[OH:1][C:2]1[CH:10]=[CH:9][C:8]([Br:11])=[C:7]([CH3:12])[C:3]=1[C:4]([OH:6])=[O:5].[C:13](Cl)(=[O:18])[C:14]([CH3:17])([CH3:16])[CH3:15].O1CCCC1.N1C=CC=CC=1>O.C(OCC)(=O)C>[C:13]([O:1][C:2]1[CH:10]=[CH:9][C:8]([Br:11])=[C:7]([CH3:12])[C:3]=1[C:4]([OH:6])=[O:5])(=[O:18])[C:14]([CH3:17])([CH3:16])[CH3:15]A mixture of 1B (6.45 g, 28 mmol), pivaloylchloride (3.62 g, 30 mmol), tetrahydrofuran (60 ml) and pyridine (2.45 ml) is stirred at room temperature for 16 hours. The reaction mixture is diluted with water and ethyl acetate. The organic phase is washed with water twice. The organic phase is concentrated in vacuo and the residue is re-crystallized from petrol ethers/diisopropylether (9:1 v/v) yielding the pure product as a white crystals, 6.3 g, (71.6%), mp. 144-145° C.
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