One-pot synthesis of octahydroqinazolinones derivatives catalyzed by [C4(mim)2](FeCl4)2 under solvent free conditions

Article abstract of DOI:10.1002/jccs.201300358

In this investigation, a practical green chemistry procedure for synthesis of octahydroqinazolinones and thiones derivatives via condensation of aldehyde, 1,3-cyclohexanedione/dimedone and urea or thiourea catalyzed by magnetic room temperature dicationic liquid under solvent free conditions is described. The catalyst was studied by UV spectroscopy, vibrating sample magnetometer, and thermogravimetric analysis. This methodology is of interest due to several advantages such as environmental benign, easy experimental procedure, good yield and reusable catalyst. We have successfully developed a simple and green catalytic procedure for the efficient synthesis of xanthenes using [C₄(mim)₂](FeCl₄)₂ and under mild reaction conditions. [C₄(mim)₂](FeCl₄)₂ can replace the ILs and other homogeneous catalysts with reasonable recovery and reusability and therefore suitable for industrial applications. Copyright

Full text of DOI:10.1002/jccs.201300358

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
One-pot Synthesis of Octahydroqinazolinones Derivatives Catalyzed by
[C4(mim)2](FeCl4)2 under Solvent Free Conditions
Bijan Mombani Godajdar* and Soghra Soleimani
Department of Chemistry, Islamic Azad University Omidiyeh Branch, Omidiyeh, Iran
(Received: Jul. 13, 2013; Accepted: Nov. 2, 2013; Published Online: ??; DOI: 10.1002/jccs.201300358)
In this investigation, a practical green chemistry procedure for synthesis of octahydroqinazolinones and
thiones derivatives via condensation of aldehyde, 1,3-cyclohexanedione/dimedone and urea or thiourea
catalyzed by magnetic room temperature dicationic liquid under solvent free conditions is described. The
catalyst was studied by UV spectroscopy, vibrating sample magnetometer, and thermogravimetric analy-
sis. This methodology is of interest due to several advantages such as environmental benign, easy experi-
mental procedure, good yield and reusable catalyst.
Keywords: One-pot condensation; Solvent free conditions; Octahydroquinazolinone; Reusable cat-
alyst.
INTRODUCTION
Multicomponent reactions have recently attracted a
because of their vanishing vapour pressure, thermal and
chemical stability, air and moisture stability, wide liquids
range, solvent capability, etc.7 However the large scale ap-
plication of ionic liquids is still far from realization because
of their high cost and difficult recovery.
considerable attention in organic synthesis owing to their
ability to produce the target products in a single operation
without isolating the intermediates. They not only reduce
the reaction time and energy but also reduce the waste
product generation.1-2
In comparison to the common monocationic ionic liq-
uids, dicationic ionic liquids are an important class of or-
ganic salts having two positive charges on the same or dif-
ferent cations. They have been proved to have a better per-
formance in terms of thermal stability, wide liquids range,
and unusual dissolution properties.8
Octahydroquinazolinone derivatives have attracted
considerable attention, due to their potential antibacterial
activity against phylococcus aureus, Escherichia coli,
Pseudomonas aeruginosa and also as a calcium antago-
nist.3,4 Although various Lewis acid catalysts are em-
ployed,5 in the extension of the Biginelli reaction, many of
these reported one-pot synthesis suffer from limitations
such as the use of expensive reagents, strong acidic condi-
tions, and long reaction times, sluggish procedures and for-
mation of many side product. Hence, to avoid these draw-
backs, the application of milder and more efficiently ap-
proaches with higher yield are needed.
Recently, magnetic ionic liquid was discovered as a
key material for green chemistry.9 Because magnetic ionic
liquid, MIL, has both general properties of ionic liquids
and strong magnetic response, the recovery system of this
MIL by using a magnetic field may be easy and does not use
high energy.10
Herein, we wish to report a simple, convenient and
efficient method for the use of 1,4¢-(butane-1,4-diyl)-bis-
(3-methylimidazolium) di[tetrachloroferrate(III)](B),
[C4(mim)2](FeC4)2, as catalyst for preparation of octahy-
droquinazolinone derivatives.
