Copper-catalyzed chemoselective oxidative o-aroylation of 2-acetylphenols, alkyl salicylates and 1,3-dicarbonyl compounds using styrene derivatives

Article abstract of DOI:10.1016/j.tet.2021.132000

A novel copper-catalyzed chemoselective oxidative O-aroylation of 2-acetylphenols, alkyl salicylates and 1,3-dicarbonyl compounds with a wide range of styrene derivatives are described. This approach provides an efficient chemoselective preparation of phenol, alkyl salicylate and enol esters in good to excellent yields. This method represents an alternative protocol for the classical esterification reactions.

Full text of DOI:10.1016/j.tet.2021.132000

Tetrahedron 84 (2021) 132000
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Copper-catalyzed chemoselective oxidative o-aroylation of 2-
acetylphenols, alkyl salicylates and 1,3-dicarbonyl compounds using
styrene derivatives
Upendra Kumar, Ajay Sharma, Naveen Kumar, Satyendra Kumar Pandey*
Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi, 221005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel copper-catalyzed chemoselective oxidative O-aroylation of 2-acetylphenols, alkyl salicylates and
1,3-dicarbonyl compounds with a wide range of styrene derivatives are described. This approach pro-
vides an efficient chemoselective preparation of phenol, alkyl salicylate and enol esters in good to
excellent yields. This method represents an alternative protocol for the classical esterification reactions.
© 2021 Elsevier Ltd. All rights reserved.
Received 23 November 2020
Received in revised form
30 January 2021
Accepted 1 February 2021
Available online 16 February 2021
Keywords:
O-Aroylation
2-Acetylphenols
Alkyl salicylates
1,3-Dicarbonyl compounds
Styrene
1. Introduction
(e)] [13] as coupling partners are documented in the literature
(Scheme 1). To the best of our knowledge aryl alkenes have not yet
Esterification is one of the most fundamental and basic reactions
in organic synthesis because ester groups are key motifs and
common building blocks present in drugs, bioactive natural prod-
ucts and valuable agrochemicals [1]. Aryl esters are traditionally
synthesized from carboxylic acid as an acyl halide, activated esters
or anhydrides with phenol derivatives. Recently, transition metal
mediated esterification of functionalized hydrocarbons are some
alternative strategies for the ester synthesis [2]. The cross dehy-
drogenative coupling (CDC) for making C-X and CeC bond is an
attractive strategy because it exploits unfunctionalized starting
material and is atom with step economic [3]. Various approaches
for the synthesis of aryl esters with transition metals such as Pd [4],
Cu[5], Rh [6], Ru[7] and Ir [8] were well known in literature.
Various CDC methods for aryl esters and carbamates synthesis
have been documented in the literature [9]. However, very specif-
ically 2-acetylphenol directing group assisted oxidative and CDC
reactions for the synthesis of ester employing aryl aldehyde [path
(a)] [10], dibenzyl ether [path (b)] [11a], benzyl alcohol [path (c)]
[11b], 2-bromoacetophenone [path (d)] [12] and aryl alkyl [path
used for the esterification of phenol derivatives. Herein, we are
reporting the oxidative esterification of 2-acetylphenols and alkyl-
2-hydroxybenzoates employing terminal aryl alkenes as o-aroyl
surrogate and also its substrate scope to 1,3-dicarbonyl compounds
esterification.
2. Results and discussion
We initiated this work with the possibilities in mind that aryl
alkenes could be activated under oxidative conditions to furnish the
coupled products. In our preliminary experiments, we used 2-
acetylphenol 1a and 4-methoxystyrene 2a as a model substrate,
tert-butyl hydroperoxide (TBHP) and 20 mol % of Cu(OAc)2 as the
catalyst. To our pleasure, we observed that when 2-acetylphenol 1a
was treated with 4-methoxystyrene 2a in the presence of 20 mol %
of Cu(OAc).2H2O, TBHP (70 wt % in H2O) as an external oxidant and
DCE as a solvent furnished the desired ester product 3aa in 51%
yield. Elimination of either TBHP or Cu(OAc)2 resulted no formation
of desired ester product 3aa. Encouraged by unprecedented result,
optimization of the reaction conditions was carried out to achieve
the best yield of the desired ester product 3aa. Details of various
optimization reaction conditions are displayed in Table 1. Substrate
* Corresponding author.
E-mail address: skpandey.chem@bhu.ac.in (S.K. Pandey).
https://doi.org/10.1016/j.tet.2021.132000
0040-4020/© 2021 Elsevier Ltd. All rights reserved.

U. Kumar, A. Sharma, N. Kumar et al.
Tetrahedron 84 (2021) 132000
substituted 2-acetylphenol with various substituted styrene com-
pounds 2a-g (Scheme 2). The reaction between 2-acetylphenol and
substituted styrene derivatives with electron donating and electron
withdrawing group such as methoxy, methyl, bromo, chloro and
fluoro were well tolerated regardless of their position on the aro-
matic ring and furnished the ester derivatives 3aa-ad and 3ae-af in
good to excellent yields. We observed that the substituted styrene
compounds with electron donating functional groups furnished
excellent yield compared to electron withdrawing groups. How-
ever, styrene derivatives having strongly electron withdrawing
group such as nitro and nitrile failed to afford the corresponding
esters. This clearly suggest a significant electronic effect on the rate
of reactions and hence on the product yields. Next, we tested
substituted 2-acetylphenols such as chloro and hydroxy with
various substituted styrene derivatives with electron donating and
electron withdrawing groups such as methoxy, methyl, bromo,
Scheme 1. CeO bond formation via CeH activation employing CDC and oxidative cross
coupling protocols.
Table 1
a
Optimization of reaction conditions
.
Entry
Catalyst (mol %)
Oxidant (eq.)
Solvent
Yield %
1.
2.
3.
4.
5.
6.
7.
8.
Cu(OAc).2H2O
CuI
CuBr2
TBHPc (4)
TBHPd (4)
TBHPd (4)
TBHPd (4)
TBHPd (4)
TBHPd (4)
TBHPd (4)
TBHPd (4)
TBHPd (4)
TBHPd (5)
Nil
DCE
DCE
DCE
DCE
DCE
DCE
DMSO
DMF
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
51%
29%
37%
35%
Trace
67%
68%
45%
78%
81%
Nil
CuCl
Cu(OTf)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Nil
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
9.
10.
11.
12.
13.
14.
15.
16.
TBHPd (5)
H2O2
Nil
<10%
Trace
Trace
Trace
K2S2O8 (5)
m-CPBA(5)
Ag2O (5)
a
Reaction conditions: 2-acetylphenol 1a (0.5 mmol), p-methoxy styrene 2a
(1.0 mmol), Copper salt (20 mol %), oxidant (quantity noted), solvent (1 mL) at 80 ꢀ
C
for 15 h under pressure tubes. bIsolated yield of pure product reported.
c
TBHP (70 wt % in H2O).
TBHP 5.5 M in decane.
d
2-acetylphenol 1a 0.5 mmol), 4-methoxystyrene 2a (1.0 mmol),
catalyst Cu(OAc)2 (20 mol %), TBHP oxidant in decane (5.5 M, 5.0
equiv) at 80 ꢀC and MeCN solvent under pressure tube furnished
the best results in 15 h (Table 1). These optimized reaction condi-
tions were used for all other reactions.
Scheme 2. Oxidative coupling of 2-acetylphenols with aryl alkenes; Reaction condi-
tions: 1a-c (0.5 mmol), 2a-g (1.0 mmol), Cu(OAc)2 (20 mol %), TBHP (5 equiv) in MeCN
(1.0 mL) at 80 ꢀC for 15 h in pressure tubes. aIsolated yield of the pure product.
