ABSTRACT
2-Methylene-3,1-benzoxathiin-4-ones reacted with nitrones at methylene moieties of 3,1-benzoxathiine rings to yield spiro 1,3-dipolar cycloadducts. The benzoxathiin-4-one rings easily occurred ring opening reaction with NaOSiMe3 and isoxazolidin-5-one derivatives were obtained in good yields. As a result, 2-methylene-3,1-benzoxathiin-4-ones can be used as a ketene equivalent.