An efficient metal-free oxidative esterification and amination of benzyl C-H bond

Article abstract of DOI:10.3390/molecules25071527

An esterification and amination of benzylic C-H bonds was developed by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) under metal- and iodide-free conditions. Both carboxylic acids and amines could be used as ideal coupling partners for the oxidati

Full text of DOI:10.3390/molecules25071527

molecules
Communication
An Efficient Metal-Free Oxidative Esterification and
Amination of Benzyl C–H Bond
Saiwen Liu 1,*, Ru Chen 2, Guowen He 1 and Jin Zhang 1,
*
1
College of Materials and Chemical Engineering, Hunan City University, Yiyang 413000, China;
zhongyihgw@163.com
Yiyang Agriculture Products Quality Detect Center, Yiyang 413000, China; chenrudaxia@163.com
Correspondence: liusaiwen7@163.com (S.L.); tccdzdc@163.com (J.Z.)
2
*
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 25 February 2020; Accepted: 26 March 2020; Published: 27 March 2020
Abstract: An esterification and amination of benzylic C–H bonds was developed by using
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) under metal- and iodide-free conditions.
Both carboxylic acids and amines could be used as ideal coupling partners for the oxidative coupling
reactions with various diarylmethanes. A close to equal amount of coupling reagents was enough to
afford the product in good to high yields.
Keywords: esterification; amination; DDQ; diarylmethanes; benzyl ester
1. Introduction
Benzyl esters, which play a key role in many biologically active compounds, can be traditionally
prepared by condensation of the corresponding benzyl alcohols with carboxylic acids in the presence
of condensation reagents or their activated derivatives such as acyl chlorides in the presence of
bases [1,2]. They also serve as the essential protecting groups in amino acids and their derivatives [3].
Therefore, development of efficient methods for rapid construction of benzyl esters has gained much
attention and great progress has been made during the past several decades. Recently, the cleavage
and functionalization of C–H bonds is of increasing interest for both academia and industry.
Generally, the transformation mainly relies on transition metals [4–6]. This strategy has also been
successfully employed for the direct esterification and amination of C–H bonds including benzylic C–H
bonds under oxidative reaction conditions. Various transition-metals efficiently catalyzed the direct
esterification [7,8] and amination [9–11] of C–H bonds. Due to the toxicity and cost of transition-metal
catalysts, increasing interest has been paid on metal-free esterifications of benzylic C–H bonds.
Since Sinha and co-workers reported a 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)
promoted acetoxylation of arylalkanes under sonochemical activation conditions in the absence
of metal catalyst [12], various efficient esterification methods have been developed under metal-free
conditions. The combination of quaternary ammonium iodides with strong oxidants was found
to be an effective strategy for direct esterification and amination of benzylic C–H bonds [13–16].
Recently, Shen and co-workers reported the C–O coupling of C–H with carboxylic acids catalyzed
by DDQ and tert-butyl nitrite using oxygen as the terminal oxidant [17]. However, large excess of
carboxylic acids or amines are necessary to get satisfied reaction yields [18]. The development of
esterification reactions using a near equal amount of reactants under metal-free conditions would be
highly desirable. Herein, we report a DDQ promoted esterification and amination of diarylmethanes
using only 1.5 equiv. of carboxylic acids and amines without the use of quaternary ammonium iodide or
metal catalyst. The chloro-containing solvent plays an important role for this efficient transformation.
Molecules 2020, 25, 1527; doi:10.3390/molecules25071527
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2. Results
2.1. Optimization of Reaction Conditions for Synthesis of Benzhydryl Benzoate 3a
We began our study by examining the reaction of diphenylmethane (1a) and with 1.5 equiv. of
benzoic acid (2a) using DDQ as oxidant in 1,2-dichloroethane (DCE) at 100 ◦C under an atmosphere of
argon. DDQ showed very good activity and the desired product benzhydryl benzoate (3a) was obtained
in 95% yield as determined by GC (Table 1, entry 1). The oxidant played an important role for this
kind of reaction. Other common oxidants, such as benzoquinone, peroxides and hydrogen peroxide,
were ineffective and no desired product was observed (entries 2–6). Solvents also played an important
role for the direct esterification. The reactions in chloro-containing solvents, such as chloroform,
dichloromethane, and tetrachloroethane, all showed very good reactivity (entries 7–9). Other solvents,
such as ethyl acetate, acetonitrile, and water, all decreased the reaction yields significantly (entries
10–13). Decreasing the reaction temperature decreased the reaction yield (entry 14). The reaction yields
decreased when the reactions were carried out under oxygen and air (entries 15 and 16). Good yield
still could be achieved when an equal amount of 2a was used (entry 17).
