Tomio Yamazaki

Synthesis of novel 5- and 6-substituted 3-arylidene-1,4-oxathiin-2(3H)-ones

The reactions of α-acetylthio-β-arylacrylic acids (2a–c) with α-halogeno ketones (3a–f), α-halogeno-β-keto esters (7a–b), and α-halogenopyruvate (9) afforded the corresponding novel 3-arylidene-1,4-oxathiin-2(3H)-ones [(4a–d), (8a–f), and (10a), respectively] having 5- and/or 6-substituents. The β-aryl-α-thioacrylic acids (1a–d) were treated with α-halogeno ketones (3a–f), (7a–b), and (9) to give the corresponding β-aryl-α-alkylthioacrylic acids (5a–d), (11a–f), and (12a–c), which were converted into the respective 3-arylidene-1,4-oxathiin-2(3H)-ones (4a–g), (8a–f), and (10a–c) by intramolecular cyclization when treated with thionyl chloride–dimethylformamide. The sulphur atom of the 1,4-oxathiin-2(3H)-ones (4d), (4g), and (8a) was smoothly oxidized with m-chloroperbenzoic acid to give the corresponding S-oxides (13a–c) in good yields.