A practicable synthesis of 2,3-disubstituted 1,4-dioxanes bearing a carbonyl functionality from α,β-unsaturated ketones using the Williamson strategy

Article abstract of DOI:10.1039/d0ob01448f

We have observed that a reagent combination of NaIO₄and NH₂OH·HCl reacts with α,β-unsaturated ketones followed by the nucleophile ethylene glycol allowing the synthesis of 2,3-disubstituted 1,4-dioxanes using cesium carbonate as a base under Williamson ether synthesis. This reaction is useful for the synthesis of functionalized 1,4-dioxane having a carbonyl functionality. A variety of 2,3-disubstituted 1,4-dioxanes have been synthesized using these reaction conditions. A probable reaction mechanism has also been proposed.

Full text of DOI:10.1039/d0ob01448f

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A practicable synthesis of 2,3-disubstituted
1,4-dioxanes bearing a carbonyl functionality from
α,β-unsaturated ketones using the Williamson
strategy†
Cite this: Org. Biomol. Chem., 2021,
19, 1278
Received 13th July 2020,
Accepted 22nd December 2020
Aramita De,a Sougata Santra, b Igor A. Khalymbadzha, b Grigory V. Zyryanovb,c
DOI: 10.1039/d0ob01448f
a
rsc.li/obc
and Adinath Majee
*
We have observed that a reagent combination of NaIO4 and 3-methylimidazolium hydrogen sulfate)8 (Scheme 1). On the
NH2OH·HCl reacts with α,β-unsaturated ketones followed by the other hand, Williamson ether synthesis is a more reliable
nucleophile ethylene glycol allowing the synthesis of 2,3-di- method (Scheme 2) and various reports are available in the lit-
substituted 1,4-dioxanes using cesium carbonate as a base under erature such as reactions in the presence of methanol: a micro-
Williamson ether synthesis. This reaction is useful for the synthesis wave absorber,9 tetrabutylammonium bisulfate (TBAB):
a
of functionalized 1,4-dioxane having a carbonyl functionality. A phase transfer catalyst,10 potassium hydride in paraffin: a
variety of 2,3-disubstituted 1,4-dioxanes have been synthesized base,11 the salt of an aromatic or aliphatic carboxylic acid: a
using these reaction conditions. A probable reaction mechanism weak alkylating agent,12 microwave irradiation using zinc as a
has also been proposed.
catalyst,13 and combinations of microwave and ultrasound.14
Besides using as a solvent, 1,4-dioxane scaffolds occur in a
large number of natural products and bioactive compounds
(Fig. 1).15a,b,16 1,4-Dioxane is used as a stabilizer in chlorinated
solvents and is also used in a wide variety of industrial pur-
poses. It is hydrophilic in nature. It is not susceptible to sorp-
tion to the soil rather retarded in groundwater. Very few
methods have been reported in the literature15 for the syn-
Introduction
In the literature, several methods have been reported for the
synthesis of ethers, such as bimolecular dehydration,1
Williamson ether synthesis2 and Mitsunobu reaction.3 In par-
ticular, for the cyclic ether synthesis, two common method-
ologies are used: (i) cyclo-dehydration of terminal diols4 and
(ii) Williamson ether synthesis via intramolecular SN2 reaction
of halogen-substituted alcohols. Cyclo-dehydration of terminal
diols, such as 1,4-butanediol, 1,5-pentanediol and diethylene
glycol, is a useful method to obtain oxygen heterocycles, such
as tetrahydrofuran, tetrahydropyran and 1,4-dioxane, which
are widely used as solvents in the chemical industry. In the
cyclo-dehydration of diethylene glycol, 1,4-dioxane can be
selectively obtained by the liquid-phase catalytic reaction in
the presence of various catalysts such as sulfated zirconia,5
alumina,6 H-ZSM-57 or a Brønsted acidic ionic liquid (1-butyl-
Scheme 1 1,4-Dioxane preparation via cyclo-dehydration reaction.
aDepartment of Chemistry, Visva-Bharati (A Central University), Santiniketan
731235, India. E-mail: adinath.majee@visva-bharati.ac.in
bDepartment of Organic and Biomolecular Chemistry, Chemical Engineering
Institute, Ural Federal University, 19 Mira Street, 620002 Yekaterinburg, Russian
Federation
cI. Ya. Postovskiy Institute of Organic Synthesis, Ural Division of the Russian
Academy of Sciences, 22 Sofi Kovalevskoy Street, 620219 Yekaterinburg, Russian
Federation
†Electronic supplementary information (ESI) available: Copies of 1H and 13C
NMR spectra. See DOI: 10.1039/d0ob01448f
Scheme 2 1,4-Dioxane preparation via Williamson ether synthesis.