Table 1. Optimization of the reaction conditions a.
Yield b (%)
Entry
Oxidant (equiv.)
Solvent
1
2
DDQ (1.2)
BQ (1.2)
DCE
DCE
95
0
3
4
5
6
7
8
9
10
11
12
13
14c
15d
16e
17f
TBHP (1.2)
tBuOOtBu (1.2)
H2O2 (1.2)
dicumyl peroxide (1.2)
DDQ (1.2)
DCE
DCE
DCE
DCE
0
0
0
0
94
93
80
10
12
0
CHCl3
CH2Cl2
Cl2CHCHCl2
EtOAc
CH3CN
H2O
pyridine
DCE
DCE
DDQ (1.2)
DDQ (1.2)
DDQ (1.2)
DDQ (1.2)
DDQ (1.2)
DDQ (1.2)
DDQ (1.2)
DDQ (0.5)
0
72
51
70
84
b
DDQ (1.2)
DDQ (1.2)
DCE
DCE
Reaction conditions: 1a (0.2 mmol), 2a (0.3 mmol), solvent (0.6 mL), 100 ◦C, 8 h, under argon. GC yield based
a
c
e
on 1a
.
At 80 ◦C. d Under O2, 45% benzophenone was detected. Under air, 28% benzophenone was detected.
f
0.2 mmol of 2a was used.
2.2. Substrate Scope for the Carboxylic Acids and Amines
With the optimized reaction conditions established, the scope of the reaction with respect to
diphenylmethane (1a) and various carboxylic acids (
aromatic carboxylic acids bearing electron-donating groups and electron-withdrawing substituents at
the para position proceeded smoothly to give the desired products in good yields (3b 3e). The position
2) was investigated (Table 2). The reactions with
–
of the substituents on the phenyl ring of benzoic acids affected the reaction yield slightly, and the use of
ortho-substituted benzoic acids also afforded the desired products in good yields. Under the optimized
conditions, halogen substituents were all well tolerated (3e–3h). Good yield was obtained when
2-bromobenzoic acid was used, and the desired product 3h was achieved in 83% yield. More bulky
substrates, such as 2,4,6-trimethylbenzoic acid, also efficiently reacted with 1a and gave the product

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in 85% yield (3j). Notably, high yield was achieved when hetero aromatic carboxylic acids, such as
3-methylthiophene-2-carboxylic acid, reacted with 1a, and the desired product 3k was obtained in
88% yield. To be our delight, aliphatic carboxylic acids, including formic acid, are also good coupling
reagents for this kind of transformation, and the desired esters were formed in high yields (3m–3p).
In addition to carboxylic acids, amines could also be used as ideal coupling partners for the oxidative
coupling reaction. Diphenylmethane smoothly coupled with benzamide and gave the aminated
product 4a in 62% yield. Moderate to good yields were obtained when sulfonamides were employed
for the coupling reaction (4b–4d).
Table 2. Reaction of 1a with various carboxylic acids and amines a.
Ph
O
Ph
O
Ph
O
Ph
O
3a
: 80%
3d
: 82%
Ph
O
Ph
O
Ph
O
Ph
O
F
F
3e
3f
: 82%
: 70%
Ph
O
S
Ph
O
3k
: 88%
Ph
O
Ph
O
Ph
O
Ph
O
C5H11
3p
: 82%
3o
: 83%
Ph
O
Ph
O
S
Ph
N
H
Ph
N
O
H
4c
: 72%
4a
: 62%
a
Reaction conditions:
1a (0.2 mmol),
carboxylic acids and amines (0.3 mmol),
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (0.24 mmol), 1,2-dichloroethane (DCE) 0.6 mL, 100 ◦C,
8 h, under argon, isolated yield.