Room temperature ionic liquids (RTILs) are gener-
ally defined as salts that are liquid at or below room temper-
ature. The combination of ammonium, pyridinium, phos-
phonium or imidazolium cations with various inorganic or
organic anions led to a large amount of liquid salts with nu-
merous possible applications e.g. in the field of organic
synthesis, catalysis, biocatalysis, material science, chemi-
cal engineering, electrochemistry or separation processes.6
The increasing interest in RTILs is related to their possible
exploitation as environmentally friendly neoteric solvents
RESULTS AND DISCUSSION
1-Butyl-3-methylimidazolium tetrachloroferrate
([bmim]FeCl4) with magnetism was synthesized and first
reported by Hayashi et al. in 2004.11 Since then, the synthe-
ses of magnetic ILs have been focused on expanding syn-
thesis with different alkyl chain length of imidazole cations
* Corresponding author. Tel: +986114448041; Email: bmombini@gmail.com
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Article
Godajdar and Soleimani
or different magnetic metal anions.12 To the best of our
knowledge, there is no report for the preparation of
[C4(mim)2](FeC4)2. Scheme I illustrates the synthetic route
for the preparation of [C4(mim)2](FeC4)2 synthesized and
characterized in this study.
shown in Figure 2. There were three main steps of weight
loss, and the decomposition events took place at 210.0 °C,
319.3 °C and 547.2 °C. On the base of weight changes, the
first process was attributed to the loss of 1-methylimida-
zole (found 12.30% calc. 13.98%). The second event corre-
sponded to the loss of 1-methyyl-3-buyl imimdazole
(found 19% calc. 22.4%). The weight loss (about 29.90%)
during 400 °C to 800 °C was attributed to the decomposi-
tion of FeCl3 and the loss of chlorine is shown in Figure 2.
According to the differential scanning calorimeter (DSC)
result (data not shown), a major endothermic peak at 285 K
was observed, which could be assigned to the melting point
of [C4(mim)2](FeCl4)2.
As shown in Scheme I, the synthesis of [C4(mim)2]-
(FeCl4)2, involves two steps. First, 1,4-dichlorobutane was
reacted with two equivalents of N-methylimidazole in
methanol and under reflux conditions to afford dicationic
RTILs in quantitative yields. In the second step, the anions
of imidazolium based room temperature dicationic ionic
liquid, Cl-, were easily changed with FeCl4 anions by the
-
simple mixing with FeCl3 under neat conditions.
In order to determine the most appropriate reaction
conditions and evaluate the catalytic efficiency of
[C4(mim)2](FeCl4)2, we studied the influence amount of
[C4(mim)2](FeCl4)2 and temperature on the reaction times
and yields. Thus, the reaction of benzaldehyde, dimedone
and urea at 100 °C was selected as a model reaction and dif-
Synthesis of [C4(mim)2](FeCl4)2 as a mag-
netic room temperature dicationic ionic
liuquid
Scheme I
Due to the paramagnetic nature of the [C4(mim)2]-
(FeCl4)2, nuclear magnetic resonance technique could not
be used to confirm its structure. Instead, UV spectra was
used to characterize the [C4(mim)2](FeCl4)2 structure. The
UV spectrum is shown in Figure 1. [C4(mim)2](FeCl4)2
spectra exhibited absorption bands in the visible region at
Fig. 1. Visible absorption spectrum of [C4(mim)2]-
(FeCl4)2.
-
534, 620 and 680 nm which are characteristic for the FeCl4
anion.13
The magnetic properties of the [C4(mim)2](FeCl4)2
and FeCl3 were measured by vibrating sample magnetom-
eter, VSM, at the room temperature. The paramagnetic
linear response of [C4(mim)2](FeCl4)2 is similar to
iron(III) chloride. From M vs. H curves, the magnetiza-
tion value for [C4(mim)2](FeCl4)2 at the same field was
found to be 0.4 emu Oe g-1, lower than of FeCl3 (0.7 emu
Oe g-1).
The thermal gravity analysis curve of catalyst under a
nitrogen atmosphere at a heating rate of 10 °C min–1is
Fig. 2. TGA curve of [C4(mim)2](FeCl4)2.
2
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One-pot Synthesis of Octahydroqinazolinones
Table 1. Optimization of the amount catalyst for the synthesis of
the corresponding products in good to excellent yield (Ta-
ble 3, Scheme II). A broad range of aromatic aldehydes
having electron donating and electron withdrawing groups
were transformed into the corresponding products in high
yields. Substituent on the aromatic ring had no obviously
effect on yield or reaction time under the above optimal
conditions. Similarly, we have studied the condensation of
aldehyde, dimedone and thiourea. The reaction of thiourea
proceeded at lower rate to give Octahydrothioquinazoli-
none.
