ZrOCl2 · 8H2O: An efficient, ecofriendly, and recyclable catalyst for ultrasound-accelerated, one-pot, solvent-free synthesis of 8-aryl-7,8-dihydro-[1,3]dioxolo[4,5-g] quinolin-6-(5H)-one and 4-aryl-3,4-dihydroquinolin-2(1 H)-one derivatives

Article abstract of DOI:10.1080/00397911.2012.718026

A convenient, one-pot, solvent-free reaction of amines, aromatic aldehydes, and Meldrum's acid to form 8-aryl-7,8-dihydro-[1,3]dioxolo[4,5-g]quinolin-6- (5H)-one and 4-aryl-3,4-dihydroquinolin-2-(1H)-one in the presence of 10 mol% ZrOCl₂ · 8H₂O under ultrasonic irradiation is described. This new protocol offers several advantages including low catalyst loading, clean reaction, easy workup, use of recyclable and ecofriendly catalyst, short reaction times, good yields, and solvent-free conditions. Copyright

Full text of DOI:10.1080/00397911.2012.718026

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ZrOCl2 · 8H2O: An Efficient, Ecofriendly,
and Recyclable Catalyst for Ultrasound-
Accelerated, One-Pot, Solvent-Free
Synthesis of 8-Aryl-7,8-dihydro-
[1,3]dioxolo[4,5-g]quinolin-6-(5H)-one
and 4-Aryl-3,4-dihydroquinolin-2(1 H)-
one Derivatives
Davood Azarifar a & Davood Sheikh a
a Department of Chemistry , University of Bu-Ali Sina , Hamedan ,
Iran
Accepted author version posted online: 26 Mar 2013.Published
online: 03 Jun 2013.
To cite this article: Davood Azarifar & Davood Sheikh (2013): ZrOCl2 · 8H2O: An Efficient, Ecofriendly,
and Recyclable Catalyst for Ultrasound-Accelerated, One-Pot, Solvent-Free Synthesis of 8-Aryl-7,8-
dihydro-[1,3]dioxolo[4,5-g]quinolin-6-(5H)-one and 4-Aryl-3,4-dihydroquinolin-2(1 H)-one Derivatives,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 43:18, 2517-2526
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Synthetic Communications1, 43: 2517–2526, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2012.718026
ZrOCl2 ꢀ 8H2O: AN EFFICIENT, ECOFRIENDLY, AND
RECYCLABLE CATALYST FOR ULTRASOUND-
ACCELERATED, ONE-POT, SOLVENT-FREE SYNTHESIS
OF 8-ARYL-7,8-DIHYDRO-[1,3]DIOXOLO[4,5-g]
QUINOLIN-6-(5H)-ONE AND 4-ARYL-3,4-
DIHYDROQUINOLIN-2(1 H)-ONE DERIVATIVES
Davood Azarifar and Davood Sheikh
Department of Chemistry, University of Bu-Ali Sina, Hamedan, Iran
GRAPHICAL ABSTRACT
Abstract A convenient, one-pot, solvent-free reaction of amines, aromatic aldehydes, and
Meldrum’s acid to form 8-aryl-7,8-dihydro-[1,3]dioxolo[4,5-g]quinolin-6-(5H)-one and
4-aryl-3,4-dihydroquinolin-2-(1H)-one in the presence of 10 mol% ZrOCl2.8H2O under
ultrasonic irradiation is described. This new protocol offers several advantages including
low catalyst loading, clean reaction, easy workup, use of recyclable and ecofriendly cata-
lyst, short reaction times, good yields, and solvent-free conditions.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Synthetic Communications1 to view the free supplemental file.
Keywords Amine; 8-aryl-7,8-dihydro-[1,3]dioxolo[4,5-g]quinolin-6-(5H)-one; 4-aryl-3,4-
dihydroquinolin-2-(1H)-one; catalyst; Meldrum’s acid; ultrasound irradiation;
ZrOCl2 ꢀ 8H2O
INTRODUCTION
In recent years, zirconium compounds have been used as efficient and benign
catalysts in synthetic organic reactions[1–4] because these compounds are relatively
nontoxic, easy to handle, and stable. As evident from their LD50 (LD50
Received May 10, 2012.
Address correspondence to Davood Azarifar, Department of Chemistry, University of Bu-Ali Sina,
Hamedan 65178, Iran. E-mail: azarifar@basu.ac.ir
2517

