[CH3:1][CH2:2][Mg+].[Br-].Br[C:6]1[CH:15]=[CH:14][C:9]([C:10]([O:12][CH3:13])=[O:11])=[C:8]([CH3:16])[CH:7]=1>O1CCCC1.[Zn+2].[Br-].[Br-].C1C=CC(P(C2C=CC=CC=2)[C-]2C=CC=C2)=CC=1.C1C=CC(P(C2C=CC=CC=2)[C-]2C=CC=C2)=CC=1.Cl[Pd]Cl.[Fe+2]>[CH2:1]([C:6]1[CH:15]=[CH:14][C:9]([C:10]([O:12][CH3:13])=[O:11])=[C:8]([CH3:16])[CH:7]=1)[CH3:2]To a stirred mixture of ZnBr2 (4.50 g, 20.0 mmol, 2.00 equiv) in tetrahydrofuran (50 mL) under nitrogen at 0° C. was added EtMgBr (6.6 mL, 2.00 equiv, 3M in THF) dropwise. After stiffing for 30 min at 0° C., the temperature was lowered to −78° C. and Pd(dppf)Cl2 (1.08 g, 1.48 mmol, 0.30 equiv) was added followed by a solution of methyl 4-bromo-2-methylbenzoate (compound 152.1, 2.30 g, 10.0 mmol, 1.00 equiv) in tetrahydrofuran (20 mL). The resulting mixture was stirred for 30 min at −78° C., warmed to room temperature, and stirred overnight. The reaction mixture was carefully quenched with 60 mL of NH4Cl (aq.) and extracted with 3×50 mL of ethyl acetate. The combined organic phases were dried (Na2SO4) and concentrated in vacuo. The residue was purified using silica gel column chromatography with ethyl acetate/petroleum ether (1:100-1:5) as eluent to furnish 1.50 g (84%) of methyl 4-ethyl-2-methylbenzoate as a brown oil.
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