Eco-friendly HClO4-SiO2 catalyzed synthesis of mono-and bis-diaryl-2h-1,4 benzothiazines

Article abstract of DOI:10.1002/jhet.795

Mono-and bis-diaryl-2H-1,4-benzothiazines were obtained in quantitative yields through silica-supported perchloric acid catalyzed reaction cascade of double condensation and 1,4 addition of diaroylacetylenes with 2-aminothiophenol at room temperature. The

Full text of DOI:10.1002/jhet.795

1336
Eco-Friendly HClO4–SiO2 Catalyzed Synthesis of Mono- and
Bis-diaryl-2H-1,4 Benzothiazines
Vol 48
Mohd. Imran Ansari,a Ravi Shankar,a Mohd. Kamil Hussain,a Ruchir Kant,b
Prakash R. Maulik,b K. Ravi Kumar,c and K. Hajelaa*
aMedicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226001,
UP, India
bMolecular and Structural Biology Division, Central Drug Research Institute, Lucknow-226001,
UP, India
cX-ray Crystallographic Division, Indian Institute of Chemical Technology, Hyderabad-500007,
AP, India
*E-mail: kanchan_hajela@cdri.res.in
Received September 24, 2010
DOI 10.1002/jhet.795
Published online 18 August 2011 in Wiley Online Library (wileyonlinelibrary.com).
Mono- and bis-diaryl-2H-1,4-benzothiazines were obtained in quantitative yields through silica-sup-
ported perchloric acid catalyzed reaction cascade of double condensation and 1,4 addition of diaroylace-
tylenes with 2-aminothiophenol at room temperature. The structures were confirmed by spectroscopic
analyses and X-ray crystallographic studies.
J. Heterocyclic Chem., 48, 1336 (2011)
INTRODUCTION
prepared either through oxidation of monomeric 1,4-
benzothiazines [9], as condensation product of 2-amino-
thiophenol with isoxazolones [10] or from a,a-dihalocar-
bonyl compounds [11]. In this article, we report a new
and expedient synthesis of mono- and bis-2H-diaryl 1,4-
benzothiazines through silica-supported perchloric acid
(HClO4–SiO2) catalyzed reaction cascade of double con-
densation and 1,4-Michael addition.
The leading contenders for eco-friendly processes are
supported reagents [1a,b]. The good thermal and me-
chanical stabilities of such reagents make them easy to
handle as free flowing powders, less toxic, noncorrosive,
and their ease of separation and regeneration. Novel
solid acid catalysts are being developed for use in or-
ganic synthesis. The newly introduced silica-supported
perchloric acid (HClO4–SiO2) has emerged as a mild
and a highly efficient, recyclable heterogenous catalyst
system [2]. Its successful application as a versatile solid
acid catalyst in a variety of multicomponent reactions/
synthetic transformations [3–5] for the synthesis of
diverse heterocyclic compounds led us to explore its
utility in the condensation reactions of diaroylacetylenes
and diaroylethylene with 2-aminothiophenol.
RESULTS AND DISCUSSION
When 1,2-diaroylacetylene (1) is mixed with 2-amino-
thiophenol (2) at room temperature (25ꢀC) with stirring in
methanol and catalyzed by silica-supported perchloric
acid, the reaction is very fast and completes within 20 min.
Two major spots seen on thin layer chromatography
(TLC) were isolated as crystalline yellow solids on purifi-
cation by column chromatography in the ratio of 80:20.
