In this work we therefore have identified a previously unreported heterocyclization based on -bromo-
crotonates and leading to thiazolopyridinium olates.
IR spectra were recorded on a PerkinElmer Spectrum BX instrument for KBr pellets and UV spectra on
1
a Lambda 20 UV/VIS spectrometer using MeOH. The H NMR spectra were recorded on a Bruker Avance
DRX-500 instrument (500 MHz) using DMSO-d with TMS as internal standard. Elemental analysis was
6
performed on a vario MICRO cube CHNS-analyzer, and halogens were determined by the Schöniger method.
Melting points were measured in Pyrex glass capillaries on a Thiele apparatus and were not corrected.
3
-Methyl[1,3]thiazolo[3,2-a]pyridin-4-ium-8-olate (4a). A mixture of the 4-methylthiazole 1a (0.30 g,
.0 mmol) and methyl 4-bromobut-2-enoate 2a (0.54 g, 3.0 mmol) was left in MeCN (20 ml) overnight at room
temperature. The solution was evaporated, the residue was dissolved in EtOH (20 ml), K CO (0.50 g,
3
2
3
3
.6 mmol) was added, and the mixture was refluxed for 2 h. The solution was cooled, filtered, and evaporated.
The residue obtained was washed with acetone. Yield 0.41 g (82%). Light-brown crystals; mp 259-261°C
-
1
(
acetone). IR spectrum, , cm : 3483, 3410, 2961, 1615, 1573, 1436, 1276, 1201, 1039, 765. UV spectrum,
1
max, nm (log ): 346 (3.96), 374 (3.38). H NMR spectrum, , ppm (J, Hz): 2.64 (3H, s, CH ); 6.95 (1H, d,
3
J = 8.0, H-7); 7.57 (1H, dd, J = 6.0, J = 8.0, H-6); 8.04 (1H, s, H-2); 8.17 (1H, d, J = 6.0, H-5). Found, %:
С 52.16; Н 4.90; N 7.58; S 17.13. C H NOS·H O. Calculated, %: C 52.44; H 4.95; N 7.64, S 17.50.
8
7
2
2
-Methylpyrido[2,1-b][1,3]benzothiazol-10-ium-4-olate (4b). A mixture of the benzothiazole 1b
(
1.15 g, 8.5 mmol) and methyl 4-bromo-3-methylbut-2-enoate 2b (1.80 g, 9.4 mmol) in MeCN (60 ml) was left
overnight at room temperature. Solvent was removed in vacuo, and the residue was dissolved in EtOH (60 ml).
K CO (1.52 g, 11.0 mmol) was added, and the mixture was refluxed for 2 h. The solution was cooled, filtered,
2
3
and evaporated, and the residue was washed with acetone. Yield 0.82 g (45%). Brown crystals; mp 224-225°C
-
1
1
(
acetone). IR spectrum, , cm : 3431, 3054, 1578, 1542, 1475, 1454, 1364, 1323, 752. H NMR spectrum, ,
ppm (J, Hz): 2.35 (3H, s, CH ); 6.64 (1H, s, H-3); 7.70-7.81 (2H, m, H-7,8); 8.30 (1H, d, J = 8.0, H-6); 8.61
3
(
1H, d, J = 8.0, H-9); 8.64 (1H, s, H-1). Found, %: С 61.59; Н 4.69; N 6.11; S 13.71. C H NOS·H O.
12 9 2
Calculated, %: C 61.78; H 4.75; N 6.00; S 13.74.
REFERENCES
1
.
L. Potikha, V. Kovtunenko, A. Turelyk, A. Turov, and A. Tolmachev, Synth. Commun., 38, 2061
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(
2
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.
A. Gebert, M. Barth, A. Linden, U. Widmer, and H. Heimgartner, Helv. Chim. Acta, 95, 737 (2012).
A. R. Katritzky and Y. Takeuchi, J. Chem. Soc. C, 874 (1971).
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49