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Silver(I)-catalyzed dehydrogenative cross-coupling
of 2-aroylbenzofurans with phosphites†
Kashanna Jajula, *a Rathod Aravind Kumar,b Ravada Kishore, *c
Prakash Raj Thommandru,c Ravula Shrikanth,ad Sirasani Satyanarayana
Pilli V. V. N. Kishoree
d
and
The silver(I)-catalyzed dehydrogenative cross-coupling reaction of 2-aroylbenzofurans with phosphites
Received 21st December 2021,
Accepted 31st December 2021
to afford 2-aroyl-3-phosphonylbenzofurans is reported. The dehydrogenative cross-coupling reaction
DOI: 10.1039/d1nj06077e
electron transfer, electrophilic addition and rearrangement of intermediates, successively, giving the
proceeds through the conversion of silver(I) cations into silver(II) cations by peroxodisulfate followed by
desired 2-aroyl-3-phosphonylbenzofurans. This reaction proceeded in moderate to good yields and
rsc.li/njc
with high regioselectivity.
Introduction
In the last two decades, organophosphorus compounds such as
phosphoramidates, phosphate esters, aryl phosphonates, and
heterocyclic phosphonates have emerged as a flourishing area
of research owing to their wide applications in medicinal
chemistry, biochemistry, photoelectric materials, catalysis,
pharmaceuticals (e.g., anti-HIV pro-drugs, cancer therapeutics,
etc.) and organic synthesis.1 Generally, phosphorus substituents regulate important biological, medicinal and material
functions; they act as ligands or directing groups for transition
metal catalysis.2 Furthermore, benzofuran is the most important heterocyclic constituent of a commonly encountered
structural motif in bioactive natural products as well as pharmaceuticals and polymers.3 Several derivatives of benzofuran
have been recognized as biologically and pharmacologically
relevant molecules.4 Besides these, a large number of
benzofuran-based compounds have anti-inflammatory and/or
antiarrhythmic,5 antidepressant,6 antimicrobial,7 antitumor,8
antioxidant,9 anti-AD (Alzheimer’s disease),10 anti-HIV/HCV,11
anti-TB, anticoagulant, analgesic, anti-diabetic, hypoglycemic
and immunosuppressive activities.12 Furthermore, many
benzofuran derivatives have been used in a wide range of
a
Department of Chemistry, Rajiv Gandhi University of Knowledge TechnologiesBasar, Nirmal-504107, India
b
Semiochemical Division, CSIR-Indian Institute of Chemical Technology,
Hyderabad 500007, India
c
Department of Chemistry, GITAM Institute of Science, GITAM (Deemed to be
University), Visakhapatnam 530045, India
d
Department of Chemistry, Osmania University, Hyderabad 500007, India
e
Chemistry Division, Department of Science and Humanities,
VFSTR (Deemed to be University), Vadlamudi, Guntur-522213, India
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1nj06077e
pharmaceutical agents and functionalized materials.13 They
can also be used as bone anabolic agents and anti-acetylcholine
agents.14 Some were also shown to exhibit activity as antiparasitic agents (including as nematicidal and antitrypanosomal),
as well as enzymatic inhibitors of monoamine oxidase (MAO),
cholesteryl ester transfer protein (CETP), bovine brain Ca2+ and
calmodulin-dependent cyclic-nucleotide phosphodiesterase,
fungal DHN-melanin biosynthesis and the production of nitric
oxide. They have been demonstrated to interact with endothelin A and B, the platelet-derived growth factor (PDGF), gp120CD4 and chemokine receptor 5 (CCR5),15 and in the PET
imaging of b-amyloid (Ab) plaques.16
The introduction of the C–P bond-forming method for the
convenient construction of organophosphorus functionalities
continues to motivate research into their synthesis, which is
urgent and highly important.17,18 A great deal of recent effort
has focused on two general strategies: (1) transition metalcatalyzed coupling reactions and (2) alkene or alkyne functionalization. Of these methods, the coupling of phosphonate
esters or phosphine oxides with electrophiles catalyzed by
transition metals18 has been recognized as one of the most
efficient, highly reliable, robust tools and a promising