One compound showed all proton merged in aromatic
region and mass value of 342 (Mþþ1), the second com-
pound showed a sharp singlet at 4.1 d ppm for two protons
and five extra aromatic protons and a mass value of 448
(Mþ). Reaction of 2-aminothiophenol with chalcones or
alkynones [12] is reported to form the seven-membered
1,5-benzothiazepine derivatives; however, there is no
report of reaction between 1,4-diaroylacetylene and 2-
Benzothiazine ring system containing compounds are
well known for their biological activities as antifungal,
cytotoxic, anti-inflammatory, antiallergic, immunostimu-
lating, antiarrythmic, and central nervous system (CNS)
depressants [6]. In particular, 1,4-benzothiazine-induced
neurotoxic effects have been hypothesized to play a role
in neurodegenerative diseases, such as Parkinson’s and
Alzheimer disease [7]. Their synthesis mainly involves
treatment of 2-aminothiophenol with a-halocarbonyl
compounds [8]. Bis-diaryl 1,4-benzothiazines have been
C
V
2011 HeteroCorporation

November 2011
Eco-Friendly HClO4–SiO2 Catalyzed
Synthesis of Mono- and Bis-diaryl-2H-1,4 Benzothiazines
1337
Scheme 1. Synthetic pathways for the synthesis of mono- and bis-diaryl-2H-1,4 benzothiazines.
aminothiophenol, although 1,4-diaroylacetylenes are
reported to form six-membered quinoxaline derivatives
with 1,2-diaminobenzenes [13].
compound being either 4 or 6 could not be ascertained. To
confirm the molecular structure between benzothiazepine
or benzothiazine skeleton, we tried to develop crystals of
4, 6, and 7. Fortunately, single crystal X-ray diffraction
studies confirmed the structure of compound 7 as 2,20-bis-
2H-3,3-diaryl-1,4-benzothiazine shown in the Oak Ridge
thermal ellipsoid plot (ORTEP) diagram (Fig. 1).
With the above observations, there existed the possibil-
ity of formation of either six- or seven- membered ring
compounds as the reaction may follow any of the two
pathways as shown in Scheme 1. (i) Conjugate addition
of the sulfhydryl group resulting in the formation of thia
Michael adduct (3) which on subsequent intramolecular
aldol condensation and dehydration may form 1,5-benzo-
thiazepine derivative (4) or (ii) initial aldol condensation
product (5) followed by intramolecular conjugate addition
by the sulfhydryl group and rearrangement to form the
1,4-benzothiazine derivative (6). Since the molecular ion
peak of second compound showed higher mass value of
approx. 448, indicated further conjugate addition of
another molecule of 2-aminothiophenol. We tried the
same reaction with two equivalents of 2-aminothiophenol,
and in just 15 min of stirring an orange-yellow solid (7)
precipitated out in quantitative yield. It showed a sharp
singlet at 4.1 d ppm for two protons and same number of
aromatic protons and also molecular ion peak of mass
value 448 (Mþ) in the mass spectrum.
This confirmed double condensation reaction but still the
formation of six- or seven-membered ring skeleton of the
Figure 1. ORTEP diagram of 7 showing its molecular structure.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1338
M. I. Ansari, R. Shankar, M. K. Hussain, R. Kant, P. R. Maulik, K. R. Kumar, and K. Hajela
Vol 48
Scheme 2. Synthesis of 1-aryl-2-[(3-arylquinoxalin-2(1H)-ylidene) ethanone 8.
This conclusively proved the first compound 6 as the
SiO2, HBF4–SiO2, and trifluoroacetic acid (TFA)–SiO2,
six-membered benzothiazine derivative, (Z)-1-phenyl-2-
(3-phenyl-2H-benzo[b][1,4]thiazin-2-ylidene)ethanone in
which the exocyclic ene proton merged with the aromatic
protons. In 13C-NMR spectrum, it shows a clear peak at
118 d ppm. It undergoes double condensation to give the
bis-compound 7 in the presence of excess thiophenol due
to the exocyclic enone system and shows a two-proton
singlet at 4.1 d ppm in the proton nuclear magnetic reso-
nance (NMR). This structure confirmation was supported
by the formation of six-membered 1-aryl-2-[(3-arylqui-
noxalin-2(1H)-ylidene) ethanone (8) on reaction of 1 with
benzene-1, 2-diamine (Scheme 2). Its X-ray crystal struc-
ture is shown in the ORTEP diagram (Fig. 2).
