Efficient synthesis of unsymmetrical dibenzothiophenes by acid-mediated intramolecular cyclization of biaryl methyl sulfoxides

Article abstract of DOI:10.1080/00397911.2010.525777

Aconvenient and high-yielding synthesis of unsymmetrical dibenzothiophenes has been achieved by an acid-mediated ring closure of the biphenyl ring having a sulfoxide substituent at the ortho position. Various functional groups are well tolerated in this methodology. Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.525777

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Efficient Synthesis of Unsymmetrical
Dibenzothiophenes by Acid-Mediated
Intramolecular Cyclization of Biaryl
Methyl Sulfoxides
Vrajesh B. Pandya a b , Mukul R. Jain a , Balaji V. Chaugule a , Jigar
S. Patel a , Bhavesh M. Parmar a , Jignesh K. Joshi a & Pankaj R.
Patel a
a Zydus Research Centre , Ahmedabad , Gujarat , India
b Department of Chemistry , Faculty of Science, M. S. University of
Baroda , Vadodara , India
Accepted author version posted online: 29 Jul 2011.Published
online: 17 Oct 2011.
To cite this article: Vrajesh B. Pandya , Mukul R. Jain , Balaji V. Chaugule , Jigar S. Patel ,
Bhavesh M. Parmar , Jignesh K. Joshi & Pankaj R. Patel (2012) Efficient Synthesis of Unsymmetrical
Dibenzothiophenes by Acid-Mediated Intramolecular Cyclization of Biaryl Methyl Sulfoxides, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
42:4, 497-505, DOI: 10.1080/00397911.2010.525777
To link to this article: http://dx.doi.org/10.1080/00397911.2010.525777
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Synthetic Communications1, 42: 497–505, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.525777
EFFICIENT SYNTHESIS OF UNSYMMETRICAL
DIBENZOTHIOPHENES BY ACID-MEDIATED
INTRAMOLECULAR CYCLIZATION OF BIARYL METHYL
SULFOXIDES
Vrajesh B. Pandya,1,2 Mukul R. Jain,1 Balaji V. Chaugule,1
Jigar S. Patel,1 Bhavesh M. Parmar,1
Jignesh K. Joshi,1 and Pankaj R. Patel1
1Zydus Research Centre, Ahmedabad, Gujarat, India
2Department of Chemistry, Faculty of Science, M. S. University of Baroda,
Vadodara, India
GRAPHICAL ABSTRACT
Abstract A convenient and high-yielding synthesis of unsymmetrical dibenzothiophenes has been
achieved by an acid-mediated ring closure of the biphenyl ring having a sulfoxide substituent at
the ortho position. Various functional groups are well tolerated in this methodology.
Keywords Cyclization; dibenzothiophene; intramolecular; sulfoxide
INTRODUCTION
Dibenzothiophenes 1 (Fig. 1) are biologically important because of their occur-
rence in a wide variety of natural products possessing useful biological activities.[1]
Also, different substituted dibenzothiophene derivatives are reported to be anti-
angiogenic agents,[2] antiobesity agents,[3] antiviral agents,[4] and agents for the treat-
ment of Pneucystis carinii pneumonia.[5] The literature discloses different approaches
for preparation of substituted dibenzothiophenes, such as disulfide ring closure,[6]
photochemical cyclization of 2-(20-methylthio)biphenyl radical,[7] sulfur insertion
in biphenyl using AlCl3,[8] fusion of 2,20-dihydroxybiphenyl with P2S5,[9] ring con-
traction of thianthrene using copper bronze[10] and cyclization of biphenyl-2-sulfonyl
chloride using AlCl3 gives dibenzothiophene dioxide,[11] which upon deoxygenation
gives dibenzothiophene.[12]
Received July 9, 2010.
ZRC Communication No. 314.
Address correspondence to Vrajesh B. Pandya, Zydus Research Centre, Sarkhej-Bavala Highway
No. 8A, Moraiya, Ahmedabad 382 213, Gujarat, India. E-mail: vrajeshpandya@zyduscadila.com
497

498
V. B. PANDYA ET AL.
Figure 1. General structure of dibenzothiophenes.
Figure 2. General structure of sulfoxide.
