Synthesis and application of 2-styryl-6,7-dichlorothiazolo[4,5-b]-quinoxaline based fluorescent dyes: Part 3

Article abstract of DOI:10.1002/jhet.5570390210

A new efficient synthesis of 2-styryl-6,7-dichlorothiazolo[4,5-b]quinoxaline based fluorescent dyes was achieved by the condensation of 2-methyl-6,7-dichlorothiazolo[4,5-b]quinoxaline with selected 4-N,N-dialkylaminoarylaldehydes and heteroarylaldehydes in the presence of piperidine. The coloristic, fluorophoric, and dyeing properties of these dyes were studied.

Full text of DOI:10.1002/jhet.5570390210

Mar-Apr 2002
Synthesis and Application of 2-Styryl-6,7-dichlorothiazolo[4,5-b]-
quinoxaline Based Fluorescent Dyes: Part 3
N. D. Sonawane* and D. W. Rangnekar
303
Dyes research laboratory, Department of Chemical Technology, University of Mumbai,
Matunga, Mumbai 400 019, India.
Received June 15, 2001
Received revised December 10, 2001
A new efficient synthesis of 2-styryl-6,7-dichlorothiazolo[4,5-b]quinoxaline based fluorescent dyes was
achieved by the condensation of 2-methyl-6,7-dichlorothiazolo[4,5-b]quinoxaline with selected 4-N,N-
dialkylaminoarylaldehydes and heteroarylaldehydes in the presence of piperidine. The coloristic, fluo-
rophoric, and dyeing properties of these dyes were studied.
J. Heterocyclic Chem., 39, 303 (2002).
Introduction.
well-established flurophores, there has been little investi-
gation of heterofused quinoxaline systems as fluorescent
styryl dyes. Styryl dyes with electron donor-acceptor moi-
eties on either side of styryl bond are particularly attractive
for their spectral sensitivity towards local host environ-
ment and optical and electronic properties.
Fluorescent heterocyclic compounds were traditionally
of interest in textile and polymer fields. Recently, these
compounds have also gained much importance in the
fields of molecular sensor [1], tunable dye lasers [2], and
related hi-tech arenas, such as display [3]. Fluorophores
also have an important role in search of new biologically
active compounds and in the development of new diagnos-
tic methods [4]. In the recent past, the fluorescence proper-
ties were used to determine the ion transport across the
membrane [5]. Organic fluorescent compounds can be tai-
lored to suppress some unwanted properties with the
enhancement of desired character to fit for specific utility.
While coumarins [6], triazoles [7], benzimidazols [8],
napthalimides [9], pyrene [10], perylenes [11], etc. are
Recently, the synthesis of novel dyes and fluorescence
compounds containing thiazoles [12], thiophenes [13],
pyridines [14], benzopyrans [15], and their application to
the textiles have been reported. In earlier work from our
laboratories, the versatility of quinoxalines has been
demonstrated for the dyestuff area [16-19]. In addition, the
thiazolo[4,5-b]quinoxaline [20] system was employed to
develop new fluorescent dyes and their detailed photo-
physical properties are investigated [21]. The thiazolo-

304
N. D. Sonawane and D. W. Rangnekar
Vol. 39
quinoxaline system has also been used as a tool/probe for
photophysical investigation [22,23]. A recent paper also
discloses the importance of 6(7)-bromothiazolo[4,5-b]-
quinoxalines nucleus for the synthesis of fluorescent styryl
dyes [24]. These results have encouraged us to explore the
utility of 2-methyl-6,7-dichlorothiazolo[4,5-b]quinoxaline
7 to produce daylight fluorescent dyes 9, 11.
In the present paper, the chemistry of new fluorescent
dyes is reported. A key goal of this work was to produce
longer wavelength absorbing fluorescent dyes based on
thiazolo[4,5-b]quinoxaline system and study the effect of
chlorine substitution on the coloristic and fluorophoric
properties of resultant styryl dyes 9a-e and 11a-e. We
reported previously that halide substitution on quinoxaline
ring of thiazolo[4,5-b]quinoxaline system results in
bathochromic shift with no significant effect on fluores-
cent properties [24]. Taking advantage of this, the synthe-
sis of longer wavelength absorbing dyes were achieved by
introduction two chlorine atoms in quinoxalinyl ring of
thiazolo[4,5-b]quinoxaline system.
various organic solvents and their dyeing properties were
assessed on polyester fibers.
