[CH:1]([NH:3][C:4]1[CH:9]=[C:8]([N+:10]([O-:12])=[O:11])[CH:7]=[CH:6][C:5]=1Br)=O.O.O.O.O.O.O.O.O.O.[S-2:23].[Na+].[Na+].O.Cl>CCO>[N+:10]([C:8]1[CH:7]=[CH:6][C:5]2[S:23][CH:1]=[N:3][C:4]=2[CH:9]=1)([O-:12])=[O:11]A solution of formamide from Step 1 (5.83 g, 23.8 mmol) and sodium sulfide nonahydrate (8.60 g, 35.8 mmol) in EtOH (120 ml) was heated to reflux for 2 h under nitrogen. After this time the reaction was cooled to RT then poured into cold water (600 ml). The resulting solution was cooled in an ice bath and acidified to pH 1 with 37% HCl. The solution was cooled in an ice bath for a further 1 h, during which time an orange precipitate formed. This solid was isolated by filtration and dried under vacuum to afford 5-nitrobenzothiazole as an orange solid (2.28 g). The above filtrate was extracted with EtOAc (3×200 ml), and the combined organic extracts dried over Na2SO4, filtered and concentrated under vacuum to afford additional 5-nitrobenzothiazole (0.89 g) as an orange solid. NMR and TLC analysis indicated that both crops of product were identical; the combined yield was 3.17 g. 1H NMR (CDCl3) δ 9.19 (s, 1H), 9.02 (d, 1H), 8.35 (dd, 1H), 8.12 (d, 1H); 13C NMR (CDCl3) δ 157.3, 153.1, 147.0, 140.2, 122.5, 120.1, 119.3. MS (ESI+) for m/z 181 [M+H]+.
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