We first investigated the scope of this coupling reaction for
2

U. Kumar, A. Sharma, N. Kumar et al.
Tetrahedron 84 (2021) 132000
chloro and fluoro which were also well tolerated irrespective of
their positions on the aromatic ring and furnished the ester de-
rivatives 3ba-bg and 3ca-cg in good to excellent yields. In the
presence of 3-hydroxyl group, selective protection of 2-
acetylphenol afforded the ester derivative 3 cc which shows the
directing group effect in this coupling reaction. The selective pro-
tection of hydroxy functional group in the 2-acetylphenol is an
important conversion in the synthesis of various biologically active
natural products [14]. Next, we explored the coupling reaction of
salicylaldehyde with substituted styrenes 2a-f which also furnished
the ester derivatives 3da-df in excellent yields.
The use of salicylic acid failed to give phenol ester which clearly
suggest the poor directing ability of the eCOOH group. Further we
explored, the scope of this coupling reaction with alkyl salicylate as
directing group. To our surprise, when methyl salicylate (oil of
wintergreen) 4a was treated with substituted. styrene 2a under the
optimized reaction conditions afforded the corresponding O-aroy-
lated ester product 5aa in 72% yield (Scheme 3). To the best of our
knowledge, this is the first report in which alkyl salicylate are
directly coupled with substituted styrene derivatives under
oxidative conditions and act as directing group.
which furnished the desired ester derivatives 5aa-ag and 5ba-bg in
good to excellent yields. Further, we tested ethyl salicylate with
substituted styrenes 2a and 2g which were also well tolerated
irrespective of their position on the aromatic ring and afforded the
esters 5da, 5ca, and 5 cg in good yields. The reactivity pattern of
substituted styrene was found identical as in case of 2-acetylphenol
as directing group, but the yields were slightly less. It may be
possible due to chelating site are electron deficient.
(Z)-Enol form of 1,3-dicarbonyl compounds have structural
analogy to those of O-hydroxy carbonyl and O-hydroxy ester
compounds so far as the positioning and orientation of hydroxy and
carbonyl groups are concerned [9,10a,11]. To unravel the scope and
potential of this method 1,3-dicorbonyl compounds were reacted
with several substituted styrene 2a-g compounds. Methyl acetoa-
cetate 6a when treated with 4-methoxystyrene 2a, p-methylstyr-
ene 2c, 4-fluorostyrene 2f and 4-chlorostyrene 2g furnished their
enol ester derivatives 7aa, 7ac, 7af and 7 ag respectively, in good
yield (Scheme 4). Generally, under several metal catalyzed reaction
condition b
-carbonyl compounds afford C(sp3)-C(sp3) bond rather
than C(sp3)-O bond [15]. Further, we tested the coupling of
dibenzoylmethane 6b having 1,3-dicarbonyl groups with 4-
methoxystyrene 2a, styrene 2b, p-methylstyrene 2c and 4-
fluorostyrene 2f which furnished the enol ester derivatives 7ba,
7bb, 7bc and 7bf in good to excellent yields. All these coupling
reactions proceeded with good yields and high stereoselectivity of
Z-enol esters with no loss in stereoselectivity which was confirmed
by NOESY experiments of products 7ac, 7af and 7 ag.
Further, we explored this coupling reaction with methyl salic-
ylate derivatives (4a-b) with substituted styrene derivatives (2a-g)
The key factors for the formation of esters could be the coor-
dinating ability of the dicarbonyl with the metals. The oxidative
coupling reaction between styrene and 2-acetylphenol was carried
Scheme 4. Oxidative coupling of styrene derivatives with b-ketoesters for the syn-
Scheme 3. Oxidative coupling of alkyl salicylate with aryl alkene. Reaction condi-
tions: 4a-d (0.5 mmol), 2a-g (1.0 mmol), Cu(OAc)2 (20 mol %), TBHP (5 equiv) in MeCN
(1.0 mL) at 80 ꢀC for 15 h in pressure tubes. aIsolated yield of the pure product.
thesis of enolesters: Reaction conditions: 6a-b (0.5 mmol), 2a-g (1.0 mmol), Cu(OAc)2
(20 mol %), TBHP (5 equiv) in MeCN (1.0 mL) at 80 ꢀC for 15 h in pressure tubes.
aIsolated Yield of the pure product.
3

U. Kumar, A. Sharma, N. Kumar et al.
Tetrahedron 84 (2021) 132000
out in the presence of TEMPO (radical quencher) which afforded
traces of the desired product shows the radical type of the mech-
anism. Based on the observation and literature reports [16], a
plausible mechanism is proposed having two paths as displayed in
Scheme 5. In path-I, styrene 2b on treatment with TBHP forms 3-
phenyl-1,2-dioxetane A intermediate which undergoes oxidative
dehydrogenation to afford 3-phenyl 1,2-dioxete B intermediate.
The intermediate B on ring fragmentation affords phenylglyoxal C
which finally provides benzoyl radical D. In path-II, Cu(II) catalyst
forms a complex with 2-acetylphenol 1a to afford the complex E.
The benzoyl radical D could react with complex E by single electron
transfer to furnish the Cu(III) complex F which undergoes reductive
elimination to afford the product 3ab and Cu(I) catalyst regenerated
oxidized to Cu(II) by TBHP.
4.1.1. 2-Acetylphenyl 4-methoxybenzoate (3aa) [11a]
Yield: 81% (109 mg); White solid; M.p. 131e133 ꢀC; Rf ¼ 0.15 (n-
hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d 8.17 (td,
J ¼ 9.00, 4.50 Hz, 2H), 7.85 (d, J ¼ 8.53 Hz, 1H), 7.57 (dt, J ¼ 7.25,
2.65 Hz,1H), 7.35 (t, J ¼ 7.26 Hz,1H), 7.23 (d, J ¼ 8.04 Hz,1H), 7.00 (d,
J ¼ 8.55 Hz, 2H), 3.90 (s, 3H), 2.54 (s, 3H); 13C NMR (125.7 MHz,
CDCl3):
d (ppm) 197.7, 164.8, 164.1, 149.5, 133.3, 132.4, 131.5, 130.1,
126.0, 123.9, 121.5, 114.0, 55.5, 29.9.
4.1.2. 2-Acetylphenyl benzoate (3 ab) [13a]
Yield: 77% (92 mg); Yellow gummy; Rf ¼ 0.33 (n-hexane/
EtOAc ¼ 24:1); 1H NMR (500 MHz, CDCl3):
8.21 (td, J ¼ 7.47, 3.6 Hz,
d
2H), 7.86 (d, J ¼ 6.65 Hz, 1H), 7.64 (dt, J ¼ 7.65, 1.60 Hz, 1H), 7.57 (dt,
J ¼ 7.70, 1.30 Hz, 1H), 7.52 (t, J ¼ 7.63 Hz, 2H), 7.36 (t, J ¼ 7.6 Hz, 1H),
7.23 (d, J ¼ 8.6 Hz, 1H), 2.54 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
3. Conclusion
d
(ppm) 197.5, 165.1, 149.3, 133.8, 133.3, 131.2, 130.2, 129.2, 128.7,
128.6, 128.5, 126.1, 123.8, 29.7.
In summary, we have developed
a novel chemoselective
approach for the copper catalyzed direct syntheses of phenol, alkyl
salicylate and enol esters in good to excellent yields employing
TBHP as oxidant. The merits of our strategy are simplicity of oper-
ation, use of inexpensive, stable, and commercially available
starting materials. The developed reactions are additive, base, and
ligand free, proceeds under mild conditions, and can be used as an
alternative approach for the classical esterification reactions.
