Potassium phthalimide: An efficient and simple organocatalyst for the one-pot synthesis of dihydropyrano[3,2-c]chromenes in aqueous media

Article abstract of DOI:10.1007/s11164-013-1508-2

A series of dihydropyrano[3,2-c]chromene derivatives were obtained via treating cyano methylene compounds (malononitrile or ethyl cyanoacetate), aromatic aldehydes, and 4-hydroxycoumarin in the presence of potassium phthalimide, as a green, mild, efficien

Full text of DOI:10.1007/s11164-013-1508-2

Res Chem Intermed
DOI 10.1007/s11164-013-1508-2
Potassium phthalimide: an efficient and simple
organocatalyst for the one-pot synthesis
of dihydropyrano[3,2-c]chromenes in aqueous media
•
Hamzeh Kiyani Fatemeh Ghorbani
Received: 13 September 2013 / Accepted: 4 December 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract A series of dihydropyrano[3,2-c]chromene derivatives were obtained via
treating cyano methylene compounds (malononitrile or ethyl cyanoacetate), aro-
matic aldehydes, and 4-hydroxycoumarin in the presence of potassium phthalimide,
as a green, mild, efficient, and commercially available organocatalyst in aqueous
media. This procedure was easily performed, which provides a straightforward route
for the synthesis of diverse dihydropyrano[3,2-c]chromene compounds. Safety,
short reaction times, environmentally friendly, no use of hazardous organic solvents,
and high yields are remarkable advantages of this process.
Keywords Three-component process Á Dihydropyrano[3,2-c]chromenes Á
Potassium phthalimide Á Cyano compounds
Introduction
Since the first multicomponent process (MCP) was described by Strecker in 1850
[1], MCPs have been demonstrated to be highly valuable tools for the expedient
creation of numerous chemical compounds including natural products and
biologically active compounds [2]. Recently, considerable attention has been
focused on MCPs owing to their high efficacy, mild conditions, simplistic
completing, environmental friendliness, and minimal reaction times [3–6]. In
addition to this, the other features of MCPs are the following: (1) simple procedures
for the formation of final products in a one-pot process from at least three starting
materials, (2) green bond-forming, (3) atomic and structural economy, (4)
minimization of waste produced, (5) easy construction of complex organic
molecules, and (6) avoidance of complicated purification processes [4–10].
H. Kiyani (&) Á F. Ghorbani
School of Chemistry, Damghan University, 36715-364 Damghan, Iran
e-mail: hkiyani@du.ac.ir
123

