1,3-Dibromo-5,5-dimethylhydantoin (DBH)/kaolin: An efficient reagent system for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under solvent-free conditions

Article abstract of DOI:10.1016/j.cclet.2012.08.008

1,3-Dibromo-5,5-dimethylhydantoin, has been used as an efficient catalyst for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in the presence of kaolin. All reactions are performed in the absence of solvent in relatively short reaction times in good to

Full text of DOI:10.1016/j.cclet.2012.08.008

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 1145–1148
www.elsevier.com/locate/cclet
1,3-Dibromo-5,5-dimethylhydantoin (DBH)/kaolin: An efficient
reagent system for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes under solvent-free conditions
a
b
Farhad Shirini a, , Nader Ghaffari Khaligh , Gholam Hossein Imanzadeh ,
*
Parisa Ghods Ghasem-Abadi a,b
a Department of Chemistry, College of Science, University of Guilan, Rasht 41335-19141, Iran
b Department of Chemistry, College of Science, University of Mohaghegh-Ardabili, Ardabil, Iran
Received 25 June 2012
Available online 21 September 2012
Abstract
1,3-Dibromo-5,5-dimethylhydantoin, has been used as an efficient catalyst for the synthesis of 14-aryl-14H-dibenzo[a,j]-
xanthenes in the presence of kaolin. All reactions are performed in the absence of solvent in relatively short reaction times in good to
high yields.
# 2012 Farhad Shirini. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Kaolin; 1,3-Dibromo-5,5-dimethylhydantoin; Xanthene derivatives; Solvent-free conditions
The xanthene derivatives, especially benzoxanthenes, have wide range of biological and therapeutic properties [1–
5]. Furthermore, due to their useful spectroscopic properties, they were used as dyes [6], in laser technologies [7], and
in fluorescent materials for visualization of biomolecule [8]. Many procedures describe the synthesis of xanthenes and
benzoxanthenes including cyclodehydrations [9–13]. In addition, 14H-dibenzo[a,j]xanthenes and related products
were prepared by reaction of 2-naphthol with formamide [14], 2-naphthol-1-methanol [15], carbon monoxide [16] and
sulfomic acid [17]. Even though various procedures were reported, disadvantages including low yields, prolonged
reaction times, use of an excess of reagents/catalysts and use of toxic organic solvents necessitate the development of
an alternative route for the synthesis of xanthene derivatives.
Kaolin is natural substance that obtained from clay. With abilities to act as good as ceramic material; (no toxicity,
ability to withstand extreme heat and pressure) it is believed that kaolin has tremendous potential to be utilized as solid
support material in both laboratory scale and industrial scale. Currently, strong interests in such natural supports were
due to eco-friendly demands in many modern industrial applications [18]. Kaolin, montmorillonite K10 and KSF
supported with transition metal chlorides were employed to esterify tert-butanol with acetic anhydride to tert-butyl
acetate with more than 98% selectivity. A noteworthy feature was the low activity of the catalysts for the dehydration
of tert-butanol below 50 8C [19]. Thermally activated Nigerian Ukpor kaolinite clay and Udi clay were shown to be
* Corresponding author.
E-mail address: shirini@guilan.ac.ir (F. Shirini).
1001-8417/$ – see front matter # 2012 Farhad Shirini. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.08.008

