Efficient synthesis of aryl-14H-dibenzo[a.j]xanthenes using NaHSO4-SiO2 or 5%WO3/ZrO2 as heterogeneous catalysts under conventional heating in a solvent-free media

Article abstract of DOI:10.1080/00397910701462658

A simpler and greener protocol has been developed for the preparation of aryl-14H-dibenzo[a.j]xanthenes: a one-pot condensation of β-naphthol and aryl aldehydes, in the presence of silica-supported sodium hydrogen sulfate (NaHSO4·SiO2) or tungstated zirco

Full text of DOI:10.1080/00397910701462658

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Efficient Synthesis of
Aryl‐14H‐dibenzo[a.j]xanthenes
using NaHSO4‐SiO2 or 5%WO3/ZrO2 as
Heterogeneous Catalysts under Conventional
Heating in a Solvent‐Free Media
Lingaiah Nagarapu a , M. Baseeruddin a , N. Vijaya Kumari a , Srinivas
Kantevari a & A. P. Rudradas a
a Organic Chemistry Division II , Indian Institute of Chemical Technology ,
Hyderabad, India
Published online: 09 Aug 2007.
To cite this article: Lingaiah Nagarapu , M. Baseeruddin , N. Vijaya Kumari , Srinivas Kantevari & A. P.
Rudradas (2007) Efficient Synthesis of Aryl‐14H‐dibenzo[a.j]xanthenes using NaHSO4‐SiO2 or 5%WO3/ZrO2 as
Heterogeneous Catalysts under Conventional Heating in a Solvent‐Free Media, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:15, 2519-2525, DOI:
10.1080/00397910701462658
To link to this article: http://dx.doi.org/10.1080/00397910701462658
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Synthetic Communicationsw, 37: 2519–2525, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701462658
Efficient Synthesis of Aryl-14H-
dibenzo[a.j]xanthenes using NaHSO4-SiO2
or 5%WO3/ZrO2 as Heterogeneous
Catalysts under Conventional Heating
in a Solvent-Free Media
Lingaiah Nagarapu, M. Baseeruddin, N. Vijaya Kumari,
Srinivas Kantevari, and A. P. Rudradas
Organic Chemistry Division II, Indian Institute of Chemical Technology,
Hyderabad, India
Abstract: A simpler and greener protocol has been developed for the preparation
of aryl-14H-dibenzo[a.j]xanthenes: a one-pot condensation of b-naphthol and
aryl aldehydes, in the presence of silica-supported sodium hydrogen sulfate
.
(NaHSO4 SiO2) or tungstated zirconia (5%WO3/ZrO2) as heterogeneous catalysts
in a solvent-free media. The present methodology offers several advantages such as
excellent yields, simple procedure, short reaction times (2–8 h), and milder conditions.
Keywords: heterogeneous, silica-supported sodium hydrogen sulfate, solvent-free,
tungstated zirconia
INTRODUCTION
Solid acids and especially those based on micelle-templated silicas and other
mesoporous high-surface-area support materials are beginning to play a signifi-
cant role in the greening of fine and specialty chemical manufacturing processes.
A wide range of important organic reactions can be efficiently catalyzed by these
materials, which can be designed to provide different types of acidity as well as
Received in India December 13, 2006
Address correspondence to Lingaiah Nagarapu, Organic Chemistry Division II,
Indian Institute of Chemical Technology, Hyderabad 500 007, India. E-mail:
nagarapu2@yahoo.co.in
2519