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Fig. 1 1,4-Dioxane containing bio-active compounds.
thesis of substituted cyclic ethers, particularly 1,4-dioxane. carbonate (Cs2CO3) as a base. It is worth mentioning that the
Therefore, directly introducing the structure of a cyclic ether is product of the first step was isolated and the next step was
an explorable and meaningful approach for the synthesis of carried out just by adding a base and solvent (Scheme 3). The
the corresponding complex molecules.
carbonyl group of α,β-unsaturated ketones remained
To synthesize polyether compounds such as dioxane unaffected under these reaction conditions. A substituted 1,4-
systems, particularly 1,4-dioxane, the intramolecular version of dioxane with a carbonyl group adjacent to the dioxane ring
these two strategies will not be useful as it is very difficult to has been synthesized as the sole product.
control the formation of polymeric products. Again, under
Williamson’s conditions, it is very difficult to synthesize 1,4-
dioxane derivatives, particularly those having the carbonyl
functional group as it is more susceptible to the alkoxide
Results and discussion
giving different products under aldol reaction or other nucleo-
philic addition or elimination depending on the substrate. It is
worth mentioning that carbonyl-containing compounds have
much importance in various fields. To the best of our knowl-
edge, only one such report is available in the literature to syn-
thesize a substituted 1,4-dioxane with a carbonyl functionality
adjacent to the dioxane ring.17
The synthetic procedure involved two steps. In the first step,
the reaction of a freshly prepared simple chalcone 1aa with 1
equiv. NaIO4 and 1.5 equiv. NH2OH·HCl as an oxidant in ethyl-
ene glycol solvent at room temperature produced 2aa in 90%
isolated yield within 30 min at room temperature (Scheme 4).
In the second step, 3-(2-hydroxyethoxy)-2-iodo-1,3-diphenylpro-
pan-1-one (2aa) was allowed to react with a base Cs2CO3 in
We are working to develop various organic reaction method-
ologies involving heterocyclic chemistry such as aziridine and
azirine based on the current working practice.18 We have
observed that a reagent of NaIO4 and NH2OH·HCl is very
effective for many organic transformations.19 Here, we use the
same reagent combination where α,β-unsaturated ketones can
be converted into β-iodo-β′-hydroxy ethers using ethylene
glycol as the nucleophile and reaction medium. This β-iodo-β′-
hydroxy ether under Williamson ether synthesis can be easily
converted to a 2,3-disubstituted 1,4-dioxane using cesium
Scheme 4 The 1st step: synthesis of 3-(2-hydroxyethoxy)-2-iodo-1,3-
diphenylpropan-1-one (2aa).
Scheme 3 Synthesis of carbonyl-substituted 1,4-dioxane.
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Table 2 Optimization of the reaction conditionsa
Scheme 5 The 2nd step: synthesis of carbonyl-substituted 1,4-dioxane
(3aa).
Entry
Base (equiv.)
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
Cs2CO3 (1)
K2CO3 (1)
Na2CO3 (1)
Ag2CO3 (1)
Li2CO3 (1)
NaOH (1)
CH3CN
Toluene
DCM
1,2-DCE
Acetone
DMF
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
60
94
CH3CN solvent at 70 °C and the desired product 3aa was iso-
lated in 94% yield within 40 min (Scheme 5). Encouraged by
this initial result, we carried out the reaction at different temp-
eratures in different solvents to optimize the reaction con-
ditions, and the results are shown in Tables 1 and 2. Here, it is
worth mentioning that for the optimization of the reaction
conditions, we have performed the second step with the crude
product of the initial step.
At first, we tested the temperature effects of this reaction. It
was found that at 70 °C temperature the reaction gave the best
result (94% yield) after 40 min in acetonitrile solvent (Table 1).
To examine the solvent effect, various common solvents such
as acetonitrile, toluene, DCM, 1,2-DCE, acetone, DMF, DMSO,
THF, 1,4-dioxane and methanol were tested (entries 1–10,
Table 2). To our delight, a 94% yield of the desired product
was obtained in acetonitrile (entry 1, Table 2). Then, a series of
other bases such as K2CO3, Na2CO3, Ag2CO3, Li2CO3, NaOH
and KOH was also investigated (entries 11–16, Table 2). The
results indicated that other bases were not so effective in pro-
moting the reaction, while Cs2CO3 gave a satisfactory yield of
the product (entry 1, Table 2) and finally, these conditions
have been accepted as optimized reaction conditions by using
1 equiv. Cs2CO3 in acetonitrile at 70 °C for 40 min (Table 2,
entry 1). Increasing the amount of the base also could not
increase the yield even after prolonged time (entry 17, Table 2).
