BF3/nano-sawdust as a green, biodegradable and inexpensive catalyst for the synthesis of highly substituted dihydro-2-oxopyrroles

Article abstract of DOI:10.1039/c4ra16625f

BF₃/nano-sawdust was used as a readily available, inexpensive, biodegradable and environmentally benign heterogeneous solid acid catalyst for the one-pot cascade synthesis of highly functionalized dihydro-2-oxypyrroles. Four-component reactions (4CRs) of dialkylacetylenedicarboxylates, primary amines and aldehydes were used for the synthesis of these compounds under thermal conditions.

Full text of DOI:10.1039/c4ra16625f

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BF3/nano-sawdust as a green, biodegradable and no expensive catalyst
for synthesis of highly substituted dihydro-2-oxopyrroles
Bi Bi Fatemeh Mirjalili*a and Reza Zare Reshquiyeaa
Received (in XXX, XXX) XthXXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
BF3/nanoꢀsawdust was used as a readily available, inexpensive, biodegradable and environmentally
benign heterogeneous solid acid catalyst for the one pot cascade synthesis of highly functionalized
dihydroꢀ2ꢀoxypyrroles. Fourꢀcomponent reactions (4CRs) of the dialkylacetylenedicarboxylates, primary
amines and aldehydes were used for synthesis of these compounds under thermal conditions.
10
been reported for the synthesis of dihydroꢀ2ꢀoxopyrroles using
MCRs
such
as
four
component
reaction
of
Introduction
dialkylacetylenedicarboxylate, aldehyde, and amines. Previously,
this protocol has been catalyzed by TiO2ꢀnanopowder,19 I2,20 pꢀ
40 toluenesulfonic acid,21 Cu(OAc)2·H2O/salicylic acid,22 AcOH,23
Dihydroꢀoxopyrrole(DPO) derivatives are important structures
exhibit biological activities such as herbicidal,1 antitumor,2
pesticidal,3 antiꢀHIV,4 antibiotics,5 antimalarial6and its
15 derivatives are crucial core structures used to create many natural
products like bilirubins,7 oteromycin,8ypaoamide9andpyrrocidine
A10(Scheme 1).
1ꢀmethylꢀ2ꢀoxopyrrolidinium
hydrogen
sulfate
([Hpyro][HSO4]),24 InCl325 and [nꢀBu4N][HSO4].26
Some of these catalysts have many limitations such as inefficient
separation of the catalyst from homogeneous reaction mixtures,20ꢀ
23
45
unrecyclable and environmentally limitations.20ꢀ25 Hence,
development of new solid acids with numerous advantages such
as costꢀeffectiveness, environmentally benign, easy workup and
good stability for oneꢀpot multicomponent synthesis of highly
substituted dihydroꢀoxopyrrole scaffolds is still in demand. In this
50 regard, our aim is developing cheap and biomaterials solid acid
catalysts for this transformation.
Cellulose is one of the most abundant natural carbon based
biopolymers containing free OH groups with nucleophilic
character. It has been used for synthesis of some compounds
55 which used in enantioselective chromatography,27 protein
immobilization,28 antibodies29 and retarded drug release.30
Sawdust is a biodegradable, natural, cheap, renewable and
readily available source of cellulose.
In this work, we have investigated about synthesis of
60 sawdust based catalyst by bonding Lewis acids to OH
groups of Dꢀglucose units. Since, sawdust is containing
cellulose with other substances such as pectin, tannin,
proteins, minerals and lignin that caused leaching in organic
mediums. Therefore, pectin, lignin, proteins and minerals
65 must be removed. For this purpose the pine sawdust was
treated respectively with NaOH, NaClO, and H2O2. For
preparation of nanoꢀsawdust, the sawdust has been treated with
concentrated H2SO4 for partial hydrolysis of its cellulose. Then,
the nanoꢀsawdust was used to synthesis of BF3/nanoꢀsawdust as a
70 new, biodegradable and green catalyst.
Scheme1. The structure of some natural compounds with dihydroꢀ2ꢀ
20 oxopyrrole motif.
