Visible Light-Catalyzed Benzylic C-H Bond Chlorination by a Combination of Organic Dye (Acr+-Mes) and N-Chlorosuccinimide

Article abstract of DOI:10.1021/acs.joc.0c01000

By combining "N-chlorosuccinimide (NCS)"as the safe chlorine source with "Acr+-Mes"as the photocatalyst, we successfully achieved benzylic C-H bond chlorination under visible light irradiation. Furthermore, benzylic chlorides could be converted to benzylic ethers smoothly in a one-pot manner by adding sodium methoxide. This mild and scalable chlorination method worked effectively for diverse toluene derivatives, especially for electron-deficient substrates. Careful mechanistic studies supported that NCS provided a hydrogen abstractor "N-centered succinimidyl radical,"which was responsible for the cleavage of the benzylic C-H bond, relying on the reducing ability of Acr?-Mes.

Full text of DOI:10.1021/acs.joc.0c01000

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Article
Visible-Light-Catalyzed Benzylic C-H Bond Chlorination by a
Combination of Organic Dye (Acr+-Mes) and N-Chlorosuccinimide
Ming Xiang, Chao Zhou, Xiu-Long Yang, Bin Chen, Chen-Ho Tung, and Li-Zhu Wu
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.0c01000 • Publication Date (Web): 20 May 2020
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Visible-Light-Catalyzed Benzylic C-H Bond Chlorination by a
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Combination
of
Organic
Dye
(Acr+-Mes)
and
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N-Chlorosuccinimide
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Ming Xiang,§ Chao Zhou,§ Xiu-Long Yang, Bin Chen, Chen-Ho Tung, and Li-Zhu
Wu*
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of
Physics and Chemistry & University of Chinese Academy of Sciences, the Chinese Academy of
Sciences, Beijing 100190, P. R. China, School of Future Technology, University of Chinese
Academy of Science, Beijing 100049, P. R. China
*E-mail: lzwu@mail.ipc.ac.cn
ABSTRACT: Combining "N-chlorosuccinimide (NCS)" as the safe chlorine source
with "Acr+-Mes" as the photocatalyst, we successfully achieved benzylic C-H bond
chlorination under visible-light irradiation. Furthermore, benzylic chlorides could be
converted to benzylic ethers smoothly in a one-pot manner by adding sodium
methoxide. This mild and scalable chlorination method worked effectively for diverse
toluene derivatives, especially for electron-deficient substrates. Careful mechanistic
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studies supported that NCS provided hydrogen abstractor "N-centered succinimidyl
radical", which was responsible for the cleavage of benzylic C-H bond, relying on the
reducing ability of Acr+-Mes.
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INTRODUCTION
Direct benzylic C-H bond chlorination is one of the most essential and
important transformations1 due to its wide applications in the pharmaceutical
synthesis2, and such transformation provides the useful feedstock for fine chemical
industry3. Up to now, numerous methods have been developed for the conversion
of toluene derivatives to benzylic chlorides. Traditionally, benzylic chlorination
reactions involved the use of explosive, corrosive or toxic chlorine sources, such
as: Cl2, SOCl2 or CCl4, under heating or irradiation conditions (Figure 1a).3b,4
These methods produced the uncontrollable amount of chlorine radical, in which
substrates needed to be acted as the solvent to avoid polychlorination, thus
restricting the promotion of reaction yields. To provide the controlled chlorine
radical, great efforts have been made by combining the stoichiometric amount of
oxidants, like peroxides, NaOCl, and chloride anion. Although previous
chlorinated processes have been optimized during the last few decades (Figure
1b),5 the drawback of such tactics was the formation of oxygenated byproduct.
Recently, many chlorinating reagents,6 such as N-chlorophthalimide (NCP),
N-chlorosuccinimide (NCS) or trichloroisocyanuric acid (TCCA), as safe,
environmentally friendly and alternative chlorine sources were increasingly used
in different chlorination reactions (Figure 1c).7 With the help of metal complex
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additives7c, sunlight irradiation7d or heating with oxidant7e, N-centered radical8
could be obtained from these reagents, which is responsible for the activation of
the benzylic C-H bond via a hydrogen atom transfer (HAT) process, then the
generated benzylic radical can abstract a chlorine atom from the N-Cl moiety to
afford benzylic chloride. Clearly, the development of simpler and milder benzylic
chlorination methods is of considerable need for chlorinated processes.
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(a) Cl2, SOCl2, CCl4 ...
Cl
R
R
(b) Oxidant + Cl
(c) NCS, NCP, TCCA ...
Figure 1. Classic chlorination methods for benzylic C-H bond.
In recent years, visible light catalysis has emerged as a powerful synthesis
tool relying on the strong redox ability of excited photocatalysts.9 Specifically,
photocatalyst should cooperate with appropriate oxidant or reductant to realize
single electron transfer (SET) process. The famous Fukuzumi dye "Acr+-Mes" is
generally recognized as a strong oxidant to realize the activation of electron-rich
arenes and alkenes under the visible light.10 Significantly, it also possesses the
reducing ability for activating hypervalent iodine reagents and halogenated
reagents.11 As a consequence, we proposed that it could be a practicable plan to
accomplish the benzylic chlorination via the combination of Acr+-Mes and
appropriate chlorinating reagent (Figure 2).12
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Our design:
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O
O
O
O
N
N
Me
Cl
[HAT]
Acr -Mes +
Me
Acr+-Mes +
h
Me
Arc+-Mes
N
Me
e-
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H
Cl
Photocatalysis based on
oxidative quenching of Acr+-Mes
R1
R1
R2
R2
Figure 2. Our design for benzylic chlorination based on oxidative quenching of
Acr+-Mes.
RESULTS AND DICUSSION
Initially to realize the benzylic C-H chlorination reaction, we selected
N-chlorophthalimide (NCP) as the chlorine source. As shown in Table 1, the
desired chlorinated product 2a was obtained in 68% yield with 100% conversion
of methylbenzene 1a when using acetonitrile as the solvent under ambient argon
atmosphere with 1 hour blue LEDs (λ = 450 ± 10 nm) irradiation (entry 1). Among
chlorine
sources
screened,
including
N-chlorosuccinimide
(NCS),
N-chloro-N-methyl-4-toluenesulfonamide (Ts-NClMe) and 4-toluenesulfonyl
chloride (Ts-Cl), NCS provided the optimal efficiency (entry 2-4). Subsequently,
examination of different solvents suggested that CH2Cl2 could give a slightly
higher yield (entries 5-7). Considering that substrate 1a was not completely
consumed after 1 hour irradiation in CH2Cl2, we prolonged the reaction time.