2518
D. AZARIFAR AND D. SHEIKH
ZrOCl2 ꢀ 8H2O, oral rat ¼ 2950 mg=kg), Zr(IV) salts are considered as low-toxic cat-
alysts.[5] Recently, several synthetically useful organic transformations using these
catalysts have been reported in the literature.[6–9]
On the other hand, in recent years, the concept of speeding up synthetic trans-
formations by ultrasound activation has attracted considerable interest in organic
synthesis. The joint application of ultrasound irradiation and solid-phase catalysts
in the reactions under solvent-free conditions gives special attributes such as
enhanced reaction rate and improved yields in chemical processes. The passage of
ultrasonic irradiation through liquid leads to cavitation, which is accompanied by
a few extreme effects such as a local increase of temperature, local high pressure,
and the formation of intense liquid microflows.[10]
Moreover, multicomponent reactions (MCRs) have emerged as efficient and
powerful tools in modern synthetic organic chemistry for the achievement of good
levels of brevity and diversity. MCRs contribute to the requirements of an environ-
mentally friendly process by reducing the number of synthetic steps, energy
consumption, and waste production. Thus, MCRs have attracted considerable
interest because of their exceptional synthetic efficiency.[11–14]
Quinoline derivatives are a well-known class of heterocyclic compounds not
only in medicinal chemistry, because of their wide occurrence in natural products[15]
and drugs,[16,17] but also in polymer chemistry, electronics, and optoelectronics for
their excellent mechanical properties.[18,19] Diblock and triblock copolymers incor-
porating polyquinoline blocks have been found to undergo hierarchical self-assembly
into a variety of nano- and meso-structures with interesting electronic and photonic
functions.[20,21] To the best of our knowledge, no reports on the synthesis of
8-aryl-7,8-dihydro-[1,3]dioxolo[4,5-g]quinolin-6-(5H)-ones have been published so
far. Recently, synthesis of quinoline derivatives via aryl radical cyclization has been
reported.[22] An easier pathway for the preparation of aminoquinoline derivatives as
potential precursors of new serotoninerg agents by palladium-catalyzed amination
reactions of quinoline triflate is described.[23] As outlined before, the development
of new and more benign approaches for the synthesis of these compounds appears
challenging because of their biological and synthetic importance.
Solvent-free organic reactions have drawn much interest, particularly from the
viewpoint of green chemistry. Solvent-free reactions have some unique advantages,
such as the elimination of harmful organic solvents, which account for a great pro-
portion of the waste materials generated in synthesis and impose health and environ-
mental risks. Solvent-free reactions also minimize pollution and handling costs
because of the simplification of the experimental procedure.[24]
RESULTS AND DISCUSSION
In continuation of our research for the synthesis of nitrogen heterocycles,[25–27]
herein, we report an efficient solvent-free and one-pot synthesis of 8-aryl-7,8-dihydro-[1,3]-
dioxolo[4,5-g]quinolin-6-(5H)-one 4a–i and 4-aryl-3,4-dihydroquinolin-2(1H)-one 4j–k
from amine 1, aldehyde 2, and Meldrum’s acid 3 using ZrOCl2 ꢀ 8H2O with ultrasound
irradiation (Scheme 1).
To establish the reaction conditions, we examined the model reaction of
3,4-methylendioxyaniline, benzaldehyde, and Meldrum’s acid using 10 mol%