Due to the wide range application of dihydroꢀoxopyrrole
derivatives in pharmaceuticals, agrochemicals, and natural
products, their synthesis remains an area of intense current
interest to the chemical synthesis. A number of synthetic routes
25 have been developed for the synthesis of dihydroꢀoxopyrrole,
including rutheniumꢀcatalyzed reaction of α,ßꢀunsaturated imines
with carbon monoxide and ethylene,11 reaction of isocyanides,
dialkylacetylenedicarboxylates,
and
benzoyl
chlorides,12
carboamination/oxidative cyclization of Cꢀacylimines with
30 alkenes,13 transannulation of 1ꢀsulfonylꢀ1,2,3ꢀtriazole with ketene
silylacetal,14 reaction of acetylene with imines, and CO2,15 Pdꢀ
catalyzed cyclization of ethyl glyoxalate and amines16 and
reaction of αꢀcyanomethylꢀßꢀketoesters and alcohols.17 Among
these versatile synthetic methods, multicomponent reactions
35 (MCRs) have attracted particular attention;18 A few methods have
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We wish to report herein its catalytic behavior for the costꢀ
effective and facile one pot cascade synthesis of highly
functionalized dihydroꢀ2ꢀoxopyrroles via 4CRs of the
dialkylacetylenedicarboxylates, amines and aldehyde under
thermal conditions.
5
Result and discussion
In order to investigate the structure of BF3/nanoꢀsawdust, we
have studied the FTꢀIR (ATR) spectra of pine sawdust and
BF3/nanoꢀsawdust (Figure 1). In sawdust FTꢀIR spectrum, two
45
10 strong bands at 3331 and 1020 cmꢀ1 were observed. In BF3/nanoꢀ
sawdust, in addition to the above mentioned bands, some bands
also appeared at 820, 913, 1264, 1424 and 1633 cmꢀ1. The band
in 916 cmꢀ1 verifies the CꢀOꢀB group on BF3/nanoꢀsawdust.
The proposed structure containing possible model for acid sites
15 formed on the catalyst is similar to the reported structure for
cellulose triphosphate gels that was prepared by phosphorylation
of trihydroxy31 groups of Dꢀglucose units and BF3/γꢀAl2O3
(Scheme 2).32
Fig. 3: EDS analysis diagram of BF3/nanoꢀsawdust
The amount of boron in the catalyst was determined. For this
purpose, a mixture of BF3/nanoꢀsawdust (0.5 g) and water (50
mL) was stirred and boiled for 1 hour. Then, the mixture was
50 cooled and titrated with 12.5 ml of standard NaOH (0.18 N) in
the presence of phenolphetalein. The boron amount in catalyst
was found to be 5.5 meq.gꢀ1. In this process, the attached boron
ꢀ
in cellulose was reacted with water, captured OH from water and
produced H that evaluated with OH (Scheme 3).
+
ꢀ
F
F
OBF2
OPO(OH)2
(HO)2OPO
B
O
Al
F2BO
OBF2
O
O
OPO(OH)2
O
O
O
F2BO
O
O
O
(HO)2OPO
m
OBF2
OBF2
m
OBF2
OPO(OH)2
OPO(OH)2
OBF2
O
F2BO
O
-
B(OH)4 H+
+ Cellulose-O-B(OH)2 - H+
+ H2O
O
F2BO
O
m
F BO
2
OBF2
(b)
(c)
(a)
55
20 Scheme 2. Proposed structure for (a) BF3/nanoꢀsawdust, (b)BF3/γꢀAl2O3
and (c) cellulose triphosphate
Scheme 3
The thermal gravimetric analysis (TGꢀDTG) pattern of BF3/nanoꢀ
sawdust was detected from 20 to 515 °C (Figure 4). The catalyst
60 is stable until 55 °C and only 15% of its weight was reduced in
115 °C due to the removal of catalyst moisture. Heating the
catalyst until 515 °C, caused 73% of its mass to be reduced. The
char yield of the catalyst in 515 °C is 30%. According to the TGꢀ
DTG diagram of BF3/nanoꢀsawdust and our study, it was revealed
65 that this catalyst is suitable for the promotion of organic reactions
below 115 °C.
25
30
Fig 1: FTꢀIR (ATR) spectrum of (a) pine sawdust and (b) BF3/nanoꢀ
sawdust.
