Metal-Free, Acid/Phosphine-Induced Regioselective Thiolation of p-Quinone Methides with Sodium Aryl/Alkyl Sulfinates

Article abstract of DOI:10.1021/acs.joc.0c02390

A simple and efficient method for the regioselective thiolation of p-quinone methides with sodium aryl/alkyl sulfinates has been established using an acid/phosphine-induced radical route under transition-metal-free conditions. A broad range of sodium aryl/alkyl sulfinates and p-quinone methides (p-QMs) are compatible for the reaction, giving the expected products with good to excellent yields. Control experiments were also performed to gain insights into the generation mechanism of thiyl radicals and hydrogen-atom transfer process. This protocol provides a safe and feasible way for the formation of carbon-sulfur bonds.

Full text of DOI:10.1021/acs.joc.0c02390

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Metal-Free, Acid/Phosphine-Induced Regioselective Thiolation of
p‑Quinone Methides with Sodium Aryl/Alkyl Sulfinates
Biquan Xiong,* Shipan Xu, Yu Liu, Ke-Wen Tang,* and Wai-Yeung Wong*
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ABSTRACT: A simple and efficient method for the regioselective
thiolation of p-quinone methides with sodium aryl/alkyl sulfinates
has been established using an acid/phosphine-induced radical
route under transition-metal-free conditions. A broad range of
sodium aryl/alkyl sulfinates and p-quinone methides (p-QMs) are
compatible for the reaction, giving the expected products with
good to excellent yields. Control experiments were also performed
to gain insights into the generation mechanism of thiyl radicals and hydrogen-atom transfer process. This protocol provides a safe
and feasible way for the formation of carbon−sulfur bonds.
Bronsted-acid-catalyzed selective 1,6-conjugated addition of
S−H bonds to p-QMs were realized by Anand et al. and Lu et
al. under ambient temperature.13
INTRODUCTION
■
Owing to the unique antibacterial, anti-inflammatory, and
antimycobacterial activities, construction of the C−S bonds for
the synthesis and applications of diarylmethyl thioethers is of
great interest in organic synthesis, materials science, as well as
in the pharmaceutical industry (Scheme 1).1,2 The well-
documented C−S bond-forming methods for the synthesis of
thioethers generally employed nucleophilic substitution of
aryl/alkyl halides with RS groups.3 In addition, introduction of
S−H bonds into an unsaturated carbon−carbon bond is also
an effective route to construct C−S bonds.4 However, most of
these protocols suffer from defects including the adoption of
smell/air-sensitive thiols, transition-metal catalysts, oxidants
(for the generation of thiyl radicals), and toxic organic
solvents.
Due to the unique bisvinylogous enone structure, p-quinone
methides (p-QMs) are considered as electron-deficient
alkenes, which have been widely employed in organic
synthesis, especially in the 1,6-conjugated addition and
intermolecular cyclization transformation.5−8 Fan et al.
established a novel and efficient catalytic asymmetric 1,6-
conjugate addition/aromatization of p-QMs with malonates,
oxindoles, and glycine derivatives via the catalysis of small
organic chiral amines.9 In 2014, Jørgensen et al. disclosed a
chiral secondary amine catalyzed asymmetric α-alkylation of
aldehydes through the 1,6-conjugated addition of enamines
with p-QMs, where a series of α-diarylmethyl-substituted
aldehydes with two contiguous stereocenters was synthesized
with good yields and excellent enantioselectivity.10 In addition,
enantioselective 1,6-boration of p-QMs was achieved by Liao
et al. through the catalysis of copper chloride and a chiral (2-
(tert-butylsulfinyl)aryl) diisopropylphosphine ligand.11 In the
presence of a chiral phosphoric acid, Li et al. discovered an
efficient protocol for the asymmetric 1,6-conjugate addition of
thioacetic acid to p-QMs.12 Very recently, the Lewis-acid- and
Thiyl radicals, which are at the center of some extremely
efficient radical reactions for the synthesis of thioethers, have
also attracted the interest of organic chemists.14 Compared
with the toxic and smelly thiophenol, sodium arylsulfinates are
a kind of odorless, stable, and easy-to-handle thiolation agent,
which are undoubtedly considered as safer and more
environmentally friendly reagents in organic synthesis. In
2017, Xu and Su et al. established an efficient protocol for the
formation of C−S bonds via a byproduct-promoted three-
component coupling of alcohols with organic halides and
thiourea.15 In addition, a novel and convenient method was
found by Lu and Yi et al. for the synthesis of alkyl/alkenyl
sulfides and phosphonothioates from sodium arylsulfinates and
alkynes, alkenes, and H-phosphine oxides in aqueous
systems.16 It should be noted that the aryl thiyl radicals were
generated in situ for the reaction. Although some elegant
studies on the selective thiolation of carbon−carbon double
bonds were achieved by these scientists, the use of p-QMs and
sodium aryl/alkyl sulfinates as starting materials has not been
reported. Herein, we demonstrate a simple and efficient
method for the regioselective thiolation of p-QMs with sodium
aryl/alkyl sulfinates by employing an acid/phosphine-induced
radical route under transition-metal-free conditions (Scheme
2).
Received: October 9, 2020
Published: January 7, 2021
https://dx.doi.org/10.1021/acs.joc.0c02390
© 2021 American Chemical Society
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Scheme 1. Important Diarylmethyl Thioethers
Scheme 2. Methods for the Synthesis of Diaryl Methyl
Thioethers from p-QMs
acid for the reaction (Table 1, entries 16−21). It is apparent
that H2SO4 emerges as the best choice. Various reducing
agents such as (EtO)2P(O)H, Zn powder, and Mn powder
were also investigated (Table 1, entries 7 and 22−24). It is
worth noting that only PPh3 showed positive results for
reduction of SO bonds. When the reaction was operated at
60 °C, the desired product was only generated in 87% yield,
but by further increasing the temperature from 80 to 100 °C,
there are no obvious effects on the reaction (Table 1, entries
25 and 26). Thus, the optimal reaction conditions are as
follows: CH3CN/H2O (1.0 mL, v:v = 1:1), PPh3 (2.2 equiv),
H2SO4 (2.0 equiv), N2, 80 °C, 3 h.
As shown in Table 2, the acid/phosphine-induced
regioselective thiolation of p-quinone methides with sodium
benzenesulfinate leading to 2,6-di-tert-butyl-4-(aryl-
(phenylthio)methyl)phenols can be applied to different kinds
of p-QMs. It is clear that 4-benzylidene-2,6-di-tert-butylcyclo-
hexa-2,5-dienone (1a), 2,6-di-tert-butyl-4-(4-
methylbenzylidene)cyclohexa-2,5-dienone (1b), 2,6-di-tert-
butyl-4-(4-ethylbenzylidene)cyclohexa-2,5-dienone (1c), and
2,6-di-tert-butyl-4-(4-(tert-butyl)benzylidene)cyclohexa-2,5-di-
enone (1d) can react efficiently with sodium benzenesulfinate
(2a) under the optimized reaction conditions, affording the
corresponding thiolation products of 3a−3d in 80−95%
isolated yields. In addition, when 2,6-di-tert-butyl-4-(4-
isopropoxybenzylidene)cyclohexa-2,5-dienone (1e), 4-(4-
(benzyloxy)benzylidene)-2,6-di-tert-butylcyclohexa-2,5-dien-
one (1f), 2,6-di-tert-butyl-4-(3-methoxybenzylidene)cyclohexa-
2,5-dienone (1g), and 2,6-di-tert-butyl-4-(2,5-
dimethoxybenzylidene)cyclohexa-2,5-dienone (1h) were em-
ployed as the substrates for the reaction, the desired thiolation
products were obtained in 78−89% yields. To our surprise,
2,6-di-tert-butyl-4-((4-hydroxy-3-methoxyphenyl)-
(phenylthio)methyl)phenol (3i) and 4-((3,5-di-tert-butyl-4-
hydroxyphenyl) (phenylthio)methyl) benzaldehyde (3j) were
synthesized with 75% and 92% yields through the 1,6-
conjugate addition reaction of 2,6-di-tert-butyl-4-(4-hydroxy-
3-methoxybenzylidene)cyclohexa-2,5-dienone (1i) and 4-
((3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1ylidene)methyl)-
benzaldehyde (1j) with 2a, where the hydroxyl and aldehyde
substituents remained after the reaction without protection.
