[CH2:1]([N:6]1[CH2:10][C:9]2([CH2:15][CH2:14][CH2:13][CH:12]([C:16]([O:18][CH3:19])=[O:17])[CH2:11]2)[O:8][C:7]1=[O:20])[C:2]([CH3:5])([CH3:4])[CH3:3].[CH3:21][Si]([N-][Si](C)(C)C)(C)C.[Na+].IC>C1COCC1>[CH3:21][C:12]1([C:16]([O:18][CH3:19])=[O:17])[CH2:13][CH2:14][CH2:15][C:9]2([O:8][C:7](=[O:20])[N:6]([CH2:1][C:2]([CH3:5])([CH3:4])[CH3:3])[CH2:10]2)[CH2:11]1To a 78° C. solution of methyl 3-neopentyl-2-oxo-1-oxa-3-azaspiro[4.5]decane-7-carboxylate (15.0 g, 52.9 mmol) in THF (41.0 mL) under N2 was added sodium bis(trimethylsilyl)amide, 1 M in THF (238 mL, 238 mmol) over 1 h using an addition funnel. The reaction mixture was stirred at −78° C. for 3 h. Iodomethane (14.9 mL, 238 mmol) was added, and the reaction was stirred at −78° C. for an additional 2 h. The reaction was quenched at −78° C. with water (5 mL) and diluted with brine (200 mL). The product was extracted into EtOAc (3×200 mL). The combined organics were dried over sodium sulfate, filtered, and concentrated to a light yellow solid. The solid was suspended in Et2O (75 mL) and collected in a frit. The collected solids were washed with cold Et2O (4×10 mL) and dried to afford the title compound (13.4 g, 81% yield) as a light yellow solid. 1H NMR (400 MHz, CDCl3) δ 3.69 (s, 3H), 3.40 (d, J=8.78 Hz, 1H), 3.29 (d, J=8.78 Hz, 1H), 3.06 (d, J=14.05 Hz, 1H), 2.92 (d, J=14.05 Hz, 1H), 2.16 (d, J=14.05 Hz, 1H), 1.77-1.93 (m, 4H), 1.43-1.69 (m, 3H), 1.35 (s, 3H), 0.96 (s, 9H). MS (m/z) 298.1 (M+H+).
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