4.1.3. 2-Acetylphenyl 4-methylbenzoate (3ac) [13a]
Yield: 80% (102 mg); White solid; M.p. 107e109 ꢀC; Rf ¼ 0.30 (n-
hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d 8.10 (d,
J ¼ 8.49 Hz, 2H), 7.85 (dd, J ¼ 7.78, 1.75 Hz, 1H), 7.58 (dt, J ¼ 7.5,
1.80 Hz, 1H), 7.36 (d, J ¼ 7.20 Hz, 1H), 7.33 (d, J ¼ 7.70 Hz, 2H), 7.23
(d, J ¼ 7.77 Hz, 1H), 2.53 (s, 3H), 2.46 (s, 3H); 13C NMR (125.7 MHz,
CDCl3):
d (ppm) 197.6, 165.1, 149.5, 144.7, 133.3, 131.5, 130.3, 130.2,
129.4, 126.5, 126.0, 123.9, 29.9, 21.8.
4. Experimental section
4.1.4. 2-Acetylphenyl 3-methoxybenzoate (3ad)
4.1. General procedure for the synthesis of 2-acetylphenyl 4-
methoxybenzoate (3aa)
Yield: 76% (102 mg); White gummy; Rf ¼ 0.17 (n-hexane/
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
7.84 (dd, J ¼ 21.26,
7.70 Hz, 2H), 7.71 (s, J ¼ 1H), 7.58 (t, J ¼ 7.71 Hz, 1H), 7.40 (dt,
J ¼ 31.30, 7.90 Hz, 2H), 7.28e7.12 (m, 2H), 3.87 (s, 3H), 2.54 (s, 3H);
To an oven-dried pressure tube charged with 2-acetylphenol 1a
(68.0 mg, 0.5 mmol), Cu(OAc)2 (18.0 mg, 20 mol %, 0.1 mmol) and
TBHP (0.50 mL, 2.50 mmol, 5.5 M in decane) in MeCN (1.0 mL) was
added 4-methoxystyrene 2a (134 mg, 1.0 mmol). The resultant re-
action mixture was allowed to stir in pressure tube at 80 ꢀC for 15 h.
After completion of reaction as monitored by TLC, the reaction
mixture was cooled at room temperature and evaporated onto
silica gel. Purification of product by silica gel column chromatog-
raphy (n-hexane/EtOAc, 15:1) furnished the 2-acetylphenyl 4-
methoxybenzoate 3aa (109 mg) in 81% yield.
13C NMR (125.7 MHz, CDCl3):
d (ppm) 197.5, 165.0, 159.7, 149.3,
133.4, 131.2, 130.4, 130.2, 129.7, 126.1, 123.8, 122.6, 120.4, 114.5, 55.4,
29.7; HRMS (ESI) Calcd. for C16H14O4Na [MþNa]þ: 293.0784, found
293.0785.
4.1.5. 2-Acetylphenyl 4-bromobenzoate (3ae) [11a]
Yield: 71% (112 mg); Yellow solid; M.p. 121e124 ꢀC; Rf ¼ 0.24 (n-
hexane/EtOAc ¼ 20:1); 1H NMR (500 MHz, CDCl3):
d 8.04 (d,
J ¼ 8.57 Hz, 2H), 7.85 (dd, J ¼ 7.63, 1.70 Hz, 1H), 7.68e7.61 (m, 2H),
7.56 (dt, J ¼ 8.11, 1.85 Hz, 1H), 7.35 (t, J ¼ 7.63 Hz, 1H), 7.21 (d,
J ¼ 7.63 Hz, 1H), 2.51 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm)
197.3,164.5,149.0,133.4,132.0,131.9,131.7,131.6,130.8,130.3,129.6,
128.2, 126.2, 123.8, 29.4.
4.1.6. 2-Acetylphenyl 4-fluorobenzoate (3af) [11a]
Yield: 67% (86 mg); Yellow gummy; Rf ¼ 0.28 (n-hexane/
EtOAc ¼ 20:1); 1H NMR (500 MHz, CDCl3):
d 8.27e8.18 (m, 2H), 7.86
(dd, J ¼ 7.85, 1.69 Hz, 1H), 7.57 (td, J ¼ 7.80, 1.77 Hz, 1H), 7.36 (t,
J ¼ 7.59 Hz, 1H), 7.22 (d, J ¼ 8.09 Hz, 1H), 7.18 (t, J ¼ 8.55 Hz, 2H),
2.53 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 197.3, 165.1 (d,
J ¼ 255.4 Hz), 164.3, 149.3, 133.6, 133.0 (d, J ¼ 10.0 Hz), 131.1, 130.5,
126.3, 125.7, 124.0, 115.9 (d, J ¼ 25.1 Hz), 29.6.
4.1.7. 2-Acetyl-5-chlorophenyl 4-methoxybenzoate (3ba)
Yield: 83% (126 mg); White solid; M.P.145e147 ꢀC; Rf ¼ 0.13 (n-
hexane/EtOAc ¼ 10:1); 1H NMR (500 MHz, CDCl3):
d 8.15 (d,
J ¼ 8.47 Hz, 2H), 7.81 (d, J ¼ 8.46 Hz, 1H), 7.33 (dd, J ¼ 8.42, 2.04 Hz,
1H), 7.26 (d, J ¼ 2.04 Hz, 1H), 7.00 (d, J ¼ 8.56 Hz, 2H), 3.90 (s, 3H),
2.51 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 196.3, 164.3,
150.1, 138.8, 132.5, 131.2, 129.8, 126.3, 124.5, 120.9, 114.1, 55.5, 29.9;
HRMS (ESI) Calcd. for C16H13ClO4Na [MþNa]þ: 327.0394, found
327.0392.
Scheme 5. The plausible reaction mechanism.
4

U. Kumar, A. Sharma, N. Kumar et al.
Tetrahedron 84 (2021) 132000
4.1.8. 2-Acetyl-5-chlorophenyl benzoate (3bb)
4.1.15. 2-Acetyl-5-hydroxyphenyl 4-methylbenzoate (3 cc) [2e]
Yield: 78% (106 mg); White solid; M. P. 72e73 ꢀC; Rf ¼ 0.31 (n-
Yield: 72% (97 mg); White solid; M. p.107e108 ꢀC; Rf ¼ 0.28 (n-
hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
8.20 (d,
hexane/EtOAc ¼ 9:1); 1H NMR (500 MHz, DMSO‑d6/CDCl3)
d 10.11
J ¼ 7.5 Hz, 2H), 7.82 (d, J ¼ 8.49 Hz, 1H), 7.67 (t, J ¼ 7.45 Hz, 1H), 7.53
(s, 1H), 8.12 (d, J ¼ 8.48 Hz, 2H), 7.79 (d, J ¼ 9.21 Hz, 1H), 7.01 (d,
J ¼ 8.48 Hz, 2H), 6.80 (dd, J ¼ 9.07, 2.34 Hz, 1H), 6.63 (d, J ¼ 2.11 Hz,
1H), 3.90 (s, 3H), 2.44 (s, 3H); 13C NMR (125.7 MHz, DMSO‑d6/
(t, J ¼ 7.71 Hz, 2H), 7.35 (dd, J ¼ 8.54, 2.09 Hz, 1H), 7.28 (d,
J ¼ 2.11 Hz, 1H), 2.52 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm)
196.2, 164.7, 150.0, 139.0, 134.1, 131.3, 130.3, 129.6, 128.8, 126.5,
CDCl3): d (ppm) 194.8, 164.0, 163.4, 162.1, 151.3, 131.9, 131.8, 121.7,
121.2, 113.4, 112.9, 110.5, 55.0, 28.9.
124.4, 29.7; HRMS (ESI) Calcd. for
297.0289, found 297.0290.
