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Paper | Special issue | Vol 101, No. 2, 2020, pp.611-620
Published online, 25th September, 2019
DOI: 10.3987/COM-19-S(F)51
5-Amino-2-thiazolylpyridine N-Oxides: Synthesis and Properties

Toshiaki Murai,* Yuuta Nakatsu, Yuki Tsuchiya, Kirara Yamaguchi, Toshifumi Maruyama, Yohei Miwa, and Shoichi Kutsumizu

*Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University , 1-1 Yanagido, Gifu, Gifu 501-1193, Japan

Abstract

5-Amino-2-thiazolylpyridine N-oxides were prepared in low to moderate yields by the oxidation of 2-pyridyl-5-aminothiazoles with m-CPBA. The molecular structures of the resulting N-oxides were unequivocally determined by X-ray analyses. The N-oxides exhibited the absorption maxima at around 415 ± 20 nm in a CHCl3 solution, while the emission spectra were observed in the range of 505 to 604 nm. The red-shift of the emission was attributed to the methoxy groups attached to the para-position of an aromatic group on the nitrogen atom at the 5-position. The N-oxides exhibited halochromism with the addition of B(C6F5)3. The change in absorption implied the formation of a 1:1 complex between N-oxide and B(C6F5)3. The emission wavelengths of the N-oxides were observed at 510 ± 25 nm in a solid state. Interestingly, one of the N-oxides having methoxy groups exhibited mechanofluorochromism. The solid-state emission of the N-oxide at 527 nm shifted to a longer wavelength (599 nm) when it was subjected to grinding.