Fe3O4@SiO2-imid-PMAn magnetic porous nanospheres as recyclable catalysts for the one-pot synthesis of 14-aryl- or alkyl-14H-dibenzo[a,j]xanthenes and 1,8-dioxooctahydroxanthene derivatives under various conditio

Article abstract of DOI:10.1039/c4nj00961d

A facile, efficient and environmentally-friendly protocol for the synthesis of 14-aryl- or alkyl-14H-dibenzo[a,j]xanthenes and 1,8-dioxooctahydroxanthenes has been developed by one-pot condensation of various aldehydes with (i) β-naphthol and (ii) cyclic

Full text of DOI:10.1039/c4nj00961d

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Graphical abstract
Synthesis of 14-aryl- or alkyl -14H-dibenzo[a,j]xanthenes and 1,8 dioxooctahydro xanthene
derivatives by Fe3O4@SiO2-imid-PMA nanocatalysts

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Fe3O4@SiO2-imid-PMAn magnetic porous nanosphere as
recyclable catalyst for the one-pot synthesis of 14-aryl- or alkyl -
14H-dibenzo[a,j]xanthenes and 1,8 dioxooctahydro xanthene
derivatives under various conditions
Mohsen Esmaeilpour (1), Jaber Javidi (2)*, Farzaneh Dehghani (1), Fatemeh Nowroozi Dodeji
(2)
(1) Chemistry Department, College of Science, Shiraz University, Shiraz, Iran
(2) Department of Pharmaceutics, School of Pharmacy, Shahid Beheshti University of
Medical Sciences, Tehran, Iran
Eꢀmail address: jaberjavidi@sbmu.ac.ir
Abstract
A facile, efficient and environmentallyꢀfriendly protocol for the synthesis of 14ꢀarylꢀ or
alkylꢀ14Hꢀdibenzo[a,j] xanthenes and 1,8ꢀdioxooctahydroxanthenes has been developed by
oneꢀpot condensation of various aldehydes with (i) βꢀnaphthol and (ii) cyclic 5,5ꢀdimethylꢀ
1,3ꢀcyclohexanedion, in the presence of Fe3O4@SiO2ꢀImidꢀ H3PMo12O40 nanoparticles as
magnetic catalyst under various conditions. Different types of aromatic and aliphatic
aldehydes are used in the reaction and in all cases the products synthesized successfully. The
present approach offers several advantages such as short reaction times, high yields, easy
purification, a cleaner reaction and ease of recovery and reusability of the catalyst by
magnetic field. Also, the aforementioned nanocatalyst can be easily recovered by a magnetic
field and reused for subsequent reactions for at least 5 times without noticeable deterioration
in catalytic activity.
Keywords
Magnetic catalyst, Oneꢀpot synthesis, Aldehydes, βꢀNaphthol, 5,5ꢀdimethylꢀ1,3ꢀ
cyclohexanedion
1. Introduction
In recent years, Kegginꢀtype heteropolyacids (HPAs) such as H3PMo12O40 (PMA) have
been used as efficient catalysts for a variety of organic reactions because of their
superacidic and redox properties, low toxicity, ease of handling, low cost, high
thermal stability, high proton mobility, water tolerance, recoverability and reusability
[1]. Although HPAs are versatile compounds in their acidic form, their main
disadvantages are high solubility in polar solvents and low surface area (<10 m2/g).
Therefore, in a homogeneous reaction the isolation of the products and the reuse of the
catalyst after reaction become difficult [1]. Therefore, in order to overcome this
problem, these materials disperse on supports (such as silica, acidic ionꢀexchange
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resins, active carbon and nanoꢀtitania) which possess large surface area. The use of
support allows the heteropolyacids to be dispersed over a large surface area and
increases theirs catalytic activity [2ꢀ3]. Conventionally, heterogeneous catalysis is
favored over homogeneous catalysis due to its ease of handling and regenerability [3ꢀ
5]. However, in practice, the separation and recovery of these heterogeneous
nanocatalysts from the reaction medium by using standard techniques such as
filtration and centrifugation is not always easy due to the nanometric size of the
particles [6ꢀ8]. To overcome this drawback, magnetic nanomaterials are supported
over a variety of organic and inorganic supports, and their magnetic properties enables
the simple and efficient recovery of the catalyst by means of an external magnet [9ꢀ
14].