C
15H11ClO3Na [MþNa]þ:
4.1.16. 2-Acetyl-5-hydroxyphenyl 4-chlorobenzoate (3 cg) [2e]
4.1.9. 2-Acetyl-5-chlorophenyl 4-methylbenzoate (3bc)
Yield: 68% (98 mg); White solid; M.p. 101e102 ꢀC; Rf ¼ 0.30 (n-
Yield: 77% (110 mg); White solid; M. p. 89e92 ꢀC; Rf ¼ 0.29 (n-
hexane/EtOAc ¼ 9:1); 1H NMR (500 MHz, DMSO‑d6):
d 10.72 (s,1H),
hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
8.08 (d,
8.09 (d, J ¼ 8.4 Hz, 1H), 7.90 (d, J ¼ 8.7 Hz, 1H), 7.67 (d, J ¼ 8.5 Hz,
1H), 6.82 (dd, J ¼ 8.6, 2.1 Hz,1H), 6.68 (d, J ¼ 2.0 Hz,1H), 2.41 (s,1H);
J ¼ 7.78 Hz, 2H), 7.80 (d, J ¼ 8.52 Hz, 1H), 7.32 (d, J ¼ 7.72 Hz, 3H),
7.26 (s, 1H), 2.51 (s, 3H), 2.45 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
13C NMR (125.7 MHz, DMSO‑d6):
d (ppm) 195.0, 163.6, 162.4, 150.9,
d
(ppm) 196.2, 164.7, 150.0, 145.0, 138.8, 131.2, 130.3, 129.7, 129.5,
138.8, 133.2, 131.7, 129.0, 128.1, 121.2, 113.2, 110.7, 28.8.
126.4, 125.9, 124.4, 29.8, 21.7; HRMS (ESI) Calcd. for C16H14O3Na
[MþNa]þ: 311.0445, found 311.0450.
4.1.17. 2-Formylphenyl 4-methoxybenzoate (3da) [13a]
Yield: 77% (98 mg); White solid; M.p. 75e76 ꢀC; Rf ¼ 0.15 (n-
4.1.10. 2-Acetyl-5-chlorophenyl 3-methoxybenzoate (3bd)
hexane/EtOAc ¼ 9:1); 1H NMR (500 MHz, CDCl3):
d 10.22 (s, 1H),
Yield: 75% (114 mg); Yellow gummy; Rf ¼ 0.16 (n-hexane/
8.17 (dd, J ¼ 7.0, 1.5 Hz, 2H), 7.94 (dd, J ¼ 7.5, 1.4 Hz, 1H), 7.66 (dt,
J ¼ 9.2,1.7 Hz,1H), 7.41 (t, J ¼ 7.6 Hz,1H), 7.32 (d, J ¼ 8.2 Hz,1H), 7.01
(d, J ¼ 9.0 Hz, 2H), 3.90 (s, 1H); 13C NMR (125.7 MHz, CDCl3):
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
7.81 (dd, J ¼ 11.83,
8.02 Hz, 2H), 7.69 (t, J ¼ 2.13 Hz, 1H), 7.43 (t, J ¼ 7.96 Hz, 1H), 7.35
(dd, J ¼ 8.53, 1.98 Hz, 1H), 7.27 (d, J ¼ 1.5 Hz, 1H), 7.20 (dd, J ¼ 8.25,
2.76 Hz, 1H), 3.88 (s, 3H), 2.52 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d
(ppm) 188.4, 164.9, 152.5, 145.0, 135.2, 130.3, 129.8, 129.4, 128.3,
126.2, 123.5, 120.8, 114.9, 55.5.
d
(ppm) 196.2, 164.6, 159.8, 150.0, 139.0, 131.3, 130.0, 129.8, 129.6,
126.5, 124.4, 122.7, 120.6, 114.6, 55.5, 29.7; HRMS (ESI) Calcd. for
C
4.1.18. 2-Formylphenyl benzoate (3 db) [13a]
16H13ClO4Na [MþNa]þ: 327.0394, found 327.0394.
Yield: 73% (82 mg); Colourless liquid; Rf ¼ 0.28 (n-hexane/
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d 10.21 (s, 1H), 8.22 (d,
4.1.11. 2-Acetyl-5-chlorophenyl 4-bromobenzoate (3be)
J ¼ 7.5 Hz, 2H), 7.94 (d, J ¼ 7.0 Hz, 1H), 7.66 (dd, J ¼ 7.0, 4.0 Hz, 2H),
7.53 (t, J ¼ 7.5 Hz, 2H), 7.40 (d, J ¼ 7.5 Hz,1H), 7.32 (d, J ¼ 8.0 Hz,1H);
13C NMR (125.7 MHz, CDCl3): 188.3, 164.9, 152.2, 135.3, 134.0, 130.3,
130.2, 128.7, 128.6, 128.3, 126.4, 123.5.
Yield: 71% (125 mg); White solid; M.p. 128e130 ꢀC; Rf ¼ 0.34 (n-
hexane/EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d 7.97 (d,
J ¼ 7.94 Hz, 2H), 7.74 (d, J ¼ 8.57 Hz, 1H), 7.60 (d, J ¼ 8.01 Hz, 2H),
7.29 (d, J ¼ 8.43 Hz, 1H), 7.19 (d, J ¼ 3.58 Hz, 1H), 2.44 (s, 3H); 13C
NMR (125.7 MHz, CDCl3):
d
(ppm) 196.1, 164.2, 149.8, 139.1, 132.2,
4.1.19. 2-Formylphenyl 4-methylbenzoate (3dc) [12]
131.8,131.4,129.4,129.3,127.8,126.6,124.5, 29.5.; HRMS (ESI) Calcd.
Yield: 75% (90 mg); White solid; M.p., 72e73 ꢀC, Rf ¼ 0.25 (n-
for C15H10BrClO3Na [MþNa]þ: 374.9394, found 374.9390.
hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d 10.22 (s, 1H),
8.12 (d, J ¼ 8.5 Hz, 2H), 7.95 (t, J ¼ 6.5 Hz,1H), 7.66 (dt, J ¼ 8.3, 2.4 Hz,
4.1.12. 2-Acetyl-5-chlorophenyl 4-fluorobenzoate (3bf)
1H), 7.42 (t, J ¼ 7.5 Hz, 1H), 7.33 (t, J ¼ 7.5 Hz, 3H), 2.46 (s, 3H); 13
C
Yield: 65% (95 mg); Yellow gummy; Rf ¼ 0.26 (n-hexane/
NMR (125.7 MHz, CDCl3): d (ppm) 188.4, 165.0, 152.6, 145.1, 135.3,
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d
8.14 (dd, J ¼ 8.32,
130.4, 129.5, 128.4, 126.4, 125.9, 123.6, 21.8.
5.46 Hz, 2H), 7.75 (d, J ¼ 7.77 Hz, 1H), 7.29 (dd, J ¼ 8.6, 1.9 Hz, 1H),
7.20 (d, J ¼ 1.74 Hz, 1H), 7.13 (t, J ¼ 8.60 Hz, 2H), 2.45 (s, 3H); 13C
4.1.20. 2-Formylphenyl 4-fluorobenzoate (3df) [12]
NMR (125.7 MHz, CDCl3):
d
(ppm) 196.3, 165.5 (d, J ¼ 263.0 Hz),
Yield: 71% (86 mg); yellow oil; Rf
¼
0.30 (n-hexane/
164.0, 150.0, 139.2, 133.2 (d, J ¼ 10.0 Hz), 131.5, 129.6, 126.8, 125.3,
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d 10.18 (s, 1H), 8.25e8.26
(m, 2H), 7.94 (dd, J ¼ 7.5, 1.5 Hz,1H), 7.68 (td, J ¼ 7.5,1.5 Hz,1H), 7.44
124.7, 116.1 (d,
C
J
¼
25.1 Hz), 29.5; HRMS (ESI) Calcd. for
15H10ClFO3Na [MþNa]þ: 315.0195 found 315.0180.
