Stereoselective synthesis of substituted alpha-amino acid
Typical procedure (aldol condensation): To a solution of (2S)-2,5-dihydro-2-isopropyl-3,6-dimethoxypyrazine (0.7 mL) in anhydrous THF (10 mL), cooled at -78 ºC, 1.6 M butyllithium in hexane (2.55 mL) is added and the mixture is stirred for 45 min. A solution of dichlorotitanium diisopropoxide (990 mg) in anhydrous THF (2 mL) is added and stirring continued for 45 min. (E)-3-(2-furyl)acrolein in THF (10 mL) is added and then the mixture stirred at -78 ºC for 6 h. The reaction mixture is allowed to warm to 0ºC and phosphate buffer solution (25 mL) is added. The solvent is evaporated in vacuo and the residue is flash chromatographed (eluent: diethyl ether) on silica gel to give the condensation compound (853 mg, 65 %).
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