A facile synthesis of 2,4-disubstituted thiazoles using MnO2

Article abstract of DOI:10.3390/molecules14124858

Structurally diverse thiazoles with electron-donating and electron-withdrawing groups were conveniently synthesized through manganese dioxide (MnO₂) oxidation of the corresponding thiazolines. The effect of substitution at the 2- and 4-positions was investigated. The desired thiazoles with aryl or vinyl substitutions at the 2- or 4-position can be obtained in good to excellent yields.

Full text of DOI:10.3390/molecules14124858

Molecules 2009, 14, 4858-4865; doi:10.3390/molecules14124858
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Communication
A Facile Synthesis of 2,4-Disubstituted Thiazoles Using MnO2
Yan-Bo Yu, Hong-Liang Chen, Li-Yi Wang, Xin-Zheng Chen and Bin Fu *
Department of Applied Chemistry, China Agricultural University, 100193, Beijing, China;
E-Mails: yuyanbo0902@163.com (Y.-B.Y.); chenhongliang1016@yahoo.cn (H.-L.C.);
Ritaxiaoyi@163.com (L.-Y.W.); xinzheng1943@126.com (X.-Z.C.)
* Author to whom correspondence should be addressed; E-Mail: fubinchem@cau.edu.cn.
Received: 21 October 2009; in revised form: 10 November 2009 / Accepted: 11 November 2009 /
Published: 26 November 2009
Abstract: Structurally diverse thiazoles with electron-donating and electron-withdrawing
groups were conveniently synthesized through manganese dioxide (MnO2) oxidation of the
corresponding thiazolines. The effect of substitution at the 2- and 4-positions was
investigated. The desired thiazoles with aryl or vinyl substitutions at the 2- or 4-position
can be obtained in good to excellent yields.
Keywords: thiazole; thiazoline; manganese dioxide; oxidation
1. Introduction
The thiazole ring is an interesting building block in a variety of natural products and bioactive
compounds useful as pharmaceuticals or agrochemical agents [1–5], and to date many methods have
been developed for the construction of thiazole ring systems. One classical and widely used method is
the condensation of α-haloketones with thioamide derivatives, which is known as the Hantzsch
reaction [6–8]. Another efficient method is the introduction of substitutions onto a thiazole core
structure through Stille coupling [9], which involves the use of organostannane intermediates. In recent
years, a new and frequently encountered method for thiazole synthesis is the conversion of thiazoline
derivatives through the use of dehydrogenating reagents such as sulfur [10], KMnO4 [11],
Cu(I)/Cu(II)/peroxide oxidation [12], MnO2 [13–16], NaH/DBU [17], and so on. Among these
dehydrogenating reagents, activated MnO2 is a very simple and convenient reagent for the synthesis of
thiazoles from thiazolines. However, all cases of MnO2 oxidation of thiazolines reported in the
literature are restricted to thiazoles bearing electron-withdrawing substituents such as carboxylates,

Molecules 2009, 14
4859
and to the best of our knowledge, no report involving the use of MnO2 for the synthesis of thiazoles
without carboxylate substitution has appeared. To investigate the generality and scope of this method
as a continuation of our research interest in thiazoline chemistry [18–20], we would like to report the
synthesis of 2,4-disubstituted thiazoles with electron-donating and electron-withdrawing groups from
the corresponding thiazolines via activated MnO2 oxidation.
2. Results and Discussion
The starting thiazolines 2 were easily prepared in one-pot reactions from the corresponding
carboxylic acids 3 or their derivatives [19,20], and commercially available amino alcohols which
provide R2 in the product (Scheme 1).
Scheme 1. The synthesis of 2,4-disubstituted thiazoles.
S
S
R1
MnO2
R1
i; ii; iii
R1 COOH
Solvent
N
1
R2
R2
N
3
2
i) SOCl2; ii) amino alcohol, Et3N; iii) P2S5, Et3N
With all kinds of thiazoline derivatives in hand, we first set out to optimize the reaction conditions.
The suspension of thiazoline 2a and excess activated MnO2 (10 equiv.) in dichloromethane (DCM)
was stirred for 24 h at room temperature [15,16]. No desired product was yielded even the reaction
temperature was elevated to the boiling point for 48 hours. Through extensive screening of solvents,
we observed that the reaction proceeded well under reflux in solvents with different polarity but
similar boiling points. The results indicated the strong correlation between the yield and the reaction
temperature. In DCE, CH3CN, or benzene, full conversion and up to 95% isolated yields can be
achieved within 12 hours. In the case of toluene, the starting material disappeared within 6 h and the
thiazole product was afforded in 80% yield. Lowering the ratio of oxidant to thiazoline led to the
significant decrease of the reaction rate. With the optimized condition in hand (DCE as solvent, 1:10
molar ratio of thiazoline to MnO2), thiazoles with different substitutions at the 2- and 4-positions were
synthesized (Table 1). In most cases, the reaction proceeded well under reflux (entries 6–16). When
one of 2- and 4-position of thiazoline is an aryl or vinyl group, the thiazole products are produced in
good to excellent yields (entries 6, 7, 9, 10, 11, 14 and 16). When both the 2- and 4-position of
thiazoline are aryl groups, the yields were improved to 95%–99 % (entries 8, 12 and 13), which can be
ascribed to the stronger conjugation effect between aryl groups and thiazoles. In contrast, when both
2- and 4-positions of thiazoline are alkyl groups, none of the desired thiazole products was obtained
(entry 17). The scope of this method was further exploited to the preparation of bis-thiazoles (Scheme 2).
The desired products were also obtained in high yield from corresponding bis-thiazolines, as illustrated
in Table 2 (entries 1–4).