The magnetic nanoparticles utilized as supports usually consist of coreꢀshell
structures; being iron oxides (FexOy) the most commonly used ones. The coating of
these magnetic nanomaterials prevents aggregation/oxidation and serves as platform
for the catalyst. For this purpose, silica has been widely used because of its stability
under different reaction conditions and due to the fact that it can be easily
functionalized for diverse applications. Recently, a number of functionalized Fe3O4
nanoparticles have been employed in a range of organic transformations [15ꢀ18].
Xanthene and its derivatives are known as an important class of heterocyclic
compounds which have been investigated extensively in recent years because they
have wide range of biological and pharmaceutical properties such as antiꢀ
inflammatory [19], antibacterial [20] and antimalarial agents [21]. Furthermore, these
compounds can be used as dyes [22], fluorescent materials for visualization of
biomolecules [23], in laser technologies [24] and are useful in the photodynamic
therapy [25]. Because of their wide range of pharmacological, industrial and synthetic
application, many methods for their preparation are reported in the literature [26].
One of these methods is the condensation reaction of aldehydes with βꢀnaphthol for
the synthesis of 14ꢀaryl or alkylꢀ14Hꢀdibenzo[a,j]xanthenes, many catalysts such as
H5PW10V2O40 [27] KAl(SO4)2.12H2O (alum) [28], NanoꢀTiO2 [29]. SuccinimideꢀNꢀ
sulfonic acid [30], MeSO3H [31], iodine [32], silica sulfuric acid [33], boric acid [34],
cyanuric chloride [35] and [Et3NꢀSO3H]Cl [36] have been used for the synthesis of
14ꢀaryl or alkylꢀ14Hꢀdibenzo[a,j]xanthenes derivatives.
Another method to synthesis of these compounds is the condensation reaction of
aldehydes with cyclic 1,3ꢀdicarbonyl compounds for the synthesis of 1,8ꢀdioxoocta
hydroxanthene. Many alternative catalysts such as Fe3+ꢀmontmorilonite [37], pꢀ
toluenesulfonic acid [38], InCl3/ionic liquid [39], pꢀdodecylbenzenesulphonic acid
[40], pentafluorophenyl ammonium triflate (PFPAT) [41], triethylbenzylammonium
chloride [42], diammoniumhydrogen phosphate under various conditions [43],
sulfonic acid under ultrasonic irradiation [44], NaHSO4–SiO2 or silica chloride [45],
amberlystꢀ15 [46], montmorilonite [47], P2O5 [48], and silica sulfuric acid [49], have
been used for the synthesis of 1,8ꢀdioxooctahydroxanthene derivatives. Unfortunately,
many of these methods have various drawbacks, such as, low yields, prolonged
reaction time, use of hazardous catalysts or organic solvents and tedious workꢀup
processes. Therefore, to avoid these limitations, the development of a new procedure
for the synthesis of xanthene derivatives would be highly desirable.
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In the present research, we wish to describe an efficient, facile, and convenient
procedure for the rapid preparation of 14ꢀarylꢀ or alkylꢀ14Hꢀdibenzo[a,j] xanthenes
and 1,8ꢀdioxooctahydroxanthene by oneꢀpot condensation of various aldehydes with
(i) βꢀnaphthol and (ii) cyclic 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedion, in the presence of
H3PMo12O40 (PMA) as catalyst (Scheme1). Compared to other substrates (silica,
acidic ionꢀexchange resins, active carbon and nano titania [3]), Fe3O4@SiO2ꢀImid
nanoparticles have various advantages such as high loading capacity, low leaching and
the simple and efficient recovery procedure.
2. Experimental
2.1. General
Chemical materials were purchased from the Merck Chemical Company in high
purity. All the solvents were distilled, dried and purified by standard procedures.
Fourier transform infrared (FTꢀIR) spectra were obtained using a Shimadzu FTꢀIR
8300 spectrophotometer. The NMR spectra were recorded on a Bruker avance DPX
250 MHz spectrometer in chloroform (CDCl3) using tetramethylsilane (TMS) as an
internal reference. All products were characterized by their melting points and
comparison with literature values. The progress of the reaction was monitored by TLC
and purification was achieved by silica gel column chromatography.
2.2. Preparation of Fe3O4@SiO2ꢀImidꢀ H3PMo12O40 nanoparticles (Fe3O4@SiO2ꢀ
ImidꢀPMAn)
The catalyst (Fe3O4@SiO2ꢀImidꢀPMAn) was synthesized by the reported procedure
[50]. Briefly, firstly Fe3O4@SiO2 core–shell was prepared by coprecipitation method.