H. Kiyani, F. Ghorbani
Carrying out MCPs in water as the reaction medium is one of the most suitable
methods, which will be a significant component of green chemistry [11–15].
On the other hand, the heterocyclic scaffold comprising chromene moiety is
present in compounds possessing a variety of biologically activities, such as
spasmolytic, diuretic, anticoagulant, antianaphylactic [16], antimicrobial [17],
antifungal [18], antibacterial [19], antioxidant [20], antileishmanial [21], antitumor
[22], local anesthetic [23], antihistaminic [24], antiallergenic [25], and treatment of
Alzheimer’s disease [26] and schizophrenia [27]. Moreover, a number of chromenes
are widely employed as pigments [28], cosmetics [29], and laser dyes [30].
Taking into consideration the above-mentioned characteristics of chromene
derivatives, significant attention has been focused on the advance of ecologically
benign methodologies towards synthesizing this heterocyclic (chromene) scaffold
by cyclization of 4-hydroxycoumarin, aldehydes, and cyano compounds (i.e.,
malononitrile and ethyl cyanoacetate).
Several synthetic routes have been widely used for the preparation of
dihydropyrano[3,2-c]chromenes. These compounds have been synthesized in the
presence of a variety of homogeneous or heterogeneous catalysts such as
hexamethylenetetramine (HMT) [31], heteropolyacid [32, 33], diammonium
hydrogen phosphate [34], DBU [35], piperidine [36], tetrabutylammonium bromide
(TBAB) [37], ionic liquid [38, 39], morpholine [40], 4-(dimethylamino)pyridine
(DMAP) [41], potassium phthalimide-N-oxyl (POPINO) [42], ruthenium complexes
[43], 3-hydroxypropanaminium acetate (HPAA) [44], silica-bonded N-propylpiper-
azine sodium n-propionate (SBPPSP) [45], silica gel [46], sulfonic acid function-
alized silica [47], 2-hydroxyethanaminium acetate [48], a-Fe2O3 [49], cellulose-
SO3H [50], potassium sodium tartrate (KNaC4H4O6Á4H2O) [51], and meglumine
[52].
Many of the procedures have their own merits. However, most of them suffer
from one or more drawbacks, including complex steps, prolonged reaction times,
low yields, tedious work-up procedures, and using expensive catalysts and organic
solvents. Therefore, the development of an efficient, rapid, simple, and green
procedure for the preparation of pyranochromenes is of considerable interest. Water
is one of the best solvents in organic transformations and has received great
attention due to its features such as being environmentally friendly, safe, non-toxic,
non-flammable, clean, green, inexpensive, and readily available. Also, the use of
water not only diminishes the risk of organic solvents but also improves the rate of
many chemical reactions [53–55].
The development of solid basic catalytic systems utilizing inexpensive, clean,
environmentally benign, and commercially available catalysts has been a challenge
in organic synthesis [56, 57]. Potassium phthalimide (PPI) is a mild, green,
inexpensive, efficient, basic recyclable catalyst and stable reagent. It has been
utilized as a reagent in the synthesis of primary amines by the Gabriel method [58,
59], the synthesis of phthalimide derivatives [60–62], and as a catalyst for the
preparation of cyanohydrin trimethylsilyl ethers [63, 64]. We have recently reported
that PPI is an efficient and green organocatalyst for the synthesis of isoxazol-5(4H)-
ones [65] and 4-aryl-7-(arylmethylene)-3,4,6,7-tetrahydro-1H-cyclopenta[d]pyrim-
idin-2(5H)-ones-/thiones [66]. Our literature survey revealed that there is no report
123

One-pot synthesis of dihydropyrano[3,2-c]chromenes
O
NH2
OH
O
:
N K
Z
O
O
+
+
N
Z
C
15 mol%
Ar
H
O
Ar
O
Z = CN (3a)
= CO2Et (3b)
O
H2 Reflux
O
,
O
1
2a-j
3
4a-n
Scheme 1 Preparation of dihydropyrano[3,2-c]chromene derivatives (4a–n) via one-pot, three-
component process of 4-hydroxycoumarin (1), aryl aldehydes (2), and cyano compounds (3a,
b) catalyzed by PPI in water
on the use of PPI as a catalyst in the synthesis of dihydropyrano[3,2-c]chromene
derivatives. For the first time, we report the applicability of PPI as a readily
available, efficient, and solid basic organocatalyst for the synthesis of a wide variety
of dihydropyrano[3,2-c]chromenes via the one-pot three-component process
(Scheme 1).
Experimental
All chemicals, unless otherwise specified, were purchased from commercial sources
and were used without further purification, with the exception of furan-2-
carbaldehyde and benzaldehyde, which were distilled before use. The products
were characterized by a comparison of their physical data with those of known
samples or by their spectral data. Melting points were measured on a Buchi 510
1
melting point apparatus and are uncorrected. H NMR and 13C NMR spectra were
recorded at ambient temperature using a BRUKER AVANCE DRX-500 and
400 MHz using DMSO-d6 as solvent. FT-IR spectra were recorded on a Perkin
Elmer RXI spectrometer. The development of reactions was monitored by thin layer
chromatography (TLC) analysis on Merck pre-coated silica gel 60 F254 aluminum
sheets, visualized by UV light.
General procedure for the synthesis of dihydropyrano[3,2-c]chromene
derivatives (4a–n)
A reaction mixture of aromatic aldehyde 2 (1 mmol), 4-hydroxycoumarin 1
(1 mmol), malononitrile or ethyl cyanoacetate 3 (1 mmol), and PPI (15 mol%) in
distilled water (5 mL) was refluxed for 10–40 min. During the reflux, the progress
of the reaction mixture was monitored by TLC analysis. After completion of the
reaction, the reaction mixture was cooled to room temperature and the precipitated
solid was filtered, washed with cold distilled water (4 mL), and air-dried to obtain
the pure products. If necessary, the solid products can be recrystallized from hot
ethanol. After removal of the water from the filtered solution, the catalyst is
recovered and used for the subsequent reaction.
123

