Umpolung Strategy with 2-Aminothiophenols: Access to 2-Arylbenzothiazine Derivatives from Alkyl Aryl Ketones

Strong Bronsted acids were found to catalyze the oxidative condensation of 2-aminothiophenols with aryl alkyl ketones in DMSO to provide a wide range of complex 2-arylbenzothiazines. With acetophenones, dimeric 2-arylbenzothiazines were formed. On the other hand, the reaction with propiophenones resulted in 2:1 adducts whereas 1:1 adducts were produced with isobutyrophenones, benzoylacetonitrile and ethyl benzoylacetate.