Sirringhaus et al. have reported synthesis of dibenzothienobisbenzothiophene
by acid-mediated intermolecular cyclization of a sulfoxide derivative.[13] This litera-
ture report involved the use of expensive and hazardous chemicals such as trifluor-
omethanesulfonic acid and pyridine, and also the reaction took a long time and
involved high temperature. The method does not have wider applicability in terms
of functional group sensitivity. Recently, Sanz et al. have reported the synthesis of
regioselectively functionalized dibenzothiophenes through anionic cyclization of
benyne-tethered aryllithiums.[14]
The aforementioned literature methods involve high-temperature reactions
using sulfur or sulfur-containing reagents or organolithium reagents. Also, some
of these methods suffer from poor yields. Direct introduction of functional groups
in dibenzothiophene nucleus also has limitations of regioselectivity. Literature meth-
ods for synthesis of 4-substituted dibenzothiophene ring involve metallation reac-
tions in dibenzothiophene ring at the 4-position followed by the addition of
appropriate electrophile.[15] Electrophilic substitution reaction on dibenzothiophene
ring goes at the 2-position. Hence the synthesis of 1- and 3-substituted dibenzothio-
phene derivatives is relatively difficult and involves multiple steps.
In continuation of our interest in synthesizing dibenzothiophenes with a variety
of substituents, herein we report a simple, cost-effective, and industrially applicable
synthesis of unsymmetrical dibenzothiophenes by acidic ring closure of sulfoxide 2
(Fig. 2) using inorganic reagents, sulfuric acid, and potassium carbonate.
RESULTS AND DISCUSSION
To access sulfoxide 2, the synthetic strategy depicted in Scheme 1 is adapted.
Several methods are reported to make the biphenyl ring system. For the sake of sim-
plicity and easy availability of substituted boronic acids, we adapted the Suzuki
coupling[16] reaction. Thus, the coupling of substituted phenylboronic acid with
substituted halobenzene gave the biphenyl ring, which upon oxidation with hydro-
gen peroxide[17] produced desired sulfoxide 2 in excellent yield.

UNSYMMETRICAL DIBENZOTHIOPHENES
499
Scheme 1. Reagents and conditions: (i) Pd(OAc)2, Na2CO3, MeOH, 70–95%; (ii) H2O2 (50%), Cat. V2O5,
MeCN, 80–90%; (iii) conc.H2SO4, 0–75 ꢀC, then aq. K2CO3, rt.
Once sulfoxide 2 was in hand, we set forth to screen the best acidic reagent to
achieve ring closure and thereby produce dibenzothiophene. Sulfuric acid was found
to give the best result in terms of yield and purity of dibenzothiophene as compared
to the other Lewis or mineral acids screened. It was also found that the cyclization
worked excellently when neat sulfuric acid was used. Sulfuric acid in solvent took a
longer time to bring the desired cyclization and also the isolated yield was less
(Table 1).
To extend the application of this reaction for the synthesis of substituted diben-
zothiophenes, sulfoxide 2 with various substituents has been synthesized and sub-
jected to cyclization in neat sulfuric acid (Table 2). It was observed that sulfoxide
2 containing electron-releasing groups produced greater yield of the corresponding
dibenzothiophenes (2a, 2b, and 2c). Electron withdrawing group such as nitro (2e)
Table 1. Screening of acidic reagents for cyclization
No.
Cyclization reagent
Solvent
Neat
Reaction time (h)
Temperature (ꢀC)
Yield (%)
1
2
3
4
5
H2SO4 (3v=w)
I2 (2 equiv.)
0.25
20
20
0–25
70
94
No reaction
No reaction
10
Toluene
Toluene
Neat
AlCl3 (2 equiv.)
TFA (3v=w)
H2SO4 (3v=w)
70
20
15
0–25
0–25
Chloroform
50

500
V. B. PANDYA ET AL.
Table 2. Synthesis of substituted dibenzothiophenes
No.
