Regioselective synthesis of biologically interesting pentacyclic polyheterocycles by sequential thio-Claisen and AlCl3 catalyzed oxy-Claisen rearrangement of 4-(4′-aryloxybut-2′-ynylthio)-1-phenyl- 1,8-naphthyridin-2(1H)-one

Article abstract of DOI:10.1139/V06-174

A number of 4-aryloxymethyl-6-phenyl-2H-thiopyrano[3,2-c][1,8]naphthyridin- 5(6H)-ones were regio-selectively synthesized in 82%-95% yields by the thermal Claisen rearrangement of 4-(4′-aryloxybut-2′-ynylthio)-1-phenyl-[1, 8]naphthyridin-2(1H)-ones. These

Full text of DOI:10.1139/V06-174

1632
Regioselective synthesis of biologically interesting
pentacyclic polyheterocycles by sequential thio-
Claisen and AlCl3 catalyzed oxy-Claisen
rearrangement of 4-(4′-aryloxybut-2′-ynylthio)-1-
phenyl-1,8-naphthyridin-2(1H)-one
K.C. Majumdar and R. Islam
Abstract: A number of 4-aryloxymethyl-6-phenyl-2H-thiopyrano[3,2-c][1,8]naphthyridin-5(6H)-ones were regio-
selectively synthesized in 82%–95% yields by the thermal Claisen rearrangement of 4-(4′-aryloxybut-2′-ynylthio)-1-
phenyl-[1,8]naphthyridin-2(1H)-ones. These products were then subjected to a second Claisen rearrangement in the
presence of a Lewis acid catalyst, anhyd. AlCl3, to give hitherto unreported pentacyclic heterocycles in 75%–90% yields.
The same final products were also obtained in low yield upon refluxing 4-aryloxymethyl-6-phenyl-2H-thiopyrano-[3,2-
c][1,8]naphthyridin-5(6H)-ones in N,N-diethyl aniline for 12–14 h. This method was found to be more effective than
thermal Claisen rearrangement.
Key words: [3,3] sigmatropic rearrangement, regioselective synthesis, phase transfer catalysis, sequential Claisen rear-
rangement, Lewis acid catalyzed Claisen rearrangement, single crystal X-ray.
Résumé : On a réalisé des synthèses régiosélectives de 4-aryloxyméthyl-6-phényl-2H-thiopyrano[3,2-c][1,8]naphtyridin-
5(6H)-ones, avec des rendements allant de 82 % à 95 %, en soumettant des 4-(4’-aryloxybut-2’-ynylthio)-1-phényl[1,8]naph-
tyridin-2(1H)-ones à un réarrangement de Claisen thermique. Ces produits ont ensuite été soumis à un deuxième réar-
rangement de Claisen, en présence d’un acide de Lewis comme catalyseur, le trichlorure d’aluminium, pour conduire à
la formation d’hétérocycles pentacycliques non rapportés jusqu’à maintenant, avec des rendements allant de 75 % à 90 %.
On a aussi obtenu ces produits avec de faibles rendements en portant les 4-aryloxyméthyl-6-phényl-2H-thiopyrano[3,2-
c][1,8]naphtyridin-5(6H)-ones au reflux dans la N,N-diéthylaniline pendant 12 à 14 h. On a trouvé que cette méthode
est plus efficace que le réarrangement thermique de Claisen.
Mots clés : réarrangement sigmatropique [3,3], synthèse régiosélective, catalyse par transfert de phase, réarrangements
de Claisen séquentiels, réarrangement de Claisen catalysé par un acide de Lewis, diffraction des rayons X par un cris-
tal unique.
[Traduit par la Rédaction] Majumdar and Islam 1639
Introduction
bioactivities of these 1,8-naphthyidinones, such as the
cytoprotective, anti-inflammatory, and antiallergic activity
of some 2,3-fused and 3,4-fused furo- and pyrano-tricyclic
compounds, justify the great interest in the naphthyridinone
moiety as a target in organic synthesis. It is well-
documented that the Claisen rearrangement (8) is an excel-
lent method for carbon–carbon bond formation and has been
successfully employed for the synthesis of a number of po-
tentially bioactive thieno[3,2-d]pyrimidinone and dihydro-
thieno[3,2-d]pyrimidinone derivatives (9). We have previously
reported the sequential [3,3] sigmatropic rearrangement of
suitably substituted but-2-ynes to give interesting results,
e.g., easy access to [6,6] and [6,5] fused polyhetrocycles
(10). In view of the medicinal importance of 1,8-
1,8-Naphthyridinones and their derivatives have attracted
considerable attention primarily because the 1,8-naphthyri-
dine skeleton is present in many compounds that have been
isolated from natural substances and exhibited various me-
dicinal and biological activities (1, 2). 4-Hydroxy-1-phenyl-
1,8-naphthyridin-2(1H)-one and its derivatives have been
used as inhibitors of sulfidopeptide leukotrienes, the major
component of SRS-A release (3). 2-Oxo-1,8-naphthyridin-3-
carboxylic acid derivatives possess potent gastric antisecre-
tary properties and anti-inflammatory activities (4–6). A
series of novel imidazo[4,5-c][1,8]naphthyridin-4(5H)-ones
exhibited potent bronchodilator activity (7). The attractive
Received 16 October 2006. Accepted 23 October 2006. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on
19 December 2006.
K.C. Majumdar1 and R. Islam. Department of Chemistry, University of Kalyani, Kalyani 741235, W.B. India.
1Corresponding author (e-mail: kcm_ku@yahoo.co.in).
Can. J. Chem. 84: 1632–1639 (2006)
doi:10.1139/V06-174
© 2006 NRC Canada

Majumdar and Islam
1633
Scheme 1. Reagent and conditions: (i) BTEAC, CHCl3, 1% aq.
Scheme 2. Reagent and conditions: (i) Chlorobenzene, reflux, 4–
NaOH, 8–10 h, stirring, RT.
6 h.
