Br[C:2]1[O:6][C:5]([CH:7]=[O:8])=[CH:4][CH:3]=1.[C:9]1(B(O)O)[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=1.C([O-])([O-])=O.[K+].[K+]>[Br-].C([N+](CCCC)(CCCC)CCCC)CCC.O.C([O-])(=O)C.[Pd+2].C([O-])(=O)C>[C:9]1([C:2]2[O:6][C:5]([CH:7]=[O:8])=[CH:4][CH:3]=2)[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=1
A solution of 5-bromo-furan-2-carbaldehyde (1.08 g, 6.16 mmol, 1 eq), phenylboronic acid (0.90 g, 7.39 mmol, 1.1 eq), tetrabutylammonium bromide (1.99 g, 6.16 mmol, 1 eq), palladium acetate (30 mg, 0.0.12 mmol 0.02 eq), K2CO3 (2.13 g, 15.4 mmol, 2.5 eq) in water (10 mL) is stirred under nitrogen at rt overnight. The reaction is diluted with 40 mL water and extracted with EtOAc (3×100 mL). The organic layers are combined and stirred with charcoal for 30 min, then dried over MgSO4 and filtered. The solvent is removed under reduced pressure to give 5-phenyl-furan-2-carbaldehyde as an oil. The product is purified by silica gel chromatography using a Biotage Flash 40M column (10% EtOAc/heptane).
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