One-pot synthesis of tetrahydrobenzo[b]pyrans catalyzed by PEG-1000 bridged primary amine functionalized dicationic ionic liquid in water

Article abstract of DOI:10.1002/jccs.201300285

A novel poly (ethylene glycol) bridged primary amine functionalized dicationic ionic liquid ([PAPEG₁₀₀₀-DIL][BF₄]) was synthesized and characterized by ¹H-NMR, ¹³C-NMR, FT-IR and ESI-MS. The thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis indicated the high thermal stability of [PA-PEG ₁₀₀₀-DIL][BF₄]. It was used as an efficient and recyclable catalyst for the synthesis of substituted tetrahydrobenzo[b]pyrans through a one-pot three-component condensation of aromatic aldehydes, malononitrile and dimedone in 86% ～ 96% yields within 10 ～ 30 min in water. This method offers several advantages such as mild reaction conditions, simple operation and environmental friendliness. Furthermore, the catalyst could be easily recovered and reused for at least five runs without obvious loss of catalytic activity.

Full text of DOI:10.1002/jccs.201300285

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
One-pot Synthesis of Tetrahydrobenzo[b]pyrans Catalyzed by PEG-1000 Bridged
Primary Amine Functionalized Dicationic Ionic Liquid in Water
a
Ying-Lei Wang, Zhuo Li, Jun Luo * and Zu-Liang Liu
b
a
a
a
School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
College of Forestry, Henan Agricultural University, Zhengzhou 450002, China
b
(Received: Jun. 3, 2013; Accepted: Aug. 13, 2013; Published Online: Oct. 7, 2013; DOI: 10.1002/jccs.201300285)
A novel poly (ethylene glycol) bridged primary amine functionalized dicationic ionic liquid ([PA-
1
13
PEG1000-DIL][BF
thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis indicated the
high thermal stability of [PA-PEG1000-DIL][BF ]. It was used as an efficient and recyclable catalyst for the
4
]) was synthesized and characterized by H-NMR, C-NMR, FT-IR and ESI-MS. The
4
synthesis of substituted tetrahydrobenzo[b]pyrans through a one-pot three-component condensation of ar-
omatic aldehydes, malononitrile and dimedone in 86% ~ 96% yields within 10 ~ 30 min in water. This
method offers several advantages such as mild reaction conditions, simple operation and environmental
friendliness. Furthermore, the catalyst could be easily recovered and reused for at least five runs without
obvious loss of catalytic activity.
Keywords: Primary amine; Poly(ethylene glycol); Ionic liquid; Tetrahydrobenzo[b]pyran; Water.
INTRODUCTION
Tetrahydrobenzo[b]pyrans and their derivatives have
tedious work-up procedures. Consequently, the investiga-
tion for the efficient and environmentally benign method to
construct these valuable heterocyclic compounds is still at-
tractive.
attracted strong interest due to their useful biological and
pharmacological properties, such as anti-coagulant, di-
uretic, spasmolytic, anticancer and anti-anaphylactic activ-
Ionic liquids (ILs) have attracted considerable atten-
tion for the application in organic transformation due to
their favorable properties in relation to green chemistry in-
cluding high thermal and chemical stability, excellent elec-
1
ity. Some 2-amino-4H-pyrans can be employed as photo-
active materials, pigments and potential biodegradable
2
agrochemicals. Furthermore, substituted 4H-pyrans also
3
constitute a structural unit of some natural products. Gen-
8
trical conductivity and negligible vapor pressure. In recent
erally, the conventional methods for the synthesis of these
heterocyclic compounds involve acid- or base-catalyzed
condensation of 5,5-dimethylcyclohexane-1,3-dione (di-
medone) with aromatic aldehydes and malononitrile. A
number of procedures have been reported using a variety of
catalysts such as hexadecyltrimethyl ammonium bromide
years, functionalized ionic liquids (FILs), which incorpo-
rate functional groups as a part of the cation and/or anion,
9
have been developed and applied in various fields. FILs
have been used not only as alternative solvents, but also as
reagents and/or catalysts in synthetic organic chemistry.