SH
Cl
S
S
S
OAr
OAr
OAr
(i)
+
(i)
N
N
O
N
N
O
N
N
O
N
N
O
Ph
1
Ph
OAr
2a–2h
Ar
Yield (%)
3a–3h
Ph
Ph
4a–4h
Ar
Yield (%)
4
a
b
c
d
e
f
4-MeC6H4
4-ClC6H4
4-OMeC6H4
2-ClC6H4
C6H5
82
82
90
95
85
3a–3h
3
a
b
c
d
e
f
4-MeC6H4
4-ClC6H4
4-OMeC6H4
2-ClC6H4
C6H5
3,5-Me2C6H3 65
2-MeC6H4 65
2,4-Me2C6H3 70
70
70
72
70
75
3,5-Me2C6H3 85
2-MeC6H4 90
2,4-Me2C6H3 85
g
h
g
h
Scheme 3.
naphthyridine and its derivatives, we became interested in
synthesizing a number of polyheterocycles derived from 4-
hydroxy-1-phenyl-1,8-naphthyridin-2(1H)-one. Here, we re-
port our focused attention on the synthesis of furothiopyrano
heterocyclic ring-fused 1,8-napthyridin-2(1H)-one by the ap-
plication of thio-Claisen and oxy-Claisen rearrangement.
S
S
SH
N
OAr
OAr
OAr
[3,3]
H
N
N
O
N
N
O
N
O
Ph
3
Ph
5
Ph
6
1,5 H shift
Results and discussion
S
S
OAr
OAr
ECR
The starting materials, 4-(4′-aryloxybut-2′-ynylthio)-1-
phenyl-[1,8]naphthyridin-2(1H)-ones (3a–3h) were synthe-
sized by phase transfer catalyzed alkylation (11) of 4-
mercapto-1-phenyl-1,8-naphthyridin-2(1H)-one (3) with 1-
aryloxy-4-chlorobut-2-ynes (2a–2h) in 65%–75% yield. 4-
Mercapto-1-phenyl-1,8-naphthyridin-2(1H)-one (1) was pre-
pared according to published procedure (12) (Scheme 1).
The substrates 3a–3h contain the propynylthio-1,8-
naphthyridinone moiety as well as the aryl prop-2-ynyl ether
moiety, which suggests two different possible [3,3] sigma-
tropic rearrangements. The aliphatic Claisen rearrangement
has the lower activation energy since the aromatic counter-
part has to disturb its aromatic sextet in the transition state.
Substrate 3a was heated in chlorobenzene (132 °C) and the
reaction was monitored by TLC until complete conversion.
Complete conversion was achieved in 4 h giving a white
solid in 95% yield. The product 4a was characterized from
elemental analysis and spectroscopic data as 4-(4′-methyl-
phenoxymethyl)-6-phenyl-2H-thiopyrano[3,2-
N
N
O
N
N
O
Ph
7
Ph
4
Scheme 4. Reagent and conditions: (i) N,N-Diethyl aniline, re-
flux, 12–14 h.
R3
R4
H
2
R
S
S
OAr
(i)
R1
O
CH3
O
N
N
O
N
N
Ph
Ph
4a, 4d, 4f
8a, 8d, 8f
R1 R2 R3 R4 Yield (%)
a
d
f
H
Cl
H
H
CH3
H
H
30
25
28
8
H
CH3
H
CH3
H
c][1,8]naphthyridin-5(6H)-one. Its 1H NMR spectrum
(600 MHz) showed two two-proton doublets at δ: 3.43 (J =
5.4 Hz, -SCH2), 5.17 (J = 1.2 Hz, -OCH2) respectively,
one proton triple triplet (tt) at δ: 6.28–6.31 (J = 1.8 Hz,
6 Hz, =CH), and a multiplet for twelve aromatic protons at
δ: 6.83–8.43. Substrates 3b–3h under similar treatment af-
forded compounds 4b–4h in 82%–90% yield (Scheme 2).
The formation of products 4a–4h from the substrates 3a–
3h is easily rationalized by the initial [3,3] sigmatropic rear-
rangement of the sulfides 3a–3h to give 5. This was fol-
lowed by enolization to 6 and subsequent [1,5] hydrogen
shift and electrocyclic ring closure (ECR) to give products
4a–4h (Scheme 3).
afford the cyclized products in 25% to 30% yields. The
products were characterized as 8a, 8d, and 8f from their ele-
mental analyses and spectroscopic data (Scheme 4).
The thermal rearrangement required very high tempera-
ture and afforded products in poor yield because of decom-
position, so we attempted Lewis acid catalyzed Claisen
rearrangement. Among different catalysts reported in litera-
ture (13), AlCl3 and its derivatives are known to be efficient
for Claisen rearrangement.
Substrate 4a, upon treatment with anhyd. AlCl3 in dry di-
chloromethane at RT for 1 h, afforded the cyclized product
8a in 90% yield. Compound 8a was characterized from ele-
mental analysis and spectroscopic data. The 1H NMR
(500 MHz) spectrum showed δH: 1.86 (s, 3H, CH3 of ring
junction), 2.31 (s, 3H, ArCH3), 2.84–2.89 (t, 1H, J =
Compounds 4a–4h contain allyl aryl ether moieties fa-
vourable for a further [3,3] sigmatropic rearrangement.
Compounds 4a, 4d, and 4f were refluxed in N,N-diethyl ani-
line to perform Claisen rearrangement of allyl aryl ether to
© 2006 NRC Canada

1634
Can. J. Chem. Vol. 84, 2006
Scheme 5. Reagent and conditions: (i) AlCl3 (1 equiv.), Dry
Scheme 6.
CH2Cl2, stirring, 2 h, RT.
R
R3
R
R3
R
R4
H
4
R2
R1
R
S
S
S
N
2
R
H
O
OAlCl2
+
O
-
S
N
S
AlCl3
S
N
AlCl3
1
OAr
(i)
OH
[3,3]
R
N
N
Ph
4
O
N
N
O
O
CH3
N
O
or
Ph
11
Ph
10
N
O
N
N
O
N
O
Ph
Ph
Ph
9g, 9h
R
4a–4h
8a–8f
S
H
R1 R2 R3 R4 Yield(%)
CH3 87
CH3 H
R1 R2 R3
R4 Yield(%)
:
OH
S
R
g
h
H
CH3 H 75
H
H
9
8
a
b
c
d
e
f
H
H
H
Cl
H
H
H
H
CH3
Cl
OCH 3 H
H
H
H
H
H
90
88
80
85
85
O
CH3
N
N
O
Ph
9
H
H
N
N
O
H
CH3
H
H
Ph
CH3 90
8
Fig. 1. Single crystal X-ray structure of compound 8a.
