To a solution of the above-prepared boronic acid (0.84 g, 3.2 mmol) and ethyl 3-methylpyrazole-5-carboxylate (0.49 g, 3.2 mmol) in 20 mL dry DCM were added pyridine (0.77 mL, 9.5 mmol) and anhydrous powder of copper(II) acetate (1.15 g, 6.3 mmol). Some activated molecular sieve powder was added afterwards. The resulting slurry was stirred for 4 days under argon. The mixture was diluted with DCM. It was filtered through celite. The blue filtrate was washed with water (×2), dried, concentrated and purified by flash column to separately afford ethyl 3-methyl-1-(6-methoxy-2-naphthyl)-1H-pyrazole-5-carboxylate [37% yield. Rf 0.80 (1:1 EtOAc:hexane). ES-MS: (M+H)+311] and ethyl 5-methyl-1-(6-methoxy-2-naphthyl)-1H-pyrazole-3-carboxylate [25% yield. Rf 0.69 (1:1 EtOAc:hexane). ES-MS: (M+H)+311]in a 1.5:1 ratio.
