[CH2:1]([C@H:8]([C@H:12]([OH:16])[C:13]([OH:15])=[O:14])[C:9]([OH:11])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.CO[C:19](OC)([CH3:21])[CH3:20]>CC(C)=O.[Cu](Cl)Cl>[CH3:20][C:19]1([CH3:21])[O:16][C@H:12]([C@H:8]([CH2:1][C:2]2[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=2)[C:9]([OH:11])=[O:10])[C:13](=[O:15])[O:14]1To a solution of (2R,3S)-2-benzyl-3-hydroxysuccinic acid (2.08 g; 9.28 mmol; 1.00 eq.) in acetone (50.0 mL) was added 2,2-dimethoxypropane (2.3 mL; 18.55 mmol; 2.0 eq.) and copper(II) chloride (124.73 mg; 0.93 mmol; 0.10 eq.). The resulting reaction mixture was stirred for 4 h at RT. The reaction mixture was evaporated and the residue taken up in CHCl3. Activated charcoal is added and the resulting mixture stirred for one hour. Filtration on a pad of celite gave the title product (single diastereoisomer) as a greenish oil (1.81 g, 74%) used in the next step without further purification.
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