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Report | Regular issue | Vol 19, No. 11, 1982, pp.2119-2129
Published online, 1st January, 1970
DOI: 10.3987/R-1982-11-2119
Ring Transformations of Oxazoles and Their Benzo Analogues. New Synthetic Route for 2H-Imidazo[2,1-b][1,3,4]thiadiazine and N-Heteroaryl-o-aminophenol

Tadashi Sasaki, Eikoh Ito, and Ikuo Shimizu

*Institute of Applied Organic Chemistry, Faculty of Engineering, Nagoya University, Chikusa, Nagoya, Aichi 464-8601, Japan


Ring transformations of certain functionalized oxazoles and their benzo analogues were studied. The α-(oxazol-2-ylthio) ketones 3a, b, c, and e gave 2H-imidazo[2,1-b][1,3,4]thiadiazines (4a, b, c, and e) on treatment with hydrazine hydrate in acetic acid. Similar treatment of ketones 3d and f-h resulted in the formation of the complex mixtures. The α-(benzoxazol-2-ylthio) ketones 5a and b reacted with ammonium acetate in acetic acid to give 2-(2-hydroxyphenylamino)thiazoles 6a and b in quantitative yields. With hydrazine, 5a afforded thiazoline derivative 7 while 5b provided 1,3,4-thiadiazine derivative 8 under the similar conditions. Aminophenols 6a and b were further converted into 1,4-benzoxazines 10a and b by treating with chloroacetone followed by phosphorus pentoxide in benzene. Mechanisms for these transformations are proposed.