the catalytic efficiency followed the order HClO4–SiO2
> H2SO4–SiO2 > TFA–SiO2 > HBF4–SiO2. With other
catalysts like TFA, para toluene sulfonic acid (PTSA),
BF3ꢁEt2O, acetic acid, and SiO2, mixture of 6 and 7 was
obtained. The formation of bis derivative was found to
be independent of catalyst loading, the best yields of 7
were obtained with silica-supported perchloric acid
(HClO4–SiO2) and in less time. An increase in the cata-
lyst loading did not have any significant effect on the
yields of either 6 or 7. The catalyst can be recovered by
simple filtration and can be reused after proper washing
and drying without any significant loss of activity.
To extend the scope of reaction, we next focussed our
attention on the reaction of 1,4-diaroylethylene with 2 under
the same reaction conditions (Scheme 3 and Table 2).
TLC of the reaction mixture showed only one major
spot which was isolated as yellow oil in 88% yield by
column chromatography. Its structure was determined
from the one-dimensional 1H- and 13C-NMR and by
using 2D correlation spectroscopy (COSY), heteronuclear
single quantum coherence (HSQC), and heteronuclear
multiple bond coherence (HMBC) sequences. The 1H-
NMR spectrum exhibited two doublet of doublets at d
2.86 and d 3.42 ppm and another doublet of doublet at d
4.89 ppm. In our opinion, the downfield doublet of dou-
blet at d 4.89 corresponds to the Ha proton being adjacent
to the carbonyl group and sulfur atom, whereas the dou-
blet of doublets at d 2.86 and d 3.42 ppm correspond for
With the confirmation of structures of compounds 6,
7, and 8, the effect of catalyst and its loading was next
studied by carrying out the above reactions using differ-
ent solid acid catalysts. The results are noted in Table 1.
When both the reactants are used in equimolar amounts
with the catalyst loading of 1 mol %, compound 6 pre-
dominates (>70%) although minor amount of bis
compound 7 is also formed. However, if thiophenol is
present in excess (2 equiv.), bis compound 7 is obtained
in almost quantitative yields with the same catalyst load-
ing of 1 mol %. The reaction was also studied using
other protic acids immobilized on silica like, H2SO4–
Table 1
Direct condensation of 1 and 2 (2 mmol) to form compound 7 using
different solid acid catalysts in methanol at room temperature (25ꢀC).
Entry
Catalyst
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
HClO4–SiO2
H2SO4–SiO2
HBF4–SiO2
BF3.EtO
20
30
40
25
35
30
20
30
85
60
48
58
55
52
62
68
PTSA
TFA–SiO2
TFA
CH3COOH
Figure 2. ORTEP diagram showing molecular structure of 8.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

November 2011
Eco-Friendly HClO4–SiO2 Catalyzed
Synthesis of Mono- and Bis-diaryl-2H-1,4 Benzothiazines
1339
Scheme 3. Synthesis of (E)-phenyl(4-phenyl-2,3-dihydrobenzo[b][1,4]thiazepin-2-yl)methanone.
the two geminal protons Hb and Hc (methylene protons,
Fig. 3). This was also confirmed from 135 distortionless
enhancement by polarization transfer (DEPT) and HSQC
experiments. In the COSY experiment, cross-peaks were
observed between the methylene proton indicating that
the Hb and Hc protons are geminal, also confirmed by the
help of HSQC experiment. The structure was fully estab-
lished from the HMBC sequences. In the HMBC spec-
trum, the proton of doublet of doublet at dHa 4.89 ppm
showed cross peak at dC 157.9 ppm (C¼¼N) and a quater-
nary aromatic carbon bonded with sulfur at dC 120.3 ppm.