Base functionalized ionic liquids are one of the important
4
a
4b
10
(
(
HTMAB), rare earth perfluorooctanoate (RE(PFO)
3
),
FILs and have aroused unprecedented interest. A number
4
S)-proline, tetramethyl ammonium hydroxide (TMAH),
c
4d
of basic ionic liquids including 1,1,3,3-N,N,N’,N’-tetra-
11a
4
e
4f
tetrabutylammonium fluoride (TBAF), MgO, N-meth-
4h
, CeCl
methylguanidinium trifluoroacetate (TMGT), 1-butyl-
11b,11c
4
g
ylimidazole, Na
4i
O, K
4j
, Ce(SO
2
SeO
4
3
·7H
2
3
PO
4
4 2
) ·
3-methyl imidazolium hydroxide ([bmim][OH]),
N,N-
4
O, LiBr, tetrabutylammonium bromide (TBAB),
k
4l
4m
4
1
H
2
dimethylaminoethylbenzyldimethylammonium chloride
+
4
,4-diazabicyclo[2.2.2]octane (DABCO) and phenyl-
n
-
11d
2 2 2 2 2
([PhCH Me N CH CH NMe ][Cl ]), triethylenetetra-
11e
ammonium trifluoroacetate ([TETA][TFA]), 4-amino-
4
o
boronic acid. Occasionally, these reactions were per-
5
formed under microwave and ultrasound irradiations or
7
in an electrocatalytic system. However, each of them suf-
6
1-(2,3-dihydroxy propyl) pyridinium hydroxide ([ADPPY]
11f
[OH]), triethylammonium acetate ([TEAA]) and 2-hy-
11g
1
1h
fers from at least one of the following limitations: low
yields, long reaction times, harsh reaction conditions, poor
catalyst recyclability, application of special apparatus and
droxyethylammonium formate have been successfully
used as catalysts for the synthesis of tetrahydrobenzo[b]py-
rans derivatives.
*
Corresponding author. Tel: +86-25-84315514; Fax: +86-25-84315030; Email: luojun@njust.edu.cn
J. Chin. Chem. Soc. 2013, 60, 1431-1436
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1431

Article
Wang et al.
o
uid has a low glass transition temperature of -37 C. In ad-
In a continuation of our research on poly(ethylene
1
glycol) functionalized bridged dicationic ionic liquids,
2
dition, the solubility of [PA-PEG1000-DIL][BF ] was deter-
4
we herein reported a novel primary amine functionalized
poly(ethylene glycol) bridged dicationic ionic liquid ([PA-
mined at room temperature. In general, it is soluble in wa-
ter, dichloromethane, acetone, acetonitrile, dimethyl sulf-
oxide (DMSO) and N,N-dimethylformamide (DMF), and
insoluble in petroleum ether, hexane, cyclohexane, ethyl
ether and ethyl acetate.
PEG1000-DIL][BF
4
]) (Scheme I) and used it as efficient and
recyclable catalyst for the preparation of tetrahydrobenzo-
[
b]pyrans derivatives in water.
[
4
PA-PEG1000-DIL][BF ] was then used to catalyze the
Scheme I The synthetic route of [PA-PEG1000-DIL]
one-pot three-component condensation to prepare tetrahy-
drobenzo[b]pyrans in water. To optimize the reaction con-
ditions, benzaldehyde, malononitrile and dimedone were
chosen as the model reactants. Selected results from our
screening experiments are summarized in Table 1. Only
[
4
BF ]
7
4
1% yield was obtained when [PA-PEG1000-DIL][BF ] was
used as both catalyst and solvent, which might result from
the inefficient mass transfer due to high viscosity of ionic
liquid (Table 1, Entry 1). The yield was lower when the re-
action was carried out in water under reflux without any
catalyst (Table 1, Entry 2). Subsequently, the influence of
catalyst loading on the reaction was examined. It is clear
that the yield was promoted along with the increase of cata-
lyst loading, and the optimal catalyst loading was 5 mol%
(
Table 1, Entries 3-7). In addition, low temperature decel-
RESULTS AND DISCUSSION
erated the reaction rate and lead to lower yields (Table 1,
Fig. 1. The TGA spectra of [PA-PEG1000-DIL][BF4].
