Hydrochloric Acid → 3-Oxo-1,3-dihydrobenzo[c]isothiazole-5-carboxylic acid

関与物質

反応手順

To a solution of Li2S (5.7 g, 0.124 mol) in H2O (1000 ml) cooled to 0° C. in an ice bath was added HCl (1M, 186 ml, 0.186 mmol) slowly with stirring. The ice bath was then removed, and 2,4-dioxo-2,4-dihydro-1H-benzo[d][1,3]oxazine-6-carboxylic acid (8.1 g, 0.050 mol) was added slowly. The suspension was stirred for 1 h and was filtered. The filtrate was purged with N2 for 30 min, and H2O2 (30%, 7.0 ml) was added, stirred for 45 min. The pH of the reaction mixture was adjusted with 6M HCl to ˜5 and the resulting suspension was filtered. The solid was washed with H2O (×3) and was dried to yield 3-oxo-1,3-dihydrobenzo[c]isothiazole-5-carboxylic acid as an off-white solid. To a solution of 3-oxo-1,3-dihydrobenzo[c]isothiazole-5-carboxylic acid 4.2 g, 27.8 mmol) in acetone (100 ml) was added MeI (5.2 ml, 83.4 mmol) and K2CO3 (7.7 g, 55.6 mmol). The mixture was heated to 60° C. for 2 h, and was filtered and concentrated. The crude product was purified by flash column chromatography on silica gel eluting with 20%→30% EtOAc-hexane to yield Intermediate 9 as a yellow solid.

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