12.3 Hz, SCH2), 3.11–3.15 (dd, 1H, J = 3.7 Hz, 13.2 Hz,
SCH2), 3.46–3.49 (dd, 1H, J = 3.7 Hz, 11.2 Hz, ring junc-
ture H), 6.84–6.85 (d, 1H, J = 8.1 Hz, ArH), 6.97–6.99 (d,
1H, J = 7.9 Hz, ArH), 7.09 (s, 1H, ArH), 7.14–7.16 (dd, 1H,
J = 4.6 Hz, 7.8 Hz, ArH), 7.29–7.30 (d, 2H, J = 7.5 Hz,
ArH), 7.44–7.47 (t, 1H, J = 7.4 Hz, ArH), 7.53–7.55 (m, 2H,
ArH), 8.26–8.27 (d, 1H, J = 7 Hz, ArH), 8.43–8.44 (d, 1H,
J = 3.3 Hz, ArH). Compounds 4b–4h were also similarly
treated to give products 8a–8f, 9g, and 9h in 75%–90%
yields (Scheme 5). The products were characterized from
their elemental analyses and spectroscopic data.
We also examined whether the charge accelerated [3,3]
sigmatropic rearrangement is applicable to the sulfides 3a–
3f. The substrates 3a–3f, when treated with anhyd. AlCl3 in
dichloromethane at RT, showed a tendency to decompose
and no traceable product was obtained, although they are
quite stable in dichloromethane at RT.
arrangement pathway. The use of a Lewis acid catalyst
avoids the problem of high temperature that led to decompo-
sition. The formation of products 8 from 4 can be rational-
ized by a series of steps involving an initial charge
accelerated [3,3] sigmatropic rearrangement to give 10, an
ether–oxygen–AlCl3 complex that may pass through a
charge-delocalized transition state followed by rapid
tautomerization to intermediate 11, and proton exchange to
give the intermediate 9, which on 5-exo-cyclization gives the
products 8, analogous to the product usually obtained in the
thermal rearrangement (Scheme 6). The single crystal X-ray
analysis of 8a showed the cis stereochemistry at the ring
juncture (Fig. 1).
The compounds 9g and 9h, upon treatment with pyridine
hydrotribromide in chloroform, afforded compounds 13g
and 13h. The formation of products 13g and 13h is thought
to occur through the intermediate bromonium ion followed
by a “6-endo” attack of the phenolic OH on the bromonium
ion 12 (Scheme 7) (10b).
The formation of products 8a–8f, 9g, and 9h from 4a–4h
is shown in Scheme 6. The isolation of the intermediate 9g
and 9h indicates that the formation of both the thermal and
catalytic rearrangement may follow the [3,3] sigmatropic re-
In summary, it has been possible to successfully perform
the sequential Claisen rearrangement of 4-(4′-aryloxybut-2′-
© 2006 NRC Canada

Majumdar and Islam
1635
Scheme 7. Reagent and conditions: (i) PyHBr3, CHCl3, 1 h, RT.
Table 1. Crystallographic data for compound 8a.
R3
R3
Compound
Empirical formula
8a
R3
R2
4
R
4
R
R2
4
R
R2
C25H20N2O2S
R1
1
Formula weight
Crystal system
Space group
412.5
Monoclinic
P21/c
H
S
R
S
1
S
R
OH
(i)
:OH
O
Br+
O
Br
O
N
N
O
N
N
a (Å)
b (Å)
c (Å)
8.4181(2)
20.3559 (6)
14.1321 (4)
90
95.269 (2)
90
2411.42 (11)
5
1.424
N
N
Ph
Ph
12
Ph
9g, 9h
13g, 13h
R1 R2 R3 R4 Yield (%)
CH3 82
α (°)
g
H
H
CH3 CH3 85
H
H
13
β (°)
h
H
γ (°)
V (Å3)
Z
ynylthio)-1-phenyl-1,8-naphthyridin-2(1H)-ones. The method
is facile, operationally simple, and allows rapid access to
two complex biologically significant heterocyclic systems.
ρcalcd (g cm–3)
µ (mm–1)
0.194
1085
F(000)
Reflections collected
Reflections independent
Goodness-of-fit
20 896
5886
1.257
Experimental2
Melting points were determined in an open capillary and are
uncorrected. IR spectra were recorded on a PerkinElmer L
120–000A spectrometer (νmax in cm–1) on KBr disks. UV
absorption spectra were recorded in EtOH on a Shimadzu
UV-2401PC spectrophotometer (λmax in nm). 1H NMR
(300 MHz, 400 MHz, 500 MHz, 600 MHz) and 13C NMR
(75.5 MHz, 125.7 MHz) spectra were recorded on a Bruker
DPX-300, Varian-400 FT-NMR, Bruker DPX-500, and
Varian-600 MHz spectrometers in CDCl3 (chemical shifts in δ)
with TMS as internal standard. Elemental analyses and mass
spectra were recorded on a Leco 932 CHNS analyzer and on
Final R indices [I > 2σ(I)]a
R1 = 0.0950, wR2 = 0.3021
butyne 2a–2f (2.4 mmol) was added a solution of benzyl
triethyl ammonium chloride (BTEAC) in 1% aq. NaOH
(50 mL) and the mixture was stirred at RT for 8–10 h. The
reaction mixture was then diluted with water (100 mL) and
the organic layer was extracted with chloroform (3 × 25 mL).
The organic layer was repeatedly washed with saturated
brine and dried (Na2SO4). The solvent was removed and the
viscous mass was chromatographed over silica gel using pe-
troleum ether – ethyl acetate (3:1) as eluant to afford the
products 3a–3f.
a JEOL JMS-600 instrument, respectively. H NMR and 13C
1
NMR spectra were recorded at the Indian Institute of Chemi-
cal Biology, Kolkata, and Bose Institute, Kolkata. Silica gel
[60–120 mesh, Spectrochem, India] was used for chromato-
graphic separation. Silica gel G [E-Merck, India] was used
for TLC. Petroleum ether refers to the fraction boiling be-
tween 60–80 °C.
Compounds 3d–3h have already been reported (12).
Compound 3a
Yield 70%; solid; mp 112–114 °C. UV–vis (EtOH) λmax
The 1-aryloxy-4-chlorobut-2-ynes (2a–2f) were prepared
according to published procedures (14–16).
(nm): 205, 222, 309, 327. IR (KBr, cm–1) νmax: 2918, 1655,
1
1578, 1509, 1436. H NMR (600 MHz, CDCl3) δH: 2.26 (s,
Single crystal X-ray study was performed on a Bruker
APEX CCD diffractometer equipped with an Oxford Instru-
ments low-temperature attachment. Data were collected us-
ing monochromated Mo Kα radiation (λa = 0.710 69 Å). The
frames were integrated in the Bruker SAINT Software pack-
age and the data were corrected for absorption using the
SADABS program. The structure was solved and refined
with the SHELX suite of programs. ORTEP-III was used to
produce the diagram. Pertinent crystallographic data for
compound 8a is summarized in Table 1.