Fig. 2. The DSC spectra of [PA-PEG1000-DIL][BF4].
The preparation route of primary amine function-
alized poly(ethylene glycol) bridged dicationic ionic liquid
is shown in Scheme I. It was readily prepared through a six-
step procedure from commercially available starting mate-
rials and reagents with good yields. Firstly, the PEG-1000
dichloride (1) and PEG-1000 bridged di-imidazolium com-
pound (2) were prepared according to our previous re-
1
2
ported method. Two methods for preparing [PA-PEG1000
-
DIL][BF ] were investigated. The first method was the
4
classical approach with the quaternization of PEG-1000
bridged di-imidazolium compound and 4-bromobutan-1-
amine hydrobromide. However, this method suffered from
tedious workup and it was almost impossible to purify the
ILs. In the other method, the quaternization of PEG-1000
bridged di-imidazolium compound and N-(4-bromobutyl)-
-
phthalimide (3) was conducted, and then the Br was ex-
-
changed with BF
4
. Finally, the target ionic liquid [PA-
PEG1000-DIL][BF
4
] could be obtained in high purity by
hydrazinolysis. The thermal property of this ionic liquid
was determined by thermal gravimetric analysis (TGA,
Fig. 1) and differential scanning calorimetry (DSC, Fig. 2).
From Fig. 1, we found that the [PA-PEG1000-DIL][BF
4
] has
good thermal stability. As depicted in Fig. 2, this ionic liq-
1432
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Synthesis of Tetrahydrobenzo[b]pyrans by [PA-PEG-DIL][BF4] in Water
Table 1. Screening reaction conditions for the model condensa-
[
tion
Table 2. Synthesis of tetrahydrobenzo[b]pyrans catalyzed by
[a]
a]
[PA-PEG1000-DIL][BF ] in water
4
R
O
O
CHO
[
PA-PEG1000-DIL][BF4]
O
O
O
+
NC
CN
+
CHO
[
PA-PEG1000-DIL][BF4]
o
O
CN
NC
CN
+
R
+
CN
H2O, 100
C
O
NH2
O
NH2
5
Catalyst
o
T ( C) Solvent t (min) Yield (%)
[b]
[
b]
Entry
Entry
R
t (min)
Product
Yield(%)
loading (%)
1
2
3
4
5
6
7
8
9
H
20
12
12
15
12
12
10
10
15
15
30
25
25
30
30
20
5a
5b
5c
5d
5e
5f
92
95
94
94
95
94
96
96
94
93
90
89
91
88
86
90
1
2
3
4
5
6
7
8
9
10
-
100
100
100
100
100
100
100
90
-
20
20
20
20
20
20
20
20
30
71
38
53
85
92
91
92
86
79
4-Cl
3-Cl
H O
2
1
H O
2
2-Cl
3
H O
2
4-Br
5
H O
2
4-F
7
H O
2
4-NO2
3-NO2
2-NO2
2,4-Cl2
4-CH3
4-OH
5g
5h
5i
10
5
H O
2
H O
2
5
80
H O
2
1
1
1
1
1
1
1
0
1
2
3
4
5
6
5j
[
a] Reaction conditions: benzaldehyde (2 mmol), malononitrile (2
mmol), dimedone (2 mmol), water (2 mL).
b] Isolated yield.
5k
5l
[
4-CH O
3
5m
5n
5o
5p
3-OH-4-CH O
3
4-Me N
2
Entries 8-9).
