Sodium Carbonate → tert-butyl 4-[4-(trifluoromethoxy)phenyl]-3,6-dihydropyridine-1(2H)-carboxylate

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Pd(PPh3)4 (87 mg, 0.0075 mmol), LiCl (190 mg, 4.5 mmol), tert-butyl 4-{[(trifluoromethyl)sulfonyl]oxy}-3,6-dihydropyridine-1(2H)-carboxylate (0.50 g 1.5 mmol), 4-(trifluoromethoxy)phenylboronic acid (0.43 g, 2.1 mmol) and aq Na2CO3 (2 mL, 2N solution) were mixed in 5.2 mL DME and heated at 85° C. for 3 h followed by cooling to room temperature and concentrated under reduced pressure. The residue was partitioned between DCM (10 mL), aq Na2CO3 (10 mL, 2N solution) and conc NH4OH (0.6 mL). The layers were separated and the aqueous layer extracted with DCM (3×10 mL). The combined organic layers were dried (Na2SO4) and concentrated. Purification by column chromatography (SiO2, Heptane/Ethylacetate/DCM 5:1:1) gave tert-butyl 4-[4-(trifluoromethoxy)phenyl]-3,6-dihydropyridine-1(2H)-carboxylate (0.27 g, 52%). The product and 5% Pd/C (30 mg) was mixed in MeOH (3 mL) and stirred under H2 (1 atm) for 24 h. The mixture was filtered through Celite and concentrated to give tert-butyl 4-[4-(trifluoromethoxy)phenyl]piperidine-1-carboxylate (0.23 g, 86%). The crude product was dissolved in a mixture of TFA (2 mL) and DCM (4 mL) and stirred at RT for 2 h. The reaction mixture was concentrated and purified by preparative HPLC to give the title compound (0.14 g, 58%, three steps 26%).

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