H. Kiyani, F. Ghorbani
Table 1 Optimization reaction conditions for the one-pot, three-component synthesis of 2-amino-5-oxo-
4-(p-tolyl)-4,5-dihydropyrano[3,2-c]chromene-3-carbon-itri-l-e (4f)
Entry
Solvent
Amounts of catalyst (mol%)
Time (min)
Temp. (°C)
Yield (%)a
1
H2O
–
30
30
30
30
30
30
25
20
20
20
20
20
20
20
20
20
20
r.t.
Trace
20
2
H2O
–
Reflux
r.t.
3
H2O
5
25
4
H2O
10
15
20
5
r.t.
30
5
H2O
r.t.
35
6
H2O
r.t.
37
7
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
45
8
H2O
10
15
20
15
15
15
15
15
15
15
80
9
H2O
94
10
11
12
13
14
15
16
17
H2O
92
EtOH
MeCN
1,4-dioxane
CH2Cl2
EtOAc
CHCl3
H2O/EtOHb
53
Trace
Trace
Trace
Trace
Trace
67
Reaction conditions: 4-hydroxycoumarin (1 mmol), 4-methylbenzaldehyde (1 mmol), malononitrile
(1 mmol), solvent (5 mL)
Optimized conditions shown in bold
a
Isolated yields
b
Ratio solvent is 1:1 (v/v)
Results and discussion
In the beginning, we first performed the search for the optimization reaction
conditions using the reaction between equimolar quantities (1 mmol) of 4-hydroxy-
coumarin (1), 4-methylbenzaldehyde (2f), and malononitrile (3a) as the model.
Various reaction conditions were investigated, including solvents, amounts of
catalyst, and temperatures. The results are summarized in Table 1.
As can be seen in Table 1, in free-catalyst conditions, the reaction did not
proceed at room temperature. Only a trace amount of 2-amino-5-oxo-4-(p-tolyl)-
4,5-dihydropyrano[3,2-c]chromene-3-carbon-itri-l-e (4f) was obtained in this case
(Table 1, entry 1). Also, it was revealed that the reaction was rather slow and
resulted in poor yield (20 %) in the absence of the catalyst when the reaction was
123