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F. Shirini et al. / Chinese Chemical Letters 23 (2012) 1145–1148
good catalysts for the preparation of n-propyl acetate [20]. Brazilian kaolinite intercalated with a porphyrin derivative
catalyzed Baeyer–Villiger oxidation of cyclohexanone to e-caprolactam by hydrogen peroxide. In the presence of the
same catalyst iodosylbenzene brings about the epoxidation of cyclooctene and oxidation of cylcohexane to
cyclohexanone [21]. Acid-treated clay (K10, bentonite, or kaolin) catalyzed the triazenes formation by diazotization
ofaryl amines followed by addition of a cyclic secondary amine [22].
1. Experimental
All chemicals were purchased from Merck or Fluka Chemical Companies. All known compounds were identified
by comparison of their melting points and spectral data with those reported in the literature. Progress of the reactions
was monitored by thin layer chromatography (TLC) using silica gel SIL G/UV 254 plates. Melting points were
determined on an electrothermal type 9200 melting point apparatus. IR spectra were recorded using a Shimadzu IR-
1
470 spectrometer with KBr plates. H NMR spectra were recorded on a Bruker Avance-400 MHz spectrometer.
At first, a mixture of arylaldehyde (1 mmol), kaolin (100 mg) and DBH (0.1 mmol) was stirred and heated on the oil
bath at 125 8C for 1 min. Then 2-naphthol (2 mmol) was added to the mixture. The resulting mixture was stirred
vigorously for an appropriate period of time, as mentioned in Table 1. The progress of the reaction was followed by
TLC (n-hexane:ethyl acetate, 8:2). After completion of the reaction, the reaction mixture was diluted with
dichloromethane (3 mL) and kaolin was filtrated. The solvent was evaporated under vacuum and the resulting solid
products were recrystallized from ethanol. The products were found to be pure and no further purification was
necessary.
1.1. Spectral data of the selected compounds
14-(Phenyl)-14H-dibenzo[a,j]xanthene: Colorless crystals; mp 184–185 8C; 1H NMR (CDCl3, 400 MHz): d 6.46
(s, 1H, CH), 6.96 (t, 1H, J = 7.2 Hz, ArH), 7.12 (t, 2H, J = 7.2 Hz, ArH), 7.36–7.58 (m, 8H, ArH), 7.74–7.81 (m, 4H,
ArH), 8.37 (d, 2H, J = 8.4 Hz, ArH); IR (KBr, cmÀ1): 3070, 3020, 1620, 1590, 1430, 1400, 1250, 1150, 1075, 825, 740.
14-(4-Methylphenyl)-14H-dibenzo[a,j]xanthenes: Colorless crystals; mp 224–225 8C; 1H NMR (CDCl3,
400 MHz): d 2.11 (s, 3H, CH3), 6.43 (s, 1H, CH), 6.93 (d, 2H, J = 7.8 Hz, ArH), 7.22–7.36 (m, 8H, ArH), 7.42–
7.81 (m, 4H, ArH), 8.37 (d, 2H, J = 8.4 Hz, ArH); IR (KBr, cmÀ1): 3068, 3022, 1620, 1590, 1512, 1395, 1248, 1110,
810, 740.
14-(3-Nitrophenyl)-14H-dibenzo[a,j]xanthenes: Yellow crystals; mp 207–208 8C; 1H NMR (CDCl3, 400 MHz): d
7.52 (s, 1H), 7.10–8.56 (m, 16H); IR (KBr, cmÀ1): 3060, 1595, 1525, 1350, 1240, 1140, 810, 750.
2. Results and discussion
In 2011, Ghasemnejad-Bosra et al. reported that 1,3-dibromo-5,5-dimethylhydantoin (DBH) (0.12 mmol, 34 mg)
is able to efficiently catalyze the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes (48–61 min, 90–96%) [23]. Based on
this study and in continuation of our ongoing research program on the development of new methods for the organic
transformations [24,25], we have found that when the same reaction is carried out in the presence of kaolin, in addition
to decreasing of the reaction time (3–40 min), the procedure became more easier (It should be noted that in the absence
of kaolin, the mixture became very sticky, which causes the difficulty in the mixing of the reactants). Optimization of
the reaction conditions showed that the best results can be obtained under the conditions presented in Scheme 1.
(0.1mmol,28 mg)
H3C Br
N
H3C
O
O
R
N
Br
R
HO
Layeredkaolin(100 mg)
Solvent-free,125oC
+
O
O
H
(1.0mmol)
(2.0mmol)
Scheme 1. Preparation of 14-aryl-14H-dibenzo[a,j]xanthenes.

