Imidazolium ionic liquids as catalyst for synthesis of (E)-3- arylidene(thio)chroman-4-ones under microwave irradiation

Article abstract of DOI:10.3184/174751912X13466926675198

Use of imidazolium ionic liquids [Bmim][CF₃COO] and [Bmim]OH as a catalyst for synthesis of 3-arylidene(thio)chroman- 4-ones by the condensation of (thio)chroman-4-ones and aromatic aldehydes under microwave irradiation conditions. A series of 3-arylidene(thio)chroman-4-ones were obtained as the only product and considerable increase of yield was founded within short time. The products 3-arylidene(thio)chromanones were assigned the (E)-configuration based on 1H NMR spectroscopic data.

Full text of DOI:10.3184/174751912X13466926675198

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 635
NOVEMBER, 635–637
Imidazolium ionic liquids as catalyst for synthesis of
(E)-3-arylidene(thio)chroman-4-ones under microwave irradiation
Hong-Ya Li*, Shu-Na Li, Quan Wang, Shu-Xiang Wang and Bao-Cheng Zhu
College of Life Science, Agricultural University of Hebei, Baoding, Hebei Province 071000, P. R. China
Useofimidazoliumionicliquids[Bmim][CF3COO]and[Bmim]OHasacatalystforsynthesisof3-arylidene(thio)chroman-
4-ones by the condensation of (thio)chroman-4-ones and aromatic aldehydes under microwave irradiation condi-
tions. A series of 3-arylidene(thio)chroman-4-ones were obtained as the only product and considerable increase of
yield was founded within short time. The products 3-arylidene(thio)chromanones were assigned the (E)-configura-
tion based on 1H NMR spectroscopic data.
Keywords: 3-arylidene(thio)chroman-4-ones, condensation, imidazolium ionic liquids, [Bmim][CF3COO], [Bmim]OH,
microwave irradiation
3-Arylidene(thio)chroman-4-ones occupy a special place in
the field of heterocyclic chemistry for their broad biological
activities such as anti-mutagenic, anti-inflammatory, antifun-
gal and antiviral activities.1–6
due to their favourable properties like non-inflammability,
negligible vapour pressure, reusability and high thermal stabil-
ity.16–18 Some applications of imidazolium ionic liquids in con-
densation reaction have been reported.19–21 To the best of our
knowledge, synthesis of 3-arylidene(thio)chroman-4-ones in
the presence of ionic liquid has not been reported in the litera-
ture. Herewereportthesynthesisof3-arylidene(thio)chroman-
4-ones using ionic liquid [Bmim]OH or [Bmim][CF3COO]
under microwave irradiation (Scheme 1).
Manymethodsforthesynthesisof3-arylidene(thio)chroman-
4-ones have been explored. In 1998, Basavaiah synthesised 3-
arylidenechroman-4-ones by the ring closure of an acrylic acid
derivative mediated by trifluroacetic anhydride in methylene
chloride.7 However, the traditional strategy for the synthesis of
3-arylidenechroman-4-ones was based on the condensation of
chroman-4-ones with aromatic aldehydes in the presence of
catalyst. These methods can be subdivided according to the
catalyst used. For a long time, acid-catalysed condensation of
two components was extensively studied. HCl, H3PO4 and
H2SO4 have been applied in many cases for this reaction.8–10
Sometimes the reaction mixture needed to be saturated with
anhydrous hydrogen chloride, which was not convenient nor
environmental friendly. For this reason, this condensation has
been improved under other reaction condition. For example,
Farkas et al. completed the reaction conveniently in hot acetic
anhydride, but sometimes it required a prolonged (e.g. 80 h)
refluxing.11 On the other hand, this transformation could also
be catalysed by base such as sodium hydroxide and sodium
methoxide,12 anhydrous potassium acetate and pyrrolidine.13
Levai et al. also used piperidine as catalyst for the condensa-
tion, however, the desired 3-arylidenechroman-4-ones were
obtained only if the aromatic aldehyde bears electron-donating