3H, CH3), 3.86–3.87 (t, 2H, J = 1.8 Hz, SCH2), 4.68–4.69 (t,
2H, J = 1.8 Hz, OCH2), 6.73 (s, 1H, =CH), 6.83–6.85 (m,
2H, ArH), 7.06–7.07 (d, 1H, J = 8.4 Hz, ArH), 7.14–7.17
(dd, 1H, J = 4.2 Hz, 7.8 Hz, ArH), 7.26–7.28 (m, 3H, ArH),
7.48–7.51 (t, 1H, J = 7.8 Hz, ArH), 7.56–7.59 (t, 2H, J =
7.8 Hz, ArH), 8.11–8.12 (dd, 1H, J = 1.8 Hz, 7.8 Hz, ArH),
8.45–8.46 (dd, 1H, J = 1.8 Hz, 4.2 Hz, ArH). MS m/z: 412
(M+). Anal. calcd. for C25H20N2O2S: C 72.81, H 4.85, N
6.79; found: C 73.04, H 4.60, N 6.96.
Compound 3b
Yield 70%; solid; mp 148–150 °C. UV–vis (EtOH) λmax
(nm): 200, 223, 327. IR (KBr, cm–1) νmax: 2921, 1662, 1578,
1488, 1435. 1H NMR (300 MHz, CDCl3) δH: 3.86 (t, 2H, J =
1.8 Hz, SCH2), 4.69 (t, 2H, J = 1.8 Hz, OCH2), 6.72 (s, 1H,
=CH), 6.86–6.89 (m, 2H, ArH), 7.14–7.29 (m, 5H, ArH),
General procedure for the preparation of 4-(4′-aryloxy-
2′-but-ynylthio)-1-phenyl-1,8-naphthyridin-2 (1H)-one
(3a–3f)
To a mixture of 4-mercapto-1-phenyl-1,8-naphthyridin-
2(1H)-one 1 (0.50 g, 2 mmol) and 1-aryloxy-4-chloro-2-
2 Supplementary data for this article are available on the journal Web site (http://canjchem.nrc.ca) or may be purchased from the Depository
of Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 5113. For more
information on obtaining material refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. CCDC 627102 contains the crystallographic
data for this manuscript. These data can be obtained, free of charge, via http://www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2006 NRC Canada

1636
Can. J. Chem. Vol. 84, 2006
7.47–7.60 (m, 3H, ArH), 8.09–8.12 (dd, 1H, J = 1.5 Hz,
7.8 Hz, ArH), 8.45–8.47 (dd, 1H, J = 1.6 Hz, 4.6 Hz, ArH).
MS m/z: 432, 434 (M+). Anal. calcd. for C24H17N2O2SCl: C
66.58, H 3.93, N 6.47; found: C 66.78, H 3.75, N 6.23.
Compound 4c
Yield 90%; solid; mp 180–182 °C. UV–vis (EtOH) λmax
(nm): 204, 226, 344. IR (KBr, cm–1) νmax: 2928, 1645, 1578,
1
1508, 1442. H NMR (400 MHz, CDCl3) δH: 3.43 (d, 2H,
J = 6 Hz, SCH2), 3.73 (s, 3H, OCH3), 5.14 (d, 2H, J = 2 Hz,
OCH2), 6.28–6.31 (t, 1H, J = 6 Hz, =CH), 6.76–6.79 (dd,
2H, J = 2.4 Hz, 6.8 Hz, ArH), 6.86–6.88 (dd, 2H, J =
2.4 Hz, 6.8 Hz, ArH), 7.17–7.20 (dd, 1H, J = 4.4 Hz,
7.6 Hz, ArH), 7.25–7.27 (m, 2H, ArH), 7.46–7.50 (t, 1H, J =
8 Hz, ArH), 7.55–7.58 (t, 2H, J = 8 Hz, ArH), 8.29–8.31
(dd, 1H, J = 1.6 Hz, 7.6 Hz, ArH), 8.42–8.43 (dd, 1H, J =
1.6 Hz, 4.4 Hz, ArH). MS m/z: 428 (M+). Anal. calcd. for
C25H20N2O3S: C 70.09, H 4.67, N 6.54; found: C 69.91, H
4.91, N 6.76.
Compound 3c
Yield 72%; solid; mp 155–157 °C. UV–vis (EtOH) λmax
(nm): 222, 298, 327. IR (KBr, cm–1) νmax: 2962, 1647, 1582,
1
1512, 1432. H NMR (400 MHz, CDCl3) δH: 3.72 (s, 3H,
OCH3), 3.86 (t, 2H, J = 2 Hz, SCH2), 4.66 (t, 2H, J = 2 Hz,
OCH2), 6.72 (s, 1H, =CH), 6.79–6.81 (d, 2H, J = 8.8 Hz,
ArH), 6.88–6.90 (d, 1H, J = 8.8 Hz, ArH), 7.14–7.17 (dd,
1H, J = 4.4 Hz, 8.4 Hz, ArH), 7.25–7.28 (m, 3H, ArH),
7.47–7.51 (t, 1H, J = 7.6 Hz, ArH), 7.55–7.59 (t, 2H, J =
7.6 Hz, ArH), 8.10–8.12 (d, 1H, J = 8.4 Hz, ArH), 8.45–8.46
(d, 1H, J = 3.6 Hz, ArH). MS m/z: 428 (M+). Anal. calcd.
for C25H20N2O3S: C 70.09, H 4.67, N 6.54; found: C 70.32,
H 4.88, N 6.36.
Compound 4d
Yield 95%; solid; mp 212–214 °C. UV–vis (EtOH) λmax
(nm): 204, 223, 343. IR (KBr, cm–1) νmax: 2924, 1651, 1579,
1
1485, 1444. H NMR (600 MHz, CDCl3) δH: 3.46 (d, 2H,
J = 6 Hz, SCH2), 5.26 (d, 2H, J = 1.8 Hz, OCH2), 6.43–6.45
(tt, 1H, J = 1.8 Hz, 6 Hz, =CH), 6.84–6.87 (dt, 1H, J =
1.2 Hz, 7.8 Hz, ArH), 6.98–6.99 (dd, 1H, J = 1.2 Hz,
8.4 Hz, ArH), 7.13–7.16 (dt, 1H, J = 1.8 Hz, 8.4 Hz, ArH),
7.18–7.20 (dd, 1H, J = 4.2 Hz, 7.8 Hz, ArH), 7.28–7.29 (m,
2H, ArH), 7.33–7.34 (dd, 1H, J = 1.2 Hz, 7.8 Hz, ArH),
7.48–7.50 (t, 1H, J = 7.8 Hz, ArH), 7.56–7.59 (m, 2H, ArH),
8.31–8.32 (dd, 1H, J = 1.8 Hz, 7.8 Hz, ArH), 8.43–8.44 (dd,
1H, J = 1.8 Hz, 4.8 Hz, ArH). MS m/z: 432, 434 (M+). Anal.
calcd. for C24H17N2O2SCl: C 66.58, H 3.93, N 6.47; found:
C 66.80, H 3.68, N 6.26.