Furthermore, various kinds of p-QMs containing electron-
withdrawing groups (e.g., bromo, fluoro, cynao, and nitro, 1k−
1p) on the aryl ring also exhibit high reactivities toward the
thiolation/1,6-conjugate addition process, affording the corre-
sponding products in 85−96% yields. For most cases, electron-
donating or electron-withdrawing groups which are located on
the aryl ring of p-QMs do not change the yields of the products
significantly. It is worth noting that 3q and 3r could be
synthesized from 4-benzylidene-2,6-dimethylcyclohexa-2,5-di-
enone (1q) and 4-benzylidene-2,6-diisopropylcyclohexa-2,5-
RESULTS AND DISCUSSION
■
At the first stage of our study, we attempted to use PPh3 and
acid as the activation reagent for reduction of the SO bond
for generation of the aryl thiyl radical followed by attack on the
CC bond of p-QMs to realize the regioselective thiolation
reaction. To test our initial hypothesis, the reaction of 4-
benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone (1a) and
sodium benzenesulfinate (2a) was investigated to delineate
the reaction parameters. The reaction of 1a with 2a was
performed at 80 °C in H2O under a N2 atmosphere with the
addition of triphenylphosphine and sulfuric acid, and the
corresponding thiolation product of 2,6-di-tert-butyl-4-
(phenyl(phenylthio)methyl)phenol (3a) was generated in
65% yield (Table 1, entry 1). To our delight, the mixed
solvent system of 1,4-dioxane and H2O (1.0 mL, v:v = 1:1)
could afford the desired product 3a in 82% yield (Table 1,
entry 2). Besides 1,4-dioxane, other water−mixed-solvent
systems, such as EA/H2O, CH2Cl2/H2O, DMF/H2O, THF/
H2O, toluene/H2O, DMSO/H2O, and CH3CN/H2O, were
further investigated (Table 1, entries 3−9), and CH3CN/H2O
gave the product in a preferable yield of 88%. The amounts of
H2SO4 and PPh3 used have significant influences on the
reaction. When we increased the amount of PPh3 to 2.2 equiv,
3a could be generated in 99% yield. With the decrease of the
use of PPh3 or sulfuric acid, the yield of 3a was decreased
sharply (Table 1, entries 10−13). In addition, it is worth
noting that the reaction would not produce any products only
in the presence of PPh3 or sulfuric acid (Table 1, entries 14
and 15). In addition, we further screened other acids such as
CF3COOH, HCl, TsOH, CH3COOH, H3PO4, and salicylic
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a
Table 1. Optimization of the Reaction Conditions
b
entry
solvent
reductant
PPh3 (2.0)
acid
H2SO4
yield
1
2
3
4
5
6
7
8
H2O
65%
82%
78%
40%
64%
86%
61%
76%
88%
99%
47%
1,4-dioxane/H2O
EA/H2O
CH2Cl2/H2O
DMF/H2O
PPh3 (2.0)
PPh3 (2.0)
PPh3 (2.0)
PPh3 (2.0)
PPh3 (2.0)
PPh3 (2.0)
PPh3 (2.0)
PPh3 (2.0)
PPh3 (2.2)
PPh3 (1.0)
PPh3 (2.2)
PPh3 (2.2)
PPh3 (2.2)
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
H2SO4
THF/H2O
toluene/H2O
DMSO/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
c
73%
56%
0%
d
H2SO4
CF3COOH
HCl
TsOH
CH3COOH
H3PO4
salicylic acid
H2SO4
H2SO4
H2SO4
H2SO4
0%
PPh3 (2.2)
PPh3 (2.2)
PPh3 (2.2)
PPh3 (2.2)
PPh3 (2.2)
PPh3 (2.2)
(EtO)2P(O)H (2.2)
Zn (2.2)
Mn (2.2)
70%
80%
25%
54%
91%
82%
22%
trace
trace
e
PPh3 (2.2)
PPh3 (2.2)
87%
99%
f
H2SO4
a
Reactions were carried out with 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone (1a, 0.2 mmol), sodium benzenesulfinate (2a, 1.2 equiv),
reductant (x eq), and acid (2.0 equiv) in solvent (1.0 mL; for the mixed solvent system, v:v = 1:1), under a N2 atmosphere stirred for 3 h at 80 °C.
b
c
d
e
f
Yield was determined by GC analysis using dodecane as the internal standard. H2SO4 (1.0 equiv). H2SO4 (0.5 equiv). 60 °C. 100 °C.
dienone (1r) with 2a in 86% and 83% yields under the present
reaction conditions, respectively. Interestingly, when 2,6-di-
tert-butyl-4-(pyridin-2-ylmethylene)cyclohexa-2,5-dienone
(1s), 2,6-di-tert-butyl-4-(thiophen-3-ylmethylene)cyclohexa-
2,5-dienone (1t), and 2,6-di-tert-butyl-4-((2,3-dihydrobenzo-
furan-6-yl)methylene)cyclohexa-2,5-dienone (1u) were used as
the substrates for the reaction, the corresponding thiolation
products of 3s−3u could be generated in 66−84% yields.
However, the ortho-heteroatom-substituted heterocyclic p-
QMs such as 2,6-di-tert-butyl-4-((5-methylfuran-2-yl)-
methylene)cyclohexa-2,5-dienone (1v) and 2,6-di-tert-butyl-4-
(thiophen-2-ylmethylene)cyclohexa-2,5-dienone (1w) showed
negative results toward the reaction, and this phenomenon
may be ascribed to the fact that the O and S atoms in the
ortho-heterocyclic ring could interrupt the reduction path of
sodium benzenesulfinate in the reaction.
As depicted in Table 3, a range of substituted sodium aryl/
alkyl sulfinates (2b-2m) were screened under the optimized
reaction conditions with 1a. It is clear that sodium aryl
sulfinates bearing electron-donating groups such as sodium 4-
methylbenzenesulfinate (2b) and sodium 4-methoxybenzene-
sulfinate (2c) exhibit high reactivity toward 4-benzylidene-2,6-
di-tert-butylcyclohexa-2,5-dienone (1a), affording the expected
thiolation products of 4a and 4b in 85% and 80% yields,
respectively. In addition, the electron-withdrawing groups
substituted in the aryl ring of sodium arylsulfinates, such as
sodium 4-chlorobenzenesulfinate (2d), sodium 4-bromoben-
zenesulfinate (2e), and sodium 2-fluorobenzenesulfinate (2f),
also showed satisfactory results, giving the desired thiolation
products of 4c−4e with 86−91% yields. When sodium
thiophene-2-sulfinate (2g) and sodium naphthalene-2-sulfinate
(2h) were employed, the corresponding products of 2,6-di-tert-
butyl-4-(phenyl(thiophen-2-ylthio)methyl)phenol (4f) and
2,6-di-tert-butyl-4-((naphthalen-2-ylthio)(phenyl)methyl)-
phenol (4g) could be synthesized in 83% and 86% yields.
Notably, different kinds of sodium alkyl sulfinates such as
sodium phenylmethanesulfinate (2i), sodium furan-2-ylmetha-
nesulfinate (2j), sodium methanesulfinate (2k), sodium
propane-1-sulfinate (2l), and sodium 2-methylpropane-2-
sulfinate (2m) are also appropriate for this transformation to
afford the thiolation products of 4h−4l in moderate to good
yields.
To our surprise, when sodium benzo[d]oxazole-2-sulfinate
(2n) was used as the thiolation reagent for this transformation,
3-((3,5-di-tert-butyl-4-hydroxyphenyl)(phenyl)methyl)benzo-
[d]oxazole-2(3H)-thione (4m) was generated in 89% yield as
the rearrangement/1,6-conjugated addition product for the
reaction. It is deduced that the benzo[d]oxazole-2-thione
radical is much more stable than the benzo[d]oxazole-2-thiol
radical, which was formed in situ through intramolecular
rearrangement of the benzo[d]oxazole-2-thiol radical during
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a
Table 2. Substrate Scope of p-QMs
a
Reaction conditions: sodium benzenesulfinate (0.24 mmol), p-QMs compound (0.2 mmol), PPh3 (0.44 mmol), H2SO4 (0.4 mmol), CH3CN/
b
H2O (1.0 mL, v:v = 1:1), N2, 80 °C, 3 h. Isolated yields.
the reaction, thus leading to the synthesis of an amination
product (Scheme 3, Figure 1).
conjugate product was derived from H2SO4. On the basis of
this result, we further performed a kinetic isotope effect (KIE)
experiment between H2SO4 and D2SO4 for this reaction. A
KIE (kH/kD) constant was determined as 3.0 (Scheme 5, eqs 3
and 4). When benzenesulfinic acid (5) was adopted as the
substrate to react with p-QMs, the corresponding 1,6-
conjugate adduct of 2,6-di-tert-butyl-4-(phenyl-
(phenylsulfonyl)methyl)phenol (6) was generated in 96%
yield. In the presence of sulfuric acid and PPh3, the SO
bonds in 6 could be reduced efficiently to afford 3a in 38% (80
°C, 3 h) and 71% (100 °C, 3 h) yields, respectively (Scheme 5,
eqs 5 and 6).