approach for C(sp2)–P or C(sp)–P bond formation. Rhodium,
palladium, manganese, iron, nickel, copper, silver, etc., have
been extensively applied to enable the phosphorylation of
alkenes/styrenes,19 alkynes,20 propargylic derivatives,21 arylboronic acids,22 aryl(pseudo) halides,23 and (hetero)arenes.24
However, there have been few reports on 2-aroylbenzofuran
derivatives,25 although the C(sp2)–P functionalization may offer
more environmentally benign and atom-economical processes
(Scheme 1). Therefore, the functionalization of benzofuran
derivatives by C–H bond activation has granted expedient
access to new kinds of benzofuran derivatives. During the past
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Table 1
Optimization of the reaction conditions
Entrya Catalyst
Oxidant/
ligand
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18c
19d
20e
21f
22
23
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8/Bipy
—
PPh3
PPh3
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
—
K2S2O8
DMF
DMF/H2O (1 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
MeCN
AcOH
CH3CN
CH3CN
DMF/H2O (8 : 1)
H2O
MeCN/H2O (8 : 1)
DCE/H2O (8 : 1)
1,4-Dioxane/H2O (8 : 1)
THF/H2O (8 : 1)
DMSO/H2O (8 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
DMF/H2O (8 : 1)
21
58
75
15
26
35
Trace
32
NA
NA
NA
Trace
15
11
24
Trace
41
55
68
37
64
NA
NA
AgNO3
AgNO3
AgNO3
Ag2CO3
Ag2SO4
AgOAc
Pd(OAc)2
Mn(CH3COO)3
Cu(OAc)2
CuCl
Cu(OAc)2
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
—
a
The reaction was carried out with 1a (0.5 mmol), 2a (1.25 mmol),
catalyst (20 mol%), and oxidant (1.5 mmol) in a solvent (2 mL) at 50 1C
in air. b Yield of 3aa. c Catalyst loading: 20 mol% for 6 h. d Catalyst
loading: 20 mol% for 24 h. e Catalyst loading: 10 mol%. f Oxidant loading:
2 equiv.
Scheme 1 Representative metal-catalyzed coupling reactions of 2aroylbenzofurans.
several years, our group has focused on the development of new and
efficient protocols26 for transition metal-catalyzed C–C bond formation. In particular, the application of C–H bond activation in the
C(sp2)–P functionalization of benzofuran derivatives interests us
greatly. Hence, herein, we report the silver nitrate-catalyzed synthesis of 2-aroyl-3-phosphonylbenzofuran derivatives (Scheme 1,
entry g).
Results and discussion
Initially, the reaction of 2-aroylbenzofuran (1a) with diethyl
phosphite (2a) was chosen as a model reaction to explore and
optimize the reaction conditions. Gratifyingly, when AgNO3
and K2S2O8 were used as a catalyst and oxidant, respectively,
their dehydrogenative cross-coupling reaction occurred in DMF
at 50 1C, affording the desired 2-aroyl-3-phosphonylbenzofuran
(3aa) with a 21% yield (Table 1, entry 1), whereas the treatment
of 1a with 2a in the presence of DMF/H2O (1 : 1) afforded 3aa in
higher yields (58%; Table 1, entry 2). Furthermore, the yield was
enhanced to 75% using an 8 : 1 ratio of DMF/H2O (Table 1,
entry 3).
New J. Chem.
Intrigued by the results, we further optimized the reaction
conditions. Various silver catalysts and other transition metal
catalysts were screened in the reaction (Table 1, entries 4–11). It
was found that only some silver salts were effective in this
transformation and among them, AgNO3 proved to be best,
giving 3aa in 75% yield (Table 1, entry 3). Thereafter, various
solvents such as H2O, MeCN/H2O, 1,2-dichloroethane–water
(DCE/H2O), 1,4-dioxane/H2O, THF/H2O, DMF/H2O and DMSO/
H2O were screened, and DMF/H2O (8 : 1) proved to be the best
choice (Table 1, entries 12–17). Moreover, if the reaction was
performed for 6 or 24 h, the phosphorylation product was
afforded in a lower yield (Table 1, entries 18 and 19). Further
study indicated that the yields of 3aa were decreased when the
amounts of the catalyst or oxidant loading were decreased
(Table 1, entries 20 and 21,). Besides, no product was formed
without K2S2O8 or AgNO3 (Table 1, entries 22 and 23). Performing the reaction at RT and 90 1C provided the desired product
3aa in much lower yields (40% and 45%, respectively).