After obtaining the optimized reaction conditions, we were
interested in exploring the substrate scope of this methodology
55
ndb
35
73
88
Trace
47
30
DMSO
THF
9
1,4-Dioxane
MeOH
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
10
11
12
13
14
15
16
17
32
ndb
ndb
ndb
ndb
ndb
ndb
85
KOH (1)
Cs2CO3 (1.5)
a Reaction conditions: 1 mmol of 2aa was reacted at 70 °C with various
bases in various solvents. b Not detected in TLC.
and the results are presented in Scheme 6. A series of substi-
tuted 1,4-dioxanes were synthesized under the optimized reac-
tion conditions in good to excellent yields (3aa–3ic). It was
observed that the α,β-unsaturated ketones substituted with
electron-donating substituents such as –Me (1ba) and –OMe
(1ca) as well as electron-withdrawing groups such as –chloro
(1da & 1ea) and –fluoro (1fa) groups reacted easily to afford the
desired products (3ba–3ea) in good yields. α,β-Unsaturated
ketones in which the ketone part was substituted with elec-
tron-donating substituents such as –Me (1ab) and –OMe (1ac)
provided the corresponding products 3ab and 3ac in 91% and
92% yields, respectively, while the reactions with electron-with-
drawing groups such as –Cl (1ad) and –Br (1ae) afforded the
desired products 3ad and 3ae in 85% and 95% yields, respect-
ively. Substitution in the phenyl rings from both sides of the
α,β-unsaturated ketones was tested and a similar reaction
affording the desired products was observed. Moderate to high
yields were observed (68–93%) for all the cases bearing both
electron-withdrawing and electron-donating functional groups
(3bb–3ic). In addition, 1-naphthaldehyde substituted
α,β-unsaturated ketone, namely, 3-(naphthalen-1-yl)-1-phenyl-
prop-2-en-1-one (1ja), also reacted smoothly under these con-
ditions to afford the product (3-(naphthalen-1-yl)-1,4-dioxan-2-
yl)(phenyl)methanone (3ja) in 82% yield.
Table 1 Temperature effects on the synthesis of 1,4-dioxanesa
Entry
Temperature (°C)
Time
Yield (%)
1
2
3
4
5
rt
12 h
6 h
1 h
40 min
40 min
ndb
<10
70
94
90
40
55
70
100
However, we were unable to synthesize large ring dioxanes.
In an attempt to achieve the synthesis, we carried out a reac-
tion taking 1,3-propanediol instead of ethylene glycol in the
initial step and obtained 3-(3-hydroxypropoxy)-2-iodo-1,3-
a Reaction conditions: 1 mmol of 2aa was reacted with Cs2CO3 (1
equiv.) in acetonitrile solvent (3 mL) at various temperatures with
different reaction times. b Not detected in TLC.
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Scheme 6 Substrate scope of the present method. Reaction conditions: For the 1st step: 1 (1 mmol), NaIO4 (1 mmol) and NH2OH·HCl (1.5 mmol) in
3 mL of ethylene glycol at room temperature for 30 min. For the 2nd step: 2 (1 mmol) and Cs2CO3 (1 mmol) in CH3CN solvent (3 mL) at 70 °C for
40 min.
Scheme 7 Additional experiment: attempt to synthesize a large ring dioxane.
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diphenylpropan-1-one (4aa) in 87% yield in the 1st step
(Scheme 7). However, 4aa remained unreacted with cesium
carbonate.
Again, it is worth mentioning that chalcones having ali-
phatic and heterocyclic moieties did not respond to afford the
desired products. After the reaction under similar conditions
we isolated only the β-iodo-β′-hydroxy ethers which are pro-
ducts formed before cyclization (2af & 2ka) in 82% and 78%
yields, respectively. Similarly, simple styrene also underwent
the 1st step but not the desired cyclization step (Scheme 8).
Finally, we carried out two control experiments to under-
stand the mechanistic pathway of the reaction. When the reac-
tion was carried out in the presence of N-iodosuccinimide
(NIS) and simple molecular iodine under similar reaction con-
ditions no product was obtained even in the 1st step
(Scheme 9).
Thus, a probable mechanism has been proposed for this
two-step conversion (Scheme 10). Based on the present experi-
ments, the literature17,20 and our previous works19 on the
preparation of iodohydrine compounds it can be suggested
that an in situ generated electrophilic iodine reagent under-
goes simple addition to the chalcone giving the intermediate
[A]. In the presence of excess ethylene glycol which acts as a
nucleophile and reacts with the intermediate [A] giving the
compound 2. Then in the presence of a base, the intra-
molecular Williamson ether synthesis, probably via the
SN2 mechanistic pathway, produces the desired product 3.
We should especially mention the intriguing stereo-
selectivity of the proposed method. Dioxanes 3 are formed as a
single trans-stereoisomer as established by the spin–spin coup-
ling constant (SSCC) between protons at C2 and C3 of the
dioxane ring. Our structural assignment is based on the fact
that trans-substituted dioxanes typically exhibit a SSCC of 9
Hz, while cis-substituted counterparts exhibit a 4 Hz SSCC.21
The observed value of 8–9 Hz is consistent with the trans-con-
figuration of substituents at positions C2 and C3 (please see
Scheme 8 Studies with other chalocones having aliphatic and hetero-
cyclic moieties as well as with styrene.