The FESEM image of nanoꢀsawdust and BF3/nanoꢀsawdust is
35 shown in figure 2. According to the FESEM date, the particles
size of catalyst is below 50 nm. Quantitative elemental
information (EDS) of BF3/nanoꢀsawdust was measured by
SEM/EDS instrument, Phenom pro X, (Figure 3). According to
this data, the weight percentage of F, O and C are 46.4, 39.3 and
40 7.9, respectively.
Fig 4: Thermal gravimetric analysis (TGꢀDTG) pattern of
BF3/nanoꢀsawdust
70
In this study, we have investigated the catalytic activity of
BF3/nanoꢀsawdust for the synthesis of dihydroꢀ2oxopyrroles via
4CRs of the dialkylacetylenedicarboxylates, amines and
aldehyde.
75 The synthesis of dihydroꢀ2ꢀoxopyrroles is in kind an
intermolecular nucleophilic addition reaction (Mannich reaction
type) included several intermediates. Therefore, it is necessary
the choosing of a suitable conditions such as catalyst, solvent and
temperature for this reaction. As a model reaction, synthesis of
Fig 2. The FESEM image of (a) nanoꢀsawdust and (b) BF3/nanoꢀsawdust
2
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methylꢀ1ꢀ(4ꢀchlorophenyl)ꢀ4ꢀ((4ꢀchlorophenyl)amino)ꢀ5ꢀoxoꢀ2,5ꢀ
dihydroꢀ1Hꢀpyrroleꢀ3 carboxylate was examined under various
condition in the presence of BF3/nanoꢀsawdust as catalyst (Table
desired product was obtained in low yield (Table 1, entry 13).
Reusability of catalyst was investigated for three cycles (Table 1,
entries 14–16). For this purpose after each run the reaction
mixture was diluted with acetone or ethanol and filtered for
1). As shown in table 1, the most yield of reaction was acquired
o
5
using of 3 mmol of formaldehyde in ethanol at 70 C and in the 15 isolation of catalyst. The obtained catalyst was then washed with
presence of 0.08 g BF3/nanoꢀsawdust after 3.5 h (Table 1, Entry
8). Effect of different solvent on the reaction was investigated
and revealed that ethanol gave the best results for this
transformation. It was be noted when the reaction was performed
chloroform followed by drying in room temperature. The
recovered catalyst was then used for the next run of the reactions.
It was found that the reactivity of the catalyst decreases
marginally for the next run (approx. 3%).
10 in the same conditions mentioned in entry 8 without catalyst,
20
Table1.Preparation of methylꢀ1(4ꢀchlorophenyl)ꢀ4ꢀ((4ꢀethylphenyl)amino)ꢀ5ꢀoxoꢀ2,5ꢀdihydroꢀ1Hꢀpyrroleꢀ3ꢀcarboxylate under various conditions.
Entry
Solvent
Catalyst
Reactant
I: II:III
Condition
Time
Yield b
1
2
3
4
5
6
7
8
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
MeOH
EtOH/MeOH1:1
CHCl3
nꢀHexane
EtOH
EtOH
EtOH
EtOH
ꢀ
2:1:1.5
2:1:1.5
2:1:1.5
2:1:1.5
2:1:2
2:1:2.5
2:1:2.5
2:1:3
2:1:3
2:1:3
2:1:3
2:1:3
R.T.
R.T.
R.T.
3h
3h
3h
3h
3h
3h
3.5h
3.5h
3.5h
3.5h
3.5h
3.5h
3.5h
3.5h
3.5h
3.5h
4h
ꢀ
BF3/nanoꢀsawdust (0.06)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
BF3/nanoꢀsawdust (0.08)
ꢀ
14%
17%
37%
52%
62%
81%
92%
60%
67%
24%
38%
20%
90%
87%
84%
86%26
79%25
89%23
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
R.T.
9
10
11
12
13
14
15
16
17
18
19
2:1:3
2:1:3
2:1:3
2:1:3
BF3/nanoꢀsawdust (0.08), 2nd run
BF3/nanoꢀsawdust (0.08), 3nd run
BF3/nanoꢀsawdust (0.08), 4nd run
[nꢀBu4N][HSO4] (10 mol%)
InCl3 (20 mol%)
MeOH
MeOH
EtOH
2:1:1
2:1:1.5c
3:1:1.5d
R.T.