Further optimization of reaction time revealed that all of 1a was converted with
the optimal yield 78% when 1a (0.3 mmol), Acr+-Mes ClO4 (5 mol %), and NCS
-
(2.0 equiv) were combined in CH2Cl2 (3 mL) irradiated by blue LEDs for 4 hours
(entries 8-9). Lastly, control experiments confirmed the nature of this
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photocatalytic reaction that no desired product was observed without the
photocatalyst or light (entry 10).
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Table 1. Optimization of the reaction conditiona
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Acr+-Mes, Chlorine Source
Cl
Blue LEDs, Ar, Solvent
1a
2a
Entry Chlorine Source Solvent
Time
(h)
1
Yield
(%)b
68
1
2
NCP
NCS
CH3CN
CH3CN
CH3CN
CH3CN
DCM
1
1
1
1
1
1
4
8
4
73
21
0
3
Ts-NClMe
Ts-Cl
NCS
4
5
76
71
43
78
75
0
6
NCS
CHCl3
DCE
7
NCS
8
NCS
DCM
9
NCS
DCM
10c
NCS
DCM
O
O
O
O
S
Cl
N
N
Cl
N
Cl
S
Cl
O
O
O
O
NCS
NCP
Ts-NClMe
Ts-Cl
aStandard conditions: 1a (0.3 mmol), Acr+-Mes (5 mol %) and Chlorine source (2.0 equiv) in
b
the solvent (3 mL) were irradiated by blue LEDs under an argon atmosphere. Determined by
+
c
GC using n-tetradecane as an internal standard. General conditions, but with no Acr -Mes or
light.
Under the optimized conditions, some representative alkylbenzene
derivatives were examined to explore the generality of this new chloration method.
As summarized in Scheme 1, both benzylic methyl and methylene groups could be
chlorinated (2a-2b, 64%-78%), though the reaction yield of ethylbenzene was
lower than that of toluene. To our delight, substrates containing different
functional groups on the aromatic ring were smoothly converted to the
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corresponding chlorides in moderate to good yields (2c-2i, 2k-2l, 64%-85%).
Electron-deficient groups such as cyan, ester carbonyl and ketone carbonyl were
tolerated well for this transformation while nitro group was also suitable for this
system albeit with low reactivity (2j, 21%). Especially, meta-electron-withdrawing
substituted toluene derivative methyl 3-methylbenzoate 1g, which has a significant
electronic property on benzylic C-H bond, showed good reactivity with 65% yield.
On the other hand, it should be pointed out that the amount of NCS needed to be
decreased to improve reaction yields of electron-rich substrates (1d) because too
much NCS would lead to the chlorination of aromatic ring. As for more
electron-rich benzene derivative like 1,3,5-trimethoxybenzene, it worked with
NCS to generate 2-chloro-1,3,5-trimethoxybenzene in 95% yield. Moreover,
substrate 1k involving a carboxylic ester group on the alkyl chain was also
competent for this reaction (2k, 65%). Notably, our reaction system would not
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result in benzylic oxidation for all substrates examined above.
Scheme 1. Scope of alkylbenzene derivatives for benzylic C-H chlorinationa
Cl
Acr+-Mes, NCS
R2
R2
R1
R1
Blue LEDs, Ar, 4 h, DCM
1
2
Ph
Cl
Cl
Cl
Cl
Cl
Ph
2a, 78%b
2b, 64%b
2d, 70%c
2c, 77%
Cl
Cl
O
Cl
O
O
Cl
O
O
CN
2g, 65%d
Cl
2f, 64%d
2h, 71%d
Cl
2e, 65%
O
Cl
Ph
O
O2N
O
2i, 76%d
2j, 21%d
2k, 65%
2l, 85%b
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aReaction conditions: 1 (0.3 mmol), Acr+-Mes (5 mol %) and NCS (2.0 equiv) in DCM (3 mL)
were irradiated by blue LEDs for 4 hours under an argon atmosphere. Isolated yields are shown.
bDetermined by GC using n-tetradecane as an internal standard (Figure S1-S3). c1.1 equiv of NCS.
d2.2 equiv of NCS.
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With respect to the more reactive substrate "diphenylmethane 1l",
corresponding benzylic chloride could be obtained in 85% yield (2l, determined by
GC). However, the product was not able to be obtained as a pure compound due to
the hydrolysis issue. We therefore transformed the benzylic chloride to the
benzylic ether by using NaOMe as the nucleophile (Scheme 2, 2l', 80%).
Moreover, diphenylmethanes bearing different electron-donating group (t-Bu, Ph
or OMe) or various electron-withdrawing group (F, Cl, COOMe or COMe) were
successfully suitable to accomplish this two-step transformation (Scheme, 2m'-2t',
55%-76%), which provided a feasible protocol for benzylic C-O bond
construction.
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Scheme 2. Scope of diphenylmethane derivatives for one-pot benzylic C-O bond
constructiona
1) Acr+-Mes, NCS, DCM, Ar, Blue LEDs
2) NaOMe, CH3OH, Air, rt.
H
O
Ph
Ar
Ph
Ar
1
2'
O
O
2m' (R = t-Bu): 61%b
2n' (R = Ph): 69%b
2o' (R = OMe): 59%b
R
2l', 80%
O
O
2q' (R' = F): 76%
O
2r' (R' = Cl): 74%
2s' (R' = COOMe): 71%c
R' 2t' (R' = COMe): 65%c
2p', 55%b
aReaction conditions: 1 (0.3 mmol), Acr+-Mes (5 mol %) and NCS (2.0 equiv) in DCM (3 mL)
were irradiated by blue LEDs for 1 hour under an argon atmosphere. Then CH3OH (3 mL) and
NaOMe (1 mmol) were added into the mixture, which was stirred for 3 hours at room temperature.
