Sodium borohydride → HCID 12096237, compound

7-bromo-2-(1,1-dimethylethyl)-2,3-dihydro-1,2-benzisothiazol-3-ol 1,1-dioxide (1.4 g, 4.4 mmol) was treated with formic acid (10 mL). The reaction was stirred at ambient temperature over 18 h, concentrated in vacuo and dissolved in methanol (10 mL). The mixture was cooled to 0° C. and treated with sodium borohydride (0.17 g, 4.4 mmol) in small portions over 20 min. The cooling bath was removed and the resulting reaction mixture stirred at ambient temperature over 18 h. The work-up consisted of slowly quenching the reaction mixture with ice, dilution with water and extraction with ethyl acetate. Drying over sodium sulfate and concentrating under reduced pressure provided the crude product that was purified by a plug of silica gel (ethyl acetate/hexane, 1:4) to afford the desired 7-bromo-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide (0.6 g, 60% over 2 steps). 1H NMR (CD3OD): δ 4.40 (s, 2H), 7.53 (m, 2H), 7.70 (m, 1H).