A novel and efficient method for the synthesis of new hydroxythioxanthone derivatives

Article abstract of DOI:10.1055/s-2004-831253

We describe the synthesis of some new hydroxythioxanthones by treatment of thiosalicylic acid (TSA) with various substituted phenols in the presence of Al₂O₃-CH₃SO₃H (AMA). Most of the reactions show high regioselectivity and produce thioxanthones in good yields.

Full text of DOI:10.1055/s-2004-831253

2900
PAPER
A Novel and Efficient Method for the Synthesis of New Hydroxythioxanthone
Derivatives
Novel Method
for
a
Synthesis
o
s
f
New H
y
h
droxythioxan
e
thone
D
eri
m
vative
s
Sharghi,* Ali Reza Salimi Beni
Department of Chemistry, Shiraz University, Shiraz 71454, Iran
E-mail: shashem@chem.susc.ac.ir
Received 5 July 2004; revised 28 July 2004
We have recently reported that a mixture of Al2O3–
CH3SO3H (AMA) is an effective reagent for Fries rear-
rangement,18 Beckmann rearrangement,19 direct conver-
sion of aromatic aldehydes to the corresponding glycol
monoesters,20 dehydration of nitriles into amides,21 and
synthesis of macrocyclic polyether-diesters.22 We report
herein that AMA also works as a good reagent for the syn-
thesis of hydroxythioxanthones by heating thiosalicylic
acid (TSA) and phenol in AMA to give the corresponding
hydroxythioxanthones in high yield (Scheme 1). To de-
velop an efficient reagent for the synthesis of hydroxy-
thioxanthone derivatives, we initially examined the
reaction of TSA (1) with resorcinol (2) (Scheme 1) in the
presence of various reagents. The reaction was monitored
via TLC and 1H NMR spectroscopy (Table 1).
Abstract: We describe the synthesis of some new hydroxythioxan-
thones by treatment of thiosalicylic acid (TSA) with various substi-
tuted phenols in the presence of Al2O3–CH3SO3H (AMA). Most of
the reactions show high regioselectivity and produce thioxanthones
in good yields.
Keywords: thioxanthone, thiosalicylic acid, methansulfonic acid,
alumina
Thioxanthone derivatives have been studied extensively
owing to their medicinal properties such as antihistaminic,
antiparasitic, neuroleptic, and antitumor activities.1–10 In
addition, various derivatives of thioxanthones are used as
activators or sensitizers in the photopolymerization of eth-
ylene-derived unsaturated monomers, particularly acry-
late derivatives.6,11–14 Moreover, alkyl-, alkoxyl- and
hydroxyl- substituted thioxanthones are particularly use-
ful as heat and ultraviolet stabilizers for polyolefins.6
As shown in Table 1, the best results were obtained using
a mixture of Al2O3 (0.300 g) and CH3SO3H (1 mL) at 110
°C for five minutes. The results also show the importance
of using both Al2O3 and CH3SO3H (compare entries 9 and
10 with 11). The use of two equivalents of phenol 115 and
one equivalent of TSA (2) for 1-hydroxythioxanthone (3)
does not improve the yield of thioxanthone in comparison
with the case where one equivalent of phenol 1 and one
equivalent of TSA (2) were used. Because of this initial
observation, it seemed advantageous to investigate this
method as a new and more suitable way to hydroxythio-
xanthones synthesis. The experimental procedure for the
preparation of hydroxythioxanthones is remarkably sim-
ple and does not require the use of any solvent or inert at-
mosphere.
