1,4-Dioxane → 2(3H)-Benzothiazolone, 6-amino-

The compound obtained in Step A (0.036 mol) is dissolved in 90 ml of methanol, and then 2.5 g of palladium-on-carbon and 18 g of ammonium formate are added in succession and the mixture is heated at reflux for 18 hours. 40 ml of dioxane are added and refluxing is continued for 24 hours. The palladium-on-carbon is then filtered off. The reaction mixture is concentrated, the resulting precipitate is filtered off, and the filtrate is evaporated under reduced pressure. The resulting residue is taken up in a 1N hydrochloric acid solution and extracted twice with 50 ml of ethyl acetate each time. The aqueous phase is rendered alkaline with a 10% potassium carbonate solution and extracted twice with 50 ml of ethyl acetate each time. The organic phase is dried and then evaporated under reduced pressure, and the resulting precipitate is recrystallised from acetonitrile.