Results and Discussion.
Synthesis of Intermediates 7.
2,3-Dihydroxy-6,7-dichloroquinoxaline 3 was synthe-
sized in good yield by condensation of corresponding 4,5-
dichloro-1,2-benzendiamine 2, prepared from 1, with
oxalic acid in refluxing 4 M hydrochloric acid [25]
(Scheme 1). The compound 3 on chlorination gave a color-
less crystalline 2,3,6,7-tetrachloroquinoxaline 4 [25],
which on subsequent reaction with sodium hydrogen sul-
fide gave dark brown solid of 2,3-dimercapto-6,7-
dichloroquinoxaline 5 [26] in quantitative yield. The
advantages of this chemistry include good yields, short
reaction times, and straightforward procedures. In most of
the cases, the products precipitated from the reaction mix-
ture in pure form.
Partial ammonolysis of compound 5, using alcoholic
ammonia, yielded bright yellow crystalline 2-amino-3-
mercapto-6,7-dichloroquinoxaline 6. Optimum conditions
for this temperature sensitive reaction, 100-120° for 3
hours, gave 71% yield. The bright yellow compound 6 was
purified by dissolving in aqueous sodium hydroxide solu-
tion followed by reprecipitation with acetic acid. It was
further purified by recrystallization from ethanol.
Refluxing compound 6 in acetic anhydride yielded brown
colored mass of 7. Following recrystallization from
The key intermediate 7 was synthesized by the interac-
tion of 2,3,6,7-tetrachloroquinoxalne 4 with sodium
hydrosulfide followed by successive reactions involving
alcoholic ammonia and refluxing acetic anhydride
(Scheme 1). The synthesis involved the condensation of 7
with 4-N,N-dialkylaminosubstitutedaryl and heteroaryl-
aldehydes in the presence of piperidine. The absorption
and emission properties of these dyes were evaluated in

Mar-Apr 2002
Synthesis and Application of 2-Styryl-6,7-dichlorothiazolo[4,5-b]quinoxaline
305
aqueous methanol, the structure was elucidated by its ele-
mental and spectral analysis. The H nmr spectrum
showed that the methyl protons of 7 are deshielded and
observed at 2.80 ppm. In aromatic region two clear sin-
glets were observed at 8.03 and 8.13 ppm for two protons
of quinoxaline ring.
and dichlorothiazolo[4,5-b]quinoxalne acceptor system
showed several features, as follows: 1) The electron donat-
ing groups in 9a-e and 11a-e generated bathochromic
shifts according to the strength of their electron donation.
2) The dyes showed high molar extinction coefficients and
the logarithms of extinction coefficients were in the range
of 4.56-4.94. 3) The dyes showed modest positive solva-
tochromism. 4) In general, the dichlorosubstitution on
quinoxalinyl ring (of styryl dyes 9a-e and 11a-e) results in
bathochromic shifts as compared with unsubstituted and
monosubstituted styryl dyes [20,24].
1
Reaction of 7 with Aryl and Heteroaryl Aldehydes.
The Knovenagel condensation reaction involving 7 with
aldehydes, using piperidine as base catalyst, occurred
smoothly, giving dyes 9a-e and 11a-e in excellent yields
(Schemes 1 and 2). In most of the cases, dyes were precip-
itated out from the reaction mass, which made work up
process simpler. The all styryl dyes were purified by
recrystallization from ethanol.
Fluorescence Spectra.
Fluorescence spectra were recorded in chloroform and
emission maxima are listed in Table 2. The compounds
exhibited reddish orange to reddish pink fluorescence in
most of the organic solvents. The fluorescence maxima of
these dyes were in the range of 593-604 nm in chloroform.