The syntheses of thioxanthone and substituted thioxan-
thones have been carried out by different methods.4–10,15
These compounds are generally synthesized by condensa-
tion of appropriately substituted potassium 2-chloroben-
zoates with thiophenoles, or condensation of substituted
thiosalicylic acids with benzene derivatives followed by
cyclization of the intermediate 2-phenylmercaptobenzoic
acids in sulfuric acid,10,16,17 AlCl3,3,6 or PPA.5
However, these methods have some disadvantages such as
low yields, long reaction times, the use of large amount of
concentrated sulfuric acid, and lack of regiochemical con-
trol in the ring closure step. Moreover, some of these
methods require two steps and are limited to specific ben-
zoic acids or benzene derivatives having electron-with-
drawing groups and are not applicable to a large number
of starting materials.
To establish the generality and applicability of this meth-
od, various substituted phenols were subjected to the same
reaction condition to furnish the corresponding thioxan-
thones in good yields (Table 2, Scheme 2).
O
OH
O
O
OH
OH
Reagent
OH
+
+
– 2 H2O
S
HO
SH
S
OH
1
2
4
3
Scheme 1
SYNTHESIS 2004, No. 17, pp 2900–2904
x
x.
x
x
.
2
0
0
4
Advanced online publication: 07.10.2004
DOI: 10.1055/s-2004-831253; Art ID: Z13404SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Novel Method for Synthesis of New Hydroxythioxanthone Derivatives
2901
R1
R1
Table 1 Results of the Reaction of 1 (1 mmol) and 2 (1 mmol) in the
O
O
Presence of Various Reagents
R2
R3
R2
R3
AMA
OH
+
Entry Conditions
Time
(h)
Temp. Yield
(°C)
Yield
(%)a
4
110 °C
– 2 H2O
R5
(%)a
S
SH
R4
R4
3
1
2a–j
3a–k
15
15
1
2
3
Concd H2SO4
18
2
r.t.
80
r.t.
–
–
–
5
5
5
Scheme 2
Concd H2SO4
Concd H2SO4 +
Al2O3
18
and 3). Similar regiochemical behavior was observed in
the reaction of pyrogallol (2g) with TSA (1) affording
1,2,3-trihydroxythioxanthone (3i) in 65% yield (Table 2,
entry 7).
4
5
H3PO4
24
24
24
r.t.
–
PPA5
100
100
100
r.t.
6
–
–
–
–
–
–
–
–
In the case of phenols that can form two products, the ma-
jor product is the thioxanthone that has one hydroxyl
group in position 1 (entries 4, 5, and 8). The regiochemi-
cal control in these reactions can be rationalized in terms
of the hydrogen-bond formation between the hydroxyl
and the carbonyl group in the corresponding thioxanth-
ones. The 1H NMR signal of the H-bonded OH group was
observed at d = 14 ppm. Reaction of 2-hydroxy-4-methyl-
toluene (2f) afforded isomer 3h in 70% yield. 4-Hydroxy-
2-methylphenol (2e) gives 3f and 3g in equal yields and
they were readily separated by column chromatography
(entry 5). Some phenols having an electron-withdrawing
group such as NO2 and/or Cl did not produce any thioxan-
thone (Table 2, entries 9 and 10). Increase of the reaction
time to 24 hours or more did not improve the yield of the
reaction.
6
PPA + Al2O3
6
7
P4O10 + CH3SO3H 16
10
–
8
CH3SO3H
CH3SO3H
Al2O3
24
24
24
9
100
100
110
140
10
–
10
11
12
CH3SO3H + Al2O3 5 min
CH3SO3H + Al2O3 5 min
60
50
a Isolated yield.
