[Cl:1][C:2]1[CH:3]=[C:4]([CH:7]=[CH:8][C:9]=1[OH:10])[CH:5]=[O:6].[H-].[Na+].[CH2:13](Br)[CH:14]=[CH2:15]>CN(C=O)C.C1COCC1.O>[CH2:15]([O:10][C:9]1[CH:8]=[CH:7][C:4]([CH:5]=[O:6])=[CH:3][C:2]=1[Cl:1])[CH:14]=[CH2:13]To a solution of 3-chloro-4-hydroxybenzaldehyde (5.0 g, 31.9 mmol) in DMF/THF 1:3 (120 mL) is added NaH (1.67 g of a 55% dispersion in mineral oil, 38.3 mmol) in four portions. The mixture is stirred at rt for 1 h before allylbromide (9.66 g, 79.8 mmol) is added. The reaction mixture is heated to 65° C. for 18 h, diluted with water (250 mL) and extracted with diethyl ether (3×250 mL). The organic extracts are washed with water (250 mL), combined and concentrated. The remaining oil is chromatographed on silic gel with heptane/EA 4:1 to afford 4-allyloxy-3-chlorobenzaldehyde (5.37 g) as an almost colourless oil. LC: tR=0.95 min.
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