Acetic Anhydride → Methyl 1-acetyl-1H-thieno[3,2-c]pyrazole-5-carboxylate

Participants

Reaction Conditions

Reaction Steps

A magnetically stirred mixture of potassium acetate (4.52 g, 46.1 mM) in toluene (100 mL) containing 4-amino-5-methyl-thiophene-2-carboxylic acid methyl ester [12.8 g, 74.7 mM, Intermediate (24)] is warmed to dissolve the amine. Acetic anhydride (13.8 mL, 124.9 mM) is added to this mixture and it is heated in an oil bath. Isoamyl nitrite (9.73 mL, 72.4 mM) is added over 30 minutes. Heating at 93° C. is continued overnight. The cooled mixture is diluted with ethyl acetate (100 mL), filtered and the filtrate is concentrated to a black solid which is purified by chromatography, eluting with heptane-25% ethyl acetate, heptane-35% ethyl acetate, heptane-40% ethyl acetate, heptane-50% ethyl acetate, heptane-60% ethyl acetate. Fractions containing pure product are combined and concentrated to afford 1-acetyl-1H-thieno[3,2-c]pyrazole-5-carboxylic acid methyl ester [9.74 g, 49.3%, Intermediate (25)].

Provenance & Evidence