As illlustrated in Table 2, when 3-hydroxy-5-methylphe-
nol (2b) and 3,5-dihydroxyphenol (2c) were employed, 1-
hydroxy-3-methylthioxanthone (3b) and 1,3-dihydroxy- In conclusion, we have found a new, efficient, and regio-
thioxanthone (3c) were isolated as regiospecific isomers selective method for the preparation of some new hydro-
in 67% and 70% yields, respectively (Table 2, entries 2 xythioxanthones in the presences of Al2O3–CH3SO3H
Table 2 The Results of Reaction of 1 (1 mmol) and 2 (1 mmol) in the Presence of AMA Reagent
Entry
Phenol 2
R1
Time/min
Mp/°C
Thioxanthonem 3
Yield%
R2
H
H
H
H
R3
R4
H
R5
H
R1
R2
H
R3
H
R4
H
1
2
3
4
2a
2b
2c
2d
OH
OH
Me
OH
Me
5
20
10
10
3a
3b
3c
3d
3e
3f
118–120
148–150
232–233
171–173
230–232
237–239
219–220
210–212
250–252
276–278
250–251
OH
OH
OH
OH
Me
OH
OH
Me
OH
OH
H
60
67
70
65
8
OH
H
OH
OH
H
H
Me
OH
Me
H
H
OH
H
H
H
OH
Me
H
Me
OH
OH
OH
Me
H
Me
H
5
2e
OH
Me
H
OH
H
10
Me
H
40
40
70
65
70
5
3g
3h
3i
Me
OH
OH
H
6
7
8
2f
Me
OH
OH
OH
OH
H
H
Me
H
H
H
H
10
20
20
H
2g
2h
OH
H
OH
H
OH
3j
OH
H
3k
OH
H
9
2i
2j
OH
OH
H
H
H
H
NO2
Cl
H
H
10 h
15 h
No Reaction
No Reaction
10
Synthesis 2004, No. 17, 2900–2904 © Thieme Stuttgart · New York

2902
H. Sharghi, A. R. S. Beni
PAPER
IR (KBr): 3250 (s), 1640 (s), 1590 (s), 1440 (s), 1270 (s), 1200 (s),
1160 (s), 1020 (s), 900 (s), 840 (s), 750 (s) cm–1.
availability and use of inexpensive reagent, operational 1H NMR (DMSO-d6): d = 6.31 (s, 1 H), 6.50 (s, 1 H), 7.52 (t, 1 H),
(AMA). This methodology is superior to the reported
methods from point of view of yield, short reaction time,
7.72 (m, 2 H), 8.70 (d, 1 H), 11.05 (s, 1 H), 14.36 (s, 1 H).
13C NMR (DMSO-d6): d = 101.4, 103.3, 107.8, 126.0, 126.9, 127.6,
128.7, 133.4, 136.6, 140.3, 164.2, 166.9, 183.3.
MS: m/z (%) = 244 (10) [M+], 216 (5), 187 (10), 115 (11), 85 (17),
69 (50), 43 (100).
simplicities, and straightforward work-up of the products.
Thiosalicylic acid, phenol derivatives, methanesulfonic acid (98%),
and Al2O3 [type 90, 70–230 mesh (Aktivitätsstufe I)] were pur-
chased from Fluka and Merck in high purity. NMR spectra were re-
corded in CDCl3 or DMSO-d6 on a Bruker Advanced Dpx-250
spectrometer (1H NMR at 250 MHz and 13C NMR at 62.9 MHz) us-
ing TMS as internal standard. IR spectra were recorded on Perkin
Elmer IR-157G and Perkin Elmer 781 spectrometers. Melting
points were taken on a Gallenkamp melting apparatus. The TLC
UV: lmax = 267, 390 nm.
Anal. Calcd for C13H8O3S (244.26): C, 63.92; H, 3.30. Found: C,
63.89; H, 3.28.
1-Hydroxy-3,4-dimethylthioxanthone (3d)
Yield: 65%; yellow needles; mp 171–173 °C.
was performed on plates coated with silica gel (silica gel 60 GF254
,
Merck) and chromatography was carried out on a column over silica
gel 60, 0.063–0.200 mm (70–230 mesh ASTM).
IR (KBr): 1620 (s), 1575 (s), 1550 (s), 1450 (s), 1350 (s), 1280 (s),
1210 (s), 1100 (s), 920 (s), 840 (s) cm–1.
