Electroorganic synthesis of gem-2,2-difluoro-3-aryl-2H-1,4-benzothiazine derivatives

Anodic fluorination of 3-aryl-2H-1,4-benzothiazine derivatives was investigated by the conventional electrolytic method in acetonitrile (MeCN) or dimethoxyethane (DME) containing various hydrogen fluoride (HF) salts as supporting electrolytes and fluorine sources. It was found that the fluorination proceeded via the formation of dehydrodimers of benzothiazines followed by the anodic fluorination of the dimeric product. Anodic fluorination of benzothiazine dehydrodimers as starting materials in Et3N·3HF/DME provided 2,2-difluorobenzothiazine derivatives in moderate to good yields depending on 3-aryl substituents.