2.3. Substrate Scope for the Diarylmethanes
To further explore the scope of the reaction, various diarylmethanes (1) were employed to react
with 2a under the optimized conditions (Table 3). A series of functional groups, including methyl,

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tert-butyl, fluoro, and chloro, were well tolerated under the optimized conditions (3t
–
3x). The position
of the substituents on the phenyl ring of diphenylmethane only slightly affected the reaction yield
3q 3s). The desired product 3y was obtained in 40% yield when 1-benzyl-4-nitrobenzene was used.
(
–
Unfortunately, this reaction condition was only suitable for diarylmethane substrates. Other benzylic
substrates, such as toluene and ethylbenzene, were not reactive under the optimized reaction conditions.
Table 3. Esterification of various diarylmethanes a.
O
O
O
O
Ph
O
Ph
O
Ph
3q
: 82%
3r
: 80%
3s
: 88%
O
O
O
O
Ph
O
Ph
O
Ph
Cl
F
F
3v
3t
: 78%
: 80%
3u
: 84%
O
O
O
Ph
O
Ph
O2N
Cl
3y
: 40%
3x
: 72%
a
Reaction conditions:
1
(0.2 mmol), 2a (0.3 mmol), DDQ (0.24 mmol), DCE 0.6 mL, 100 ◦C, 8 h, under argon,
isolated yield.
2.4. Mechanism
To gather more information about the reaction mechanism, the radical scavenger
2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) was added. No product was obtained from the
reaction between diphenylmethane and benzoic acid with the influence of two equivalents of TEMPO
(Scheme 1). This indicates that the present reaction process may involve radical intermediates.

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O
DDQ (1.2 eq.), Ar
+
no reaction
OH
TEMPO (2 eq.)
DCE, 100 oC, 8 h
1a
2a
Scheme 1. Radical trapping experiment.
A plausible mechanism to rationalize this transformation is illustrated in Scheme 2. The reaction
of DDQ with diphenylmethane 1a generates a benzyl radical
and DDQH· via hydrogen atom transfer
(HAT). The radicals continue to be transformed into the corresponding benzyl cation and DDQH anion
I
via single electron transfer (SET) [17,18]. Finally, the benzoic acid 2a of the proton is abstracted by
DDQH– and reacts with the cation II to obtain the desired product 3a and reduced hydroquinone
DDQH2. However, the reason why the reaction only works well in chloro-containing solvents is not
clear at this stage.
Scheme 2. Proposed mechanism for the esterification of diarylmethanes.
3. Materials and Methods
3.1. General Information
All experiments were carried out under an atmosphere of argon. Flash column chromatography
1
was performed over silica gel 48–75
µ
m. H-NMR and 13C-NMR spectra were recorded on a Bruker-AV
(400 and 100 MHz, respectively) instrument (Billerica, MA, USA) internally referenced to SiMe4 or
chloroform signals. MS analyses were performed on an Agilent 5975 GC-MS instrument (EI) (Santa
Clara, CA, USA). The new compounds were characterized by 1H NMR, 13C NMR, MS, and HRMS.
The structure of known compounds were further corroborated by comparing their 1H-NMR, 13C-NMR,
and MS data with those in the literature. All reagents were used as received from commercial
sources without further purification. Diarylmethane derivatives
literatures [19].
1 were synthesized based on relevant

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3.2. General Procedure for the Synthesis of Benzhydryl Benzoate
An oven-dried pressure tube (10 mL) was charged with diphenylmethane (1a, 33.4
µL, 0.2 mmol),
benzoic acid (2a, 36.6 mg, 0.3 mmol), DDQ (54.5 mg, 0.24 mmol), and DCE (0.6 mL). The reaction vessel
was flushed with argon and sealed. The resulting solution was heated to 100 ◦C for 8 h. After cooling
to room temperature, the volatiles were removed under vacuum and the residue was purified by
column chromatography (silica gel, petroleum ether/ethyl acetate = 9:1) to give 3a as white solid; yield:
46.1 mg (80%). (NMR spectra for all compounds shown in the Supplementary Materials).