Reflux
3h
4h
AcOH (2 eq)
aReactions were run with the following steps: (a) dimethylacetylendicarboxylate(1 mmol) and 4ꢀchloroaniline (1
mmol) were added into 4 mL solvent and kept at room temperature for 15 min; (b) 4ꢀchloroaniline (1 mmol),
formaldehyde and catalyst were added to the above mixture respectively, and then stirred at rt/ 70 °C for desired time.
bIsolated yield after recrystallization in ethanol.
cDiethylacetylenedicarboxylate instead of dimethylacetylenedicarboxylate was used.
d4ꢀBromoaniline instead of 4ꢀchloroaniline was used.
25
spectrometer, operating at an ionization potential of 70 eV.
Finally, with optimized reaction conditions obtained for the
synthesis of IV, from the amount of reactant, solvent, amount of
catalyst and reaction temperature point of view, the scope of this
transformation was explored. Accordingly, for synthesis of
30 different dihydroꢀ2ꢀoxopyrrole derivatives were examined and
high yields were noticed in most of the cases (Table 2)
Melting points were obtained with a Buchi melting point Bꢀ540
45 B.V.CHI apparatus. Quantitative elemental information (EDS) of
BF3/nanoꢀsawdust was measured by SEM/EDS instrument,
Phenom pro X.
Preparation of nanoꢀsawdust:
Experimental section
Pine sawdust (4 g), was first treated with a solution of 17.5% w/v
50 sodium hydroxide in water bath maintained at 100 °C for 12
hours to remove tannin, pectin, proteins and minerals. The
residue was alpha cellulose that is not soluble in 17.5% w/v
sodium hydroxide solution. The alkali treated fibers were washed
repeatedly. The stock was then bleached with 100ml of 1:1
55 dilution of 5 % w/v sodium hypochlorite solution at 80 °C for 8
hrs. The resulting was then treated with 10 mlof 20 % v/v
hydrogen peroxide at 50°C for 2 hours due to the removal of the
insoluble lignin. The resultant was hydrolyzed by refluxing with
sulfuric acid (65% H2SO4 with fiber to liquor ratio of 1:20) for 2
Materials and methods:
All chemicals and solvents were purchased from the Merck and
35 Fluka Chemical Companies in high purity. Materials were used
from the commercial reagent grade. FTꢀIR spectra were recorded
onan attenuated total reflectanceꢀfouriertransform infrared (ATRꢀ
FTIR) spectrophotometer (Bruker, Eqinox 55). 1H NMR and 13C
NMR spectra were recorded at 400 MHz and 100 MHz,
40 respectively, on a BrukerDXRꢀ400 spectrometer using CDCl3as
solvent and tetramethylsilane as internal standard. Mass spectra
(MS) were recorded on
a FINNIGANꢀMAT 8430 mass
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Table 2.Synthesis of dihydroꢀ2ꢀoxopyrrole derivatives in the
presence of BF3/nanoꢀsawdust at 70 oC.a
14
15
4ꢀClꢀC6H4
Me 4ꢀCl
175 – 17722
3.5h 89%
148ꢀ15019
4h
92%
4ꢀClꢀC6H4
Me 4ꢀCl
5
Entry R1
R2 R3
Product
Time Yieldb M.P. Ref
175ꢀ17622
128ꢀ13023
125ꢀ12620
4h
4h
4h
84%
88%
81%
1
2
3
4ꢀMeꢀC6H4
Me 4ꢀMe
136ꢀ13822
154ꢀ15622
138ꢀ14023
3h
3h
4h
88%
91%
95%
16
17
18
PhCH2
PhCH2
PhCH2
Me 4ꢀCl
4ꢀMeꢀC6H4
4ꢀEtꢀC6H4
Et 4ꢀMe
Me 4ꢀBr
Me 4ꢀEt
Et
H
4h
5h
80%
83%
4
5
4ꢀEtꢀC6H4
Et 4ꢀEt
98ꢀ100
aFor entry of 1ꢀ13,18 The amount of amine (mmol):
dialkylacetylenedicarboxylate (mmol): formaldehyde (mmol): BF3/nanoꢀ
sawdust(g) equal to 2:1:3:0.08
4ꢀOMeꢀC6H4
Me 4ꢀOMe
160ꢀ16220
for entry of 14ꢀ17 The amount of amine (mmol):
dialkylacetylenedicarboxylate (mmol): aldehyde (mmol): BF3/nanoꢀ
sawdust(g) equal to 2:1:2:0.08
bIsolated yields after recrystallization in ethanol.