Isolated yields are shown. b1.1 equiv of NCS. c2.2 equiv of NCS and irradiation for 3 hours; after
adding NaOMe, the mixture was heated to reflux for 12 hours.
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Considering that light penetration affected photocatalytic reaction efficiency
significantly, special reaction equipment, like the continuous flow setup, was
needed for the large-scale reaction.13 However, a scale-up reaction for 1i (5.5
mmol, 1.08 g) gave 2i in 71% yield, which was comparable with that of a
small-scale reaction for 1i (0.3 mmol, 76% yield), without an aid of a flow
technology (Scheme 3a). In addition, cyclic aliphatic hydrocarbons could be
chlorinated14 albeit with relatively low yields (39-45%), which further expanded
the substrate scope of this new chlorination method (Scheme 3b). Because the
excited Acr+-Mes could not oxidize substrate alkane to cation radical, we
speculated that the direct oxidation/deprotonation pathway could be excluded in
our photoredox reaction. Furthermore, the competition experiment with
diphenylketone derivatives were operated in our reaction condition to provide the
corresponding product in 15% and 21% yields respectively (Scheme 3c), which
indicated there was no obvious regioselectivity between primary and secondary
C-H bonds. Finally, when N-bromosuccinimide (NBS) was used as the bromine
resource, 1i could directly provide the bromide product 3i with 60% yield, which
highlights the versatility of this strategy (Scheme 3d).
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Scheme 3. (a) Gram-Scale benzylic C-H chlorination of 1i; (b) Alphatic C-H
chlorination; (c) The competition experiment; (d) Benzylic C-H bromination of 1i.
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(a)
Cl
Acr+-Mes, NCS
Ph
Ph
5
6
Blue LEDs, Ar, 8 h, DCM
O
O
7
8
9
1i, (1.08 g, 5.5 mmol)
(b)
2i, [gram-scale] 71%
Cl
Acr+-Mes, NCS
n = 1: 39%
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n = 2: 45%
n
Blue LEDs, Ar, 4 h, DCM
n
(c)
Ph
Cl
Ph
Acr+-Mes, 1eq NCS
(15%)
Cl
(0.3 mmol)
(0.3 mmol)
O
+
O
+
Blue LEDs, Ar, 4 h, DCM
Ph
Ph
O
(21%)
O
(d)
Br
Acr+-Mes, NBS
Ph
Ph
Blue LEDs, Ar,4 h, DCM
3i,
O
60%
O
To shed light on the reaction mechanism, several control experiments were
carried out. 1) No chlorination product was afforded in the absence of NCS under
standard condition, ruling out the effect of CH2Cl2 in chlorination (Figure S4a). 2)
when
2
equiv
2,2,6,6-tetramethyl-1-piperidinyloxy
(TEMPO)
or
2,6-di-tert-butyl-4-methylphenol (BHT) as radical inhibitors was added into the
model condition, the yield of desired product was suppressed to trace and almost
all of substrate 1l was remained (Figure S4b). 3) We observed benzylic bromide
under our chlorination conditions with diethyl bromomalonate (DEBM), and
DEBM did not give benzylic bromide when combining with photocatalyst
Acr+-Mes (Figure S4c), which indicated that benzylic radical was involved in our
system. 4) In the absence of substrate toluene, NCS was also reduced to
succinimide relying on photocatalyst Acr+-Mes (Figure S5). Thus, the excited
Acr+-Mes could reduce NCS, and solvent CH2Cl2 provided hydrogen source for
the reduction product succinimide. 5) When replacing oxidant NCS with O2, no
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benzaldehyde or benzoic acid could be detected and nearly all substrate 1a and 1l
were remained after 4 hours of irradiation (Figure S6), which meant that the
excited Acr+-Mes could not directly oxidize them in CH2Cl2. Although we could
not exclude the possibility that the reaction proceeded via direct oxidation of
substrates by excited photocatalyst, especially for electron-rich ones, it was not the
main reaction process in our reaction system. 6) We conducted time-resolved
transient absorption spectrum to confirm the SET from the charge-separated state
Acr·-Mes·+ to NCS.15 As shown in Figure 3, the lifetime of Acr·-Mes·+ was
decreased with increasing concentration of NCS, and the quenching rate constant
was obtained from the slope of the liner plot of kdecay versus [NCS] to be 1.1 × 107
M-1s-1.10b Meanwhile, the rate constant of electron transfer from toluene to
Acr·-Mes·+ was 2.0 × 106 M-1s-1 according to Fukuzumi’s report.16 These
observations collectively supported that this photoredox reaction was initiated
through the oxidative quenching of Acr+-Mes, namely the SET oxidation of the
excited Acr+-Mes by NCS. 7) Although benzylic radical would react with NCS
directly to afford benzylic chloride resulting in radical chain propagation process,
the time profile of benzylic chlorination using diphenylmethane 1l as substrate
revealed that continuous visible-light irradiation was necessary to this
photocatalytic transformation and the propagating chain reaction was short-lived
(Figure S7). We therefore speculated that Acr+-Mes·+, coming from oxidation of
Acr·-Mes·+, would oxidize benzylic radical regenerating Acr+-Mes, which restarted
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the short chain propagation under illumination.
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Figure 3. Quenching experiments (a) Decay of transient absorbance of Acr·-Mes·+ at
500 nm in the absence and presence of NCS (0-8 mM) in deaerated MeCN containing
Acr+-Mes (0.05 mM) after nanosecond laser flash photolysis (λex = 430 nm). (b) Plot
of kdecay versus [NCS] for the reaction of Acr·-Mes·+ with NCS.
Not only that, related electrochemical potential and binding dissociation energy
data also match with our experiment results. The reduction potential (Ered) of NCS
*
is -0.27 V vs SCE, which is higher than the oxidation potential of Acr+-Mes·+ (Eox
= -0.57 V vs SCE),17 so the electron transfer from the excited Acr+-Mes to NCS is
thermodynamically feasible. The reduced NCS would then leave a chlorine anion
to generate the succinimidyl radical. Furthermore, the bond dissociation energy of
benzylic C-H bond (89.7 kcal mol-1) is lower than that of N-H bond strength in
succinimide (118 kcal mol-1),18 so it is reasonable that the succinimidyl radical can
abstract a hydrogen atom from benzylic C-H bond to give benzylic radical.