3.3. Product Characterization
Benzhydryl benzoate (3a) [17]: white solid, 80% yield (46.1 mg), 1H NMR (400 MHz, CDCl3, ppm)
(d, J = 7.6 Hz, 2H), 7.58 (d, J = 7.0 Hz, 1H), 7.43–7.46 (m, 6H), 7.36 (t, J = 7.4 Hz, 4H), 7.30 (d, J = 7.2 Hz,
2H), 7.12 (s, 1H); 13C NMR (100 MHz, CDCl3, ppm)
165.6, 140.4, 133.1, 130.1, 129.8, 128.6, 128.5, 128.0,
δ 8.15
δ
127.2, 77.5. MS (EI) m/z (%) 288, 183, 166 (100), 152, 105, 77.
Benzhydryl 4-methylbenzoate (3b) [20]: white solid, 80% yield (48.3 mg), 1H NMR (400 MHz, CDCl3,
ppm)
ppm)
δ
8.03 (d, J = 8.0 Hz, 2H), 7.27–7.44 (m, 12H), 7.10 (s, 1H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3,
165.7, 143.9, 140.5, 129.9, 129.2, 128.6, 128.0, 127.6, 127.2, 77.3, 21.7. MS (EI) m/z (%) 302, 166
δ
(100), 152, 119, 91.
Benzhydryl 3-methylbenzoate (3c): White solid, 84% yield (50.7 mg), 1H NMR (400 MHz, CDCl3, ppm)
δ
7.94 (m, 2H), 7.30–7.45 (m, 12H), 7.12 (s, 1H), 2.41 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
δ 165.8,
140.4, 138.3, 134.0, 132.5, 130.3, 128.6, 128.4, 128.0, 127.2, 127.0, 77.4, 21.4; MS (EI) m/z (%) 302, 166 (100),
152, 119, 91; HRMS calcd. for: C21H18NaO2 [M + Na]+: 325.1201, found m/z 325.1205.
Benzhydryl 2-methylbenzoate (3d) [21]: colorless liquid, 82% yield (49.5 mg), 1H NMR (400 MHz, CDCl3,
ppm)
ppm)
δ
8.08 (d, J = 7.6 Hz, 1H), 7.31–7.46 (m, 13H), 7.01 (s, 1H), 2.61 (s, 3H); 13C NMR (100 MHz, CDCl3,
166.4, 140.7, 140.5, 132.2, 131.9, 130.8, 129.5, 128.6, 128.0, 127.2, 125.9, 77.4, 22.0; MS (EI) m/z (%)
δ
302, 166 (100), 152, 119, 91.
Benzhydryl 4-fluorobenzoate (3e) [22]: colorless liquid, 70% yield (42.9 mg), 1H NMR (400 MHz, CDCl3,
ppm)
δ
8.10 (t, J = 6.8 Hz, 2H), 7.20–7.37 (m, 10H), 7.04–7.09 (m, 3H); 13C NMR (100 MHz, CDCl3,
ppm) δ 165.9 (d, J = 259.2 Hz), 164.7, 140.2, 132.4 (d, J = 9.3 Hz), 130.0, 128.6, 128.0, 127.2, 115.6 (d, J =
21.9 Hz), 77.7; MS (EI) m/z (%) 306, 183, 166 (100), 152, 123, 95.
Benzhydryl 2-fluorobenzoate (3f) [23]: colorless liquid, 82% yield (50.2 mg), 1H NMR (400 MHz, CDCl3,
ppm)
δ
7.91 (d, J = 7.2 Hz, 1H), 7.69 (d, J = 7.6 Hz, 1H), 7.47 (d, J = 7.2 Hz, 4H), 7.32–7.40 (m, 8H), 7.14
163.5, 162.2 (d, J = 258.9 Hz), 140.2, 134.7 (d, J = 9.0 Hz),
(s, 1H); 13C NMR (100 MHz, CDCl3, ppm)
δ
132.4, 128.6, 128.0, 127.2, 124.1 (d, J = 4.0 Hz), 118.8, 117.1 (d, J = 22.4 Hz), 78.0; MS (EI) m/z (%) 306, 183,
166 (100), 152, 123, 95.
Benzhydryl 2-chlorobenzoate (3g) [23]: colorless liquid, 81% yield (52.3 mg), 1H NMR (400 MHz, CDCl3,
ppm) δ δ
7.93 (d, J = 7.6 Hz, 1H), 7.30–7.46 (m, 13H), 7.13 (s, 1H); 13C NMR (100 MHz, CDCl3, ppm)
164.6, 140.0, 134.1, 132.7, 131.7, 131.2, 130.1, 128.6, 128.0, 127.3, 126.6, 78.4; MS (EI) m/z (%) 322, 183, 166
(100), 152, 139, 77.
