反应详情

Dimethyl zink (4.58 g, 48.0 mmol) is added to a solution of 5-bromo-6-methyl-pyridine-2-carboxylic acid ethyl ester (11.7 g, 48.0 mmol, see preparation of 5-isobutyl-6-methyl-pyridine-2-carboxylic acid) and Pd(dppf) (392 mg, 0.48 mmol) in dioxane (40 mL). The mixture becomes warm and is stirred at rt for 1 h. Another portion of dimethyl zink (4.58 g, 48.0 mmol) is added. The mixture is stirred at 100° C. for 2 h, then at 80° C. for 72 h before it is cooled to rt, and diluted with EA (250 mL) and ice-water (150 mL). The mixture is acidified with 2 N aq. HCl, the org. phase is separated and the aq. phase is extracted with EA (3×100 mL) and DCM (2×75 mL). The combined org. extracts are dried over Na2SO4, filtered and concentrated. The crude product is purified by MPLC on silica gel (heptane:EA gradient) to give 5,6-dimethyl-pyridine-2-carboxylic acid ethyl ester (434 mg) as a brownish oil; LC-MS: tR=0.61 min, [M+1]+=179.98, 1H NMR (CDCl3): δ 1.45 (t, J=7.0 Hz, 3H), 2.37 (s, 3H), 2.62 (s, 3H), 4.48 (q, J=7.3 Hz, 2H), 7.55 (d, J=7.8 Hz, 1H), 7.90 (d, J=7.8 Hz, 1H).

1. temperatureThe mixture becomes warm
2. stirringThe mixture is stirred at 100° C. for 2 h
3. temperatureat 80° C. for 72 h before it is cooled to rt
4. customphase is separated
5. extractionthe aq. phase is extracted with EA (3×100 mL) and DCM (2×75 mL)
6. dry with materialextracts are dried over Na2SO4
7. filtrationfiltered
8. concentrationconcentrated
9. customThe crude product is purified by MPLC on silica gel (heptane:EA gradient)