Electrodimerization of N-Alkoxyamides for Zinc(II) Catalyzed Phenolic Ester Synthesis under Mild Reaction Conditions

Article abstract of DOI:10.1002/adsc.201701646

An electrochemical On-Off method for phenolic ester synthesis from N-alkoxyamides has been reported. This one-pot protocol begins with rapid and selective electrodimerization of the amide using n-Bu₄NI (TBAI) as an electrocatalyst. The reaction proceeds further in the absence of current via Zn catalyzed C?N bond activation of the amide dimer followed by its coupling with phenol to form the ester. The present methodology is ligand-free and takes place under mild reaction conditions. This transformation incorporates a wide variety of phenols and amide substrates leading to the formation of functionalized esters highlighting its versatility. (Figure presented.).

Full text of DOI:10.1002/adsc.201701646

Title: Electrodimerization of N-Alkoxyamides for Zinc(II) Catalyzed
Phenolic Ester synthesis under mild reaction conditions
Authors: Kripa Subramanian, Subhash Laxman Yedage, and
Bhalchandra Bhanage
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201701646
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10.1002/adsc.201701646
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Electrodimerization of N-Alkoxyamides for Zinc(II) Catalyzed
Phenolic Ester synthesis under mild reaction conditions
Kripa Subramaniana, Subhash L.Yedagea and Bhalchandra M. Bhanagea*
a Department of Chemistry, Institute of Chemical Technology, Mumbai-400 019, India.
Phone: (+) 91 22 33612603, e-mail: bm.bhanage@ictmumbai.edu.in, bm.bhanage@gmail.com
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.
Abstract. An electrochemical On-Off method for phenolic
ester synthesis from N-alkoxyamides has been reported.
Keywords:
Electrodimerization;
N-alkoxyamides;
This one-pot protocol begins with rapid and selective
electrodimerization of the amide using n-Bu4NI (TBAI) as
an electrocatalyst. The reaction proceeds further in the
absence of current via Zn catalyzed C-N bond activation of
the amide dimer followed by its coupling with phenol to
form the ester. The present methodology is ligand-free and
Acylation; Zinc triflate; Phenolic esters
takes place under mild reaction conditions.
This
transformation incorporates a wide variety of phenols and
amide substrates leading to the formation of functionalized
esters highlighting its versatility.
Introduction
Esters are the cornerstone of essential oils, and
perfumeries. Besides, phenolic esters are important
building blocks found in various biologically active
molecules, agrochemicals and natural products[1]
(Figure 1). Phenols/phenolic compounds are common
byproducts of many industrial processes viz.
manufacture of dyes, plastics, drugs, antioxidants,
paper, and petroleum. So considering the toxicity
they pose to the environment, conversion of phenols
to useful/industrially and biologically important
products like esters are highly desirable.
Conventionally, phenolic esters have been prepared
by the reaction of acyl halides, carboxylic acids and
anhydrides with phenols or via esterification or trans-
esterification reactions catalyzed by strong acids/
bases.[2] Furthermore, recently, Liu et al. have
reported the use of diacyl disulfide as an acylating
agent for phenyl ester synthesis.[3] However, most of
these protocols suffer from the use of a stoichiometric
or excess amount of reagents, reactive substrates, and
rigorous reaction conditions, and therefore
advanced/improved methodologies are still preferred.
Despite their inherent chemical inertness amides
have gained popularity as acyl donors by providing
alternative synthetic routes towards ester synthesis.[4]
The most developed strategy to obtain selective C-N
bond activation of amides is by the use of a transition
metal catalyst wherein the amide pre-complexes with
the metal and provides the desired acyl group.[5]
Among amides, generally, the sterically - controlled
Figure 1. Representative examples of biologically
important and naturally occurring phenyl esters.
tertiary amides offer a good acyl source for the
synthesis of esters while metal catalyzed C-N bond
cleavage of secondary amides is challenging due to
the formation of
a
five-membered stable
metallacycle.[5,6] Of late, the transition metal
catalyzed/oxidant-mediated C-N bond activation of
secondary amides viz. N-alkoxyamides, leading to the
formation of the rigid N-N dimer is an emerging
powerful strategy for ester synthesis via
intramolecular rearrangement.[7]
1
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10.1002/adsc.201701646
Advanced Synthesis & Catalysis
Results and Discussion
Although several methods are available for ester
synthesis from amides, there are only a few reports
on activation of amides for the synthesis of phenolic
esters[5b,5c,8] (Scheme 1). Thus versatile, flexible and
sustainable methodologies for the synthesis of
phenolic esters from amides are still being looked-for.
As it is well known that electroorganic synthesis is
one of the most efficient tools for environmentally
benign reactions, we envisioned that the use of
electrochemistry can offer a mechanistically distinct
and significantly sustainable pathway to the
dimerization of amides leading towards ester
synthesis. Furthermore, this method is essentially
clean and safe because here electron serves as a
potentially renewable reagent that avoids the need of
stoichiometric redox reagents. This minimizes the
waste produced thereby enabling to continue the
reaction further for the synthesis of industrially
important products.
To achieve the goal, we first developed a TBAI-
catalyzed protocol for the electrochemical N-N
dimerization of N-alkoxyamides, because C-N bond
of dimers is regarded as a good acyl source and most
reactive for cross-coupling reactions. To demonstrate
this idea N-methoxybenzamide 1a, was chosen as the
model substrate for electrodimerization.
Table 1. Optimization of Reaction Conditionsa)
Yield
Catalyst
(mol %)
Time Temp.
Entry
Base
(%)b)
3aa/4a
12/74
51/38
(h)
(°C)
1
2
Zn(OAc)2 (10)
ZnCl2 (10)
K2CO3
K2CO3
24
24
20
20
3
4
Zn(TFA)2 (10)
K2CO3
K2CO3
24
24
20
20
56/25
76/16
Zn(OTf)2 (10)
MgCl2.6H2O
(10)
MgSO4.7H2O
(10)
5
6
K2CO3
K2CO3
24
24
20
20
59/28
53/36
7
8
9
Zn(OTf)2 (20)
Zn(OTf)2 (5)
-
Zn(OTf)2 (10)
Zn(OTf)2 (10)
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
24
24
24
21
18
21
21
21
21
21
21
21
21
20
20
20
20
20
20
20
20
20
20
-20
0
76/16
53/39
48/31
76/16
67/25
68/21
0/76
20/66
0/74
0/76
10
11
12
13
14
15
16
17
18
19
Zn(OTf)2 (10) Na2CO3
Scheme 1. Previous reports and present work on
deaminative coupling of phenols with various amides
Zn(OTf)2 (10)
Zn(OTf)2 (10)
Zn(OTf)2 (10)
Zn(OTf)2 (10)
Zn(OTf)2 (10)
Zn(OTf)2 (10)
Zn(OTf)2 (10)
NaOH
Et3N
DMAP
-
K2CO3
K2CO3
K2CO3
In this regard, most recently we had reported an
electrochemical method for carboxylic and hindered
ester synthesis from N-alkoxyamides via its
homodimerization using constant current electrolysis
(CCE).[9] Inspired by this work, subsequently, we
attempted to explore/extend this electrochemical
dimerization for the synthesis of phenolic esters.
Considering the fact that metal triflate catalyzed
acylations are very effective and zinc catalyzed
reactions are sustainable alternatives to precious/
toxic transition metal catalysts, we tried to develop
Zn(OTf)2 catalyzed acylation of amides.[10] Moreover,
the Zn catalyst is inexpensive, easily available and
also meets the problem of toxicity to a great extent.
In this paper, we report an electrochemical On-Off
method for the synthesis of phenolic esters wherein
N-alkoxyamides are first dimerized electrochemically
using Pt-Cu electrode system and TBAI as the
catalyst. The amide dimer is then acylated using
phenols in the presence of Zn(OTf)2 catalyst, at room
temperature (20 °C) without passing current. To the
best of our knowledge, this is the first report on the
synthesis of phenyl esters from N-alkoxyamides. The
results of our investigations are described herein.