Molecules 2009, 14
Table 1. The conversion of thiazolines to thiazoles by MnO2 oxidationa.
4860
Entry Compd.
R1
Ph
Ph
Ph
Ph
Ph
Ph
Ph
R2
Me
Me
Me
Me
Me
i-Pr
i-Bu
Ph
Me
i-Pr
Bn
Ph
Ph
Solvent
DCM
DCE
Benzene
CH3CN
Toluene
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
Time(h) Yield(%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
1a
1a
1a
1a
1a
1b
1c
1d
1e
1f
48
12
12
12
6
–
95
90
90
80
90
90
99
90
77
70
95
95
80
95
76
–
12
12
12
12
12
12
12
12
12
12
12
24
Ph
2-Py
2-Py
2-Furyl
2-Furyl
2-thienyl
PhCH=CH-
PhCH=CH-
Me
1g
1h
1i
1j
1k
1l
i-Pr
Ph
Ph
1m
Me
i-Pr
a The reactions were run under reflux in different solvents.
Scheme 2. The synthesis of 2,4-disubstituted bis-thiazoles.
S
S
R2
R2
R2
N
N
MnO2
R2 DCE
N
N
R1
R1
S
S
4
5
Table 2. The conversion of bis-thiazolines to bis-thiazoles by MnO2 oxidationa.
Entry
Compd.
5a
R1
R2
Reaction time Yield
1
i-Pr
12
12
6
80
85
80
2
3
5b
5c
Me
N
N
i-Pr
4
5d
Ph
8
70
a The reactions were run under reflux in DCE.