152ꢀ15425
5h
85%
6
4ꢀOMeꢀC6H4
Et 4ꢀOMe
R4CHO for entry of 1-13,18was formaldehyde, entry 14,16-17
wasbenzaldehyde and entry 15 was 4-methylbenzaldehyde.
3h
3h
90%
91%
7
4ꢀBrꢀC6H4
4ꢀBrꢀC6H4
4ꢀClꢀC6H4
4ꢀClꢀC6H4
3ꢀNO2ꢀC6H4
Me 4ꢀBr
Et 4ꢀBr
Me 4ꢀCl
Et 4ꢀCl
Me 3ꢀNO2
181ꢀ18222
165ꢀ16622
173ꢀ17422
165ꢀ16726
204ꢀ206
hours at 60 °C with strong agitation. Resulting mixture was
cooled to room temperature and diluted by adding an excess of
distilled water. Then, the suspension was repeatedly centrifuged
10 at 12000 rpm for 8 minutes using a refrigerated centrifuge
(AppendorfCentrifuge 5417R). After each run, the nanoꢀsawdust
(as white powder) was washed with distillated water and
centrifuged until the supernatant was become neutral.
8
3.5h 92%
9
Preparation of BF3/nanoꢀsawdust:
15 In a ventilated room, a 25 mL suction flask equipped with a
constantꢀpressure dropping funnel containing BF3.Et2O (1 mL)
and gas inlet tube for conducting HF, charged with 1 g nanoꢀ
sawdust and chloroform, BF3.Et2O was added drop wise over a
period of 3 min at room temperature. The mixture was stirred for
20 one hour at room temperature. The resulted mixture was filtered.
The obtained white solid was washed with chloroform and dried
at room temperature.
3h
2h
2h
95%
79%
85%
10
11
Typical procedure for synthesis of dihydroꢀ2ꢀoxopyrroles:
12
13
3ꢀNO2ꢀC6H4
4ꢀNO2ꢀC6H4
Et 3ꢀNO2
191ꢀ192
206ꢀ208
In a roundꢀbottom flask (50 mL) equipped with a reflux
25 condenser, firstly, a mixture of substituted amine (1 mmol) and
dialkylacetylenedicarboxylate (1 mmol) in absolute ethanol (4
mL) was stirred for 30 min. Then, other substituted amine (1
mmol), formaldehyde 37% (3 mmol) or substituted benzaldehyde
(2mmol) and BF3/nanoꢀsawdust (0.08 g) in absolute ethanol (3
3h
75%
Et 4ꢀNO2
4|
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40
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50
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mL) were added to the above mixture and stirred in 70°C. The
progress of the reaction was monitored by TLC. After completion
of the reaction, the mixture was allowed to be cooled,filtered off
and washed with EtOH (3×10 mL) to remove all unreacted
substrates.For separation of catalyst from solid product, it was
washed with chloroform (15 mL). The chloroform was
evaporated and the crude solid product was recrystallized from
ethanol to give the corresponding dihydroꢀ2ꢀoxopyrroles.
7
8
9
5
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Conclusions
10 In summary, BF3/nanoꢀsawdust as a green, cheap, natural,
biodegradable and readily available biopolymer solid acid
catalyst introduced. We have shown that various substituted
dihydroꢀ2ꢀoxopyrrole derivatives can be successfully synthesis by
an operationally simple and high efficient oneꢀpot fourꢀ
15 component procedure using BF3/nanoꢀsawdust. This protocol has
many advantages including high conversions, low catalyst
loading, lowꢀcost, easy workup and operational simplicity, which
makes this method more attractive.
18 J. Zhu, H. Bienayme, Multicomponent Reactions, 1st ed., Wileyꢀ
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20 The Research Council of Yazd University is gratefully
acknowledged for financial support of this study.
70
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Notes and references
aDepartment of Chemistry, College of Science, Yazd University, Yazd,
Iran. P.O. Box 89195ꢀ741,I.R.Iran; Eꢀmail: fmirjalili@yazd.ac.ir
25 † Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
‡ Footnotes should appear here. These might include comments relevant
to but not central to the matter under discussion, limited experimental and
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DOI: 10.1039/C4RA16625F
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