The mixture of FeCl3.6H2O (1.3g, 4.8mmol) in water (15ml) was added to the solution
of polyvinyl alcohol (PVA 15000), as a surfactant, and FeCl2.4H2O (0.9g, 4.5mmol)
in water (15 ml), which was prepared by completely dissolving PVA in water
followed by addition of FeCl2.4H2O. The resultant solution was left to be stirred for
30 min in 80oC. Then, hexamethylentetraamine (1.0mol/l) was added dropwise with
vigorous stirring to produce a black solid product when the reaction media reaches pH
10. The resultant mixture was heated on water bath for 2h at 60oC and the black
magnetite solid product was separated and washed with ethanol three times and was
then dried at 80oC for 10h.Then Fe3O4 nanoparticle (0.50g, 2.1mmol) was dispersed in
the mixture of ethanol (50mL), deionized water (5mL) and tetraethoxysilane
(0.20mL), followed by the addition of 5.0mL of NaOH (10wt%). This solution was
stirred mechanically for 30 min at room temperature. Then the product, Fe3O4@SiO2,
was separated by an external magnet, and was washed with deionized water and
ethanol three times and dried at 80oC for 10 h.
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In the second step Fe3O4@SiO2ꢀImid was synthesis. Fe3O4@SiO2 (1g) was added to
the solution of 3ꢀchlorotriethoxypropylsilane (1 mmol, 0.241 g) and imidazole (1
mmol, 0.0680 g) in pꢀxylene (20 mL) and the resultant mixture was under reflux for
24h under nitrogen atmosphere. After refluxing for about 24 h, the mixture was cooled
to room temperature, filtered by an external magnet and the product was washed with
xylene to remove any reacted species and dried at 70 oC for 6 h.
PMAn nanoparticles were prepared in tertiary step. In a typical procedure, 5 mmol of
bulk H3PMo12O40 (PMAb) was dispersed in 50 mL nꢀOctane and the resulting
dispersion was stirred vigorously for 30 min at room temperature to form a
homogeneous dispersion. This dispersion was transferred into a Teflonꢀlined stainless
autoclave filling 80% of the total volume. The autoclave was sealed and maintained at
150oC for 12 h. The autoclave was then cooled to room temperature. Finally, the
resulted powder was filtered and washed for several times by Octane, and dried in a
vacuum at 80oC for 12 h.
In last step, Fe3O4@SiO2ꢀImid (1.0g) was added to an acetonitrile solution of PMAn
(1.0mmol) in 20mL was taken in a roundꢀbottom flask. The mixture was refluxed for
24h under nitrogen atmosphere. After 24h, the mixture was filtered by an external
magnet, washed with acetonitrile and dichloromethane, and dried at 70oC for 6h. FTꢀ
IR spectrum of the catalyst showed the expected bands, including distinctive bands
due to anchoring of PMAn onto Fe3O4@SiO2ꢀImid. Fig. 1 represents the procedure
for the preparation of Fe3O4@SiO2ꢀImidꢀPMAn step by step.
2.3. General procedure for the synthesis of alkyl or arylꢀ14Hꢀdibenzo[a,j]xanthenes
(Method A)
A mixture of βꢀnaphthol (2 mmol), aldehyde (1 mmol), and Fe3O4@SiO2ꢀImidꢀPMAn
(0.03g) in 1,2ꢀdichloroethane (5mL) was refluxed for the appropriate time. Progress
of the reaction was monitored by TLC utilizing petroleum ether and ethyl acetate with
a molar ratio of 2:1 acts as mobile solvent. After completion of the reaction, the
mixture was cooled and diluted with hot ethanol (20 mL). The catalyst was removed
by using magnetic field or filtration and then the solvent was evaporated and the crude
product was recrystallized from ethanol to afford the corresponding pure product.
2.4. General procedure for the synthesis of alkyl or arylꢀ14Hꢀdibenzo[ a,j]xanthenes
(Method B)
To a mixture of aldehyde (1 mmol) and βꢀnaphthol (2 mmol), Fe3O4@SiO2ꢀImidꢀ
PMAn (0.03g) was added and the mixture was heated on an oil bath at 110 oC with
good stirring for the appropriate time. The progress of the reaction was monitored by
TLC (nꢀhexane:ethyl acetate, 7:2), after completion of the reaction, hot EtOH (10 mL)
was added and the mixture stirred for 10 min. Then, the catalyst was removed by
using magnetic field. A solid precipitated that was collected by filtration and washed
with H2O and then dried to give the corresponding 14ꢀaryl or alkylꢀ14Hꢀdibenzo[a,j]
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xanthenes (3a-o). For further purification this product was recrystallized from ethanol
to afford the pure products.
