Unexpected Products from Mesoionic 1,3-Thiazinium and Oxazinium Olates: A Novel Access to 3,5-Diaryl-1,3-thiazine-2,4,6-trione and Alkoxy-3,5-diphenyl-3H-1,3-oxazine-2,6-dione Derivatives

Abstract

The condensation of (chlorocarbonyl)ketenes 1 with N-phenylthiocarbamates 2 and N-phenylcarbamates 6 is postulated to lead to the formation of unstable mesoionic 1,3-thiazinium 4-olates I or 1,3-oxazinium 4-olates II, respectively. At room temperature, appropriately substituted mesoionic 1,3-thiazinium 4-olates I eliminated the corresponding alkene with generation of 3,5-diaryl-1,3-thiazine-2,4,6-trione derivatives 3. However, the methoxy-substituted compound 5 was stable at room temperature at least for several weeks. In the case of the mesoionic1,3-oxazinium 4-olates II an alkyl group migration affords 4-alkoxy-3,5-diphenyl-3H-1,3-oxazine-2,6-diones 7.