F. Shirini et al. / Chinese Chemical Letters 23 (2012) 1145–1148
1147
Table 1
Kaolin/DBH catalyzed synthesis of xanthene derivatives.a
Entry
R
Time (min)
Yield (%)b
Mp (8C)
Found
Reported
1
2
C6H5–
30
35
40
9
85
83
81
90
85
86
91
89
87
90
95
87
184–185
197–198
224–225
236–237
213–215
208–210
287–288
190–191
291–293
207–208
314–315
289–291
–
181–183
198
3-CH3–C6H4–
4-CH3–C6H4–
4-F–C6H4–
3
226–228
236
4
5
2-Cl–C6H4–
3-Cl–C6H4–
4-Cl–C6H4–
3-Br–C6H4–
4-Br–C6H4–
3-NO2–C6H4–
4-NO2–C6H4–
4-CN–C6H4–
Cinnammaldehyde
Valeraldehyde
10
25
5
213–215
209–210
289–290
190–191
296
6
7
8
15
6
9
10
11
12
13
14
9
210–211
310–312
293–295
–
3
12
–
c
–
c
–
–
–
–
a
Products were characterized by 1H NMR, IR and melting point and also by comparison with the reported in literature data [9,17,26–32].
b
c
Isolated yields.
Mixture of products.
Br
N
H 3
C
Br
N
H 3
C
H
3 C
O
O
H 3
C
O
O
Br
N
N
Br
Layered kaolin
I
II
R
R
R
R
Br
O
H
Br
+
Br
Br
O
HO
O
H
O
H
OH
HO
- H O B r
HO
R
R
R
H
-H 2 O
O
O
HO
OH HO
III
IV
Scheme 2. Proposed mechanism.
After optimization of the reaction conditions different types of aromatic aldehydes were subjected to the requested
reaction under the determined conditions. As shown in Table 1, aryl-aldehydes were converted into their
benzoxanthene derivatives in good to high isolated yields (Table 1, 81–95%), although the reaction times were
significantly affected by the electron-withdrawing and releasing substituents on the benzene ring. The electron-
withdrawing substituted benzaldehydes reacted very well and produced corresponding 14-aryl-14H-dibenzo[a,j]-
xanthenes in good to excellent yields in shorter times than arylaldehydes with electron-donating groups. Because of
the formation of the mixture of products, the method is not useful for the preparation of xanthenes derivatives from
aliphatic and double bond containing aldehydes (Table 1, entries 13, 14).
Although the actual mechanism of the reaction is unclear, a reasonable explanation due to the high catalytic activity
of DBH and mechanistic operation of DBH in similar reactions [33] is shown in Scheme 2. On the basis of this

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F. Shirini et al. / Chinese Chemical Letters 23 (2012) 1145–1148
mechanism, 1,3-dibromo-5,5-dimehtylhydantion produces the bromonium cation (Br+) and activates the carbonyl
group by the formation of oxygen cation I. The reaction follows by the nucleophilic attack of 2-naphthol on the
activated carbonyl of I to afford II which is O-activated by Br+. Then the second 2-naphthol attacks on II to generate
III. In the last step, the corresponding 14-aryl-14H-dibenzo[a,j]xanthenes is produced from IV by releasing H2O. It is
important to note that in the absence of kaolin a trace amount of the product is produced during a long reaction time.
This result shows that kaolin may have the following roles for the promotion of the reaction: (i) a support for placing
the reactants and catalyst closer together, and (ii) a support for adsorption of the produced water (Scheme 2).
In conclusion, we have demonstrated a mild and efficient protocol for the preparation of 14-aryl-14H-
dibenzo[a,j]xanthenes using kaolin/DBH reagent system. Short reaction times, easy work-up, and high yields of
products are noteworthy advantages of this protocol. Furthermore, the use of an inexpensive, approximately non-toxic,
commercially available, and highly efficient catalyst under solvent-free conditions makes the current method
economically acceptable and industrially applicable. We have also proposed a plausible mechanism for the present
reaction. The present methodology also has several other advantages such as: high reaction rates and excellent yields,
no side reactions, ease of preparation and handling of the catalyst, cost efficiency of the catalyst and simple
experimental procedure.
Acknowledgment
We are thankful to the University of Guilan Research Council for the partial support of this work.
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