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(S)-3,5-Dichloro-1-(1-cyclopropyl-2-methoxyethyl)pyrazin-2(1H)-one (15.0 g, 57.0 mmol) and 6-(difluoromethoxy)-2,5-dimethylpyridin-3-amine (10.7 g, 57.0 mmol) were combined under N2 in a 2 L, 3-neck, round-bottomed flask equipped with a thermometer and an addition funnel. THF (570 mL) was added and the mixture was cooled to 0° C. NaHMDS (119.7 mL, 119.7 mmol, 1 M in THF) was added dropwise via addition funnel over 20 min at a rate to maintain the internal temperature below 5° C. After the addition was complete, the reaction mixture was stirred at 0° C. for an additional 15 min. The reaction was quenched by the addition of saturated aqueous NH4Cl (60 mL). The mixture was transferred to a separatory funnel containing water (400 mL) and the aqueous layer was extracted with ether (3×300 mL). The combined organic layers were washed with brine, dried over MgSO4, filtered and concentrated. The product was purified by column chromatography on silica gel (30% ethyl acetate in hexanes) to afford (S)-5-chloro-1-(cyclopropyl-2-methoxyethyl)-3-[6-(difluoromethoxy)-2,5-dimethylpyridin-3-ylamino]pyrazin-2(1H)-one (22.1 g, 94% yield) as a pale yellow solid which was subsequently recrystallized from heptane to furnish colorless needles: mp 103.4-104.4° C.; [α]25D−41.9 (c 0.807, CHCl3); 1H NMR (400 MHz, CDCl3) δ 8.42 (s, 1H), 8.02 (s, 1H), 7.46 (t, J=74.0 Hz, 1H), 6.96 (s, 1H), 4.19-4.14 (m, 1H), 3.75 (dd, JAB=10.3, JAX=6.3 Hz, 1H), 3.67 (dd, JBA=10.3, JBX=3.5 Hz, 1H), 3.34 (s, 3H), 2.44 (s, 3H), 2.26 (s, 3H), 1.32-1.26 (m, 1H), 0.81-0.74 (m, 1H), 0.63-0.54 (m, 1H), 0.52-0.47 (m, 1H), 0.36-0.29 (m, 1H); HRMS (ESI) m/e 415.1360 [(M+H)+, calcd for C18H22N4O3ClF2 415.1349]. Anal. Calcd for C18H21N4O3ClF2: C, 52.11; H, 5.10; N, 13.50. Found: C, 52.05; H, 4.99; N, 13.48.

1. customequipped with a thermometer and an addition funnel
2. temperatureto maintain the internal temperature below 5° C
3. additionAfter the addition
4. customThe reaction was quenched by the addition of saturated aqueous NH4Cl (60 mL)
5. customThe mixture was transferred to a separatory funnel
6. additioncontaining water (400 mL)
7. extractionthe aqueous layer was extracted with ether (3×300 mL)
8. washThe combined organic layers were washed with brine
9. dry with materialdried over MgSO4
10. filtrationfiltered
11. concentrationconcentrated
12. customThe product was purified by column chromatography on silica gel (30% ethyl acetate in hexanes)