Substituent on 2
Substituent on 1
Temperature (ꢀC)
Time (h)
Yield (%)
a
R1 ¼ R2 ¼ R3 ¼ H
R1 ¼ R3 ¼ H,
R2 ¼ 4-F
R1 ¼ R2 ¼ R3 ¼ H
R1 ¼ R3 ¼ H,
R2 ¼ 3-F
0–25
0–25
0.5
0.5
94
92
b
c
d
e
f
R1 ¼ R3 ¼ H,
R2 ¼ 2-CH3
R1 ¼ R3 ¼ H,
R2 ¼ 1-CH3
0–25
0–25
0–75
0–25
0.5
1
97
75
49
74
R1 ¼ R3 ¼ H,
R2 ¼ 4-COOCH3
R1 ¼ R3 ¼ H,
R2 ¼ 4-NO2
R1 ¼ R3 ¼ H,
R2 ¼ 3-COOCH3
R1 ¼ R3 ¼ H,
R2 ¼ 3-NO2
2
R1 ¼ 3-OCH3,
R2 ¼ 4-COOCH3,
R3 ¼ H
R1 ¼ 2-OCH3,
R2 ¼ 3-COOCH3
R3 ¼ H
1
g
R1 ¼ 2-CH3,
R2 ¼ H,
R1 ¼ 1-CH3,
R2 ¼ H,
0–25
0–25
0.25
0.25
82
85
R3 ¼ 50-COCH3
R1 ¼ 2-CH3,
R2 ¼ H,
R3 ¼ 8-COCH3
R1 ¼ 1-CH3,
R2 ¼ H,
h
R3 ¼ 50-CH2CH3
R1 ¼ 3-COCH3,
R2 ¼ R3 ¼ H
R1 ¼ 2-COOCH3,
R2 ¼ R3 ¼ H
R3 ¼ 8-CH2CH3
R1 ¼ 2-COCH3,
R2 ¼ R3 ¼ H
R1 ¼ 1-COOCH3,
R2 ¼ R3 ¼ H
i
j
0–25
0–25
0.25
1
70
55
and ester (2d) resist cyclization and hence gave relatively lesser yields. Most of the
reactions were completed at 25 ꢀC within 30 min, except for reactions with ring
systems bearing electron-withdrawing groups (2d, 2e, and 2f). The 1-substituted
dibenzothiophenes have been effectively synthesized, as can be seen from examples
2c and 2j. Substituents on both rings are possible through this methodology (2 h
and 2 g).
The proposed mechanism of the reaction is shown in Scheme 2. The first step
involves protonation of sulfoxide followed by nucleophilic attack of neighboring
aromatic ring. Dehydration eventually led to aromatization, furnishing salt 8. The
demethylation of salt using base gives the desired dibenzothiophene derivatives. This
mechanism correlates with our experimental observation of poor yield and more
reaction time for electron-withdrawing group substituted sulfoxide as it destabilizes
the positively charged transition state. Nenaidenko et al. have reviewed the synthetic
capabilities of sulfonium salts with mechanistic aspects.[18] Nucleofugality of the
group attached to the S atom is one of the main factors that determines direction
of nucleophilic attack on sulfonium salt. In our case, biaryl sulfide is a good leaving
group compared to methyl in sulfonium salt 8 and also methyl group provides an

UNSYMMETRICAL DIBENZOTHIOPHENES
501
Scheme 2. Proposed mechanism for cyclization.
electrophilic center for the nucleophile, that is, hydroxide ion generated from
aqueous potassium carbonate.
CONCLUSION
In summary, a convenient and efficient method for the synthesis of unsym-
metrical dibenzothiophene derivatives has been reported. The advantage of the
described methodology over the reported ones is incorporation of substituents in
the dibenzothiophene core with ease and good yields. The present method utilizes
inexpensive and environmentally friendly reagents. Further, the duration of the
reaction is very short and also reactions are accomplished at low temperature.
This method gives access to a substituent at every position of dibenzothiophene.
1-Subsituted dibenzothiophene, which is difficult to make by direct substitution reac-
tion on dibenzothiophene, can be easily prepared by this method. This methodology
has potential applications for the synthesis of sulfur-containing fused heterocycles.
EXPERIMENTAL
Melting points were recorded with a Thomas–Hoover capillary melting-point
apparatus and are uncorrected. Infrared (IR) spectra were recorded with an Fourier
transform (FT-IR) instrument as a thin film or using KBr pellets, and are expressed
1
in centimetersꢁ1. H (400 MHz) and 13C (100 MHz) NMR spectra were recorded
using dimethylsulfoxide (DMSO) as a solvent. Ultra performance liquid chromato-
graphy (UPLC) purity were recorded in 0.05% TFA in water–ACN as a mobile
phase and BEH C18, 2.1 ꢂ 100 mm column as a stationary phase. Elemental analyses
were carried out with a C, Hanalyzer. Thin-layer chromatography (TLC) was per-
formed on precoated plates (0.25 mm, silica gel 60 F254). Column chromatography
was carried out with silica gel (100–200 mesh). The reactions were carried out in
oven-dried glassware under dry N2. MeOH and ACN were purified and dried before
use. Distilled n-hexane and EtOAc were used for column chromatography.
