Synthesis of Pyran Annulated Heterocyclic Compounds under Catalyst Free Conditions Using Aqueous Ethylene Glycol

Full text of DOI:10.1080/00304948.2020.1812360

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/uopp20
Synthesis of Pyran Annulated Heterocyclic
Compounds under Catalyst Free Conditions Using
Aqueous Ethylene Glycol
Sushama S. Kauthale , Sunil U. Tekale , László Kótai , Pravin S. Kendrekar &
Rajendra P. Pawar
To cite this article: Sushama S. Kauthale , Sunil U. Tekale , László Kótai , Pravin S. Kendrekar
& Rajendra P. Pawar (2020): Synthesis of Pyran Annulated Heterocyclic Compounds under
Catalyst Free Conditions Using Aqueous Ethylene Glycol, Organic Preparations and Procedures
International, DOI: 10.1080/00304948.2020.1812360
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Published online: 27 Oct 2020.
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ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
https://doi.org/10.1080/00304948.2020.1812360
OPPI BRIEF
Synthesis of Pyran Annulated Heterocyclic Compounds
under Catalyst Free Conditions Using Aqueous
Ethylene Glycol
a
a
b
, Pravin S. Kendrekarc, and
ꢀ
ꢀ ꢀ
Sushama S. Kauthale , Sunil U. Tekale , Laszlo Kotai
Rajendra P. Pawara
b
aDepartment of Chemistry, Deogiri College, Aurangabad, India; Research Center for Natural Sciences,
c
Hungarian Academy of Sciences, Budapest, Hungary; Department of Health Sciences, Central University
of Technology, Bloemfontein, South Africa
ARTICLE HISTORY Received 5 December 2019; Accepted 1 June 2020
Recently, development of environmentally benign and clean synthetic protocols has
become a goal of modern organic synthesis. Consequently design and development of
catalyst-free reactions have both received tremendous attention in the area of green
organic synthesis. Efforts are being made to reduce toxicity levels of catalysts by multi-
directional modifications leading to the development of organic reactions under cata-
lyst-free conditions.1 Multi-component reactions (MCRs) in aqueous media without
catalysts are highly desirable tools of green chemistry.2–3 As a commonly-available
chemical, ethylene glycol (EG) has been used for protection of carbonyl compounds in
organic synthesis,4 and in a large number of industrial processes.5 EG is emerging as an
efficient and promising solvent for such organic transformations as the synthesis of pyr-
ans,6 4H-pyrimidobenzothiazoles,7 pyrimidines,8 2-arylbenzothiazoles and azomethines.9
Considerable attention has been focused on the synthesis, reactions and biological
activities of dihydropyrano[c]chromene derivatives.10 Coumarins and dihydropyrano[c]-
chromenes constitute the skeleton of such commercial drugs as warfarin, hymecromone
and coumatetralyl.11,12 Pyran derivatives are useful owing to their promising biological
activities.13,14 They are as well used as photoactive materials.15 Pyran derivatives were
reported as inhibitors of insulin-regulated amino peptidase related to enhancement of
memory and learning functions.16 Besides this, pyran derivatives are also well docu-
mented for anticancer and antibacterial activity.17 Consequently, numerous catalysts
have been developed for the synthesis of these compounds including the use of pipera-
zine,18 copper nanoparticles,19 morpholine,20 phenylboronic acid,21 poly(4-vinylpyri-
dine),22
silica-bonded
N-propylpiperazine
sodium
n-propionate,23
4-
(dimethylamino)pyridine,24 amino functionalized silica gel,25 Ce1Mg0.6Zr0.4O226, neat
silica gel,27 urea,28 and 1,4-diazabicyclo[2.2.2]octane under microwave irradiation.29
Each of these methods has its own value, but in many cases there are also such draw-
backs as long reaction times, use of volatile solvents, low yields or harsh reaction condi-
tions. In continuation of our interest in the development of efficient and convenient
CONTACT Rajendra P. Pawar
rppawar@yahoo.com
Department of Chemistry, Deogiri College, Station Road,
Aurangabad (MS) 431 005, India
ß 2020 Taylor & Francis Group, LLC