4a
[C4(mim)2](FeCl4)2
Entry
Time (h)
Yield (%)
(mol %)
1
2
3
4
0
1
1
1
1
0
10
20
30
60
87
88
a Reaction conditions: benzaldehyde (1 mmol), dimedone (1
mmol), urea (3 mmol) and X % mol of [C4(mim)2](FeCl4)2
Table 2. Effect of temperature on the synthesis of 4ab
Three-component one-pot synthesis of
Octahydroquinazolinone catalyzed by
[C4(mim)2](FeCl4)2
Scheme II
Temperature/
°C
[C4(mim)2](FeCl4)2
(mol %)
Time
(h)
Yield
(%)
25
20
20
20
20
20
1
1
1
1
1
0
60
55
66
87
88
80
100
120
b Reaction conditions: benzaldehyde (1 mmol), dimedone (1
mmol), urea (3 mmol) and 20% mol of [C4(mim)2](FeCl4)2,
solvent-free.
ferent amount of catalyst were investigated. The results are
illustrated in Table 1.
According to Table 1, the reaction without catalyst
under solvent free conditions was performed in order to es-
tablish the true effectiveness of the catalyst. It was found
that Octahydroquinazolinone was not made after 1h of
heating. The best result was obtained with 1: 1: 3 ratios of
aldehydes, dimedone, urea and 20% mol of [C4(mim)2]-
(FeCl4)2 after 1h at 100 °C.
The Cyclocondensation of 1,3-cyclohexanedione
with aldehydes and urea was also investigated. The reac-
tion of benzaldehyde was performed with 1,3-cyclohex-
anedione and urea under the same conditions. Interestingly,
the reaction was incomplete even after 3 h and only 5% of
the product was obtained. However, when the reaction
was performed in [C4(mim)2](FeCl4)2 at 100 °C, 91% of
1,2,3,4,5,6,7,8-octahydro-4-phenylquinazoline-2,5-dione
was obtained in 1 h. The generality of the condensation was
confirmed by carrying out reactions of different aldehydes
with 1,3-cyclohexanedione and urea (Scheme II). The re-
sults are listed in (Table 3, 4l-4o).
The excess of urea could be easily removed by simple
washing with cold deionised water. Thus, urea as an addi-
tional reagent was used to complete the reaction.
Next the effect of temperature on the rate of the reac-
tion was studied using the reaction of benzaldehyde, dime-
done, and urea in the presence of the optimum quantity of
[C4(mim)2](FeCl4)2 under solvent free conditions (Table
2). It was observed that the reaction did not proceed at
In view of the above experimental facts, we propose a
tentative mechanism for this multicomponent reaction,
which is depicted in Scheme II. Initially the counter-cation,
C4(mim)22+, of the ionic liquid, [C4(mim)2](FeCl4)2, acts as
a Lewis acid, catalyzed Knoevenagel condensation be-
tween the aldehyde and dimedone to generate adduct A,
which acts as Michael acceptor. The urea/thiourea attacks
to in adduct Ain a Michael-type fashion to produce an open
chain intermediate B. Intermediate B undergoes intramo-
lecular cyclization by the reaction of nucleophilic amino
o
room temperature. At 100 C, the reaction proceeded
smoothly to give the corresponding product in good yield.
Further increase in temperature to, 120 °C had little effect
on the rate of reaction. Therefore, we kept reaction temper-
ature at 100 oC as optimal temperature.
The generality of this reaction was examined using
several types of aldehydes. In all cases, the reactions gave
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Article
Godajdar and Soleimani
Table 3. Synthesis of various octahydroquinazolinone and
octahydrothioquinazolinone derivatives
Table 4. Comparison of the synthesis of 2a using different
catalysts
Time Yieldc
Time Yield
M.P (°C)Ref
Entry
Reaction condition
Entry
R
X
R'
(min)
(%)
(h)
(%)
4a
4b
4c
4d
4e
4f
H
4-Cl
3-F
O
O
O
O
O
O
O
S
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
60
60
87
91
87
84
86
86
83
81
82
80
79
85
88
84
81
290-29116
>30016
1
2
3
4
5
6
Conc.H2SO4/Ethanol/80 °Co[15 ]
Conc.H2SO4/H2O/RT[14]
9
3
6
2
5
1
70
85
54
67
15
87
133-13616
247-24916
297-30016
280-28216
301-30316
283-28616
273-27616
273-27516
283-28616
273-2767d
274-2787d
282-2837d
195-1987d
HClO4-SiO2(0.025 mmol)/CH3CN/ [16]
VCl3/CH3CN/Reflux[17]
60
3-OMe
3-NO2
3-Cl
4-NO2
H
60
TMSCl/CH3CN/Reflux[18]
60
[C4(mim)2](FeCl4)2/solvent-free/100 °C
50
4g
4h
4i
60
90
3-Cl
4-OMe
4-Br
H
S
100
120
120
60
perature and the precipitated product was separated by fil-
tration; then washed with water and dried. The solid prod-
uct was crystallized from aqueous ethanol to afford the
pure product. The aqueous phase was concentrated; the cat-
alyst was separated by a strong magnetic field of 1.5T. The
residue catalyst was washed with a mixed of ethyl ether and
deionized water and dried in a vacuum oven at 60 °C for
overnight and reused in the next run. The catalyst could be
reused for fourth times without significant decrease in
catalytic activity (Fig. 3).