On the basis of above discussion, a likely mechanism of this chlorination
reaction is outlined in Scheme 4. Initially, Acr+-Mes is excited by visible light,
forming the charge-separated state Acr·-Mes·+ via the intramolecular electron
transfer. NCS would oxidize Acr·-Mes·+, and further release Cl- with the
generation of N-centered succinimidyl radical 4 and Acr+-Mes·+. Subsequently, 4
abstracts a hydrogen atom from substrate 1 to give benzylic radical 5. Next, 5
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accepts a chlorine atom from NCS affording benzylic chloride 2 and hydrogen
abstractor 4, which results in chain propagation reaction. Finally, Acr+-Mes·+ may
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oxidizes 5 or some electron-rich substrates to accomplish photocatalytic cycle.
Scheme 4. Proposed mechanism
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O
1
O
O
- Cl
HAT
N
N
Cl
NH
4
Acr+-Mes +
O
O
O
O
NCS
4
SET
Ar
R
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N
Cl
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SET
Oxidative
Quenching
Cycle
1
Cl
2
O
Ar
R
Acr -Mes +
Acr+-Mes
Ar
R
6
hv
In summary, we have developed a novel method for benzylic C-H bond
chlorination using NCS as the cheap and safe chlorine source. Hydrogen abstractor
"N-centered succinimidyl radical" was obtained through oxidative quenching of
Acr+-Mes, which was employed for hydrogen-atom-transfer process of benzylic C-H
bond. This mild and effective chlorinated reaction only needs one equivalent of
substrate, and works for a broad scope of alkylbenzenes. Remarkably, it could achieve
the gram-scale transformation in a satisfactory yield, and avoid oxidation of benzylic
C-H bond. Additional investigation in developing inert C-H bond functionalization
based on this photocatalytic protocol is underway in our group.
EXPERIMENTAL SECTION
General information
13
1H NMR and C NMR spectra were recorded using a Bruker Avance DPX 400
MHz and 100 MHz instrument and referenced to the internal solvent signals. Mass
spectra were obtained using a Q-Exactive instrument. GC quantitative analysis was
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performed using a SHIMADZU 2010plus instrument (Helium as the carrier gas,
n-tetradecane as an internal standard, SH-Rtx-5 capillary column, FID detector). In
the transient absorption spectral measurements, the samples were purged with argon
for 15 min. Excitation was provided by using an Nd:YAG laser (third harmonic, 10 ns)
at 532 nm. The detector was a xenon lamp on the Edingburge LP920 apparatus from
Analytical Instruments. The values of lifetime were calculated by exponential
function fitting with luminescence spectrometer software L900. Commercially
available reagents and solvents were used without further purification. All
photoreactions were performed using common dry, inert atmosphere techniques.
Irradiation with blue light was performed using High Power UV 1W®TaoYuan LED
(λ = 450 ± 10 nm, 300 mA). For the irradiation, the material of the reaction vessel is
common glass; the distance from the light source is about 0.5 cm. No filters were used
in the general procedures. Reactions were monitored by TLC, and column
chromatography purification processes were carried out using silica gel GF254.
General Procedure for the Synthesis of Diphenylmethane Derivatives.
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Prepared (1m, 1o, 1p, 1s, 1t) according to literature methods.19 A mixture of phenyl
boronic acid (4 mmol), potassium carbonate (1382 mg, 10 mmol), benzyl bromide
(475 ul, 4 mmol) in acetone-water (3:1, 40 mL) was stirred at room temperature until
the reaction mixture became homogeneous. Then, the mixture was cooled in an ice
bath and PdCl2 (12 mg, 0.068 mmol) was added at 0 °C under an argon atmosphere.
Stirring was continued at room temperature for 15 hours. The acetone was removed
under reduced pressure and the product was extracted with diethyl ether (10 mL × 3).
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The combined organic phases were dried over MgSO4 and evaporated under reduced
pressure. Purification by column chromatography (eluting with pure hexane to
hexane/ethyl acetate 10:1) to afforded the product. While 1m, 1o, 1p and 1s were
afforded as colorless oils, only, 1t was obtained as a white solid. Data for
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1
1-benzyl-4-(tert-butyl)benzene (1m): Yield: 770.6 mg, 86%. H NMR (400 MHz,
CDCl3) δ 7.33 - 7.16 (m, 7H), 7.11 (d, J = 8.1 Hz, 2H,), 3.95 (s, 2H), 1.30 (s, 9H);
13C{1H} NMR (100 MHz, CDCl3) δ 149.0, 141.4, 138.2, 129.1, 128.7, 128.6, 126.1,
125.5, 41.6, 34.5, 31.6. Data for 1-benzyl-4-methoxybenzene (1o): Yield: 649.4 mg,
1
82%. H NMR (400 MHz, CDCl3) δ 7.31 - 7.24 (m, 2H), 7.18 (t, J = 7.6 Hz, 3H),
7.10 (d, J = 8.0 Hz, 2H), 6.83 (d, J = 7.7 Hz, 2H), 3.92 (s, 2H), 3.78 (s, 3H); 13C{1H}
NMR (100 MHz, CDCl3) δ 158.1, 141.7, 133.4, 130.0, 129.0, 128.6, 126.1, 114.0,
1
55.4, 41.2. Data for 1-benzyl-2-methoxybenzene (1p): Yield: 633.6 mg, 80%. H
NMR (400 MHz, CDCl3) δ 7.35 - 7.16 (m, 6H), 7.09 (d, J = 7.5 Hz, 1H), 6.91 (t, J =
13
7.2 Hz, 2H), 4.01 (s, 2H), 3.85 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 157.5,
141.2, 130.5, 129.8, 129.1, 128.4, 127.5, 125.9, 120.6, 110.6, 55.5, 36.0. Data for
1
methyl 4-benzylbenzoate (1s): Yield: 777.4 mg, 86%. H NMR (400 MHz, CDCl3) δ
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7.95 (d, J = 8.0 Hz, 2H), 7.36 - 7.11 (m, 7H), 4.03 (s, 2H), 3.89 (s, 3H); C{1H}
NMR (100 MHz, CDCl3) δ 167.2, 146.7, 140.3, 130.0, 129.1, 128.8, 128.3, 126.5,
1
52.1, 42.1. Data for 1-(4-benzylphenyl)ethan-1-one (1t): Yield: 714.0 mg, 85%. H
NMR (400 MHz, CDCl3) δ 7.88 (d, J = 7.4 Hz, 2H), 7.38 - 7.12 (m, 7H), 4.03 (s, 2H),
13
2.57 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 197.9, 146.9, 140.2, 135.4, 129.2,
129.1, 128.8, 126.6, 42.1, 26.7. Other information of them could be found literature
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methods.19
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General procedure for the benzylic chlorination reaction.