Molecules 2009, 14
4861
3. Conclusions
In conclusion, we have demonstrated that thiazoles bearing different electron-donating and
electron-withdrawing groups can be conveniently synthesized from the corresponding thiazolines
using activated MnO2 in dichloroethane. The critical effects of the reaction temperature and the
substitutions on the thiazoline ring were investigated. The scope of this method was further extended
to the preparation of 2,4-disubstituted thiazoles with diverse groups.
4. Experimental
NMR spectra were recorded on a Bruker Avance DPX300 spectrometer with tetramethylsilane as
internal standard and CDCl3 as solvent. Infrared spectra were obtained on a Nicolet AVATAR 330
FT-IR spectrometer. Elemental analyses were carried out on an Elementar Vario EL instrument.
Melting points were measured on an XT-4 melting point apparatus and were uncorrected. Solvents
were purified and dried following standard procedures.
4.1. Synthesis of Thiazolines
All thiazolines were prepared according to the literature [19,20].
4.2. Typical Procedure for Oxidation of Thiazolines to Thiazoles
To a solution of 4-methyl-2-phenylthiazoline (177 mg, 1 mmol) in 1,2-dichloroethane (10 mL) was
added activated MnO2 (860 mg, 10 mmol). The mixture was then refluxed for 12 h under a nitrogen
atmosphere. After filtration, the mixture was evaporated in vacuo. The residue was chromatographed
on silica gel (ethyl Acetate-hexane, 10:1) to give 176 mg (95% yield) of 4-methyl-2-phenylthiazole
1
(1a) [21] as a colorless oil; H-NMR: δ 7.94–7.91(m, 2H), 7.43–7.39 (m, 3H), 6.85 (t, J = 0.96 Hz,
1H), 2.50 (d, J = 0.96 Hz, 3H); 13C-NMR: δ 167.44, 153.71, 133.72, 129.65, 128.75, 126.34, 113.30, 17.14.
4.3. Spectral Data of Other Thiazole Compounds
1
1b [11]: H-NMR: δ 7.96–7.91(m, 2H, ArH), 7.44–7.37 (m, 3H, ArH), 6.86 (s, 1H), 3.21–3.11 (m,
13
1H), 1.35 (d, J = 6.90 Hz, 6H); C-NMR: δ 167.29, 164.87, 134.08, 129.63, 128.79, 126.52, 110.88,
31.05, 22.40.
1c: colorless oil; IR (KBr, cm−1): 3063, 2955, 2928, 1516, 1461, 1244, 763; 1H-NMR: δ 7.95–7.91 (m,
2H, ArH), 7.49–7.35 (m, 3H, ArH), 6.85 (d, J = 0.63 Hz, 1H), 2.67 (dd, J = 9.0, 0.75 Hz, 2H),
13
2.16–2.06 (m, 1H), 0.97 (d, J = 6.60 Hz, 6H); C-NMR: δ 167.16, 157.77, 133.93, 129.57, 128.74,
128.43, 113.45, 40.78, 28.38, 22.35; Anal. Calcd. for C13H15NS (217.34): C 71.84, H 6.96, N 6.44.
Found: C 71.96, H 6.85, N 6.23.
1d [22]: white solid, mp: 90.5 °C–92.0 °C (lit. [22] 91.0–92.0°C); 1H-NMR: δ 8.05–7.98 (m, 4H),
13
7.47–7.42 (m, 6H), 7.41–7.34 (m, 1H); C-NMR: δ 167.74, 156.21, 134.48, 133.72, 129.53, 128.83,
128.65, 128.08, 126.54, 126.34, 112.54.

