Citric Acid → ethyl 2-[4-[((3S)-1-tert-butoxycarbonyl-3-pyrrolidinyl)oxy]phenyl]-3-(5-cyano-2-benzofuranyl)acrylate

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3.12 g of ethyl 2-[4-[((3S)-1-tert-butoxycarbonyl-3-pyrrolidinyl)oxy]phenyl]-2-oxoacetate was dissolved in 100 ml of tetrahydrofuran, followed by the addition of 4.65 g of (5-cyano-2-benzofuranyl)methyltriphenylphosphonium chloride. To the thus prepared solution was added 400 mg of 60% sodium hydride. With stirring, to the resulting mixture was added dropwise 3 ml of ethanol, followed by stirring at room temperature for 1 hour. The resulting reaction solution was neutralized with 10% citric acid solution, extracted with ethyl acetate, and then dried to distill off the solvent. Thereafter, the residue thus obtained was subjected to silica gel column chromatography using a toluene/ethyl acetate mixture as an elution solvent, thereby obtaining 3.1 g of ethyl 2-[4-[((3S)-1-tert-butoxycarbonyl-3-pyrrolidinyl)oxy]phenyl]-3-(5-cyano-2-benzofuranyl)acrylate in the form of viscous oil as a mixture of E and Z forms. A portion of the thus obtained compound was separated into E and Z forms.

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