The proton signal at dHb 3.42 ppm and dHc 2.86 ppm
showed cross-peaks to a carbonyl carbon at dC 196.1 ppm
(C¼¼O). Cross-peaks of proton at dHa 4.89 ppm showed
stronger cross-coupling with carbon at dC 157.9 ppm
(C¼¼N) than the carbonyl carbon and protons Hb and Hc
showed stronger cross-coupling with carbonyl carbon at
dC 196.1 ppm (C¼¼O) than carbon at dC 157.9 ppm
(C¼¼N). This HMBC correlation confirmed the presence
of a seven-membered cyclic ring establishing the structure
of the compound 8 as phenyl (4-phenyl-2,3-dihydro-ben-
zo[b][1,4]thiazepin-2-yl)methanone, shown in Figure 3.
In summary, to the best of our knowledge this is the
first report of an expedient and eco-friendly synthesis of
mono- and bis-diaryl-2H-1,4 benzothiazines through the
coupling of 1,2-diaroylacetylene and 2-aminothiophenol
using heterogenous catalyst system which is recyclable,
easy to use, and environmentally benign. Further, it was
observed that diaroylacetylenes and ethylenes react dif-
ferently with 2-aminothiophenol under the same reaction
conditions forming different heterocyclic compounds.
The stability of six-membered ring and its dimerisation
to a more stable bis-derivative may be the driving force
for the preferred formation of 1,4-benzothiazine deriva-
tives with 1,2-diaroylacetylenes.
EXPERIMENTAL
Melting points were taken in open capillaries on an electri-
cally heated melting point apparatus Complab and are uncor-
rected. Infra red (IR) spectra were recorded on Perkin-Elmer
RX-1 spectrophometer using KBr pellets. 1H-NMR and 13C-
NMR spectra were recorded on Bruker DPX-200 (200 MHz for
1
1H and at 50 MHz for 13C) or DRX-300 (300 MHz for H and
at 75 MHz for 13C) spectrometers using CDCl3 as solvent. Tet-
ramethylsilane served as an internal standard in 1H-NMR and
CDCl3 in 13C spectra. Silica gel (60–120 mesh) was used for
column chromatography while silica gel (230–400 mesh) was
used for flash chromatography. TLC was run on precoated silica
gel 60F 254 and RP-18 F 254 (Merck) plates. Detection of spots
was done either by iodine vapors or spraying with 1% ceric sul-
fate in 1M H2SO4 followed by heating at 100ꢀC. All the com-
pounds were characterized by spectroscopic data and elemental
analysis carried was out on Vario EL-III, German analyzer.
(E)-1-Phenyl-2H-benzo[b][1,4]thiazin-2-ylidene)ethanone
(6). Diaroylacetylene (1, 236 mg, 1 mmol) was dissolved in
methanol (2 mL) and stirrred for 2 min. Silica-supported
perchloric acid (HClO4–SiO2, 1.62 mg, 1 mol %) was then
added to the solution, followed by 2-aminothiophenol (2,
Table 2
Direct condensation of 1,4-diaroylethylene and 2 (2 mmol) to form
compound 9 using different solid acid catalysts in methanol at room
temperature (25ꢀC).