(t, J ¼ 7.5 Hz, 1H), 7.31 (d, J ¼ 8.5 Hz, 1H), 7.21 (t, J ¼ 9.5 Hz, 2H); 13
C
NMR (125.7 MHz, CDCl3):
d
(ppm) 188.4, 165.3 (d, J ¼ 255.0 Hz),
4.1.13. 2-Acetyl-5-chlorophenyl 4-chlorobenzoate (3bg)
164.0, 151.9, 135.3, 133.0, 132.7(d, J ¼ 10.0 Hz), 130.4, 0128.3, 126.6,
Yield: 71% (109 mg); Yellow gummy; Rf ¼ 0.24 (n-hexane/
125.0, 123.5, 115.8 (d, J ¼ 16.3 Hz).
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d
8.12 (d, J ¼ 8.52 Hz,
2H), 7.82 (d, J ¼ 8.55 Hz, 1H), 7.51 (d, J ¼ 8.58 Hz, 2H), 7.36 (dd,
4.1.21. Methyl 2-((4-methoxy benzoyl) oxy) benzoate (5aa)
J ¼ 9.01, 2.27 Hz, 1H), 7.27 (d, J ¼ 1.95 Hz, 1H), 2.52 (s, 3H); 13C NMR
Yield: 72% (103 mg); Colourless solid, M.p.120e122 ꢀC; Rf ¼ 0.20
(125.7 MHz, CDCl3):
d
(ppm) 196.1, 164.0, 149.8, 140.6, 139.1, 131.7,
(n-hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d 8.18 (d,
131.4, 129.3, 129.1, 127.3, 126.6, 124.4, 29.5; HRMS (ESI) Calcd. for
J ¼ 8.29 Hz, 2H), 8.05 (d, J ¼ 7.63 Hz, 1H), 7.57 (d, J ¼ 7.90 Hz, 1H),
C
15H10Cl2O3Na [MþNa]þ: 330.9962 found 330.9895.
7.33 (t, J ¼ 7.64 Hz, 1H), 7.23 (d, J ¼ 8.27 Hz, 1H), 6.99 (d, J ¼ 8.75 Hz,
2H), 3.87 (s, 3H), 3.73 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm)
4.1.14. 2-Acetyl-5-hydroxyphenyl 4-methoxybezoate (3ca) [2e]
165.0, 164.9, 163.8, 150.8, 133.6, 132.3, 131.7, 125.8, 124.0, 123.5,
121.7, 113.8, 55.4, 52.0; HRMS (ESI) Calcd. for C16H14O5Na [MþNa]þ:
309.0733, found 309.0736.
Yield: 75% (107 mg); White solid; M.p. 95e97 ꢀC; Rf ¼ 0.22 (n-
hexane/EtOAc ¼ 9:1); 1H NMR (500 MHz, DMSO‑d6/CDCl3):
d 10.15
(s, 1H), 8.12 (d, J ¼ 8.45 Hz, 2H), 7.79 (d, J ¼ 8.68 Hz, 1H), 7.01 (dd,
J ¼ 8.79, 3.21 Hz, 2H), 6.80 (dd, J ¼ 8.58, 2.46 Hz, 1H), 6.63 (d,
J ¼ 2.42 Hz, 1H), 3.91 (s, 3H), 2.44 (s, 3H); 13C NMR (125.7 MHz,
4.1.22. Methyl 2-(benzoyloxy) benzoate (5 ab) [11a]
Yield: 64% (82 mg); Colourless less liquid; Rf ¼ 0.33 (n-hexane/
DMSO‑d6/CDCl3):
d
(ppm) 194.8, 164.0, 163.4, 162.1, 151.3, 131.9,
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d
8.14 (d, J ¼ 7.52 Hz,
131.8, 121.7, 121.2, 113.4, 112.9, 110.5, 55.0, 28.9.
2H), 7.98 (d, J ¼ 8.34 Hz, 1H), 7.49e7.56 (m, 2H), 7.43 (t, J ¼ 7.60 Hz,
5

U. Kumar, A. Sharma, N. Kumar et al.
Tetrahedron 84 (2021) 132000
2H), 7.26 (t, J ¼ 7.62 Hz,1H), 7.14 (d, J ¼ 8.28 Hz,1H), 3.64 (s, 3H); 13
C
4.1.29. Methyl 4-methyl-2-((4-methylbenzoyl) oxy) benzoate (5bc)
[2a]
NMR (125.7 MHz, CDCl3):
d (ppm) 165.3, 165.0, 150.7, 133.8, 133.5,
131.8, 130.2, 129.4, 128.5, 126.0, 123.9, 123.4, 52.1.
Yield: 58% (82 mg); Colorless liquid; Rf ¼ 0.37 (n-hexane/
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
8.10 (d, J ¼ 7.93 Hz,
2H), 7.96 (d, J ¼ 7.96 Hz, 1H), 7.31 (d, J ¼ 7.87 Hz, 2H), 7.15 (d,
J ¼ 8.04 Hz, 1H), 7.04 (s, 1H), 3.71 (s, 3H), 2.45 (s, 3H), 2.42 (s, 3H);
4.1.23. Methyl 2-((4-methylbenzoyl) oxy) benzoate (5ac)
Yield: 67% (90 mg); Colourless gummy; Rf ¼ 0.35 (n-hexane/
13C NMR (125.7 MHz, CDCl3):
d (ppm) 165.5, 165.1, 150.8, 145.1,
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
8.11 (d, J ¼ 8.52 Hz, 2H),
d
144.3, 131.8, 130.3, 129.3, 126.9, 126.8, 124.5, 120.5, 52.0, 21.7, 21.4.
8.06 (d, J ¼ 7.77 Hz, 1H), 7.59 (t, J ¼ 7.74 Hz, 1H), 7.34 (t, J ¼ 7.25 Hz,
1H), 7.31 (d, J ¼ 8.23 Hz, 2H), 7.22 (d, J ¼ 7.91 Hz, 1H), 3.72 (s, 3H),
2.44 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 165.4, 165.1,
4.1.30. Methyl 2-((4-bromobenzoyl) oxy)-4-methylbenzoate (5be)
Yield: 56% (97 mg); Yellow gummy, Rf ¼ 0.28 (n-hexane/
150.8, 144.3, 133.7, 131.8, 130.2, 129.2, 126.7, 125.9, 124.0, 123.5, 52.1,
21.7; HRMS (ESI) Calcd. for C16H14O4Na [MþNa]þ: 293.0784, Found
293.0785.
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
8.08 (d, J ¼ 8.23 Hz, 2H),
d
7.97 (d, J ¼ 8.06 Hz, 1H), 7.66 (d, J ¼ 8.24 Hz, 2H), 7.17 (d, J ¼ 8.00 Hz,
1H), 7.04 (s, 1H), 3.72 (s, 3H), 2.43 (s, 3H); 13C NMR (125.7 MHz,
CDCl3):
d (ppm) 164.8, 164.8, 150.6, 145.3, 132.0, 131.9, 131.7, 128.7,
4.1.24. Methyl 2-((3-methoxy benzoyl) oxy) benzoate (5ad)
128.6, 127.1, 124.4, 120.3, 52.0, 21.5; HRMS (ESI) Calcd. for
16H13BrO4Na [MþNa]þ: 370.9889, found 370.9893.