9/83
17/75
48/44
30
a)Reaction Conditions: N-methoxybenzamide (1a, 0.5
mmol), p-cresol (2a, 0.6 mmol), base (1 mmol), b)G.C.
yield.
Based on our previous successful usage of Pt-Cu
electrode system for carboxylic ester synthesis from
N-alkoxyamides, we decided to move ahead with the
same electrolytic system rather than exploring other
options[9]. Hence the electrolysis of 1a was carried
out at a constant current density of 1 mA cm-2 in an
undivided cell containing Pt plate anode and Cu plate
cathode. TBAI was used as both, the redox catalyst as
well as supporting electrolyte and DMF (N,N-
dimethylformamide) as the solvent. The progress of
the reaction was monitored using TLC (Thin Layer
Chromatography) until the starting material was
utilized completely.
2
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10.1002/adsc.201701646
Advanced Synthesis & Catalysis
withdrawing
group
containing
4-nitro-N-
It was observed that temperature of electrolysis
methoxybenzamide did not react, thereby the starting
material was recovered. Additionally, amides bearing
fused benzene rings were also successfully converted
to the respective esters 3fa (70%) and 3ga (54%).
However, amides containing substituents at ortho
position hindered the reaction and hence 2-methyl-N-
methoxybenzamide resulted in only 33% of 3ha and
2-chloro-N-methoxybenzamide did not yield any
ester. Interestingly, amide with an external double
bond could also be converted to the corresponding
ester 3ma (74%). Heterocyclic N-alkoxyamide viz.
played a major role in the stability of the dimer.
During electrolysis at -20 °C, the conductivity of the
system diminished drastically, leading to substantial
reduction in the extent of dimerization. Next, at 0 °C,
dimerization proceeded smoothly leading to ~95%
conversion of 1a to the dimer. At 20 °C, even though
the conversion of 1a was ~95%, the stability of dimer
was low due to it's in situ rearrangement to the
corresponding methoxy ester 4a. Further, during
electrolysis at temperatures beyond 20 °C, the
stability of dimer was found to be very low, resulting
in its rapid rearrangement to 4a. So the optimum
temperature for electrolysis was set at 0 °C. Further,
out of several TBAI loadings (20, 30, 40, 50 mol %),
a loading 40 mol % was found to be ideal.
Consequently, we observed that maximum
electrodimerization occurred when electrolysis was
carried out by using 40 mol % TBAI at 0 °C for 3.5 h.
Next, optimization of metal catalyzed acylation of
the dimer with p-cresol 2a was carried out in the
absence of electric current as shown in Table 1.
Initially, a few Zn(II) and a couple of Mg(II) catalysts,
were screened. Among the tested Zn(II) catalysts,
Zn(OTf)2 afforded the corresponding phenyl ester
3aa in the highest yield (Table 1, entries 1-4). Mg(II)
salts were also found to be active but resulted in
comparatively lower yields of 3aa (Table 1, entries 5
and 6). Further, a catalyst loading of 10 mol % was
found to be optimum for obtaining the maximum
yield of 3aa (Table 1, entries 4, 7-9). Next, the utility
of several organic and inorganic bases was assessed.
As compared to other bases, the conversion of dimer
to phenyl ester 3aa was more facile in the presence of
K2CO3 (Table 1, entries 10, 12-16). In view of fact
that temperature plays a major role in deciding the
selectivity of 3aa over 4a, the acylation reaction was
monitored at different temperatures (Table 1, entries
10, 17-19). Maximum yield of 3aa was obtained
when acylation was carried out at 20 °C.
N-methoxyfuran-2-carboxamide
yielded
the
respective ester 3na (66%). Furthermore, aliphatic N-
alkoxyamides were also successfully transformed to
the corresponding esters (3oa–3qa) in appreciable
yields. Unfortunately, highly hindered amides could
not be tolerated and thus the ester 3ra was not
observed.
Table 2. Substrate scope for Zn(II) catalyzed ester
synthesis from various N-methoxyamides
Concisely, following were the optimal reaction
conditions used for further investigations: CCE of 0.5
mmol N-methoxybenzamide at 1 mA cm-2 using 40
mol % TBAI and 15 mL DMF at 0 °C for 3.5 h. This
is followed by the addition of 0.6 mmol p-cresol, 1
mmol K2CO3 and 10 mol % Zn(OTf)2, stirred at
20 °C for 21 h without passing electric current.
During the course of electrolysis, the potential of the
working electrode was between 5-8 V.
Reaction parameters: a)1a-1r (0.5 mmol), Pt-Cu electrodes,
1mA cm-2, TBAI (40 mol %), DMF (15 mL), 0 °C, 3.5 h.
b)2a (0.6 mmol), Zn (OTf)2 (10 mol %), K2CO3 (1 mmol),
20 °C, 21 h. Yield of isolated pure product.
With the optimized reaction parameters in hand,
we evaluated the substrate scope of the reaction
making use of various amide and phenol substrates.
To start with, as shown in Table 2, several N-
methoxyamides possessing various functionalities on
the benzene ring were screened. In general, the
Further, by fixing 1a as the amide we focussed our
attention on the scope of different phenols as shown
in Table 3. Firstly, phenols containing various
electron donating groups were screened. The
electrodimerization
of
N-methoxybenzamide
electrodimerization
of
N-methoxybenzamide
followed by Zn(II) catalyzed coupling with p-cresol
yielded 73% of the corresponding ester 3aa. It was
observed that amides with various electron donating
(3ba-3ea) and electron withdrawing substituents (3ja,
3ka) were tolerated but, strongly electron
followed by Zn(II) catalyzed coupling with m-cresol
produced the corresponding ester 3ab in 68% yield.
Similarly, 3,4-dimethoxyphenyl ester 3ac (63%)
could be synthesized by using 3,4-dimethoxyphenol
3
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10.1002/adsc.201701646
Advanced Synthesis & Catalysis
and the ester 3ad (61%) containing a 3,4-
methylenedioxy unit could be successfully
synthesized from sesamol. Next, phenols bearing
electron withdrawing substituents were well tolerated
and thus yielded the corresponding esters (3ae-3ai).
On the other hand, phenols bearing substituents in the
ortho positions were quite challenging and
comparatively yielded the lesser product (3aj-3al).
Organo-fluorine compounds are considered as very
important moieties in pharmaceutical compounds.
Phenyl esters containing trifluoromethyl 3am (60%),
5-bromo-2,3-difluoro 3an (40%) and 2,4-difluoro 3ao
(43%) substituents could also be synthesized using
this protocol. Lastly, heterocyclic phenol, 4-
hydroxypyridine could not be coupled with the amide
and thus the ester 3ap was not formed.
Scheme 2. Reactivity of internal phenol containing N-
methoxyamide for the synthesis of cyclic ester
Subsequently, control experiments were carried out
at standard reaction conditions as shown in (Scheme
3, entries i-vi). It was found that primary and tertiary
amides did not undergo coupling with p-cresol to
yield the ester 3aa. Out of the various secondary
amides screened, only those bearing N-OR groups
were tolerated. It was also observed that the reaction
was facile only with electrochemical initiation, via
the electric current On-Off method and not feasible
either in the absence of current or fully in the
presence of current. In order to get insights into the
reaction mechanism, the electrolysis was performed
under standard conditions in the presence of 60
mol % of a radical scavenger, viz., (2,2,6,6-
tetramethylpiperidine-1-yl)oxyl (TEMPO). Here only
trace amount of ester 3aa was isolated. This indicated
that the reaction proceeded via a radical mechanism.