Molecules 2009, 14
4862
1
1e [23]: white solid, mp: 85.0–86.0 °C (lit. [23] 84.0–84.5 °C); H-NMR: δ 8.60–8.58 (m, 1H),
8.18–8.14 (m, 1H), 7.79–7.73 (m, 1H), 7.30–7.26 (m, 1H), 6.99 (d, J = 0.84 Hz, 1H), 2.52 (d, J = 0.84
Hz, 3H); 13C-NMR: δ 167.92, 153.81, 151.12, 149.06, 136.53, 123.87, 119.17, 115.84, 16.96.
1
1f: colorless oil; IR (KBr, cm−1): 3060, 2920, 1738, 1365, 1217; H-NMR: δ 8.60–8.58 (m, 1H),
8.21–8.18 (m, 1H), 7.79–7.73 (m, 1H), 7.29–7.25 (m, 1H), 6.98 (d, J = 0.84 Hz, 1H), 3.19–3.14 (m,
13
1H), 1.36 (d, J = 6.90 Hz, 6H); C-NMR: δ 167.96, 165.07, 151.61, 149.26, 136.71, 124.01, 119.57,
113.45, 30.96, 22.31; Anal. Calcd. for C11H12N2S (204.30): C 64.67, H 5.92, N 13.71. Found: C 64.88,
H 5.91, N 13.45.
1
1g: colorless oil; IR (KBr, cm−1): 3120, 1569, 1495, 1473, 1299, 1133, 810, 769; H-NMR: δ 7.49
(t, J = 1.20 Hz, 1H), 7.35–7.22 (m, 5H, ArH), 6.97 (dd, J = 2.1, 0.6 Hz, 1H), 6.69 (s, 1H), 6.51
(dd, J = 4.80, 3.33 Hz, 1H), 4.17 (s, 2H); 13C-NMR: δ 157.81, 151.51, 149.04, 143.41, 138.89, 129.08,
128.54, 126.48, 113.59, 112.08, 108.79, 37.91; Anal. Calcd. for C14H11NOS (241.32): C 69.68, H 4.59,
N 5.80. Found: C 69.75, H 4.85, N 5.93.
1h: white solid, mp: 72.3–72.9°C; IR (KBr, cm−1): 3060, 2970, 1738, 1452, 1217, 1015, 750;
1H-NMR: 7.96 (d, J = 1.32 Hz, 1H), 7.94 (s, 1H), 7.53 (d, J = 1.14 Hz, 1H), 7.46–7.32 (m, 4H, ArH),
7.08 (d, J = 3.45Hz, 1H), 6.55 (dd, J = 3.30, 1.80 Hz, ArH); 13C-NMR: 157.79, 156.26, 149.09,
143.48, 134.19, 128.66, 128.20, 126.46, 112.13, 111.83, 108.98; Anal. Calcd. for C13H9NOS (227.89):
C: 68.52, H: 3.98, N: 6.15. Found: C 68.66, H 4.05, N 6.13.
1i [24]: colorless oil; 1H-NMR: δ 7.96–7.93 (m, 2H), 7.52 (dd, J = 3.60, 1.14 Hz, 1H), 7.44–7.32 (m, 5H),
7.05 (dd, J = 5.40, 3.60 Hz, 1H); 13C-NMR: δ 161.15, 155.56, 137.30, 133.95, 128.50, 127.99, 127.60,
127.45, 126.38, 126.26, 111.74.
1j: colorless oil; IR (KBr, cm−1): 3034, 1738, 1476, 1365, 1217; 1H-NMR: δ 7.52–7.48 (m, 2H, ArH),
7.38–7.24 (m, 5H, ArH), 6.78 (s, 1H,), 3.16–3.06 (m, 1H), 1.33 (d, J = 6.90 Hz, 6H); 13C-NMR:
δ 166.20, 164.50, 135.85, 133.72, 128.70, 128.57, 126.89, 121.88, 110.26, 30.89, 22.29; Anal. Calcd.
for C14H15NS (229.35): C 73.32, H 6.59, N 6.11. Found: C 73.55, H 6.72, N 6.33.
1
1k [25]: colorless oil; H-NMR: δ 7.95–7.92 (m, 2H), 7.58–7.55 (m, 2H), 7.47–7.32 (m, 9H);
13C-NMR: δ 166.76, 156.26, 135.82, 134.52, 134.42, 128.88, 128.75, 128.70, 128.20, 127.12, 126.44,
121.68, 112.09.
1
1l [26]: white solid, mp: 64.0–65.5 °C (lit. [26] 64°C); H-NMR: δ 7.89–7.85 (m, 2H), 7.44–7.38 (m,
13
2H), 7.34–7.28 (m, 2H), 2.77 (s, 3H); C-NMR: δ 165.80, 155.22, 134.59, 129.01, 128.69, 127.95,
126.54, 126.34, 112.19, 19.31.
5a: colorless oil; IR (KBr, cm−1): 2961, 1569, 1509, 1429, 1270, 742; 1H-NMR: δ 8.45 (t, J = 1.75 Hz,
1H), 7.98 (dd, J = 7.80, 1.50 Hz, 2H), 7.47 (t, J = 7.80 Hz, 1H), 6.90 (d, J = 0.72 Hz, 1H), 3.23–3.13
(m, 2H), 1.37 (d, J = 6.90 Hz, 12H); 13C-NMR: δ 166.38, 164.89, 134.65, 129.23, 127.53, 124.37,
111.22, 30.98, 22.32; Anal. Calcd. for C18H20N2S2 (328.51): C 65.81, H 6.14, N 8.53. Found: C 65.95,
H 6.25, N 8.44.