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A 10 mL reaction tube equipped with magnetic stirring bar was charged with
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-
Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (80.1 mg, 0.6 mmol, 2 equiv),
3 mL CH2Cl2, alkylbenzene derivate (0.3 mmol, 1 equiv). The reaction tube was
sealed and the reaction mixture was degassed by bubbling with argon for 15 minutes.
The mixture was stirred and irradiated with blue LEDs (λ = 450 ± 10 nm) for 4 hours
at room temperature. After that, the mixture was concentrated in vacuo, and then
purified by column chromatography on silica gel (eluting with pure hexane to
hexane/ethyl acetate 10:1) to afford the desired benzylic chloride. Note: The identity
of volatile products (2a, 2b, 2l) were confirmed by GC analysis using n-tetradecane as
an internal standard because the products 2a, 2b are volatile, and 2l couldn't be
obtained as a pure compound due to the hydrolysis issue.
General procedure for one-pot benzylic C-O bond construction.
Initially, a 10 mL reaction tube equipped with magnetic stirring bar was charged with
-
Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (80.1 mg, 0.6 mmol, 2 equiv),
3 mL CH2Cl2, diphenylmethane derivate (0.3 mmol, 1 equiv). The reaction tube was
sealed and the reaction mixture was degassed by bubbling with argon for 15 minutes.
The mixture was stirred and irradiated with blue LEDs (λ = 450 ± 10 nm) for 1 h at
room temperature. Then CH3OH (3 mL) and NaOMe (54.0 mg, 1 mmol) were added
into the mixture, which was stired for 3 hours at room temperature. After that, the
solution was diluted with H2O (10 mL), and extracted with CH2Cl2 (10 mL × 3). The
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combined organic phase was dried (Na2SO4) and concentrated in vacuo. The mixture
was purified by column chromatography on silica gel (eluting with pure hexane to
hexane/ethyl acetate 10:1) to afford the desired benyzlic ether.
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Experiment Procedure for gram-scale synthesis.
To a 100 mL Pyrex tube (inner diameter: 3.5 cm, length: 14 cm) equipped with a
magnetic stir bar was charged with 4-methylbenzophenone 1i (1079.1 mg, 5.5 mmol,
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1 equiv), Acr+-Mes ClO4 (113.2 mg, 0.275 mmol, 5 mol %), NCS (1615.4 mg, 12.1
mmol, 2.2 equiv), 55 mL CH2Cl2. The mixture was strictly deaerated and irradiated
by blue LEDs (λ = 450 ± 10 nm) for 8 hours at room temperature. After that, the
mixture was concentrated in vacuo, and then purified by column chromatography on
silica gel (eluting with pure hexane to hexane/ethyl acetate 10:1) to afford the desired
benzylic chloride 2i in 71% yield (1.08 g).
Experiment procedure for the competition reaction.
A 10 mL reaction tube equipped with magnetic stirring bar was charged with
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Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (40.0 mg, 0.3 mmol, 1 equiv),
3 mL CH2Cl2, 4-methylbenzophenone 1i (0.3 mmol, 58.9 mg, 1 equiv) and
4-ethylbenzophenone (0.3 mmol, 63.1 mg, 1 equiv). The reaction tube was sealed and
the reaction mixture was degassed by bubbling with argon for 15 minutes. The
mixture was stirred and irradiated with blue LEDs (λ = 450 ± 10 nm) for 4 hours at
1
room temperature. After that, the mixture was analyzed by H NMR directly using
1,3,5-trimethoxybenzene as an internal standard. The competition reaction provided
the corresponding product with 15% and 21% yields for primary and secondary C-H
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bonds respectively.
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Experiment procedure for benzylic bromination reaction.
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Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NBS (117.5 mg, 0.66 mmol, 2.2
equiv), 3 mL CH2Cl2, 4-methylbenzophenone 1i (0.3 mmol, 58.9 mg, 1 equiv). The
reaction tube was sealed and the reaction mixture was degassed by bubbling with
argon for 15 minutes. The mixture was stirred and irradiated with blue LEDs (λ = 450
± 10 nm) for 4 hours at room temperature. After that, the mixture was concentrated in
vacuo, and then purified by column chromatography on silica gel (eluting with pure
hexane to hexane/ethyl acetate 10:1) to afford the desired benzylic bromide 3i.
Experiment procedures for the control experiments (Figure S4).
Figure S4a: A 10 mL reaction tube equipped with magnetic stirring bar was charged
-
with Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), toluene 1a (31.7 µL, 0.3 mmol,
1 equiv), 3 mL CD2Cl2. The reaction tube was sealed and the reaction mixture was
degassed by bubbling with argon for 15 minutes. Then, the mixture was stirred and
irradiated with blue LEDs (λ = 450 ± 10 nm) for 4 hours at room temperature. After
1
that, the mixture was analyzed by H NMR directly using 2,2-diphenylacetonitrile as
an internal standard. The yield of chlorination product was 0% and almost all of
substrate 1l was remained.
Figure S4b: A 10 mL reaction tube equipped with magnetic stirring bar was charged
with Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (80.1 mg, 0.6 mmol, 2
-
equiv), BHT (132.2 mg, 0.6 mmol) or TEMPO (93.7 mg, 0.6 mmol), 3 mL CH2Cl2,
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diphenylmethane 1l (50.5 mg, 0.3 mmol, 1 equiv). The reaction tube was sealed and
the reaction mixture was degassed by bubbling with argon for 15 minutes. Then, the
mixture was stirred and irradiated with blue LEDs (λ = 450 ± 10 nm) for 1 hour at
room temperature. After that, the mixture was analyzed by GC using n-tetradecane as
an internal standard. The yield of desired product was trace and almost all of substrate
1l was remained.