2.5. General procedure for the synthesis of 1,8ꢀdioxooctahydroxanthene
Derivatives
A mixture of 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedione (2 mmol), aldehyde (1 mmol) and
Fe3O4@SiO2ꢀImidꢀPMAn (0.03g) in ethanol (5mL) was refluxed for the appropriate
time. During the procedure, the reaction was monitored by TLC. Upon completion,
the reaction mixture was cooled to room temperature and diluted with hot ethanol (20
mL). The catalyst was removed by using magnetic field or filtration and then the
solvent was evaporated and the crude product was recrystallized from ethanol to
afford the corresponding pure product.
3. Results and discussion
In our previous work [50] the Fe3O4@SiO2ꢀImidꢀPMAn nano catalysts were
characterized by various methods such Transmission electron microscopy (TEM),
Scanning electron microscopy (SEM), Dynamic light scattering (DLS), Fourier
transform infrared (FTꢀIR) and etc. As shown in Fig. 1 Fe3O4@SiO2ꢀImidꢀPMAn
nanoparticles have spherical shapes with approximately 50 nm diameters. The size
distribution of it is centered at a value of 55 nm. The presence of vibration bands in
556, 794, 864, 956, 1055, 1095, 1454 and 2792ꢀ2985 cmꢀ1 in FTꢀIR spectrum of it
relevanted to the FeꢀO, MoꢀOeꢀMO, MoꢀOcꢀMO, MoꢀOt, PꢀO, SiꢀOꢀSi, C=N and CH
respectively. The band at 1443 cmꢀ1 for Fe3O4@SiO2ꢀImid is assigned to the C=N of
the imidazole group, which is shifted toward 1454 cmꢀ1 in Fe3O4@SiO2ꢀImidꢀPMAn
which could be due to the change in environment of the doubleꢀbonded nitrogen in
imidazole. Also, a small band between at 1400ꢀ1420 cmꢀ1 is the characteristic band of
the CꢀN bond which can be attributed to anchoring of imidazole to the propyl group.
At the first stage for the synthesis of 14ꢀaryl or alkylꢀ14Hꢀdibenzoꢀ[a,j]xanthenes, the
reaction of 2ꢀnaphthol (2 mmol) and benzaldehyde (1 mmol) was investigated in the
presence of Fe3O4@SiO2ꢀImidꢀPMAn as a catalyst in various solvents and also under
solvent free conditions in present of various amount of catalyst and different
temperature .
The results were summarized in Table 1.
In order to evaluate the optimum amount of catalyst required for this condensation, the
reaction was carried out in the presence varying amount of the nanocatalysts and the
results are presented in Table 1. The best result was achieved by carrying out the
reaction with 0.03g of Fe3O4@SiO2ꢀimidꢀPMAn nanocatalyst (Table1, entries 1,9).
The results show clearly that nanocatalyst is effective for this transformation and in
the absence of it, the reaction did not take place even after higher reaction time
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(Table1, entry10). Use of a higher amount of catalysts did not improve the yield
(Table1, entries 13) while a decrease in the amount of catalysts decreases the yield
(Table1, entries 11,12). As it was shown in Table 1, solvent free condition at 110 ºC
(Table1, entry 9) and using 1,2ꢀdichloro ethane as a solvent at reflux with 0.03g
catalyst (Table1, entry 1) are obviously the best choices for these reactions. The use
of other organic solvents like THF, H2O, MeOH, CH3CO2Et, CH3CN and EtOH
afforded the desired product in lower yields (Table1, entries 2ꢀ8).
Then, we also briefly examined the effect of different temperatures. The effect of
temperature was studied by carrying out the model reaction at different temperatures
in the presence of Fe3O4@SiO2ꢀImidꢀPMAn under solvent free conditions (Table1,
entries 14ꢀ18) and the best result was obtained at 110oC (Table1, entry9).
After optimizing the reaction conditions, we next investigated the generality of this
condition using 2ꢀnaphthol (2 mmol) and several aldehydes (1 mmol) in 1,2ꢀdichloro
ethane as a solvent at reflux (Method A) and solvent free condition at 110ºC with 0.03
g catalyst (Method B). The results are summarized in Table2. A wide range of
aldehydes containing electronꢀwithdrawing and electronꢀdonating groups were
investigated. Aldehydes containing electronꢀwithdrawing groups such as, chloro,
bromo, flouro and nitro underwent condensation in short reaction times with excellent
isolated yields with both of conditions (Table2, entries 4ꢀ10). Aldehydes containing
electronꢀdonating groups such as methyl, methoxy and hydroxyl required longer
reaction time. (Table2, entries 2,3 and 11). The catalytic system also worked well
with aliphatic aldehydes (Table2, entries 12ꢀ15) to generate the corresponding
xanthenes.