2520
L. Nagarapu et al.
high degrees of reaction selectivity. The solid acids generally have high turnover
numbers and can be easily separated from the organic components.[1] Use of
solid-supported reagents[2] have received considerable attention, in organic
synthesis because of their ease of handling, shorter reaction times, greater selec-
tivity, simple workup and recoverability of catalysts.
The synthesis of xanthenes, especially benzoxanthenes, has attracted the
attention of organic chemists because of their wide range of biological and
therapeutic properties.[3] Many procedures have been reported for the
synthesis of xanthenes and benzoxanthenes; they involve cyclodehydrations,[4]
alkylations g to the heteroatoms,[5] trapping of benzynes by phenols,[6] cyclo-
condensation between 2-hydroxyaromatic aldehydes and 2-tetralone,[7] the
reaction of b-naphthol with aldehydes or acetals under acidic conditions, and
intramolecular phenyl carbonyl coupling reactions of benzaldehydes and
acetophenones.[8] In addition, 14H-dibenzo[a.j]xanthenes and related products
are prepared by reaction of b-naphthol with formamide,[9] 2-naphthol-
1-methano,[10] carbon monoxide,[11] and sulfomic acid.[12]
RESULTS AND DISCUSSION
However, these methodologies suffer from one or more disadvantages such as
low yield, lack of easy availability/preparation of the starting materials,
prolonged reaction time (16 h to 5 d), use of toxic organic solvents, and
requirement of excess of reagent/catalyst or special apparatus. Thus, there
is a need for development of an alternate route to construct the xanthene
derivatives. During the course of our studies directed toward the development
of practical and environmentally friendly procedures for some important
transformations,[13] we developed an efficient, convenient, and facile
method for the preparation of benzoxanthenes by condensation of aldehydes
.
with b-naphthol by use of NaHSO4 SiO2 or 5%WO3/ZrO2 as heterogeneous
catalysts under solvent-free conditions (Scheme 1).
[14]
.
Recently, NaHSO4 SiO2 and 5%WO3/ZrO2,
inexpensive and eco-
friendly catalysts, have been effectively utilized in organic synthesis as acid
catalysts or accelerators, which are easily separable from the reaction
products[15] and work under heterogeneous conditions. The NaHSO4 SiO2
.
could be conveniently prepared[16] from the readily available NaHSO4,
silica gel, and 5%WO3/ZrO2 from zirconium oxychloride (ZrOCl2) and
ammonium meta tungstate.[17]
Scheme 1.

Aryl-14H-dibenzo[a.j]xanthenes
2521
In the conventional reaction procedure, b-naphthol was heated under
solvent-free conditions with various aromatic aldehydes in the presence of
.
NaHSO4 SiO2 or 5%WO3/ZrO2 at 1258C (Scheme 1) to afford the
products (Table 1) in good yield, and the products were isolated, extracting
them into petroleum ether, affording 14H-dibenzo[a.j]xanthenes in high
.
purity. The reactions required 6 to 8 h with NaHSO4 SiO2 and only 2 to
6 h by use of 5%WO3/ZrO2 as catalysts to afford products in 82–94%
yield. There was no significant change in the yield of the catalysts.
REUSABILITY OF CATALYST
Next, we investigated the reusability and recycling of 5%WO3/ZrO2. At first,
we put b-naphthol, p-chlorobenzaldehyde, and 0.1 mmol of 5%WO3/ZrO2
together, and then the mixture was stirred at 1258C under solvent-free
media. When the reaction was completed, the catalyst was separated by
simple filtration by diluting with EtOAc, and recovered 5%WO3/ZrO2 was
reused in subsequent reactions without significant decrease in activity even
after five runs (Table 2).
In conclusion, a convenient and efficient process for the synthesis of
aryl-14H-dibenzo[a.j]xanthenes by condensation of various aromatic
.
aldehydes with b-naphthol using NaHSO4 SiO2 or 5%WO3/ZrO2 as solid
support at 1258C has been developed. This simple procedure combined
with ease of recovery and reuse of catalysts make this method an economic,
benign, and a waste-free chemical process for the synthesis of aryl-14H-
dibenzo[a.j]xanthenes. We believe that this procedure is a convenient,
economic, and a user-friendly process for the synthesis of aryl-14H-
dibenzo[a.j]xanthenes.
EXPERIMENTAL
Conventional Method
A
mixture of the aldehyde (1 mmol), b-naphthol (2 mmol), and
.
NaHSO4 SiO2 or 5%WO3/ZrO2 (0.1 mmol) was stirred at 1258C for the
appropriate time according to Table 1. Completion of the reaction was
indicated by TLC. The reaction mixture was cooled to 258C, EtOAc
(20 mL) was added, and the mixture was stirred for 10 min and filtered
(to separate catalyst). The catalyst was washed with ethyl acetate
(2 Â 10 mL). The combined ethyl acetate extracts were washed with water
(2 Â 10 mL) and dried over Na2SO4. The solvent solid thus obtained was
washed with hexane or cold ethanol. All products were characterized by
comparison of their physical constants and spectral data with those for
authentic samples.

