Yield: 85%

Reaction Conditions:

Stage #1:diethyl isopentylmalonate with sodium hydride in diethyl ether;N,N-dimethyl-formamide at 25;
Stage #2:methyl iodide in diethyl ether;N,N-dimethyl-formamide at 25; for 3 h;
Stage #3: with hydrogenchloride in diethyl ether;water;N,N-dimethyl-formamide

Steps:

2 2-Methyl-2-(3-methyl-butyl)-malonic acid diethyl ester
2-Methyl-2-(3-methyl-butyl)-malonic acid diethyl ester A solution of diethyl isopentylmalonate (2.31 g, 10 mmol) in a 6:2 mixture of anhydrous N,N-dimethylformamide/diethyl ether (8 mL) was stirred under a nitrogen environment at 25° C. and treated with a 60% oil dispersion of sodium hydride (480 mg, 12 mmol). The reaction mixture was stirred until the evolution of hydrogen gas ceased. The reaction was then treated dropwise via syringe with iodomethane (1.87 mL, 30 mmol) and stirred for 3 h at 25° C. The reaction was quenched with a 1.0 M aqueous hydrochloric acid solution (30 mL) and extracted with diethyl ether (2*50 mL). The combined organic layers were washed with a saturated aqueous sodium bicarbonate solution (50 mL) and brine (50 mL), dried over sodium sulfate, filtered, and concentrated in vacuo to give 2-methyl-2-(3-methyl-butyl)-malonic acid diethyl ester (2.09 g, 85%) as a clear oil. ¹H NMR (400 MHz, CDCl₃) δ: 0.88 (d, 6H, J=6.9 Hz), 1.06-1.12 (m, 2H), 1.24 (t, 6H, J=7.0 Hz), 1.38 (s, 3H), 1.51 (septet, 1H, J=6.6 Hz), 1.82-1.87 (m, 2H), 4.12-4.20 (m, 4H). LC-MS (ESI) calculated for C₁₃H₂₄O₄: 244.3, found 245.3 [M+H⁺].

References:

Ellis, David;Li, Liansheng;Tran, Chinh V.;Ruebsam, Frank;Zhou, Yuefen US2009/62263, 2009, A1 Location in patent:Page/Page column 22