According to the above results, a plausible mechanism for
the regioselective thiolation of p-QMs compound with sodium
aryl/alkyl sulfinates is proposed in Scheme 6. The present
reaction might involve two possible paths. In the presence of
sulfuric acid and PPh3, the corresponding thiyl radical (D)
In order to demonstrate the practical application of this
protocol, we conducted a large-scale reaction of 4-benzylidene-
2,6-di-tert-butylcyclohexa-2,5-dienone (1a, 10 mmol) with
sodium benzenesulfinate (2a, 12 mmol) and generated 3a in
83% yield (3.35 g, Scheme 4). In addition, a series of control
experiments was performed under the optimized reaction
conditions (Scheme 5). When the reaction was conducted with
the addition of a radical scavenger 2,2,6,6-tetramethylpiper-
idine N-oxyl (TEMPO), there were only trace amounts of 3a
detected after the reaction (Scheme 5, eqs 1 and 2). This result
proves that a phenyl thiyl radical may be produced during the
reaction. When acetonitrile-d3 and D2O were employed as a
mixed solvent for the reaction, 3a was generated in 94% yield
and there was no deuterization signal found for 3a. It is
deduced that the hydrogen atom for the thiolation/1,6-
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a
Table 3. Substrate Scope of Sodium Aryl/Alkyl Sulfinates
a
Reaction conditions: 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone (1a, 0.2 mmol), sodium aryl/alkyl sulfinate (2, 0.24 mmol), PPh3 (0.44
b
mmol), H2SO4 (0.4 mmol), CH3CN/H2O (1.0 mL, v:v = 1:1), N2, 80 °C, 3 h. Isolated yields.
Scheme 3. Rearrangement/1,6-Conjugated Addition of Sodium Benzo[d]oxazole-2-sulfinate to 2a
QMs with generation of the intermediate radical E. Through
the assistance of an acid, E could undergo the hydrogen-atom
transfer process to yield the final 1,6-conjugated adduct (Path
1). On the other hand, the 1,6-conjugate addition products of
F and G could be synthesized first through the reaction of
benzenesulfinic acid (B) and phenylsulfanol (C) with p-QMs.
In the presence of sulfuric acid and PPh3, the final product can
be formed correspondingly through selective reduction of the
SO bonds. Triphenylphosphine oxide was generated as the
byproduct for the reaction (Path 2). According to the control
experiment results in Scheme 4 (eqs 5 and 6), it is deduced
that Path 1 might be the fast step for the reaction.
CONCLUSIONS
■
In summary, we developed a convenient and highly efficient
method for the synthesis of diaryl methyl thioethers through
Figure 1. ORTEP drawing of compound 4m.18 Hydrogen atoms are
omitted for clarity; ellipsoids are drawn at 50% probability. Selected
the 1,6-conjugate addition of sodium aryl/alkyl sulfinates with
p-QMs. The approach avoids the use of highly toxic
thiophenols and transition metals, and the reaction can be
performed under mild conditions. Through the control
experiments, this transformation might be achieved with two
different paths. To the best of our knowledge, the
regioselective thiolation of p-QMs with sodium aryl/alkyl
sulfinates has not been exploited previously, and the salient
features of this transformation include its broad substrate
scope, absence of transition metals, and good regioselectivity.
bond lengths [Angstroms] and angles [degrees]: N1−C1 1.360(3),
N1−C2 1.416(3), N1−C8 1.478(3), C1−S1 1.646(2), C1−O1
1.371(3), C15−O2 1.382(3); C9−C8−C18 116.4(2), N1−C8−C18
109.5(2), C8−N1−C1 123.1(2), C8−N1−C2 127.5(2), N1−C1−S1
108.3(2), O1−C1−S1 122.2(2), N1−C1−O1 108.3(2).
could be formed through the acidification and reduction of
sodium aryl/alkyl sulfinate (A). Then the thiyl radical (D)
proceeds through radical addition at the olefinic moiety of p-
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Scheme 4. Large-Scale Synthesis of 3a
Scheme 5. Control Experiments for the Reaction Mechanism
in a Dean−Stark apparatus (oil bath). Piperidine (2.0 equiv) was
added dropwise over 1 h, and the reaction mixture was refluxed for 6−
12 h. After cooling just below the boiling point of the mixture, acetic
anhydride (2.0 equiv) was added and stirring was continued for 15
min. Then the reaction mixture was poured into ice−water, extracted
with DCM, and dried over Na2SO4, the solvent was evaporated, and
the residue was dried in vacuo. Pure p-QMs product was obtained by
passing the crude product through a short silica gel column using n-
hexane as eluent. Some other substituents (e.g., −Cl, −OMe, −Ph) in
substituted p-QMs failed to get the isolated products in the reactions
of 2,6-dimethoxyphenol, 2,6-dichlorophenol, and 2,6-diphenylphenol
with benzaldehyde.
This protocol also exhibits high potential for the construction
of biologically active diarylmethyl thioethers.
EXPERIMENTAL SECTION
■
General Considerations. All solvents used in the reactions were
freshly distilled. The other reagents were recrystallized or distilled as
necessary. All reactions were performed under an atmosphere of dry
nitrogen unless specified otherwise. 1H (400 MHz) and 13C{1H} (100
MHz) spectra were recorded on a 400 MHz spectrometer in CDCl3.
1H NMR chemical shifts were reported using TMS as the internal
standard, while 13C{1H} NMR chemical shifts were reported relative
to CDCl3. The electron ionization method was used for HRMS
measurements, and the mass analyzer type was double focusing.
General Procedure for the Preparation of p-Quinone
Methides (p-QMs). According to the reported procedure,8f 1.0
General Procedure. A mixture of p-quinone methides (p-QMs)
(0.2 mmol), RSO2Na (0.24 mmol, 1.2 equiv), H2SO4 (0.4 mmol, 2.0
equiv), and PPh3 (0.44 mmol, 2.2 equiv) were dissolved in CH3CN/
H2O (1.0 mL, v:v = 1:1) under a N2 atmosphere stirred for 3.0 h at 80
°C in an oil bath. Upon completion of the reaction, the mixture was
concentrated under vacuum. Removal of the solvent under a reduced
pressure gave the crude product; pure product was obtained by
passing the crude product through a short silica gel column using n-
hexane/EtOAc (80:1−5:1) as eluent.
equiv of 2,6-di-tert-butylphenol and 1.0 equiv of aldehyde were
dissolved in toluene (0.25 M) and the mixture was heated to 140 °C
2,6-Di-tert-butyl-4-(pyridin-2-ylmethylene)cyclohexa-2,5-dien-
one (1s). According to the general procedure, workup and flash
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Scheme 6. Plausible Mechanism
column chromatography (n-hexane/EtOAc 80:1) gave product 2s
(2.2 g, 7.5 mmol, 75%) as a yellow solid. 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 8.72−8.74 (m, 2H), 7.70−7.74 (m, 1H), 7.39−
7.41 (m, 1H), 7.20−7.23 (m, 1H), 6.95−6.98 (m, 2H), 1.34 (d, J =
5.4 Hz, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ =
186.7 (s), 155.2 (s), 150.1 (s), 149.8 (s), 148.5 (s), 138.3 (s), 136.5
(s), 135.5 (s), 134.5 (s), 129.2 (s), 127.2 (s), 35.6 (s), 35.1 (s), 29.7
(s), 29.6 (s). HRMS (ESI) m/z: calcd for C20H26NO [M + H]+,
296.2014; found, 296.2011.