Yield: 65% (92 mg); Colourless liquid; Rf ¼ 0.25 (n-hexane/
C
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
7.97 (dd, J ¼ 7.85,
1.90 Hz, 1H), 7.73 (d, J ¼ 7.69 Hz, 1H), 7.63 (d, J ¼ 2.79 Hz, 1H), 7.50
(dt, J ¼ 8.15, 2.24 Hz, 1H), 7.33 (t, J ¼ 8.46 Hz, 1H), 7.25 (t, J ¼ 7.53 Hz,
1H), 7.14 (d, J ¼ 7.95 Hz, 1H), 7.08 (dd, J ¼ 8.39, 3.34 Hz, 1H), 3.77 (s,
4.1.31. Methyl 2-((4-chlorobenzoyl) oxy)-4-methylbenzoate (5bg)
Yield: 54% (82 mg); Colourless solid, M.p. 85e87 ꢀC; Rf ¼ 0.22
(n-hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d 8.15 (d,
3H), 3.65 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 165.2, 164.9,
J ¼ 8.27 Hz, 2H), 7.97 (d, J ¼ 8.11 Hz, 1H), 7.49 (d, J ¼ 8.28 Hz, 2H),
7.16 (d, J ¼ 8.05 Hz, 1H), 7.03 (s, 1H), 3.72 (s, 3H), 2.42 (s, 3H); 13C
159.6, 150.7, 133.8, 131.8, 130.7, 129.5, 126.0, 123.8, 123.4, 122.6,
120.1, 114.5, 55.4, 52.1; HRMS (ESI) Calcd. for C16H14O5Na [MþNa]þ:
309.0733 found 309.0738.
NMR (125.7 MHz, CDCl3):
d (ppm) 164.8, 164.6, 150.6, 145.2, 139.9,
131.8, 131.6, 128.9, 128.1, 127.0, 124.3, 120.2, 52.0, 21.4; HRMS (ESI)
Calcd. for C16H13ClO4Na [MþNa]þ: 327.0394, found 327.0394.
4.1.25. Methyl 2-((4-bromobenzoyl) oxy) benzoate (5ae)
Yield: 61% (102 mg); Yellow gel; Rf
¼
0.34 (n-hexane/
8.08 (d, J ¼ 7.63 Hz,
4.1.32. Ethyl 2-((4-methoxybenzoyl) oxy)-4-methylbenzoate (5ca)
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d
Yield: 73% (114 mg); Colourless gel; Rf ¼ 0.20 (n-hexane/
3H), 7.66 (d, J ¼ 8.37 Hz, 2H), 7.61 (t, J ¼ 7.93 Hz, 1H), 7.36 (t,
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
8.17 (d, J ¼ 8.48 Hz, 2H),
d
J ¼ 7.91 Hz, 1H), 7.23 (d, J ¼ 7.92 Hz, 1H), 3.74 (s, 3H); 13C NMR
7.96 (d, J ¼ 8.05 Hz, 1H), 7.13 (d, J ¼ 8.02 Hz, 1H), 7.02 (s, 1H), 6.98 (d,
J ¼ 8.66 Hz, 2H), 4.18 (q, J ¼ 7.15 Hz, 2H), 3.87 (s, 3H), 2.40 (s, 3H),
(125.7 MHz, CDCl3):
d (ppm) 164.8, 164.7, 150.6, 133.9, 131.9, 131.7,
128.7, 128.3, 126.2, 123.8, 123.2, 52.2; HRMS (ESI) Calcd. for
1.08 (t, J ¼ 7.14 Hz, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 165.0,
C
15H11BrO4Na [MþNa]þ: 356.9733, found 356.9731.
164.8,163.7, 150.6, 144.8,132.3,131.8, 126.7, 124.4, 121.9, 121.0, 113.7,
60.8, 55.4, 21.3, 13.9; HRMS (ESI) Calcd. for C18H18O5Na [MþNa]þ:
337.1044, found 337.1047.
4.1.26. Methyl 2-((4-chlorobenzoyl) oxy) benzoate (5 ag)
Yield: 58% (84 mg); Colourless solid, M. p. 102e104 ꢀC; Rf ¼ 0.37
4.1.33. Ethyl 2-((4-chlorobenzoyl) oxy)-4-methylbenzoate (5 cg)
(n-hexane/EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d 8.16 (d,
Yield: 60% (95 mg); Colourless solid, M.p. 106e109 ꢀC; Rf ¼ 0.35
J ¼ 8.28 Hz, 2H), 8.08 (dd, J ¼ 7.89, 1.78 Hz, 1H), 7.61 (td, J ¼ 7.78,
1.75 Hz,1H), 7.50 (d, J ¼ 8.21 Hz, 2H), 7.37 (t, J ¼ 7.62 Hz,1H), 7.23 (d,
(n-hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d 8.15 (d,
J ¼ 8.10 Hz, 1H), 3.75 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm)
J ¼ 8.40 Hz, 2H), 7.98 (d, J ¼ 8.10 Hz, 1H), 7.48 (d, J ¼ 8.39 Hz, 2H),
7.16 (d, J ¼ 8.25 Hz, 1H), 7.02 (s, 1H), 4.19 (q, J ¼ 6.89 Hz, 2H), 2.41 (s,
164.8, 164.5, 150.6, 140.1, 133.9, 131.9, 131.6, 128.9, 128.0, 126.2,
123.9, 123.2, 52.2; HRMS (ESI) Calcd. for C15H11ClO4Na [MþNa]þ:
313.0238 found 313.0229.
3H), 1.11 (t, J ¼ 7.15 Hz, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm)
164.5, 164.5, 150.4, 145.0, 140.0, 131.9, 131.6, 128.9, 128.1, 127.0,
124.2, 120.7, 60.9, 21.4, 13.9; HRMS (ESI) Calcd. for C17H15ClO4Na
[MþNa]þ: 341.0551, found 341.0551.
4.1.27. Methyl 2-((4-methoxybenzyol) oxy)-4-methylbenzoate
(5ba)
4.1.34. Ethyl 2-((4-methoxybenzoyl) oxy) benzoate (5da)
Yield: 63% (95 mg); Colourless solid, M.p. 117e119 ꢀC; Rf ¼ 0.29
Yield: 70% (105 mg); Colourless liquid, Rf ¼ 0.19 (n-hexane/
(n-hexane/EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d 8.17 (d,
EtOAc ¼ 9:1); 1H NMR (500 MHz, CDCl3):
8.17 (d, J ¼ 8.50 Hz, 2H),
d
J ¼ 8.75 Hz, 2H), 7.95 (d, J ¼ 8.07 Hz, 1H), 7.14 (d, J ¼ 7.93 Hz, 1H),
7.03 (s,1H), 7.00 (d, J ¼ 8.75 Hz, 2H), 3.89 (s, 3H), 3.71 (s, 3H), 2.42 (s,
8.06 (d, J ¼ 7.68 Hz, 1H), 7.56 (t, J ¼ 7.90 Hz, 1H), 7.33 (d, J ¼ 7.68 Hz,
1H), 7.20 (d, J ¼ 8.05 Hz, 1H), 6.98 (d, J ¼ 8.64 Hz, 2H), 4.20 (q,
J ¼ 7.43 Hz, 2H), 3.85 (s, 3H), 1.09 (t, J ¼ 7.16 Hz, 3H); 13C NMR
3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 165.1, 165.1, 163.8, 150.9,
145.0, 132.3, 131.8, 126.7, 124.5, 121.9, 120.6, 113.8, 55.5, 51.9, 21.4;
HRMS (ESI) Calcd. for C17H16O5Na [MþNa]þ: 323.0890, found
323.0890.
(125.7 MHz, CDCl3):
d (ppm) 164.8, 164.7, 163.8, 150.5, 133.5, 132.2,
131.7, 125.8, 124.0, 123.8, 121.7, 113.7, 61.0, 55.3, 13.8; HRMS (ESI)
Calcd. for C17H16O5Na [MþNa]þ: 323.0890 found 323.0859.