With the optimal reaction conditions in hand, we embarked
on a study of the reaction generality and the scope of the
substrates for this transformation. A wide range of 2aroylbenzofurans with different substituents and various phosphites were screened. Different ring-substituted (–Me, –OMe,
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Table 2
Paper
Substrate scope of 2-aroylbenzofurans
–Br, –Cl, –CN, –NO2, etc.) 2-aroylbenzofurans were suitable
substrates for this reaction (Table 2), although lower yields of
the desired products were obtained for 2-aroylbenzofurans
containing electron-deficient substituents.
We further checked for the substrate scope and generality by
varying the structures of the phosphites, as shown in Table 3. In
general, both dialkylphosphites and diarylphosphite compounds
were used to prepare different 2-aroyl-3-phosphonylbenzofurans by
the above-mentioned method. The dialkylphosphites underwent the
condensation smoothly with good yields, whereas the diarylphosphites gave low yields of different 2-aroyl-3-phosphonylbenzofurans
and required a comparatively longer time. However, 5,5-dimethyl1,3-dioxanephosphite did not react with 1a.
Plausible pathway
On the basis of the current information,27 a plausible mechanism for the conversion is shown in Scheme 2. The formation
of 2-aroyl-3-phosphonylbenzofuran (3aa) apparently starts with
the conversion of silver(I) cation into silver(II) cation by peroxodisulfate. Then, diethyl phosphite (2a) is deprived of an electron by the silver(II) ion to form the cation radical 4. The
electrophilic addition of cation radical 4 to 2-aroylbenzofuran
(1a) leads to the intermediate 5, which may lose a hydrogen
cation, an electron and another hydrogen cation successively,
giving the desired 2-aroyl-3-phosphonylbenzofuran (3aa).
Table 3
Substrate scope of phosphites
Scheme 2
A possible pathway for the formation of 3aa.
Finally, to express the practical applicability of this protocol
on a preparative scale, some reactions were carried out at a
gram scale (5.0 mmol) using the following combinations of
substrates: 1a with 2a and 1a with 2b. As expected, the reactions
proceeded smoothly to afford the target compounds in high
yields as obtained in similar reactions at the milligram scale,
which demonstrated the practical utility of this method.
Conclusions
In conclusion, we developed an efficient route for the AgNO3/
K2S2O8-mediated direct C(sp2)–P functionalization of 2aroylbenzofurans. This method provides straightforward access
to obtain various 2-aroyl-3-phosphonylbenzofurans. Further
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study on the reaction scope and applications of this method are
still underway in our laboratory.
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Experimental procedure
Materials and method
Solvents were dried according to known methods as appropriate. 1H, 13C spectra (1H, 400 MHz; 13C, 100 MHz) were recorded
using a 400 MHz spectrometer in CDCl3 with shifts referenced
to SiMe4 (d = 0 ppm). IR spectra were recorded on a FT-IR
spectrophotometer. Mass spectra were recorded using ESI-MS
(Micromass VG Autospec) and HRMS (ESI-TOF analyzer) equipment. Organic extracts were dried over anhydrous Na2SO4. The
CHN elemental analysis was performed using an Elementar
Vario micro cure analyzer, and the results were in good agreement with calculated values. Column chromatography was
performed on silica gel (100–200 mesh) using an ethyl acetate
(EtOAc)/hexane mixture.
General procedures for the synthesis of dialkyl 2-aroylbenzofuran-3ylphosphonates 3
The 2-aroylbenzofurans28 (0.111 g, 0.5 mmol), phosphite
(0.172 g, 1.25 mmol), AgNO3 (0.016 g, 0.1 mmol, 20 mol%),
and K2S2O8 (0.405 g, 1.5 mmol) in DMF/H2O (8 : 1) (1.6 mL :
0.2 mL) were charged into a 25 mL round bottomed flask in air.
The mixture was stirred at 50 1C for 12 h. After cooling to room
temperature, it was extracted with EtOAc (3 25 mL). The
combined ethyl acetate extract was washed with brine (75 mL),
dried over anh. Na2SO4 and filtered. The solvent was removed
under vacuum and the resulting crude product was purified by
silica gel chromatography using a hexane/ethyl acetate (80 : 20)
mixture to afford compounds 3. Details on the yields for all the
compounds are presented in Tables 2 and 3.