4j
S
4k
4l
S
O
O
O
O
4m
4n
4o
4-Br
4-Cl
2-OMe
H
60
H
60
H
70
c Isolated yield
function to carbonyl group followed by dehydration C to
form octahydroqinazolinone.
In order to show the merit of the present work in com-
pared the results of the synthesis of Octahydroquinazo-
linone (Table 3-entry 1) in the presence of H2SO4/Ethanol,
H2SO4/H2O, HClO4-SiO2, VCl3/CH3CN and TMSCl/
CH3CN with respect to the reaction times (Table 4). The
yield of product in the presence of [C4(mim)2](FeCl4)2 is
comparable with these catalysts. However, other catalysts
in Table 4 required longer reaction times than [C4(mim)2]-
(FeCl4)2.
Scheme III Proposed reaction mechanism
EXPERIMENTAL
General remarks: Melting points were measured on an
Success of the above reactions prompted us to inves-
tigate the recyclability of catalyst. We carried out our study
by using the reaction benzaldehyde, dimedone and urea
and under optimal conditions as a model study. After com-
pletion of the reaction (the progress of the reaction was
monitored by TLC), the mixture was cooled to room tem-
Fig. 3. Recyclability of the catalyst.
4
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CHEMICAL SOCIETY
One-pot Synthesis of Octahydroqinazolinones
Electrothermal 9100 apparatus andare uncorrected. H & 13C
NMR spectra were recorded on a Bruker Advanced DPX 400
MHz instrument spectrometer using TMS as the internal standard
in CDCl3. IR spectra were recorded on a BOMEM MB-Series
1988 FT-IR spectrometer. Aldehydes and ethylacetoacetate were
purchased from Merck Company in high purity. Products were
characterized by comparison of their physical and spectroscopic
data with those of known samples. The purity determination of
the products and reaction monitoring were accomplished by TLC
on silica gel Poly Gram SILG/UV 254 plates.
9.42 (sbr, 1H, NH); 10.37 (sbr, 1H, NH).
1
4a: Mp 290-292 °C, IR (KBr) nmax 3320 (br), 2963 (br),
1708 (s), 1672 (s), 1445 (w), 1367 (s) cm-1. 1H NMR (400 MHz,
CDCl3), d = 0.96 (s, 3H, Me); 1.10 (s, 3H, Me); 2.18 (q, 2H, CH2);
2.39 (q, 2H, CH2); 5.26 (d, 1H, CH); 7.32-7.21 (m, 5H, Ar); 7.45
(s, 1H, NH); 9.37 (s, 1H, NH). 4j: Mp 273-275 °C; IR (KBr) nmax
3250 (br), 3140 (br), 2954 (br), 1640 (vs), 1582 (vs), 1373 (s),
1168 (s) cm-1; 1H NMR (400 MHz, CDCl3), d = 0.98 (s, 3H, Me);
1.10 (s, 3H, Me); 2.13 (q, 2H, CH2); 3.11 (s, 2H, CH2); 3.75 (s,
3H, OCH3), 5.17 (d, 1H, CH); 6.81 (d, 2H, Ar); 7.20 (d, 2H, Ar);
9.42 (s, 1H, NH); 10.34 (s, 1H, NH).
Procedure for the preparation of [C4(mim)2])Cl)2: 1,4-
Dicholorobutane (1 mmol) was reacted with 1-methylimidazole
(2 mmol), respectively, stirred in methanol, refluxed for 24 h, and
then precipitated from ethyl acetate to obtain the required product
(white solid 1a, yield 94%).
ACKNOWLEDGEMENTS
We gratefully acknowledge financial support from
the Research Council of Islamic Azad University, Science
and Research Branch of Omidiyeh.
Procedure for the preparation of [C4(mim)2](FeCl4)2 as
a magnetic room temperature dicationic ionic liquid:
[C4(mim)2](FeCl4)2, was prepared by mixing crystal powder of
[C4(mim)2](Cl)2 (1 mmol) with anhydrous FeCl3 (2 mmol) at
room temperature for 3 h, a dark brown liquid was obtained. The
obtained [C4(mim)2](FeCl4)2 was extracted with small amount of
ethyl acetate. The solvent was evaporated and resulting clear
brown liquid was dried in vacuum oven at 60 °C for 24 h. The
[C4(mim)2](FeCl4)2 was obtained in high yield.
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