The fluorescence of styryl dyes 9a-e and 11a-e was strong
in chloroform, dichloromethane and ethyl acetate and
remarkably weak in other solvents like methanol and ace-
tone (not shown). For example, compound 9b in
dichloromethane possesses 143 times greater fluorescence
than in methanol. The dyes possess good fluorescence effi-
ciencies and are in the range of 0.40-0.59 relative to the
ketone red laser dye (Table 2). Fluorescence maxima var-
ied with the polarity of the solvents employed. The fluo-
rescence maxima of all dyes shifted from reddish orange in
chloroform and in ethyl acetate, to pink in methanol and in
acetone (Table 2). Stokes shifts were calculated in both
Visible Absorption Spectra and Solvatochromism.
The visible absorption spectra of 9a-e and 11a-e were
recorded in solvents of varying polarity (chloroform, ethyl
acetate, acetone, methanol), to assess the solvatochromic
properties of these dyes (Table 1). Absorption maxima
were observed at 507-552 nm in chloroform. Examination
of absorption spectra of this dialkylaminophenyl donor
Table
1
Visible Spectral Data [a] (in nm) of 9a-e and 11a-e
Dye No. Chloroform
Ethyl
Acetone
Methanol
Acetate
CHCl (Log ε)
3
9a
9b
9c
9d
507 (4.61)
520 (4.56)
516 (4.77)
525 (4.80)
528 (4.69)
552 (4.94)
518 (4.66)
522 (4.72)
533 (4.56)
532 (4.75)
495
506
506
517
521
549
512
511
520
520
499
520
514
524
527
553
510
513
523
524
504
524
525
536
538
564
514
518
525
525
-1
wavenumbers (cm ) and wavelength (nm) (Table 2) and
are highest in acetone, with compound 9a showing highest
Stokes shift and 11a the lowest, in acetone.
9e
11a
11b
11c
11d
11e
Dyeing Properties.
Dyes 9a-e and 11a-e were applied to polyester fibers as
fluorescent disperse dyes. The dyes produced the color
range from reddish orange to pink. The dyeing properties
such as pick up, light fastness and sublimation fastness
[a] The concentrations of dyes were between 4-8µM.
Table 2
Fluorescence Spectral Data of 9a-e and 11a-e in (λ
in nm)
max
Dye CHCl (φ) [a]
No.
CH Cl
AcOEt CH OH CH COCH
Stokes shifts in acetone
Wavenumber (cm ) Wavelength(nm)
3
2
2
3
3
3
-1
9a
9b
9c
9d
9e
11a
11b
11c
11d
11e
594 (0.51)
600 (0.46)
597 (0.59)
602 (0.43)
603 (0.40)
604 (0.44)
594 (0.45)
593 (0.48)
599 (0.47)
599 (0.51)
602
616
609
617
620
612
610
610
614
617
607
610
603
602
604
604
602
606
608
609
657
654
648
647
649
628
650
653
668
655
656
4796
4010
4070
3722
3731
2651
4363
4432
4172
4247
157
137
136
127
129
95
146
151
146
150
657
650
651
656
648
656
664
669
674
[a] The quantum efficiency of dyes in choloroform were calculated relative to Keton Red laser dye in same solvent.

306
N. D. Sonawane and D. W. Rangnekar
Vol. 39
overnight. The dark brown precipitate was collected by filtration,
washed with water, dried and recrystallized from 30% aqueous
methanol to yield 1.57 g (71%) of 7 as pale orange yellow crys-
were evaluated on polyester fabric and summarized in
Table 3.
These novel dyes possessed excellent sublimation fast-
ness. Typical of fluorescent dyes the light fastness of all
dyes was poor.
1
tals, mp 139-140°; H nmr (60 MHz, deuteriochloroform): δ 2.80
(s, 3H, CH ), 8.03 (s, 1H, aromatic), 8.13 (s, 1H, aromatic); ms:
3
+
+
+
m/z 270 (M ), 269 (M - 1), 255 (M - CH ).
3
Anal. Calcd. for C H Cl N S: C, 44.46; H, 1.87; N, 15.55.
Found: C, 44.29; H, 1.94; N, 15.68.
10
5
2 3
Table
3
Dyeing Properties of 9a-e and 11a-e
2-[2-(4-N,N-Dimethylaminophenyl)ethenyl]-6,7-dichlorothia-
zolo[4,5-b]quinoxaline (9a).