General procedure for the preparation of compounds
4a–4h
Compounds 3a–3h (1 mmol) were refluxed in chloroben-
zene (5 mL) for 4–6 h. The reaction was monitored by TLC.
The chlorobenzene was removed at reduced pressure and the
residual mass was chromatographed over silica gel. Elution
of the column with petroleum ether removed residual chloro-
benzene and the rearranged products 4a–4h were obtained
by eluting the column with petroleum ether – ethyl acetate
(4:1).
Compound 4a
Compound 4e
Yield 82%; solid; mp 175–177 °C. UV–vis (EtOH) λmax
Yield 85%; solid; mp 186–188 °C. UV–vis (EtOH) λmax
(nm): 204, 225, 343. IR (KBr, cm–1) νmax: 2925, 1646, 1629,
(nm): 206, 222, 337. IR (KBr, cm–1) νmax: 2921, 1655, 1574,
1
1
1582, 1509, 1443. H NMR (600 MHz, CDCl3) δH: 2.26 (s,
1443. H NMR (400 MHz, CDCl3) δH: 3.43 (d, 2H, J =
3H, CH3), 3.43–3.44 (d, 2H, J = 5.4 Hz, SCH2), 5.17 (d, 2H,
J = 1.2 Hz, OCH2), 6.28–6.31 (tt, 1H, J = 1.8 Hz, 6 Hz,
=CH), 6.83–6.85 (m, 2H, ArH), 7.02–7.04 (d, 1H, J =
8.4 Hz, ArH), 7.17–7.20 (dd, 1H, J = 4.8 Hz, 7.8 Hz, ArH),
7.26–7.28 (m, 3H, ArH), 7.48–7.50 (tt, 1H, J = 1.2 Hz,
4.8 Hz, ArH), 7.56–7.58 (m, 2H, ArH), 8.30–8.31 (dd, 1H,
J = 1.8 Hz, 7.8 Hz, ArH), 8.42–8.43 (dd, 1H, J = 1.8 Hz,
4.8 Hz, ArH). 13C NMR (125.7 MHz, CDCl3) δc: 20.87,
24.95, 69.02, 115.34, 115.44, 117.54, 118.61, 125.54,
128.97, 129.29, 129.95, 130.19, 130.31, 134.16, 136.95,
137.51, 146.18, 149.36, 150.69, 156.90, 160.45. MS m/z:
412 (M+). Anal. calcd. for C25H20N2O2S: C 72.81, H 4.85, N
6.79; found: C 73.07, H 5.02, N 6.58.
6 Hz, SCH2), 5.19 (s, 2H, OCH2), 6.28–6.31 (t, 1H, J =
6 Hz, =CH), 6.91–6.94 (m, 3H, ArH), 7.17–7.27 (m, 5H,
ArH), 7.46–7.50 (t, 1H, J = 8 Hz, ArH), 7.54–7.58 (t, 2H,
J = 8 Hz, ArH), 8.29–8.31 (dd, 1H, J = 1.6 Hz, 8 Hz, ArH),
8.42–8.43 (dd, 1H, J = 1.6 Hz, 4.4 Hz, ArH). MS m/z: 398
(M+). Anal. calcd. for C24H18N2O2S: C 72.36, H 4.52, N
7.03; found: C 72.57, H 4.35, N 7.22.
Compound 4f
Yield 85%; solid; mp 165–167 °C. UV–vis (EtOH) λmax
(nm): 206, 224, 341. IR (KBr, cm–1) νmax: 2913, 1663, 1583,
1
1448. H NMR (600 MHz, CDCl3) δH: 2.25 (s, 6H, CH3),
3.44–3.45 (d, 2H, J = 6 Hz, SCH2), 5.15 (d, 2H, J = 2 Hz,
OCH2), 6.31–6.33 (t, 1H, J = 6 Hz, =CH), 6.57 (s, 1H,
ArH), 6.58 (s, 1H, ArH), 7.18–7.20 (dd, 1H, J = 4.8 Hz,
7.8 Hz, ArH), 7.27–7.28 (m, 3H, ArH), 7.48–7.50 (t, 1H, J =
7.2 Hz, ArH), 7.56–7.59 (t, 2H, J = 7.8 Hz, ArH), 8.30–8.31
(dd, 1H, J = 1.2 Hz, 7.8 Hz, ArH), 8.42–8.43 (dd, 1H, J =
1.2 Hz, 4.8 Hz, ArH). MS m/z: 426 (M+). Anal. calcd. for
C26H22N2O2S: C 73.23, H 5.16, N 6.57; found: C 73.04, H
5.39, N 6.78.
Compound 4b
Yield 82%; solid; mp 204–206 °C. UV–vis (EtOH) λmax
(nm): 205, 226, 342. IR (KBr, cm–1) νmax: 2961, 2921, 1646,
1
1576, 1491, 1443. H NMR (500 MHz, CDCl3) δH: 3.43 (d,
2H, J = 6 Hz, SCH2), 5.17 (s, 2H, OCH2), 6.25–6.27 (t, 1H,
J = 6 Hz, =CH), 6.85–6.87 (d, 2H, J = 8.8 Hz, ArH), 7.17–
7.20 (m, 3H, ArH), 7.24–7.25 (m, 2H, ArH), 7.47–7.50 (t,
1H, J = 7.4 Hz, ArH), 7.55–7.58 (t, 2H, J = 7.4 Hz, ArH),
8.30–8.31 (dd, 1H, J = 1.3 Hz, 7.9 Hz, ArH), 8.43–8.44 (dd,
1H, J = 1.3 Hz, 4.5 Hz, ArH). MS m/z: 432, 434 (M+). Anal.
calcd. for C24H17N2O2SCl: C 66.58, H 3.93, N 6.47; found:
C 66.35, H 4.12, N 6.64.