General Procedure for Suzuki Coupling
Sodium carbonate (2 mmol) was added to a mixture of substituted halobenzene
(3 or 7) (1 mmol) in dry methanol (10 v=w) placed in a round-bottomed flask

502
V. B. PANDYA ET AL.
attached with condenser followed by palladium acetate (2 mol%). Substituted phe-
nylboronic acid (4 or 6) (1 mmol) was added in one lot, and the reaction mixture
was subjected to reflux. After 5 h, the reaction mixture was cooled to 25–30 ꢀC.
Methanol (3 v=w) was added, and the mixture was vacuum filtered through a sin-
tered glass funnel using celite as a filter aid to furnish a residue. The residue obtained
was purified by flash chromatography using 100 to 200-mesh silica gel as a stationary
phase and n-hexane–ethyl acetate as a mobile phase (yield 70–90%).
General Procedure for Oxidation
A solution of biphenyl compound (5) (1 mmol) and V2O5 (0.1 mmol) in aceto-
nitrile (5 mL) was cooled at 0 ꢀC by keeping a round-bottomed flask in an ice bath
under a nitrogen environment. Aqueous hydrogen peroxide (1.2 mmol, 50%) was
added to the reaction mixture and it was stirred at 10 ꢀC for 1 h. After 1 h, the reac-
tion mixture was diluted with water (15 mL) and extracted with ethyl acetate
(25 mL). The organic layer was dried over anhydrous sodium sulfate, filtered, and
evaporated to offer the corresponding sulfoxide (yield ¼ 80–90%).
General Procedure for Cyclization
Sulfoxide compound (2) (0.5 g) was added in portions to stirred concentrated
H2SO4 (1.5 mL, 3 v=w) in a one-necked, round-bottomed flask containing a guard
tube at 0–5 ꢀC. The reaction mixture was stirred at 25 ꢀC for 0.5–2 h. The reaction
mixture was poured on ice-cold water (10 mL) and then made basic with aqueous
potassium carbonate solution (pH 8). The aqueous layer was extracted with ethyl
acetate (2 ꢂ 15 mL). The organic layer was dried over anhydrous sodium sulfate,
filtered, and evaporated to give the titled compound (yield ¼ 49–97%).
Spectral Data of Synthesized Compounds
Dibenzo[b,d]thiophene (1a). White solid, mp: 98 ꢀC, IR (KBr): nmax 3051,
1583, 1415, 1307, 1230, 1130, 1066, 929, 734, 495 cmꢁ1
;
1H NMR (400 MHz,
1
DMSO-d6): d 7.47–7.53 (m, 4H), 7.99–8.04 (m, 2H), 8.34–8.38 (m, 2H); H NMR
(400 MHz, CDCl3): d 7.43–7.47 (m, 4H), 7.83–7.87 (m, 2H), 8.13–8.18 (m, 2H);
13C NMR (100 MHz, DMSO-d6): d 122.0, 123.0, 124.7, 127.0, 135.0, 138.5. CHNS:
Calculated for C12H8S: C, 78.22; H, 4.38; S, 17.40. Found: C, 78.32; H, 4.34; S,17.20.
3-Fluorodibenzo[b,d]thiophene (1b). White solid, mp: 101 ꢀC; IR (KBr):
;
nmax 3387, 1604, 1440, 1396, 1315, 1240, 891, 840, 758, 732 cmꢁ1 1H NMR
(400 MHz, DMSO-d6): d 7.32–7.37 (m, 1H), 7.46–7.51 (m, 2H), 7.92–7.95 (m, 1H),
7.98–8.02 (m, 1H), 8.30–8.32 (m, 1H), 8.33– 8.38 (m, 1H); 13C NMR (100 MHz,
DMSO-d6): d 109.3, 112.8, 121.8, 122.9, 123.4, 124.9, 126.6, 131.7, 134.2, 138.50,
140.0; ESI-MS: m=z: 225.4 (M þ Na)þ. CHNS: Calculated for C12H7FS: C, 71.26;
H, 3.49; S, 15.85. Found: C, 70.90; H, 3.36; S, 15.98.