1
Benzhydryl 2-bromobenzoate (3h) [24]: white solid, 83% yield (61.0 mg), H NMR (400 MHz, CDCl3,
ppm) δ δ
7.96 (t, J = 7.2 Hz, 1H), 7.10–7.48 (m, 13H), 7.07 (s, 1H); 13C NMR (100 MHz, CDCl3, ppm)
165.1, 139.9, 134.6, 132.8, 132.0, 131.6, 128.6, 128.1, 127.3, 127.2, 122.0, 78.5. MS (EI) m/z (%) 366, 183, 167
(100), 152, 77.
Benzhydryl 2-methoxybenzoate (3i) [24]: colorless liquid, 70% yield (44.6 mg), 1H NMR (400 MHz, CDCl3,
ppm)
CDCl3, ppm)
m/z (%) 318, 183, 167 (100), 152, 135, 77.
δ
7.91 (d, J = 7.6 Hz, 1H), 7.28–7.50 (m, 11H), 7.10 (s, 1H), 6.97–7.00 (m, 2H); 13C NMR (100 MHz,
δ
165.1, 159.6, 140.6, 133.8, 132.0, 128.5, 127.8, 127.3, 126.6, 120.2, 112.2, 77.3, 56.0. MS (EI)

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Benzhydryl 2,4,6-trimethylbenzoate (3j): colorless liquid, 85% yield (56.2 mg), 1H NMR (400 MHz, CDCl3,
ppm)
7.30–7.43 (m, 10H), 7.17 (s, 1H), 6.84 (s, 2H), 2.29 (s, 3H), 2.17 (s, 6H); 13C NMR (100 MHz,
CDCl3, ppm)
δ
δ
169.3, 140.1, 139.4, 135.2, 130.9, 128.5, 128.4, 128.0, 127.4, 77.5, 21.2, 19.7. MS (EI) m/z (%)
330, 167 (100), 155, 147, 77; HRMS calcd. for: C23H22NaO2 [M + Na]+: 353.1514, found m/z 353.1509.
Benzhydryl 3-methylthiophene-2-carboxylate (3k): colorless liquid, 88% yield (54.3 mg), 1H NMR (400 MHz,
CDCl3, ppm)
CDCl3, ppm)
δ
δ
7.30–7.46 (m, 11H), 7.07 (s, 1H), 6.94 (d, J = 4.8 Hz, 1H), 2.59 (s, 3H); 13C NMR (100 MHz,
161.7, 146.7, 140.4, 131.8, 130.3, 128.6, 127.9, 127.1, 126.7, 77.2, 16.0; MS (EI) m/z (%) 308,
167 (100), 152, 125, 77; HRMS calcd. for: C19H16NaO2S [M + Na]+: 331.0765, found m/z 331.0768.
Benzhydryl cinnamate (3l) [25]: white solid, 82% yield (51.6 mg), 1H NMR (400 MHz, CDCl3, ppm)
7.76 (d, J = 16.0 Hz, 1H), 7.54 (m, 2H), 7.30–7.39 (m, 13H), 7.02 (s, 1H), 6.57 (d, J = 16.4 Hz, 1H); 13
δ
C
NMR (100 MHz, CDCl3, ppm) δ 166.0, 145.4, 140.3, 134.4, 130.4, 128.9, 128.6, 128.2, 127.9, 127.2, 118.1,
77.1; MS (EI) m/z (%) 314, 268, 236, 167 (100), 131, 77.
Benzhydryl formate (3m) [26]: colorless liquid, 80% yield (34.0 mg), 1H NMR (400 MHz, CDCl3, ppm)
δ
8.24 (s, 1H), 7.26–7.36 (m, 10H), 7.01 (s, 1H); 13C NMR (100 MHz, CDCl3, ppm)
δ
159.9, 139.6, 128.6,
128.1, 127.2, 76.6. MS (EI) m/z (%) 212, 184, 166 (100), 152, 77.
Benzhydryl acetate (3n) [17]: colorless liquid, 93% yield (42.1 mg), 1H NMR (400 MHz, CDCl3, ppm)
δ
7.28–7.35 (m, 10H), 6.89 (s, 1H), 2.16 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
δ 170.0, 140.3, 128.5,
127.9, 127.2, 76.9, 21.3. MS (EI) m/z (%) 226, 184, 165 (100), 152, 105, 77.