or slightly electron-withdrawing substituents, whereas 3-
aryl-4-chromone is the solely isolable product instead of the
expected 3-arylidenechroman-4-one for the substrates with
strongly electron-withdrawing groups.14,15
Results and discussion
When (thio)chroman-4-one (1) reacted with substituted
benzaldehyde (2) in the presence of [Bmim][CF3COO] under
microwave irradiation, 3-arylidene(thio)chroman-4-ones (3a–
n) were obtained. As shown in Table 1, using imidazolium
ionic liquid [Bmim][CF3COO] as the catalyst, the condensa-
tion of (thio)chromanones with aromatic aldehydes gave the
product 3-arylidene(thio)chromanone in 72.1–87.6% yields
within 2–4 min under microwave irradiation. Compared with
other existing methods, the main advantages of the present
procedure are shorter reaction time, single product and
good yield. For example, when chroman-4-one reacted with
4-nitrobenzaldehyde in the presence of 85% phosphoric acid
by heating at 80 °C for 6 h, 3-(4-nitrobenzylidene)chroman-
4-one (3i) was obtained in 67% yields. If the reaction catalysed
by piperidine was heated for 2 h at 150 °C, the 3-(4-nitroben-
zyl) chromone instead of the expected 3-(4-nitrobenzylidene)
chroman-4-one was got in 81% yield.14,22 Whereas, the present
method offered 3-(4-nitrobenzylidene) chroman-4-one in
82.0% yield within only 3.5 min.
The structures of the products can be inferred from elemen-
1
Ionic liquids have attracted extensive research interest in
recent years as environmentally benign solvents or catalysts
tal analyses, IR, and H NMR spectra. The properties of the
1
products are shown below. H NMR spectroscopy can give
Scheme 1
* Correspondent. E-mail: lihy77@sina.com

636 JOURNAL OF CHEMICAL RESEARCH 2012
obtained with an AVANCE- 400 (400 MHz) spectrometer using TMS
as internal standard and CDCl3 as solvent. Elemental analyses were
performed on a Vagio-EL instrument.
definitive assignments of stereochemistry to cis- and trans-
exocyclic α, β-unsaturated ketones when both isomers are
available.23,24 The olefinic proton (H-9) cis to the carbonyl
group is deshielded relative to the corresponding trans-proton.
The olefinic proton (H-9) in E-isomers appeared as singlet at
7.81 ppm, while the same proton in Z-isomers appeared in the
range of 6.78 and 7.07 ppm. In addition, the protons (CH2)
adjacent to double bond are also useful in distinguishing the
isomers. The protons at the 2-position of the (Z)-isomer are
shielded relative to those of the (E)-isomer owing to the greater
distance from the side-chain phenyl group. In (E)-isomers, the
protons appeared in the range of 5.20–5.36 ppm and in (Z)-
isomers these protons were appeared in the range of 4.93–4.98
ppm. Thus the product obtained, the benzylic proton signal of
which occurs at about 7.84–7.98 ppm, is (E)-3-benzylidene-
Synthesis of ionic liquid [Bmim]OH and [Bmim][CF3COO]
Ionic liquid [Bmim]OH and [Bmim][CF3COO] were synthesised
according to literature methods.25,26
Synthesis of (thio)chroman-4-ones
(Thio)chroman-4-ones were prepared according to the literature.27
Synthesis of 3-arylidene(thio)chroman-4-ones 3a–n; general procedure
Compound 2 (5.0 mmol) was added to a solution of 1 (5.5 mmol) in
ethanol (10 mL) in the presence of catalyst (20 mg). The mixture was
irradiated in the microwave synthesis system (400 W) for the period
of time as indicated in Table 1 (monitored by TLC). Distilled water
(15 mL) was added to the reaction mixture, which was then extracted
with EtOAc (3×15 mL). The combined organic extracts were dried
(Na2SO4), filtered, and concentrated in vacuo to provide crude prod-
uct, which was then purified by column chromatography on silica gel
(200–300 mesh), eluted with petroleum ether (30–60 °C)or a mixture
of petroleum ether and ethyl acetate (V/V=4/1).