In order to show the advantage of Fe3O4@SiO2ꢀImidꢀPMAn over some of the reported
catalysts in the literature, we showed a reaction of 2ꢀnaphthol (2 mmol) and
benzaldehyde (1 mmol) in the presence of Fe3O4@SiO2ꢀImidꢀPMAn (Table3). In
comparison with the other reported catalysts in literature, we observed that
Fe3O4@SiO2ꢀImidꢀPMAn gives better yield in shorter reaction time in compare with
some of these catalysts and is comparable with some another ones (Table3,
entries1,2).
For optimization of the reactions parameters for 1,8ꢀdioxooctahydroxanthene
derivatives the reaction of benzaldehyde (1mmol), 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedione
(2mmol) was investigated in the presence of Fe3O4@SiO2ꢀImidꢀPMAn as a catalyst in
various solvents and also under solvent free conditions in present of various amount of
catalyst and different temperature. The results were summarized in Table4.
As it was shown in Table4, ethanol as a solvent at reflux with 0.03g catalyst is
obviously the best choices for this reaction (Table4, entry 1). The use of other organic
solvents like toluene, THF, H2O, MeOH, CH3CO2Et and also solvent free conditions
afforded the desired product in lower yields (Table4, entries 2ꢀ8).
After optimizing the reaction conditions, we next investigated the generality of this
condition using 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedione (2 mmol) and several aldehydes
(1 mmol) in ethanol as a solvent at reflux with 0.03g catalyst. The results are
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summarized in Table5. A wide range of aromatic aldehydes containing electronꢀ
withdrawing and electronꢀdonating groups such as, chloro, bromo,flouro,hydroxyl,
methyl, methoxy, and nitro were investigated. In all of theme excellent isolated yields
were obtained in short reaction times (Table5).
A plausible mechanism for the synthesis of 14ꢀarylꢀ or alkyl ꢀ14Hꢀdibenzo[a,j]
xanthenes and 1,8ꢀdioxooctahydroxanthenes catalyzed by Fe3O4@SiO2ꢀImidꢀPMAn is
shown in Scheme2. As it is shown in Scheme2A, prior activation of the carbonyl
group of aldehyde by H+ to give intermediate [I], followed by a nucleophilic attack
from C1 of βꢀnaphthol, provides intermediate [II], which serves as an electrophile,
ready for attack by a second molecule of βꢀnaphthol. Then, cyclodehydration of
intermediate [III] and dehydration afford the desired product. Also, we propose that
one molecule of 5,5ꢀdimethylꢀ1, 3ꢀcyclohexanedione was firstly condensed with an
activated aldehyde [I] to afford intermediate [II]' (Scheme2B). Then another molecule
of 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedione reacted with [II]' via Michael addition reaction
to give the intermediate [III]'. Finally, cyclodehydration of the intermediate [III]' gave
the expected products 1,8ꢀdioxoꢀoctahydroxanthenes.
A comparison among Fe3O4@SiO2ꢀimidꢀPMAn and the other catalysts, which were reported
in the literature, in the synthesis of 1,8ꢀdioxooctahydroxanthene, revealed advantages of
Fe3O4@SiO2ꢀimidꢀPMAn over the most of them in term of higher yield and shorter reaction
time (Table6, entry 10). According to these findings, it can be seen that Fe3O4@SiO2ꢀimidꢀ
PMAn is a very efficient catalysts useful in the synthesis of xanthene derivatives (Table6).
The reusability of the catalyst is an important benefit especially for commercial
applications. Thus, the recovery and reusability of nanocatalyst was investigated
forpreparation of 14ꢀ(Phenyl)ꢀ14Hꢀdibenzo[a,j]xanthene (Method A), (Method B) and
3,4,6,7ꢀtetrahydroꢀ3,3,6,6ꢀtetramethylꢀ9ꢀphenylꢀ2Hꢀxantheneꢀ1,8(5H,9H)ꢀdione under
optimized conditions (Fig. 2). The catalyst was recovered by a magnetic field and the
remaining solid was washed with ethyl acetate (3×10 mL), dried and the catalyst
reused for subsequent reactions for at least 5 times without any activation process.
The amounts of the nano heteropolyacid leaching for the reactions under the
optimized conditions were detected. The molybdenum (Mo) amount in reaction
medium after each reaction cycle was measured through ICP and details are shown in
Table 7. The analysis of the reaction mixture by the ICP technique showed the
leaching of H3PMo12O40 was negligible.