Entry
Catalyst
Time (min)
Yield (%)
1
2
3
4
5
6
7
HClO4–SiO2
HBF4–SiO2
H2SO4–SiO2
TFA–SiO2
TFA
20
30
35
25
25
25
30
88.4
54
58
60
61
52.98
62.39
BF3ꢁEtO
AcOH/piperidine
Figure 3. Significant HMBC (H ! C) correlation of compound 9.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1340
M. I. Ansari, R. Shankar, M. K. Hussain, R. Kant, P. R. Maulik, K. R. Kumar, and K. Hajela
Vol 48
0.106 mL, 1 mmol). The reaction mixture was stirred for
20 min at room temperature (25ꢀC). Thereafter, the progress
of the reaction was checked on TLC which showed complete
consumption of 1 and formation of two major spots. The solu-
tion was filtered to remove the solid catalyst and washed with
methanol (2 mL). Excess of methanol was removed under
reduced pressure. The crude residue was washed with water to
remove acidic impurities and extracted with ethylacetate. After
drying over anhydrous sodium sulfate and removal of excess
ethylacetate, the mixture was purified by flash column chroma-
tography (90:10, EtOAc/hexane). Two compounds were iso-
lated, one as pale yellow solid 6 (73.45%), m.p. 147–151ꢀC;
m/z 342 [Mþ1]; IR: 3021, 2360(C¼¼N), 1216, 760 cmꢂ1;1H-
NMR (300 MHz, CDCl3): d 7.35–7.46 (m, 5H), 7.46–7.52 (m,
2H), 7.52–7.58 (m, 3H), 7.68–7.76 (m, 3H), 7.77–7.83 (m,
2H) ppm; 13C-NMR (300 MHz, CDCl3): d 118.1, 123.4,
125.6, 127.8, 128.70, 129.2, 129.8, 131.1, 132.5, 138.1, 138.9,
139.2, 142.4, 157.8, 188.6 ppm; Anal. Calcd. for C22H15NOS:
C, 77.39; H, 4.43; N, 4.10. Found: C, 78.00; H, 5.10; N, 3.95.
high resolution mass spectroscopy (HRMS) (ESI) calcd for
[C22H15NOS þ H]þ 342.0952, found 342.0963 and a second
orange-yellow solid 7 (12%), m.p. 234–35ꢀC, m/z 448(Mþ);
1H-NMR (300 MHz, CDCl3): d 4.1 (s, 2H, SACH), 6.94–6.91
(m, 2H), 7.17–7.12 (m, 2H), 7.45–7.30 (m, 9H), 7.70–7.64 (m,
5H) ppm; 13C-NMR (300 MHz, CDCl3): d 31.1, 120.1, 126.8,
127.0, 127.6, 127.8, 128.2, 128.3, 130.5, 137.9, 142.9, 156.0
ppm; Anal. Calcd. for C28H20N2S2: C, 74.97; H, 4.49; N, 6.24.
Found: C, 75.04; H, 4.16; N, 5.95.
Bruker SMART APEX CCD diffractometer at 293(2) K. Struc-
ture solutions by direct methods and refinements by full-matrix
least-squares methods on F2. Programs: SMART (Bruker,
2001), SAINT (Bruker, 2001) and SHELXTL-NT [Bruker
AXS, Madison, WI, 1997]. CCDC (deposit No. 803514) con-
tains the supplementary crystallographic data. These data can
be obtained free of charge from www.ccdc.cam.uk/conts/retrie-
ving.html [or from the Cambridge Crystallographic Data Cen-
ter, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (internet)
þ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
1-Phenyl-2-(3-phenylquinoxalin-2(1H)-ylidene) ethanone
(8). This was synthesized by the process as described for 6.
The crude solid was purified by flash column chromatography
using EtOAc/hexane (90:10) to give the pure compound 8 as
yellow solid (86%), m.p. 76–77ꢀC, m/z 325 (Mþ1); IR: 3020
(NH), 1591 (C¼¼O), 1534, 1216, 761cmꢂ1
;
1H-NMR (300
MHz, CDCl3): d 6.41 (s, CH), 7.44–7.41 (m, 4H), 7.76–7.58
(m, 5H), 7.90–7.79 (m, 4H), 7.93 (d, J ¼ 7.98, 1H), 15.85 (s,
NH) ppm; 13C-NMR (300 MHz, CDCl3): d 91.2, 119.6, 125.9,
126.5, 128.2, 128.4, 128.6, 128.7, 128.8, 129.3, 130.7, 130.8,
132.1, 137.2, 137.3, 138.1, 147.6, 156.8, 181.3 ppm; Anal.