Table 3. Substrate scope for Zn(II) catalysed ester
synthesis from various phenols
Reaction parameters: a)1a (0.5 mmol), Pt-Cu electrodes,
1mA cm-2, TBAI (40 mol %), DMF (15 mL), 0 °C, 3.5 h.
b)2b-2p (0.6 mmol), Zn (OTf)2 (10 mol %), K2CO3 (1
mmol), 20 °C, 21 h. Yield of isolated pure product.
Further, we envisaged that amide containing an
internal phenol could also be converted to the
corresponding cyclic ester. Accordingly, 5a was
subjected to standard reaction conditions, to
successfully produce 5b with 61% yield highlighting
the versatility and applicability of the protocol
(Scheme 2).
Scheme 3. Control Experiments
Intending to establish the practicality of the
protocol the electrochemical reaction of N-
methoxybenzamide and p-cresol for the synthesis of
p-tolyl benzoate was scaled up to gram level
producing 52% yield under standard conditions as
shown in Scheme 4.
4
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10.1002/adsc.201701646
Advanced Synthesis & Catalysis
phenoxide ion to the second carbonyl carbon of the
resulting zinc-dimer intermediate E takes place
leading to the formation of 3aa and F, finally
regenerating the metal catalyst.
Scheme 4: Electrochemical gram scale synthesis of the
ester from N-methoxyamide
Conclusion
We have developed a new electrochemical method
for the synthesis of phenolic esters from N-
alkoxyamides. The protocol was compatible with
various amide and phenol substrates. Interestingly,
the method was also viable for the synthesis of cyclic
esters from amide bearing a phenol substituent within,
highlighting the versatility. The reaction was scaled
unto grams showing its practicability. The developed
methodology has the following features: (i) a novel
one-pot electrochemical On-Off method for rapid N-
N dimerization of readily available N-methoxyamides
under mild conditions, (ii) chemoselective cleavage
of C-N bond of dimer under mild conditions in the
absence of current (iii) Zn(OTf)2 as novel catalytic
system for coupling of phenol with the amide dimer
(iv) ligand-free catalytic system and (v) the reaction
was suitable for the synthesis of highly functionalized
phenolic esters from amides.
On the basis of control experiments and former
literature reports,[9,11-13] we propose a plausible
reaction mechanism for the protocol as shown in
Scheme 5. Initially, when electric current is On, the
electrochemical oxidation of the iodide ion at anode
leads to the formation of an iodine radical[11e,11f]
which in turn abstracts the hydrogen radical from N-
methoxybenzamide, 1a converting it to a radical
intermediate
A
which immediately undergoes
dimerization to form the N-N homo dimer, B
liberating HI which further undergoes oxidation to
produce I- and H+ and this catalytic cycle continues.
Further, some amount of B undergoes rearrangement
to form the methoxy ester 4a. The H+ produced at the
anode moves towards the cathode and the expected
hydrogen evolution is suppressed due to the presence
of n-Bu4N+ ions which eventually gets adsorbed on
the cathode surface.[11g]
Experimental Section
Instruments and reagents
The electrolysis was carried out using a regulated DC
power
supply
generated
by
MetrohmAutolab
PGSTAT302N. NMR spectra were recorded with an
Agilent Technologies (1H NMR at 500 or 400 MHz, 13C
NMR at 125 or 100 MHz) spectrometer. The chemical
shifts are reported in ppm relative to TMS as the internal
standard and the coupling constant in Hz. A GC-MS-QP
2010 instrument (Rtx-17, 30 m × 25 mm ID, film thickness
(df ) = 0.25 μm) (column flow 2 mL min−1, 80 °C to
240 °C at 10 °C min−1 rise) was used for the mass analysis.
GC yields were obtained using Perkin Elmer Clarus 400
instruments with an ELITE-1 column. The IR spectra were
recorded in ATR (Attenuated Total Reflectance) mode by
using Perkin Elmer Spectrum two FT-IR spectrometer.
HRMS were recorded with an Agilent Technologies ESI
Q-TOF (time-of-flight) mass spectrometer. All reactions
were carried out in oven-dried glass wares. Other
chemicals and solvents obtained from commercial sources
like Sigma Aldrich, Alfa Aesar, and Spectrochem were
used without further purification. Analytical TLC of
products was performed with 60F254 silica gel plates (0.25
mm thickness). Products were purified by column
chromatography with silica gel (60-120 mesh) using
petroleum ether/EtOAc.
Scheme 5. Plausible reaction mechanism
General electrochemical On-Off procedure for the
synthesis of esters from N-alkoxyamides and phenols
A 25 mL peer shaped three-necked undivided cell
equipped with a platinum plate (30mm x 15mm) anode and
copper plate (30mm x 15mm) cathode was connected to a
regulated DC power supply. N-methoxybenzamide 1a (0.5
mmol, 75.6 mg) and TBAI (0.2 mmol, 74 mg) dissolved in
15 mL DMF were then added into the cell. Electrolysis
was carried out under CCE of 1 mA cm-2 at 0 °C until the
starting material was completely consumed as determined
by TLC. The mixture was constantly stirred during
electrolysis. After switching off the current, p-cresol 2a
(0.6 mmol, 65 mg), Zn(OTf)2 (10 mol %, 18 mg) and
K2CO3 (1 mmol, 138.2 mg) were added to the reaction
mixture and stirring was continued at 20 °C for 21 h. Later,
There are extensive reports on zinc catalyzed
nucleophilic reactions via the formation of chelate
intermediates.[12] Generally, in carbonyl compounds,
zinc co-ordinates with carbonyl oxygen to form an
intermediate of type C.[13] Herein when the electric
current is Off zinc co-ordinates with the dimer B to
form the metal-dimer chelate C. This is followed by
the nucleophilic addition of phenoxide ion to the
carbonyl carbon of C forming the intermediate D at
the expense of TfOH thereby producing the phenyl
ester 3aa. Further, nucleophilic addition of the
5
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10.1002/adsc.201701646
Advanced Synthesis & Catalysis
the reaction mixture was diluted with ethyl acetate and
washed twice with water. The organic layer was separated
and dried over Na2SO4, filtered and concentrated in vacuo.
The product 3aa was then purified by column
chromatography.
CDCl3) δC/ppm 165.3, 157.2, 148.8, 135.4, 130.0, 129.9,
126.9, 125.5, 121.4, 35.2, 31.1, 20.9. IR (ATR) ν (cm−1)
2967, 2871, 1729, 1507, 1458, 1269, 1182, 1073, 702, 509.
GCMS (EI, 70 eV) m/z (%) 268.15 (4.65), 162.15 (12.95),
161.15 (100), 146.15 (11.06), 118.10 (10.08), 91.10 (6.51),
77.05 (4.56).
Procedure for the synthesis of cyclic ester from amide
containing an internal phenol
p-Tolyl 3-methylbenzoate (3ea)[16]
A 25 mL peer shaped three-necked undivided cell
equipped with a platinum plate (30mm x 15mm) anode and
copper plate (30mm x 15mm) cathode was connected to a
regulated DC power supply. 2′-hydroxy-N-methoxy-[1,1′-
biphenyl]-2-carboxamide 5a (0.5 mmol, 122 mg) and
TBAI (0.2 mmol, 74 mg) dissolved in 15 mL DMF were
then added into the cell. Electrolysis was carried out under
CCE of 1 mA cm-2 at 0 °C until the starting material was
completely consumed as determined by TLC. The mixture
was constantly stirred during electrolysis. After switching
off the current, Zn(OTf)2 (10 mol %, 18 mg) and K2CO3 (1
mmol, 138.2 mg) were added to the reaction mixture and
stirring was continued at 20 °C for 21 h. Later, the reaction
mixture was diluted with ethyl acetate and washed twice
with water. The organic layer was separated and dried over
Na2SO4, filtered and concentrated in vacuo. The product
5b was then purified by column chromatography.