4.1.28. Methyl 2-(benzoyloxy)-4-methylbenzoate (5bb)
4.1.35. 4-Ethoxy-4-oxobut-2-en-2yl 4-methoxybenzoate (7aa)
Yield: 60% (81 mg); Colourless gummy; Rf ¼ 0.31 (n-hexane/
Yield: 68% (90 mg); Colourless liquid; Rf ¼ 0.35 (n-hexane/
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
8.22 (d, J ¼ 7.41 Hz, 2H),
EtOAc ¼ 9:1); 1H NMR (500 MHz, CDCl3): 8.07 (d, J ¼ 8.62 Hz, 2H),
d
7.97 (d, J ¼ 7.67 Hz, 1H), 7.62 (d, J ¼ 7.63 Hz, 1H), 7.51 (t, J ¼ 7.65 Hz,
2H), 7.15 (d, J ¼ 8.12 Hz, 1H), 7.04 (s, 1H), 3.71 (s, 3H), 2.42 (s, 3H);
6.95 (d, J ¼ 9.15 Hz, 2H), 5.67 (s,1H), 4.06 (q, J ¼ 6.77 Hz, 2H), 3.86 (s,
3H), 2.13 (s, 3H), 1.10 (t, J ¼ 7.14 Hz, 3H); 13C NMR (125.7 MHz,
13C NMR (125.7 MHz, CDCl3):
d
(ppm) 165.5, 165.0, 150.8, 145.1,
CDCl3): d (ppm) 163.8, 163.7, 163.2, 160.0, 132.2, 121.5, 113.7, 108.6,
133.4, 131.8, 130.2, 129.6, 128.5, 126.9, 124.4, 120.4, 51.9, 21.4; HRMS
59.9, 55.3, 21.6, 13.9; HRMS (ESI) Calcd. for C14H16O5Na [MþNa]þ:
(ESI) Calcd. for C16H14O4Na [MþNa]þ: 293.0784, found 293.0785.
287.0890, Found 287.0892.
6

U. Kumar, A. Sharma, N. Kumar et al.
Tetrahedron 84 (2021) 132000
4.1.36. 4-Ethoxy-4-oxobut-2-en-2-yl 4-methylbenzoate (7ac)
131.4, 129.1, 128.7, 128.3, 126.3, 125.6, 115.9 (d, J ¼ 31.4 Hz), 110.1;
HRMS (ESI) Calcd. for C22H15FO3Na [MþNa]þ: 369.0897, Found
369.0893.
Yield: 65% (81 mg); Colourless liquid; Rf ¼ 0.26 (n-hexane/
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
8.01 (d, J ¼ 7.86 Hz,
2H), 7.26 (d, J ¼ 7.92 Hz, 2H), 5.67 (s, 1H), 4.05 (q, J ¼ 7.15 Hz, 2H),
2.40 (s, 3H), 2.12 (s, 3H), 1.09 (t, J ¼ 7.15 Hz, 3H); 13C NMR
Declaration of competing interest
(125.7 MHz, CDCl3):
d (ppm) 163.5, 163.4, 159.8, 144.1, 130.0, 129.0,
126.4, 108.6, 59.7, 21.4, 13.8; HRMS (ESI) Calcd. for C14H16O4Na
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
[MþNa]þ: 271.0941, Found 271.0926.
4.1.37. 4-Ethoxy-4-oxobut-2-en-2-yl 4-fluorobenzoate (7af)
Yield: 53% (67 mg); Yellow gummy; Rf ¼ 0.30 (n-hexane/
Acknowledgments
EtOAc ¼ 15:1); 1H NMR (500 MHz, CDCl3):
d
8.14 (dd, J ¼ 8.38,
5.29 Hz, 2H), 7.15 (t, J ¼ 8.59 Hz, 2H), 5.70 (s, 1H), 4.06 (q,
S.K.P. is thankful to the Science and Engineering Research Board,
New Delhi, for generous funding of the project (grant no. CRG/
2020/005562). U.K., A.S. and N.K. thank CSIR New Delhi for research
fellowships.
J ¼ 6.90 Hz, 2H), 2.14 (s, 3H), 1.12 (t, J ¼ 7.14 Hz, 3H); 13C NMR
(125.7 MHz, CDCl3):
d
(ppm) 165.0 (d, J ¼ 251.4 Hz), 163.7, 162.7,
159.9, 132.8 (d, J ¼ 12.6 Hz), 125.6, 115.7 (d, J ¼ 12.6 Hz), 108.7, 59.9,
21.5, 13.9; HRMS (ESI) Calcd. for C13H13FO4Na [MþNa]þ: 275.0690,
Found 275.0685.
Appendix. ASupplementary data
4.1.38. 4-Ethoxy-4-oxobut-2-en-2yl 4-chlorobenzoate (7 ag)
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132000.
Yield: 60% (80 mg); Colourless liquid; Rf ¼ 0.27 (n-hexane/
EtOAc ¼ 10:1); 1H NMR (500 MHz, CDCl3):
d
8.06 (d, J ¼ 8.17 Hz,
2H), 7.45 (d, J ¼ 8.00 Hz, 2H), 5.70 (s, 1H), 4.06 (q, J ¼ 6.87 Hz, 2H),
References
2.14 (s, 3H), 1.12 (t, J ¼ 7.14 Hz, 3H); 13C NMR (125.7 MHz, CDCl3):
d
(ppm) 163.5,162.7,159.7,139.9,131.5,128.8,127.7,108.8, 60.0, 21.5,
[1] (a) D.V. Rosato, M.V. Rosato, Plastic Product Material and Process Selection
Handbook, Elesevier, New York, 2004;
14.0; HRMS (ESI) Calcd. for C13H13ClO4Na [MþNa]þ: 291.0394,
(b) W. Riemenschneider, H.M. Bolt, Esters, Organic. Ullmann’s Encyclopedia of
Industrial Chemistry, Wiley-VCH, Weinheim, 2005;
(c) R.W. Dugger, J.A. Ragan, D.H.B. Ripin, Org. Process Res. Dev. 9 (2005)
253e258;
(d) J.S. Carey, D. Laffan, C. Thomson, M.T. Williams, Org. Biomol. Chem. 4
(2006) 2337e2347;
Found 291.0370.
4.1.39. 3-Oxo-1,3-diphenylprop-1-en-1-yl 4-methyoxybenzoate
(7ba)
Yield: 70% (125 mg); Colourless liquid; Rf ¼ 0.28 (n-hexane/
(e) J. Otera, Esterification: Methods, Reaction and Application, second ed.,
Wiley-VCH, Weinheim, 2010.
EtOAc ¼ 10:1); 1H NMR (500 MHz, CDCl3):
8.13 (d, J ¼ 8.51 Hz, 2H),
d
7.96 (d, J ¼ 7.59 Hz, 2H), 7.74 (d, J ¼ 7.45 Hz, 2H), 7.52 (t, J ¼ 7.27 Hz,
1H), 7.44 (q, J ¼ 8.15, 7.61 Hz, 5H), 7.31 (s, 1H), 6.98 (d, J ¼ 8.65 Hz,
[2] (a) R.C. Larock, Comprehensive Organic Transformations: A Guide to Func-
tional Group Preparations, second ed., Wiley-VCH, New York, 1999;
(b) W.-J. Yoo, C.-J. Li, Tetrahedron Lett. 48 (2007) 1033e1035;
(c) K. Ekoue-Kovi, C. Wolf, Chem. Eur J. 14 (2008) 6302e6315;
(d) X.-F. Wu, C. Darcel, Eur. J. Org Chem. (2009) 1144e1147;
(e) J.I. Sheikh, V.N. Ingle, H.D. Juneja, P. Ali, R. Dongre, Der Pharma Chem. 2
(2010) 130e137;
2H), 3.89 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 188.5, 164.0,
163.5, 157.3, 138.8, 134.2, 132.7, 132.6, 131.0, 128.9, 128.5, 128.2,
126.2, 121.5, 113.9, 110.1, 55.5; HRMS (ESI) Calcd. for C23H18O4Na
[MþNa]þ: 381.1097, Found 381.1075.
(f) B. Xu, X. Liu, J. Haubrich, C.M. Friend, Nat. Chem. 2 (2010) 61e65;
(g) S. Dana, D. Chowdhury, A. Mandal, F.A.S. Chipem, M. Baiya, ACS Catal. 11
(2018) 10173e10179.
