Methyl cyanoacetate → Dimethyl 2-cyano-3-(2,4,5-trifluorophenyl)pentanedioate

To a solution of 15 mL (64 mmol, 25% in methanol) of sodium methoxide in 200 mL of methanol was added 5.5 mL (62 mmol) of methyl cyanoacetate and the mixture was stirred at ambient temperature for 30 min. To this solution was added 14 g (62 mmol) of the product of step A in 50 mL of methanol and the resulting yellow mixture was heated to reflux for 6 h. The mixture was then quenched carefully at ambient temperature with 1N aqueous hydrochloric acid (100 mL) and concentrated to remove methanol. The resulting mixture was extracted with three 300-mL portions of ethyl acetate, and the organic phases combined and washed sequentially with 1N hydrochloric acid, saturated aqueous sodium bicarbonate solution, and saturated aqueous brine (100 mL each). The organic phase was then dried over magnesium sulfate, filtered, and evaporated in vacuo to yield a viscous oil. The crude material was purified by flash chromatography on a Biotage Horizon® system (silica gel, 0 to 25% ethyl acetate/hexanes gradient) to give the title compound as a mixture of stereoisomers. 1H NMR (CDCl3): δ 7.33-6.96 (m, 2H), 4.23-3.93 (series of m, 2H), 3.81-3.67 (series of s, 6H), 3.05-2.84 (m, 2H).