tert-Butyl (triphenylphosphoranylidene) acetate → (E)-2-[4-(2-tert-butoxycarbonyl-vinyl)-phenylsulfanyl]-acetic acid ethyl ester

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Reaction Steps

A solution of 2.24 g of (4-formyl-phenylsulfanyl)-acetic acid ethyl ester and 4.72 g of (triphenylphosphoranylidene)-acetic acid tert-butyl ester in 50 ml of dichloromethane was kept at 20° for 15 h. The solvent was evaporated in vacuo and the remaining oil was chromatographed on silica gel using dichloromethane/hexane (1:1) as eluent to give 2.53 g of (E)-2-[4-(2-tert-butoxycarbonyl-vinyl)-phenylsulfanyl]-acetic acid ethyl ester as a colorless oil. To a solution of this material in 20 ml of tetrahydrofuran were added 8 ml of 2N aqueous sodium hydroxide, and the mixture was stirred for 2 h at 20°. The clear solution was diluted with 20 ml of ethyl acetate and then extracted with 30 ml of water. The aqueous layer was cooled with ice, acidified to pH 2.8 by the addition of 3N HCl, and the mixture was extracted with 60 ml of ethyl acetate. The organic layer was dried over sodium sulfate, evaporated in vacuo, and the residue was crystallized from ethyl acetate/hexane to give 1.78 g (E)-2-[4-(2-tert-butoxycarbonyl-vinyl)-phenylsulfanyl]-acetic acid as white crystals.

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