The typical procedure was applied to N-methoxy-3-
methylbenzamide 1e (0.5 mmol, 83 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ea
afforded an off-white crystalline solid (69 mg, yield 61%):
1H NMR (400 MHz, CDCl3) δH/ppm 8.00 (dd, J = 8.3, 1.2
Hz, 2H), 7.45 – 7.35 (m, 2H), 7.21 (d, J = 8.2 Hz, 2H),
7.08 (d, J = 8.5 Hz, 2H), 2.44 (s, 3H), 2.37 (s, 3H). 13C
NMR (100 MHz, CDCl3) δC/ppm 165.5, 148.7, 138.3,
135.4, 134.2, 130.6, 130.0, 129.6, 128.4, 127.3, 121.4, 21.3,
20.9. IR (ATR) ν (cm−1) 2924, 1733, 1508, 1272, 1181,
1064, 736, 513. GCMS (EI, 70 eV) m/z (%) 226.15
(10.79), 120.20 (10.36), 119.15 (100), 92.10 (3.17), 91.10
(39.59), 65.05 (12.32), 39.05 (3.26).
p-Tolyl 2-naphthoate (3fa)[17]
The typical procedure was applied to N-methoxy-2-
naphthamide 1f (0.5 mmol, 101 mg) and p-cresol 2a (0.6
mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3fa
p-Tolyl benzoate (3aa)[14]
The
typical
procedure
was
applied
to
N-
1
methoxybenzamide 1a (0.5 mmol, 76 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3aa
afforded a white solid (92 mg, yield 70%): H NMR (400
MHz, CDCl3) δH/ppm 8.78 (s, 1H), 8.19 (dd, J = 8.6, 1.8
Hz, 1H), 8.04 – 7.86 (m, 3H), 7.65-7.54 (m, 2H), 7.29 –
7.20 (m, 2H), 7.14 (d, J = 8.5 Hz, 2H), 2.38 (s, 3H). 13C
NMR (100 MHz, CDCl3) δC/ppm 165.5, 148.8, 135.8,
135.5, 132.5, 131.8, 130.0, 129.5, 128.5, 128.3, 127.8,
126.9, 126.8, 125.5, 121.4, 20.9. IR (ATR) ν (cm−1) 1738,
1506, 1268, 1187, 1077, 764, 510. GCMS (EI, 70 eV) m/z
(%) 262.30 (8.38), 156.20 (12.30), 155.25 (100), 128.20
(6.47), 127.20 (56.26), 126.20 (7.90), 101.15 (2.88), 77.10
(7.76), 51.10 (2.08).
1
afforded a white solid (77 mg, yield 73%): H NMR (400
MHz, CDCl3) δH/ppm δ 8.22 (dd, J = 6.8, 1.6 Hz, 2H),
7.69 – 7.59 (m, 1H), 7.57 – 7.45 (m, 2H), 7.29 – 7.18 (m,
2H), 7.11 (dd, J = 8.5, 1.8 Hz, 2H), 2.38 (s, 3H). 13C NMR
(100 MHz, CDCl3) δC/ppm δ 165.4, 148.7, 135.5, 133.5,
130.1, 130.0, 129.7, 128.5, 121.4, 20.9. IR (ATR) ν (cm−1)
2922, 1726, 1508, 1451, 1266, 1196, 703. GCMS (EI, 70
eV) m/z (%)212.20 (11.42), 106.16 (8.07), 105.15 (100),
77.10 (34.12), 51.05 (6.39).
p-Tolyl 1-naphthoate (3ga)[18]
p-Tolyl 4-methylbenzoate (3ba)[3]
The typical procedure was applied to N-methoxy-1-
naphthamide 1g (0.5 mmol, 101 mg) and p-cresol 2a (0.6
mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ga
The typical procedure was applied to N-methoxy-4-
methylbenzamide 1b (0.5 mmol, 83 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ba
1
afforded a white solid (71 mg, yield 54%): H NMR (400
1
afforded a white solid (77 mg, yield 68%): H NMR (400
MHz, CDCl3) δH/ppm 9.21 – 9.07 (m, 1H), 8.51 (dd, J =
7.3, 1.2 Hz, 1H), 8.16 – 8.05 (m, 1H), 7.94 (dd, J = 8.2, 1.4
MHz, CDCl3) δH/ppm 8.08 (d, J = 8.3 Hz, 2H), 7.33 – 7.16
(m, 4H), 7.08 (d, J = 8.5 Hz, 2H), 2.44 (s, 3H), 2.36 (s, 3H). Hz, 1H), 7.74 – 7.65 (m, 1H), 7.64-7.53 (m, 2H), 7.43 –
13C NMR (100 MHz, CDCl3) δC/ppm 165.4, 148.7, 144.3,
135.4, 130.2, 129.9, 129.2, 126.9, 121.4, 21.7, 20.9. IR
(ATR) ν (cm−1) 2923, 2854, 1725, 1608, 1505, 1266, 1195,
1070, 747, 504. GCMS (EI, 70 eV) m/z (%) 226.25 (6.12),
120.20 (9.12), 119.20 (100), 91.15 (26.99), 77.10 (1.85),
65.10 (8.31), 51.05 (1.16), 39.05 (1.64)
7.14 (m, 4H), 2.44 (s, 3H). 13C NMR (100 MHz, CDCl3)
δC/ppm 166.1, 148.8, 135.6, 134.3, 134.0, 131.7, 131.2,
130.1, 128.7, 128.2, 126.4, 126.1, 125.8, 124.6, 121.6, 21.0.
IR (ATR) ν (cm−1) 1727, 1505, 1234, 1185, 1114, 982, 778,
507. GCMS (EI, 70 eV) m/z (%) 262.15 (7.74), 156.15
(12.61), 155.15 (100), 128.15 (6.00), 127.15 (52.45),
126.15 (6.96), 101.10 (2.63), 77.05 (6.39), 51.05 (1.84).
p-Tolyl 4-methoxybenzoate (3ca)[14]
The typical procedure was applied to N,4-
dimethoxybenzamide 1c (0.5 mmol, 91 mg) and p-cresol
2a (0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9/1) of the product 3ca
p-Tolyl 2-methylbenzoate (3ha)[19]
The typical procedure was applied to N-methoxy-2-
methylbenzamide 1h (0.5 mmol, 83 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ha
1
afforded a white solid (52 mg, yield 43%): H NMR (400
1
MHz, CDCl3) δH/ppm 8.14 (d, J = 8.9 Hz, 2H), 7.20 (d, J =
8.2 Hz, 2H), 7.07 (d, J = 8.5 Hz, 2H), 6.97 (d, J = 8.9 Hz,
2H), 3.88 (s, 3H), 2.36 (s, 3H). 13C NMR (100 MHz,
CDCl3) δC/ppm 165.1, 163.8, 148.8, 135.3, 132.2, 129.9,
122.0, 121.4, 113.8, 55.5, 20.9. IR (ATR) ν (cm−1) 3005,
2930, 1724, 1509, 1454, 1256, 1164, 1071,762, 515.
