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.
Abstract o‐Aminothiophenol reacted with ketones and β‐keto esters in the presence of alumina under mild and solvent‐free conditions to afford the corresponding benzothiazolines in high yields. Alumina can be reused for subsequent reactions without any loss of the activity.