3-(Acetylsulfanyl)propanoyl chloride → (+/-)-1-[3-(Acetylthio)-1-oxopropyl]-4,5-dihydro-3-(2-thienyl)-1H-pyrazole-5-carboxylic acid

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Reaction Steps

(±)-4,5-Dihydro-3-(2-thienyl)-1H-pyrazole-5-carboxylic acid is dissolved in aqueous Na2CO3 (1.38 g) at pH 8.6. The temperature is lowered to 5° C. and 3-(acetylthio)propionyl chloride (4.15 g) and a 25% solution of Na2CO3 are added simultaneously maintaining the pH at 8-9. The final pH is 8.9 and the reaction is stirred for 2 hours at room temperature. It is then extracted with ethyl acetate and the ethyl acetate is discarded. The aqueous layer is made strongly acid with 20% HCl and the gummy precipitate is extracted with ethyl acetate. The ethyl acetate is dried over MgSO4 and removed to yield a viscous residue (7.2 g) which is triturated with ether to yield 5.1 g of material, melting point 127°-130° C., dec. After recrystallization from CH3CN (very soluble) the melting point is constant at 134°-136° C., dec.

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