Calcd. for C22H16N2O: C, 81.46; H, 4.97; N, 8.64. Found: C,
80.19; H, 4.71; N, 8.42. HRMS (EI) calcd for C22H16N2O
[M]þ 324.1263, found 324.1268.
The structure of the compound 8 was characterized by sin-
gle crystal X-ray diffraction studies. The molecule consists of
four rings (I, II, III, IV), which all are almost planar (the mean
˚
deviation of fitted atoms is 0.005, 0.002, and 0.012 A, respec-
2,20-Bis-2H-3,3-diaryl-1,4-benzothiazine (7). This was
synthesized by reacting 1 (1 equiv.) with two equivalents of 2
following the procedure described above. The reaction was
complete within 15 min with the precipitation of the bis com-
pound 7 in almost quantitative yield. The compound was dis-
solved in excess of ethanol and filtered to remove the catalyst.
The catalyst was washed with ethanol (four to five times) and
dried for reuse. Crystallization from ethanol gave pure com-
pound 7 (85%). The spectral data was exactly the same as
described above. The structure of compound 7 was absolutely
confirmed by single crystal X-ray diffraction analysis.
tively from the least square plane formed by atoms C17 to
C22 for ring I, C11 to C16 for ring II, and C6, C5, C4, N2,
C1, C2, N1, C3, C8, and C7 for ring III and IV. At atom C10
of the molecule, a carbonyl group is substituted. X-ray study
further reveals that the keto–enol tautomerisation [14,15] occur
in the molecule due to intramolecular proton sharing between
nitrogen of ring IV and oxygen atom of carbonyl group
(N1AH1. . .O1) and this affects in elongation of single bond
˚
distance (N1AH1 ¼ 1.164 A) and double bond of carbonyl
˚
group(C10AO1¼ 1.29 A). The crystal data of 8, C22H16N2O,
˚
˚
M ¼ 324.37, triclinic, P1, a ¼ 9.260(1) A, b ¼ 9.930(2) A, c
ꢀ
ꢀ
ꢀ
˚
¼ 10.820(2) A, a ¼ 79.37(3) , b ¼ 65.46(3) , c ¼ 68.97(3) ,
The compound 7 crystallizes in P2(1)/c space group and
two molecules of compound are in asymmetric unit. The mole-
cule consists of two similar halves joined to form dimer
V ¼ 844.0(3) A , Z ¼ 2, Dc ¼ 1.276 g cmꢂ3, l(Mo-Ka) ¼
3
˚
0.08 mmꢂ1, F(0 0 0) ¼ 340.0, rectangular block, yellowish,
size ¼ 0.2 ꢃ 0.3 ꢃ 0.35 mm3, 9790 reflections measured (Rint
¼ 0.021), 3881 unique, wR2 ¼ 0.1394 for all data, conven-
tional R ¼ 0.0473 for 2891 Fo > 4r(Fo) and 0.0634 for all
3881data, Goodness of fit S ¼ 1.039 for all data and 230 pa-
rameters and zero restraints. Unit cell determination and inten-
sity data collection was performed on a Bruker SMART
APEX CCD diffractometer at 293(2) K. Structure solutions by
direct methods and refinements by full-matrix least-squares
methods on F2. Programs: SMART (Bruker, 2001), SAINT
(Bruker, 2001), and SHELXTL-NT [Bruker AXS, Madison,
WI, 1997]. CCDC (deposit No.803515) contains the supple-
mentary crystallographic data. These data can be obtained free
of charge from www.ccdc.cam.uk/conts/retrieving.html.
˚
through single covalent bond between C1 and C1A (1.54 A).