Molecules 2009, 14
4863
5b [27]: white solid, mp: 126–126.5°C; 1H-NMR: δ 8.14(d, J = 7.80 Hz, 2H), 7.86 (t, J = 7.80 Hz, 1H),
13
7.02 (d, J = 0.90 Hz, 2H), 2.53 (d, J = 0.85 Hz, 6H); C-NMR: δ 165.80, 155.22, 134.59, 128.69,
127.95, 126.34, 112.19, 19.31.
5c: white solid, mp: 61.5–62.0 °C; IR (KBr, cm−1): 3068, 2926, 1564, 1510, 1498, 1011, 669;
1H-NMR: δ 8.17 (d, J = 7.80 Hz, 2H), 7.85 (t, J = 7.80 Hz, 1H), 7.01 (d, J = 0.66 Hz, 2H), 3.21–3.12
(m, 2H), 1.37 (d, J = 6.90 Hz, 12H); 13C-NMR: δ 167.68, 165.28, 151.28, 137.80, 119.86, 113.93,
31.10, 22.44; Anal. Calcd. for C17H19N3S2 (329.50): C: 61.97, H: 5.81, N: 12.75. Found: C: 61.99, H:
5.85, N: 12.90.
1
5d: colorless oil; IR (KBr, cm−1): 2920, 1569, 1485, 1270, 1174, 1072, 731; H-NMR: δ 7.98 (d,
J = 1.38Hz, 4H), 7.45–7.30 (m, 8H), 3.11 (t, J = 7.74Hz, 4H), 2.25–2.20 (m, 2H); 13C-NMR: δ 174.92,
155.01, 134.67, 128.69, 127.99, 126.42, 113.29, 51.32, 36.64, 16.61; Anal. Calcd. for C22H18N2S2
(374.54): C 70.55, H 4.84, N 7.48. Found: C 70.69, H 4.85, N 7.62.
Acknowledgements
This work was financially supported by the Ministry of Science and Technology of China (No.
2006BAE01A01) and the Innovation Programme for National Undergraduated Students.
References and Notes
1. Rivkin, A.; Cho, Y.S.; Gabarda, A.E.; Yoshimura, F.; Danishefsky, S.J. Application of Ring-
Closing Metathesis Reactions in the Synthesis of Epothilones. J. Nat. Prod. 2004, 67, 139–143.
2. Ganesh, T.; Schilling, J.K.; Palakodety, R.K.; Ravindra, R.; Shanker, N.; Bane, S.; Kingston,
D.G.I. Synthesis and biological evaluation of fluorescently labeled epothilone analogs for tubulin
binding studies. Tetrahedron 2003, 59, 9979–9984.
3. Plazzi, P.V.; Bordi, F.; Silva, C.; Morini, G.; Caretta, A.; Barocelli, E.; Vitali, T.
Heteroarylaminoethyl and heteroaryithioethyl imidazoles. Synthesis and H3-receptor affinity.
Eur. J. Med. Chem. 1995, 30, 881–889.
4. Bai, N.; Sha, Y.W.; Meng, G. Efficient and Eco-Friendly Preparation of 4-Methyl-5-formyl-
thiazole. Molecules 2008, 13, 943–947.
5. Hu, D.J.; Liu, S.F.; Huang, T.H.; Tu, H.Y.; Zhang, A.D. Synthesis and herbicidal activities of
novel 4-(4-(5-methyl-3-arylisoxazol-4-yl)thiazol-2-yl)piperidyl carboxamides and thio-carboxamides.
Molecules 2009, 14, 1288–1303.
6. Aitken, K.M.; Aitken, R.A. Synthesis of 2,4-diacetylthiazole and 2,5-diacetylthiazole.
Tetrahedron 2008, 64, 4384–4386.
7. Potewar, T.M.; Ingale, S.A.; Srinivasan, K.V. Efficient synthesis of 2, 4-disubstituted thiazoles
using ionic liquid under ambient conditions: A practical approach towards the synthesis of
Fanetizole. Tetrahedron 2007, 63, 11066–11069.
8. Narender, M.; Reddy, M.S.; Sridhar. R.; Nageswar, Y.V.D.; Rao, K.R. Aqueous phase synthesis
of thiazoles and aminothiazoles in the presence of β-cyclodextrin. Tetrahedron Lett. 2005, 46,
5953–5955.