4.1.40. 3-Oxo-1,3-diphenylprop-1-en-1yl benzoate (7bb) [13a]
[3] C.-J. Li, Acc. Chem. Res. 42 (2009) 335e344.
[4] (a) C. Liu, J. Wang, L. Meng, Y. Deng, Y. Li, A. Lei, Angew. Chem. Int. Ed. 50
(2011) 5144e5148;
Yield: 67% (110 mg); Colourless liquid; Rf ¼ 0.38 (n-hexane/
EtOAc ¼ 19:11H NMR (500 MHz, CDCl3):
d
8.19 (d, J ¼ 7.76 Hz, 2H),
(b) C. Liu, S. Tang, L. Zheng, D. Liu, H. Zhang, A. Lei, Angew. Chem. Int. Ed. 51
(2012) 5662e5666;
(c) C.J. Hu, X.H. Zhang, Q.P. Ding, T. Lv, S.P. Ge, P. Zhong, Tetrahedron Lett. 53
(2012) 2465e2468.
7.96 (d, J ¼ 7.56 Hz, 2H), 7.75 (d, J ¼ 7.49 Hz, 2H), 7.63 (t, J ¼ 7.54 Hz,
1H), 7.51 (q, J ¼ 7.68 Hz, 3H), 7.44 (q, J ¼ 8.56, 7.42 Hz, 5H), 7.34 (s,
1H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 188.3, 163.8, 157.2, 138.7,
[5] (a) W. Wang, F. Luo, S. Zhang, J. Cheng, J. Org. Chem. 75 (2010) 2415e2418;
(b) L. Cheng, Y. Sun, W. Wang, C. Yao, T.-J. Li, J. Org. Chem. 84 (2019)
3074e3082.
134.0, 133.6, 132.7, 131.1, 130.4, 129.1, 128.9, 128.6, 128.5, 128.2,
126.2, 110.0.
[6] (a) Z. Ye, W. Wang, F. Luo, S. Zhang, J. Cheng, Org. Lett. 11 (2009) 3974e3977;
(b) T. Zweifel, J.-V. Nauborn, H. Grutzmacher, Angew. Chem. Int. Ed. 48 (2009)
559e563.
[7] (a) J. Zhang, G. Leitus, Y. Ben-David, D. Milstein, J. Am. Chem. Soc. 127 (2005)
10840e10841;
4.1.41. 3-Oxo-1,3-diphenylprop-1-en-1yl 4-methylbenzoate (7bc)
Yield: 61% (104 mg); Colourless liquid; Rf ¼ 0.35 (n-hexane/
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d
8.07 (d, J ¼ 8.36 Hz,
2H), 7.95 (d, J ¼ 7.70 Hz, 2H), 7.74 (d, J ¼ 7.51 Hz, 2H), 7.49 (d,
J ¼ 7.49 Hz, 1H), 7.42 (q, J ¼ 8.00, 7.58 Hz, 5H), 7.32 (s, 1H), 7.29 (d,
(b) J. Zhang, M. Gandelman, L.J.W. Shimon, D. Milstein, Dalton Trans. 1 (2007)
107e113;
(c) N.A. Owston, A.J. Parker, J.M. Williams, J. Chem. Commun.
624e625;
5 (2008)
J ¼ 8.20 Hz, 2H), 2.42 (s, 3H); 13C NMR (125.7 MHz, CDCl3):
d (ppm)
188.3, 163.8, 157.2, 144.5, 138.7, 134.0, 132.6, 131.0, 130.4, 129.3,
128.8, 128.6, 128.5, 128.2, 126.4, 126.1, 109.9, 21.7; HRMS (ESI) Calcd.
for C23H18O3Na [MþNa]þ: 365.1148, Found 365.1138.
(d) C. Gunanthan, L.J.W. Shimon, D. Milstein, J. Am. Chem. Soc. 131 (2009)
3146e3147.
[8] (a) T. Suzuki, K. Morita, M. Tsuchida, K. Hiroi, Org. Lett. 14 (2002) 2361e2363;
(b) T. Suzuki, K. Morita, Y. Matsuo, K. Hiroi, Tetrahedron Lett. 44 (2003)
2003e2006;
(c) T. Suzuki, T. Matsuo, K. Watanabe, T. Katoh, Synlett 9 (2005) 1453e1455.
[9] (a) S.K. Rout, S. Guin, K.K. Ghara, A. Banerjee, B.K. Patel, Org. Lett. 14 (2012)
3982e3986;
4.1.42. 3-Oxo-1,3-diphenylprop-1-en-1-yl 4-fluorobenzoate (7bf)
Yield: 57% (98 mg); Yellow gummy; Rf ¼ 0.30 (n-hexane/
EtOAc ¼ 19:1); 1H NMR (500 MHz, CDCl3):
d
8.20 (dd, J ¼ 8.56,
(b) W. Ali, S.K. Rout, S. Guin, A. Modi, A. Banerjee, B.K. Patel, Adv. Synth. Catal.
357 (2015) 515e522;
(c) B.D. Barve, Y.-C. Wu, M. El-Shazly, D.-W. Chuang, Y.-B. Cheng, J.-J. Wang, F.-
R. Chang, J. Org. Chem. 79 (2014) 3206e3214.
5.42 Hz, 2H), 7.95 (d, J ¼ 7.69 Hz, 2H), 7.74 (d, J ¼ 7.44 Hz, 2H), 7.52
(d, J ¼ 7.13 Hz, 1H), 7.45 (q, J ¼ 9.35, 7.36 Hz, 5H), 7.34 (s, 1H), 7.17 (t,
J ¼ 8.51 Hz, 2H); 13C NMR (125.7 MHz, CDCl3):
d (ppm) 188.3, 165.2
(d, J ¼ 260.7 Hz),162.9,157.2, 138.8,134.0,133.2(d, J ¼ 5.0 Hz),133.0,
[10] G.S. Kumar, C.U. Maheswari, R.A. Kumar, M.L. Kantam, K.R. Reddy, Angew.
Chem. Int. Ed. 50 (2011) 11748e11751.
7

U. Kumar, A. Sharma, N. Kumar et al.
Tetrahedron 84 (2021) 132000
[11] (a) S. Sharma, J. Park, M. Kim, J.H. Kwak, Y.H. Jung, I.S. Kim, Tetrahedron 69
(2013) 9391e9397;
[14] Q. Yang, C. Draghici, J.T. Njardarson, F. Li, B.R. Smith, P. Das, Org. Biomol. Chem.
12 (2014) 330e334.
(b) J. Park, S.H. Han, S. Sharma, S. Han, Y. Shin, N.K. Mishra, J.H. Kwak, C.H. Lee,
J. Lee, I.S. Kim, J. Org. Chem. 79 (2014) 4735e4742.
[12] S. Baruah, S. Borthakur, S. Gogoi, Chem. Commun. 53 (2017) 9133e9135.
[13] (a) S.K. Rout, S. Guin, A. Banerjee, N. Khatun, A. Gogoi, B.K. Patel, Org. Lett. 15
(2013) 4106e4109;
[15] C.J. Scheuermann, Chem. Asian J. 5 (2010) 436e451.
[16] (a) C. Zhang, N. Jiao, J. Am. Chem. Soc. 132 (2010) 28e29;
(b) G. Majji, S. Guin, S.K. Rout, A. Behera, B.K. Patel, Chem. Commun. 50 (2014)
12193e12196;
(c) X. Cui, T.-T. Zhang, X. Zhang, G. Yu, P.-H. Lin, Dalton Trans. 49 (2020)
6495e6503.
(b) A. Nakisa, M. Karimi, E. Yazdani, A. Heydari, Appl. Organomet. Chem. 31
(2017), e3674.
8