[CH3:1][C:2]([CH3:5])([O-])[CH3:3].[K+].[CH3:7][O:8][C:9](=[O:26])[C@@H:10]1CC(=O)C[N:11]1[C:16]([O:18][CH2:19][C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1)=[O:17].[Cl-].[NH4+]>C(OCC)C.[Br-].C[P+](C1C=CC=CC=1)(C1C=CC=CC=1)C1C=CC=CC=1>[CH3:7][O:8][C:9](=[O:26])[C@@H:10]1[CH2:3][C:2](=[CH2:5])[CH2:1][N:11]1[C:16]([O:18][CH2:19][C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1)=[O:17]
Potassium t-butoxide (1.41 g, 12.6 mmol) was suspended in diethyl ether (100 ml). To the suspension was added methyltriphenylphosphonium bromide (4.80 g, 13.4 mmol), and the resulting mixture was stirred at 5° C. for 15 minutes. To the mixture was added (S)-1-benzyloxycarbonyl-4-oxoproline methyl ester (2.50 g, 9.0 mmol) in diethyl ether (30 ml), and the resulting mixture was stirred at 35° C. for 3 hours. At the end of this time, the reaction mixture was added to a saturated solution of ammonium chloride (50 ml) under ice cooling, and then partitioned. The organic layer was washed with water, dried over anhydrous magnesium sulfate and the solvent was removed by distillation under reduced pressure. The residue was purified by column chromatography through silica gel (eluent, ethyl acetate:hexane=1:3), to give the title compound (1.80 g) as a pale yellow oil (yield 72%).
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