Compound 4g
Yield 90%; solid; mp 195–197 °C. UV–vis (EtOH) λmax
(nm): 204, 223, 339. IR (KBr, cm–1) νmax: 2924, 1653, 1575,
1
1492, 1443. H NMR (600 MHz, CDCl3) δH: 2.26 (s, 3H,
© 2006 NRC Canada

Majumdar and Islam
1637
CH3), 3.45–3.46 (d, 2H, J = 6 Hz, SCH2), 5.20 (d, 2H, J =
1.2 Hz, OCH2), 6.34–6.36 (tt, 1H, J = 1.8 Hz, 6 Hz, =CH),
6.81–6.87 (m, 1H, ArH), 7.07–7.12 (m, 2H, ArH), 7.18–7.20
(dd, 1H, J = 4.8 Hz, 7.8 Hz, ArH), 7.26–7.28 (m, 3H, ArH),
7.48–7.51 (m, 1H, ArH), 7.56–7.59 (m, 2H, ArH), 8.31–8.32
(dd, 1H, J = 1.8 Hz, 7.8 Hz, ArH), 8.43–8.44 (dd, 1H, J =
1.8 Hz, 4.8 Hz, ArH). MS m/z: 412 (M+). Anal. calcd. for
C25H20N2O2S: C 72.81, H 4.85, N 6.79; found: C 72.55, H
5.02, N 7.02.
SCH2), 3.52–3.54 (d, 1H, J = 8.5 Hz, ring juncture H), 6.87–
6.88 (d, 1H, J = 8.3 Hz, ArH), 7.13–7.17 (m, 2H, ArH),
7.25–7.30 (m, 3H, ArH), 7.41–7.55 (m, 3H, ArH), 8.25–8.27
(d, 1H, J = 7.4 Hz, ArH), 8.45–8.46 (m, 1H, ArH). 13C
NMR (125.7 MHz, CDCl3) δc: 24.75, 29.03, 51.92, 86.99,
112.72, 114.70, 118.39, 124.77, 125.71, 126.55, 128.63,
128.74, 129.49, 129.69, 130.62, 134.30, 137.42, 145.97,
149.45, 151.22, 156.58, 160.44. MS m/z: 432, 434 (M+).
Anal. calcd. for C24H17N2O2SCl: C 66.58, H 3.93, N 6.47;
found: C 66.84, H 4.14, N 6.69.
Compound 4h
Yield 85%; solid; mp 178–180 °C. UV–vis (EtOH) λmax
Compound 8c
(nm): 200, 226, 341. IR (KBr, cm–1) νmax: 2918, 1651, 1579,
Yield 80%; solid; mp 226–228 °C. UV–vis (EtOH) λmax
1503, 1444. H NMR (300 MHz, CDCl3) δH = 2.22 (s, 3H,
(nm): 204, 224, 333. IR (KBr, cm–1) νmax: 2938, 1650, 1582,
1
1
CH3), 2.26 (s, 3H, CH3), 3.43 (d, 2H, J = 6 Hz, SCH2), 5.16
(s, 2H, OCH2), 6.32–6.36 (t, 1H, J = 6 Hz, =CH), 6.74–6.93
(m, 3H, ArH), 7.16–7.28 (m, 3H, ArH), 7.47–7.60 (m, 3H,
ArH), 8.30–8.32 (d, 1H, J = 7.8 Hz, ArH), 8.42–8.44 (dd,
1H, J = 1.2 Hz, 4.4 Hz, ArH). MS m/z: 426 (M+). Anal.
calcd. for C26H22N2O2S: C 73.23, H 5.16, N 6.57; found: C
73.49, H 5.40, N 6.38.
1484, 1441. H NMR (500 MHz, CDCl3) δH: 1.87 (s, 3H,
CH3 of ring junction), 2.86–2.91 (dd, 1H, J = 11.5 Hz,
13 Hz, SCH2), 3.13–3.16 (dd, 1H, J = 3.8 Hz, 13 Hz, SCH2),
3.48–3.51 (dd, 1H, J = 3.8 Hz, 11.3 Hz, ring juncture H),
3.78 (s, 3H, OCH3), 6.71–6.71 (dd, 1H, J = 2.5 Hz, 8.7 Hz,
ArH), 6.86–6.92 (m, 2H, ArH), 7.14–7.16 (dd, 1H, J =
4.6 Hz, 7.9 Hz, ArH), 7.29–7.30 (d, 2H, J = 7.4 Hz, ArH),
7.44–7.47 (t, 1H, J = 7.4 Hz, ArH), 7.50–7.60 (m, 2H, ArH),
8.25–8.27 (dd, 1H, J = 1.4 Hz, 7.9 Hz, ArH), 8.43–8.44 (dd,
1H, J = 1.4 Hz, 4.5 Hz, ArH). 13C NMR (125.7 MHz,
CDCl3) δc: 24.72, 29.12, 52.35, 56.45, 86.18, 111.08, 111.69,
114.35, 118.30, 126.94, 127.05, 128.68, 129.67, 129.74,
134.27, 137.51, 145.76, 149.45, 151.04, 151.91, 154.65,
160.53. MS m/z: 428 (M+). Anal. calcd. for C25H20N2O3S: C
70.09, H 4.67, N 6.54; found: C 69.85, H 4.48, N 6.72.
General procedure for the preparation of 8a–8f, 9g,
and 9h
Compound 4a–4f (0.5 mmol) was dissolved in dry
dichloromethane (10 mL) and anhyd. AlCl3 (0.06 g,
0.5 mmol) was added. The reaction mixture was stirred at
RT for 0.5–2.0 h. Crushed ice was added to the reaction
mixture and was extracted with dichloromethane. The com-
bined extracts were washed with water (20 mL), brine
(20 mL), and dried (Na2SO4). The solvent was removed and
the residual viscous mass was chromatographed over silica
gel using petroleum ether – ethyl acetate (3:1) as eluant to
afford the products 8a–8f, 9g, and 9h.
Compound 8d
Yield 85%; solid; mp 162–164 °C. UV–vis (EtOH) λmax
(nm): 206, 224, 290, 321, 332. IR (KBr, cm–1) νmax: 2926,
1
1655, 1584, 1444. H NMR (600 MHz, CDCl3) δH: 1.92 (s,
3H, CH3 of ring junction), 2.90–2.94 (dd, 1H, J = 11.4 Hz,
13.2 Hz, SCH2), 3.13–3.16 (dd, 1H, J = 3.6 Hz, 13.2 Hz,
SCH2), 3.58–3.61 (dd, 1H, J = 3.6 Hz, 11.4 Hz, ring junc-
ture H), 6.84–6.86 (t, 1H, J = 7.8 Hz, ArH), 7.13–7.16 (dd,
1H, J = 4.8 Hz, 7.8 Hz, ArH), 7.17–7.19 (m, 2H, ArH),
7.29–7.30 (d, 2H, J = 6.6 Hz, ArH), 7.45–7.48 (t, 1H, J =
8.4 Hz, ArH), 7.55–7.57 (t, 2H, J = 8.4 Hz, ArH), 8.24–8.25
(dd, 1H, J = 1.8 Hz, 7.8 Hz, ArH), 8.43–8.44 (dd, 1H, J =
1.8 Hz, 4.8 Hz, ArH). MS m/z: 432, 434 (M+). Anal. calcd.
for C24H17N2O2SCl: C 66.58, H 3.93, N 6.47; found: C
66.32, H 4.15, N 6.66.
