3-Methyl-2-butenoic acid → 1-(1H-1,2,3-Benzotriazol-1-yl)-3-methylbut-2-en-1-one

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Reaction Steps

1H-Benzotriazole (2.14 g, 18.0 mmol, 4 equiv.) was dissolved in dichloromethane (25 ml) and thionyl chloride (330 μl, 4.5 mmol, 1 equiv.) was added at room temperature. (450 mg, 4.5 mmol) 3-Methyl-but-2-enoic acid [CAS 541-47-9] was added and the mixture was stirred for 2 hours at room temperature. The suspension was filtered and the filtrate was extracted once with 2N NaOH solution and twice with dichloromethane. The organic extracts were combined, dried over sodium sulfate and evaporated to dryness. The crude product was purified by flash chromatography on a silica gel column eluting with an ethyl acetate:cyclohexane gradient 0:100 to 50:50. The desired 1-benzotriazol-1-yl-3-methyl-but-2-en-1-one (810 mg, 90% yield) was obtained as a light yellow solid, MS: m/e=202.1 (M+H+).

Provenance & Evidence