1
Benzhydryl pivalate (3o) [22]: white solid, 83% yield (44.5 mg), H NMR (400 MHz, CDCl3, ppm)
δ
7.30–7.36 (m, 10H), 6.84 (s, 1H), 1.27 (s, 9H); 13C NMR (100 MHz, CDCl3, ppm)
δ 177.3, 140.7, 128.9,
127.8, 126.9, 76.6, 39.0, 27.2. MS (EI) m/z (%) 268, 211, 183, 167 (100), 152, 57.
Benzhydryl hexanoate (3p) [27]: colorless liquid, 82% yield (46.3 mg), 1H NMR (400 MHz, CDCl3, ppm)
7.30–7.36 (m, 10H), 6.90 (s, 1H), 2.43 (t, J = 7.4 Hz, 2H), 1.66–1.72 (m, 2H), 1.27–1.31 (m, 4H), 0.89 (t, J
= 7.4 Hz, 3H); 13C NMR (100 MHz, CDCl3, ppm)
172.8, 140.5, 128.5, 127.9, 127.1, 76.7, 34.6, 31.3, 24.7,
22.3, 13.9. MS (EI) m/z (%) 282, 184, 166 (100), 152, 77.
δ
δ
Phenyl(p-tolyl)methyl benzoate (3q) [17]: white solid, 82% yield (49.6 mg), 1H NMR (400 MHz, CDCl3,
ppm) 8.16 (d, J = 7.2 Hz, 2H), 7.60 (t, J = 7.2 Hz, 1H), 7.31–7.50 (m, 9H), 7.18 (d, J = 7.6 Hz, 2H), 7.11 (s,
1H), 2.35 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
165.6, 140.5, 137.7, 137.5, 133.1, 130.5, 129.8, 129.3,
δ
δ
128.5, 128.4, 127.9, 127.2, 127.1, 77.4, 21.1. MS (EI) m/z (%) 302, 197, 180 (100), 165 (100), 105, 77.
Phenyl(m-tolyl)methyl benzoate (3r): colorless liquid, 80% yield (48.4 mg), 1H NMR (400 MHz, CDCl3,
ppm)
δ
8.17 (d, J = 7.6 Hz, 2H), 7.60 (t, J = 7.2 Hz, 1H), 7.27–7.50 (m, 10H), 7.11–7.13 (m, 2H), 2.36 (s,
165.6, 140.5, 140.3, 138.2, 133.1, 130.5, 129.8, 128.8, 128.5, 128.5,
3H); 13C NMR (100 MHz, CDCl3, ppm)
δ
128.4, 127.9, 127.2, 124.2, 77.6, 21.5. MS (EI) m/z (%) 302, 197, 180, 165 (100), 105, 77. HRMS calcd. for:
C21H18NaO2 [M]+: m/z 325.11990, found m/z 325.12047.
Phenyl(o-tolyl)methyl benzoate (3s): colorless liquid, 88% yield (53.2 mg), 1H NMR (400 MHz, CDCl3,
8.15 (d, J = 7.6 Hz, 2H), 7.22–7.61 (m, 13H), 2.39 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
ppm) δ δ
165.6, 139.6, 138.2, 136.0, 133.1, 130.7, 130.1, 129.8, 128.5, 128.4, 128.0, 127.9, 127.5, 127.2, 126.2, 75.0,
19.5; MS (EI) m/z (%) 302, 179 (100), 165, 105, 77; HRMS calcd. for: C21H18NaO2 [M + Na]+: 325.1199,
found 325.1202.
(4-Fluorophenyl)(phenyl)methyl benzoate (3t): colorless liquid, 80% yield (49.0 mg), 1H NMR (400 MHz,
CDCl3, ppm)
δ
8.15 (d, J = 7.2 Hz, 2H), 7.61 (d, J = 7.0 Hz, 1H), 7.33–7.51 (m, 9H), 7.13 (s, 1H), 7.06 (t, J
165.5, 162.5 (d, J = 245.4 Hz), 140.1, 136.2, 133.2,
= 8.6 Hz, 2H); 13C NMR (100 MHz, CDCl3, ppm)
δ
132.7 (d, J = 9.0 Hz), 129.8, 129.1 (d, J = 8.0 Hz), 128.6, 128.5, 128.1, 127.0, 111.5 (d, J = 21.5 Hz), 76.8.