The simple recovery and reuse of catalyst is highly
preferable in terms of green synthetic process. The reus-
ability of [PA-PEG1000-DIL][BF ] was exemplified on the
2-Furyl
[a] Reaction conditions: aromatic aldehyde (2 mmol), malono-
nitrile (2 mmol), dimedone (2 mmol), [PA-PEG1000-DIL][BF4]
o
(0.1 mmol), water (2 mL), 100 C.
4
[
b] Isolated yield.
above model reaction. After the separation of product by
filtration, the liquor containing the catalyst was reused for
the next run without any treatment. As shown in Fig. 3, the
(
such as nitro and halides) (Table 2, Entries 2-10) required
[
4 2
PA-PEG1000-DIL][BF ]/H O system could be reused at
a shorter reaction time but provided higher yields than
those with electron-donating groups (such as methyl, hy-
droxyl, methoxyl and N,N-dimethylamino) (Table 2, En-
tries 11-15). Notably, the sterically demanding ortho and
meta substituents did not hamper the reaction (Table 2, En-
tries 2-4 and Entries 7-9). Moreover, heteroaromatic alde-
hyde could also successfully convert to the corresponding
tetrahydrobenzo[b]pyran product with excellent yield (Ta-
ble 2, Entry 16).
least five runs without obvious loss of the catalytic activ-
ity.
Subsequently, we investigated the scope and general-
ity of the present method by the reaction of various aro-
matic aldehydes with malononitrile and dimedone under
the optimized conditions. The results are listed in Table 2.
Aromatic aldehydes with electron-withdrawing groups
CONCLUSION
In summary, we have prepared a novel primary amine
functionalized poly(ethylene glycol) bridged dicationic
ionic liquid and used it as catalyst for the synthesis of tetra-
hydrobenzo[b]pyran derivatives by the one-pot three-com-
ponent reaction of aromatic aldehydes, malononitrile and
dimedone in water. The attractive features of this protocol
are environmental benign, mild reaction conditions, short
reaction times, excellent yields, broad substrate scope, sim-
ple work-up procedure and good reusability.
Fig. 3. The recycling of [PA-PEG1000-DIL][BF
system.
4 2
]/H O
J. Chin. Chem. Soc. 2013, 60, 1431-1436
© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1433

Article
Wang et al.
EXPERIMENTAL
4H), 3.59 (t, J = 6.9 Hz, 4H), 3.54-3.40 (m, 88H), 1.85-1.75 (m,
General. All reagents were commercially available and
4H), 1.59-1.50 (m, 4H).
used without further purification. Melting points were determined
1
on digital melting-point apparatus and are uncorrected. H NMR
4
Synthesis of [PA-PEG1000-DIL][BF ]. Amixture of hydra-
zine hydrate (80%, 30 mL) and 4 in methanol (60 mL) was heated
under reflux for 12 h. Then the solvent and excess hydrazine hy-
drate was removed by evaporation in vacuum, the residue ob-
1
3
and C NMR were recorded on Bruker Avance III (500 MHz) and
tetramethylsilane (TMS) was used as internal standard. Mass
spectra were taken on Agilent Liquid chromatography-mass spec-
trometry (LC-MS) 1100 series instrument in the electrospray ion-
ization [positive electrospray ionization (ESI)] mode. IR spectra
were recorded in KBr disks with a Shimadzu Prestige-21 FT-IR
spectrometer. The thermo gravimetric analysis (TGA) was per-
formed on Mettler Toledo TGA/SDTA851e thermal analyzer.
Samples were loaded into an aluminium oxide crucible and
tained was dissolved in CH
2 2
Cl and the phthalhydrazide precipi-
tated was filtered off. After the solvent was removed, ionic liquid
4
[PA-PEG1000-DIL][BF ] was finally obtained (21.5 g, yield 80%).