1
chroman-4-one. In support of this conclusion, the H NMR
spectra of the products also showed a double peaks signals at
5.27 ppm, the signal is due to the protons (CH2). The observed
split of the signal is attributed to a small long-range allylic
coupling (1.4–1.6 Hz).
In order to investigate the effect of basic ionic liquid on the
condensation, we also tried the reactions of 6-chlorochroman-
4-one with aromatic aldehydes catalysed by basic imidazolium
liquid [Bmim]OH under microwave irradiation (Scheme 1).
The desired condensation products (E)-6-chloro-3-benzyli-
denechroman-4-ones were obtained with 77.6–88.2% in short
time (Table 2). From the results summarised in Table 2, we
found that basic imidazolium liquid [Bmim]OH can be also
used as catalyst in the condensation successfully.
(E)-6-chloro-3-benzylidenechroman-4-one (3a): IR (cm−1): 1675
1
(C=O), 1600, 1460, 820, 800 (C6H6), 1580 (C=C–C=O). H NMR:
δ 5.36 (d, 2H, CH2, J = 1.6 Hz), 6.94 (d, 1H, H8, J = 8.8 Hz), 7.98 (d,
1H, H5, J = 2.6 Hz), 7.90 (s, 1H, =CH), 7.26–7.46 (m, 6H, ArH). 13
C
NMR: 67.90, 119.74, 122.70, 127.08, 129.34, 129.92, 130.14, 130.73,
131.02, 132.21, 136.67, 137.13, 160.90, 180.76. Anal. Calcd for
C16H11O2Cl: C, 70.99; H, 4.10. Found: C, 71.06; H, 3.83%.
(E)-6-chloro-3-(2-chlorobenzylidene)chroman-4-one (3b): IR (cm−1):
1
1665 (C=O), 1610, 1450, 820, 780 (C6H6), 1590 (C=C–C=O). H
NMR: δ 5.18 (d, 2H, CH2, J = 1.6 Hz), 6.94 (d, 1H, H8, J = 8.8 Hz),
7.99 (d, 1H, H5, J = 2.6 Hz), 7.44 (dd, 1H, H7, J1 = 8.8 Hz, J2 = 2.6 Hz),
7.98 (s, 1H, =CH), 7.26–7.44 (m, 4H, ArH). 13C NMR: 67.58, 119.74,
122.72, 126.70, 127.24, 127.49, 130.14, 130.30, 130.73, 131.63,
132.65, 134.99, 135.31, 135.86, 159.72, 181.03 Anal. Calcd for
C16H10O2Cl2: C, 62.97; H, 3.30. Found: C, 62.80; H, 3.53%.
(E)-6-chloro-3-(2,4-dichlorobenzylidene)chroman-4-one (3c): IR
(cm−1): 1657 (C=O), 1610, 1450, 820, 760 (C6H6), 1595 (C=C–C=O).
1H NMR: δ 5.15 (d, 2H, CH2, J = 1.6 Hz), 6.94 (d, 1H, H8, J = 8.8 Hz),
7.99 (d, 1H, H5, J = 2.6 Hz), 7.44 (dd, 1H, H7, J1 = 8.8 Hz, J2 = 2.6 Hz),
7.89 (s, 1H, =CH), 7.32 (dd, 1H, H5′, J1 = 1.8 Hz, J2 = 8.2 Hz), 7.06
(d, 1H, H6′, J = 8.2 Hz), 7.72 (d, 1H, H3′, J = 1.8 Hz). 13C NMR:
67.53, 119.76, 122.62, 127.14, 127.26, 127.63, 130.12, 130.94,
131.17, 132.13, 134.02, 135.78, 135.99, 136.13, 159.68, 180.77. Anal.
Calcd for C16H9O2Cl3: C, 56.59; H, 2.67. Found: C, 56.48; H, 2.93%.
In summary, we have found a fast and efficient method
for the synthesis of (E)-3-arylidenechroman-4-ones catalysed
by imidazolium ionic liquids through the condensation of
chroman-4-one and aromatic aldehydes under microwave
irradiation.