QUINOLIN-6-(5H)-ONE DERIVATIVES
2519
Scheme 1. ZrOCl2 ꢀ 8H2O-catalyzed, ultrasound-promoted synthesis of 8-aryl-7,8-dihydro-[1,3]-
dioxolo[4,5-g]quinolin-6-(5H)-ones 4a–i and 4-aryl-3,4-dihydroquinolin-2(1H)-ones 4j–k.
ZrOCl2 ꢀ 8H2O catalyst (Table 1, entry 1). The reaction was conducted using various
solvents such as MeOH, MeCN, EtOAc, dimethyl formamide (DMF), CCl4, Et2O,
and n-hexane as well as nonsolvent conditions under both conventional and ultra-
sound irradiation conditions at different temperatures with various catalyst loadings
(Table 1). As seen in this table, the best result in terms of the reaction time and yield
was obtained when the reaction was conducted using 10 mol% catalyst under nonsol-
vent and ultrasound irradiation conditions at 30–40 ꢁC. However, the yields obtained
Table 1. Screening of the reaction parameters on the synthesis of 8-aryl-7,8-dihydro-[1,3]-dioxolo-
[4,5-g]quinolin-6(5H)-onea
Entry
Conditions
Method
Catalyst loading (mol%)
Time (min)
Yield (%)b
1
2
Solvent-free=30–40 ꢁC
MeOH=30–40 ꢁC
MeCN=30–40 ꢁC
EtOAc=30–40 ꢁC
DMF=30–40 ꢁC
CCl4=30–40 ꢁC
Et2O=30–40 ꢁC
n-hexane=30–40 ꢁC
Solvent-free=30–40 ꢁC
Solvent-free=30–40 ꢁC
Solvent-free=30–40 ꢁC
Solvent-free=rt
Solvent-free=60 ꢁC
Solvent-free=100 ꢁC
Solvent-free=reflux
MeOH=rt
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Ultrasound
Thermal
10
10
10
10
10
10
10
10
5
30
40
40
40
40
40
40
40
30
30
30
40
40
40
40
40
40
40
40
40
40
40
40
95
80
83
84
85
79
83
70
89
92
89
82
81
81
75
79
82
83
84
77
76
75
65
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
15
20
10
10
10
10
10
10
10
10
10
10
10
10
Thermal
Thermal
Thermal
Thermal
MeCN=rt
EtOAc=rt
Thermal
Thermal
DMF=rt
CHCl3=rt
Thermal
Thermal
Et2O=rt
CCl4=rt
n-Hexane =rt
Thermal
Thermal
Thermal
a3,4-Methylendioxyaniline (0.137 g, 1 mmol), benzaldehyde (1 mmol), Meldrum’s acid (0.15 g, 1 mmol),
solvent (2 mL), ZrOCl2 ꢀ 8H2O (10 mol%).
bIsolated yields.

2520
D. AZARIFAR AND D. SHEIKH
Table 2. Effects of the catalyst on the ultrasound-promoted model reaction under
solvent-free conditiona
Entry
Catalyst
Time (min)
Yield (%)b
1
2
3
4
5
ZrOCl2 ꢀ 8H2O
MnCl2 ꢀ 4H2O
CdCl2 ꢀ 2H2O
Cd(NO3)2 ꢀ 4H2O
CeCl3 ꢀ 7H2O
30
30
30
30
30
95
79
74
69
74
a3,4-Methylendioxyaniline (0.137 g, 1 mmol), benzaldehyde (1 mmol), Meldrum’s
acid (0.15 g, 1 mmol), catalyst (10 mol%).
bIsolated yields.
using the solvents MeOH (80%), MeCN (83%), EtOAc (84%), and DMF (85%) were
comparable with that obtained under solvent-free conditions. In addition, the superi-
ority of ZrOCl2 ꢀ 8H2O as the catalyst over other metal halides such as
MnCl2 ꢀ 4H2O, CdCl2 ꢀ 2H2O, Cd(NO3)2 ꢀ 4H2O, and CeCl3 ꢀ 7H2O was studied under
ultrsound irradiation and nonsolvent conditions at 30–40 ꢁC as summarized in
Table 2. Among the catalysts examined, ZrOCl2 ꢀ 8H2O (10 mol%) exhibited the
greatest efficiency (entry 1).
To generalize this methodology, we subjected a series of other aromatic alde-
hydes having electron-donating as well as electron-withdrawing substituents to
obtain the corresponding 8-aryl-7,8-dihydro-[1,3]-dioxolo-[4,5-g]quinolin-6(5-
H)-ones and 4-aryl-3,4-dihydroquinolin-2(1H)-ones under the optimized conditions
(Table 3). In general, both types of substituents furnished faster reaction rates, offer-
ing the products in good yields (Table 3). On the other hand, it appears that the steric
effects do not influence the rates and yields of the reactions significantly. This can be
seen, for example, by comparing the reactions for 2- and 4-chlorobenzaldehyde
(entries e and f) or the reactions for 2- and 4-methoxybenzaldehyde (entries c and
d) in Table 3. Also we subjected a series of other aromatic amines such as anilin,
amines having electron-donating and electron-withrawing substituents, to obtain
the corresponding 8-aryl-7,8-dihydro-[1,3]-dioxolo-[4,5-g]quinolin-6(5H)-ones and
4-aryl-3,4-dihydroquinolin-2(1H)-ones under the optimized conditions (Table 3).
In general, both simple anilnes and amines having electron-donating substituents
furnished faster reaction rates, offering the products in good yields, but amines hav-
ing electron-withrawing substituents have very poor yield (Table 3). Generally, all
the products 4a–k exhibit two distinguished peaks at ranges d 3.15–2.74 ppm as a
multiplet for H-7 and d 4.76–4.05 ppm as a triplet for H-8 protons. Also, the
=
expected peaks for C-7, C-8, and C O carbon atoms were clearly exhibited at the
ranges d 41.8–22.6, 43.7–31.9 and 176.5–168.1 ppm respectively in their 13C NMR
spectra.
After completion of the reaction, hot absolute ethanol was added and the cata-
lyst was absorbed on the magnetic stirring bar. The separated catalyst was washed
with hot ethanol, dried in an oven at 120 ꢁC for 2 h, and reused directly with fresh
substrates under the optimized conditions. As shown in Table 4, it was noticed that
the catalyst can be recycled and reused for four consecutive runs without any notice-
able drop in its catalytic activity.