1
the ESI† also). Thus, in the H NMR spectrum of dioxanes 3,
Scheme 9 Control experiments with other iodine sources.
Scheme 10 Proposed reaction mechanism.
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the characteristic signals of protons at C2 and C3 are regis- boiling in a range of 60–80 °C unless otherwise mentioned.
tered as doublets with vicinal SSCC 8–9 Hz at 4.8–4.9 ppm. Melting points were determined on a glass disk with an elec-
The remaining dioxane ring protons (at C5 and C6 carbon tric hot plate. All solvents were dried and distilled before use.
atoms) and aromatic protons were registered as multiplets at Commercially available substrates were freshly distilled before
4.0 and 6.7–7.7 ppm, respectively. In the 13C NMR spectrum, the reaction. All reactions involving moisture-sensitive reac-
all expected signals are observed as: atoms C2 and C3 at tants were executed using oven-dried glassware. All the
80 ppm and atoms C5 and C6 at 66 ppm; a carbonyl atom at α,β-unsaturated ketones were prepared according to a pre-
195 ppm and aryl carbons in the range 127 to 160 ppm.
The high stereoselectivity of the proposed method was
attributed to the trans-configuration of the starting chalcone
viously reported method.22
Typical procedure for the synthesis of compounds 3
and selectivity of the following transformations: iodination of The synthetic procedure involved two steps. In the first step,
the trans-chalcone gives trans-iodonium cyclic cation A, and α,β-unsaturated ketone (1 mmol), sodium periodate
1
the ring opening of this cyclic iodonium intermediate with (1 mmol) and hydroxylamine hydrochloride (1.5 mmol) were
ethylene glycol yields erythro-iodoether 2 followed by configur- taken with ethylene glycol solvent (3 mL) in a sealed tube. The
ation inversion during the SN2 substitution of iodine forming reaction mixture was stirred for 30 min at room temperature.
the dioxane ring (Scheme 10).
After completion (TLC) the reaction mixture was diluted with a
1 : 1 mixture of water/ethyl acetate (10 mL, v/v) followed by
washing with brine solution (1 × 10 mL) and sodium thiosul-
fate solution (1 × 10 mL). Then the combined organic layer
was dried over anhydrous Na2SO4. After the evaporation of the
Conclusions
Alkoxide is very useful in organic synthesis acting as a nucleo- solvent the crude product was obtained.
phile and a base depending on the reaction conditions.
In the second step, the crude product was dissolved in
Synthesis of ethers following this concept has been well acetonitrile solvent (3 mL) and cesium carbonate (1 equiv.)
studied in organic chemistry and it is one of the best strategies was added to that solution. The reaction mixture was stirred
known as Williamson ether synthesis. This reaction can be for 40 min at 70 °C. After completion (TLC) the reaction
useful in intermolecular and intramolecular ways for the mixture was diluted with a 1 : 1 mixture of water/ethyl acetate
preparation of simple and mixed ethers for acyclic systems and (10 mL, v/v) followed by washing with brine solution (1 ×
cyclic systems. But the synthesis of functionalized 1,4-dioxanes 10 mL). Then the combined organic layer was dried over anhy-
is very limited under these conditions, particularly the carbo- drous Na2SO4. Evaporation of the solvent furnished the crude
nyl functional group as it is more susceptible to the alkoxide product which was subjected to column chromatography using
giving different products under aldol reaction or other nucleo- ethyl acetate–petroleum ether as the eluent to obtain the ana-
philic addition or elimination depending on the substrate. We lytically pure product.
have shown that using the reagent combination of NaIO4 and
3-(2-Hydroxyethoxy)-2-iodo-1-phenyl-3-(p-tolyl)propan-1-one
NH2OH·HCl an α,β-unsaturated ketone can be converted into a (2ba). Colourless liquid, Rf = 0.60 (petroleum ether/EtOAc =
β-iodo-β′-hydroxy ether using the nucleophile ethylene glycol 80/20); 1H NMR (CDCl3, 400 MHz): δ 8.05–8.03 (m, 2H),
which allows the synthesis of a substituted 1,4-dioxane with a 7.61–7.58 (m, 1H), 7.50–7.47 (m, 2H), 7.34 (m, J = 8.0 Hz, 2H),
carbonyl functionality adjacent to the dioxane ring under 7.22 (m, J = 8.0 Hz, 2H), 5.41 (m, J = 10.0 Hz, 1H), 5.09 (m, J =
Williamson ether synthesis using cesium carbonate as a base. 10.0 Hz, 1H), 3.63–3.40 (m, 4H), 2.39 (s, 3H). Anal. Calcd for
During the reaction, the trans-configuration of the substituents C18H19IO3: C, 52.70; H, 4.67%; Found: C, 52.76; H, 4.70%.
at the double bond was preserved and, as a consequence, the
formation of a single diastereomeric dioxane was observed.