1
H NMR (500 MHz, d-DMSO, ppm) d 9.25 (s, 2H), 7.83 (s, 2H),
7.78 (s, 2H), 4.37-4.33 (m, 4H), 4.21 (t, J = 7.2 Hz, 4H), 3.79-3.75
(m, 4H), 3.67-3.28 (m, 107H), 2.70 (t, J = 7.2 Hz, 4H), 1.84 (dt, J
1
= 14.8, 7.3 Hz, 4H), 1.45 (dt, J = 14.6, 7.3 Hz, 4H); C NMR (126
3
o
-1
o
heated at a rate of 20 C·min from 50 C to 500 C under N
o
2
. The
MHz, d-DMSO, ppm) d 136.88, 123.32, 122.65, 70.23, 70.06,
-
69.99, 68.56, 49.30, 48.72, 27.07, 26.04; IR (cm ) 3421, 2865,
1
differential scanning calorimetry (DSC) was performed on a
o
Mettler Toledo DSC823e, and heated at a rate of 10 C·min from
-1
1563, 1453, 1348, 1297, 1250, 1088, 946, 844, 757, 643, 546;
o
50 C to 200 C under N
o
2+
ESI-MS: 396.45 (M /2, n = 16), 410.63 (M /2, n = 17), 424.51
2+
-
2
. N-(4-bromobutyl)phthalimide (3) was
2
(M /2, n = 18), 440.00 (M /2, n = 19).
+
2+
synthesized by a modified synthetic procedure described in the
3
literature.
1
General procedure for the synthesis of tetrahydroben-
zo[b]pyran derivatives. Aromatic aldehyde (2 mmol), malono-
Synthesis of primary amine functionalized poly(ethyl-
ene glycol) bridged dicationic ionic liquid
nitrile (2 mmol), dimedone (2 mmol) and [PA-PEG1000-DIL][BF
4
]
1
Synthesis of N-(4-bromobutyl)phthalimide (3). A mix-
3
(0.1 mmol) were added into H O (2 mL), the mixture was stirred
2
ture of phthalimide (7.4 g, 0.05 mol), K CO (20.7 g, 0.15 mol)
2
3
under reflux for certain time. The end of the reaction was moni-
tored by TLC. After completion of the reaction, the reaction mix-
ture was cooled to room temperature, the precipitate was filtered
out and washed with water. The resulting solid was purified by
recrystallization from ethanol (95%) to afford the pure product.
All the products are reported compounds and their melting points
and 1,4-dibromobutane (18.1 mL, 0.15 mol) was stirred in ace-
o
tone (100 mL) at 50 C for 12 h. The solvent was then evaporated
under vacuum and the residue was dissolved in water (100 mL)
and CH
aqueous solution was extracted with CH
combined organic solution was dried over Na
2
Cl
2
(50 mL). The organic layer was separated out and the
Cl (3 × 50 mL). The
SO , filtered and
2
2
1
and H NMR data were found to be identical with those reported
2
4
concentrated to give the crude product, pure N-(4-bromobutyl)-
phthalimide was obtained as a colorless solid by column chroma-
tography (silicagel, ethyl acetate/petroleum = 1:4), 12.2 g, yield
in literature.
Characterization data of products. 5a: White solid; M.
o
4d
o
1
P.: 229-230 C (Lit. M. P.: 228-230 C); H NMR (500 MHz,
d-DMSO, ppm) d 7.32-7.16 (m, 5H), 6.10 (s, 2H), 4.32 (s, 1H),
2.56-2.46 (m, 2H), 2.24 (d, 1H), 2.15 (d, 1H), 1.05 (s, 3H), 0.98 (s,
o
1
6%. M. P.: 73-74 C; H NMR (500 MHz, CDCl
8
3
, ppm) d 7.85
(
dd, J = 5.4, 3.1 Hz, 2H), 7.72 (dd, J = 5.5, 3.0 Hz, 2H), 3.73 (t, J =
o
3H). 5b: White solid; M. P.: 210-212 C (Lit. M. P.: 209-210 C);
4g
o
6
.8 Hz, 2H), 3.45 (t, J = 6.4 Hz, 2H), 1.95-1.81 (m, 4H).