Synthesis of Hydroxythioxanthone Derivatives 3a–k; Typical
Procedure
1H NMR (CDCl3): d = 2.30 (s, 3 H), 2.37 (s, 3 H), 6.78 (s, 1 H), 7.46
(t, 1 H), 7.58 (d, 1 H), 7.62 (t, 1 H), 8.55 (d, 1 H), 14.13 (s, 1 H).
To a mixture of CH3SO3H (98%, 1 mL) and Al2O3 (acidic type,
0.300 g) were added thiosalicylic acid (TSA) (0.154 g, 1 mmol) and
then the appropriate phenol (1 mmol). The mixture was stirred and
heated in an oil bath at 110 °C for 5–20 min. The reaction progress
was monitored by TLC. After completion of the reaction, the mix-
ture was poured into water and extracted with EtOAc (2 × 50 mL).
The organic layer was washed with a sat. aq solution of NaHCO3
(50 mL). The organic layer was dried over CaCl2 and evaporated in
vacuum to give an impure residue. Chromatography of the crude
products was performed on a column of silica gel eluted with n-hex-
ane–EtOAc, to give yellow or red crystalline products as shown in
Table 2.
13C NMR: (CDCl3): d = 15.2, 21.8, 115.9, 122.0, 126.3, 126.7,
129.4, 133.0, 137.0, 138.0, 145.7, 160.0, 163.5.
MS: m/z (%)= 256 (32) [M+], 135 (31), 122 (71), 107 (100), 91 (32),
77 (47), 43 (51).
UV: lmax = 257, 272, 316, 412 nm.
Anal. Calcd for C15H12O2S (256.32): C, 70.29; H, 4.72. Found: C,
70.16; H, 4.69.
4-Hydroxy-1,2-dimethylthioxanthone (3e)
Yield: 8%; green needles; mp 230–232 °C.
IR (KBr): 1620 (s), 1580 (s), 1440 (s), 1400 (s), 1310 (s), 1230 (m),
1200 (m), 1100 (s), 950 (s), 870 (s), 800 (s), 750 (m) cm–1.
1H NMR (DMSO-d6): d = 2.20 (s, 3 H), 2.53 (s, 3 H), 7.01 (s, 1 H),
7.46 (t, 1 H), 7.61 (d, 1 H), 7.70 (t, 1 H), 8.23 (d, 1 H), 10.68 (s, 1 H).
13C NMR (DMSO-d6): d = 17.9, 20.9, 118.9, 123.0, 126.4, 128.7,
129.1, 130.9, 131.5, 132.2, 135.82, 136.1, 141.2, 149.9, 183.1.
MS: m/z (%) = 256 (36) [M+], 135 (34), 122 (70), 107 (100), 77 (50),
43 (52).
1-Hydroxythioxanthone (3a)
Yield: 60%; yellow needles; mp 118–120 °C.
IR (KBr): 1620 (s), 1580 (s), 1450 (s), 1350 (s), 1250 (s), 1180 (s),
900 (s), 830 (s), 780 (s), 720 (s) cm–1.
1H NMR (CDCl3): d = 6.91 (d, 1 H), 7.04 (d, 1 H), 7.45 (t, 1 H), 7.47
(t, 1 H), 7.51 (d, 1 H), 7.63 (t, 1 H), 8.57 (d, 1 H), 14.06 (s, 1 H).
13C NMR (CDCl3): d = 114.2, 116.3, 126.5, 127.2, 127.6, 128.9,
134.0, 136.0, 137.5, 138.3, 164.5, 185.3.
MS: m/z (%) = 228 (100) [M+], 200 (17), 171 (36).
UV: lmax = 264, 311, 390 nm.
Anal. Calcd for C15H12O2S (256.32): C, 70.29; H, 4.72. Found: C,
70.26; H, 4.76.
UV: lmax = 262, 313, 408 nm.
Anal. Calcd for C13H8O2S (228.26): C, 68.40; H, 3.53. Found: C,
68.36; H, 3.57.