1-(4-Chlorophenyl)-3-(2-hydroxyethoxy)-2-iodo-3-(p-tolyl)propan-
1-one (2bd). Colourless liquid, Rf = 0.60 (petroleum ether/
EtOAc = 80/20); 1H NMR (CDCl3, 400 MHz): δ 8.00–7.95 (m,
2H), 7.48–7.45 (m, 2H), 7.35–7.33 (m, 2H), 7.26–7.22 (m, 2H),
5.35 (m, J = 10.0 Hz, 1H), 5.07 (m, J = 10.0 Hz, 1H), 3.62–3.41
(m, 4H), 2.39 (s, 3H). Anal. Calcd for C18H18ClIO3: C, 48.62; H,
4.08%; Found: C, 48.68; H, 4.15%.
Experimental section
General information
All reagents were purchased from commercial sources and
Phenyl(3-phenyl-1,4-dioxan-2-yl)methanone (3aa). Off-white
used without further purification. 1H NMR spectra were gum (252 mg, yield 94%); Rf = 0.50 (petroleum ether/EtOAc =
recorded on a 400 MHz spectrometer with solutions in CDCl3. 92/8); 1H NMR (CDCl3, 400 MHz): δ 7.70–7.67 (m, 2H),
Chemical shifts are expressed in parts per million (δ), the 7.43–7.39 (m, 1H), 7.31–7.23 (m, 4H), 7.18–7.11 (m, 3H), 4.88
signals are reported as s (singlet), d (doublet), t (triplet), m (d, J = 8.8 Hz, 1H), 4.81 (d, J = 8.8 Hz, 1H), 4.02–3.95 (m, 4H).
(multiplet), and dd (doublet of doublets), and coupling con- 13C NMR (CDCl3, 100 MHz): δ 195.4, 137.1, 135.9, 133.4, 128.8,
stants (J) are given in Hz. 13C NMR spectra were recorded at 128.6, 128.4, 127.6, 81.1, 79.9, 66.75, 66.68. Anal. Calcd for
100 MHz in CDCl3 solution. TLC was performed on silica gel C17H16O3: C, 76.10; H, 6.01%; Found: C, 76.06; H, 6.05%.
coated glass slides. Silica gel (60–120 mesh) was used for
Phenyl(3-(p-tolyl)-1,4-dioxan-2-yl)methanone (3ba). Yellow
column chromatography. Petroleum ether refers to the fraction liquid (220 mg, yield 78%); Rf = 0.60 (petroleum ether/EtOAc =
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91/9); 1H NMR (CDCl3, 400 MHz): δ 7.74–7.72 (m, 2H), (CDCl3, 100 MHz): δ 193.7, 163.8, 137.2, 131.2, 128.9, 128.5,
7.47–7.43 (m, 1H), 7.32–7.28 (m, 2H), 7.20 (d, J = 8.0 Hz, 2H), 128.4, 127.6, 113.7, 81.0, 80.0, 66.8, 66.7, 55.5. Anal. Calcd for
7.00 (d, J = 8.0 Hz, 2H), 4.89–4.79 (m, 2H), 4.04–3.98 (m, 4H), C18H18O4: C, 72.47; H, 6.08%; Found: C, 72.41; H, 6.02%.
2.22 (s, 3H). 13C NMR (CDCl3, 100 MHz): δ 195.5, 138.3, 135.9,
(4-Chlorophenyl)(3-phenyl-1,4-dioxan-2-yl)methanone (3ad).
134.1, 133.4, 129.1, 128.9, 128.4, 127.5, 81.2, 79.8, 66.8, 66.7, Yellow liquid (257 mg, yield 85%); Rf = 0.45 (petroleum ether/
21.2. Anal. Calcd for C18H18O3: C, 76.57; H, 6.43%; Found: C, EtOAc = 93/7); 1H NMR (CDCl3, 400 MHz): δ 7.65–7.63 (m, 2H),
76.51; H, 6.38%.
7.31–7.25 (m, 4H), 7.23–7.16 (m, 3H), 4.86–4.78 (m, 2H),
(3-(4-Methoxyphenyl)-1,4-dioxan-2-yl)(phenyl)methanone (3ca). 4.05–3.97 (m, 4H). 13C NMR (CDCl3, 100 MHz): δ 194.4, 140.0,
Yellow liquid (256 mg, yield 86%); Rf = 0.50 (petroleum ether/ 136.9, 134.1, 130.2, 128.8, 128.5, 127.6, 81.3, 80.0, 66.8, 66.7.
EtOAc = 93/7); 1H NMR (CDCl3, 400 MHz): δ 7.67–7.65 (m, 2H), Anal. Calcd for C17H15ClO3: C, 67.44; H, 4.99%; Found: C,
7.40–7.36 (m, 1H), 7.25–7.15 (m, 4H), 6.66–6.63 (m, 2H), 4.80 67.40; H, 4.92%.
