Ethyl 3-methyl-4-oxo-4,7-dihydroisothiazolo[5,4-b]pyridine-5-carboxylate → 3-Methyl-4-oxo-4,7-dihydroisothiazolo[5,4-b]pyridine-5-carboxylic acid

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Reaction Steps

Ethyl 3-methyl-4-oxo-4,7-dihydroisothiazolo[5,4-b]pyridine-5-carboxylate (18 g, 75.55 mmol) was suspended in 2 N NaOH (100 mL) and the mixture was heated at reflux for 3 h. After hydrolysis was complete, the reaction was filtered to yield a dark brown solid. The solid was washed with water (100 mL) and acetone (50 mL), then air dried to provide 3-methyl-4-oxo-4,7-dihydroisothiazolo[5,4-b]pyridine-5-carboxylic acid as a dark brown powder (15 g, 79% yield). LC/MS m/z 210.8 [M+H]+, retention time 0.67 min (RP-C18, 10-99% CH3CN/0.05% TFA over 3 min). 1H NMR (400 MHz, DMSO-d6) δ 8.92 (s, 1H), 2.75 (s, 3H).

Provenance & Evidence