1,4-Dihydroxy-3-methylthioxanthone (3f)
Yield: 40%; red needles; mp 237–239 °C.
1-Hydroxy-3-methylthioxanthone (3b)
Yield: 67%; yellow cubes; mp 148–150 °C.
IR (KBr): 3450 (w) 1640 (s), 1580 (s), 1360 (s), 1300 (s), 1230 (v),
1180 (s), 920 (s), 850 (m), 780 (s), 730 (s) cm–1.
IR (KBr): 1630 (s), 1580 (s), 1490 (m), 1450 (s), 1410 (s), 1350 (s),
1300 (m), 1190 (s), 900 (s), 860 (s), 840 (s), 750 (s), 700 (s) cm–1.
1H NMR (CDCl3): d = 2.41 (s, 3 H), 6.71 (s, 1 H), 6.83 (s, 1 H), 7.51
(m, 3 H), 8.53 (d, 1 H), 14.00 (s, 1 H).
13C NMR (CDCl3): d = 22.5, 115.3, 116.5, 118.3, 125.9, 126.5,
128.1, 129.6, 133.1, 138.4, 144.0, 147.8, 164.2, 185.2.
MS: m/z (%) = 242 (100) [M+], 213 (21), 184 (13), 43 (14).
1H NMR (DMSO-d6): d = 2.33 (s, 3 H), 6.78 (s, 1 H), 7.57 (t, 1 H),
7.75 (t, 1 H), 7.87 (d, 1 H), 8.45 (d, 1 H), 9.26 (s, 1 H), 13.47 (s, 1 H).
13C NMR (DMSO-d6): d = 17.5, 114.8, 126.9, 127.3, 127.4, 128.7,
133.8, 135.5, 138.2, 141.4, 158.3, 185.2.
MS: m/z (%) = 258 (100) [M+], 242 (43), 213 (35), 184 (16), 115
(10), 89 (13), 69 (27), 50 (33).
UV: lmax = 255, 273, 323, 424 nm.
UV: lmax = 268, 313, 405 nm.
Anal. Calcd for C14H10O3S (258.29): C, 65.10; H, 3.90. Found: C,
65.03; H, 3.82.
Anal. Calcd for C14H10O2S (242.29): C, 69.40; H, 4.16. Found: C,
69.32; H, 4.14.
1,4-Dihydroxy-2-methylthioxanthone (3g)
Yield: 40%; yellow needles; mp 219–220 °C.
1,3-Dihydroxythioxanthone (3c)
Yield: 70%; orange cubes; mp 232–233 °C.
IR (KBr): 3300 (w), 1630 (s), 1600 (s), 1480 (s), 1390 (s), 1300 (s),
1090 (s), 750 (s) cm–1.
Synthesis 2004, No. 17, 2900–2904 © Thieme Stuttgart · New York

PAPER
Novel Method for Synthesis of New Hydroxythioxanthone Derivatives
2903
1H NMR (DMSO-d6): d = 2.61 (s, 3 H), 6.26 (d, 1 H), 7.48 (m, 2 H),
13C NMR (DMSO-d6): d = 113.5, 123.0, 126.5, 126.7, 126.8, 128.1,
7.68 (m, 2 H), 8.28 (d, 1 H), 9.93 (s, 1 H).
128.3, 129.4, 129.9, 132.9, 137.3, 156.8, 178.9.
MS: m/z = 228 (100) [M+], 200 (34), 171 (31).
UV: lmax = 204, 253, 270, 405 nm.
13C NMR (DMSO-d6): d = 14.6, 120.8, 124.8, 125.8, 126.4, 127.1,
127.5, 128.9, 129.3, 131.0, 132.3, 135.9, 154.8, 182.6.
MS: m/z (%) = 258 (100) [M+], 242 (43), 213 (35), 184 (16), 115
(10), 89 (13), 69 (27), 50 (33).
Anal. Calcd for C13H8O2S (228.26): C, 68.40; H, 3.53. Found: C,
68.48; H, 3.50.
