To a solution of the aldehyde from Example 3 (160 mg) and 2-methyl-2-butene (6 mL) in 2-methyl-2-propanol (35 mL) was added a solution of NaClO2 (1 g) and NaH2PO4 (1 g) in 10 mL of H2O. The mixture was stirred for 2 h at r.t., and concentrated. The residue was then taken into 50 mL of pH 7 buffer solution (1M) and extracted with EtOAc (50 mL). The extract was dried over MgSO4 and concentrated. The residue was purified by flash chromatography, eluting with 3:1 EtOAc/hexane containing 1% HOAc to give 150 mg of the title compound as a white solid.
