To an ice-cooled solution of ethyl 4-chloro-6-((3-ethoxy-3-oxopropyl)(phenyl)amino)-2-(methylthio)pyrimidine-5-carboxylate (23.0 g, 54.25 mmol) in tetrahydrofuran (400 mL), LDA [generated at 0° C. using diisopropylamine (25.37 mL, 179.4 mmol) and n-BuLi (74.2 mL, 173.9 mmol) in tetrahydrofuran (300 mL)] was added dropwise. The reaction mixture was further stirred for additional 1 h and water (500 mL) was added to the reaction mixture. The organic layer was separated and the aqueous layer was extracted using EtOAc (200 mL×2). The combined organic layer was washed with water (500 mL) and brine (500 mL); dried over anhydrous sodium sulphate and concentrated under reduced pressure to give crude product. Crude product from two batches of the same size were combined and purified by silica gel column chromatography (polarity) to provide ethyl 4-chloro-2-(methylthio)-5-oxo-8-phenyl-5,6,7,8-tetrahydropyrido[2,3-d]pyrimidine-6-carboxylate (21 g, 51.2% yield). 1H NMR (400 MHz, CDCl3): δ 7.48-7.43 (m, 2H), 7.37-7.28 (m, 3H), 4.37 (dd, J=7.2, 13.6 Hz, 1H), 4.27 (q, J=7.2 Hz, 2H), 4.11 (dd, J=4.8, 13.6 Hz, 1H), 3.75 (dd, J=4.8, 7.2 Hz, 1H), 2.17 (s, 3H), 1.29 (t, J=7.2 Hz, 3H). LCMS [M+H]: 378