2,6-Di-tert-butyl-4-(thiophen-3-ylmethylene)cyclohexa-2,5-dien-
one (1t). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 80:1) gave product 2t
(2.4 g, 7.9 mmol, 79%) as a yellow solid. 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 7.65−7.66 (m, 1H), 7.52−7.53 (m, 1H), 7.42−
7.44 (m, 1H), 7.31−7.32 (m, 1H), 7.08 (s, 1H), 6.98−6.99 (m, 1H),
1.33 (d, J = 3.4 Hz, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 186.4 (s), 149.2 (s), 147.6 (s), 137.8 (s), 135.8 (s), 135.3
(s), 130.9 (s), 128.7 (s), 128.6 (s), 127.5 (s), 126.9 (s), 35.5 (s), 35.0
(s), 29.6 (s), 29.5 (s). HRMS (ESI) m/z: calcd for C19H25OS [M +
H]+, 301.1626; found, 301.1625.
2,6-Di-tert-butyl-4-(thiophen-2-ylmethylene)cyclohexa-2,5-dien-
one (1w). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 80:1) gave product 2w
(2.3 g, 7.8 mmol, 78%) as a yellow solid. 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 7.86−7.87 (m, 1H), 7.55−7.56 (m, 1H), 7.32−
7.33 (m, 1H), 7.19 (s, 1H), 7.10−7.12 (m, 1H), 6.95−6.96 (m, 1H),
1.35 (d, J = 19.1 Hz, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 186.2 (s), 149.3 (s), 147.4 (s), 139.3 (s), 135.3 (s), 134.2
(s), 134.0 (s), 131.2 (s), 129.0 (s), 127.9 (s), 127.0 (s), 35.7 (s), 35.0
(s), 29.6 (s), 29.5 (s). HRMS (ESI) m/z: calcd for C19H25OS [M +
H]+, 301.1626; found, 301.1623.
2,6-Di-tert-butyl-4-(phenyl(phenylthio)methyl)phenol (3a). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 80:1) gave product 3a (76.8 mg,
0.19 mmol, 95%) as a yellow oil.13a 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.45−7.47 (m, 2H), 7.26−7.30 (m, 2H), 7.19−7.22
(m, 3H), 7.11−7.17 (m, 5H), 5.45 (s, 1H), 5.11 (s, 1H), 1.37 (s,
18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 152.9
(s), 141.6 (s), 136.4 (s), 135.7 (s), 131.4 (s), 131.1 (s), 128.6 (s),
128.5 (s), 128.4 (s), 127.0 (s), 126.6 (s), 125.1 (s), 57.9 (s), 34.4 (s),
30.3 (s).
2,6-Di-tert-butyl-4-((phenylthio)(p-tolyl)methyl)phenol (3b). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 80:1) gave product 3b (72.8 mg,
0.174 mmol, 87%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.26−7.28 (m, 2H), 7.12−7.14 (m, 2H), 7.00−7.08
(m, 7H), 5.35 (s, 1H), 5.02 (s, 1H), 2.21 (s, 3H), 1.29 (s, 18H).
13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 152.9 (s), 138.6
(s), 136.6 (s), 135.6 (s), 131.7 (s), 131.0 (s), 129.2 (s), 128.6 (s),
128.5 (s), 128.2 (s), 126.5 (s), 125.1 (s), 57.7 (s), 34.4 (s), 30.3 (s),
21.2 (s). HRMS (ESI) m/z: calcd for C28H35OS [M + H]+, 419.2409;
found, 419.2405.
2,6-Di-tert-butyl-4-((phenylthio)(p-tolyl)ethyl)phenol (3c). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 80:1) gave product 3c (70.0 mg,
0.162 mmol, 81%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.28−7.30 (m, 2H), 7.12−7.14 (m, 2H), 7.02−7.08
(m, 7H), 5.35 (s, 1H), 5.02 (s, 1H), 2.49−2.55 (m, 2H), 1.29 (s,
18H), 1.12 (t, J = 7.6 Hz, 3H). 13C{1H} NMR (100 MHz, CDCl3, 25
°C, TMS): δ = 152.8 (s), 143.0 (s), 138.8 (s), 136.6 (s), 135.6 (s),
131.7 (s), 131.0 (s), 128.6 (s), 128.2 (s), 128.0 (s), 126.5 (s), 125.1
(s), 57.7 (s), 34.4 (s), 30.3 (s), 28.5 (s), 21.2 (s). HRMS (ESI) m/z:
calcd for C29H37OS [M + H]+, 433.2565; found, 433.2560.
2,6-Di-tert-butyl-4-((4-(tert-butyl)phenyl)(phenylthio)methyl)-
phenol (3d). According to the general procedure, workup and flash
2,6-Di-tert-butyl-4-((2,3-dihydrobenzofuran-6-yl)methylene)-
cyclohexa-2,5-dienone (1u). According to the general procedure,
workup and flash column chromatography (n-hexane/EtOAc 80:1)
1
gave product 2u (2.6 g, 7.6 mmol, 76%) as a yellow solid. H NMR
(400 MHz, CDCl3, 25 °C, TMS): δ = 7.46−7.47 (m, 1H), 7.25 (s,
1H), 7.18−7.19 (m, 1H), 7.03 (s, 1H), 6.90−6.91 (m, 1H), 6.76−
6.78 (m, 1H), 4.56 (t, J = 8.7 Hz, 2H), 3.17 (t, J = 8.7 Hz, 2H), 1.24
(d, J = 5.3 Hz, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 186.5 (s), 161.5 (s), 148.8 (s), 147.0 (s), 143.4 (s), 135.5
(s), 131.7 (s), 130.1 (s), 128.8 (s), 128.2 (s), 127.9 (s), 127.4 (s),
109.9 (s), 71.9 (s), 35.4 (s), 35.0 (s), 29.6 (s), 29.5 (s), 29.4 (s).
HRMS (ESI) m/z: calcd for C23H29O2 [M + H]+, 337.2168; found,
337.2166.
2,6-Di-tert-butyl-4-((5-methylfuran-2-yl)methylene)cyclohexa-
2,5-dienone (1v). According to the general procedure, workup and
flash column chromatography (n-hexane/EtOAc 80:1) gave product
1
2v (2.5 g, 8.4 mmol, 84%) as a yellow solid. H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 8.17−8.18 (m, 1H), 6.91−6.92 (m, 1H),
6.60−6.65 (m, 2H), 6.17−6.17 (m, 1H), 2.42 (s, 3H), 1.35 (d, J =
19.1 Hz, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ =
185.8 (s), 157.2 (s), 151.7 (s), 148.5 (s), 147.1 (s), 135.0 (s), 128.8
(s), 127.2 (s), 126.4 (s), 120.4 (s), 109.6 (s), 35.5 (s), 35.0 (s), 29.6
(s), 29.5 (s) 14.2 (s). HRMS (ESI) m/z: calcd for C20H27O2 [M +
H]+, 299.2011; found, 299.2007.
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column chromatography (n-hexane/EtOAc 60:1) gave product 3d
(73.6 mg, 0.16 mmol, 80%) as a colorless oil.13a 1H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.37−7.39 (m, 2H), 7.29−7.31 (m, 2H),
7.19−7.23 (m, 2H), 7.11−7.17 (m, 5H), 5.41 (s, 1H), 5.10 (s, 1H),
1.37 (s, 18), 1.29 (s, 9H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 152.8 (s), 149.9 (s), 138.6 (s), 136.6 (s), 136.0 (s), 131.7
(s), 131.2 (s), 128.7 (s), 127.9 (s), 126.5 (s), 125.4 (s), 125.2 (s),
57.7 (s), 34.4 (s), 31.4 (s), 30.3 (s), 30.2 (s).
flash column chromatography (n-hexane/EtOAc 30:1) gave product
3j (79.7 mg, 0.184 mmol, 92%) as a colorless oil. H NMR (400
1
MHz, CDCl3, 25 °C, TMS): δ = 9.96 (s, 1H), 7.79−7.81 (m, 2H),
7.61−7.63 (m, 2H), 7.11−7.25 (m, 7H), 5.50 (s, 1H), 5.19 (s, 1H),
1.38 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ =
192.0 (s), 153.2 (s), 148.8 (s), 136.0 (s), 135.4 (s), 135.2 (s), 131.4
(s), 130.3 (s), 130.0 (s), 129.1 (s), 128.8 (s), 127.1 (s), 125.1 (s),
57.8 (s), 34.4 (s), 30.2 (s). HRMS (ESI) m/z: calcd for C28H33O2S
[M + H]+, 433.2201; found, 433.2200.