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Figure S4c: A 10 mL reaction tube equipped with magnetic stirring bar was charged
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with Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (80.1 mg, 0.6 mmol, 2
equiv), diethyl bromomalonate (DEBM, 256 ul, 1.5 mmol), 3 mL CH2Cl2,
diphenylmethane 1l (50.5 mg, 0.3 mmol, 1 equiv). The reaction tube was sealed and
the reaction mixture was degassed by bubbling with argon for 15 minutes. Then, the
mixture was stirred and irradiated with blue LEDs (λ = 450 ± 10 nm) for 1 hour at
room temperature. After that, the mixture was analyzed by GC using n-tetradecane as
an internal standard. The desired product (bromomethylene)dibenzene and
(chloromethylene)dibenzene could be afforded with 13% and 61% yields respectively.
However, it couldn't produce the benzylic bromide product under the same condition
just without the NCS.
Model benzylic chlorination reaction in the absence of substrate toluene (Figure
S5).
A 10 mL reaction tube equipped with magnetic stirring bar was charged with
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Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (80.1 mg, 0.6 mmol, 2 equiv),
1
3 mL CH2Cl2. We first concentrated the mixture in vacuo and detected H NMR
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spectrum of them in CDCl3 before irradiation. Subsequently, the mixture of Acr+-Mes
and NCS in an argon-saturated DCM (3 mL) was irradiated by blue LEDs for 10 min,
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30 min and 4 hours, and corresponding H NMR spectra were detected. It was very
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clear that NCS (δ 2.93) was gradually converted into succinimide (δ 2.76) as the
reaction progress.
Model benzylic chlorination reaction replacing oxidant NCS with O2 (Figure S6).
A 10 mL reaction tube equipped with magnetic stirring bar was charged with
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Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (80.1 mg, 0.6 mmol, 2 equiv),
1a or 1l (0.3 mmol, 1 equiv.), 3 mL CH2Cl2 under the air. Subsequently, the mixture
of was irradiated by blue LEDs for 1 hour, 2 hours, 3 hours and 4 hours, and the
residue of substrate substrate was detected by GC using n-tetradecane as an internal
standard. The result indicated after 4 hours of irradiation, nearly all substrate toluene
was remained (1a, 93%; 1l, 97%).
Experiment procedure for the light-dark cycle experiment (Figure S7).
Six 10 mL reaction tubes were equipped with magnetic stirring bars, and each tube
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was charged with Acr+-Mes ClO4 (6.2 mg, 0.015 mmol, 5 mol %), NCS (80.1 mg,
0.6 mmol, 2 equiv), 3 mL CH2Cl2, diphenylmethane 1l (50.5 mg, 0.3 mmol, 1 equiv).
The reaction tubes were sealed and the reaction mixtures were degassed by bubbling
with argon for 15 minutes. Then, each mixture was stirred and irradiated with blue
LEDs (λ = 450 ± 10 nm) at room temperature. The first one: stir with light for 5 mins;
The second one: stir with light for 5 mins, then without light for 5 mins; The third
one: stir with light for 5 mins, then without light for 5 mins, then with light for 5
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mins; The fourth one: stir with light for 5 mins, then without light for 5 mins, then
with light for 5 mins, then without light for 5 mins; The fifth one: stir with light for 5
mins, then without light for 5 mins, then with light for 5 mins, then without light for 5
mins, then with light for 5 mins; The sixth one: stir with light for 5 mins, then without
light for 5 mins; then with light for 5 mins, then without light for 5 mins, then with
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light for
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mins, then without light for
5
mins. After that,
2,6-di-tert-butyl-4-methylphenol BHT (132.2mg, 0.6 mmol) was added to terminate
the reaction. At last, the yield was determined by acquiring GC using n-tetradecane as
an internal standard.
2-(chloromethyl)-1,1'-biphenyl (2c). Yield: 46.8 mg, 77%. Colorless oil. Purified
by column chromatography on silica gel (eluting with pure hexane to hexane/ethyl
acetate 10:1). 1H NMR (400 MHz, CDCl3) δ 7.61 - 7.54 (m, 1H), 7.53 - 7.36 (m, 7H),
13
7.34 - 7.29 (m, 1H), 4.56 (s, 2H); C{1H} NMR (100 MHz, CDCl3) δ 142.3, 140.4,
135.2, 130.6, 130.5, 129.3, 128.6, 128.5, 128.1, 127.6, 44.6; HRMS (EI): m/z calcd
for C13H11Cl [M]+ 202.0544, found 202.0557.
4-(chloromethyl)-1,1'-biphenyl (2d). Yield: 42.6 mg, 70%. White solid. Purified by
column chromatography on silica gel (eluting with pure hexane to hexane/ethyl
acetate 10:1). 1H NMR (400 MHz, CDCl3) δ 7.65 - 7.58 (m, 4H), 7.55 - 7.44 (m, 4H),
13
7.43 - 7.36 (m, 1H), 4.67 (s, 2H); C{1H} NMR (100 MHz, CDCl3) δ 141.5, 140.6,
136.6, 129.2, 129.0, 127.7, 127.6, 127.3, 46.2; HRMS (EI): m/z calcd for C13H11Cl
[M]+ 202.0544, found 202.0553.
4'-(chloromethyl)-[1,1'-biphenyl]-2-carbonitrile (2e). Yield: 44.4 mg, 65%. White
solid. Purified by column chromatography on silica gel (eluting with pure hexane to
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hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.77 (d, J = 7.7 Hz, 1H),
7.65 (t, J = 7.7 Hz, 1H), 7.61 - 7.49 (m, 5H), 7.46 (t, J = 7.6 Hz, 1H), 4.65 (s, 2H);
13C{1H} NMR (100 MHz, CDCl3) δ 145.5, 138.9, 138.7, 134.5, 133.6, 130.7, 129.8,
129.6, 128.5, 119.2, 112.1, 46.4; HRMS (EI): m/z calcd for C14H10ClN [M]+
227.0497, found 227.0506.