1
Synthesis of compound 4. A mixture of 2 (20.5 g) and 3 in
H NMR (500 MHz, d-DMSO, ppm) d 7.32 (d, J = 8.0 Hz, 2H),
o
toluene (80 mL) was stirred at 70 C for 48 h. An oily liquid grad-
ually precipitated from the toluene solution along with the reac-
tion. After completion, the solvent was removed in vacuum and
the residue was washed repeatedly with ethyl acetate, followed by
evaporation under reduced pressure to yield yellow oil. Subse-
7.18 (d, J = 8.0 Hz, 2H), 7.06 (s, 2H), 4.18 (s, 1H), 2.54-2.48 (m,
2H), 2.25 (d, J = 16.0 Hz, 1H), 2.10 (d, J = 16.0 Hz, 1H), 1.04 (s,
o
4a
3H), 0.96 (s, 3H). 5c: White solid; M. P.: 224-226 C (Lit. M. P.:
o
224-225 C); H NMR (500 MHz, d-DMSO, ppm) d 7.28-7.18 (m,
1
4H), 4.56 (s, 2H), 4.40 (s, 1H), 2.50-2.46 (m, 2H), 2.25 (s, 2H),
o
1.12 (s, 3H), 1.06 (s, 3H). 5d: White solid; M. P.: 215-217 C
quently, NaBF
4
(8.4 g) and CH
2
Cl
2
(50 mL) were added and the
4
g
o
1
mixture was stirred at ambient temperature for 48 h. After filtra-
(Lit. M. P.: 215-216 C); H NMR (500 MHz, d-DMSO, ppm) d
7.36-7.14 (m, 4H), 7.04 (s, 2H), 4.58 (s, 1H), 2.58-2.46 (m, 2H),
2.24 (d, J = 16.0 Hz, 1H), 2.08 (d, J = 16.0 Hz, 1H), 1.04 (s, 3H),
tion and removal of solvent, 4 was obtained and used directly for
1
the next reaction. H NMR (500 MHz, d-DMSO, ppm) d 9.18 (s,
o
4d
0.98 (s, 3H). 5e: White solid; M. P.: 208-210 C (Lit. M. P.:
2
H), 7.86-7.81 (m, 8H), 7.80 (d, J = 1.5 Hz, 2H), 7.78 (d, J = 1.4
o
207-209 C); H NMR (500 MHz, d-DMSO, ppm) d 7.50 (d, J =
1
Hz, 2H), 4.36-4.31 (m, 4H), 4.21 (t, J = 7.1 Hz, 4H), 3.78-3.73 (m,
1434
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Synthesis of Tetrahydrobenzo[b]pyrans by [PA-PEG-DIL][BF4] in Water
8
2
1
.0 Hz, 2H), 7.14 (d, J = 8.0 Hz, 2H), 7.06 (s, 2H), 4.22 (s, 1H),
.56-2.44 (m, 2H), 2.25 (d, J = 16.0 Hz, 1H), 2.13 (d, J = 16.0 Hz,
o
H), 1.07 (s, 3H), 0.99 (s, 3H). 5f: White solid; M. P.: 190-192 C
21002050), the “Zijin Star Project” and the “Excellence
Initiative Project” of NUST.
1
1c
o
1
Lit. M. P.: 190-191 C); H NMR (500 MHz, d-DMSO, ppm) d
(
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7
2
1
.23-7.15 (m, 2H), 7.10-7.04 (m, 2H), 7.01 (s, 2H), 4.20 (s, 1H),
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o
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4
Lit. M. P.: 179-181 C); H NMR (500 MHz, d-DMSO, ppm) d
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o
1
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2
2
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o
08-209 C (Lit. M. P.: 208-211 C); H NMR (500 MHz, d-
4a
o
1
DMSO, ppm) d 7.98-7.42 (m, 4H), 4.98 (s, 2H), 4.54 (s, 1H),
.50-2.44 (m, 2H), 2.26 (s, 2H), 1.06 (s, 3H), 1.02 (s, 3H). 5i: Yel-
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2
o
low solid; M. P.: 228-229 C (Lit. M. P.: 227-230 C); H NMR
4m
o
1
4
. (a) Jin, T. S.; Wang, A. Q.; Wang, X.; Zhang, J. S.; Li, T. S.