4-((4-Bromophenyl)(phenylthio)methyl)-2,6-di-tert-butylphenol
(3k). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 40:1) gave product 3k (89.7 mg,
0.186 mmol, 93%) as a colorless oil.13a 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 7.31−7.34 (m, 2H), 7.24−7.26 (m, 2H), 7.06−
7.17 (m, 5H), 7.01 (s, 2H), 5.33 (s, 1H), 5.08 (s, 1H), 1.30 (s, 18H).
13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 153.1 (s), 140.8
(s), 135.9 (s), 131.5 (s), 131.2 (s), 130.8 (s), 130.1 (s), 128.7 (s),
128.1 (s), 126.8 (s), 125.0 (s), 120.8 (s), 57.3 (s), 34.4 (s), 30.3 (s).
4-((2-Bromophenyl)(phenylthio)methyl)-2,6-di-tert-butylphenol
(3l). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 3l (92.6 mg,
0.192 mmol, 96%) as a colorless oil.13a 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 7.85−7.87 (m, 1H), 7.49−7.51 (m, 1H), 7.27−
7.30 (m, 1H), 7.04−7.24 (m, 8H), 6.01 (s, 1H), 5.14 (s, 1H), 1.38 (s,
18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 153.0
(s), 140.7 (s), 136.2 (s), 135.7 (s), 133.9 (s), 132.9 (s), 130.1 (s),
129.8 (s), 128.7 (s), 128.5 (s), 127.7 (s), 126.4 (s), 125.3 (s), 124.5
(s), 55.5 (s), 34.4 (s), 30.3 (s).
2,6-Di-tert-butyl-4-((4-isopropoxyphenyl)(phenylthio)methyl)-
phenol (3e). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 40:1) gave product 3e
1
(75.8 mg, 0.164 mmol, 82%) as a colorless oil. H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.26−7.29 (m, 2H), 7.12−7.15 (m, 2H),
7.04−7.10 (m, 5H), 6.72−6.74 (m, 2H), 5.33 (s, 1H), 5.04 (s, 1H),
4.41−4.46 (m, 1H), 1.30 (s, 18H), 1.22 (d, J = 6.4 Hz, 6H). 13C{1H}
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 156.8 (s), 152.8 (s),
136.5 (s), 135.6 (s), 133.5 (s), 131.7 (s), 131.1 (s), 129.4 (s), 128.6
(s), 126.5 (s), 125.1 (s), 115.7 (s), 69.9 (s), 57.3 (s), 34.4 (s), 30.3
(s), 22.1 (s). HRMS (ESI) m/z: calcd for C30H39O2S [M + H]+,
463.2671; found, 463.2668.
4-((4-(Benzyloxy)phenyl)(phenylthio)methyl)-2,6-di-tert-butyl-
phenol (3f). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 50:1) gave product 3f
1
(79.6 mg, 0.156 mmol, 78%) as a colorless oil. H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.22−7.31 (m, 7H), 7.04−7.13 (m, 7H),
6.80−6.82 (m, 2H), 5.34 (s, 1H), 5.03 (s, 1H), 4.93 (s, 2H), 1.29 (s,
18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 157.8
(s), 152.9 (s), 137.0 (s), 136.5 (s), 135.7 (s), 134.0 (s), 131.7 (s),
131.1 (s), 129.5 (s), 128.6 (s), 128.5 (s), 128.0 (s), 127.6 (s), 126.5
(s), 125.1 (s), 114.7 (s), 70.0 (s), 57.3 (s), 34.4 (s), 30.3 (s). HRMS
(ESI) m/z: calcd for C34H39O2S [M + H]+, 511.2671; found,
511.2668.
2,6-Di-tert-butyl-4-((4-fluorophenyl)(phenylthio)methyl)phenol
(3m). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 3m (75.2 mg,
0.178 mmol, 89%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.32−7.36 (m, 2H), 7.06−7.18 (m, 6H), 7.02 (s, 2H),
6.88−6.92 (m, 2H), 5.37 (s, 1H), 5.07 (s, 1H), 1.30 (s, 18H).
13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 161.8 (d,
2,6-Di-tert-butyl-4-((3-methoxyphenyl)(phenylthio)methyl)-
phenol (3g). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 10:1) gave product 3g
1
(73.8 mg, 0.17 mmol, 85%) as a colorless oil. H NMR (400 MHz,
1J(C,F) = 244.0 Hz), δ = 153.0 (s), 137.3 (d, 1J(C,F) = 3.2 Hz), 136.0
(s), 135.8 (s), 131.2 (s), 131.1 (s), 129.9 (d, 1J(C,F) = 8.0 Hz), 128.7
(s), 126.7 (s), 125.0 (s), 115.2 (d, 1J(C,F) = 21.4 Hz), 57.2 (s), 34.4
(s), 30.2 (s). HRMS (ESI) m/z: calcd for C27H32FOS [M + H]+,
423.2158; found, 423.2153.
CDCl3, 25 °C, TMS): δ = 7.19−7.23 (m, 3H), 7.11−7.17 (m, 5H),
7.03−7.07 (m, 2H), 6.73−6.76 (m, 1H), 5.42 (s, 1H), 5.12 (s, 1H),
3.76 (s, 3H), 1.37 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 159.6 (s), 152.9 (s), 143.2 (s), 136.4 (s), 135.7 (s), 131.3
(s), 131.1 (s), 129.4 (s), 128.7 (s), 126.6 (s), 125.1 (s), 120.8 (s),
113.9 (s), 112.7 (s), 57.9 (s), 55.2 (s), 34.4 (s), 30.3 (s). HRMS
(ESI) m/z: calcd for C28H35O2S [M + H]+, 435.2358; found,
435.2354.
2,6-Di-tert-butyl-4-((3-fluorophenyl)(phenylthio)methyl)phenol
(3n). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 3n (71.8 mg,
1
0.17 mmol, 85%) as a colorless oil. H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.09−7.25 (m, 10H), 6.87−6.92 (m, 1H), 5.42 (s,
1H), 5.15 (s, 1H), 1.38 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3,
25 °C, TMS): δ = 162.8 (d, 1J(C,F) = 244.4 Hz), 153.1 (s), 144.3 (d,
1J(C,F) = 6.6 Hz), 135.8 (s), 131.2 (s), 130.8 (s), 129.8 (d, 1J(C,F) =
2,6-Di-tert-butyl-4-((2,4-dimethoxyphenyl)(phenylthio)methyl)-
phenol (3h). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 10:1) gave product 3h
1
(82.6 mg, 0.178 mmol, 89%) as a colorless oil. H NMR (400 MHz,
8.3 Hz), 128.7 (s), 126.8 (s), 125.0 (s), 124.4 (s), 124.1 (d, 1J(C,F) =
2.9 Hz), 115.3 (d, 1J(C,F) = 22.2 Hz), 114.0 (d, 1J(C,F) = 21.1 Hz),
57.5 (s), 34.4 (s), 30.2 (s). HRMS (ESI) m/z: calcd for C27H32FOS
[M + H]+, 423.2158; found, 423.2155.
CDCl3, 25 °C, TMS): δ = 7.22−7.23 (m, 1H), 7.13−7.15 (m, 4H),
6.99−7.08 (m, 3H), 6.60−6.67 (m, 2H), 5.90 (s, 1H), 5.01 (s, 1H),
3.63 (d, J = 10.0 Hz, 6H), 1.30 (s, 18H). 13C{1H} NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 153.7 (s), 152.8 (s), 150.9 (s), 136.9 (s),
135.5 (s), 131.4 (s), 131.1 (s), 130.2 (s), 128.6 (s), 126.1 (s), 125.2
(s), 114.8 (s), 113.0 (s), 112.1 (s), 56.4 (s), 55.8 (s), 49.6 (s), 34.4
(s), 30.3 (s). HRMS (ESI) m/z: calcd for C29H37O3S [M + H]+,
465.2463; found, 465.2460.