Experimental
Melting points were uncorrected and were measured with micro-
melting point apparatus X-4. The reactions were carried out in a
microwave synthesis system SXL9-1. IR spectra were recorded on a
1
FTS- 40 spectrometer (KBr). H NMR and 13C NMR spectra were
Table 1 Synthesis of (E)-3-arylidene(thio)chroman-4-ones catalysed by ionic liquid [Bmim][CF3COO] under microwave irradiation
Compd
R
Ar
X
Reaction time /min
Yield /%
Melting point (lit.) /°C
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
Cl
Cl
C6H5-
O
O
O
O
O
O
O
O
O
O
O
O
S
3
76.5
84.6
80.5
83.4
85.6
87.6
75.8
76.2
82.0
72.1
83.0
75.5
87.2
85
162–163
167–168.5
2-ClC6H4-
4
Cl
2,4-ClC6H3-
4-ClC6H4-
4-NO2C6H4-
3-NO2C6H4-
4-CH3OC6H4-
C6H5-
4-NO2C6H4-
4-CH3OC6H4-
4-NO2C6H4-
4-CH3OC6H4-
4-CH3OC6H4-
3-NO2C6H4-
4
4
2.5
3
3
4
179.5–180
Cl
207.5–208.5
194–195
Cl
Cl
217–218
Cl
162–163
H
110–112 (110–112[7])
H
3.5
4
236 (235–236[14]
132–133
197–198
182
)
H
CH3
CH3
CH3
CH3
3
4
3
173–174
192–193.5
S
2
Table 2 Synthesis of (E)-3-arylidenechroman-4-ones catalysed by ionic liquid [Bmim]OH under microwave irradiation
Compd
R
Ar
Reaction time /min
Yield/%
Melting point /°C
3a
3b
3c
3d
3e
3f
Cl
Cl
Cl
Cl
Cl
Cl
Cl
C6H5-
3
78.9
83.8
87.4
87.9
88.2
86.5
77.6
163
167–168
179.5–180
208–208.5
194–195
217
2-ClC6H4-
4
2,4-ClC6H3-
4-ClC6H4-
4-NO2C6H4-
3-NO2C6H4-
4-CH3OC6H4-
2.5
3
2.5
3
3
3g
162

JOURNAL OF CHEMICAL RESEARCH 2012 637
(E)-6-chloro-3-(4-chlorobenzylidene)chroman-4-one (3d): IR (cm−1):
1660 (C=O), 1620, 1450, 820, 770 (C6H6), 1585 (C=C–C=O). H
(E)-6-methyl-3-(4-methoxybenzylidene)thiochroman-4-one (3m):
IR (KBr) ν: 1675, 1600, 1575, 1458, 820, 780 cm−1. 1H NMR: δ 2.36
(s, 3H, CH3), 3.85 (s, 3H), 4.12 (s, 2H, CH2), 6.95 (d, 2H, H3′, 5′, J =
8.4 Hz), 7.20–7.25 (m, 2H), 7.37 (d, 2H, H2′, 6′, J = 8.4 Hz), 7.74
(s, 1H, =CH), 7.99 (s, 1H, H5). 13C NMR: 20.92, 29.41, 55.39, 114.24,
127.58, 127.78, 130.22, 130.56, 131.29, 131.42, 131.71, 132.34,
133.99, 135.68, 137.47, 137.55, 160.24, 186.12. Anal. Calcd For
C18H16O2S: C, 72.94; H, 5.44. Found: C, 72.95; H, 5.40%.
1
NMR: δ 5.15 (d, 2H, CH2, J = 1.6 Hz), 6.91 (d, 1H, H8, J = 8.8 Hz),
7.92 (d, 1H, H5, J = 1.8 Hz), 7.41 (dd, 1H, H7, J1 = 8.8 Hz, J2 = 1.8 Hz),
7.89 (s, 1H, =CH), 7.29 (d, 2H, H2′, 6′, J = 8.4 Hz), 7.08 (d, 2H, H3′, 5′,
J = 8.4 Hz). 13C NMR: 67.58, 119.69, 122.68, 126.47, 127.24, 127.54,
129.14, 130.76, 131.24, 132.56, 135.88, 136.45, 159.51, 180.92. Anal.