1-Methyldibenzo[b,d]thiophene (1c). White solid; mp: 74 ꢀC; IR (KBr):
1
nmax 3387, 3059, 2949, 1905, 1438, 1307, 1028, 773, 738, 729, 707 cmꢁ1; H NMR
(400 MHz, DMSO-d6): d 2.87 (s, 3H), 7.30 (d, J ¼ 8 Hz, 1H), 7.38–7.42 (m, 1H),

UNSYMMETRICAL DIBENZOTHIOPHENES
503
7.49–7.54 (m, 2H), 7.87 (d, J ¼ 8 Hz, 1H), 8.02–8.06 (m, 1H), 8.37–8.41 (m, 1H);13C
NMR (100 MHz, DMSO-d6): d 22.1, 120.6, 122.9, 124.6, 125.0, 126.1, 126.4, 127.1,
133.0, 134.6, 135.8, 138.7, 138.9. CHNS: Calculated for C13H10S: C, 78.75; H, 5.08;
S, 16.17. Found: C, 78.30; H, 5.05; S, 16.11.
Methyldibenzo[b,d]thiophene-3-carboxylate (1d). White solid, mp:
138 ꢀC; IR (KBr): nmax 2939, 1712, 1597, 1442, 1388, 1288, 1253, 1112, 974, 848,
754 cmꢁ1 1H NMR (400 MHz, DMSO-d6): d 3.90 (s, 3H), 7.55–7.60 (m, 2H),
;
8.04–8.10 (m, 2H), 8.44–8.47 (m, 1H), 8.51 (d, J ¼ 8.4 Hz, 1H), 8.67 (d, J ¼ 1.6 Hz,
1H); 13C NMR (100 MHz, DMSO-d6): d 52.3, 122.0, 122.9, 123.0, 124.0, 125.0,
125.1, 127.9, 128.1, 134.0, 138.1, 138.7, 140.2, 165.9. CHNS: Calculated for
C14H10O2S: C, 69.40; H, 4.16; S, 13.23. Found: C, 69.48; H, 4.17; S, 13.41.
3-Nitrodibenzo[b,d]thiophene (1e). Yellow solid; mp: 150 ꢀC; IR (KBr):
1
nmax 2962, 1604, 1518, 1448, 1330, 1261, 1103, 1022, 879, 771, 738 cmꢁ1; H NMR
(400 MHz, DMSO-d6): d 7.61–7.66 (m, 2H), 8.14 (d, J ¼ 8 Hz, 1H), 8.32 (dd,
J ¼ 8.8 Hz, 2 Hz, 1H), 8.52 (d, J ¼ 8 Hz, 1H), 8.60 (d, J ¼ 8.8 Hz, 1H), 9.08 (d,
J ¼ 2 Hz, 1H);13C NMR (100 MHz, DMSO-d6): d 118.5, 119.6, 122.5, 123.3, 123.5,
125.3, 128.8, 133.2, 139.1, 140.0, 141.3, 145.8; ESI-MS: m=z: 230 (M þ H)þ, CHNS:
Calculated for C12H7NO2S: C, 62.87; H, 3.08; N, 6.11; S, 13.99. Found: C, 62.86; H,
3.10; N, 6.10; S, 13.95.
Methyl 2-methoxydibenzo[b,d]thiophene-3-carboxylate (1f). White
solid, mp: 128 ꢀC; IR (KBr): nmax 3347, 1610, 1450, 1366, 1345, 1250, 891, 840,
760, 740 cmꢁ1;1H NMR (400 MHz, DMSO-d6): d 3.82 (s, 3H), 3.96 (s, 3H),
7.51–7.57 (m, 2H), 8.03 (d, J ¼ 8.4 Hz, 1H), 8.10 (s, 1H), 8.29 (s, 1H), 8.49 (d,
J ¼ 8.4 Hz, 1H); 13C NMR (100 MHz, DMSO-d6): d 52.0, 56.3, 105.3, 120, 123.0,
23.1, 124.6, 125.2, 127.9, 129.5, 134.4, 139.0, 140.8, 156.1, 165.9; ESI-MS: m=z:
273 (M þ H)þ. CHNS: Calculated for C15H12O3S: C, 66.16; H, 4.44; S, 11.77.
Found: C, 66.15; H, 4.51; S, 11.65.