MS (EI) m/z (%) 306, 201, 184 (100), 165, 105, 77. HRMS calcd. for: C20H15FNaO2 [M]+: m/z 329.09483,
found m/z 329.09537.

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(2-Fluorophenyl)(phenyl)methyl benzoate (3u): colorless liquid, 84% yield (51.5 mg), 1H NMR (400 MHz,
CDCl3, ppm) 8.15 (d, J = 7.5 Hz, 2H), 7.47–7.60 (m, 6H), 7.28–7.37 (m, 5H), 7.15 (t, J = 7.4 Hz, 1H), 7.07
(t, J = 9.2 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm)
165.3, 160.1 (d, J = 246.8 Hz), 139.4, 133.2, 130.2,
δ
δ
129.8, 129.7 (d, J = 8.2 Hz), 128.6, 128.5, 128.1, 128.1, 127.9 (d, J = 13.2 Hz), 126.9, 124.3 (d, J = 3.6 Hz),
115.8 (d, J = 21.3 Hz), 71.8 (d, J = 2.9 Hz). MS (EI) m/z (%) 306, 184 (100), 165, 105, 77. HRMS calcd. for:
C20H15FNaO2 [M]+: m/z 329.09483, found m/z 329.09526.
(4-Chlorophenyl)(phenyl)methyl benzoate (3v): colorless liquid, 78% yield (50.4 mg), 1H NMR (400 MHz,
CDCl3, ppm)
NMR (100 MHz, CDCl3, ppm)
128.2, 127.1, 76.8. MS (EI) m/z (%) 322, 200, 165 (100), 105, 77.
δ C
8.13 (d, J = 7.6 Hz, 2H), 7.59 (t, J = 7.2 Hz, 1H), 7.31–7.49 (m, 11H), 7.08 (s, 1H); 13
δ
165.5, 139.9, 138.9, 133.9, 133.3, 131.5, 129.8, 128.8, 128.7, 128.6, 128.5,
(4-Tert-butylphenyl)(phenyl)methyl benzoate (3w): colorless liquid, 76% yield (52.4 mg), 1H NMR (400 MHz,
CDCl3, ppm) 8.15 (d, J = 7.5 Hz, 2H), 7.57 (t, J = 7.1 Hz, 1H), 7.44–7.47 (m, 4H), 7.29–7.37 (m, 7H), 7.11
(s, 1H), 1.30 (s, 9H); 13C NMR (100 MHz, CDCl3, ppm)
165.6, 150.9, 140.5, 137.3, 133.0, 130.5, 129.8,
δ
δ
128.5, 128.4, 127.8, 127.1, 127.0, 125.5, 77.4, 34.6, 31.3; MS (EI) m/z (%) 344, 239, 222 (100), 207, 105, 77;
HRMS calcd. for: C24H24NaO2 [M + Na]+: 367.1669, found 367.1669.
(4-Chlorophenyl)(p-tolyl)methyl benzoate (3x): colorless liquid, 72% yield (48.5 mg), 1H NMR (400 MHz,
CDCl3, ppm)
δ
8.12 (d, J = 7.5 Hz, 2H), 7.58 (t, J = 7.2 Hz, 1H), 7.46 (t, J = 7.6 Hz, 2H), 7.31–7.37 (m, 6H),
165.5, 139.1, 138.0,
7.17 (d, J = 7.7 Hz, 2H), 7.05 (s, 1H), 2.34 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
δ
136.9, 133.8, 133.2, 130.2, 129.8, 129.4, 128.7, 128.5, 128.5, 127.1, 76.7, 21.1. MS (EI) m/z (%) 336, 214 (100),
179 (100), 165, 105, 77. HRMS calcd. for: C21H17ClNaO2 [M]+: m/z 359.08093, found m/z 359.08145.