GCMS (EI, 70 eV) m/z (%) 242.15 (4.86), 136.15 (9.31),
135.15 (100), 77.10 (12.17), 64.05 (3.13), 51.05 (1.04).
afforded a yellow oil (37 mg, yield 33%): H NMR (400
MHz, CDCl3) δH/ppm 8.16 (d, J = 7.6 Hz, 1H), 7.53-7.43
(m, 1H), 7.31 (d, J = 7.6 Hz, 2H), 7.23 (d, J = 8.3 Hz, 2H),
7.10 (d, J = 8.5 Hz, 2H), 2.68 (s, 3H), 2.38 (s, 3H). 13C
NMR (100 MHz, CDCl3) δC/ppm 166.0, 148.7, 141.2,
135.4, 132.6, 131.9, 131.1, 130.0, 128.7, 125.9, 121.5, 21.9,
20.9. IR (ATR) ν (cm−1) 2924, 1735, 1507, 1457, 1242,
1192, 1041, 733. GCMS (EI, 70 eV) m/z (%) 226.15
(4.49), 120.15 (9.15), 119.15 (100), 91.10 (32.68), 65.05
(9.42), 39.05 (2.40).
p-Tolyl 4-(tert-butyl)benzoate (3da)[15]
The typical procedure was applied to 4-(tert-butyl)-N-
methoxybenzamide 1d (0.5 mmol, 104 mg) and p-cresol
2a (0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3da
p-Tolyl 4-chlorobenzoate (3ja)[3]
The typical procedure was applied to 4-chloro-N-
methoxybenzamide 1j (0.5 mmol, 93 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ja
1
afforded a white solid (86 mg, yield 64%): H NMR (400
MHz, CDCl3) δH/ppm 8.13 (d, J = 8.5 Hz, 2H), 7.52 (d, J =
8.6 Hz, 2H), 7.21 (d, J = 7.7 Hz, 2H), 7.08 (d, J = 8.5 Hz,
2H), 2.37 (s, 3H), 1.37 (s, 9H). 13C NMR (100 MHz,
1
afforded a white solid (75 mg, yield 61%): H NMR (400
MHz, CDCl3) δH/ppm 8.12 (d, J = 8.7 Hz, 2H), 7.47 (d, J =
6
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701646
Advanced Synthesis & Catalysis
8.6 Hz, 2H), 7.22 (d, J = 8.2 Hz, 2H), 7.08 (d, J = 8.5 Hz,
2H), 2.37 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm
164.5, 148.5, 140.0, 135.7, 131.5, 130.0, 128.9, 128.1,
121.2, 20.9. IR (ATR) ν (cm−1) 1730, 1588, 1509, 1400,
1266, 1074, 1009, 804, 752, 506. GCMS (EI, 70 eV) m/z
(%) 246.20 (16.51), 141.15 (33.66), 140.15 (8.05), 139.15
(100), 113.05 (8.02), 111.05 (24.95), 77.10 (3.69), 75.05
(8.38), 50.05 (2.24).
6.89 (m, 2H), 2.57 (q, J = 7.6 Hz, 2H), 2.34 (s, 3H), 1.25
(d, J = 7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm
173.1, 148.5, 135.3, 129.9, 121.2, 27.7, 20.8, 9.1. IR
(ATR) ν (cm−1) 2925, 1762, 1507, 1463, 1353, 1200, 1168,
1141, 805. GCMS (EI, 70 eV) m/z (%) 164.10 (10.38),
109.10 (8.12), 108.10 (100), 79.05 (5.77), 77.05 (10.88),
57.05 (17.10), 45.05 (12.51).
p-Tolyl cyclohexanecarboxylate (3qa)[3]
p-Tolyl 4-fluorobenzoate (3ka)[20]
The
typical
procedure
was
applied
to
N-
The typical procedure was applied to 4-fluoro-N-
methoxybenzamide 1k (0.5 mmol, 85 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ka
methoxycyclohexanecarboxamide 1q (0.5 mmol, 79 mg)
and p-cresol 2a (0.6 mmol, 65 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3qa afforded a white solid (73 mg,
1
1
afforded a white solid (67 mg, yield 58%): H NMR (400
yield 67%): H NMR (400 MHz, CDCl3) δH/ppm 7.16 (d,
MHz, CDCl3) δH/ppm 8.30 – 8.13 (m, 2H), 7.31 – 7.13 (m,
4H), 7.08 (d, J = 8.5 Hz, 2H), 2.37 (s, 3H). 13C NMR (100
MHz, CDCl3) δC/ppm 167.3, 164.8, 164.4, 148.6, 135.6,
132.7 (d, J = 9.5 Hz), 130.0, 125.9, 121.3, 115.7 (d, J =
22.0 Hz), 20.9. IR (ATR) ν (cm−1) 1732, 1599, 1508, 1264,
1198, 1155, 1074, 861, 508. GCMS (EI, 70 eV) m/z (%)
230.10 (7.65), 124.05 (7.80), 123.10 (100), 95.05 (28.82),
77.05 (4.23), 51.05 (2.33), 44.00 (3.48).
J = 7.9 Hz, 2H), 6.93 (d, J = 8.5 Hz, 2H), 2.63– 2.46 (m,
1H), 2.33 (s, 3H), 2.14 – 1.98 (m, 2H), 1.81 (dd, J = 9.3,
4.0 Hz, 2H), 1.68–1.53 (m, 3H), 1.34 – 1.24 (m, 3H). 13C
NMR (100 MHz, CDCl3) δC/ppm 174.7, 148.6, 135.2,
129.8, 121.2, 43.2, 29.0, 25.7, 25.4, 20.8. IR (ATR) ν
(cm−1) 2930, 1744, 1506, 1449, 1312, 1201, 1186, 1150,
1122, 1014, 501. GCMS (EI, 70 eV) m/z (%) 218.10
(11.14), 111.10 (25.47), 110.10 (38.83), 109.10 (7.16),
108.10 (72.85), 107.10 (18.51), 91.05 (3.33), 84.10 (6.72),
83.10 (100), 77.05 (10.36), 67.05 (7.08), 55.05 (40.59),
41.05 (15.56).
p-Tolyl cinnamate (3ma)[3]
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1m (0.5 mmol, 89 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ma
m-Tolyl benzoate (3ab)[24]
The
typical
procedure
was
applied
to
N-
1
afforded a white solid (88 mg, yield 74%): H NMR (400
methoxybenzamide 1a (0.5 mmol, 76 mg) and m-cresol 2b
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
MHz, CDCl3) δH/ppm 7.86 (d, J = 16.0 Hz, 1H), 7.62 –
7.54 (m, 2H), 7.46 – 7.38 (m, 3H), 7.19 (d, J = 8.1 Hz, 2H), petroleum ether/ethyl acetate = 9.5/0.5) of the product 3ab
1
7.04 (d, J = 8.5 Hz, 2H), 6.62 (d, J = 16.0 Hz, 1H), 2.35 (s,
3H). 13C NMR (100 MHz, CDCl3) δC/ppm 165.6, 148.5,
146.4, 135.4, 134.2, 130.6, 129.9, 129.0, 128.3, 121.3,
117.4, 20.9. IR (ATR) ν (cm−1) 1720, 1633, 1505, 1309,
1193, 1137, 996, 764, 681, 507, 487. GCMS (EI, 70 eV)
m/z (%) 238.15 (5.25), 132.15 (10.14), 131.15 (100),
103.10 (30.15), 77.05 (15.49), 51.05 (3.52).
afforded a pale yellow oil (72 mg, yield 68%): H NMR
(400 MHz, CDCl3) δH/ppm 8.25 (d, J = 8.2 Hz, 2H), 7.659
– 7.62 (m, 1H), 7.59 – 7.47 (m, 2H), 7.34 (t, J = 7.7 Hz,
1H), 7.17 – 7.02 (m, 3H), 2.42 (s, 3H). 13C NMR (100
MHz, CDCl3) δC/ppm 165.3, 151.0, 139.7, 133.6, 130.2,
129.7, 129.2, 128.6, 126.7, 122.4, 118.7, 21.4. IR (ATR) ν
(cm−1) 1732, 1450, 1233, 1143, 1062, 704. GCMS (EI, 70
eV) m/z (%) 212.20 (15.70), 106.15 (10.73), 105.20 (100),
77.10 (48.48), 51.05 (11.75).
p-Tolyl furan-2-carboxylate (3na)[21]
The typical procedure was applied to N-methoxyfuran-2-
carboxamide 1n (0.5 mmol, 71 mg) and p-cresol 2a (0.6
mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3na
3,4-Dimethoxyphenyl benzoate (3ac)[14]
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1a (0.5 mmol, 76 mg) and 3,4-
dimethoxyphenol 2c (0.6 mmol, 92 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3ac afforded an off-white solid (81
1
afforded a pale yellow oil (67 mg, yield 66%): H NMR
(400 MHz, CDCl3) δH/ppm 7.65 (s, 1H), 7.36 (d, J = 3.6
Hz, 1H), 7.20 (d, J = 8.1 Hz, 2H), 7.08 (d, J = 8.5 Hz, 2H),
6.56 (d, J = 1.8 Hz, 1H), 2.35 (s, 3H). 13C NMR (100 MHz, mg, yield 63%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.18
CDCl3) δC/ppm 157.1, 147.0, 144.0, 135.7, 130.0, 121.3,
119.3, 112.1, 20.9. IR (ATR) ν (cm−1) 1733, 1508, 1471,
1292, 1194, 1167, 1086, 1012, 756, 510. GCMS (EI, 70
eV) m/z (%) 202.10 (15.29), 96.05 (5.84), 95.05 (100),
91.10 (2.04), 77.05 (4.27), 67.05 (3.64).