Dye No. Color on polyester fiber Light fastness Sublimation Fastness
A mixture of 7 (2.70 g, 0.01 mole) and 8a (1.49 g, 0.01 mole)
in absolute ethanol (10 ml) and piperidine (2-3 drops) was stirred
at reflux for 8 hours. The precipitate was filtered, washed with
ethanol, dried and recrystallized from ethanol to yield 3.35 g
9a
9b
9c
9d
9e
11a
11b
11c
11d
11e
Brilliant orange
Luminescent red
Brilliant red
Bright reddish pink
Bright reddish pink
Pink
1
1
1
1
1
1
1
1
1
1
4
4
5
5
4
5
5
5
5
5
1
(83%) of 9a as red crystalline solid, mp >300°; H nmr (300
MHz, deuteriochloroform): δ 3.21 (s, 6H, N(CH ) ), 6.65 (d, 2H,
3 2
Dark scarlet
aromatic, J = 8.8Hz), 7.13 (d, 1H, olefinic CH, J = 15.3 Hz), 7.51
(d, 2H, aromatic, J = 8.8 Hz), 7.72 (d, 1H, olefinic CH, J = 15.7
Hz), 8.18 (s, 1H, aromatic), 8.24 (s, 1H, aromatic); ms: m/z 401
Fluorescent scarlet
Dark reddish pink
Pink
+
+
(M ), 400 (M - 1).
Anal. Calcd. for C
H Cl N S: C, 56.87; H, 3.52; N, 13.96.
19 14 2 4
Found: C, 56.69; H, 3.61; N, 13.81.
EXPERIMENTAL
2-[2-(4-N,N-Diethylaminophenyl)ethenyl]-6,7-dichlorothia-
zolo[4,5-b]quinoxaline (9b).
1
All melting points are uncorrected and expressed in °C. The H
nmr spectra were recorded on either a Verian-300 MHz or a
Hitachi-60MHz instrument, using tetramethylsilane as internal
standard. Chemical shifts are given in δ (ppm). Mass spectra
were recorded on a Varian Mat-311 instrument (70 eV).
Absorption and fluorescence emission spectra were recorded on a
Beckmann model-25 spectrophotometer and a SPEX 1681fluo-
rolog T-Format fluoremeter, respectively. For fluorescence mea-
surements, the excitation wavelength was wavelength of maxi-
mum absorption. Evaluation of 1.0% dye shades on polyester
fabric (1.0% o.w.f.) was carried out according to standard fast-
ness testing procedures [27]. The B02: 1978 test was used to
assess the light fastness, and sublimation fastness was evaluated
using P01: 1978 test, with polyester as an adjacent fabric at 180°
± 2°C [27].
The procedure described above for 9a were employed, except
that 8b was used in place of 8a. Crude 9b was recrystallized from
ethanol to yield 3.46 g (80%) of 9b as dark red crystalline solid,
1
mp 247-250°; H nmr (300 MHz, deuteriochloroform): δ 1.32 (t,
6H, N(C H ) , J = 7.3 Hz), 3.43 (q, 4H, N(C H ) , J = 7.3 Hz),
2
5 2
2 5 2
6.66 (d, 2H, aromatic, J = 8.8 Hz), 7.17 (d, 1H, olefinic CH, J =
15.4 Hz), 7.50 (d, 2H, aromatic, J = 8.8 Hz), 7.73 (d, 1H, olefinic
CH, J = 15.7 Hz), 8.18 (s, 1H, aromatic), 8.26 (s, 1H, aromatic);
+
+
ms: m/z 429 (M ), 428 (M - 1).
Anal. Calcd. for C Cl N S: C, 58.74; H, 4.23; N, 13.04.
H
21 18
2 4
Found: C, 58.85; H, 4.14; N, 13.13.
2-[2-(4-N,N-Dimethylamino-2-methoxyphenyl)ethenyl]-6,7-
dichlorothiazolo[4,5-b]quinoxaline (9c).
The procedure described above for 9a were employed, except
that 8c was used in place of 8a. Crude 9c was recrystallized from
ethanol to yield 3.68 g (85%) of 9c as black red crystalline solid,
Aldehydes 8a-b were obtained from Aldrich chemicals and 8c,
10a were procured from M/S Jalan Dyes & chemicals, Boisar,
Maharashtra, India. Coumarin aldehydes 10b-10e was synthe-
sized from corresponding 7-(N,N-dialkylamino)coumarins via a
Vilsmeier reaction [28].
1
mp >300°; H nmr (300 MHz, deuteriochloroform): δ 3.12 (s,
6H, N(CH ) ), 3.90 (s, 3H, OCH ), 6.11 (d, 1H, aromatic, J = 2.2
3 2
3
Hz), 6.30 (dd, 1H, aromatic, J =8.8, 2.2 Hz), 7.25 (d, 1H, olefinic
CH, J = 15.4 Hz), 7.52 (d, 1H, aromatic, J = 8.8 Hz), 7.84 (d, 1H,
olefinic CH, J = 15.6 Hz), 8.18 (s, 1H, aromatic), 8.25 (s, 1H,
2-Methyl-6,7-dichlorothiazolo[4,5-b]quinoxaline (7).
A mixture of 5 (2 g) [26] and alcoholic ammonia (20 ml satu-
rated at 20°) was heated in an autoclave at 100-120° for 3 hours.
The reaction mixture was evaporated and the residue was dissolved
in 5% aqueous solution of sodium hydroxide (50ml) at 50-60°. The
mixture was filtered and the filtrate was neutralized with acetic
acid to produce a bright yellow precipitate. The precipitate was iso-
lated by filtration, washed with water, dried and recrystallized from
hot ethanol to yield 1.67 g (68%) of 6 as yellow crystals.
+
+
aromatic); ms: m/z 431 (M ), 430 (M - 1).
Anal. Calcd. for C Cl N OS: C, 55.69; H, 3.74; N, 12.98.
H
20 16
2 4
Found: C, 55.81; H, 3.85; N, 12.85.
2-[2-(4-N,N-Diethylamino-2-methoxyphenyl)ethenyl]-6,7-
dichlorothiazolo[4,5-b]quinoxaline (9d).
The procedure described above for 9a were employed, except
that 8d was used in place of 8a. Crude 9d was recrystallized from
ethanol to yield 3.41 g (74%) of 9d as dark red crystalline solid,
Anal. Calcd. for C H Cl N S: C, 39.04; H, 2.05; N, 17.07.
8
5
2 3
Found: C, 39.16; H, 2.12; N, 16.98.
1
Compound 6 (2 g) was stirred in refluxing acetic anhydride
(120 ml) for 4 hours. The excess anhydride was removed by vac-
uum distillation, and the residue obtained was diluted with 5%
aqueous solution of sodium bicarbonate (50 ml) and left
mp 205-208°; H nmr (300 MHz, deuteriochloroform): δ 1.34 (t,
6H, N(C H ) , J =7.3 Hz ), 3.45 (q, 4H, N(C H ) , J =7.3 Hz),
2
5 2
2 5 2
3.92 (s, 3H, OCH ), 6.14 (d, 1H, aromatic, J = 2.2 Hz), 6.32 (dd,
3
1H, aromatic, J =8.7, 2.2 Hz), 7.27 (d, 1H, olefinic CH, J = 15.7

Mar-Apr 2002
Synthesis and Application of 2-Styryl-6,7-dichlorothiazolo[4,5-b]quinoxaline
307
Hz), 7.50 (d, 1H, aromatic, J = 8.7 Hz), 7.91 (d, 1H, olefinic CH,
J = 15.6 Hz), 8.16 (s, 1H, aromatic), 8.26 (s, 1H, aromatic); ms:
Anal. Calcd. for C H Cl N O S: C, 57.95; H, 3.65; N,
24 18 2 4 2
11.26. Found: C, 58.09; H, 3.44; N, 11.49.
+
+
m/z 459 (M ), 458 (M - 1).
Anal. Calcd. for C Cl N OS: C, 57.52; H, 4.39; N, 12.19.
2-[2-(7-N,N-Di-n-butylamino-3-coumarinyl)ethenyl]-6,7-
dichlorothiazolo[4,5-b]quinoxaline (11d).
H
22 20
2 4
Found: C, 57.67; H, 4.56; N, 12.38.
The procedure described above for 9a were employed,
except that 10d was used in place of 8a. Crude 11d was recrys-
tallized from ethanol to yield 4.20 g (76%) of 11d as dark
2-[2-(4-N,N-Di-n-butylamino-2-methoxyphenyl)ethenyl]-6,7-
dichlorothiazolo[4,5-b]quinoxaline (9e).
1
The procedure described above for 9a were employed, except
that 8e was used in place of 8a. Crude 9e was recrystallized from
solid, mp 220-225°; H nmr (300 MHz, deuteriochloroform): δ
0.99 (t, 6H, N(C H ) , J =7.3 Hz ), 1.38 (m, 4H, N(C H ) ),
4
9 2
4 9 2
1
ethanol to yield 3.66 g (71%) of 9e as red solid, mp 161-163°; H
1.56 (m, 4H, N(C H ) ), 3.38 (t, 4H, N(C H ) J = 7.7 Hz),
4 9 2 4 9 2,
nmr (300 MHz, deuteriochloroform): δ 0.99 (t, 6H, N(C H ) ,
6.48 (d, 1H, aromatic, J =1.5 Hz), 6.62 (dd, 1H, aromatic, J =
8.8, 1.6 Hz), 7.37 (d, 1H, aromatic, J = 8.8 Hz), 7.84 (s, 1H,
aromatic), 7.91 (d, 1H, olefinic CH, J = 15.4 Hz), 8.01 (d, 1H,
olefinic CH, J = 15.7 Hz), 8.23 (s, 1H, aromatic), 8.31 (s, 1H,
4
9 2
J = 7.3 Hz), 1.25-1.45 (m, 4H, N(C H ) ), 1.58-1.68 (m, 4H,
4
9 2
N(C H ) ), 3.35 (t, 4H, N(C H ) , J = 7.3 Hz), 3.93 (s, 3H,
4
9 2
4 9 2
OCH ), 6.09 (d, 1H, aromatic, J = 2.2 Hz), 6.31 (dd, 1H, aro-
3
+
matic, J = 8.79 2.2Hz), 7.36 (d, 1H, olefinic CH, J = 15.7 Hz),
7.49 (d, 1H, aromatic, J = 8.8 Hz), 8.11 (d, 1H, olefinic CH, J =
15.8 Hz), 8.17 (s, 1H, aromatic), 8.24 (s, 1H, aromatic); ms: m/z
aromatic); ms: m/z 553 (M ).
Anal. Calcd. for C
H Cl N O S: C, 60.76; H, 4.73; N,
28 26 2 4 2
10.11. Found: C, 60.52; H, 4.56; N, 10.21.
+
+
515 (M ), 514 (M - 1).
Anal. Calcd. for C
2-[2-(7-N,N-Di-n-hexylamino-3-coumarinyl)ethenyl]-6,7-
dichlorothiazolo[4,5-b]quinoxaline (11e).
H
Cl N OS: C, 60.58; H, 5.47; N, 10.87.
2 4
26 28
Found: C, 60.74; H, 5.59; N, 10.72.
The procedure described above for 9a were employed, except
that 10e was used in place of 8a. Crude 11e was recrystallized from
2-[3-(1,3-Dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1-
propenyl]-6,7-dichlorothiazolo[4,5-b]quinoxaline (11a).
ethanol to yield 4.75 g (78%) of 11e as dark solid, mp 230-232°;
1
The procedure described above for 9a were employed, except
that 10a was used in place of 8a. Crude 11a was recrystallized
from ethanol to yield 3.67 g (81%) of 11a as dark red crystals
H nmr (300 MHz, deuteriochloroform): δ 0.92 (t, 6H, N(C H ) ,
6
13 2
J =7.3 Hz), 1.35 (m, 8H, N(C H ) ), 1.58 (m, 8H, N(C H ) ),
6
13 2
6 13 2
3.35 (t, 4H, N(C H ) J = 7.7 Hz), 6.45 (d, 1H, aromatic, J =1.8
6
13 2,
1
solid, mp 295-298°; H nmr (300 MHz, deuteriochloroform): δ
Hz), 6.59 (dd, 1H, aromatic, J = 8.8, 1.6 Hz), 7.34 (d, 1H, aromatic,
J = 8.8 Hz), 7.80 (s, 1H, aromatic), 7.87 (d, 1H, olefinic CH, J =
15.4 Hz), 7.98 (d, 1H, olefinic CH, J = 15.8 Hz), 8.21 (s, 1H,
1.70 (s, 6H, 2CH ), 3.32 (s, 3H, N-CH ), 5.68 (d, 1H, olefinic
3
3
CH, J = 12.8 Hz), 6.54 (d, 1H, olefinic CH, J = 13.9 Hz), 6.84 (d,
1H, olefinic CH, J = 8.1 Hz), 7.04 (t, 1H, aromatic, J = 7.0 Hz),
7.25-7.30 (m, 2H, aromatic), 8.13 (s, 1H, aromatic), 8.20 (s, 1H,
+
aromatic), 8.28 (s, 1H, aromatic) ms: m/z 609 (M ).
Anal. Calcd. for C
H Cl N O S: C, 63.05; H, 5.62; N, 9.18.
32 34 2 4 2
+
aromatic), 8.28 (t, 1H, aromatic, J = 9.8 Hz); ms: m/z 453 (M ).
Found: C, 63.23; H, 5.45; N, 9.23.
Anal. Calcd. for C
Found: C, 60.80; H, 4.12; N, 12.47.
H Cl N S: C, 60.93; H, 4.00; N, 12.35.
23 18 2 4
Acknowledgements.
The research project was supported by University Grants
Commission, New Delhi, India. The authors are also grateful to
Prof. N. Periasamy (TIFR, Mumbai) for fluorescence spectro-
scopic measurements.
2-[2-(7-N,N-Dimethylamino-3-coumarinyl)ethenyl]-6,7-dichloro-
thiazolo[4,5-b]quinoxaline (11b).
The procedure described above for 9a were employed, except
that 10b was used in place of 8a. Crude 11b was recrystallized
from ethanol to yield 3.24 g (69%) of 11b as blackish red crys-
REFERENCES AND NOTES
1
talline solid, mp 288-290°; H nmr (300 MHz, deuteriochloro-
form): δ 3.11 (s, 6H, N(CH ) ), 6.42 (d, 1H, aromatic, J = 1.6
3 2
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Hz), 6.66 (dd, 1H, aromatic, J = 8.8, 1.6 Hz), 7.37 (d, 1H, aro-
matic, J = 8.7 Hz), 7.80 (s, 1H, aromatic), 7.93 (d, 1H, olefinic
CH, J = 15.5 Hz), 8.04 (d, 1H, olefinic CH, J = 15.7 Hz), 8.22 (s,
+
1H, aromatic), 8.30 (s, 1H, aromatic); ms: m/z 469 (M ).
Anal. Calcd. for C
H Cl N O S: C, 56.30; H, 3.01; N,
22 14 2 4 2
11.93. Found: C, 56.44; H, 3.15; N, 11.79.
2-[2-(7-N,N-Diethylamino-3-coumarinyl)ethenyl]-6,7-dichloro-
thiazolo[4,5-b]quinoxaline (11c).
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The procedure described above for 9a were employed, except
that 10c was used in place of 8a. Crude 11c was recrystallized
from ethanol to yield 3.58 g (72%) of 11c as blackish red solid, mp
1
276-278°; H nmr (300 MHz, deuteriochloroform): δ 1.21 (t, 6H,
N(C H ) , J = 7.0 Hz), 3.43 (q, 4H, N(C H ) ), 6.44 (d, 1H, aro-
2
5 2
2 5 2
matic, J = 1.6 Hz), 6.67 (dd, 1H, aromatic, J = 8.7, 1.6 Hz), 7.35
(d, 1H, aromatic, J = 8.8 Hz), 7.78 (s, 1H, aromatic), 7.91 (d, 1H,
olefinic CH, J = 15.6 Hz), 8.02 (d, 1H, olefinic CH, J = 15.7 Hz),
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Biophys. Acta 1110, 151 (1992).
+
8.19 (s, 1H, aromatic), 8.28 (s, 1H, aromatic); ms: m/z 497 (M ).

308
N. D. Sonawane and D. W. Rangnekar
Vol. 39
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th
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