Diethyl (2-benzoylbenzofuran-3-yl)phosphonate (3aa)
Yellow oil. IR (KBr, cm 1) 2925, 1666, 1540, 1446; 1H NMR
(400 d MHz; CDCl3): d 8.15 (d, J = 7.0 Hz, 1H), 8.03 (d, J = 7.5 Hz,
2H), 7.65 (t, J = 7.5 Hz, 1H), 7.59 (dd, J = 8.5, 6.4 Hz, 1H), 7.55
(d, J = 7.0 Hz, 2H), 7.50 (dd, J = 8.0, 6.1 Hz, 1H), 7.45 (t, J =
7.5 Hz, 1H), 7.42–7.41 (m, 4H), 4.29–4.18 (m, 4H), 1.33 (t, J =
6.5 Hz, 6H). 13C NMR (100 MHz, CDCl3): d 184.8, 177.3, 156.0,
(d, J = 23.4 Hz), 154.4 (d, J = 14.2 Hz), 136.1, 133.9, 130.2, 128.5,
127.6, 127.5, 124.7, 123.8, 113.4, 112.0, 111.7, 62.8, 16.3, 16.2.
31
P-NMR: (162 MHz, CDCl3): d 10.05 (s). HRMS (ESI): m/z
359.1047. Anal. calc. for C19H19O5P: C, 63.69; H, 5.34. Found:
C, 63.81; H, 5.28.
Dimethyl (2-benzoylbenzofuran-3-yl)phosphonate (3ab)
Yellow oil. IR (KBr, cm 1) 2980, 1662, 1538, 1442; 1H NMR
(400 d MHz; CDCl3): d 8.13 (d, J = 7.16 Hz, 1H), 8.05 (d, J =
7.0 Hz, 2H), 7.67 (t, J = 7.5 Hz, 1H), 7.62 (dd, J = 8.5, 6.5 Hz, 1H),
7.56 (d, J = 7.0 Hz, 2H), 7.54 (dd, J = 7.9, 6.1 Hz, 1H), 7.45
(t, J = 7.5 Hz, 1H), 3.89 (s, 3H), 3.87 (s, 3H); 13C NMR (100 MHz,
CDCl3): d 184.5, 156.4, 156.2, 156.3 (d, J = 23.2 Hz), 154.5
(d, J = 14.1 Hz), 136.0, 139.9, 130.2, 128.6, 127.9, 127.5, 127.4,
New J. Chem.
124.9, 123.8, 112.1, 53.38, 53.37. 31P-NMR: (162 MHz, CDCl3)
d 13.2 (s); ESI MS: m/z 331 [(M + H)+]; anal. calc. for C17H15O5P:
C, 16.82; H, 4.58; found: C, 61.94; H, 4.52.
Diisopropyl (2-benzoylbenzofuran-3-yl)phosphonate (3ad)
Yellow oil. IR (KBr, cm 1) 2978, 1667, 1545, 1449; 1H NMR
(400 d MHz; CDCl3): d 8.20 (d, J = 7.0 Hz, 1H), 8.04 (d, J = 7.0 Hz,
2H), 7.65 (t, J = 7.6 Hz, 1H), 7.60 (d, J = 7.0 Hz, 1H), 7.55
(d, J = 7.0 Hz, 2H), 7.54 (d, J = 7.0 Hz, 1H), 7.45 (t, J = 7.0 Hz, 1H),
7.49–7.83 (m, 2H), 1.37 (d, J = 5.4 Hz, 6H), 1.2 (d, J = 5.8 Hz, 6H);
13
C NMR (100 MHz, CDCl3): d 185.1, 155.7, (d, J = 15.1 Hz),
154.3 (d, J = 9.0 Hz), 136.3, 133.8, 130.1, 128.5, 127.8, 127.6,
127.4, 124.5, 123.9, 114.5, 112.4, 111.9, 71.6, 71.5, 24.0, 23.7;
31
P-NMR: (162 MHz, CDCl3) d 7.6 (s); ESI MS: m/z 387 [(M + H)+].
Anal. calc. for C21H23O5P: C, 65.28; H, 6.00. Found: C, 65.30;
H, 5.94.