(d, J = 8.8 Hz, 1H), 4.71 (d, J = 9.2 Hz, 1H), 3.95–3.90 (m, 4H),
(3-Bromophenyl)(3-phenyl-1,4-dioxan-2-yl)methanone (3ae).
3.62 (s, 3H). 13C NMR (CDCl3, 100 MHz): δ 195.6, 159.7, 135.8, Yellow liquid (330 mg, yield 95%); Rf = 0.55 (petroleum ether/
133.4, 129.3, 128.9, 128.4, 113.8, 81.1, 79.4, 66.8, 66.7, 55.3. EtOAc = 92/8); 1H NMR (CDCl3, 400 MHz): δ 7.70–7.69 (m, 1H),
Anal. Calcd for C18H18O4: C, 72.47; H, 6.08%; Found: C, 72.40; 7.55–7.53 (m, 1H), 7.48–7.45 (m, 1H), 7.23–7.21 (m, 2H),
H, 6.02%.
7.14–7.05 (m, 4H), 4.76 (d, J = 8.8 Hz, 1H), 4.70 (d, J = 8.8 Hz,
(3-(2-Chlorophenyl)-1,4-dioxan-2-yl)(phenyl)methanone (3da). 1H), 3.96–3.92 (m, 4H). 13C NMR (CDCl3, 100 MHz): δ 194.2,
Orange gum (212 mg, yield 70%); Rf = 0.55 (petroleum ether/ 137.5, 136.8, 136.2, 131.7, 129.9, 128.8, 128.5, 127.5, 127.2,
EtOAc = 93/7); 1H NMR (CDCl3, 400 MHz): δ 7.72–7.70 (m, 2H), 122.7, 81.3, 79.9, 66.7, 66.6. Anal. Calcd for C17H15BrO3: C,
7.58–7.56 (m, 1H), 7.42–7.38 (m, 1H), 7.26–7.21 (m, 3H), 58.81; H, 4.35%; Found: C, 58.75; H, 4.29%.
7.08–7.04 (m, 2H), 5.22 (d, J = 8.8 Hz, 1H), 4.99 (d, J = 8.4 Hz,
p-Tolyl(3-(p-tolyl)-1,4-dioxan-2-yl)methanone (3bb). Yellow
1H), 4.09–4.02 (m, 4H). 13C NMR (CDCl3, 100 MHz): δ 195.1, gum (246 mg, yield 83%); Rf = 0.55 (petroleum ether/EtOAc =
135.7, 135.1, 133.4, 133.3, 129.7, 129.6, 128.94, 128.89, 128.1, 92/8); 1H NMR (CDCl3, 400 MHz): δ 7.65 (d, J = 8.4 Hz, 2H),
127.0, 82.2, 76.3, 66.9, 66.7. Anal. Calcd for C17H15ClO3: C, 7.20 (d, J = 8.0 Hz, 2H), 7.10 (d, J = 8.0 Hz, 2H), 7.00 (d, J = 8.0
67.44; H, 4.99%; Found: C, 67.39; H, 5.04%.
Hz, 2H), 4.86–4.80 (m, 2H), 4.02–3.97 (m, 4H), 2.33 (s, 3H),
(3-(4-Chlorophenyl)-1,4-dioxan-2-yl)(phenyl)methanone (3ea). 2.22 (s, 3H). 13C NMR (CDCl3, 100 MHz): δ 195.0, 144.3, 138.2,
Yellow liquid, 218 mg (yield 72%); Rf = 0.60 (petroleum ether/ 134.2, 133.5, 129.12, 129.07, 129.0, 127.5, 81.1, 79.7, 66.8, 66.7,
EtOAc = 90/10); 1H NMR (CDCl3, 400 MHz): δ 7.75–7.73 (m, 21.7, 21.2. Anal. Calcd for C19H20O3: C, 77.00; H, 6.08%;
2H), 7.50–7.46 (m, 1H), 7.35–7.31 (m, 2H), 7.28–7.25 (m, 2H), Found: C, 76.95; H, 6.01%.
7.18–7.15 (m, 2H), 4.85–4.80 (m, 2H), 4.03–3.98 (m, 4H). 13C
(4-Chlorophenyl)(3-(p-tolyl)-1,4-dioxan-2-yl)methanone (3bd).
NMR (CDCl3, 100 MHz): δ 195.1, 135.8, 135.7, 134.3, 133.7, Yellow liquid (237 mg, yield 75%); Rf = 0.60 (petroleum ether/
129.1, 128.9, 128.6, 127.5, 81.0, 79.0, 66.8. Anal. Calcd for EtOAc = 93/7); 1H NMR (CDCl3, 400 MHz): δ 7.61–7.57 (m, 2H),
C17H15ClO3: C, 67.44; H, 4.99%; Found: C, 67.41; H, 4.95%.