2
S. S. KAUTHALE ET AL.
Scheme 1. EG:H2O promoted catalyst-free one-pot multicomponent synthesis of pyran annulated
heterocyclic compounds.
methodologies for the synthesis of biologically active heterocyclic compounds,30 we now
report on the preparation of pyran annulated derivatives (5a-n), namely 3,4-dihydropyr-
ano[c]chromenes and tetrahydrobenzo[b]pyrans. This has been achieved by the one-pot
three component condensation of aldehydes (1), malononitrile (2) and 4-hydroxycou-
marin (3) or dimedone (4) under catalyst free conditions in EG:water (1:1) within 3-5 h
(Scheme 1, Table 1). The procedure is noteworthy for its simplicity and convenience.
To determine the optimum conditions, the reaction of 4-chlorobenzaldehyde
(1 mmol), 4-hydroxycoumarin (1 mmol) and malononitrile (1 mmol) was chosen. We
investigated solvents, temperatures and times as reaction variables, and the results are
summarized in Table 2. The work-up procedure consisted of simply pouring the reac-
tion mixture into ice cold water to precipitate the solid, isolated by filtration. As can be
seen (Entry 14), the best outcome was obtained in EG:H2O (1:1) at reflux (100 ꢀC)
within 3.5 hours. As seen from Table 1, under the optimized conditions, diversely sub-
stituted aromatic aldehydes smoothly afforded the corresponding products in very good
to excellent yields.
Aromatic aldehydes having electron-withdrawing groups (Table 1, Entries 9, 10, 13)
on the aromatic ring were observed to react faster than those with electron-donating
groups. ortho-Substituted aromatic aldehydes resulted in lower yields and required com-
paratively longer times, most probably due to steric effects (Table 1, Entries 5, 6, 7).
We explored the analogous reactions with dimedone as the dicarbonyl partner. These
reactions were rapid and high-yielding (Table 1, Entries 11, 12, 13 and 14). The reac-
tions were remarkably clean and no column chromatographic purification was required.
Authenticity of all of the products was established by comparing their melting points
with those reported in literature cited in the table and by analysis of spectral data, viz.,
13
1H NMR, C NMR, IR and mass spectra. For novel compounds, satisfactory elemental
analyses were obtained.
In summary, we have found a simple and convenient procedure for the one-pot
MCR synthesis of pyran annulated heterocyclic compounds under catalyst free condi-
tions using aqueous ethylene glycol. In the preparation of these useful compounds, the
method offers ease of operation and high yields, as well as adhering to the green prin-
ciple of eliminating the need for a catalyst.
Experimental section
Chemicals were purchased from SD Fine or Sigma Aldrich and used without further
purification. Reactions were monitored on silica-gel coated aluminium TLC plates

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
3
Table 1. Yields of aqueous ethylene glycol promoted synthesis of pyran annulated heterocyc-
lic compounds.
mp (oC)
Obs.
[Lit.] [Ref.]
Entry
1
X
1,3-Dicarbonyl
Product
Time (h)
3
Yield (%)1
89
H
4-Hydroxycoumarin
255-256
[255-256] [19]
2
3
4
5
6
4-Cl
4-Hydroxycoumarin
4-Hydroxycoumarin
4-Hydroxycoumarin
4-Hydroxycoumarin
4-Hydroxycoumarin
3.5
3.5
4
90
86
89
87
84
258-260
[260-262] [18]
4-Br
252-254
[250-252] [31]
3,4-(OMe)2
229-230
[230-233] [18]
2,4-Cl2
4
258-259
[258-260] [31]
5-Br, 2-F
5
231-233 [P]2
(continued)

4
S. S. KAUTHALE ET AL.
Table 1. Continued.
mp (oC)
Obs.
[Lit.] [Ref.]
Entry
7
X
1,3-Dicarbonyl
Product
Time (h)
5
Yield (%)1
88
2-Cl,4-F
4-Hydroxycoumarin
256-257 [P]
8
9
2-Thiophene
4-Hydroxycoumarin
4-Hydroxycoumarin
4
82
80
219-220
[220-222] [32]
4-OH
4.5
265-266
[265-267] [21]
10
4-NO2
4-Hydroxycoumarin
3
90
257-259
[258-260] [23]
11
12
H
Dimedone
Dimedone
3
90
88
230-232
[232-233] [18]
4-OMe
3.5
201-202
[198-200] [32]
(continued)