Calcd for C16H10O2Cl2: C, 62.97; H, 3.30, Found: C, 62.78; H,
3.53%.
(E)-6-methyl-3-(3-nitrobenzylidene)thiochroman-4-one (3n): IR
(E)-6-chloro-3-(4-nitrobenzylidene)chroman-4-one (3e): IR (cm−1):
(KBr) ν: 1660, 1570, 1480, 840, 800 cm−1. HMNR (CDCl3) δ: 2.41
1
1
1670 (C=O), 1600, 1460, 840, 720 (C6H6), 1570 (C=C–C=O). H
(S, 3H, CH3), 4.11 (S, 2H, CH2), 7.28 (S, 1H), 7.66–8.27 (m, 7H,
ArH); 13C NMR: 20.90, 29.42, 119.86, 122.42, 124.20, 127.56,
129.25, 131.29, 131.42, 131.71, 132.34, 133.99, 135.68, 137.47,
142.10, 144.62, 186.14. Anal. Calcd for C17H13O3NS: C, 65.58; H,
4.21; N, 4.50. Found: C, 65.56; H, 4.25; N, 4.46%.
NMR: δ 5.30 (s, 2H, CH2), 6.93 (d, 1H, H8, J = 8.8 Hz), 7.90 (d, 1H,
H5, J = 1.8 Hz), 7.40 (dd, 1H, J1 = 8.8 Hz, J2 = 1.8 Hz), 7.99 (s, 1H,
=CH), 8.19 (d, 2H, J = 8.4 Hz), 7.54 (d, 2H, J = 8.4 Hz). 13C NMR:
67.33, 119.83, 124.02, 124.71, 127.83, 130.22, 130.68, 133.07,
134.09, 136.23, 140.42, 147.98, 159.60, 180.53. Anal. Calcd for
C16H10O4NCl: C, 60.87; H, 3.19; N, 4.44. Found: C, 60.63; H, 3.51; N,
4.43%.
Received 24 June 2012; accepted 20 August 2012
Paper 1201380 doi: 10.3184/174751912X13466926675198
Published online: 12 November 2012
(E)-6-chloro-3-(3-nitrobenzylidene)chroman-4-one (3f): IR (cm−1):
1
1665 (C=O), 1600, 1510, 810, 780 (C6H6), 1580 (C=C–C=O). H
NMR: δ 5.33 (s, 2H, CH2), 6.97 (d, 1H, H8, J = 8.8 Hz), 8.29 (d, 1H,
J= 7.2 Hz), 8.16 (s, 1H, H2′), 7.99 (s, 1H, =CH), 7.26–7.90 (m, 4H,
Ar). 13C NMR: 67.45, 119.76, 122.60, 124.42, 124.72, 129.79, 130.24,
130.82, 133.02, 133.46, 134.12, 137.16, 140.26, 148.12, 159.43,
180.92. Anal. Calcd for C16H10O4NCl: C, 60.87; H, 3.19; N, 4.44.
Found: C, 60.68; H, 3.51; N, 4.43%.
References
1
2
P. Chen and J.S. Yang, Chem. Pharm. Bull., 2007, 55, 655.
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3
4
5
6
7
(E)-6-chloro-3-(4-methoxybenzylidene)chroman-4-one (3g): IR
(cm−1): 1670 (C=O), 1620, 1480, 840, 800 (C6H6), 1575 (C=C–C=O).
