[OH:1][C:2]1[C:9]([CH3:10])=[CH:8][C:5]([CH:6]=[O:7])=[CH:4][C:3]=1[CH3:11].C([O-])([O-])=O.[K+].[K+].Br[CH2:19][C@H:20]1[NH:24][C:23](=[O:25])[CH2:22][CH2:21]1>CN(C=O)C>[CH3:10][C:9]1[CH:8]=[C:5]([CH:4]=[C:3]([CH3:11])[C:2]=1[O:1][CH2:19][C@@H:20]1[CH2:21][CH2:22][C:23](=[O:25])[NH:24]1)[CH:6]=[O:7]To a solution of 4-hydroxy-3,5-dimethylbenzaldehyde (2.65 g, 17.7 mmol) in DMF (100 mL) was added K2CO3 (3.66 g, 26.6 mmol). The mixture was stirred at room temperature under nitrogen for 30 minutes. Then, a solution of (S)-5-(bromomethyl)pyrrolidin-2-one (3.15 g, 17.7 mmol) in DMF (100 mL) was added, and the mixture heated at reflux for 16 hours. The mixture was then concentrated, ethyl acetate (250 mL) added, and the organic phase washed sequentially with water (2×150 mL), and brine (200 mL), dried (Na2SO4), filtered, and concentrated. The residue was purified by silica gel chromatography, eluting with 100% ethyl acetate to 10% MeOH/ethyl acetate, followed by a second chromatography, eluting with 1:1 CH2Cl2/92:7:1 CHCl3/MeOH/concentrated NH4OH to 100% 92:7:1 CHCl3/MeOH/concentrated NH4OH, to afford (S)-3,5-dimethyl-4-((5-oxopyrrolidin-2-yl)methoxy)benzaldehyde as a white solid (0.200 g, 5%).
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