Molecules 2009, 14
4864
9. Hämmerle, J.; Spina, M., Schnürch, M.; Mihovilovic, M.D.; Stanetty, P. A Comparative Study on
Stille Cross-Coupling Reactions of 2-Phenylthiazoles and 2-Phenyloxazoles. Synthesis 2008, 19,
3099–3107.
10. Friedrich, A.; Max, T.; Karl, G. Concomitant reaction of elementary sulfur and gaseous ammonia
on ketones. XXIX. Syntheses and properties of 2-aryl-3-thiazolines and 2-arylthiazoles. Justus
Liebigs Ann. Chem. 1961, 639, 133–146.
11. Aitken, R.A.; Armstrong, D.P.; Galt, R.H.B.; Mesher, S.T.E. Synthesis and oxidation of chiral 2-
thiazolines (4,5-dihydro-1,3-thiazoles). J. Chem. Soc. Perkin Trans. 1997, 1, 935–943.
12. Meyers, A.I.; Tavares, F.X. Oxidation of oxazolines and thiazolines to oxazoles and thiazoles
application of the Kharasch-Sosnovsky reaction. J. Org. Chem. 1996, 61, 8207–8215.
13. Fernandez, X.; Duňach, E. Asymmetric synthesis of 2-alkyl-3-thiazoline carboxylates:
stereochemistry of the MnO2-mediated oxidation of cis- and trans-2-alkyl-thiazolidine-(4R)-
carboxylates. Tetrahedron Asymmetry 2001, 12, 1279–1286.
14. Fernandez, X.; Fellous, R.; Lizzani-Cuvelier, L.; Loiseau, M.; Duňach, E. Chemo- and
regioselective synthesis of alkyl-3-thiazoline carboxylates. Tetrahedron Lett. 2001, 42,
1519–1521.
15. You, S.L.; Kelly, J.W. The total synthesis of bistratamides F–I. Tetrahedron 2005, 61, 241–249.
16. You, S.L.; Kelly, J.W. Highly efficient biomimetic total synthesis and structural verification of
Bistratamides E and J from Lissoclinum bistratum. Chem. Eur. J. 2004, 10, 71–75.
17. Mislin, G.L.; Burger, A.; Abdallah, M. A. Synthesis of new thiazole analogues of pyochelin, a
siderophore of Pseudomonas aeruginosa and Burkholderia cepacia. A new conversion of
thiazolines into thiazoles. Tetrahedron 2004, 60, 12139–12145.
18. Cheng, X.M.; Zheng, Z.B.; Li, N.; Qin, Z.H.; Fu, B.; Wang, N.D. Synthesis of novel C3
symmetric tris(thiazoline) ligands and their application in the allylic oxidation reaction.
Tetrahedron Asymmetry 2008, 19, 2159–2163.
19. Lu, X.H.; Qi, Q.Q.; Xiao, Y.M.; Li, N.; Fu, B. A convenient one-pot synthesis of arene-centered
tris(thiazoline) compounds. Heterocycles 2009, 78, 1031–1039.
20. Liu, L.; Zheng, Z.B.; Qin, Z.H.; Fu, B. Yuan, H.Z. Synthesis and biological activity of 2-indolyl
oxazoline and thiazoline derivatives. Chin. J. Org. Chem. 2008, 28, 1841–1845.
21. Taku, A.; Takuya, A.; Takahide, F.; Yutaka, I.; Fumitoshi, K.; Naoto, C. Ruthenium- and
Rhodium-Catalyzed Direct Carbonylation of the Ortho C-H Bond in the Benzene Ring of N-
Arylpyrazoles. J. Org. Chem. 2004, 69, 4433–4440.
22. Yoshihide, I.; Hideo, T. Facile preparation of thiazoles from 1H-1-(1'-alkynyl)-5-methyl-1,2,3-
benziodoxathiole 3,3-dioxide with thioamides. Synlett 2008, 17, 2637–2641.
23. Knott, R.F.; Breckenridge, J.G. Analogs of 2,2'-bipyridyl with isoquinoline and thiazole rings.
Part I. Can. J. Chem. 1954, 32, 512–521.
24. Singh, S. P.; Subhash, S. Synthesis and phototoxicity of some 2-(phenyl- or 2- or 3-thienyl)-4-
substituted thiazoles. Indian J. Chem. Sect. B: Org. Chem. Incl. Med. Chem. 1988, 27B, 941–943.
25. Takao, S.; Hideo, N.; Yoshinori, K.; Masafumi, S.; Hiroshi, Y.; Palladium-catalyzed reactions of
terminal acetylenes and olefins with halo-1,3-azoles. Chem. Pharm. Bull. 1987, 35, 823–828.

Molecules 2009, 14
4865
26. Makoto, U.; Hideo, T. Environmentally benign preparation of heteroaromatics from ketones or
alcohols, with macroporous polystyrenesulfonic acid and (diacetoxyiodo)benzene, followed by
thioamide, amidine, and 2-aminopyridine. Synthesis 2004, 16, 2673–2677.
27. Veli-Matti, M.; Paivi, L.; Ilkka, H.; Harri, T.; Cristina, M.; Jouko, K. Novel thiazole-containing
complexing agents and luminescence of their europium(III) and terbium(III) chelates. Helv. Chim.
Acta 1996, 79, 295–306.
Sample Availability: Samples of the compounds are available from the authors.
© 2009 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
This article is an open-access article distributed under the terms and conditions of the Creative
Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).