One-pot synthesis of dihydropyrano[3,2-c]chromenes
carried out in refluxing water for 30 min (Table 1, entry 2), which indicated that the
catalyst was necessary for this transformation, albeit, increasing reaction time
showed no significant change in the yield of the reaction. The yield also increased
slightly by adding an amount of PPI to the reaction mixture at room temperature
(Table 1, entry 3). The effect of catalyst loading on the completion of the reaction at
room temperature was also studied. As can be seen in Table 1, when the amount of
catalyst was increased to 20 mol% at room temperature, a slight improvement in the
yield was achieved (Table 1, entries 4–6). In the next step, the reaction was carried
out with various amounts of catalyst in water under reflux conditions. It was found
that, by increasing the amount of catalyst from 5 to 15 mol% under reflux
conditions, the yield of 2-amino-5-oxo-4-(p-tolyl)-4,5-dihydropyrano[3,2-c]chro-
mene-3-carbonitrile (4f) was improved (Table 1, entries 7–9). A larger loading
amount of the catalyst (20 mol%) neither increased the yield nor shortened the
conversion time (Table 1, entry 10). Furthermore, the model reaction was
implemented using the other bases such as Et3N, NaOH, K2CO3, and Na2CO3. In
the presence of these bases after 2 h, only a trace amount of product 4f was
observed. On the other hand, the EtOH, and a mixture of EtOH:H2O (1:1, v/v)
afforded a lower yield of the desired product 4f under similar conditions (Table 1,
entries 11, 17). Also, performing the reaction in the other organic solvents such as
MeCN, 1,4-dioxane, CH2Cl2, EtOAc, and CHCl3 le d to a trace amount of product
4f (Table 1, entries 12–16). Hence, the 15 mol% catalyst loading and refluxing in
water was considered to be the best conditions for this type of reaction (Table 1,
entry 9, the optimum conditions shown in bold).
Using the optimized conditions (water, 15 mol% PPI, reflux), a series of products
4a–n were synthesized with this simple reaction procedure. The reaction time and
percentage yield for each of the products are presented in Table 2.
The results indicated that this PPI-catalyzed three-component reaction worked
well for a wide range of aryl aldehydes possessing various functional groups
including electron-donating and electron-withdrawing substituents. In all cases, the
reaction proceeded smoothly. The electronic nature of the functional groups on the
phenyl ring at C-4 position has no significant effect on the yield of products;
however, the reaction times are affected. Substrates with electron-withdrawing
groups (Table 2, entries 2–4, 12–13) reacted rapidly, whereas electron-donating
groups (Table 2, entries 6–9 and 14) decreased the reactivity, requiring a longer
reaction time. In addition to the aryl aldehydes, the reaction with electron-rich
aromatic heterocyclic aldehydes such as furan-2-carbaldehyde was also smoothly
developed and a high yield achieved (Table 2, entry 10). It should be noted that the
purification of the title compounds is very easy. After cooling the reaction mixture
to room temperature, the solid products were formed, which can be easily separated
by simple filtering. The desired products are sufficiently pure. If further purification
is required, they can be recrystallized from ethanol. It was found that this reaction
involving less reactive ethyl cyanoacetate (Table 2, entries 12–14) gave corre-
sponding products in lower yields and required longer reaction times than
malononitrile, which may be ascribed to the competency of the cyanide group in
stabilizing the reaction intermediates compared to the ester group [42, 67, 68].
123

