Methanol → [6-Methoxy-7-methyl-3-oxo-4-(2-trimethylsilanyl-ethoxy)-1,3-dihydro-isobenzofuran-5-yl]-acetaldehyde

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A solution of 6-[6-methoxy-7-methyl-3-oxo-4-(2-trimethylsilanyl-ethoxy)-1,3-dihydro-isobenzofuran-5-yl]-4-methyl-hex-4-enoic acid methyl ester (618 mg, 1.42 mmol) in MeOH (10 mL), CH2Cl2 (10 mL) and pyridine (50 μL, 0.618 mmol) was cooled to −70° C. using a dry ice/acetone bath according to the procedure of Smith, D. B. et al., J. Org. Chem., 1996, 61, 6, 2236. A stream of ozone was bubbled through the reaction via a gas dispersion tube until the reaction became blue in color (15 minutes). The ozone line was replaced with a stream of nitrogen and bubbling continued for another 15 minutes, by which time the blue color had disappeared. To this solution at −70° C. was added thiourea (75.7 mg, 0.994 mmol) in one portion, and the cooling bath was removed. The reaction was allowed to warm to room temperature and stirred for 15 hours. The reaction was worked up by filtration to remove solid thiourea S-dioxide, and then partitioned between CH2Cl2 and water. The organic layer was removed. The aqueous layer was washed with CH2Cl2 one more time and the organic extracts were combined. The organic layer was washed with aqueous 1N HCl, saturated NaHCO3 and brine. The organic extracts were dried in vacuo and the residue was purified to by silica gel chromatography to afford 357 mg (75%) of the product as a white solid. 1H NMR (300 MHz, CDCl3) δ−0.01 (s, 9H), 1.05-1.15 (m, 2H), 2.15 (s, 3H), 3.69 (s, 3H), 3.78 (d, 2H, J=1 Hz), 4.27-4.39 (m, 2H), 5.11 (s, 2H), 9.72 (d, 1H, J=1 Hz) ppm.

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