[I-].[CH3:2][S+](C)(C)=O.[H-].[Na+].[O:9]=[C:10]1[CH2:15][CH2:14][CH2:13][CH:12]([C:16]([O:18][CH3:19])=[O:17])[CH2:11]1>CS(C)=O.O>[O:9]1[C:10]2([CH2:15][CH2:14][CH2:13][CH:12]([C:16]([O:18][CH3:19])=[O:17])[CH2:11]2)[CH2:2]1To a solution of trimethylsulfoxonium iodide (53.3 g, 242 mmol) in dry DMSO (300 mL) under N2, was added sodium hydride (9.69 g, 242 mmol) portionwise over 30 min. This light yellow mixture was stirred at RT for 1 h. The reaction mixture was then cooled in an ice bath and treated with methyl 3-oxocyclohexanecarboxylate (29.0 g, 186 mmol) dropwise while maintaining a temperature at or below 27° C. The resulting reaction mixture was allowed to warm slowly to RT and stir overnight. The reaction was diluted with water and extracted with DCM. The combined organics were washed with water, dried over MgSO4, filtered, and concentrated to provide methyl 1-oxaspiro[2.5]octane-5-carboxylate (31.8 g, 85% yield) which was used without further purification. 1H NMR (400 MHz, CDCl3) δ 3.66 (s, 3H), 2.71 (m, 1H), 2.65 (d, J=1.76 Hz, 2H), 2.00 (dd J=11.8, 13.6 Hz, 2H), 1.74-1.85 (m, 2H), 1.60-1.74 (m, 1H), 1.40-1.56 (m, 2H), 1.17-1.32 (m, 1H).
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