Dibutyl (2-benzoylbenzofuran-3-yl)phosphonate (3ae)
Yellow oil. IR (KBr, cm 1) 2958, 1666, 1540, 1452; 1H NMR
(400 d MHz; CDCl3): d 8.15 (d, J = 7.0 Hz, 1H), 8.01 (d, J = 7.0 Hz,
2H), 7.66 (t, J = 7.5 Hz, 1H), 7.60 (dd, J = 8.0, 6.1 Hz, 1H), 7.55
(d, J = 7.0 Hz, 2H), 7.50 (dd, J = 8.0, 6.1 Hz, 1H), 7.42 (t, J =
7.0 Hz, 1H), 4.12–4.06 (m, 4H), 1.67–1.63. (m, 4H), 1.39–1.34
(m, 4H), 0.92 (t, J = 7.0 Hz, 3H), 0.87 (t, J = 7.0 Hz, 3H); 13C NMR
(100 MHz, CDCl3): d 182.9, 162.6, 154.7, 154.4, 139.2, 132.2,
130.3, 128.3, 125.0, 124.0, 117.7, 116.7, 113.9, 112.4, 63.0, 62.9,
29.5, 29.1, 16.4, 16.2, 14.0; 31P-NMR: (162 MHz, CDCl3): d 7.2 (s);
ESI MS: m/z 415 [(M + H)+]; anal. calc. for C23H27O5P: C, 66.66;
H, 6.57. Found: C, 66.78; H, 6.51.
Diethyl (2-benzoyl-5-bromobenzofuran-3-yl)phosphonate (3ba)
Yellow oil. IR (KBr, cm 1) 2925, 1667, 1590, 1446; 1H NMR
(400 d MHz; CDCl3): d 8.31 (d, J = 7.0 Hz, 1H), 8.11 (d, J = 7.0 Hz,
2H), 7.65 (t, J = 7.5 Hz, 1H), 7.60 (dd, J = 8.0, 6.0 Hz, 1H), 7.55
(d, J = 7.0 Hz, 2H), 7.54 (dd, J = 8.0, 6.1 Hz, 1H), 7.49 (t, J =
7.6 Hz, 1H), 4.28–4.21 (m, 4H), 1.35–1.32 (m, 6H); 13C NMR
(100 MHz, CDCl3): d 184.4, 156.9, (d, J = 22.1 Hz), 153.0 (d, J =
13.0 Hz), 135.8, 133.4, 130.7, 130.1, 129.4, 128.7, 128.6, 128.4,
126.4, 125.9, 118.1, 113.5, 63.0, 16.3, 16.2; 31P-NMR: (162 MHz,
CDCl3) d 12.07 (s); ESI MS: m/z 437 [(M + H)+]; anal. calc. for
C19H18BrO5P: C, 52.19; H, 4.15; found: C, 52.31; H, 4.09.
Diethyl (2-benzoyl-5-chlorobenzofuran-3-yl)phosphonate (3da)
Yellow oil. IR (KBr, cm 1) 2982, 1655, 1541, 1444; 1H NMR
(400 d MHz; CDCl3): d 8.13 (dd, J = 7.0, 1.0 Hz, 1H), 7.99
(dd, J = 8.5, 1.3 Hz, 2H), 7.66 (td, J = 7.3 Hz, 1H), 7.54 (s, 1H),
7.51 (dd, J = 8.3, 2.1 Hz, 2H), 7.46 (dd, J = 8.9, 2.3 Hz, 1H), 4.29–
4.17 (m, 4H), 1.32 (t, J = 6.5 Hz, 6H); 13C NMR (100 MHz,
CDCl3): d 184.5, 157.1 (d, J = 22.8 Hz), 152.6 (d, J = 14.5 Hz),
135.8, 134.0, 133.2, 130.6, 130.1, 129.4, 128.7, 128.6, 128.0,
123.3, 113.0, 63.0, 62.9, 16.3, 16.2; 31P-NMR: (162 MHz, CDCl3):
9.1 (s); ESI MS: m/z 393 [(M + H)+]; anal. calc. for C19H18ClO5P:
C, 58.10; H, 4.62. Found: C, 58.22; H, 4.56.