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methyl 4-(chloromethyl)benzoate (2f). Yield: 35.4 mg, 64%. Colorless solid.
Purified by column chromatography on silica gel (eluting with pure hexane to
1
hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 8.03 (d, J = 8.2 Hz, 2H),
7.46 (d, J = 8.2 Hz, 2H), 4.61 (s, 2H), 3.92 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3)
δ 166.7, 142.4, 130.4, 130.2, 128.6, 52.3, 45.5; HRMS (EI): m/z calcd for C9H9ClO2
[M]+ 184.0286, found 184.0296.
methyl 3-(chloromethyl)benzoate (2g). Yield: 35.9 mg, 65%. Colorless oil.
Purified by column chromatography on silica gel (eluting with pure hexane to
hexane/ethyl acetate 10:1). 1H NMR (400 MHz, CDCl3) δ 8.11 - 7.95 (m, 2H), 7.59 (d,
J = 7.3 Hz, 1H), 7.44 (t, J = 7.6 Hz, 1H), 4.62 (s, 2H), 3.93 (s, 3H); C{1H} NMR
13
(100 MHz, CDCl3) δ 166.7, 138.0, 133.1, 130.8, 129.8, 129.7, 129.0, 52.4, 45.6;
HRMS (ESI): m/z calcd for C9H9ClO2 [M]+ 184.0286, found 184.0281.
1-(4-(chloromethyl)phenyl)ethan-1-one (2h). Yield: 35.9 mg, 71%. White solid.
Purified by column chromatography on silica gel (eluting with pure hexane to
1
hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.95 (d, J = 8.2 Hz, 2H),
7.48 (d, J = 8.2 Hz, 2H), 4.61 (s, 2H), 2.60 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3)
δ 197.5, 142.6, 137.3, 128.9, 128.8, 45.4, 26.7; HRMS (EI): m/z calcd for C9H9ClO
[M]+ 168.0337, found 168.0344.
(4-(chloromethyl)phenyl)(phenyl)methanone (2i). Yield: 52.6 mg, 76%. Colorless
solid. Purified by column chromatography on silica gel (eluting with pure hexane to
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hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.78 (d, J = 8.1 Hz, 4H),
7.61 - 7.53 (m, 1H), 7.53 - 7.41 (m, 4H), 4.62 (s, 2H); 13C{1H} NMR (100 MHz,
CDCl3) δ 195.9, 141.7, 137.5, 137.4, 132.6, 130.4, 130.0, 128.4, 128.3, 45.4; HRMS
(EI): m/z calcd for C14H11ClO [M]+ 230.0493, found 230.0500.
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1-(chloromethyl)-4-nitrobenzene (2j). Yield: 11.0 mg, 21%. White solid. Purified
by column chromatography on silica gel (eluting with pure hexane to hexane/ethyl
acetate 10:1). 1H NMR (400 MHz, CDCl3) δ 8.23 (d, J = 7.1 Hz, 4H), 7.58 (d, J = 7.1
13
Hz, 4H), 4.66 (s, 2H); C{1H} NMR (100 MHz, CDCl3) 148.0, 144.4, 129.5, 124.1,
44.6; HRMS (ESI): m/z calcd for C7H6ClNO2 [M]+ 171.0082, found 171.0078.
methyl 3-chloro-3-phenylpropanoate (2k). Yield: 38.7 mg, 65%. Colorless oil.
Purified by column chromatography on silica gel (eluting with pure hexane to
1
hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.42 (d, J = 7.3 Hz, 2H),
7.40 - 7.31 (m, 3H), 5.36 (dd, J = 9.1, 5.7 Hz, 1H), 3.71 (s, 3H), 3.19 (dd, J = 16.0,
13
9.1 Hz, 1H), 3.04 (dd, J = 16.0, 5.7 Hz, 1H); C{1H} NMR (100 MHz, CDCl3) δ
170.1, 140.5, 128.9, 128.9, 127.0, 58.2, 52.1, 44.9; HRMS (EI): m/z calcd for
C10H11ClO2 [M]+ 198.0443, found 198.0448.
(methoxymethylene)dibenzene (2l'). Yield: 47.6 mg, 80%. Colorless oil. Purified
by column chromatography on silica gel (eluting with pure hexane to hexane/ethyl
1
acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.41 - 7.28 (m, 8H), 7.24 (dd, J = 7.8,
13
5.8 Hz, 2H), 5.24 (s, 1H), 3.38 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 142.3,
128.5, 127.6, 127.1, 85.7, 57.1; HRMS (EI): m/z calcd for C14H14O [M]+ 198.1040,
found 198.1048.
1-(tert-butyl)-4-(methoxy(phenyl)methyl)benzene (2m'). Yield: 46.5 mg, 61%.
Colorless oil. Purified by column chromatography on silica gel (eluting with pure
1
hexane to hexane/ethyl acetate 10:1). H NMR (400 MHz, DMSO-d6) δ 7.37 - 7.29
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(m, 6H), 7.29 - 7.19 (m, 3H), 5.28 (s, 1H), 3.25 (s, 3H), 1.24 (s, 9H); C{1H} NMR
(100 MHz, DMSO-d6) δ 149.5, 142.5, 139.4, 128.2, 127.1, 126.4, 126.1, 125.0, 84.0,
56.3, 34.1, 31.1; HRMS (EI): m/z calcd for C18H22O [M]+ 254.1666, found 254.1683.
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4-(methoxy(phenyl)methyl)-1,1'-biphenyl (2n'). Yield: 56.8 mg, 69%. White solid.
Purified by column chromatography on silica gel (eluting with pure hexane to
1
hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.55 (dd, J = 7.5, 5.4 Hz,
4H), 7.44 - 7.36 (m, 6H), 7.33 (q, J = 7.4 Hz, 3H), 7.27 - 7.22 (m, 1H), 5.28 (s, 1H),
13
3.41 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 142.2, 141.3, 141.0, 140.5, 128.9,
128.6, 127.7, 127.5, 127.4, 127.3, 127.2, 127.1, 85.4, 57.2; HRMS (EI): m/z calcd for
C20H18O [M]+ 274.1353, found 274.1363.
