Potassium Carbonate → tert-butyl(3S)-4-((1R)-1-(6-fluoro-3-pyridinyl)ethyl)-3-methyl-1-piperazinecarboxylate

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A mixture of 5-(1-bromoethyl)-2-fluoropyridine (Example 146, Step 2; 8.95 g, 43.9 mmol) and (S)-tert-butyl 3-methylpiperazine-1-carboxylate (9.22 g, 46.1 mmol) (CNH Technologies Inc.) in acetonitrile (200 mL) was treated with K2CO3 (7.27 g, 52.6 mmol) and KI (1.456 g, 8.77 mmol). The mixture was placed into a pre-heated (70° C.) oil bath and allowed to stir under an inert atmosphere overnight. The heating bath was then removed and the reaction mixture was allowed to cool to ambient temperature. The reaction mixture was diluted with chloroform (200 mL) and water (300 mL). The organic layer was separated, and the aqueous layer was extracted with chloroform (1×100 mL). The combined organic layers were then washed with a saturated brine solution, dried over Na2SO4, filtered, and concentrated. The crude material was adsorbed onto silica gel and purified by column chromatography (120 g silica gel, 0% to 40% EtOAc/hexanes) to provide tert-butyl(3S)-4-((1R)-1-(6-fluoro-3-pyridinyl)ethyl)-3-methyl-1-piperazinecarboxylate (5.02 g, 15.52 mmol, 35.4% yield) (lower Rf diastereomer) as a viscous yellow-orange oil. m/z (ESI, +ve) 324.1 (M+H)+. 1H NMR (400 MHz, CDCl3) δ 8.09-8.14 (m, 1H); 7.75 (td, J=8.0, 2.2 Hz, 1H); 6.90 (dd, J=8.5, 2.8 Hz, 1H); 3.94 (br. s., 1H, =); 3.55 (br. s., 1H); 3.37 (br. s., 2H); 3.20 (br. s., 1H); 2.71 (ddd, J=11.3, 7.6, 3.5 Hz, 1H); 2.43 (dd, J=9.6, 5.5 Hz, 2H); 1.43 (s, 9H); 1.38 (d, J=6.8 Hz, 3H); 0.99 (d, J=6.3 Hz, 3H).

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