[OH:1][C:2]1[C:9]([OH:10])=[C:8]([O:11][CH3:12])[CH:7]=[CH:6][C:3]=1[CH:4]=[O:5].[C:13]([O-])([O-])=O.[K+].[K+].Br[CH:20]([CH3:22])[CH3:21].O.CCO[C:27]([CH3:29])=O>CN(C=O)C>[CH:20]([O:1][C:2]1[C:9]([O:10][CH:27]([CH3:29])[CH3:13])=[C:8]([O:11][CH3:12])[CH:7]=[CH:6][C:3]=1[CH:4]=[O:5])([CH3:22])[CH3:21]
To a solution of 21 (26.70 g, 158.7 mmol) in DMF (150 mL) under nitrogen, was added K2CO3 (65.84 g, 476.3 mmol) followed by 2-bromopropane (44.72 mL, 476.3 mmol) and heated to reflux (90° C.) for 12 hours. Water (200 mL) and EtOAc (200 mL) were added to the reaction mixture, the phases were separated, and the aqueous phase was extracted with EtOAc (3×200 mL). The combined organic solutions were dried over MgSO4 and concentrated under reduced pressure. Purification by flash column chromatography (silica gel, elution with hexane) provided 32.85 g (1.30.2 mmol, 82%) of the diusopropyl-protected aldehyde 22 as a yellow oil.
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