Additionally, size of catalysts after each reaction cycle was investigated by DLS and
results are shown in Table 8. As show, the size of catalysts will be increased after each
cycle. Generally, leaching of H3PMo12O40 and increasing of catalyst size lead to the
yield of reaction will decreased.
4. Conclusion
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In summary, we have developed a simple, convenient, and efficient procedure for preparing a
variety of 14ꢀsubstitutedꢀ 14Hꢀdibenzo[a,j]xanthenes by the reactions of various aldehydes
with βꢀnaphthol in the presence of a catalytic amount of Fe3O4@SiO2ꢀImidꢀPMAn
nanoparticles under dichloroethane and solventꢀfree conditions. Also, the present
methodology shows that Fe3O4@SiO2ꢀImidꢀPMAn is an efficient magnetic catalyst in the
oneꢀpot synthesis of 1,8ꢀdioxooctahydroxanthene derivatives in ethanol under reflux
conditions. The procedure offers several advantages including cleaner reaction profiles, high
reaction rates and excellent yields, simple experimental and workꢀup procedures, no side
reactions and use of recyclable and environmentally benign nature of catalyst.
Acknowledgements
Authors are grateful to the council of Iran National Science Foundation and University
of Shiraz for their unending effort to provide financial support to undertake this work.
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Fig. 1. Preparation and characterization of Fe3O4@SiO2ꢀImidꢀPMAn.
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Scheme.1: Fe3O4@SiO2ꢀImidꢀPMAnꢀcatalyzed synthesis of xanthenes derivatives.
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Scheme.2: (A) Plausible mechanism for the synthesis of 14ꢀarylꢀ or alkyl ꢀ14Hꢀdibenzo[a,j]
xanthenes and (B) 1,8 dioxooctahydro xanthenes catalyzed by Fe3O4@SiO2ꢀimidꢀPMAn
nanoparticles.
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Fig. 2: a) Recyclability of the catalyst for the oneꢀpot synthesis of 14ꢀ(Phenyl)ꢀ14Hꢀ
dibenzo[a,j]xanthene (a) Method Aa, (b) Method Bb and 3,4,6,7ꢀtetrahydroꢀ3,3,6,6ꢀ
tetramethylꢀ9ꢀphenylꢀ2Hꢀxantheneꢀ1,8(5H,9H)ꢀdionec. b) Photo images of magnetic fieldꢀ
responsive of Fe3O4@SiO2ꢀimidꢀPMAn nanoparticles (before magnetic field and under
magnetic field).
aReaction condition: benzaldehyde (1 mmol), βꢀnaphthol (2 mmol), Fe3O4@SiO2ꢀImidꢀPMAn (0.03g),
ClCH2CH2Cl (5mL), reflux.
bReaction condition: benzaldehyde (1 mmol), βꢀnaphthol (2 mmol), Fe3O4@SiO2ꢀImidꢀPMAn (0.03g), Solventꢀ
free, 110oC.
c Reaction condition: benzaldehyde (1 mmol), 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedione (2 mmol), Fe3O4@SiO2ꢀImidꢀ
PMAn (0.03g), EtOH (5mL), reflux.
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Table.1: Effect of solvent, temperature and catalyst amount on the reaction of 2ꢀnaphthol and
benzaldehyde.a
Entry
Solvent
ClCH2CH2Cl
EtOH
Catalyst (g)
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
ꢀ
Temperature (oC) Time (h) Yield (%)b
1
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
110oC
140oC
110oC
110oC
110oC
r.t
1.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
1.5
10
93
82
51
58
54
67
14
23
95
ꢀ
2
3
CH2Cl2
4
CH3CN
5
CH3CO2Et
MeOH
6
7
H2O
8
THF
9
Solventꢀfree
Solventꢀfree
Solventꢀfree
Solventꢀfree
Solventꢀfree
Solventꢀfree
Solventꢀfree
Solventꢀfree
Solventꢀfree
Solventꢀfree
10
11
12
13
14
15
16
17
18
0.01
0.02
0.04
0.03
0.03
0.03
0.03
0.03
1.5
1.5
1.5
5
17
45
93
18
46
81
89
95
60oC
4
90oC
100oC
120oC
2.5
1.5
1.5
a Reaction condition: 2ꢀnaphthol (2 mmol) and benzaldehyde (1 mmol).
b Isolated yield.
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Table.2: The oneꢀpot synthesis of 14ꢀaryl or alkylꢀ14Hꢀdibenzoꢀ[a,j]xanthenes using
Fe3O4@SiO2ꢀImidꢀPMAn.