(d, J = 8.4 Hz, 2H), 7.67- 7.57 (m, 1H), 7.55 – 7.43 (m,
2H), 6.87 (dd, J = 9.4, 1.4 Hz, 1H), 6.76 (s, 2H), 3.87 (d, J
= 5.4 Hz, 6H). 13C NMR (100 MHz, CDCl3) δC/ppm 165.5,
149.4, 146.9, 144.5, 133.6, 130.1, 129.5, 128.6, 113.0,
111.2, 105.8, 56.2, 56.0. IR (ATR) ν (cm−1) 2921, 1730,
1505, 1229, 1148, 1060, 718, 605. GCMS (EI, 70 eV) m/z
(%) 258.15 (22.52), 106.10 (7.99), 105.10 (100), 77.05
(25.72), 51.00 (3.51).
p-Tolyl 2-phenylpropanoate (3oa)[22]
The typical procedure was applied to N-methoxy-2-
phenylpropanamide 1o (0.5 mmol, 90 mg) and p-cresol 2a
(0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3oa
3,4-Methylenedioxyphenyl benzoate (3ad)[14]
The
typical
procedure
was
applied
to
N-
1
afforded a pale yellow oil (74 mg, yield 62%): H NMR
methoxybenzamide 1a (0.5 mmol, 76 mg) and 3,4-
methylenedioxyphenol 2d (0.6 mmol, 83 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
(400 MHz, CDCl3) δH/ppm 7.44 – 7.37 (m, 2H), 7.34 (d, J
= 8.1 Hz, 2H), 7.31 – 7.24 (m, 1H), 7.10 (d, J = 7.9 Hz,
2H), 6.86 (d, J = 8.4 Hz, 2H), 3.94 (q, J = 7.1 Hz, 1H),
9.5/0.5) of the product 3ad afforded a white solid (74 mg,
2.29 (s, 3H), 1.60 (d, J = 7.1 Hz, 3H). 13C NMR (100 MHz, yield 61%): H NMR (400 MHz, CDCl3) δH/ppm 8.18 (d,
1
CDCl3) δC/ppm 173.2, 148.6, 140.2, 135.4, 129.8, 128.8,
127.6, 127.3, 121.1, 45.7, 20.9, 18.6. IR (ATR) ν (cm−1)
1752, 1506, 1453, 1195, 1165, 1135, 1074, 1018, 749, 697.
GCMS (EI, 70 eV) m/z (%) 240.15 (1.56), 133.10 (10.24),
132.10 (95.21), 108.10 (44.37), 106.10 (9.37), 105.10
(100), 104.10 (14.62), 103.10 (10.68), 79.10 (17.22), 78.05
(7.53), 77.05 (22.18), 51.05 (5.42).
J = 8.4 Hz, 2H), 7.66 – 7.45 (m, 3H), 6.82 (dd, J = 8.3, 1.6
Hz, 1H), 6.74 (s, 1H), 6.69 – 6.61 (m, 1H), 5.99 (d, J = 1.6
Hz, 2H). 13C NMR (100 MHz, CDCl3) δC/ppm 165.4,
148.1, 145.4, 145.2, 133.6, 130.1, 129.4, 128.6, 114.0,
108.0, 103.9, 101.7. IR (ATR) ν (cm−1) 1726, 1480, 1449,
1243,1120, 1034, 705. GCMS (EI, 70 eV) m/z (%) 242.20
(14.51), 106.15 (7.94), 105.15 (100), 77.10 (34.71), 51.05
(6.25).
p-Tolyl propionate (3pa)[23]
The
typical
procedure
was
applied
to
N-
4-Chlorophenyl benzoate (3ae)[24]
methoxypropionamide 1p (0.5 mmol, 52 mg) and p-cresol
2a (0.6 mmol, 65 mg). Silica gel chromatography (eluent:
petroleum ether/ethyl acetate = 9.5/0.5) of the product 3pa
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1a (0.5 mmol, 76 mg) and 4-
chlorophenol 2e (0.6 mmol,
77 mg). Silica gel
1
afforded a colourless oil (48 mg, yield 59%): H NMR
chromatography (eluent: petroleum ether/ethyl acetate =
(400 MHz, CDCl3) δH/ppm 7.16 (d, J = 7.9 Hz, 2H), 7.01 –
9.5/0.5) of the product 3ae afforded a white solid (74 mg,
7
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701646
Advanced Synthesis & Catalysis
1
yield 64%): H NMR (400 MHz, CDCl3) δH/ppm 8.19 (d,
J = 7.0 Hz, 2H), 7.68 – 7.56 (m, 1H), 7.55 – 7.44 (m, 2H),
7.28 – 7.11 (m, 2H), 7.07 – 6.92 (m, 2H), 3.81 (s, 3H). 13C
NMR (100 MHz, CDCl3) δC/ppm 164.7, 151.3, 140.0,
133.40, 130.3, 129.4, 128.5, 126.9, 122.9, 120.8, 112.5,
55.9. IR (ATR) ν (cm−1) 3065, 3001, 2975, 1735, 1605,
1451, 1260, 1200, 1110, 1065, 1025, 760, 710. GCMS (EI,
70 eV) m/z (%) 228.20 (13.49), 139.10 (0.19), 106.15
(8.03), 105.15 (100), 77.10 (31.79), 51.05 (5.75).
J = 8.3 Hz, 2H), 7.69-7.6 (m, 1H), 7.51 (t, J = 6.9 Hz, 2H),
7.39 (d, J = 7.0 Hz, 2H), 7.17 (dd, J = 8.8, 1.8 Hz, 2H). 13
C
NMR (100 MHz, CDCl3) δC/ppm 164.9, 149.4, 133.8,
131.3, 130.2, 129.5, 129.2, 128.6, 123.1. IR (ATR) ν
(cm−1) 1732, 1486, 1200, 1058, 807, 703, 513. GCMS (EI,
70 eV) m/z (%) 232.05 (4.64), 106.10 (8.31), 105.10 (100),
77.05 (34.52), 51.00 (7.62).
