Tin tetrachloride → Methyl 3-amino-1H-thieno[3,2-c]pyrazole-5-carboxylate

Participants

Reaction Steps

To an ice-cooled suspension of methyl 5-cyano-4-nitro-thiophene-2-carboxylate (0.10 mol, 21.0 g) in 120 mL of hydrochloric acid 37% was added, dropwise, a solution of sodium nitrite (0.12 mol, 8.3 g) in 12 mL of water. After 1.5 hours, the cold suspension was added dropwise to a preformed solution of tin chloride (0.80 mol, 151.7 g) in 120 mL of hydrochloric acid 37%, at 5° C. After 3 hours, the cold suspension was filtered and the moist solid was treated with 350 mL of boiling water, for 30 min. The hot cloudy solution was clarified by filtration through a cloth filter. The liquors were ice-cooled and treated, dropwise, with 180 mL of sodium hydroxide 17%. The obtained solid was filtered off and dried, under vacuum, at 50° C., to give 7.3 g of the title compound as a yellow solid (37% yield).

Provenance & Evidence