4-((3,5-Di-tert-butyl-4-hydroxyphenyl)(phenylthio)methyl)-
benzonitrile (3o). According to the general procedure, workup and
flash column chromatography (n-hexane/EtOAc 20:1) gave product
1
3o (78.1 mg, 0.182 mmol, 91%) as a colorless oil. H NMR (400
MHz, CDCl3, 25 °C, TMS): δ = 7.45−7.50 (m, 4H), 7.09−7.17 (m,
5H), 7.00 (s, 2H), 5.38 (s, 1H), 5.12 (s, 1H), 1.31 (s, 18H). 13C{1H}
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 152.2 (s), 146.2 (s),
135.0 (s), 134.0 (s), 131.2 (s), 130.5 (s), 128.9 (s), 127.8 (s), 127.4
(s), 126.2 (s), 123.9 (s), 117.8 (s), 109.7 (s), 56.7 (s), 33.4 (s), 29.1
(s). HRMS (ESI) m/z: calcd for C28H32NOS [M + H]+, 430.2205;
found, 430.2201.
2,6-Di-tert-butyl-4-((4-nitrophenyl)(phenylthio)methyl)phenol
(3p). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 3p (79.0 mg,
0.176 mmol, 88%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 8.22−8.23 (m, 1H), 7.97−8.00 (m, 1H), 7.71−7.73
(m, 1H), 7.35−7.39 (m, 1H), 7.14−7.17 (m, 2H), 7.09−7.12 (m,
3H), 7.04 (s, 2H), 5.44 (s, 1H), 5.13 (s, 1H), 1.31 (s, 18H). 13C{1H}
2,6-Di-tert-butyl-4-((4-hydroxy-3-methoxyphenyl)(phenylthio)-
methyl)phenol (3i). According to the general procedure, workup and
flash column chromatography (n-hexane/EtOAc 10:1) gave product
3i (67.5 mg, 0.15 mmol, 75%) as a colorless oil. 1H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.21−7.23 (m, 2H), 7.12−7.18 (m, 5H),
7.00−7.01 (m, 1H), 6.90−6.93 (m, 1H), 6.81−6.83 (m, 1H), 5.57 (s,
1H), 5.40 (s, 1H), 5.13 (s, 1H), 3.82 (s, 3H), 1.38 (s, 18H). 13C{1H}
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 152.9 (s), 146.4 (s),
144.6 (s), 136.4 (s), 135.6 (s), 133.5 (s), 131.6 (s), 131.3 (s), 128.6
(s), 126.6 (s), 125.0 (s), 121.4 (s), 114.2 (s), 110.9 (s), 57.8 (s), 55.9
(s), 34.4 (s), 30.3 (s). HRMS (ESI) m/z: calcd for C28H35O3S [M +
H]+, 451.2307; found, 451.2305.
4-((3,5-Di-tert-butyl-4-hydroxyphenyl)(phenylthio)methyl)-
benzaldehyde (3j). According to the general procedure, workup and
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Article
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 153.4 (s), 148.2 (s),
144.1 (s), 136.2 (s), 134.9 (s), 134.5 (s), 131.9 (s), 130.0 (s), 129.3
(s), 128.9 (s), 127.4 (s), 125.0 (s), 123.5 (s), 122.1 (s), 57.5 (s), 34.4
(s), 30.2 (s). HRMS (ESI) m/z: calcd for C27H32NO3S [M + H]+,
450.2103; found, 450.2100.
2,6-Dimethyl-4-(phenyl(phenylthio)methyl)phenol (3q). Accord-
ing to the general procedure, workup and flash column chromatog-
raphy (n-hexane/EtOAc 10:1) gave product 3q (55.1 mg, 0.172
mmol, 86%) as a yellow oil.13a 1H NMR (400 MHz, CDCl3, 25 °C,
TMS): δ = 7.40−7.42 (m, 2H), 7.24−7.30 (m, 2H), 7.09−7.22 (m,
6H), 7.01 (s, 2H), 5.43 (s, 1H), 4.57 (s, 1H), 2.18 (s, 6H). 13C{1H}
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 151.4 (s), 141.5 (s),
136.6 (s), 132.5 (s), 130.1 (s), 128.6 (s), 128.5 (s), 127.1 (s), 126.3
(s), 123.1 (s), 56.8 (s), 16.1 (s).
column chromatography (n-hexane/EtOAc 20:1) gave product 4b
(69.5 mg, 0.16 mmol, 80%) as a colorless oil.17a 1H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.40−7.42 (m, 2H), 7.24−7.28 (m, 2H),
7.14−7.19 (m, 3H), 7.10 (s, 2H), 6.67−6.69 (m, 2H), 5.27 (s, 1H),
5.10 (s, 1H), 3.69 (s, 3H), 1.37 (s, 18H). 13C{1H} NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 159.3 (s), 152.9 (s), 141.9 (s), 135.6 (s),
135.2 (s), 131.7 (s), 128.5 (s), 128.4 (s), 127.0 (s), 126.2 (s), 125.2
(s), 114.2 (s), 59.7 (s), 55.2 (s), 34.4 (s), 30.3 (s).
2,6-Di-tert-butyl-4-(((4-chlorophenyl)thio)(phenyl)methyl)-
phenol (4c). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 20:1) gave product 4c
(79.9 mg, 0.182 mmol, 91%) as a colorless oil.17a 1H NMR (400
MHz, CDCl3, 25 °C, TMS): δ = 7.35−7.37 (m, 2H), 7.19−7.22 (m,
2H), 7.10−7.14 (m, 1H), 7.00−7.05 (m, 6H), 5.34 (s, 1H), 5.06 (s,
1H), 1.29 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS):
δ = 153.0 (s), 141.1 (s), 135.8 (s), 134.8 (s), 132.7 (s), 132.6 (s),
132.0 (s), 128.8 (s), 128.5 (s), 128.4 (s), 127.2 (s), 125.2 (s), 58.2
(s), 34.4 (s), 30.3 (s).
2,6-Diisopropyl-4-(phenyl(phenylthio)methyl)phenol (3r). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 10:1) gave product 3r (62.4 mg,
1
0.166 mmol, 83%) as a yellow oil. H NMR (400 MHz, CDCl3, 25
4-(((4-Bromophenyl)thio)(phenyl)methyl)-2,6-di-tert-butylphe-
nol (4d). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 20:1) gave product 4d
(82.9 mg, 0.172 mmol, 86%) as a colorless oil.17a 1H NMR (400
MHz, CDCl3, 25 °C, TMS): δ = 7.43−7.45 (m, 2H), 7.18−7.30 (m,
5H), 7.11 (s, 2H), 7.04−7.07 (m, 2H), 5.42 (s, 1H), 5.14 (s, 1H),
1.37 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ =
153.0 (s), 141.1 (s), 135.8 (s), 135.5 (s), 132.7 (s), 131.7 (s), 131.0
(s), 128.6 (s), 128.4 (s), 127.3 (s), 125.2 (s), 120.7 (s), 58.0 (s), 34.4
(s), 30.3 (s).
°C, TMS): δ = 7.42−7.44 (m, 2H), 7.27−7.30 (m, 2H), 7.09−7.24
(m, 6H), 7.04 (s, 2H), 5.48 (s, 1H), 4.72 (s, 1H), 3.03−3.13 (m, 2H),
1.19−1.21 (m, 12H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 149.1 (s), 141.5 (s), 136.4 (s), 133.5 (s), 132.7 (s), 130.9
(s), 128.6 (m), 128.4 (m), 128.3 (m), 127.0 (s), 126.5 (s), 123.7 (s),
57.6 (s), 27.3 (s), 22.7 (s). HRMS (ESI) m/z: calcd for C25H29OS
[M + H]+, 377.1939; found, 377.1936.
2,6-Di-tert-butyl-4-((phenylthio)(pyridin-2-yl)methyl)phenol (3s).
According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 5:1) gave product 3s (53.5 mg,
1
2,6-Di-tert-butyl-4-(((2-fluorophenyl)thio)(phenyl)methyl)phenol
(4e). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4e (74.3 mg,
0.176 mmol, 88%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.37−7.39 (m, 2H), 7.16−7.20 (m, 2H), 7.00−7.11
(m, 5H), 6.76−6.88 (m, 2H), 5.49 (s, 1H), 5.02 (s, 1H), 1.28 (s,
18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 162.0 (d,
1J(C,F) = 244.0 Hz), 153.0 (s), 141.1 (s), 135.6 (s), 134.3 (d, 1J(C,F)
0.132 mmol, 66%) as a yellow oil. H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 8.56−8.57 (m, 1H), 7.58−7.65 (m, 2H), 7.23−7.24
(m, 2H), 7.12−7.18 (m, 6H), 5.59 (s, 1H), 5.14 (s, 1H), 1.37 (s,
18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 160.9
(s), 153.2 (s), 149.3 (s), 136.7 (s), 135.8 (s), 131.2 (s), 130.2 (s),
128.7 (s), 126.7 (s), 125.3 (s), 122.7 (s), 122.0 (s), 59.3 (s), 34.4 (s),
30.2 (s). HRMS (ESI) m/z: calcd for C26H32NOS [M + H]+,
406.2205; found, 406.2202.