QUINOLIN-6-(5H)-ONE DERIVATIVES
2521
Table 3. Ultrasound-promoted synthesis of 8-aryl-7,8-dihydro-[1,3]-dioxolo-[4,5-g]quinolin-6(5H)-ones
4a–i and 4-aryl-3,4-dihydroquinolin-2(1H)-one 4j–k catalyzed by ZrOCl2 ꢀ 8H2O (10 mol%) under
solvent-free conditionsa
Entry
ArCHO 2
Product 4
Time (min)
Yield (%)b
a
C6H5
30
95
b
c
d
4-MeC6H4
35
35
35
83
84
82
2-MeOC6H4
4-MeOC6H4
e
2-ClC6H4
30
90
f
4-ClC6H4
25
91
g
2,4-Cl2C6H3
30
93
(Continued )

2522
D. AZARIFAR AND D. SHEIKH
Table 3. Continued
Product 4
Entry
ArCHO 2
Time (min)
Yield (%)b
h
2-NO2C6H4
30
88
i
3-BrC6H4
30
92
j
C6H5
45
80
k
2,4-Cl2C6H3
40
82
l
C6H5
90
Trace
m
C6H5
90
Trace
(Continued )

QUINOLIN-6-(5H)-ONE DERIVATIVES
Table 3. Continued
2523
Entry
ArCHO 2
Product 4
Time (min)
Yield (%)b
n
C6H5
90
Trace
o
C6H5
90
Trace
aAniline derivatives (1 mmol), benzaldehyde derivatives (1 mmol), Meldrum’s acid (0.15 g, 1 mmol), sol-
vent (2 mL), ZrOCl2 ꢀ 8H2O (10 mol%).
bIsolated yields.
The possible pathway to explain the formation of the products 4a–k is depicted
in Scheme 2. As illustrated in this mechanism, the ZrOCl2 ꢀ 8H2O catalyst initially
activates the aldehyde 2 to undergo the Knoevenagel condensation with the Mel-
drum’s acid 3 under ultrasound irradiation to generate the intermediate heterodyne
5. Subsequent addition of the amine 1 to this heterodyne 5 occurs to provide the
intermediate 6, which undergoes intramolecular nucleophilic attack on the carbonyl
carbon followed by successive decarboxylation to result in the formation of the
products 4a–k.
Scheme 2. A Putative pathway for the ZrOCl2 ꢀ 8H2O-catalyzed synthesis of 8-aryl-7,8-dihydro-[1,3]-
dioxolo-[4,5-g]quinolin-6(5H)-ones 4a–k.