UV: lmax = 400 nm.
2,4-Dihydroxythioxanthone (4)
Yield: 5%; green needles; mp 220–222 °C.
Anal. Calcd for C14H10O3S (258.29): C, 65.10; H, 3.90%. Found: C,
65.17; H, 3.80.
IR (KBr): 3250 (br), 1580 (s), 1400 (s), 1350 (s), 1250 (s), 1150 (s),
1000 (s), 740 (s) cm–1.
2-Hydroxy-1,4-dimethylthioxanthone (3h)
Yield: 70%; yellow needles; mp 210–212 °C.
1H NMR (DMSO-d6): d = 6.79 (d, 1 H), 7.40 (d, 1 H), 7.53 (t, 1 H),
IR (KBr): 1610 (s), 1590 (s), 1450 (s), 1400 (s), 1320 (s), 1270 (s),
1080 (s), 950 (s), 930 (s) cm–1.
1H NMR (DMSO-d6): d = 2.41 (s, 3 H), 2.57 (s, 3 H), 7.17 (s, 1 H),
7.51 (t, 1 H), 7.67 (d, 1 H), 7.75 (t, 1 H), 8.25 (d, 1 H), 9.78 (s, 1 H).
13C NMR (DMSO-d6): d = 14.6, 19.5, 121.9, 125.0, 126.0, 126.5,
129.0, 129.3, 130.9, 131.9, 132.2, 134.0, 135.3, 145.1, 185.1.
MS: m/z (%) = 256 (100) [M+], 228 (69), 213 (46), 184 (26), 165
(14), 69 (15), 51 (20).
7.72 (t, 1 H), 7.83 (d, 1 H), 8.42 (d, 1 H), 9.93 (s, 1 H), 10.99 (s, 1 H).
13C NMR (DMSO-d6): d = 104.8, 106.1, 126.5, 127.5, 128.1, 129.2,
130.4, 132.67, 137.4, 154.3, 157.0, 167.4, 179.0.
MS: m/z = 244 (100) [M+], 216 (22), 187 (17), 115 (20), 69 (23), 43
(20).
UV: lmax = 271, 410 nm.
Anal. Calcd for C13H8O3S (244.26): C, 63.92; H, 3.30. Found: C,
63.84; H, 3.25.
UV: lmax = 205, 255, 405 nm.
Anal. Calcd for C15H12O2S (256.32): C, 70.29; H, 4.72. Found: C,
70.36; H, 4.65.
Acknowledgment
We gratefully acknowledge the support of this work by the Shiraz
University Research Council.
1,2,3-Trihydroxythioxanthone (3i)
Yield: 65%; red needles; mp 250–252 °C.
IR (KBr): 1630 (s), 1580 (s), 1440 (s), 1350 (s), 1270 (s), 1180 (s),
1110 (s), 1100 (s), 810 (s), 730 (s), 710 (s) cm–1.
References
1H NMR (DMSO-d6): d = 6.29 (s, 1 H), 6.58 (d, 1 H), 7.53 (t, 1 H),
(1) Foster, B. J.; Wiegand, R. A.; Partricia, S. P.; LoRusso, M.;
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(5) Archer, S.; Mattoccia, L. P.; Cioli, D.; Seyed-Mozaffari, A.;
Zayed, A. H. J. Med. Chem. 1988, 31, 254.
(6) Showalter, H. D. H.; Angelo, M. M.; Berman, E. M. J. Med.
Chem. 1988, 31, 1527.
(7) Laidlaw, G. M.; Collins, J. C.; Archer, S.; Rosi, D.;
Schulenberg, J. W. J. Org. Chem. 1973, 38, 1743.
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H.-A.; Shin, M.-S.; Yoon, Y.-J.; Park, K. H. J. Heterocycl.
Chem. 1999, 36, 793.
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34, 1637.