= 1.7 Hz), 131.0 (s), 129.0 (d, 1J(C,F) = 8.0 Hz), 128.4 (d, 1J(C,F) =
2,6-Di-tert-butyl-4-((phenylthio)(thiophen-3-yl)methyl)phenol
(3t). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 5:1) gave product 3s (64.0 mg,
1
3.8 Hz), 127.2 (s), 125.2 (s), 124.2 (d, J(C,F) = 3.7 Hz), 122.9 (d,
1J(C,F) = 17.8 Hz), 115.4 (d, 1J(C,F) = 22.7 Hz), 56.9 (d, 1J(C,F) =
1
0.156 mmol, 78%) as a yellow oil. H NMR (400 MHz, CDCl3, 25
2.3 Hz), 34.4 (s), 30.3 (s). HRMS (ESI) m/z: calcd for C27H32FOS
°C, TMS): δ = 7.46−7.55 (m, 4H), 7.32−7.38 (m, 4H), 7.11 (s, 2H),
5.35 (s, 1H), 5.26 (s, 1H), 1.35 (s, 18H). 13C{1H} NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 154.2 (s), 138.1 (s), 135.9 (s), 133.2 (s),
132.8 (s), 129.1 (s), 128.7 (s), 128.5 (s), 127.2 (s), 126.0 (s), 125.9
(s), 122.8 (s), 72.7 (s), 34.3 (s), 30.1 (s). HRMS (ESI) m/z: calcd for
C25H31OS2 [M + H]+, 411.1816; found, 411.1812.
2,6-Di-tert-butyl-4-((2,3-dihydrobenzofuran-6-yl)(phenylthio)-
methyl)phenol (3u). According to the general procedure, workup and
flash column chromatography (n-hexane/EtOAc 30:1) gave product
3u (75.0 mg, 0.168 mmol, 84%) as a yellow oil. 1H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.29 (s, 1H), 7.11−7.23 (m, 8H), 6.70−
6.71 (m, 1H), 5.41 (s, 1H), 5.12 (s, 1H), 4.55 (t, J = 8.7 Hz, 2H),
3.17 (t, J = 8.7 Hz, 2H), 1.39 (s, 18H). 13C{1H} NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 159.1 (s), 152.8 (s), 136.7 (s), 135.6 (s),
133.7 (s), 131.9 (s), 131.0 (s), 128.6 (s), 128.1 (s), 127.2 (s), 126.4
(s), 125.1 (s), 124.9 (s), 108.9 (s), 71.4 (s), 57.6 (s), 34.4 (s), 30.3
(s), 29.8 (s). HRMS (ESI) m/z: calcd for C29H35O2S [M + H]+,
447.2358; found, 447.2356.
2,6-Di-tert-butyl-4-(phenyl(p-tolylthio)methyl)phenol (4a). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4a (71.1 mg,
0.17 mmol, 85%) as a colorless oil.17a 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.44−7.46 (m, 2H), 7.25−7.28 (m, 2H), 7.15−7.20
(m, 1H), 7.10−7.12 (m, 4H), 6.94−6.96 (m, 2H), 5.38 (s, 1H), 5.10
(s, 1H), 2.23 (s, 3H), 1.36 (s, 18H). 13C{1H} NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 152.9 (s), 141.8 (s), 136.8 (s), 135.6 (s),
132.5 (s), 132.1 (s), 131.7 (s), 129.5 (s), 128.5 (s), 128.4(s), 127.0
(s), 125.2 (s), 58.6 (s), 34.4 (s), 30.3 (s), 21.2 (s).
[M + H]+, 423.2158; found, 423.2154.
2,6-Di-tert-butyl-4-(((2-fluorophenyl)thio)(phenyl)methyl)phenol
(4f). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4f (68.1 mg,
0.166 mmol, 83%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.34−7.36 (m, 2H), 7.20−7.23 (m, 2H), 7.14−7.17
(m, 2H), 7.05 (s, 2H), 6.74−6.77 (m, 2H), 5.21 (s, 1H), 5.01 (s, 1H),
1.31 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ =
153.1 (s), 141.1 (s), 135.7 (s), 134.9 (s), 133.9 (s), 130.8 (s), 130.0
(s), 128.6 (s), 128.4 (s), 127.2 (s), 127.1 (s), 125.2 (s), 61.7 (s), 34.4
(s), 30.3 (s). HRMS (ESI) m/z: calcd for C25H31OS2 [M + H]+,
411.1816; found, 411.1813.
2,6-Di-tert-butyl-4-((naphthalen-2-ylthio)(phenyl)methyl)phenol
(4g). According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4g (78.0 mg,
0.172 mmol, 86%) as a colorless oil.17a 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 7.69−7.71 (m, 1H), 7.57−7.83 (m, 3H), 7.49−
7.53 (m, 2H), 7.26−7.38 (m, 5H), 7.16−7.21 (m, 3H), 5.58 (s, 1H),
5.10 (s, 1H), 1.34 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C,
TMS): δ = 153.0 (s), 141.5 (s), 135.8 (s), 133.8 (s), 133.6 (s), 132.0
(s), 131.4 (s), 129.7 (s), 128.9 (s), 128.5 (s), 128.4 (s), 128.1 (s),
127.6 (s), 127.3 (s), 127.2 (s), 126.3 (s), 125.9 (s), 125.3 (s), 57.9
(s), 34.4 (s), 30.3 (s).
4-((Benzylthio)(phenyl)methyl)-2,6-di-tert-butylphenol (4h). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4h (76.1
mg, 0.182 mmol, 91%) as a colorless oil.17a 1H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.32−7.34 (m, 2H), 7.16−7.23 (m, 4H),
7.07−7.14 (m, 6H), 5.03 (s, 1H), 4.79 (s, 1H), 3.43 (s, 2H), 1.31 (s,
18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 152.9
2,6-Di-tert-butyl-4-(((4-methoxyphenyl)thio)(phenyl)methyl)-
phenol (4b). According to the general procedure, workup and flash
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J. Org. Chem. 2021, 86, 1516−1527

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
(s), 141.8 (s), 138.3 (s), 135.8 (s), 131.4 (s), 129.1 (s), 128.6 (s),
128.5 (s), 128.4 (s), 127.1 (s), 127.0 (s), 125.2 (s), 53.8 (s), 36.8 (s),
34.5 (s), 30.4 (s).
chromatography (n-hexane/EtOAc 80:1) gave product 3a′ (76.8
mg, 0.19 mmol, 91%) as a yellow oil.13a 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 7.38−7.40 (m, 2H), 7.18−7.24 (m, 2H), 7.10−
7.15 (m, 3H), 7.05−7.09 (m, 5H), 5.38 (s, 0.75 H), 5.04 (s, 1H), 1.30
(s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 151.8
(s), 140.5 (s), 135.3 (s), 134.6 (s), 130.3 (s), 130.1 (s), 127.5 (s),
127.4 (s), 127.3 (s), 126.0 (s), 125.5 (s), 124.1 (s), 56.9 (s), 33.4 (s),
29.2 (s).
2,6-Di-tert-butyl-4-(((furan-2-ylmethyl)thio)(phenyl)methyl)-
phenol (4i). According to the general procedure, workup and flash
column chromatography (n-hexane/EtOAc 20:1) gave product 4i
1
(61.5 mg, 0.15 mmol, 75%) as a colorless oil. H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.43−7.45 (m, 2H), 7.30−7.36 (m, 3H),
7.22−7.25 (m, 1H), 7.20 (s, 2H), 6.30 (s, 1H), 6.04 (s, 1H), 5.13 (s,
1H), 5.02 (s, 1H), 3.52 (s, 2H), 1.40 (s, 18H). 13C{1H} NMR (100
MHz, CDCl3, 25 °C, TMS): δ = 152.9 (s), 151.6 (s), 141.0 (s), 140.4
(s), 134.7 (s), 130.0 (s), 127.5 (s), 127.4(s), 126.0 (s), 124.0 (s),
109.3 (s), 106.4 (s), 52.9 (s), 33.3 (s), 29.2 (s), 27.7 (s). HRMS
(ESI) m/z: calcd for C26H33O2S [M + H]+, 409.2201; found,
409.2198.