H. Kiyani, F. Ghorbani
123

One-pot synthesis of dihydropyrano[3,2-c]chromenes
123

H. Kiyani, F. Ghorbani
123

One-pot synthesis of dihydropyrano[3,2-c]chromenes
123

H. Kiyani, F. Ghorbani
123

One-pot synthesis of dihydropyrano[3,2-c]chromenes
123

H. Kiyani, F. Ghorbani
123

One-pot synthesis of dihydropyrano[3,2-c]chromenes
O
O
K+
N
HN
N
Z
C
NC
H
Z
O
O
PPI
O
NC
Z
N
C
Z
+
O
O
H
Ar
Ar
O
Ar
OH
H
-
8
- HN
2
7
6
N
3a,b
O
H 2
O
O
-
O
O
K+
K+
O
H
O
Ar
CN
Z
HN
N
O
O
Knoevenagel
products
O
O
O
O
O
-
1
10
9
N
O
a d d i t i o n
M i c h a e l - t y p e
Ar
O
Ar
O
O
Ar
O
O
O
H
H
C
Z
Z
NH2
Z
O
O
Intramolecular nucleophilic
cyclization
N K+
O
+
C
NH
N
O
O
Michael adducts
PPI
4a-n
11
12
Scheme 2 Proposed mechanism for the formation of dihydropyrano[3,2-c]chromenes (4a–n)
A possible mechanism for the formation of final products (4) is proposed in
Scheme 2. The removal of acidic hydrogen from active methylene nitriles (3a, 3b)
by PPI, leads to nitrile anion 6. The arylidene nitrile intermediates (Knoevenagel
products, 10) are formed via the Knoevenagel condensation reaction of aldehydes
(2) with the intermediate nitrile anion 6. Then, the Michael-type addition of the
enolizable compound to the intermediate 10 results in the in situ formation of
intermediate 11 (Michael adducts), which subsequently undergoes intramolecular
nucleophilic cyclization (Thorpe–Ziegler type reaction) and tautomerization to
afford the desired compounds.
In order to validate the suggested mechanism, we conducted the synthesis of 4f in
two steps under similar conditions (Scheme 3). In the first step, the Knoevenagel
condensation component 13 was prepared. Measuring the melting point of the solid
product 13, and comparison with known compounds (prepared according to Ref.
[69]), confirmed the formation of arylidene malononitrile intermediate 13 in this
step. Also, the FT-IR spectrum of intermediate 13 showed a nitrile peak at
2,222 cm-1, indicating the presence of a malononitrile moiety. Then, the reaction
between intermediate 13 and 4-hydroxycoumarin (1), can give product 4f in similar
to the one-pot version. Additional evidence was obtained by TLC analysis of the
model reaction. TLC analysis 7 min after initiation of the reaction showed that spots
of the 3-methylbenzaldehyde and malononitrile disappeared and a new spot was
123

H. Kiyani, F. Ghorbani
OH
O
NH2
CN
O
O
CN
H
NC
O
PPI H
2O
,
1
+
NC
CN
H
C
3
H
3C
H
C
3
O
O
2f
3a
13
4f
Scheme 3 The synthesis of 4f from 2f and 3a in two steps under an optimal conditions reaction
NH2
CN
O
O
OH
O
O
O
O
NC
CN
PPI H
2O
,
3a
H
+
CH3
O
H
O
3C
H
C
O
3
1
2f
14
4f
Scheme 4 The synthesis of 4f from 1 and 2f in two steps under an optimal conditions reaction
established. The new spot is related to condensation product 13. This fact offers
evidence in support of the suggested pathway.
Another pathway could be proposed for the reaction, as seen in Scheme 4. Under
optimal reaction conditions, the reaction between 4-hydroxycoumarin (1) and
4-methylbenzaldehyde (2f) was investigated. Increasing the reaction time to 45 min
did not lead exclusively to the formation of 14. It can be concluded that the reaction
proceeds via the suggested mechanism in Scheme 2.
In this reaction, the catalyst is recoverable. The catalyst was recovered by
evaporation of the solvent from the filtrate solution after each run. The catalyst
recycled was applied to consecutive runs in four series of the same model reaction
under the optimized conditions for up to four runs (1st use: 94 %, isolated yield; 2nd
use: 91 % isolated yield; 3rd use: 87 % isolated yield; and 4th use: 82 % isolated
yield). Decreasing the yield is probably related to a slight reduction in the catalytic
activity of the catalyst or a decrease in the amount of the catalyst recycled, which is
attributed to the handling.
Conclusion
In summary, we have developed an efficient PPI-catalyzed one-pot, three-
component methodology for the synthesis of a variety of dihydropyrano[3,2-
c]chromene derivatives in high to excellent yields. This approach is very simple
from the experimental point of view and would permit easy access to large families
of dihydropyrano[3,2-c]chromenes. Clean, avoiding the use of hazardous organic
solvents, minimizing the amount of waste for each organic transformation,
reasonable reaction times, easy purification, aqueous conditions, efficiency, green,
inexpensive, mild, and economic availability of the organocatalyst are the other
noticeable features of this method.
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One-pot synthesis of dihydropyrano[3,2-c]chromenes
Acknowledgment The authors are grateful to the Research Council of Damghan University for partial
financial support of this work.
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