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1
1
Yellow oil. IR (KBr, cm ) 2920, 1639, 1541, 1462; H NMR
(400 d MHz; CDCl3): d 8.06 (d, J = 7.0 Hz, 1H), 7.89 (d, J = 7.5 Hz,
2H), 7.51 (d, J = 7.0 Hz, 1H), 7.43 (dt, J = 8.2 Hz, 1H), 7.41 (d, J =
7.5 Hz, 2H), 7.34 (t, J = 8.5 Hz, 1H), 4.23–4.08 (m, 4H), 1.25 (t, J =
6.7 Hz, 6H); 13C NMR (100 MHz, CDCl3): d 183.0, 162.7, 154.8,
154.7, 154.5, 139.3, 132.3, 130.4, 5, 125.1, 124.1, 117.8, 116.8,
112.1, 63.1, 63.0, 16.3, 16.2; 31P-NMR: (162 MHz, CDCl3): 9.2 (s);
ESI MS: m/z 404 [(M + H)+]; anal. calc. for C19H18NO7P: C, 56.58;
H, 4.50, N, 3.47. Found: C, 56.70; H, 4.49, N, 3.46.
Diethyl (2-(4-cyanobenzoyl)benzofuran-3-yl)phosphonate (3ga)
Yellow oil. IR (KBr, cm 1) 2918, 1671, 1539, 1460; 1H NMR
(400 d MHz; CDCl3): d 8.15 (d, J = 7.0 Hz, 1H), 8.13 (d, J = 7.5 Hz,
2H), 7.81 (d, J = 7.0 Hz, 2H), 7.59 (dt, J = 8.2 Hz, 1H), 7.54 (dt, J =
7.5 Hz, 1H), 7.43 (dt, J = 7.5 Hz, 1H), 4.34–4.18 (m, 4H), 1.34
(t, J = 6.5 Hz, 6H); 13C NMR (100 MHz, CDCl3): d 183.0, 162.9
(d, J = 23.2 Hz), 154.6 (d, J = 14.9 Hz), 140.4, 139.3, 132.3, 132.2,
130.4, 130.3, 129.4, 128.5, 125.1, 124.1, 123.2, 121.5, 112.1, 63.1,
63.0, 16.4, 16.3; 31P-NMR: (162 MHz, CDCl3): 10.1 (s); ESI MS:
m/z 384 [(M + H)+]; anal. calc. for C20H18NO5P: C, 62.66; H, 4.73,
N, 3.65. Found: C, 62.78; H, 4.72, N, 3.64.
Diethyl (2-(4-chlorobenzoyl)benzofuran-3-yl)phosphonate (3ha)
White solid. Mp: 173–175 1C. IR (KBr, cm 1) 2970, 1655, 1587,
1484; 1H NMR (400 d MHz; CDCl3): d 8.14 (d, J = 7.0 Hz, 1H),
7.97 (d, J = 8.7 Hz, 2H), 7.58 (d, J = 8.7 Hz, 1H), 7.52–7.48 (m,
3H), 7.42 (t, J = 7.5 Hz, 1H), 4.32–4.15 (m, 4H), 1.32 (t, J = 6.5 Hz,
6H); 13C NMR (100 MHz, CDCl3): d 183.4, 155.6 (d, J = 23.2 Hz),
154.4 (d, J = 14.7 Hz), 140.5, 134.4, 131.5, 128.9, 128.6, 127.9,
124.9, 123.9, 112.6, 62.7, 62.6, 16.3, 16.2; 31P-NMR: (162 MHz,
CDCl3): 9.1 (s); ESI MS: m/z 393 [(M + H)+]; anal. calc. for
C19H18ClO5P: C, 58.10; H, 4.62. Found: C, 58.22; H, 4.56.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
JK and RK thank UGC-DSK (New Delhi) for the Dr D. S. Kothari
fellowship. JK also thanks Prof. K. C. Kumaraswamy, University
of Hyderabad, for his expert suggestions. RK acknowledges the
DST for the financial support under the early career research
award scheme (project no. ECR/2018/000637). We also thank
the Director, CSIR-IICT, for the support.
Notes and references
1 (a) D. T. Kolio, Chemistry and Application of H-Phosphonates,
Elsevier Science, Amsterdam, 2006; (b) W. Tang and
X. Zhang, Chem. Rev., 2003, 103, 3029; (c) S. Vander Jeught
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New J. Chem.