To a solution of 5-chloro-6-isopropoxy-nicotinic acid isopropyl ester (235 mg, 0.912 mmol) in dioxane (5 mL), 2,4,6-trimethyl-cyclotriboroxane (114 mg, 0.912 mmol), Cs2CO3 (386 mg, 1.19 mmol) and tri-tert.-butylphosphine (7.4 mg, 36 μmol) is added. The mixture is degassed and put under argon before Pd2(dba)3 (17 mg, 18 μmol) is added. The mixture is stirred at 100° C. for 18 h. The mixture is cooled to rt, diluted with water and sat. aq. NaHCO3-solution and extracted with EA. The org. extract is dried over MgSO4, filtered and concentrated. The crude product is purified on prep. TLC plates with heptane:EA 9:1 to give 6-isopropoxy-5-methyl-nicotinic acid isopropyl ester (90 mg) as a colourless oil; LC-MS: tR=1.08 min; [M+1]+=238.08; 1H NMR (CDCl3): δ 1.35-1.41 (m, 12H), 2.20 (s, 3H), 5.20-5.30 (m, 1H), 5.37-5.48 (m, 1H), 7.95 (s, 1H), 8.67 (s, 1H). The title compound can be obtained by hydrolising 6-isopropoxy-5-methyl-nicotinic acid isopropyl ester according to the procedure given in step d) of the preparation of 5,6-diisobutyl-nicotinic acid.