Synlett 2004, 5, 871; (b) Wang, L. M.; Shao, J. H.; Tian, H.;
Wang, Y. H.; Liu, B. J. Fluorine. Chem. 2006, 127, 97; (c)
Saeed, B.; Morteza, B.; Ali, M. A.; Barahman, M. Synlett
(
(
500 MHz, d-DMSO, ppm) d 7.96-7.48 (m, 4H), 5.97 (s, 2H), 5.06
s, 1H), 2.46 (s, 2H), 2.15 (m, 2H), 1.08 (s, 3H), 0.97 (s, 3H). 5j:
o
4c
o
1
White solid; M. P.: 193-194 C (Lit. M. P.: 192-194 C); H
NMR (500 MHz, d-DMSO, ppm) d 7.56 (s, 1H), 7.39 (d, J = 8.0
Hz, 1H), 7.24 (d, J = 8.0 Hz, 1H), 7.13 (s, 2H), 4.71 (s, 1H),
2
006, 2, 263; (d) Saeed, B.; Masoumeh, S. A.; Morteza, B.
Catal. Commun. 2007, 8, 1724; (e) Shijay, G.; Cheng, H. T.;
Chi, T.; Ching, F. Y. Tetrahedron 2008, 64, 9143; (f)
Mohammad, S.; Hassan, S. Catal. Lett. 2008, 126, 275; (g)
Lian, X. Z.; Huang, Y.; Li, Y. Q.; Zheng, W. J. Monatshefte
fur Chemie 2008, 139, 129; (h) Rahim, H.; Soma, M.;
Khadijeh, B. Catal. Commun. 2008, 9, 307; (i) Gowravaram,
S.; Arundhathi, K.; Sudhakar, K.; Sastry, B. S.; Yadav, J. S.
Synth. Commun. 2009, 39, 433; (j) Pore, D. M.; Undale, K.
A.; Dongare, B. B.; Desai, U. V. Catal. Lett. 2009, 132, 104;
(k) Mohammad, R. I.; Elaheh, M. Phosphorus Sulfur 2009,
2
1
.63-2.47 (m, 2H), 2.27 (d, J = 16.0 Hz, 1H), 2.13 (d, J = 16.0 Hz,
o
H), 1.07 (s, 3H), 1.00 (s, 3H). 5k: White solid; M. P.: 214-216 C
4
g
o
1
Lit. M. P.: 214-215 C); H NMR (500 MHz, d-DMSO, ppm) d
(
7
4
1
.08 (d, J = 8.0 Hz, 2H), 7.02 (d, J = 8.0 Hz, 2H), 6.94 (s, 2H),
.12 (s, 1H), 2.58-2.46 (m, 2H), 2.28 (s, 3H), 2.24 (d, J = 16.0 Hz,
H), 2.10 (d, J = 16.0 Hz, 1H), 1.06 (s, 3H), 0.98 (s, 3H). 5l: Yel-
o
4d
o
1
low solid; M. P.: 203-205 C (Lit. M. P.: 204-205 C); H NMR
500 MHz, d-DMSO , ppm) d 7.12-6.76 (m, 4H), 5.36 (s, 2H),
.24 (s, 1H), 2.44 (s, 2H), 2.24-2.16 (m, 2H), 1.10 (s, 3H), 1.05 (s,
(
3
1
84, 3134; (l) Sun, W. B.; Zhang, P.; Fan, J.; Chen, S. H.;
4
o
H). 5m: Yellow solid; M. P.: 201-202 C (Lit. M. P.: 201-203
1
C); H NMR (500 MHz, d-DMSO, ppm) d 7.05 (d, J = 8.0 Hz,
4m
Zhang, Z. H. Synth. Commun. 2010, 40, 587; (m) Akbar, M.;
Mohammad, A. B. F. Acta Chim. Slov. 2010, 57, 931; (n)
Daryoush, T.; Jessica, A. B.; Sophia, I. B. Synth. Commun.
