Malonate Ion → 1,1-Bis(propan-2-yl) 3,3-dimethoxycyclobutane-1,1-dicarboxylate

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A 1 L, two-necked flask containing 95% NaH (5.04 g, 210 mmol) was charged with 75 mL of DMF, evacuated, placed under a nitrogen atm, and cooled in an ice bath. Diisopropyl malonate (34.0 mL, 191 mmol) was carefully added dropwise via addition funnel under a positive flow of nitrogen (reaction vented through a needle placed in a septum on the second neck of the flask). After the addition of the malonate, the solution became very thick and yellow in color. After stirring for 1 h, the reaction was charged with 1,3-dibromo-2,2-dimethoxypropane (25.0 g, 95.4 mmol) in one portion and the reaction was heated to 140° C. for 24 h, upon which time the reaction became thick and orange in color. Saturated ammonium chloride (300 mL) was added and the mixture was extracted with hexanes (3×, 500 mL). The organic layers were combined, washed with water (2×, 500 mL), saturated bicarbonate (2×, 500 mL), water (2×, 500 mL), and brine (1×, 500 mL), then dried over Na2SO4, filtered and concentrated to an oil. Short path distillation (4-5 torr, oil bath temperature at 60° C. to 143° C.) afforded the title compound as a clear oil; 1H NMR (400 MHz, CDCl3) δ 1.24 (d, 12H, J=6.0 Hz), 2.70 (s, 4H), 3.15 (s, 6H), 5.06 (m, 2H).

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