[CH2:1]([C:4]1([C:19]([OH:21])=[O:20])[CH2:8][CH2:7][CH2:6][N:5]1[C:9]([O:11][CH2:12][C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=1)=[O:10])[CH:2]=[CH2:3].[Li].[CH2:23](I)C=C.[Cl-].[NH4+]>C1COCC1.CCCCCC.C1COCC1>[CH2:1]([C:4]1([C:19]([O:21][CH3:23])=[O:20])[CH2:8][CH2:7][CH2:6][N:5]1[C:9]([O:11][CH2:12][C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=1)=[O:10])[CH:2]=[CH2:3]Synthesis of (RS)-2-allyl-N-(benzyloxycarbonyl)proline ##STR5## N-benzyloxycarbonylproline methyl ester (13 g) in THF (20 ml) was added dropwise to lithium dilsopropylamide (27.5 ml, 2M in hexane/THF) in THF (100 ml) at -78° C. under nitrogen. The mixture was stirred for 30 minutes and then allyl iodide (5.5 ml) was added dropwise and the mixture stirred for a further 30 minutes and then allowed to warm to ambient temperature. The mixture was then added to aqueous ammonium chloride (200 ml) and extracted with ether (2×200 ml). The ether layer was evaporated and the residue was purified by chromatography on silica using a gradient of hexane increasing to 20% ethyl acetate:hexane. The appropriate fractions, evaporated to dryness, gave methyl (RS)-2-allyl-N-(benzyloxycarbonyl)prolinate (9 g) as an oil.
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