(4-Nitrophenyl)(phenyl)methyl benzoate (3y): colorless liquid, 40% yield (26.7 mg), 1H NMR (400 MHz,
CDCl3, ppm)
δ
8.22 (d, J = 8.5 Hz, 2H), 8.14 (d, J = 7.5 Hz, 2H), 7.61 (d, J = 8.4 Hz, 3H), 7.49 (t, J = 7.6 Hz,
165.3, 147.4, 138.9, 133.5, 130.7,
2H), 7.34–7.44 (m, 5H), 7.16 (s, 1H).13C NMR (100 MHz, CDCl3, ppm)
δ
130.1, 129.8, 128.9, 128. 7, 128.6, 127.8, 127.3, 123.9, 76.5. MS (EI) m/z (%) 333, 211, 165, 105 (100), 77.
N-Benzhydrylbenzamide (4a) [28]: white solid, 62% yield (35.6 mg), 1H NMR (400 MHz, CDCl3, ppm)
δ
7.85 (d, J = 7.6 Hz, 2H), 7.54 (t, J = 7.2 Hz, 1H), 7.47 (t, J = 7.4 Hz, 2H), 7.32–7.40 (m, 10H), 6.68 (d, J
= 6.8 Hz, 1H), 6.48 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm)
166.6, 141.5, 134.3, 131.7,
δ
131.0, 128.8, 128.7, 127.6, 127.1, 57.5. MS (EI) m/z (%) 287, 182, 165, 105 (100), 77.
N-Benzhydrylbenzenesulfonamide (4b) [29]: white solid, 76% yield (49.2 mg), 1H NMR (400 MHz, CDCl3,
ppm)
δ
7.70 (d, J = 7.6 Hz, 2H), 7.49 (t, J = 7.4 Hz, 1H), 7.36 (t, J = 7.6 Hz, 2H), 7.11–7.23 (m, 10H), 5.63
140.4, 132.4, 131.0,
(d, J = 7.2 Hz, 1H), 5.11 (d, J = 6.8 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm)
δ
128.8, 128.6, 127.7, 127.4, 127.2, 61.4. MS (EI) m/z (%) 322, 246, 182 (100), 167, 104, 77.
N-Benzhydryl-4-methylbenzenesulfonamide (4c) [29]: white solid, 70% yield (47.2 mg), 1H NMR (400 MHz,
CDCl3, ppm)
1H), 2.32 (s, 3H); 13C NMR (100 MHz, CDCl3, ppm)
61.4, 21.4. MS (EI) m/z (%) 336, 182 (100), 167, 91, 77.
δ
7.50 (d, J = 8.0 Hz, 2H), 7.04–7.20 (m, 12H), 5.51 (d, J = 6.8 Hz, 1H), 4.94 (d, J = 6.4 Hz,
δ
143.1, 140.7, 137.6, 129.3, 128.5, 127.5, 127.4, 127.2,
N-Benzhydrylmethanesulfonamide (4d) [30]: white solid, 67% yield (35.0 mg), 1H NMR (400 MHz, CDCl3,
ppm)
7.36–7.41 (m, 10H), 5.79 (d, J = 6.8 Hz, 1H), 4.99 (d, J = 6.4 Hz, 1H), 2.30 (s, 3H); 13C NMR
δ
(100 MHz, CDCl3, ppm)
104, 77.
δ 140.7, 128.9, 128.0, 127.5, 61.3, 41.9. MS (EI) m/z (%) 259, 180 (100), 165,
4. Conclusions
In summary, we have developed a DDQ-promoted esterification and amination of benzylic C–H
bonds under metal- and iodide-free conditions. A close to equal amount of coupling reagents is enough
to afford the product in good to high yields. Functional groups, such as methyl, methoxy, fluoro, chloro,
and bromo, were all well tolerated under the optimized reaction conditions. This method affords an

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efficient alternative route for the synthesis of esters and amides. The scope, mechanism, and synthetic
applications of this reaction are under investigation.
Supplementary Materials: The supplementary materials are available online.
Author Contributions: Conceptualization, S.L. and J.Z.; methodology, R.C.; writing—original draft preparation,
S.L. and G.H.; writing—review and editing, S.L.
Funding: We gratefully thank the Normal Project Foundation of Hunan Provincial Education Department
(18C0845), the Key Project Foundation of Hunan Provincial Education Department (18A396, 19A085), and the
Natural Science Foundation of Hunan Province (2017JJ2018).
Conflicts of Interest: The authors declare no conflict of interest.
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