(10) Okabayashi, I.; Fujiwara, H. J. Heterocycl. Chem. 1994, 31,
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(11) Morita, H.; Mori, S.; Yamaoka, T. Bull. Chem. Soc. Jpn.
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1994, 90, 83.
7.64 (m, 2 H), 8.38 (s, 1 H), 11.06 (s, 1 H), 14.31 (s, 1 H).
13C NMR (DMSO-d6): d = 103.1, 108.19, 126.2, 126.6, 127.25,
128.7, 129.0, 131.5, 133.2, 137.3, 153.56, 153.6, 183.7.
MS: m/z = 260 (100) [M+], 231 (11), 186 (13), 158 (14), 69 (19), 45
(14).
UV: lmax = 253, 290, 385 nm.
Anal. Calcd for C13H8O4S (260.26): C, 59.99; H, 3.10. Found: C,
60.06; H, 3.02.
1,4-Dihydroxytioxanthone (3j)
Yield: 70%; red needles; mp 276–278 °C.
IR (KBr): 1630 (s), 1580 (s), 1480 (s), 1450 (s), 1350 (s), 1220 (s),
910 (s), 800 (s), 740 (s), 710 (s) cm–1.
1H NMR (DMSO-d6): d = 6.87 (d, 1 H), 7.24 (d, 1 H), 7.60 (t, 1 H),
7.81 (t, 1 H), 7.98 (d, 1 H), 8.48 (d, 1 H), 10.43 (s, 1 H), 13.35 (s, 1
H).
13C NMR (DMSO-d6): d = 113.37, 114.01, 121.55, 124.32, 127.07,
127.30, 127.62, 128.88, 133.88, 138.13, 144.14, 157.34, 185.53.
MS: m/z = 244 (100) [M+], 187 (18), 115 (16).
UV: lmax = 255, 273, 339, 439 nm.
(13) Neumann, M. G.; Gehlen, M. H.; Encinas, M. V.; Allen, N.
S. J. Chem. Soc., Faraday Trans. 1997, 93, 1517.
(14) Williams, E. L.; Ran, R.; Pittman, C. U. Chem. Abstr. 1998,
129, 276511g.
(15) Ran, R.; Pittman, U. C. J. Heterocycl. Chem. 1993, 30, 1673;
and references cited therein.
Anal. Calcd for C13H8O3S (244.26): C, 63.92; H, 3.30. Found: C,
63.84; H, 3.24.
2-Hydroxythioxanthone (3k)
Yield: 5%; green needles; mp 250–251 °C.
IR (KBr): 1630 (s), 1600 (m), 1450 (s), 1320 (s), 1230 (s), 1130 (s),
1100 (s), 930 (s), 850 (s), 810 (s) cm–1.
1H NMR (DMSO-d6): d = 7.27 (d, 1 H), 7.56 (t, 1 H), 7.70 (d, 1 H),
7.74 (s, 1 H), 7.80 (t, 1 H), 7.86 (d, 1 H), 8.45 (d, 1 H), 10.17 (s, 1 H).
(16) Okabayashi, I.; Fujiwara, H.; Tanaka, C. J. Heterocycl.
Chem. 1991, 28, 1977.
Synthesis 2004, No. 17, 2900–2904 © Thieme Stuttgart · New York

2904
H. Sharghi, A. R. S. Beni
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(b) Lewis, J. R.; Paul, J. G. J. Chem. Soc., Perkin Trans. 1
1981, 770.
(18) Sharghi, H.; Kaboudin, B. J. Chem. Res., Synop. 1998, 628.
(19) Sharghi, H.; Hosseini Sarvari, M. J. Chem. Res., Synop.
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(21) Sharghi, H.; Hosseini Sarvari, M. Synth. Commun. 2003, 33,
205.
(22) Sharghi, H.; Hosseini Sarvari, M. Tetrahedron 2003, 59,
3627.
Synthesis 2004, No. 17, 2900–2904 © Thieme Stuttgart · New York