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■ A New Synthesis 1,3-Thiazin-4-ones via 1,3-Oxazinium Salts from N-Acetoacetylcarboxamides

Yutaka Yamamoto,* Yutaka Azuma, and Shuhei Ohnishi

*Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai 981-8558, Japan

Abstract

In the formation of 1,3-oxazinium salts from N-acetoacetylcarboxamides (1), the effect of acids such as 70% perchloric acid (3a), 98% sulfuric acid (3b), 36% hydrochloric acid (3c), saturated hydrogen chloride-ethanol solution (3d), trifluoroacetic acid (3e), and acetic acid (3f) was examined by the established method leading to the pyrazole (5) via 1,3-oxazinium salt (2), and the order was as follows; 3a > 3b > 3e > 3d > 3c (3f was uneffective). The result was applied to synthesize 2-substituted 1,3-thiazine derivatives (7a-e, 8a,b) via 1,3-oxazinium salts from 1a-f and hydrogen sulfide in the presence of acetic anhydride in satisfactory yields.