[C:1]([O:5][C:6](=[O:15])[C:7]1[CH:12]=[C:11]([CH3:13])[N:10]=[C:9](Cl)[CH:8]=1)([CH3:4])([CH3:3])[CH3:2].CN1C(=O)C[CH2:19][CH2:18]1.C([Mg]Br)C>C1COCC1>[C:1]([O:5][C:6](=[O:15])[C:7]1[CH:12]=[C:11]([CH3:13])[N:10]=[C:9]([CH2:18][CH3:19])[CH:8]=1)([CH3:4])([CH3:3])[CH3:2]To a red solution of 2-chloro-6-methyl-isonicotinic acid tert.-butyl ester (2.95 g, 13.0 mmol), Fe(acac)3 (512 mg, 1.45 mmol) and NMP (1.58 g, 16.0 mmol) in THF (400 mL), a solution of ethylmagnesium bromide (1.81 g, 13.6 mmol) in THF is slowly added at −77° C. The brown solution turns green-grey. The suspension is warmed to rt, stirred for 30 min before the yellow solution is again cooled to −70° C. and another portion of the Grignard reagent (1.38 g, 10.4 mmol) is added. The reaction mixture is warmed to rt, stirred for 16 h and then carefully quenched with 1 N aq. HCl (100 mL) and diluted with diethyl ether. The org. layer is separated and the aq. phase is extracted with diethyl ether. The combined org. extracts are dried over MgSO4, filtered and evaporated. The crude product is purified by MPLC on silica gel to give 2-ethyl-6-methyl-isonicotinic acid tert.-butyl ester as a yellow oil which is dissolved in 4 N HCl in dioxane (50 mL). The solution is stirred at 50° C. for 16 h before the solvent is evaporated to give 2-ethyl-6-methylisonicotinic acid hydrochloride as a beige powder; LC-MS: tR=0.28 min; [M+1]+=166.25; 1H NMR (CDCl3): δ 8.19 (s, 2H), 3.12 (q; J=7.6 Hz, 2H), 2.84 (s, 3H), 1.43 (t, J=7.6 Hz, 3H).
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