4-Nitrophenyl benzoate (3af)[25]
2,6-Dimethoxyphenyl benzoate (3ak)[27]
The
typical
procedure
was
applied
to
N-
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1a (0.5 mmol, 76 mg) and 4-
nitrophenol 2f (0.6 mmol, 84 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3af afforded pale yellow crystals
methoxybenzamide 1a (0.5 mmol, 76 mg) and 2,6-
dimethoxyphenol 2k (0.6 mmol, 92 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9/1) of the product 3ak afforded a white solid (30 mg,
1
1
(46 mg, yield 38%): H NMR (400 MHz, CDCl3) δH/ppm
yield 23%): H NMR (400 MHz, CDCl3) δH/ppm 8.24 (d,
8.31 (d, J = 7.1 Hz, 1H), 8.29 – 8.06 (m, 3H), 7.73 – 7.61
(m, 1H), 7.60 – 7.45 (m, 3H), 7.45 – 7.35 (m, 1H). 13C
NMR (100 MHz, CDCl3) δC/ppm 164.2, 155.7, 145.4,
134.5, 130.6, 130.3, 128.9, 128.8, 125.3, 122.6. IR (ATR)
ν (cm−1) 1784, 1735, 1519, 1452, 1346, 1206, 1055,995,
699. GCMS (EI, 70 eV) m/z (%) 243.05 (0.20), 139.10
(0.29), 106.10 (8.73), 105.10 (100), 77.05 (34.91), 51.05
(7.04).
J = 8.6 Hz, 2H), 7.66 – 7.57 (m, 1H), 7.49 (t, J = 6.9 Hz,
2H), 7.20 – 7.12 (m, 1H), 6.65 (dd, J = 8.5, 1.6 Hz, 2H),
3.80 (d, J = 1.6 Hz, 6H). 13C NMR (100 MHz, CDCl3)
δC/ppm 164.5, 152.6, 133.3, 130.4, 129.4, 128.9, 128.4,
126.3, 105.0, 56.2. IR (ATR) ν (cm−1) 2923, 2845, 1738,
1605, 1480, 1255, 1110, 1061, 769, 714. GCMS (EI, 70
eV) m/z (%) 258.25 (16.06), 106.15 (8.13), 105.15 (100),
77.10 (24.52), 51.05 (3.80).
3-Nitrophenyl benzoate (3ag)[14]
[1,1′-biphenyl]-2-yl benzoate (3al)[14]
The
typical
procedure
was
applied
to
N-
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1a (0.5 mmol, 76 mg) and 3-
nitrophenol 2g (0.6 mmol, 84 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3ag afforded a white solid (68 mg,
methoxybenzamide 1a (0.5 mmol, 76 mg) and [1,1′-
biphenyl]-2-ol 2l (0.6 mmol, 102 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3al afforded a white solid (52 mg,
1
1
yield 56%): H NMR (400 MHz, CDCl3) δH/ppm 8.23 –
yield 23%): H NMR (400 MHz, CDCl3) δH/ppm 8.04 (d,
8.09 (m, 4H), 7.7 – 7.63 (m, 1H), 7.62 – 7.58 (m, 1H), 7.5
– 7.5 (m, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 164.5,
162.3, 151.2, 134.5, 134.2, 130.5, 130.3, 130.1, 128.8,
128.75, 120.8, 117.6. IR (ATR) ν (cm−1) 1785, 1731, 1527,
1347, 1206, 1055, 998, 694. GCMS (EI, 70 eV) m/z (%)
243.15 (0.14), 213.15 (0.15), 139.15 (0.27), 106.10 (7.80),
105.10 (100), 77.10 (35.06), 51.05 (7.60).
J = 8.0 Hz, 2H), 7.62 – 7.53 (m, 1H), 7.53 – 7.40 (m, 6H),
7.40 – 7.23 (m, 5H). 13C NMR (100 MHz, CDCl3) δC/ppm
165.1, 148.0, 137.5, 135.0, 133.4, 131.0, 130.1, 129.4,
129.0, 128.5, 128.4, 128.2, 127.4, 126.4, 123.0. IR (ATR)
ν (cm−1) 1732, 1478, 1434, 1247, 1189, 1060, 750, 698.
GCMS (EI, 70 eV) m/z (%) 274.25 (17.69), 106.15 (9.18),
105.15 (100), 77.10 (31.41), 51.05 (4.62).
4-Chloro-3-nitrophenyl benzoate (3ah)[26]
3-(Trifluoromethyl)phenyl benzoate (3am)[14]
The
typical
procedure
was
applied
to
N-
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1a (0.5 mmol, 76 mg) and 4-chloro-3-
nitrophenol 2h (0.6 mmol, 91 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3ah afforded a pale yellow solid (87
mg, yield 55%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.17
(d, J = 8.3 Hz, 2H), 7.84 (s, 1H), 7.71 – 7.64 (m, 1H), 7.60
(dd, J = 8.8, 1.5 Hz, 1H), 7.57 – 7.49 (m, 2H), 7.48 – 7.41
(m, 1H). 13C NMR (100 MHz, CDCl3) δC/ppm 164.2,
149.4, 147.9, 134.4, 132.6, 130.3, 128.8, 128.2, 127.0,
124.1, 119.5. IR (ATR) ν (cm−1) 3101, 2923, 1735, 1529,
1344, 1241, 1044, 698. GCMS (EI, 70 eV) m/z (%) 277.05
(0.28), 139.10 (0.19), 106.10 (8.07), 105.10 (100), 77.05
(30.92), 51.00 (5.53)
methoxybenzamide 1a (0.5 mmol, 76 mg) and 3-
(trifluoromethyl)phenol 2m (0.6 mmol, 97 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3am afforded a colorless oil (80 mg,
1
yield 60%): H NMR (400 MHz, CDCl3) δH/ppm 8.25 –
8.16 (m, 2H), 7.70 – 7.62 (m, 1H), 7.59 – 7.48 (m, 5H),
7.47 – 7.40 (m, 1H). 13C NMR (100 MHz, CDCl3) δC/ppm
164.7, 151.0, 133.9, 132.5 – 131.5 (m), 130.2, 130.0, 128.9,
128.7, 125.4, 122.7, 122.7 (q, J = 3.8 Hz), 119.1 (q, J = 3.9
Hz). IR (ATR) ν (cm−1) 1739, 1450, 1327, 1243, 1167,
1124, 1056, 889, 694. GCMS (EI, 70 eV) m/z (%) 266.15
(0.71), 247.15 (2.84), 106.15 (9.31), 105.15 (100), 77.10
(46.09), 51.05 (12.52).
6-Bromonaphthalen-2-yl benzoate (3ai)[14]
5-Bromo-2,3-difluorophenyl benzoate (3an)[14]
The
typical
procedure
was
applied
to
N-
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1a (0.5 mmol, 76 mg) and 6-
bromonaphthalen-2-ol 2i (0.6 mmol, 134 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3ai afforded a white solid (113 mg,
methoxybenzamide 1a (0.5 mmol, 76 mg) and 5-Bromo-
2,3-difluorophenol 2n (0.6 mmol, 126 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3an afforded a white solid (63 mg,
1
1
yield 69%): H NMR (400 MHz, CDCl3) δH/ppm 8.24 (d,
yield 40%): H NMR (400 MHz, CDCl3) δH/ppm 8.18 (d,
J = 8.1 Hz, 2H), 8.02 (s, 1H), 7.80 (d, J = 8.9 Hz, 1H),
7.75 – 7.62 (m, 3H), 7.61 – 7.49 (m, 3H), 7.38 (d, J = 9.0
Hz, 1H). 13C NMR (100 MHz, CDCl3) δC/ppm 165.2,
148.9, 133.8, 132.5, 132.2, 130.2, 130.0, 129.8, 129.3,
128.6, 128.6, 122.4, 119.6, 118.8. IR (ATR) ν (cm−1) 2921,
1731, 1583, 1450, 1237, 1058, 893, 679, 701. GCMS (EI,
J = 8.5 Hz, 2H), 7.71 – 7.63 (m, 1H), 7.53 (t, J = 7.0 Hz,
2H), 7.34 – 7.21 (m, 2H). 13C NMR (100 MHz, CDCl3)
δC/ppm 163.4, 152.4 (d, J = 11.5 Hz), 149.8 (d, J = 11.4
Hz), 144.2 (d, J = 14.2 Hz, 141.8 – 140.1 (m), 134.3, 130.5,
128.8, 127.8, 122.6 (d, J = 3.6 Hz), 118.4 (d, J = 20.4 Hz),
115.0 (dd, J = 9.7, 5.0 Hz). IR (ATR) ν (cm−1) 3077, 1748,
70 eV) m/z (%) 326.20 (5.74), 316.50 (3.22), 114.15 (4.75), 1619, 1504, 1421, 1305, 1242, 1067, 1009, 863, 697, 574.
