The oxidation of 3-acylbenzothiazolines (IV) with m-chloroperbenzoic acid gave 3-acylbenzothiazoline sulfoxides (V) and sulfone (VI) in high yield. The stereochemistry of the compounds V is discussed on the basis of nuclear magnetic resonance spectroscopic studies. Reaction of the compound V with refluxing acetic anhydride resulted in the formation of novel ring expansion products, 4-acylbenzothiazine derivatives. A mechanism involving the sulfenic anhydride as an intermediate is proposed for this ring expansion.
Thermal rearrangement of 2,2-disubstituted benzothiazoline I-oxides (1) in aprotic solvent afforded the corresponding 1,4-benzothiazines (2) and (3). The thermal reaction performed in the presence of electron-deficient acetylenic compounds produced new tricyclic compounds (7) whose structures have been established by an X-Ray crystal structure determination.
HORI MIKIO; KATAOKA TADASHI; SHIMIZU HIROSHI; UEDA NORIHIRO, TETRAHEDRON LETT., 1981, 22, NO 18, 1701-1704