R
Product
Method A
Method B
Mp (oC)
Reported
Time (h) Yield (%)a Time (h) Yield (%)a Found
1
(185)5
2
2.5
3
93
89
86
95
92
88
90
92
86
90
91
83
84
82
80
1.5
2
95
91
91
94
93
94
92
94
87
91
93
85
83
84
79
3a
3b
3c
3d
3e
3f
1
2
C6H5
183ꢀ185
228ꢀ229
204ꢀ206
206ꢀ207
214ꢀ216
290ꢀ291
(229)51
(204)51
(297)51
(215)51
(289)51
4ꢀMeC6H4
4ꢀMeOC6H4
4ꢀBrC6H4
2ꢀClC6H4
4ꢀClC6H4
4ꢀFC6H4
2
3
2.5
1.5
1.5
1.5
2
1.5
o.75
0.5
0.5
1.5
1.5
1
4
5
6
(238ꢀ240)48
(213)51
3g
3h
3i
7
239ꢀ240
214
8
2ꢀO2NC6H4
3ꢀO2NC6H4
4ꢀO2NC6H4
4ꢀHOC6H4
C6H5CH2
CH3CH2
2
212ꢀ213
312ꢀ313
138ꢀ140
(210ꢀ211)48
(310ꢀ311)51
(139ꢀ140)48
9
2
3j
10
11
12
13
3
2
3k
3l
(178ꢀ180)48
(150ꢀ151)51
(152ꢀ154)51
(155ꢀ157)51
3
2
181ꢀ182
149ꢀ150
153ꢀ154
152ꢀ153
3
2.5
2.5
3
3m
3n
3o
4
14 CH3CH2CH2
15 (CH3)2CH
4
Method A: ClCH2CH2Cl. Method B: Solventꢀfree.
a Isolated yield.
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Table.3: Comparing the catalytic activity of Fe3O4@SiO2ꢀImidꢀPMAn with the reported
catalysts in the preparation of 14ꢀ(phenyl)ꢀ14Hꢀdibenzo[a,j]xanthene.
Entry
Catalyst
Fe3O4@SiO2ꢀImidꢀPMAn
Fe3O4@SiO2ꢀImidꢀPMAn
Heterohpolyacid
I2
Condition
Solventꢀfree/110 °C
ClCH2CH2Cl, reflux
Solventꢀfree/100 °C
Solventꢀfree/90 °C
Neat/125 oC
Time (h)
Yield (%)
Ref.
1
2
3
4
5
6
7
8
1.5
95
93
This work
2
This work
0.5ꢀ1.5
80ꢀ91
90
51
32
52
53
54
33
33
55
56
2.5
2
91
K5CoW12O40_3H2O
Cellulose sulfuric acid
Sulfamic acid
Neat/110 oC
Neat/125 oC
Neat/125 oC
1.5
8
81
93
4
89
pꢀTsOH
9
90
10
11
12
Silica sulfuric acid
Dowexꢀ50W
ClCH2CH2Cl, reflux
Neat/100 oC
1.5
2
78
Neat/125 oC
94
Amberlystꢀ15
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Table.4: Effect of solvent, temperature and catalyst amount on the condensation of 5,5ꢀ
dimethylꢀ1,3ꢀcyclohexanedione with benzaldehyde over Fe3O4@SiO2ꢀimidꢀPMAn
nanocatalyst.a
Entry
Solvent
Catalyst(g)
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
ꢀ
Conditions
reflux
reflux
reflux
reflux
reflux
reflux
reflux
110oC
reflux
reflux
reflux
reflux
r.t
Time (h) Yield (%)b
1.5
2
94
85
76
66
56
48
28
87
ꢀ
1
EtOH
2
CH3CN
CH3CO2Et
MeOH
Toluene
THF
2
3
2
4
2
5
2
6
2
7
H2O
2
8
Solventꢀfree
EtOH
10
3
9
0.01
0.02
0.04
0.03
0.03
33
79
94
17
62
10
11
12
13
14
EtOH
2
EtOH
1.5
8
EtOH
EtOH
60oC
5
EtOH
a Reaction condition: benzaldehyde (1mmol), 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedione (2mmol).
b Isolated yield.