1-(9-Methyldibenzo[b,d]thiophen-2-yl)ethanone (1g). White solid, mp:
1678, 1356, 1313, 1244, 879, 840, 767 cmꢁ1 1H NMR
;
125 ꢀC; IR (KBr): n
max
(400 MHz, DMSO-d6): d 2.72 (s, 3H), 2.94 (s, 3H), 7.38 (d, J ¼ 7.2 Hz, 1H), 7.49
(t, J ¼ 7.6 Hz, 1H), 7.95 (d, J ¼ 8 Hz, 1H), 8.11 (dd, J ¼ 8.4, 1.6 Hz, 1H), 8.21 (d,
J ¼ 8.4 Hz, 1H), 8.90 (d, J ¼ 1.6 Hz, 1H); 13C NMR (100 MHz, DMSO-d6): d 21.8,
26.7, 120.8, 121.9, 124.6, 125.5, 127, 127.5, 132.5, 133.3, 134.9, 135.6, 139.3, 143.8,
197.3; ESI-MS: m=z: 240.8 (M þ H)þ; CHNS. Calculated for C15H12OS: C, 74.97;
H, 5.03; S, 13.34. Found: C, 74.90; H, 4.99; S, 13.10.
8-Ethyl-1-methyldibenzo[b,d]thiophene (1h). Semisolid, IR (KBr): nmax
1
2999, 1460, 1217, 1033, 758 cmꢁ1; H NMR (400 MHz, DMSO-d6): d 1.30 (t, 3H),
2.83 (q, 2H), 7.29 (d, J ¼ 7.6 Hz, 1H), 7.38 (d, J ¼ 7.6 Hz, 1H), 7.40 (d, J ¼ 8.4 Hz,
1H), 7.85 (d, J ¼ 7.6 Hz, 1H), 7.94 (d, J ¼ 8.4 Hz, 1H), 8.20 (d, J ¼ 0.8 Hz, 1H);
13C NMR (100 MHz, DMSO-d6): d 16.0, 22.2, 28.4, 120.6, 122.6, 124.0, 126.2,
126.4, 127.0, 133.0, 134.6, 135.9, 136.0, 139.2, 140.2. CHNS: Calculated for
C15H14S: C, 79.60; H, 6.23; S, 14.17; Found. C, 79.37; H, 6.33; S, 14.32.
1-(Dibenzo[b,d]thiophen-2-yl)ethanone (1i). White solid, mp: 125 ꢀC; IR
;
(KBr): nmax 1664, 1446, 1354, 1269, 964, 754, 603 cmꢁ1 1H NMR (400 MHz,

504
V. B. PANDYA ET AL.
DMSO-d6): d 2.77 (s, 3H), 7.51–7.58 (m, 2H), 7.74 (t, 1H), 8.05–8.09 (m, 1H), 8.36
(d, J ¼ 8 Hz, 1H), 8.42–8.46 (m, 1H), 8.70 (d, J ¼ 8 Hz, 1H); 13C NMR (100 MHz,
DMSO-d6): d 26.5, 122.0, 122.8, 124.8, 124.8, 126.7, 127.4, 130.1, 130.3, 133.4,
136.6, 137.5, 141.1, 197.7. CHNS: Calculated for C14H10OS: C, 74.31; H, 4.45; S,
14.17. Found: C, 74.38; H, 4.43; S, 14.27.
Methyldibenzo[b,d]thiophene-1-carboxylate (1j). White solid, mp: 88 ꢀC;
1
IR (KBr): n
1664, 1446, 1354, 1269, 964, 754, 603 cmꢁ1; H NMR (400 MHz,
max
DMSO-d6): d 4.02 (s, 3H), 7.47–7.51 (m, 1H), 7.54–7.57 (m, 1H), 7.59–7.61 (m,
1H), 7.72 (dd, J ¼ 8, 4 Hz, 1H), 8.10 (d, J ¼ 8 Hz, 1H), 8.21 (d, J ¼ 8 Hz, 1H), 8.26
(dd, J ¼ 8, 4 Hz, 1H); 13C NMR (100 MHz, DMSO-d6): d 52.8, 123.2, 124.6, 124.7,
125.5, 126.1, 126.2, 127.5, 128.4, 131.0, 132.9, 139.2, 139.9, 168.7; ESI-MS: m=z:
265.16 (MþNa)þ. CHNS: Calculated for C14H10O2S: C, 69.40; H, 4.16; S, 13.21.
Found: C, 69.47; H, 4.28; S, 13.15.
ACKNOWLEDGMENT
We are thankful to the Zydus Group management for encouragement and the
analytical department for support.
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