A new approach for the synthesis of some 1,4-benzoxathiin 4,4-dioxide derivatives

A series of 1,4-benzoxathiin 4,4-dioxide derivatives have been prepared by a new synthetic route. The reactions of 2-chloro-4-nitrobenzenethiol 1 with 1-aryl-2-chloroethanones 2 in the presence of sodium hydroxide give 1-aryl-2-(2-chloro-4-nitrophenylthio)ethanones 3 which on oxidation with 30% aqueous hydrogen peroxide afford 1-aryl-2-(2-chloro-4-nitrophenylsulfonyl)ethanones 4. By the reactions of compounds 4 with 2-[3 or 4-(bromomethyl)phenyl]benzoxazole in the potassium carbonate, triethylbenzylammonium chloride and dimethylformamide system, 2-aryl-3-arylmethyl-7-nitro-1,4-benzoxathiin 4,4-dioxides 5 or 6 are obtained via a tandem alkylation-cyclization process.