A solution of diisopropylamine (1.9 mL, 13.64 mmol) in dry tetrahydrofuran (19.5 mL) and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (6.5 mL) cooled to −78° C. under nitrogen was treated with a 2.5M solution of n-butyllithium in hexanes (5.5 mL, 13.64 mmol). The reaction mixture was stirred at −78° C. for 45 min and then treated dropwise with a solution of (3-chloro-4-methylsulfanyl-phenyl)-acetic acid methyl ester (prepared as in Example 4, 2.42 g, 10.49 mmol) in dry tetrahydrofuran (19.5 mL) and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (6.5 mL). The reaction mixture turned bright yellow. The reaction mixture was allowed to stir at −78° C. for 15 min, then at 0° C. for an additional 30 min, and then re-cooled to −78° C. At this point, a solution of 2-iodomethyl-6,10-dioxa-spiro[4.5]decane (prepared as in Example 43, 3.85 g, 13.64 mmol) in dry tetrahydrofuran (10 mL) and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (3 mL) was added dropwise. The reaction mixture stirred at −78° C. for 30 min and was then allowed to warm to 25° C., where it was stirred for 24 h. The reaction mixture was concentrated in vacuo to remove tetrahydrofuran. The aqueous residue was diluted with ethyl acetate (200 mL), and the organic layer was washed with a saturated aqueous lithium chloride solution (2×200 mL), water (200 mL), and a saturated aqueous sodium chloride solution. The organic layer was dried over magnesium sulfate, filtered, and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 230–400 mesh, 25% ethyl acetate/hexanes) afforded the 2-(3-chloro-4-methylsulfanyl-phenyl)-3-(6,10-dioxa-spiro[4.5]dec-2-yl)-propionic acid methyl ester (2.27 g, 56%) as a yellow oil: EI-HRMS m/e calcd for C19H25ClO4S (M)+ 384.1162 found 384.1181.
