ether = 1:10 (v/v)], FTIR νmax (neat): 3419,
NMR (600 MHz, CDCl3): δ 8.07 (d, J = 8.1 Hz, 2H), 7.81 (d, J = 8.0
Hz, 2H), 4.72 (s, 2H); 13C{1H} NMR (151 MHz, CDCl3): δ 189.9,
3747
https://dx.doi.org/10.1021/acs.joc.0c02471
J. Org. Chem. 2021, 86, 3741−3749

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
2933, 2157, 1672, 1596, 1328, 1152, 1006, 866, 654 cm−1, melting
Engineering, Southwest University, Chongqing 400715,
China; orcid.org/0000-0002-6405-285X; Email: heyh@
swu.edu.cn
Zhi Guan − Key Laboratory of Applied Chemistry of
Chongqing Municipality, School of Chemistry and Chemical
Engineering, Southwest University, Chongqing 400715,
China; orcid.org/0000-0002-0369-6141;
Email: guanzhi@swu.edu.cn
1
range: 111−113 °C; H NMR (600 MHz, CDCl3): δ 7.61 (s, 2H),
4.70 (s, 2H), 3.78 (s, 3H), 2.34 (s, 6H); 13C{1H} NMR (151 MHz,
CDCl3): δ 190.1, 162.8, 132.1, 129.6, 112.0, 59.8, 43.0, 16.3; HRMS
(ESI-TOF) m/z: [M + H]+ calcd for C12H14NO2S 236.0740; found:
236.0739.
1-Phenyl-3-thiocyanatopropan-2-one (3o). Isolated yield (9.9
mg, 26%), yellow solid, Rf value = 0.2 [EtOAc/petroleum ether =
1
1:10 (v/v)]; H NMR (600 MHz, CDCl3): δ 7.40−7.36 (m, 2H),
7.33 (t, J = 7.1 Hz, 1H), 7.22 (t, J = 7.6 Hz, 2H), 4.02 (s, 2H), 3.86 (s,
2H); 13C{1H} NMR (151 MHz, CDCl3): δ 198.8, 132.2, 129.3,
128.0, 126.2, 111.0, 48.8, 43.3; HRMS (ESI-TOF) m/z: [M + H]+
calcd for C10H10NOS 192.0478; found: 192.0477.
Authors
Zhi-Lv Wang − Key Laboratory of Applied Chemistry of
Chongqing Municipality, School of Chemistry and Chemical
Engineering, Southwest University, Chongqing 400715,
China
Jie Chen − Key Laboratory of Applied Chemistry of
Chongqing Municipality, School of Chemistry and Chemical
Engineering, Southwest University, Chongqing 400715,
China
1-Phenyl-2-thiocyanatopropan-1-one (3p).19 Isolated yield (14.9
mg, 39%), yellow solid, Rf value = 0.2 [EtOAc/petroleum ether =
1:10 (v/v)], melting range: 76−77 °C; 1H NMR (600 MHz, CDCl3):
δ 7.96−7.91 (m, 2H), 7.67 (t, J = 7.4 Hz, 1H), 7.54 (t, J = 7.8 Hz,
2H), 5.08 (q, J = 7.1 Hz, 1H), 1.87 (d, J = 7.1 Hz, 3H); 13C{1H}
NMR (151 MHz, CDCl3): δ 194.8, 134.6, 133.3, 129.2, 128.8, 111.4,
49.9, 19.8.
1-Phenyl-2-thiocyanatobutan-1-one (3q). Isolated yield (12.5
mg, 30%), yellow solid, Rf value = 0.2 [EtOAc/petroleum ether =
1:10 (v/v)]; H NMR (600 MHz, CDCl3): δ 7.98−7.88 (m, 2H),
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.joc.0c02471
1
7.67 (t, J = 7.4 Hz, 1H), 7.54 (t, J = 7.7 Hz, 2H), 5.00 (t, J = 5.9 Hz,
1H), 2.30 (m, 1H), 2.19 (m, 1H), 1.06 (t, J = 7.3 Hz, 3H); 13C{1H}
NMR (151 MHz, CDCl3) δ 194.7, 134.6, 134.1, 129.3, 128.8, 111.5,
55.9, 26.2, 10.2; HRMS (ESI-TOF) m/z: [M + H]+ calcd for
C11H12NOS 206.0634; found: 206.0634.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was financially supported by the National Natural
Science Foundation of China (Nos. 21977084 and 22078268).
■
1-(Benzo[b]thiophen-3-yl)-2-thiocyanatoethan-1-one (3r). Iso-
lated yield (20.5 mg, 44%), yellow solid, Rf value = 0.2 [EtOAc/
1
petroleum ether = 1:10 (v/v)]; H NMR (600 MHz, DMSO-d6) δ
9.14 (s, 1H), 8.58 (d, J = 8.0 Hz, 1H), 8.14 (d, J = 7.5 Hz, 1H), 7.56
(t, J = 6.9 Hz, 1H), 7.51 (t, J = 6.9 Hz, 1H), 5.09 (s, 2H); 13C{1H}
NMR (151 MHz, DMSO-d6) δ 187.4, 142.4, 139.7, 136.3, 132.1,
126.6, 126.2, 124.8, 123.6, 113.4, 42.3.
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4-Phenylthiazol-2(3H)-one (6).22 Isolated yield (425.3 mg, 96%),
white solid, Rf value = 0.2 [EtOAc/petroleum ether = 1:10 (v/v)]; 1H
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13C{1H} NMR (151 MHz, DMSO-d6): δ 172.9, 133.8, 129.6, 128.7,
128.4, 124.8, 98.0.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.joc.0c02471.
■
sı
Additional screening data; mechanistic investigation;
and copies of 1H, 13C{1 H}, 19F NMR, and IR spectra of
all new products (ZIP)
AUTHOR INFORMATION
Corresponding Authors
Yan-Hong He − Key Laboratory of Applied Chemistry of
Chongqing Municipality, School of Chemistry and Chemical
■
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