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
5
Table 1. Continued.
mp (oC)
Obs.
[Lit.] [Ref.]
Entry
13
X
1,3-Dicarbonyl
Dimedone
Product
Time (h)
3
Yield (%)1
92
4-NO2
178-180
[176-177] [32]
14
4-Cl
Dimedone
3.5
87
215-216
[217-218] [18]
1Isolated yields from reactions of aldehyde (2 mmol), malononitrile (2 mmol) and dimedone or 4-hydroxycoumarin
(2 mmol) in EG:H2O (1:1) (2 mL) at 100 ꢀC.
2[P] present work.
(Merck) in ethyl acetate: n-hexane as the mobile phase. Melting points of the products
were determined on a digital melting point apparatus (Optics Technology) using capilla-
1
ries open at one end and were uncorrected. H (400 MHz) and 13C (100 MHz) NMR
spectra were recorded on a Bruker ACF 200 spectrometer and chemical shifts were
reported on d ppm scale in the specified solvents. First order coupling constants were
in the range of 5-7 Hz and are not individually reported. IR spectra were recorded on
Shimadzu FTIR spectrophotometer (Prestige-IR21) using KBr pellets. Mass spectra were
recorded on Thermo Finnigan Surveyor MS-Q spectrometer.
General procedure for the aqueous ethylene glycol promoted synthesis of 3,4-
dihydropyrano[c]chromenes and tetrahydrobenzo[b]pyrans
A mixture of aldehyde (2 mmol) and malononitrile (2 mmol) in (1:1) ethylene glycol:
H2O (2 mL) was stirred at room temperature for 10 minutes. An appropriate amount of
4-hydroxycoumarin or dimedone (2 mmol) was then added and the reaction mixture
was refluxed at 100 ꢀC for the specified time (Table 1). The progress of the reaction was
monitored by TLC in 50% ethyl acetate:n-hexane in the case of dihydropyrano[c]chro-
menes and 30% ethyl acetate:n-hexane in the case of tetrahydrobenzo[b]pyrans. After
completion of the reaction as monitored by TLC, the reaction mixture was poured into
ice cold water. The resulting precipitated solid was collected by filtration, washed with
cold water (3 x 5 mL) to remove any traces of ethylene glycol and further purified by
recrystallization from ethanol. Many of the products were known compounds, identified
by comparison of their melting points with those in the literature cited in Table 1.
Complete characterization of novel compounds (5f and 5g) and examples of representa-
tive spectroscopic data for known compounds are provided below.

6
S. S. KAUTHALE ET AL.
Table 2. Optimization of reaction conditions for the model reaction of 4-chlorobenzaldehyde,
malononitrile and 4-hydroxycoumarin.
Entry
Reaction conditions
H2O, 100 oC, reflux, 5h
Yield (%)a
1
37
2
3
4
5
6
7
8
9
10
11
12
13
14
Dioxane : H2O (1:1), 100 oC, reflux, 5 h
EtOH: H2O (1:1), 80 oC, reflux, 5h
MeOH: H2O (1:1), 70 oC, reflux, 5h
IPA: H2O (1:1), 80 oC, reflux, 5h
Acetone : H2O (1:1), 60 oC, reflux, 5
ACN : H2O (1:1), 85 oC, reflux, 5h
DMSO : H2O (1:1), 100 oC, reflux,5h
THF: H2O (1:1), 70 oC, reflux, 5 h
Triethanol amine, 80 oC, reflux, 5h
EG, 100 oC, reflux, 5h
Trace
64
70
40
58
25
30
40
80
61
78
Glycerol : H2O (1:1), 100 oC, reflux, 3.5 h
PEG : H2O (1:1), reflux, 4 h
87-91 [ref 33]
90 [Present work]
EG : H2O (1:1) , reflux, 3.5 h
aYields for the model reaction of 4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol) and 4-hydroxycou-
marin (1 mmol).
2-Amino-4-(4-bromophenyl)-4, 5-dihydro-5-oxopyrano [3, 2-c]-chromene-3-carboni-
trile (5c)
1
M.P. ¼ 252-254 ꢀC; H NMR (400 MHz, DMSO-d6): d ¼ 7.6-7.9 (brs, 2H, -NH2), 7.45
(m, 6H), 7.25 (s, 2H), 4.51 (s, 1H) ppm; 13C NMR (100.6 MHz, DMSO-d6) d ¼ 159.53,
157.95, 153.54, 152.16, 142.71, 132.99, 131.33, 129.97, 124.66, 122.51, 120.20, 116.58,
112.93, 103.43, 57.40 ppm; IR (KBr) ꢀ ¼ 3400, 3305, 2205, 1710, 1650, 1502, 1460, 1211,
1070, 696 cmꢁ1; MS (70 eV): m/z ¼ 395.2 (M þ 1)þ.
2-Amino-4-(2, 4-dichlorophenyl)-4, 5-dihydro-5-oxopyrano[3,2-c]-chromene-3-carboni-
trile (5e)
1
M.P. ¼ 256-257 ꢀC; H NMR (400 MHz, DMSO-d6): d ¼ 7.9 (d, 1H), 7.71 (t, 1H), 7.59
(s, 1H), 7.49 (m, 4H), 7.35 (m, 2H), 4.95 (s, 1H) ppm; 13C NMR (100.6 MHz, DMSO-
d6) d ¼ 159.38, 158.10, 154.13, 152.21, 139.39, 133.33, 133.10, 132.66, 132.35, 128.83,
127.84, 124.72, 122.51, 118.64, 116.61, 112.79, 102.45, 55.98 ppm; IR (KBr) ꢀ ¼ 3464,
3298, 3066, 2200, 1712, 1660, 1060, 750 cmꢁ1; MS (70 eV): m/z ¼ 384.7 (M þ 1)þ.
2-Amino-4-(5-bromo-2-fluorophenyl)-4,5-dihydro-5-oxopyrano[3,2-c]chromene-3-car-
bonitrile (5f)
1
M.P. ¼ 231-233 ꢀC; H NMR (400 MHz, DMSO-d6): d ¼ 7.6-7.95 (brs, 2H, -NH2), 7.15
(s, 1H), 5.91 (m, 6H), 4.75 (s, 1H) ppm; 13C NMR (100.6 MHz, DMSO-d6) d ¼ 159.51,
158.26, 154.16, 152.21, 133.05, 132.66, 132.43, 132.29, 132.05, 131.97, 124.67, 122.51,
118.87, 117.79, 116.32, 112.92, 101.84, 55.75 ppm; IR (KBr) ꢀ ¼ 3458, 3225, 2904, 2198,
1695, 1604, 1560, 1053, 761 cmꢁ1; MS (70 eV): m/z ¼ 412.5 (M þ 1)þ.
Anal. Calcd for C19H10BrFN2O3: C, 55.23; H, 2.44; N, 6.78. Found: C, 55.38; H, 2.56; N, 6.83.
2-Amino-4-(2-chloro-4-fluorophenyl)-4,5-dihydro-5-oxopyrano[3,2-c]chromene-3-car-
bonitrile (5g)
1
M.P. ¼ 256-257 ꢀC; H NMR (400 MHz, DMSO-d6): d ¼ 7.6-7.9 (brs, 2H, NH2), 7.45
(m, 6H), 7.12 (s, 1H), 4.99 (s, 1H) ppm; 13C NMR (100.6 MHz, DMSO-d6): d ¼ 161.93,