3
o
2
H), 6.96 (s, 2H), 6.84 (d, J = 8.0 Hz, 2H), 4.16 (s, 1H), 3.72 (s,
H), 2.54-2.44 (m, 2H), 2.25 (d, J = 16.0 Hz, 1H), 2.09 (d, J = 16.0
2
011, 41, 2701; (o) Sara, N.; Raouf, B.; Bertrand, C.;
3
Abdelmadjid, D. C. R. Chimie 2012, 15, 394.
Hz, 1H), 1.05 (s, 3H), 0.97 (s, 3H). 5n: White solid; M. P.:
5. (a) Ipsita, D.; Pulak, J. B. Tetrahedron Lett. 2004, 45, 8625;
(b) Anil, S.; Sanjay, K.; Jagir, S. S. Synlett 2006, 12, 1928;
o
4a
38-240 C (Lit. M. P.: 237-239 C); H NMR (500 MHz,
o
1
2
(
c) Feng, C.; Wang, Q. Y.; Lu, C. F.; Yang, G. C.; Chen, Z. X.
d-DMSO, ppm) d 6.85 (s, 1H), 6.78-6.56 (m, 3H), 5.25 (s, 2H),
Comb. Chem. High T. Scr. 2012, 15, 100.
4
3
.30 (s, 1H), 3.88 (s, 3H), 2.40 (s, 2H), 2.26-2.22 (m, 2H), 1.10 (s,
6
7
. (a) Li, J. T.; Xu, W. Z.; Yang, L. C.; Li. T. S. Synth. Commun.
o
H), 1.06 (s, 3H). 5o: Yellow solid; M. P.: 223-225 C (Lit. M.
4m
2
004, 34, 4565; (b) Davood, A.; Razieh, N. Y.; Fatemeh, S.;
o
1
P.: 223-225 C); H NMR (500 MHz, d-DMSO, ppm) d 7.25-7.13
m, 4H), 4.68 (s, 2H), 4.42 (s, 1H), 2.96 (s, 6H), 2.52-2.48 (m,
H), 2.25 (s, 2H), 1.04 (s, 3H), 0.98 (s, 3H). 5p: White solid; M.
Zahra, A. Lett. Org. Chem. 2012, 9, 435.
(
. (a) Michail, N. E.; Alexander, S. D.; Sergey, K. F.; Sergey, V.
G.; Ruslan, F. N.; Fedor, M. M.; Gennady, I. N. Eur. J. Org.
Chem. 2006, 4335; (b) Lida, F.; Majid, M. H.; Azadeh, F.;
Khadijeh, B. Tetrahedron Lett. 2007, 48, 5379.
2
o
4l
o
1
P.: 225-227 C (Lit. M. P.: 225-226 C); H NMR (500 MHz,
d-DMSO, ppm) d 7.36-6.18 (m, 3H), 5.26 (s, 2H), 4.44 (s, 1H),
8
9
. (a) Bourbigou, H. O.; Magna, D. M. Appl. Catal. A Gen.
2
.53 (s, 2H), 2.29 (s, 2H), 1.09 (s, 3H), 1.02 (s, 3H).
2
010, 373, 1; (b) Jason, P. H.; Tom, W. Chem. Rev. 2011, 111,
508; (c) Reddy, B. P.; Rajesh, K.; Vijayakumar, V. J. Chin.
3
ACKNOWLEDGEMENTS
Chem. Soc. 2011, 58, 384.
This project was financially sponsored and supported
by the National Natural Science Foundation of China (No.
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Chem. Int. Ed. 2010, 49, 2834; (c) Chen, H. L.; Wei, G. T. J.
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