[C:1]1([S:7]([C:10]2[CH:15]=[CH:14][C:13]([OH:16])=[C:12]([C:17](=[O:19])[CH3:18])[CH:11]=2)(=[O:9])=[O:8])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[CH3:20][C:21]([CH:23]([O:26][CH3:27])[O:24][CH3:25])=O.N1CCCC1>C1(C)C=CC=CC=1>[CH3:25][O:24][CH:23]([O:26][CH3:27])[C:21]1([CH3:20])[CH2:18][C:17](=[O:19])[C:12]2[CH:11]=[C:10]([S:7]([C:1]3[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=3)(=[O:9])=[O:8])[CH:15]=[CH:14][C:13]=2[O:16]1In 100 ml of toluene were dissolved 10 g of the compound obtained in step 4, 6.5 ml of pyruvic aldehyde dimethyl acetal and 1.5 ml of pyrrolidine. The resultant solution was heated to reflux for 16 hours and concentrated reduced pressure to obtain residue, which was purified by silica gel column chormatography using as an eluent a mixture of hexane and ethyl acetate (2:1) to obtain 11 g of the title compound.
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