1H NMR: δ 3.87 (s, 3H, OCH3), 5.38 (s, 2H, CH2), 6.93 (d, 1H, H8,
J = 8.8 Hz), 7.97 (d, 1H, H5, J = 1.8 Hz), 7.44 (dd, 1H, H7, J1 = 8.8 Hz,
J2 = 1.8 Hz), 7.85 (s, 1H, =CH), 7.29 (d, 2H, H2′, 6′, J = 8.4 Hz), 6.98
(d, 2H, H3′, 5′, J = 8.4 Hz). 13C NMR: δ 55.42, 67.91, 114.33, 119.56,
122.87, 126.75, 127.12, 127.22, 127.90, 132.21, 135.41, 138.13,
159.34, 160.92, 180.99. Anal. Calcd for C17H13O3Cl: C, 67.89; H,
4.36. Found: C, 67.76; H, 4.34%.
8
9
N.K. Sangwan and S.N. Rastogi, Indian J. Chem. Sect. B, 1981, 20, 135.
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(E)-3-(4-methoxybenzylidene)chroman-4-one (3j): IR (cm−1): 1660
1
(C=O), 1600, 1480, 840, 780 (C6H6), 1580 (C=C–C=O). H NMR:
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R. Mercier and B. Laude, Bull. Soc. Chim. Fr., 1993, 130, 788.
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δ 3.86 (s, 3H, OCH3), 5.38 (d, 2H, CH2, J = 1.6 Hz), 6.94 (m, 1H, H8),
8.02 (m, 1H, H5), 7.47 (m, 1H, H7), 7.08 (m, 1H, H6), 7.84 (s, 1H,
=CH), 7.27 (d, 2H, H2′, 6′, J = 8.4 Hz), 6.96 (d, 2H, H3′, 5′, J = 8.4 Hz).
13C NMR: 54.96, 67.34, 113.82, 115.28, 123.36, 123.77, 126.65,
127.63, 128.71, 131.46, 135.52, 137.83, 159.81, 160.16, 180.77. Anal.
Calcd for C17H14O3: C, 76.68; H, 5.30. Found: C, 76.70; H, 5.34%.
(E)-6-methyl-3-(4-nitrobenzylidene)chroman-4-one (3k): IR (cm−1):
1
1670 (C=O), 1600, 1460, 840, 740 (C6H6), 1575 (C=C–C=O). H
NMR: δ 2.35 (s, 1H, CH3), 5.26 (d, 2H, CH2, J = 1.4 Hz), 6.89 (d, 1H,
H8, J = 8.4 Hz), 7.82 (s, 1H, H5), 7.34 (d, 1H, H7, J = 8.4 Hz), 7.84
(s, 1H, =CH), 8.30 (d, 2H, H2′, 6′, J = 8.4 Hz), 7.46 (d, 2H, H3′, 5′, J =
8.4 Hz). 13C NMR: 20.42, 67.57, 119.76, 124.16, 124.78, 127.86,
130.32, 130.88, 133.17, 134.08, 136.17, 140.54, 148.06, 159.48,
180.88. Anal. Calcd for C17H13O4N: C, 69.15; H, 4.44; N, 4.74. Found:
C, 69.10; H, 4.45; N, 4.78%.
22 V. Siddaiah, C.V. Rao, S. Venkateswarlu, A.V. Krishnaraju and
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and P.C. Teague, J. Org. Chem., 1970, 6, 2286.
(E)-6-methyl-3-(4-methoxybenzylidene)chroman-4-one (3l): IR
(cm−1): 1675 (C=O), 1610, 1480, 860, 780 (C6H6), 1580 (C=C–C=O).
1H NMR: δ 2.35 (s, 1H, CH3), 3.88 (s, 3H, OCH3), 5.36 (d, 2H, CH2,
J = 1.6 Hz), 6.98 (m, 1H, H8), 7.95 (m, 1H, H5), 7.52 (m, 1H, H7), 7.02
(m, 1H, H6), 7.89 (s, 1H, =CH), 7.23 (d, 2H, H2′, 6′, J = 8.4 Hz), 6.92
(d, 2H, H3′, 5′, J = 8.4 Hz). 13C NMR: 20.98, 55.39, 67.43, 114.24,
127.08, 128.64, 129.34, 129.92, 130.26, 131.02, 134.42, 136.67,
137.13, 159.62, 160.16, 180.96. Anal. Calcd for C18H16O3: C, 77.12;
H, 5.75. Found: C, 77.20; H, 5.72%.
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