2524
D. AZARIFAR AND D. SHEIKH
Table 4. Recycling of ZrOCl2 ꢀ 8H2O as the catalyst in
the synthesis of 8-aryl-7,8-dihydro-[1,3]dioxolo[4,5-g]
quinolin-6-(5H)-one 4a
Cycle
Yield (%)
1
2
3
4
95
94
93
92
EXPERIMENTAL
Chemicals used in this work were purchased from Aldrich and Merck chemical
companies and used without purification. Infrared (IR) spectra were recorded on a
Shimadzu 435-U-04 Fourier transform (FT) spectrophotometer from KBr pellets.
1H NMR and 13C NMR spectra were measured for samples in CDCl3 with a BRU-
KER DRX-400 AVANCE instrument at 400 and 100 MHz and also a Jeol FX 90Q
instrument at 90 MHz and 22.5 MHz respectively, using tetramethylsilane (TMS) as
an internal reference. Low-resolution (LR) MS (EI, 70 eV): FINNIGAN-MAT 8430
spectrometer. Melting points were measured on a SMPI apparatus. Elemental
analyses for C, H, and N atoms were performed using a Perkin–Elmer 2400 series
analyzer. Ultrasonication was performed in a TRANSSONI 660=H ultrasound clea-
ner with a frequency of 35 KHz and an output power of 70 W. The reactions were
performed in open vessels.
A flask containing a mixture of amine 1 (1 mmol), aldehyde 2 (1 mmol),
Meldrum’s acid 3 (0.15 g, 1 mmol), and ZrOCl2 ꢀ 8H2O (0.033 g, 0.1 mmol) was
placed in a water bath and sonicated at 30–40 ꢁC for an appropriate time (Table 3)
until the reaction was completed as monitored by thin-layer chromatography (TLC)
(n-hexane=EtOAc; 2:1) analysis. The reaction mixture was then washed with water
and the crude product was purified on 20 ꢂ 20 cm2 TLC plates coated with silica
gel 60 HF-254 using n-hexane=EtOAc (2:1) as eluent. The separated products were
first exposed to air for a few minutes and then dried in an oven at 100 ꢁC. For further
purification, the products were crystallized from MeOH. The structures of these pro-
ducts were found to fit the expected 8-aryl-7,8-dihydro-[1,3]-dioxolo-[4,5-g]quinolin-
6(5H)-one 4a–i and 4-aryl-3,4-dihydroquinolin-2-(1H)-one derivatives 4j–k based on
1
their spectral (IR, H and 13C NMR, MS) and spectral data for 4a:
Brown solid; mp 193–195 C. IR (KBr), n: 3191 (NH), 1674 (C O) cmꢃ1; MS
ꢁ
=
1
(EI, 70 ev): m=z (%): 267 [Mþ]; H-NMR (CDCl3, 400 MHz): d 8.49 (s, 1H, NH),
7.41–7.21 (m, 5H, Ar-H), 6.33 (s, 1H, Ar-H), 5.19 (s, 2H, -OCH2), 4.30–4.27 (t, 1H,
H8), 3.15–3.08 (m, 2H, H7); 13C NMR (CDCl3, 100 MHz): d 168.1, 129.6, 129.5,
129.2, 129.1, 129.0, 128.9, 128.8, 128.7, 128.5, 128.3, 97.7, 43.7, 39.7. Anal. calcd.
for C16H13NO3: C, 71.91; H, 4.86; N, 5.24%. Found: C, 71.76; H, 4.74; N, 5.12%.
CONCLUSION
In conclusion, we have explored a simple, convenient, efficient, and ecofriendly
protocol for the synthesis of 8-aryl-7,8-dihydro-[1,3]-dioxolo-[4,5-g]quinolin-6(5H)-ones

QUINOLIN-6-(5H)-ONE DERIVATIVES
2525
and 4-aryl-3,4-dihydroquinol-2-(1H)-one via a one-pot, three-component reaction
employing ZrOCl2 ꢀ 8H2O as a nontoxic and efficient catalyst under ultrasound
irradiation. The procedure offers several advantages, including mild and neutral
conditions, good yields of the products, elimination of solvent, operational simplicity,
minimum environmental impact, and easy workup.
ACKNOWLEDGMENT
We thank the Research Council of the University of Bu-Ali Sina for financial
support to carry out this research.
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