1-methoxy-4-(methoxy(phenyl)methyl)benzene (2o'). Yield: 40.4 mg, 59%.
Colorless oil. Purified by column chromatography on silica gel (eluting with pure
1
hexane to hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.41 - 7.28 (m,
4H), 7.25 (d, J = 8.6 Hz, 3H), 6.85 (d, J = 8.6 Hz, 2H), 5.20 (s, 1H), 3.77 (s, 3H), 3.36
(s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 159.3, 142.6, 134.6, 128.5, 128.4, 127.5,
127.0, 114.0, 85.2, 57.0, 55.4; HRMS (EI): m/z calcd for C15H16O2 [M]+ 228.1145,
found 228.1161.
1-methoxy-2-(methoxy(phenyl)methyl)benzene (2p'). Yield: 37.7 mg, 55%.
Colorless oil. Purified by column chromatography on silica gel (eluting with pure
1
hexane to hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.46 (d, J = 7.6
Hz, 1H), 7.38 (d, J = 7.6 Hz, 2H), 7.28 (t, J = 7.5 Hz, 2H), 7.25 - 7.19 (m, 2H), 6.96 (t,
J = 7.5 Hz, 1H), 6.84 (d, J = 8.2 Hz, 1H), 5.68 (s, 1H), 3.79 (s, 3H), 3.38 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3) δ 156.8, 142.2, 130.7, 128.5, 128.3, 127.2, 127.1,
127.0, 120.9, 110.7, 78.9, 57.2, 55.6; HRMS (EI): m/z calcd for C15H16O2 [M]+
228.1145, found 2281161.
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1-fluoro-4-(methoxy(phenyl)methyl)benzene (2q'). Yield: 49.3 mg, 76%.
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6
Colorless oil. Purified by column chromatography on silica gel (eluting with pure
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8
1
hexane to hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.35 - 7.22 (m,
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7H), 7.06 - 6.92 (m, 2H), 5.21 (s, 1H), 3.36 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3)
δ 162.3 (d, J = 245.6 Hz), 142.0, 138.1 (d, J = 3.1 Hz), 128.7 (d, J =8.1 Hz), 128.6,
127.7, 127.0, 115.4 (d, J = 21.4 Hz), 84.8, 57.1; 19F NMR (375 MHz, CDCl3) δ
-115.22; HRMS (EI): m/z calcd for C14H13FO [M]+ 216.0945, found 216.0957.
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1-chloro-4-(methoxy(phenyl)methyl)benzene (2r'). Yield: 51.6 mg, 74%.
Colorless oil. Purified by column chromatography on silica gel (eluting with pure
1
hexane to hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.34 - 7.29 (m,
13
4H), 7.28 (s, 4H), 7.25 (dd, J = 5.7, 2.8 Hz, 1H), 5.20 (s, 1H), 3.36 (s, 3H); C{1H}
NMR (100 MHz, CDCl3) δ 141.7, 140.9, 133.3, 128.7, 128.7, 128.4, 127.9, 127.0,
84.9, 57.1; HRMS (EI): m/z calcd for C14H13ClO [M]+ 232.0650, found 232.0659.
methyl 4-(methoxy(phenyl)methyl)benzoate (2s'). Yield: 54.6 mg, 71%.
Colorless oil. Purified by column chromatography on silica gel (eluting with pure
1
hexane to hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.99 (d, J = 8.2
Hz, 2H), 7.43 (d, J = 8.2 Hz, 2H), 7.33 (d, J = 4.3 Hz, 4H), 7.29 - 7.25 (m, 1H), 5.28
13
(s, 1H), 3.89 (s, 3H), 3.38 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 167.1, 147.5,
141.5, 129.9, 129.4, 128.7, 128.0, 127.2, 126.8, 85.2, 57.2, 52.2; HRMS (EI): m/z
calcd for C16H16O3 [M]+ 256.1094, found 256.1098.
1-(4-(methoxy(phenyl)methyl)phenyl)ethan-1-one (2t'). Yield: 46.8 mg, 65%.
Colorless oil. Purified by column chromatography on silica gel (eluting with pure
1
hexane to hexane/ethyl acetate 10:1). H NMR (400 MHz, CDCl3) δ 7.94 - 7.91 (m,
1H), 7.91 - 7.89 (m, 1H), 7.45 (d, J = 8.2 Hz, 2H), 7.33 (d, J = 4.4 Hz, 4H), 7.28 -
7.25 (m, 1H), 5.28 (s, 1H), 3.39 (s, 3H), 2.57 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3) δ 197.9, 147.7, 141.4, 136.5, 128.7, 128.7, 128.0, 127.1, 127.0, 85.1, 57.2,
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26.7; HRMS (EI): m/z calcd for C16H16O2 [M]+ 240.1145, found 240.1157.
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6
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8
9
(4-(bromomethyl)phenyl)(phenyl)methanone (3i). Yield: 49.5 mg, 60%. White
solid. Purified by column chromatography on silica gel (eluting with pure hexane to
hexane/ethyl acetate 10:1). 1H NMR (400 MHz, CDCl3) δ 7.85 - 7.75 (m, 4H), 7.64 -
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7.57 (m, 1H), 7.55 - 7.41 (m, 4H), 4.54 (s, 2H); C{1H} NMR (100 MHz, CDCl3) δ
196.1, 142.2, 137.6, 137.5, 132.7, 130.7, 130.1, 129.1, 128.5, 32.4; HRMS (ESI): m/z
calcd for C14H11BrO [M+H]+ 275.0067, found 275.0058.
SUPPORTING INFORMATION
The Supporting Information is available free of charge at http://pubs.acs.org. Copies
of 1H and 13C NMR spectra for all products.
AUTHOR INFORMATION
Corresponding Author
*E-mail: lzwu@mail.ipc.ac.cn.
Author Contributions
§M.X. and C.Z. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We are grateful for financial support from the Ministry of Science and Technology of
China (2017YFA0206903), the National Natural Science Foundation of China
(21861132004), the Strategic Priority Research Program of the Chinese Academy of
Science (XDB17000000), the Key Research Program of Frontier Sciences of the
Chinese Academy of Science (QYZDY-SSW-JSC029), and K. C. Wong Education
Foundation.
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