Dimethyl malonate → Dimethyl 3-cyclopentene-1,1-dicarboxylate

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The dimethyl diester 2 was prepared employing Depres and Greene's procedure. To a flame dried round-bottomed flask was placed dimethyl malonate (ACROS, 99+%, 26.7 g, 23.1 mL, 200 mmol) and anhydrous dimethylformamide (DMF, 300 mL). The mixture was cooled to 0° C. under an atmosphere of nitrogen while stirring. To this solution was then added lithium hydride (ACROS, 98%, 4.06 g,500 mmol) powder in one portion. The resulting mixture was allowed to stir at 0° C. until the evolution of hydrogen ceased (˜3 hours). To this heterogeneous mixture was then slowly added cis-1,4-dichloro-2-butene (ACROS, 95%, 30 g, 25.3 mL, 228 mmol). The resulting mixture was allowed to slowly come to room temperature and then allowed to stir for 72 hours (the color of the heterogeneous mixture changed from white to brown overnight). The reaction progress was monitored by TLC (silica gel, 20% ethyl ether/hexanes). The reaction mixture was diluted with 20% ethyl ether/hexanes (500 mL) and the solution poured into cold water (350 mL). The organic phase was separated, washed successively with water (300 mL) and brine (300 mL), dried over anhydrous sodium sulfate and concentrated under reduced pressure to give a light yellow solid. The crude material was recrystallized from refluxing hexanes (or ethyl ether). The desired dimethyl diester 2 was obtained as white needles in 50% yield. Mp (DSC) 63.48° C., 1H-NMR (CD13, 300 MHz) δ5.56 (s, 2H), 3.68 (2s, 6H), 2.97 (s, 4H); 13C-NMR (CDCl3, 300 MHz) δ172.47, 127.64, 58.60, 52.66, 40.78; FT-IR (CH2Cl2) (cm−1) 3061, 2955, 1733, 1624, 1436, 1266, 1076, 975.

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