7.22–7.19 (m, 3H), 7.10 (d, J = 8.0 Hz, 2H), 6.94 (d, J = 7.6 Hz,
(3-(4-Fluorophenyl)-1,4-dioxan-2-yl)(phenyl)methanone (3fa). 2H), 4.76–4.68 (m, 2H), 3.97–3.92 (m, 4H), 2.17 (s, 3H). 13C
Yellow liquid (229 mg, yield 80%); Rf = 0.45 (petroleum ether/ NMR (CDCl3, 100 MHz): δ 194.3, 139.8, 138.4, 134.1, 133.8,
EtOAc = 92/8); 1H NMR (CDCl3, 400 MHz): δ 7.74–7.72 (m, 2H), 130.2, 129.1, 128.6, 127.3, 81.3, 79.7, 66.7, 66.6, 21.1. Anal.
7.49–7.46 (m, 1H), 7.34–7.29 (m, 4H), 6.91–6.86 (m, 2H), Calcd for C18H17ClO3: C, 68.25; H, 5.41%; Found: C, 68.20; H,
4.87–4.81 (m, 2H), 4.05–3.99 (m, 4H). 13C NMR (CDCl3, 5.35%.
1
100 MHz): δ 195.3, 162.7 (d, JC–F = 244 Hz), 135.7, 133.7,
(4-Chlorophenyl)(3-(2-methoxyphenyl)-1,4-dioxan-2-yl)metha-
4
3
133.1, 129.4 (d, JC–F = 8 Hz), 128.7 (d, JC–F = 30 Hz), 115.4 (d, none (3gd). Yellow gum (246 mg, yield 74%); Rf = 0.50 (pet-
2JC–F = 22 Hz), 81.1, 79.2, 66.9, 66.7. Anal. Calcd for C17H15FO3: roleum ether/EtOAc = 92/8); 1H NMR (CDCl3, 400 MHz): δ
C, 71.32; H, 5.28%; Found: C, 71.27; H, 5.25%.
7.61–7.59 (m, 2H), 7.55–7.52 (m, 1H), 7.20–7.18 (m, 2H),
(3-Phenyl-1,4-dioxan-2-yl)(p-tolyl)methanone (3ab). Off- 7.12–7.10 (m, 1H), 6.96–6.93 (m, 1H), 6.42 (d, J = 8.0 Hz, 1H),
white gum (257 mg, yield 91%); Rf = 0.50 (petroleum ether/ 5.10 (d, J = 8.8 Hz, 1H), 4.78 (d, J = 8.4 Hz, 1H), 4.08–4.03 (m,
EtOAc = 93/7); 1H NMR (CDCl3, 400 MHz): δ 7.62 (d, J = 8.4 Hz, 3H), 3.97–3.92 (m, 1H), 3.34 (s, 3H). 13C NMR (CDCl3,
2H), 7.33–7.30 (m, 2H), 7.22–7.15 (m, 3H), 7.09 (d, J = 8.0 Hz, 100 MHz): δ 193.9, 155.8, 139.3, 134.2, 130.0, 129.6, 128.2,
2H), 4.90–4.83 (m, 2H), 4.04–3.98 (m, 4H), 2.32 (s, 3H). 13C 127.4, 125.6, 120.9, 109.9, 84.0, 74.5, 67.1, 66.7, 54.5. Anal.
NMR (CDCl3, 100 MHz): δ 195.0, 144.4, 137.2, 133.4, 129.2, Calcd for C18H17ClO4: C, 64.97; H, 5.15%; Found: C, 65.02; H,
129.0, 128.5, 128.4, 127.6, 81.0, 80.0, 66.8, 66.7, 21.8. Anal. 5.11%.
Calcd for C18H18O3: C, 76.57; H, 6.43%; Found: C, 76.51; H,
6.38%.
(3-(2-Chlorophenyl)-1,4-dioxan-2-yl)(p-tolyl)methanone (3db).
Orange gum (225 mg, yield 71%); Rf = 0.50 (petroleum ether/
(4-Methoxyphenyl)(3-phenyl-1,4-dioxan-2-yl)methanone (3ac). EtOAc = 94/6); 1H NMR (CDCl3, 400 MHz): δ 7.64–7.62 (m, 2H),
Yellow gum (274 mg, yield 92%); Rf = 0.60 (petroleum ether/ 7.59–7.56 (m, 1H), 7.23–7.21 (m, 1H), 7.08–7.04 (m, 4H), 5.23
EtOAc = 94/6); 1H NMR (CDCl3, 400 MHz): δ 7.72–7.69 (m, 2H), (d, J = 8.8 Hz, 1H), 4.97 (d, J = 8.4 Hz, 1H), 4.09–3.98 (m, 4H),
7.33–7.30 (m, 2H), 7.22–7.15 (m, 3H), 6.77–6.75 (m, 2H), 2.31 (s, 3H). 13C NMR (CDCl3, 100 MHz): δ 194.6, 144.2, 135.2,
4.87–4.82 (m, 2H), 4.05–3.97 (m, 4H), 3.80 (s, 3H). 13C NMR 133.5, 133.2, 129.7, 129.6, 129.1, 129.0, 128.9, 127.0, 82.1, 76.4,
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66.9, 66.7, 21.7. Anal. Calcd for C18H17ClO3: C, 68.25; H,
5.41%; Found: C, 68.20; H, 5.46%.