Compound 8a
Yield 90%; solid; mp 150–152 °C. UV–vis (EtOH) λmax
(nm): 206, 224, 296, 320, 332. IR (KBr, cm–1) νmax: 2924,
1
1655, 1583, 1488, 1441. H NMR (500 MHz, CDCl3) δH:
1.86 (s, 3H, CH3 of ring junction), 2.31 (s, 3H, ArCH3),
2.84–2.89 (t, 1H, J = 12.3 Hz, SCH2), 3.11–3.15 (dd, 1H,
J = 3.7 Hz, 13.2 Hz, SCH2), 3.46–3.49 (dd, 1H, J = 3.7 Hz,
11.2 Hz, ring juncture H), 6.84–6.85 (d, 1H, J = 8.1 Hz,
ArH), 6.97–6.99 (d, 1H, J = 7.9 Hz, ArH), 7.09 (s, 1H,
ArH), 7.14–7.16 (dd, 1H, J = 4.6 Hz, 7.8 Hz, ArH), 7.29–
7.30 (d, 2H, J = 7.5 Hz, ArH), 7.44–7.47 (t, 1H, J = 7.4 Hz,
ArH), 7.53–7.55 (m, 2H, ArH), 8.26–8.27 (d, 1H, J = 7 Hz,
ArH), 8.43–8.44 (d, 1H, J = 3.3 Hz, ArH). 13C NMR
(125.7 MHz, CDCl3) δc: 21.26, 24.75, 29.28, 52.04, 86.05,
111.26, 114.83, 118.30, 125.10, 127.08, 128.68, 128.81,
129.68, 129.71, 130.14, 130.38, 134.30, 137.53, 145.85,
149.45, 151.03, 155.71, 160.56. MS m/z: 412 (M+). Anal.
calcd. for C25H20N2O2S: C 72.81, H 4.85, N 6.79; found: C
72.58, H 4.64, N 6.98.
Compound 8e
Yield 85%; solid; mp 214–216 °C. UV–vis (EtOH) λmax
(nm): 203, 224, 287, 332. IR (KBr, cm–1) νmax: 2919, 1644,
1
1583, 1461, 1443. H NMR (500 MHz, CDCl3) δH: 1.88 (s,
3H, CH3 of ring junction), 2.85–2.89 (t, 1H, J = 12.3 Hz,
SCH2), 3.13–3.16 (d, 1H, J = 10.5 Hz, SCH2), 3.52 (d, 1H,
J = 8.8 Hz, ring juncture H), 6.90–6.97 (m, 2H, ArH), 7.15–
7.20 (m, 2H, ArH), 7.25–7.30 (m, 3H, ArH), 7.46–7.55 (m,
3H, ArH), 8.26–8.27 (d, 1H, J = 7.5 Hz, ArH), 8.44 (d, 1H,
J = 2.1 Hz, ArH). MS m/z: 398 (M+). Anal. calcd. for
C24H18N2O2S: C 72.36, H 4.52, N 7.03; found: C 72.54, H
4.77, N 6.81.
Compound 8b
Yield 88%; solid; mp 260–262 °C. UV–vis (EtOH) λmax
(nm): 205, 224, 301, 321, 332. IR (KBr, cm–1) νmax: 2921,
1
1652, 1583, 1470, 1442. H NMR (500 MHz, CDCl3) δH:
Compound 8f
Yield 90%; solid; mp 284–286 °C. UV–vis (EtOH) λmax
1.88 (s, 3H, CH3 of ring junction), 2.85–2.90 (t, 1H, J =
12.2 Hz, SCH2), 3.12–3.15 (dd, 1H, J = 2.6 Hz, 13 Hz,
© 2006 NRC Canada

1638
Can. J. Chem. Vol. 84, 2006
(nm): 207, 224, 288, 320, 332. IR (KBr, cm–1) νmax: 2925,
NaHCO3 (3 × 25 mL) and water (3 × 25 mL), and dried
(Na2SO4). The residual mass after removal of the solvent
was subjected to column chromatography over silica gel us-
ing petroleum ether – ethyl acetate (6:1) as eluant to give
cyclized products 13g and 13h.
1
1655, 1584, 1441. H NMR (500 MHz, CDCl3) δH: 1.79 (s,
3H, CH3 of ring junction), 2.26 (s, 3H, ArCH3), 2.36 (s, 3H,
ArCH3), 2.68–2.74 (t, 1H, J = 12.6 Hz, SCH2), 3.07–3.11
(dd, 1H, J = 3.8 Hz, 13.1 Hz, SCH2), 3.39–3.43 (dd, 1H, J =
3.8 Hz, 12.4 Hz, ring juncture H), 6.55 (s, 1H, ArH), 6.62 (s,
1H, ArH), 7.15–7.17 (dd, 1H, J = 4.6 Hz, 7.9 Hz, ArH),
7.30–7.31 (d, 2H, J = 7.4 Hz, ArH), 7.45–7.48 (t, 1H, J =
7.4 Hz, ArH), 7.53–7.57 (t, 2H, J = 7.8 Hz, ArH), 8.28–8.30
(dd, 1H, J = 1.6 Hz, 7.9 Hz, ArH), 8.44–8.45 (dd, 1H, J =
1.6 Hz, 4.6 Hz, ArH). MS m/z: 426 (M+). Anal. calcd. for
C26H22N2O2S: C 73.23, H 5.16, N 6.57; found: C 73.47, H
4.97, N 6.35.
