[H-].[Na+].CCCCCC.[OH:9][C:10]1[CH:15]=[CH:14][C:13]([CH2:16][C:17]([O:19][CH2:20][C:21]2[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=2)=[O:18])=[CH:12][CH:11]=1.Br[CH2:28][C:29]([O:31][C:32]([CH3:35])([CH3:34])[CH3:33])=[O:30]>CN(C=O)C>[CH2:20]([O:19][C:17]([CH2:16][C:13]1[CH:12]=[CH:11][C:10]([O:9][CH2:28][C:29]([O:31][C:32]([CH3:35])([CH3:34])[CH3:33])=[O:30])=[CH:15][CH:14]=1)=[O:18])[C:21]1[CH:22]=[CH:23][CH:24]=[CH:25][CH:26]=1Sodium hydride (50% w/w dispersion in mineral oil, 2.1 g) was treated under argon with repeated washes of hexane. The oil-free residue was suspended in dry DMF (130 ml) and the product from step (i) (10 g) added in three portions to the cooled (4° C.) stirred mixture. Stirring was continued for a further 15 minutes when tertiary butyl bromoacetate (7.0 ml) was added dropwise over 15 minutes. After 1 hour at 4° C., the mixture was stirred for 6 hours at ambient temperature. The solvent was evaporated in vacuo and the residue partitioned between ethyl acetate and water. The aqueous phase was re-extracted with further ethyl acetate and the combined organic phases washed with water and brine, then dried (MgSO4) and evaporated. The residue, after purification by flash chromatography on silica eluting with dichloromethane, gave tertiary butyl 4-(benzyloxycarbonylmethyl)phenoxyacetate, 7.5 g, as a colourless oil: NMR (CDCl3) d 7.31(5H, m), 7.20(2H, m), 6.85(2H, m), 5.12(2H, s), 4.49(2H, s), 3.60(2H, s), 1.48(9H, s); m/e 356 (M.)+.
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