Acknowledgements
(4-Chlorophenyl)(3-(2-chlorophenyl)-1,4-dioxan-2-yl)methanone A. Majee acknowledges financial support from the CSIR-Major
(3dd). Yellow liquid (229 mg, yield 68%); Rf = 0.45 (petroleum Research Project (Ref. No. 02(0383)/19/EMR-II). S. Santra is
1
ether/EtOAc = 90/10); H NMR (CDCl3, 400 MHz): δ 7.69–7.66 thankful to the Russian Science Foundation, Russia for
(m, 2H), 7.60–7.58 (m, 1H), 7.25–7.18 (m, 3H), 7.13–7.05 (m, funding (Grant # 20-73-10205). We are thankful to the
2H), 5.20 (d, J = 8.8 Hz, 1H), 4.91 (d, J = 8.8 Hz, 1H), 4.10–3.99 DST-FIST and UGC-SAP program of the Department of
(m, 4H). 13C NMR (CDCl3, 100 MHz): δ 193.9, 139.8, 135.0, Chemistry, Visva-Bharati.
133.9, 133.3, 130.3, 129.8, 129.6, 128.9, 128.5, 127.2, 82.7, 76.3,
66.9, 66.7. Anal. Calcd for C17H14Cl2O3: C, 60.55; H, 4.19%;
Found: C, 60.60; H, 4.12%.
(3-(2-Bromophenyl)-1,4-dioxan-2-yl)(4-methoxyphenyl)metha-
Notes and references
none (3hc). Yellow liquid (272 mg, yield 72%); Rf = 0.50 (pet-
roleum ether/EtOAc = 91/9); 1H NMR (CDCl3, 400 MHz): δ
7.75–7.72 (m, 2H), 7.58–7.55 (m, 1H), 7.29–7.26 (m, 2H),
7.03–6.99 (m, 1H), 6.74–6.71 (m, 2H), 5.22–5.20 (m, 1H),
4.96–4.94 (m, 1H), 4.09–3.98 (m, 4H), 3.80 (s, 3H). 13C NMR
(CDCl3, 100 MHz): δ 193.3, 163.6, 136.9, 133.0, 131.4, 129.9,
129.2, 128.7, 127.6, 123.8, 113.4, 82.1, 78.5, 66.9, 66.7, 55.5.
Anal. Calcd for C18H17BrO4: C, 57.31; H, 4.54%; Found: C,
57.25; H, 4.59%.
(3-(3-Bromophenyl)-1,4-dioxan-2-yl)(p-tolyl)methanone (3ib).
Yellow liquid (311 mg, yield 86%); Rf = 0.55 (petroleum ether/
EtOAc = 92/8); 1H NMR (CDCl3, 400 MHz): δ 7.73–7.72 (m, 1H),
7.66–7.64 (m, 1H), 7.57–7.54 (m, 1H), 7.19–7.15 (m, 3H),
7.02–7.00 (m, 2H), 4.81 (d, J = 8.8 Hz, 1H), 4.73 (d, J = 8.8 Hz,
1H), 4.01–3.99 (m, 4H), 2.23 (s, 3H). 13C NMR (CDCl3,
100 MHz): δ 194.4, 138.6, 137.6, 136.1, 133.9, 131.8, 129.9,
129.2, 127.4, 127.3, 122.7, 81.6, 79.8, 66.8, 66.7, 21.2. Anal.
Calcd for C18H17BrO3: C, 59.85; H, 4.74%; Found: C, 59.93; H,
4.69%.
(3-(3-Bromophenyl)-1,4-dioxan-2-yl)(4-methoxyphenyl)metha-
none (3ic). Yellow liquid (351 mg, yield 93%); Rf = 0.60 (pet-
roleum ether/EtOAc = 93/7); 1H NMR (CDCl3, 400 MHz): δ
7.75–7.74 (m, 1H), 7.65–7.62 (m, 1H), 7.55–7.52 (m, 1H),
7.21–7.13 (m, 3H), 6.73–6.71 (m, 2H), 4.79 (d, J = 8.8 Hz, 1H),
4.70 (d, J = 9.2 Hz, 1H), 3.98–3.97 (m, 4H), 3.69 (s, 3H). 13C
NMR (CDCl3, 100 MHz): δ 194.3, 159.8, 137.5, 136.0, 131.7,
129.9, 129.0, 128.7, 127.2, 122.6, 113.8, 81.4, 79.4, 66.7, 66.6,
55.2. Anal. Calcd for C18H17BrO4: C, 57.31; H, 4.54%; Found:
C, 57.25; H, 4.50%.
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Conflicts of interest
There are no conflicts to declare.
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