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
7
159.47, 158.07, 154.04, 152.19, 136.66, 133.13, 132.18, 124.69, 122.50, 118.70, 116.59,
116.38, 114.98, 114.77, 112.82, 102.64, 56.27 ppm; IR (KBr) ꢀ ¼ 3453, 3208, 2910, 2186,
1684, 1603, 1553, 1052, 708 cmꢁ1; MS (70 eV): m/z ¼ 370.08 (M þ 1)þ.
Anal. Calcd for: C, 61.89; H, 2.73; N, 7.60. Found: C, 61.62; H, 2.85; N, 7.42.
2-Amino-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4-phenyl-4H-chromene-3-carboni-
trile (5k)
1
M.P. ¼ 230-232 ꢀC; H NMR (400 MHz, DMSO-d6): d ¼ 7.32 (t, 2H), 7.16 (m, 3H),
7.10 (s, 2H, -NH2), 4.19 (s, 1H), 2.52 (s, 2H), 2.24 (dd 1H), 2.12 (dd, 1H), 1.04 (s, 3H,
-CH3), 0.96 (s, 3H, -CH3) ppm; 13C NMR (100.6 MHz, DMSO-d6): d ¼ 195.61, 162.46,
158.47, 144.72, 128.30, 127.12, 126.54, 119.69, 112.73, 58.30, 35.56, 31.77, 28.38,
26.78 ppm; IR (KBr) ꢀ ¼ 3390, 3250, 3195, 2200, 1685 cmꢁ1; MS (70 eV): m/z ¼ 295
þ
(M þ 1) .
2-Amino-5,6,7,8-tetrahydro-4-(4-methoxyphenyl)-7,7-dimethyl-5-oxo-4H-chromene-3-
carbonitrile (5l)
1
M.P. ¼ 201-202 ꢀC; H NMR (400 MHz, DMSO-d6): d ¼ 7.07 (dd, 2H), 6.97 (s, 2H,
-NH2), 6.83 (dd, 2H), 4.71 (s, 1H), 3.76 (s, 3H, -OCH3), 2.5 (s, 2H), 2.23 (d, 1H), 2.1
(d, 1H), 1.03 (s, 3H, -CH3), 0.98 (s, 3H, -CH3) ppm; 13C NMR (100.6 MHz, DMSO-d6)
d ¼ 195.59, 162.08, 158.41, 157.90, 136.82, 128.19, 119.75, 113.65, 113.01, 58.62, 34.75,
31.73, 28.39, 26.76 ppm; IR (KBr) ꢀ ¼ 3320, 2970, 2199, 1688, 1641, 1605, 1508, 1370,
1213, 889 cmꢁ1
.
Acknowledgment
The authors thank the Director of the Sophisticated Analytical Instrumentation Facility, Panjab
University, Chandigarh, for providing spectral data.
ORCID
ꢀ
ꢀ
ꢀ
Laszlo Kotai
http://orcid.org/0000-0001-6375-3120
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