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Table.5 : Fe3O4@SiO2ꢀImidꢀPMAn catalyzed synthesis of 1,8ꢀdioxoꢀoctahydroxanthenes.a
Entry
R
Product
Time (h) Yield (%)b
Mp (oC)
Reported
Found
C6H5
1.5
2
94
87
84
85
93
95
90
91
90
88
94
92
86
82
85
204ꢀ205
207ꢀ208
245ꢀ247
180ꢀ182
238ꢀ240
225ꢀ227
224ꢀ226
231ꢀ233
245ꢀ246
169ꢀ170
224ꢀ226
250ꢀ251
249
(203ꢀ204)57
(208ꢀ209)58
(242ꢀ244)57
(177ꢀ180)59
(240ꢀ241)57
(226ꢀ227)60
(225ꢀ227)57
(230ꢀ232)57
(251ꢀ253)61
(170ꢀ172)57
(225ꢀ227)59
(248ꢀ251)60
(248ꢀ250)58
(202ꢀ205)58
(177ꢀ178)62
3a
3b
3c
3d
3e
3f
1
2
4ꢀMeC6H4
4ꢀMeOC6H4
3ꢀMeOC6H4
4ꢀBrC6H4
2
3
2
4
1.5
1.25
1.25
1
5
4ꢀFC6H4
6
2ꢀClC6H4
3g
3h
3i
7
4ꢀClC6H4
8
2ꢀNO2C6H4
3ꢀNO2C6H4
4ꢀNO2C6H4
2,4ꢀCl2C6H4
4ꢀHOC6H4
2ꢀHOC6H4
PhCH=CH2
1.25
1.5
1.25
1.25
2
9
3j
10
11
12
13
14
15
3k
3l
3m
3n
3o
2
203ꢀ204
178ꢀ180
2.5
aReaction condition: aromatic aldehyde (1 mmol), 5,5ꢀdimethylꢀ1,3ꢀcyclohexanedione (2 mmol), Fe3O4@SiO2ꢀ
ImidꢀPMAn (0.03g) , EtOH (5mL), reflux.
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Table.6: Comparison of the efficiency of Fe3O4@SiO2ꢀImidꢀPMAn with reported catalysts
for the synthesis of 1, 8ꢀdioxooctahydroxanthene.
Entry
Catalyst
Condition
CH3CN/Reflux
Solventꢀfree/110 °C
EtOH/90 °C
Time (h)
Yield (%)
88ꢀ96
88ꢀ94
81ꢀ94
54ꢀ82
90ꢀ96
84ꢀ94
78–91
75–90
90–98
82ꢀ95
Ref.
1
2
PMA/SiO2
4ꢀ5
3ꢀ3.5
5
63
64
TBAHS
65
3
HPWA/MCMꢀ41
PPA/SiO2
CH3CN/Reflux
CH3CN/Reflux
EtOH /100 °C
10ꢀ12
5
66
4
46
5
Amberlystꢀ15
Fe+3ꢀmontmorillonite
6
37
55
6
Solventꢀfree/100 °C
Solventꢀfree/100 °C
CH3CN/Reflux
EtOH/ Reflux
2–5
1ꢀ2
6
7
Dowexꢀ50W
47
8
Montmorillonite K10
NaHSO4ꢀSiO2
Fe3O4@SiO2ꢀImidꢀPMAn
9
45
10
1ꢀ2.5
This work
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Table 7. Ratio of PMA leaching (%) in each reaction cycle.
Ratio of PMA leaching (%)
Run 14ꢀarylꢀ14Hꢀdibenzoꢀ[a,j]xanthenesa
1,8ꢀdioxooctahydroxantheneb
Method A
0.10
Method B
0.12
1
2
3
4
5
0.15
0.26
0.35
0.43
0.50
0.15
0.26
0.30
0.43
0.19
0.29
0.33
0.46
a 14ꢀ(Phenyl)ꢀ14Hꢀdibenzo[a,j]xanthene
b 3,4,6,7ꢀtetrahydroꢀ3,3,6,6ꢀtetramethylꢀ9ꢀphenylꢀ2Hꢀxantheneꢀ1,8(5H,9H)ꢀdione
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Table 8. The size of catalysts in each reaction cycle.
Size of catalysts by DLS (nm)
Run 14ꢀarylꢀ14Hꢀdibenzoꢀ[a,j]xanthenesa
1,8ꢀdioxooctahydroxantheneb
Method A
Method B
1
2
3
4
5
55
58
60
65
70
55
59
63
67
71
55
58
61
65
68
a 14ꢀ(Phenyl)ꢀ14Hꢀdibenzo[a,j]xanthene
b 3,4,6,7ꢀtetrahydroꢀ3,3,6,6ꢀtetramethylꢀ9ꢀphenylꢀ2Hꢀxantheneꢀ1,8(5H,9H)ꢀdione
22