Each monomer unit is having three rings A, B, C and A0, B0,
C0. Ring A, C, A0, and C0 are almost planar. The ring B and
B0 adopts distorted envelope conformations with C and C1A
forming the flaps, respectively. (The deviation of atom C1 is
˚
ꢂ0.859(1) A from the least square mean plane through atom
C2, N1, C3, C4, and S1 for ring B. The deviation of atom
˚
C1A is 0.859(1) A from the least square mean plane through
atom C2A, N1A, C3A, C4A, and S1A for ring B0). The crystal
data of 7, C28H20N2S2, M ¼ 448.58, monoclinic, P2(1)/c, a ¼
ꢀ
˚
ꢀ
˚
˚
7.094(4) A, b ¼ 11.927(6) A, c ¼ 12.693(6) A, a ¼ 90 , b ¼
3
ꢀ
˚
91.294(1) , c ¼ 90 , V ¼ 1073.76 A , Z ¼ 2, Dc ¼ 1.387 g
cmꢂ3, l(Mo-Ka) ¼ 0.27 mmꢂ1, F(0 0 0) ¼ 468.0, rectangular
block, yellowish, size ¼ 0.275 ꢃ 0.15 ꢃ 0.3 mm3, 12,240
(E)-Phenyl(4-phenyl-2,3-dihydrobenzo[b][1,4]thiazepin-2-
yl)methanone (9). The reaction was performed in the similar
manner as described for compound 6 using diaroylethylene
and compound 2 in equimolar quantities. The crude residue
obtained on workup was purified by flash column chromatog-
raphy using EtOAc/hexane (90:10) giving one major product 9
reflections measured (Rint ¼ 0.0146), 4893 unique, wR2
¼
0.106 for all data, conventional R ¼ 0.0365 for 4372 Fo >
4r(Fo) and 0.04 for all 4893 data, goodness of fit S ¼ 1.059
for all data and 289 parameters and zero restraints. Unit cell
determination and intensity data collection was performed on a
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

November 2011
Eco-Friendly HClO4–SiO2 Catalyzed
Synthesis of Mono- and Bis-diaryl-2H-1,4 Benzothiazines
1341
[3] Gopal, K. L.; Sharma, G.; Kumar, R.; Chakraborti, A. K.
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5967.
isolated as yellow oil, (88.39%), m/z 344 [Mþ1]; IR: 3021,
2360(C¼¼N), 1731(C¼¼O), 1219, 761 cmꢂ1
;
1H-NMR (300
MHz, CDCl3): d 2.86 (dd, J ¼ 2.9 Hz, 17.7 Hz, 1H), 3.42 (dd,
J ¼ 10.1, 17.7 Hz, 1H), 4.89 (dd, J ¼ 2.9 Hz, 10.1 Hz, 1H),
6.98–7.11 (m, 1H, ArH), 7.12–7.23 (m, 2H, ArH), 7.23–7.33
(m, 2H, ArH), 7.33–7.55 (m, 5H, ArH), 7.62–7.76 (m, 2H,
ArH), 7.94–8.11 (m, 2H, ArH), 13C-NMR (300 MHz, CDCl3):
d 29.8, 38.3, 120.3, 126.6, 127.2, 127.2, 127.6, 127.8, 127.9,
128.1, 128.2, 128.3, 128.3, 128.6, 128.8, 131.1, 133.6, 136.6,
142.5, 157.9, 197.1 ppm; Anal. Calcd. for C22H17NOS: C,
76.94; H, 4.99; N, 4.08. Found: C, 77.54.19; H, 5.36; N, 4.16.
HRMS (ESI) exact mass calcd for [C22H17NOS þ H]þ
344.1109, found 344.1118.
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Acknowledgments. The authors, Mohd. Imran Ansari, Ravi
Shankar and Mohd. Kamil Hussain are thankful to CSIR for JRF &
SRF fellowships. Financial assistance from Ministry of Health &
Family Welfare is highly acknowledged and all are also grateful to
SAIF for spectroscopic analysis of the compounds. PRM thank
CSIR, New Delhi, for the Grant-in-aid of Emeritus Scientistship
Scheme [No.:21(0766)/09/EMR-II], CDRI Commun. no. 7999.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet