A two-component protocol for synthesis of 3-(2-(substituted phenylamino)thiazol-4-yl)-2H-chromen-2-ones

Article abstract of DOI:10.3906/kim-1204-81

An efcient 2-component synthesis of a series of 3-(2-(substituted phenylamino)thiazol-4-yl)-2H-chromen-2- ones (3a-j) was achieved by the reaction of 3-(2-thiocyanatoacetyl)-2H-chromen-2-one (1) with a variety of suitably substituted anilines in 1:1 molar ratio in ethanol. The structures of the products were established by elemental analyses, and UV-vis, FTIR, 1H and 13C NMR, and mass spectroscopy. 3-(2-(4-Methylphenylamino)thiazol-4-yl)-2H-chromen- 2- one (3j) was further characterized by single crystal X-ray diffraction study. This compound, C19H14N2 OS, crystallizes in the orthorhombic space group Pna21, with Z = 4, and unit cell parameters a = 13.0785(11), b = 25.746(2), c = 4.7235(3) A, α=β=γ= 90°. TUeBITAK.

Full text of DOI:10.3906/kim-1204-81

Turk J Chem
Turkish Journal of Chemistry
(2013) 37: 383 – 393
¨
http://journals.tubitak.gov.tr/chem/
˙
c
⃝ TUBITAK
doi:10.3906/kim-1204-81
Research Article
A two-component protocol for synthesis of 3-(2-(substituted
phenylamino)thiazol-4-yl)-2H -chromen-2-ones
Aamer SAEED,1,∗ Mubeen ARIF,1 Madiha IRFAN,1 Michael BOLTE2
1
Department of Chemistry, Quaid-I-Azam University, Islamabad, Pakistan
2Institute of Inorganic and Analytical Chemistry, Goethe University, Frankfurt/Main, Germany
Received: 28.04.2012
•
Accepted: 13.03.2013
•
Published Online: 10.06.2013
•
Printed: 08.07.2013
Abstract: An efficient 2-component synthesis of a series of 3-(2-(substituted phenylamino)thiazol-4-yl)-2H -chromen-2-
ones (3a–j) was achieved by the reaction of 3-(2-thiocyanatoacetyl)-2H -chromen-2-one (1) with a variety of suitably
substituted anilines in 1:1 molar ratio in ethanol. The structures of the products were established by elemental analyses,
and UV-vis, FTIR, 1 H and 13 C NMR, and mass spectroscopy. 3-(2-(4-Methylphenylamino)thiazol-4-yl)-2H -chromen-2-
one (3j) was further characterized by single crystal X-ray diffraction study. This compound, C19 H14 N2 OS, crystallizes
in the orthorhombic space group Pna21, with Z = 4, and unit cell parameters a = 13.0785(11), b = 25.746(2), c =
◦
˚
4.7235(3) A, α = β = γ = 90 .
Key words: 3-Thiazolcoumarins, crystal structure
1. Introduction
Coumarins, also called benzo-α-pyrones, comprise a very large and important family of compounds that occur
widely in nature. They are found in a wide range of plants such as tonka bean, vanilla grass, cinnamon, sweet
clover, strawberries, apricots, and cherries. A number of coumarin derivatives are used in the pharmaceutical
industry as precursor molecules for the synthesis of many synthetic pharmaceutical compounds including antico-
agulants and vitamin K antagonists, while others are used in the treatment of lymphedema.1 Coumarin deriva-
tives exhibit antibacterial, antifungal,2,3 anticancer,4 anti-HIV,5,6 antitubercular,7 antiacylcholineestrase,8
antimutagenic,9 anthelmintic,10 anticoagulant,11 anti-inflammatory, antihepatitis C,12 and analgesic13 prop-
erties.
Moreover, many coumarin derivatives are used as inhibitors of heat shock protein,14 nonpeptidic protease
inhibitors,15 inhibitors of 17β -hydroxysteroid dehydrogenase (17β -HSD) type 1,16 TNF-α inhibitors,17 and
monoamine oxidase inhibitors.18 4-Methylcoumarins bearing different functionalities are well-known antioxidant
and radical scavengers.19
Thiazole derivates have been isolated and synthesized in view of their versatile pharmacological activities.
Some thiazole analogues are used as fungicidal,20 cardiotonic,21 bactericidal,22 anti-inflamatory,23 antiviral,24
anti-arrhythmic,25 and antitumor26 agents. Thiazoles are used as drugs for the treatment of hypertention27
HIV infections,28 and pain.29 Many thiazoles are fibrinogin receptor antagonists with antithrombotic activity,30
inhibitors of bacterial DNA gyrase B,31 and lypoxygenase inhibitors.32 Aminothiazoles are known to be ligands
∗Correspondence: aamersaeed@yahoo.com
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of estrogen receptors33 as well as a novel class of adenosine receptor antagonists.34 The thiazoline ring present
in vitamin B1 serves as an electron sink and its coenzyme form is important for the decarboxylation of alpha-
ketoacids.35
Both coumarins and thiazoles exhibit a wide range of fluorescence emission properties.36,37 Coumarins
can be used as memory media in different devices,38 as colorimetric chemosensors,39 and as dyes for efficient dye-
sensitized solar cells.40 Similarly, thiazole derivatives have a wide range of applications as ferroelectric displays41
and optical brighteners42 and in flow cytometry43 and DNA detection.44 Coumarins also exhibit interesting
fluorescence properties. These properties have led to their widespread application as sensitive fluorescent probes
in a wide range of systems. Furthermore, photobiological properties of coumarins were also studied.
Coumarins are also known as tannin activators. They block out short-wave radiation (280 to 315 nm)
but allow the longer wave radiation that gives a nice tan. In addition, studies have shown that coumarins
are rapidly and extensively absorbed through human, rat, and mouse skin, and that the compounds remain
metabolically unchanged during absorption.
Taking into account the aforesaid biological and synthetic significance of coumarins on one hand and the
multifunctional value of the thiazole ring in drug design on the other, the endeavor of the current work was the
synthesis of some new thiazolyl-bearing coumarins to combine their valuable effects in a single structural entity.
2. Experimental
Rf -values were determined using aluminum pre-coated silica gel plates Kieselgel 60 F254 from Merck (Germany).
Melting points were determined using a Gallenkamp melting point apparatus (MP-D) and are uncorrected.
Infrared spectra were recorded using an FTS 3000 MS, Bio-Rad Marlin (Excalibur Model) spectrophotometer.
1 H NMR spectra were obtained using a Bruker 300 NMR MHz spectrometer in CDCl3 , DMSO-d6 , and C3 D6 O
solutions using TMS as an internal reference. Chemical shifts are given in δ-scale (ppm). Abbreviations s, d,
dd, t, and at are used for singlet, doublet, double doublet, triplet, and apparent triplet, respectively; m stands
for a multiplet. 13 C NMR spectra (75 MHz) were measured in CDCl3 , DMSO-d6 , and C3 D6 O solutions.
LCMS spectra were recorded using an EI source of 70 eV on an Agilent Technologies 6890N. Ultraviolet-visible
(UV-vis) spectra were measured on a Shimadzu Pharma-spec 1700 UV-Visible Spectrophotometer.
Data were collected on a STOE IPDS II 2-circle diffractometer with graphite-monochromated MoKα
radiation. Empirical absorption correction was performed using MULABS46 in PLATON.47 The structure was
solved by direct methods using the program SHELXS and refined against F2 with full-matrix least-squares
techniques using the program SHELXL-97.48 H atoms bonded to C were refined using a riding model. The H
atom bonded to N was freely refined; 5383 reflections measured, 2623 unique (R int = 0.0385), R1 = 0.0379,
˚
wR2 = 0.0821 for all data, GooF = 1.074, highest peak in final difference map 0.181 e-/A3. The absolute
structure was determined: Flack-x-parameter –0.02(8).
3-(2-Thiocyanatoacetyl)-2H -chromen-2-one (1) was prepared by treating 3-(2-bromoacetyl)-2H -chromen-
2-one with KSCN in dry acetone. The solid separated was purified by recrystallization in ethanol.
General procedure for the synthesis of 3-(2-(substituted phenylamino)thiazol-4-yl)-2H -chromen-
2-ones (3a–j)
To a stirred solution of 3-(2-thiocyanatoacetyl)-2H -chromen-2-one (1) (1 mmol) in 30 mL of ethanol was added
portionwise suitably substituted aniline (1.2 mmol) and the reaction mixture was refluxed for 4–5 h. The
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progress of the reaction was monitored with TLC using petroleum ether:ethyl acetate (4:1). The solid products
appeared either by cooling the reaction mixture or by pouring it on ice-cold water. The solid separated was
purified by recrystallization in ethanol.
3-(2-(2-Chlorophenylamino)thiazol-4-yl)-2H -chromen-2-one (3a)
Mp 249–251 ◦ C, (Lit45 150–151 ◦ C), yield 70%. Rf : 0.4 (a). IR (pure cm−1): 3303 (N-H), 3154 (Csp2 -H),
1707 (C=O), 1603 (C=N), 1557 (C=C aromatic). 1 H NMR (300 MHz, C3 D6 O) in δ (ppm) and J (Hz): 9.78
1
(1H, s, NH), 8.73 (1H, s, Ar-H), 8.12 (1H, d, J = 7.5 Hz, Ar-H), 7.89 (1H, s, thiazole H-5), 7.86 (1H, dd, J =
2
1.51 Hz, J = 7.2 Hz, Ar-H), 7.76–7.70 (2H, m, Ar-H), 7.59–7.52 (2H, m, Ar-H) 7.51–7.46 (2H, m, Ar-H). 13 C
NMR: (75 MHz, C3 D6 O) in δ (ppm): 162.3 (C=N), 157.9 (C=O), 152.2, 144.7, 144.4, 137.1, 130.5, 129.7,
127.6, 126.2, 124.7, 123.0, 119.6, 118.5, 116.0, 115.5, 113.6, 110.3. UV-Vis λmax/nm (chloroform) 296. LCMS
m/z [M-H]+ : 355 g/mol. Found C, 60.99; H, 3.21; Cl, 9.84; N, 7.98; S, 9.12. Calc. for C18 H11 ClN2 O2 S: C,
60.93; H, 3.12; Cl, 9.99; N, 7.90; S, 9.04%.
3-(2-(3-Chlorophenylamino)thiazol-4-yl)-2H -chromen-2-one (3b)
Mp 255–257 ◦ C (Lit45 134–135 ◦ C), yield 72%. Rf : 0.39 (a). IR (pure cm−1): 3316 (N-H), 3135 (Csp2 -H),
1702 (C=O), 1610 (C=N), 1597–1503 (C=C aromatic). 1 H NMR (300 MHz, C3 D6 O) in δ (ppm) and J
(Hz): 9.72 (1H, s, NH), 8.75 (1H, s, Ar-H), 8.02 (1H, at, Ar-H), 7.93 (1H, s, thiazole H-5), 7.86–7.83 (1H, m,
Ar-H), 7.79–7.76 (1H, m, Ar-H), 7.69–7.63 (1H, m, Ar-H) 7.46–7.37 (3H, m, Ar-H) 7.08–7.04 (1H, m, Ar-H).
13 C NMR: (75 MHz, C3 D6 O) in δ (ppm): 162.4 (C=N), 158.5 (C=O), 152.1, 145.4, 144.0, 139.0, 136.0, 130.0,
129.2, 128.0, 124.6, 122.7, 119.7, 119.0, 118.9, 115.5, 113.4, 110.3. UV-Vis λmax/nm (chloroform) 299. LCMS
m/z [M-H]+ : 355 g/mol. Found C, 61.89; H, 3.40; Cl, 10.02; N, 7.71; S, 9.28%. Calc. for C18 H11 ClN2 O2 S:
C, 60.93; H, 3.12; Cl, 9.99; N, 7.90; S, 9.04%.
3-(2-(4-Chlorophenylamino)thiazol-4-yl)-2H -chromen-2-one (3c)
Mp 269–273 ◦ C (Lit45 186–188 ◦ C); yield 73%. Rf : 0.41 (a). IR (pure cm−1): 3293 (N-H), 3079 (Csp2 -H),
1695 (C=O), 1604 (C=N), 1536 (C=C aromatic). 1 H NMR (300 MHz, DMSO-d6) in δ (ppm) and J (Hz):
10.5 (1H, s, NH), 8.71 (H, s, Ar-H), 7.07 (1H, d, J = 6.6 Hz, Ar-H), 7.83–7.80 (3H, m, Ar-H), 7.47–7.39 (5H,
m, Ar-H, thiazol H-5). 13 C NMR (75 MHz, DMSO-d6) in δ (ppm): 162.6 (C=N), 159.2 (C=O), 152.7, 144.0,
140.3, 139.2, 132.2 (2C), 129.4, 129.4, 125.1, 120.6, 120.0, 119.7, 119.0 (2C), 116.3, 110.7. UV-Vis λmax/nm
(chloroform) 295. LCMS m/z [M-H]− 353 g/mol. Found C, 61.04; H, 3.21; Cl, 9.9.92; N, 7.85; S, 9.11. Calc.
for C18 H11 ClN2 O2 S: C, 60.93; H, 3.12; Cl, 9.99; N, 7.90; S, 9.04%.
3-(2-(2-Methylphenylamino)thiazol-4-yl)-2H -chromen-2-one (3d)
Mp 231–233 ◦ C, (Lit45 174–175 ◦ C), yield 73%. Rf 0.41 (a). IR (pure cm−1): 3309 (N-H), 3172 (Csp2 -H),
1709 (C=O), 1608 (C=N), 1581 (C=C aromatic). 1 H NMR (300 MHz, DMSO-d6) in δ (ppm) and J (Hz):
10.20 (1H, s, NH), 8.62 (1H, s, Ar-H), 7.62 (1H, d, J = 6.9 Hz, Ar-H), 7.56 (1H, dd, 1J = 1.2 Hz, 2J = 7.6
Hz, Hz, Ar-H), 7.49–7.43 (4H, m, Ar-H), 7.38–7.32 (2H, m, Ar-H), 2.31 (3H, s, methyl). 13 C NMR: (75 MHz,
DMSO-d6) in δ (ppm): 163.6 (C=N), 159.7 (C=O), 152.5, 143.6, 139.1, 137.7, 132.8, 131.4, 130.1, 129.2,
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128.2, 125.4, 120.6, 119.5, 118.7, 118.5, 116.3, 111.8, 20.64. UV-Vis λmax/nm (chloroform) 300. LCMS m/z
[M-H]+ 335 g/mol. Found C, 68.17; H, 4.29; N, 8.428; S, 9.51. Calc. for C19 H14 N2 O2 S: C, 68.24; H, 4.22; N,
8.38; S, 9.59%.
3-(2-(4-Methylphenylamino)thiazol-4-yl)-2H -chromen-2-one (3e)
Mp 208–210 ◦ C, yield 75% Rf : 0.39 (a). IR (pure cm−1): 3301 (N-H), 3194–3078 (Csp2-H), 1698 (C=O),
1602 (C=N), 1506 (C=C aromatic). 1 H NMR (300 MHz, CDCl3) in δ (ppm) and J (Hz): 8.56 (1H, s, Ar-H),
7.85 (1H, s, thiazole H-5), 7.59–7.56 (2H, m, Ar-H), 7.38–7.28 (5H, m, Ar-H, NH), 7.19 (2H, d, J = 8.4 Hz,
Ar-H), 2.359 (3H, s, methyl). 13 C NMR: (75 MHz, CDCl3) in δ (ppm): 164.6 (C=N), 159.7 (C=O), 152.8,
143.8, 138.8, 137.5, 133.5, 131.3, 130.0 (2C), 128.2, 124.5, 120.7, 119.6, 119.2, 116.3 (2C), 109.8, 20.84. UV-Vis
λmax/nm (chloroform) 299. LCMS m/z [M-H]+ 335 g/mol. Found C, 68.31; H, 4.29; N, 8.8.29; S, 9.63. Calc.
for C19 H14 N2 O2 S: C, 68.24; H, 4.22; N, 8.38; S, 9.59%.
3-(2-(3-Nitrophenylamino)thiazol-4-yl)-2H -chromen-2-one (3f)
Mp 193–195 ◦ C, (reported 168–170 ◦ C), yield 70%. Rf 0.21 (a). IR (pure cm−1): 3135 (N-H), 3066 (Csp2 -H),
1711 (C=O), 1603 (C=N), 1579–1489 (C=C aromatic). 1 H NMR (300 MHz, DMSO-d6) in δ (ppm) and J
(Hz): 10.963 (1H, s, NH), 9.06 (1H, s, Ar-H), 8.72 (1H, s, thiazole H-5), 7.98 (1H, d, J = 7.2 Hz, Ar-H),
7.86–7.801 (3H, m, Ar-H), 7.68–7.63 (2H, m, Ar-H), 7.49–7.44 (2H, m, Ar-H). 13 C NMR: (75 MHz, DMSO-d6)
in δ (ppm): 162.5 (C=N), 158.5 (C=O), 150.4, 149.1, 145.6, 144.23, 131.2, 129.4, 127.5, 126.2, 124.7, 122.5,
120.5, 114.5, 111.2, 110.7. UV-Vis λmax/nm (chloroform) 275. LCMS m/z [M-H]+ : 366 g/mol. Found C,
59.11; H, 3.11; N, 11.58; S, 8.69. Calc. for C18 H11 N3 O4 S: C, 59.17; H, 3.03; N, 11.50; S, 8.78%.
3-(2-(2-Methoxyphenylamino)thiazol-4-yl)-2H -chromen-2-one (3g)
Mp 179–181 ◦ C, (reported 158–160 ◦ C), yield 75%. Rf : 0.41 (a); IR (pure cm−1): 3226 (N-H), 3137 (Csp2 -H),
1710 (C=O), 1605 (C=N), 1570 (C=C aromatic). 1 H NMR (300 MHz, CDCl3) in δ (ppm) and J (Hz): 8.64
(1H, s, Ar-H), 8.13–8.10 (1H, m, Ar-H), 7.91 (1H, s, thiazole H-5), 7.84 (1H, s, NH), 7.67–7.64 (1H, m, Ar-H),
7.57–7.53 (1H, m, Ar-H), 7.39–7.38 (2H, m, Ar-H), 7.11–7.02 (2H, m, Ar-H), 6.96–6.93 (1H, m, Ar-H), 3.95
(3H, s, methoxy). 13 C NMR: (75 MHz, CDCl3) in δ (ppm): 162.8 (C=N), 159.7 (C=O), 152.9, 147.5, 143.9,
138.9, 131.2, 129.7, 124.5, 122.3, 121.1, 120.8, 116.3, 110.2, 110.1, 55.77. UV-Vis λmax/nm (chloroform) 303.
LCMS m/z [M-H]− : 349 g/mol Found C, 65.06; H, 4.12; N, 7.87; S, 9.21. Calc. for C19 H14 N2 O3 S: C, 65.13;
H, 4.03; N, 7.99; S, 9.15%.
3-(2-(4-Methoxyphenylamino)thiazol-4-yl)-2H -chromen-2-one (3h)
Mp 196–199 ◦ C, yield 78%. Rf 0.28 (a). IR (pure cm−1): 3219 (N-H), 3135 (Csp2 -H), 1715 (C=O), 1564
(C=C aromatic), 1601 (C=N). 1 H NMR (300 MHz, DMSO-d6): δ 10.1 (1H, s, NH), 8.67 (1H, s, Ar-H), 7.95
(1H, d, J = 7.5 Hz, Ar-H), 7.68–7.60 (3H, m, Ar-H), 7.47–7.38 (2H, m, Ar-H), 7.72 (1H, s, thiazole H-5), 6.97
(2H, d, J = 7.3 Hz, Ar-H). 13 C NMR: (75 MHz, DMSO-d6) in δ (ppm): 162.5 (C=N), 159.0 (C=O), 150.9,
150.3, 146.2, 140.0, 135.7, 129.0, 127.9, 126.6, 124.0, 121.5, 120.1, 116.5 (2C), 115.2 (2C), 112.9, 55.7. UV-Vis
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λmax/nm (chloroform) 302. LCMS m/z [M-H]− : 349 g/mol Found C, 65.19; H, 4.07; N, 8.03; S, 9.09. Calc.
for C19 H14 N2 O3 S: C, 65.13; H, 4.03; N, 7.99; S, 9.15%.
3-(2-(2,3-Diflourophenylamino)thiazol-4-yl)-2H -chromen-2-one (3i)
Mp 195–197 ◦ C, yield 71%. Rf 0.53 (a). IR (pure cm−1): 3284 (N-H), 3132 (Csp2 -H), 1712 (C=O), 1606
(C=N), 1567 (C=C aromatic). 1 H NMR (300 MHz, C3 D6 O) in δ (ppm) and J (Hz): 10.1 (1H, s, NH),
8.63 (1H, s, Ar-H), 8.61–8.55 (1H, m, Ar-H), 7.92 (1H, dd, 1J = 1.2 Hz, 2J = 7.8 Hz, Ar-H), 7.79 (1H, s,
thiazole H-5), 7.65–7.59 (1H, m, Ar-H), 7.45–7.29 (3H, m, Ar-H), 7.19–7.12 (1H, m, Ar-H). 13 C NMR (75 MHz,
C3 D6 O) in δ (ppm): 163.6 (C=N), 159.2 (C=O), 152.7, 143.6, 139.0, 132.1, 129.4, 126.1, 125.1, 121.6, 120.6,
119.7, 116.3, 111.9, 111.6, 111.3, 104.4, 104.0. UV-Vis λmax/nm (chloroform) 305. LCMS m/z [M-H]− : 355
g/mol. Found C, 60.59; H, 2.89; F, 10.71; N, 7.79; S, 9.06. Calc. for C18 H10 F2 N2 O2 S: C, 60.67; H, 2.83; F,
10.66; N, 7.86; S, 9.00%.
3-(2-(4-Bromo-2-flourophenylamino)thiazol-4-yl)-2H -chromen-2-one (3j)
Mp 233–235 ◦ C, yield 69%. Rf 0.53 (a). IR (pure cm−1): 3309 (N-H), 3145, 3061 (Csp2 -H), 1708 (C=O),
1610 (C=N), 153 (C=C aromatic). 1 H NMR (300 MHz, C3 D6 O) in δ (ppm) and J (Hz): 9.53 (1H, s, NH),
8.81 (1H, s, Ar-H), 8.89–8.83 (1H, m, Ar-H), 7.99 (1H, s, thiazole H-5), 7.89–7.86 (1H, m, Ar-H), 7.69–7.66
(1H, m, Ar-H), 7.49–7.39 (5H, m, Ar-H). 13 C NMR: (75 MHz, C3 D6 O): in δ (ppm): 162.2 (C=N), 159.5
(C=O), 159.0, 150.6, 146.2, 140.2, 129.2, 128.7, 128.0, 127.5, 126.9, 125.3, 122.6, 121.7, 121.2, 119.5, 114.9,
113.2. UV-Vis λmax/nm (chloroform) 303. LCMS m/z [M-H]− : 416 g/mol Found C, 51.88; H, 2.51; Br, 19.11;
F, 4.47; N, 6.78; S, 7.60. Calc. for C18 H10 BrFN2 O2 S: C, 51.81; H, 2.42; Br, 19.15; F, 4.55; N, 6.71; S, 7.68%.
3. Results and discussion
The reaction sequence leading to the formation of thiazolyl-2H -chromen-2-ones is depicted in the Scheme.
The starting material 3-(2-thiocyanatoacetyl)-2H -chromen-2-one (1) is readily accessible via the reaction of
3-(2-bromoacetyl)-2H -chromen-2-one with potassium thiocyanate in dry acetone.28 Treatment of the latter
with an equimolar quantity of a variety of suitably substituted anilines (2a–j) in ethanol furnished the title
thiazolyl-2H -chromen-2-ones (3a–j).
O
NH2
O
O
O
O
S
N
EtOH/reflux
R
R
N
N
H
S
(1)
(2)
(3a-j)
3a 2-Cl; 3b 3-Cl
3c 4-Cl; 3d 2-Me
3e 4-Me; 3f 3-NO2
3g 2-OMe; 3h 4-OMe
3i 2,3-diF; 3j 2-F, 4-Br
Scheme. Synthesis of 3-(2-(substituted phenylamino)thiazol-4-yl)-2H -chromen-2-ones.
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All 3-(2-(substituted phenylamino)thiazol-4-yl)-2H -chromen-2-ones were characterized using spectro-
scopic analysis including IR, 1 H NMR, 13 C NMR, and UV and in some cases by mass spectrometry. All
the compounds are fluorescent under UV-light. Their fluorescent properties were studied using a luminescence
spectrophotometer and emitted wavelengths were recorded.
IR spectra of all compounds had strong N-H absorptions at about 3316–3219 cm−1 and displayed
absorptions at about 1715–1695 cm−1 and 1610–1601 cm−1 assigned to C=O and C=N functions, respectively.
In the UV-vis spectra λmax are observed at 287.5–302.0 nm.
In the 1 H NMR spectral data for all the compounds, there was a characteristic singlet in the range
10.5–8.50 ppm, indicative of NH. A thiazolyl proton appeared in the range 8.00–7.30 ppm and the remaining
protons appeared at their respective chemical shift values. Compounds 3c, 3e, and 3h are para substituted
with electron-donating substituents. The protons of the aniline ring are making part of an AB system. In the
case of compound 3c there is a 4-proton multiplet at 7.47–7.39 showing that these protons have close chemical
shifts, and in 3e signals at 7.38–7.28 and 7.19 ppm for 2 protons each, clearly indicating an AB system. 13 C
NMR spectral data show significant peaks for C=N of thiazole moiety and C=O in the range 164.6–162.0 ppm
and 159.9–158.3 ppm, respectively. The deshielded value of C=N of the thiazole skeleton can be justified by
the 2 neighboring electron-withdrawing sulfur and nitrogen atoms.
The structure of 3e was unequivocally confirmed by single crystal X-ray analysis (Figure 1).46 Single
crystals suitable for X-ray diffraction studies were obtained by slow evaporation of ethanol. Figures 2 and 3
show the packing diagrams with a view onto the bc-plane and the ab-planes respectively. Hydrogen bonds are
˚
drawn as dashed lines. The molecule is almost planar (r.m.s. deviation for all non-H atoms 0.076 A). Bond
lengths and angles are in the usual ranges. The molecules are connected by N-H...O hydrogen bonds to zigzag
chains running along [2 0 1].
Figure 1. Molecular structure with displacement ellipsoids at the 50% probability level.
3.1. Photophysical properties
Absorption properties of the synthesized compounds were determined in dilute chloroform solution and the
results are given in the Table. In the absorption spectra of the compounds 2 bands appear from 270 to 430 nm.
The major absorption band is due to π−π* transition from the basic coumarin skeleton. The addition of phenyl
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substituted thiazole at position 3 of coumarin moiety causes the shoulder, which is shifted bathochromically
according to the nature and position of the substituents. According to the common rule, electron-donating
groups shifted the absorption to longer wavelengths, while electron-withdrawing substituents did the opposite.49
Figure 2. Packing diagram with view onto the bc-plane. Hydrogen bonds are drawn as dashed lines.
The maximum shift in absorption wavelength observed for (-OMe) substituents is due to their high
electron donating nature, while the minimum was observed for (-NO2) group and the rest showed a similar
trend. The shift to longer wavelength can also be attributed to formation of aggregates of H-type and J-type.50,51
Fluorescence is a form of photoluminescence and these studies were performed to determine the wave-
length of emitted light. Fluorescence was measured in dilute chloroform solution. Compounds (3b, 3c, 3j)
Table. Absorption data of compounds 3a–3j.
Sr. no. Compound
R
2-Cl
3-Cl
4-Cl
2-Me
4-Me
λmax (nm)
296, 343
299, 363
295, 367
300, 367
299, 362
275, 356
303, 372
302, 364
305, 352
303, 362
1
2
3
4
5
3a
3b
3c
3d
3e
3f
6
3-NO2
2-OMe
4-OMe
2,3-difloro
4-Br-2-F
7
8
9
10
3g
3h
3i
3j
389

SAEED et al./Turk J Chem
show their emitted wavelength in the range 392–424 nm with the appearance of 2 emission bands. The marked
difference from the absorption maxima may be due to the intermolecular charge transfer (ICT) from the nitrogen
donor to the carbonyl acceptor of the coumarin moiety.52 Moreover, the observed difference of 3c from 3b and
3j was because of the presence of a donor group, i.e. halogen, at the para position of nitrogen, accumulating
the charge, which might cause a little disturbance in aggregation. The color of emitted light is in the blue
region (Figure 5). The fluorescent properties of these compounds are enhanced and shifted to the blue region
due to attachment of thiazole moiety to the third position of coumarin, which is emitted up to 350–380 nm.
The fluorescent properties of the compounds indicate that they can be used as chemical sensors, fluorescent
labeling, dyes, and biological detectors and in fluorescent lamps.
Figure 3. Packing diagram with view onto the ab-plane. Hydrogen bonds are drawn as dashed lines.
Their use as chemosensors is due to the chelating ability of C=N and C=O groups and it is known
that these groups exhibit a high affinity to transition and posttransition metal cations but less binding affinity
toward alkali metal and alkaline earth metal cations.53−56
390

SAEED et al./Turk J Chem
3.5
3
3a
3b
3c
3d
3e
3f
2.5
2
1.5
1
3g
3h
3i
0.5
0
3j
230
330
430
Wavelength (nm)
530
630
Figure 4. UV/Vis absorption spectra of 3a-3j in CHCl3 .
Figure 5. Photoluminescence spectra of some selected
compounds in CHCl3 at 10−5 M.
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