2522
L. Nagarapu et al.
.
Table 1. NaHSO4 SiO2 or WO3/ZrO2-catalyzed synthesis of aryl-14H-dibenzo
[a.j]xanthenes
.
NaHSO4 SiO2
WO3/ZrO2
Time
(h)
Yield
(%)a
Time
(h)
Yield
(%)a
Entry
1
Aldehyde
8.0
8.0
8.0
88
87
91
6.0
96
94
93
2
3
6.0
3.0
4
5
8.0
8.0
89
88
2.0
3.0
92
90
6
8.0
92
5.0
88
7
8
6.0
6.0
93
92
3.0
3.0
93
90
9
8.0
94
3.0
88
89
10
11
8.0
7.5
89
91
3.0
3.0
89
(continued)

Aryl-14H-dibenzo[a.j]xanthenes
Table 1. Continued
2523
.
NaHSO4 SiO2
WO3/ZrO2
Time Yield
Time
(h)
Yield
(%)a
Entry
12
Aldehyde
(h)
(%)a
8.0
92
3.0
78
13
14
8.0
7.0
82
92
3.0
3.0
76
86
aYields refer to pure products, and all products were characterized by comparison of
1
their physical data and H NMR, IR, and mass spectral data with those of authentic
samples.
Representative Spectral Data
14-(4-Chlorophenyl)-14H-dibenzo[a.j]xanthene (Table 2, entry 4): Mp. 286–
2888C, IR (KBr) 3026, 2914, 1621, 1590, 1241, 829, 805, 740 cm21. 1H NMR
(200 MHz, CDCl3): d 6.42 (s, 1H), 7.10 (d, J ¼ 9.6 Hz, 2H), 7.62–7.30
(m, 12H), 8.30 (d, J ¼ 9.4 Hz, 2H). 13C NMR (75 MHz, CDCl3): d 35.43,
116.51, 117.26, 122.85, 124.19, 126.63, 127.94, 128.23, 128.81, 129.25,
130.24, 147.55. Anal. calcd. for C27H17ClO: C, 82.54; H; 4.36. Found: C,
82.56; H, 4.44.
14-(2,4-Dichlorophenyl)-14H-dibenzo[a.j]xanthene (Table 2, entry 6): Mp.
253–2558C, IR (KBr,) 3066, 2933, 1619, 1592, 1248, 835, 804, 741 cm21
.
Table 2. Recycling of 0.1 mmol of 5%WO3/ZrO2
Entry
Time (h)
Yield (%)a
0
1
2
3
4
5
2.0
2.5
3.0
3.5
4.0
5.0
92
91
91
89
88
87
aIsolated yields.

2524
L. Nagarapu et al.
1H NMR (200 MHz, CDCl3): d 6.71 (s, 1H), 6.90 (d, J ¼ 9.5 Hz, 1H),
7.23–7.82 (m, 12H), 8.60 (d, J ¼ 9.5 Hz, 2H). 13C NMR (50 MHz, CDCl3):
d 42.8, 125.8, 126.8, 131.6, 132.9, 133.3, 135.4, 135.8, 137.0, 137.6, 138.9,
139.6, 140.1, 141.4, 150, 157.5. Anal. calcd. for C27H16Cl2O: C, 75.89; H;
3.77. Found: C, 75.91; H, 3.75.
14-(4-Methylphenyl)-14H-dibenzo[a.j]xanthene (Table 2. entry 14): Mp.
230–2318C, IR (KBr) 3020, 2908, 1620, 1591, 1509, 1457, 1430, 1247,
1
959, 837, 810, 739 cm21. H NMR (200 MHz, CDCl3): d 2.18 (s, 3H), 6.39
(s, 1H), 6.90 (d, J ¼ 9.6 Hz, 2H), 7.32–7.80 (m, 12H), 8.36 (d, J ¼ 9.4 Hz,
2H). 13C NMR (50 MHz, CDCl3): d 19.1, 35.4, 115.7, 116.2, 121.3, 122.7,
125.2, 126.4, 127.4, 129.2, 129.5, 134.0, 140.8, 146.6. Anal. calcd. for
C28H20O: C, 90.29; H; 5.41. Found: C, 90.32; H, 5.44.
ACKNOWLEDGMENTS
The authors are thankful to M. Hari Babu, head, Organic Chemistry Division
II, IICT, for helpful discussions, and B.S.R. thanks CSIR, New Delhi, for
financial assistance.
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