106.15 (7.94), 105.15 (100), 77.10 (24.03), 57.10 (4.54),
51.05 (2.73).
GCMS (EI, 70 eV) m/z (%) 312.00 (0.65), 106.10 (8.40),
105.10 (100), 77.05 (36.71), 51.00 (9.44).
2-Methoxyphenyl benzoate (3aj)[14]
2,4-Difluorophenyl benzoate (3ao)[14]
The
typical
procedure
was
applied
to
N-
The
typical
procedure
was
applied
to
N-
methoxybenzamide 1a (0.5 mmol, 76 mg) and 2-
methoxyphenol 2j (0.6 mmol, 74 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9/1) of the product 3aj afforded a colorless oil (48 mg,
methoxybenzamide 1a (0.5 mmol, 76 mg) and 2,4-
difluorophenol 2o (0.6 mmol, 78 mg). Silica gel
chromatography (eluent: petroleum ether/ethyl acetate =
9.5/0.5) of the product 3ao afforded a colorless oil (50 mg,
1
1
yield 42%): H NMR (400 MHz, CDCl3) δH/ppm 8.21 (d,
yield 43%): H NMR (400 MHz, CDCl3) δH/ppm 8.21 (d,
8
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10.1002/adsc.201701646
Advanced Synthesis & Catalysis
J = 8.1 Hz, 2H), 7.65 (t, J = 7.4 Hz, 1H), 7.52 (t, J = 7.8
Hz, 2H), 7.33 – 7.18 (m, 1H), 7.05 – 6.84 (m, 2H). 13C
NMR (100 MHz, CDCl3) δC/ppm 164.1, 161.4 (d, J = 10.5
Hz), 159.0 (d, J = 10.6 Hz), 155.5 (d, J = 12.6 Hz), 153.0
(d, J = 12.5 Hz), 134.8 (d, J = 3.9 Hz), 134.6 (d, J = 4.0
Hz), 134.0, 130.4, 128.7, 128.5, 124.5 (d, J = 2.0 Hz),
124.4 (d, J = 2.0 Hz), 111.4 (d, J = 4.0 Hz), 111.2 (d, J =
3.9 Hz), 105.2 (dd, J = 26.9, 22.3 Hz). IR (ATR) ν (cm−1)
1744, 1619, 1506, 1453, 1240, 1187, 1052, 1023, 963, 703.
GCMS (EI, 70 eV) m/z (%)234.15 (2.05), 106.15 (10.54),
105.20 (100), 77.15 (57.90), 51.05 (18.94).
[3] H.-X. Liu, Y.-Q. Dang, Y.-F., Yuan, Z.-F. Xu, S.-X.
Qiu, H.-B. Tan, Org. Lett. 2016, 18, 5584 – 5587.
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Chemistry, 2nd Ed.; Oxford University Press: New
York, 2012; b) Y.-H. Su, Z. Wu, S. -K. Tian, Chem.
Commun. 2013, 49, 6528 – 6530; c) L. M. Berreau, M.
M. M.-Grzyska, A. M. Arif, Inorg. Chem. 2000, 39,
4390 – 4391; d) S. M. A. H. Siddiki, A. S. Touchy, M.
Tamura, K. Shimizu, RSC Adv. 2014, 4, 35803 –
35807; e) M. V. De Almeida, D. H. R. Barton, I.
Bytheway, J. A. Ferreira, M. B. Hall, W. Liu, D. K.
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6H-benzo[c]chromen-6-one (5b)[28]
The typical procedure was applied to 2′-hydroxy-N-
methoxy-[1,1′-biphenyl]-2-carboxamide 5a (0.5 mmol, 122
mg). Silica gel chromatography (eluent: petroleum
ether/ethyl acetate = 9.5/0.5) of the product 5b afforded a
1
white solid (60 mg, yield 61%): H NMR (400 MHz,
CDCl3) δH/ppm 8.39 (d, J = 7.9 Hz, 1H), 8.08 (dd, J = 25.1,
8.1 Hz, 2H), 7.87 – 7.76 (m, 1H), 7.57 (t, J = 7.6 Hz, 1H),
7.52 – 7.42 (m, 1H), 7.40-7.28 (m, 2H). 13C NMR (100
MHz, CDCl3) δC/ppm 161.2, 151.3, 134.8, 134.7, 130.6,
130.4, 128.9, 124.5, 122.7, 121.7, 121.2, 118.0, 117.8. IR
(ATR) ν (cm−1) 2923, 1728, 1607, 1455, 1262, 1076, 742.
GCMS (EI, 70 eV) m/z (%) 196.00 (5.30), 168.00 (3.80),
139.00 (5.00), 43.95 (17.40), 39.95 (100).
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Procedure for the gram scale synthesis of methyl
benzoate
A 250 mL round-bottomed flask with detachable three
neck lid equipped with a cylindrical platinum gauze (d = h
= 4.5 cm) anode and copper plate (4.5 cm x 6.0 cm)
cathode were connected to a regulated DC power supply.
N-methoxybenzamide (10 mmol, 1.5 g) and TBAI (4 mmol,
1.5 g) dissolved in 150 mL DMF were then added to the
cell. Electrolysis was carried out under CCE of 1 mA cm-2
at 0 °C for 4.5 h. The mixture was constantly stirred during
electrolysis. After switching off the current, p-cresol (12
mmol, 1.3 g), Zn(OTf)2 (10 mol %, 363.5 mg) and K2CO3
(20 mmol, 2.8 g) were added to the reaction mixture and
stirring was continued at 20 °C for 24 h. Later, the reaction
mixture was diluted with ethyl acetate and washed thrice
with water. The organic layer was separated and dried over
Na2SO4, filtered and concentrated in vacuo. The product
was then purified by column chromatography.
[6] a) A. B. Charette, P. Chua, Synlett 1998, 163 – 165;
b) S. L. Yedage, B. M. Bhanage, Green Chem. 2016,
18, 5635 – 5642; J. Org. Chem. 2016, 81, 4103 – 4111.
[7] a) N. Zhang, R. Yang, D. Z.-Negrerie, Y. Du, K. Zhao,
J. Org. Chem. 2013, 78, 870 5− 8711; b) L. Zhou, S.
Tang, X. Qi, C. Lin, K. Liu, C. Liu, Y. Lan, A. Lei,
Org. Lett. 2014, 16, 3404 – 3407.
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1874, 140-156; b) C. Xiuling, S. Shaofa, W. Minghu,
W. Jian, G. Haibing, L. Yan, (Hubei Institute of
Science
106831285(A), 2017.
and
Technology),
Chinese
Patent
Acknowledgments
K. S. is thankful to the University Grants Commission of India
(UGC) for providing the Basic Scientific Research (BSR)
fellowship and S. L. Y. is thankful to the Council of Scientific and
Industrial Research (CSIR), Govt. of India, for providing the
Senior Research Fellowship (SRF).
[9] K. Subramanian, S. L. Yedage, B. M. Bhanage, J.
Org. Chem. 2017, 82, 10025 – 10032.
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2014, 55, 6935 – 6938; b) Y. Kita, Y. Nishii, A.
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Advanced Synthesis & Catalysis
FULL PAPER
Electrodimerization of N-Alkoxyamides for
Zinc(II) Catalyzed Phenolic Ester synthesis under
mild reaction conditions
Adv. Synth. Catal. Year, Volume, Page – Page
Kripa Subramanian, Subhash L.Yedage,
Bhalchandra M. Bhanage*
11
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