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.joc.0c02390.
1
Crystallographic data; H and 13C{1H} NMR spectra
2,6-Di-tert-butyl-4-(phenyl(propylthio)methyl)phenol (4j). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4j (66.6 mg,
(PDF)
FAIR data which includes primary NMR FID files for
compounds 2s−2w, 3a−3u, 3a′, 4a−4m, and 6 (ZIP)
1
0.18 mmol, 88%) as a colorless oil. H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.44−7.46 (m, 2H), 7.30−7.34 (m, 2H), 7.19−7.24
(m, 3H), 5.12 (s, 1H), 4.98 (s, 1H), 1.96 (s, 3H), 1.40 (s, 18H).
13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 152.8 (s),
141.48 (s), 135.7 (s), 131.7 (s), 128.5 (s), 128.4 (s), 127.0 (s), 124.9
(s), 56.4 (s), 34.4 (s), 30.3 (s), 16.0 (s). HRMS (ESI) m/z: calcd for
C22H31OS [M + H]+, 343.2096; found, 343.2093.
Accession Codes
CCDC 2010097 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
2,6-Di-tert-butyl-4-(phenyl(propylthio)methyl)phenol (4k). Ac-
cording to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4k (66.6 mg,
1
AUTHOR INFORMATION
Corresponding Authors
0.18 mmol, 90%) as a colorless oil. H NMR (400 MHz, CDCl3, 25
■
°C, TMS): δ = 7.36−7.38 (m, 2H), 7.20−7.24 (m, 2H), 7.10−7.14
(m, 3H), 5.03 (s, 1H), 4.99 (s, 1H), 2.20−2.31 (m, 2H), 1.45−1.50
(m, 2H), 1.32 (s, 18H), 0.84 (t, J = 7.2 Hz, 3H). 13C{1H} NMR (100
MHz, CDCl3, 25 °C, TMS): δ = 152.8 (s), 142.4 (s), 135.7 (s), 132.0
(s), 128.5 (s), 128.4 (s), 126.9 (s), 124.9 (s), 54.5 (s), 34.5 (s), 34.4
(s), 30.4 (s), 22.5 (s), 13.7 (s). HRMS (ESI) m/z: calcd for
C24H35OS [M + H]+, 371.2409; found, 371.2405.
2,6-Di-tert-butyl-4-((tert-butylthio)(phenyl)methyl)phenol (4l).
According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 20:1) gave product 4l (56.8 mg,
0.148 mmol, 74%) as a colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C, TMS): δ = 7.48−7.50 (m, 2H), 7.25−7.29 (m, 2H), 7.14−7.21
(m, 3H), 5.13 (s, 1H), 5.08 (s, 1H), 1.40 (s, 18H), 1.22 (s, 9H).
13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 152.6 (s), 144.1
Biquan Xiong − Department of Chemistry and Chemical
Engineering, Hunan Institute of Science and Technology,
Yueyang 414006, P. R. China; Department of Applied
Biology and Chemical Technology, The Hong Kong
Polytechnic University, Hung Hom, Hong Kong, P. R. China;
orcid.org/0000-0002-6490-6384; Email: xiongbiquan@
126.com
Ke-Wen Tang − Department of Chemistry and Chemical
Engineering, Hunan Institute of Science and Technology,
Yueyang 414006, P. R. China; orcid.org/0000-0002-
1194-2664; Email: tangkewen@sina.com
Wai-Yeung Wong − Department of Applied Biology and
Chemical Technology, The Hong Kong Polytechnic
University, Hung Hom, Hong Kong, P. R. China;
orcid.org/0000-0002-9949-7525; Email: wai-
yeung.wong@polyu.edu.hk
(s), 135.7 (s), 133.4 (s), 128.4 (s), 128.3 (s), 126.7 (s), 125.0 (s),
52.7 (s), 44.5 (s), 34.5 (s), 31.4 (s), 30.4 (s). HRMS (ESI) m/z: calcd
for C25H37OS [M + H]+, 385.2565; found, 385.2564.
3-((3,5-Di-tert-butyl-4-hydroxyphenyl)(phenyl)methyl)benzo[d]-
oxazole-2(3H)-thione (4m). According to the general procedure,
workup and flash column chromatography (n-hexane/EtOAc 20:1)
Authors
1
gave product 4m (82.1 mg, 0.178 mmol, 89%) as a colorless oil. H
Shipan Xu − Department of Chemistry and Chemical
Engineering, Hunan Institute of Science and Technology,
Yueyang 414006, P. R. China
Yu Liu − Department of Chemistry and Chemical Engineering,
Hunan Institute of Science and Technology, Yueyang 414006,
P. R. China; orcid.org/0000-0003-4555-8238
NMR (400 MHz, CDCl3, 25 °C, TMS): δ = 7.41 (s, 1H), 7.25−7.28
(m, 4H), 7.16−7.19 (m, 2H), 7.02−7.10 (m, 3H), 6.90−6.94 (m,
1H), 6.42−6.44 (m, 1H), 5.21 (s, 1H), 1.26 (s, 18H). 13C{1H} NMR
(100 MHz, CDCl3, 25 °C, TMS): δ = 181.0 (s), 153.8 (s), 147.1 (s),
136.9 (s), 136.1 (s), 131.0 (s), 128.7 (s), 128.3 (s), 128.2 (s), 126.5
(s), 125.8 (s), 124.2 (s), 123.9 (s), 112.4 (s), 110.4 (s), 65.3 (s), 34.4
(s), 30.2 (s). HRMS (ESI) m/z: calcd for C28H32NO2S [M + H]+,
446.2154; found, 446.2151.
2,6-Di-tert-butyl-4-((tert-butylthio)(phenyl)methyl)phenol (6).
According to the general procedure, workup and flash column
chromatography (n-hexane/EtOAc 5:1) gave product 6 (83.8 mg,
0.192 mmol, 96%) as a colorless oil.17b 1H NMR (400 MHz, CDCl3,
25 °C, TMS): δ = 7.60−7.63 (m, 2H), 7.55−7.57 (m, 2H), 7.47−
7.51 (m, 1H), 7.30−7.36 (m, 5H), 7.19 (s, 2H), 5.25 (s, 1H), 5.20 (s,
1H), 1.35 (s, 18H). 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS):
δ = 154.2 (s), 138.5 (s), 135.9 (s), 133.4 (s), 133.2 (s), 130.0 (s),
129.1 (s), 128.7 (s), 128.5 (s), 128.4 (s), 127.1 (s), 123.2 (s), 76.8
(s), 34.3 (s), 30.2 (s).
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.joc.0c02390
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (21606080), Natural Science Foundation
of Hunan Province (2019JJ50203), Scientific Research Fund of
the Hunan Provincial Education Department (19A197),
Innovation Research Group Project of the Natural Science
2,6-Di-tert-butyl-4-(phenyl(phenylthio)methyl)phenol (3a′). Ac-
cording to the general procedure, workup and flash column
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J. Org. Chem. 2021, 86, 1516−1527

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Article
Liu, X.; Wei, W.; Yang, D.; He, C.; Zhang, T.; Wang, H. Molecular
Iodine-Mediated Difunctionalization of Alkenes with Nitriles and
Thiols Leading to β-Acetamido Sulfides. J. Org. Chem. 2016, 81,
2252−2260. (d) Yang, D.; Sun, P.; Wei, W.; Meng, L.; He, L.; Fang,
B.; Jiang, W.; Wang, H. Metal-free iodine-catalyzed direct cross-
dehydrogenative coupling (CDC) between pyrazoles and thiols. Org.
Chem. Front. 2016, 3, 1457−1461. (e) Wang, L.; Yue, H.; Yang, D.;
Cui, H.; Zhu, M.; Wang, J.; Wei, W.; Wang, H. Metal-free Oxidative
Coupling of Aromatic Alkenes with Thiols Leading to (E)-Vinyl
Sulfones. J. Org. Chem. 2017, 82, 6857−6864.
Foundation of Hunan Province (No. 2020JJ1004), and Hunan
Provincial Innovation Foundation for Postgraduate
(CX20201132). W.-Y.W. thanks the Hong Kong Polytechnic
University (1-ZE1C) and the Endowed Professorship in
Energy from Ms Clarea Au (847S) for financial support.
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■
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