Compound 13g
Yield 82%; solid; mp 146–148 °C. UV–vis (EtOH) λmax
(nm): 207, 224, 286, 323, 334. IR (KBr, cm–1) νmax: 2923,
1
1651, 1584, 1443. H NMR (300 MHz, CDCl3) δH: 2.22 (s,
3H, ArCH3), 2.82 (t, 1H, J = 12.6 Hz, SCH2), 3.18–3.23 (dd,
1H, J = 4 Hz, 13 Hz, SCH2), 3.54–3.57 (d, 1H, J = 9.5 Hz,
OCH2), 3.97–4.02 (dd, 1H, J = 4 Hz, 13 Hz, ring juncture
H), 4.89–4.92 (d, 1H, J = 9.5 Hz, OCH2), 6.58–6.90 (t, 1H,
J = 7.3 Hz, ArH), 7.01–7.04 (d, 1H, J = 7.3 Hz, ArH), 7.14–
7.33 (m, 4H, ArH), 7.49–7.61 (m, 3H, ArH), 8.30–8.33 (d,
1H, J = 8.1 Hz, ArH), 8.46–8.47 (d, 1H, J = 2.8 Hz, ArH).
MS m/z: 490, 492 (M+). Anal. calcd. for C25H19N2O2SBr: C
61.09, H 3.86, N 5.70; found: C 61.27, H 4.07, N 5.86.
Compound 9g
Yield 87%; solid; mp 128–130 °C. UV–vis (EtOH) λmax
(nm): 205, 224, 337. IR (KBr, cm–1) νmax: 3475, 2921, 1638,
1
1579, 1444, 1281. H NMR:(300 MHz, CDCl3) δH: 2.27 (s,
3H, ArCH3), 3.39–3.44 (dd, 1H, J = 3.3 Hz, 12.2 Hz, SCH2),
3.66–3.73 (dd, 1H, J = 8.4 Hz, 12.3 Hz, SCH2), 4.33–4.36
(dd, 1H, J = 3.1 Hz, 5 Hz, ring juncture H), 5.02 (s, 1H,
OH), 5.41 (s, 1H, =CH2), 6.70 (s, 1H, =CH2), 6.79–6.84 (t,
1H, J = 7.3 Hz, ArH), 6.95–7.15 (m, 3H, ArH), 7.26–7.31
(m, 2H, ArH), 7.48–7.60 (m, 3H, ArH), 8.21–8.24 (d, 1H,
J = 8.1 Hz, ArH), 8.42–8.43 (d, 1H, J = 3.2 Hz, ArH). MS
m/z: 412 (M+). Anal. calcd. for C25H20N2O2S: C 72.81, H
4.85, N 6.79; found: C 72.99, H 5.10, N 6.55.
Compound 13h
Yield 85%; solid; mp 140–142 °C. UV–vis (EtOH) λmax
(nm): 207, 224, 294, 334. IR (KBr, cm–1) νmax: 2924, 1655,
1
1584, 1443. H NMR (500 MHz, CDCl3) δH: 2.18 (s, 3H,
ArCH3), 2.29 (s, 3H, ArCH3), 2.83–2.88 (dd, 1H, J =
12.4 Hz, 13 Hz, SCH2), 3.17–3.20 (dd, 1H, J = 4.2 Hz,
13.2 Hz, SCH2), 3.54–3.56 (d, 1H, J = 9.6 Hz, OCH2), 3.93–
3.96 (dd, 1H, J = 4.2 Hz, 12.2 Hz, ring juncture H), 4.89–
4.91 (d, 1H, J = 9.6 Hz, OCH2), 6.84 (s, 1H, ArH), 6.95 (s,
1H, ArH), 7.16–7.18 (dd, 1H, J = 4.6 Hz, 8 Hz, ArH), 7.28–
7.32 (m, 2H, ArH), 7.46–7.50 (m, 1H, ArH), 7.56–7.59 (t,
2H, J = 7.8 Hz, ArH), 8.30–8.32 (dd, 1H, J = 1.6 Hz,
7.9 Hz, ArH), 8.45–8.47 (dd, 1H, J = 1.6 Hz, 4.6 Hz, ArH).
MS m/z: 504, 506 (M+). Anal. calcd. for C26H21N2O2SBr: C
61.78, H 4.15, N 5.54; found: C 61.57, H 4.38, N 5.36.
Compound 9h
Yield 75%; solid; mp 230–232 °C. UV–vis (EtOH) λmax
(nm): 205, 224, 337, 344. IR (KBr, cm–1) νmax: 3475, 2921,
1
1640, 1579, 1444, 1281. H NMR (300 MHz, CDCl3) δH:
2.11 (s, 3H, ArCH3), 2.22 (s, 3H, ArCH3), 3.35–3.59 (d, 1H,
J = 11 Hz, -SCH2) 3.65–3.72 (t, 1H, J = 9.8 Hz, SCH2),
4.28–4.30 (d, 1H, J = 6.5 Hz, ring juncture H) 4.84 (s, 1H,
OH), 5.37 (s, 1H, =CH2), 6.65 (s, 1H, =CH2), 6.77 (s, 1H,
ArH), 6.88 (s, 1H, ArH), 7.13–7.15 (m, 1H, ArH), 7.26–7.30
(m, 2H, ArH), 7.48–7.58 (m, 3H, ArH), 8.22–8.24 (d, 1H,
J = 7.9 Hz, ArH), 8.43–8.44 (d, 1H, J = 3.1 Hz, ArH). MS
m/z: 426 (M+). Anal. calcd. for C26H22N2O2S: C 73.23, H
5.16, N 6.57; found: C 73.09, H 5.33, N 6.71.
Acknowledgements
We thank the Council of Scientific and Industrial
Research (CSIR, New Delhi) for financial assistance. RI is
thankful to CSIR (New Delhi) for a Junior Research Fellow-
ship. We are grateful to Professor A.T. Khan of the Indian
Institute of Technology, Guwahati, for the X-ray crystallo-
graphic analysis of compound 8a. We also thank the Depart-
ment of Science and Technology (DST, New Delhi) for
providing a UV–vis spectrophotometer and an FT-IR spec-
trometer under the Fund for Improvement of S&T Infra-
structure in Universities and Higher Educational Institutions
(DST-FIST) programme.
General procedure for the preparation of compounds
8a, 8d, and 8f
A mixture of compounds 4a, 4d, and 4f (1 mmol) in N,N-
diethylaniline (5 mL) was refluxed for 12–14 h. The reaction
mixture was cooled, poured into ice-cold 6 (N) HCl (30 mL),
and extracted with CHCl3 (3 × 20 mL). The CHCl3 layer
was washed with water and dried over Na2SO4. Removal of
CHCl3 gave a viscous liquid, which was chromatographed
over silica gel. Elution of the column with petroleum ether –
ethyl acetate (4:1) furnished products 10a, 10d, and 4f.
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General procedure for the cyclization of the compounds
9g and 9h
The brominating agent, solid pyridine hydrobromide
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© 2006 NRC Canada

Majumdar and Islam
1639
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© 2006 NRC Canada