[CH3:1][O:2][C:3]1[C:12]2[C:7](=[C:8]([CH3:13])[CH:9]=[CH:10][CH:11]=2)[C:6]([CH:14]=[O:15])=[CH:5][CH:4]=1.CC(=CC)C.[O-:21]Cl=O.[Na+]>CC(O)(C)C.O>[CH3:1][O:2][C:3]1[C:12]2[C:7](=[C:8]([CH3:13])[CH:9]=[CH:10][CH:11]=2)[C:6]([C:14]([OH:21])=[O:15])=[CH:5][CH:4]=1To a solution of 4-methoxy-8-methyl-1-naphthaldehyde (above Step-4 intermediate) (4.4 g, 22 mmol) in tBuOH (50 mL) and 2-methyl-2-butene (23.3 mL, 220 mmol) at 0° C. was added, a solution of NaClO2 (6.0 g, 66 mmol) and NaH2PO4 (9.1 g, 66 mmol) in water (40 mL) drop wise and the reaction mixture was stirred at RT overnight. After completion (TLC), the solvent was evaporated and the residue was basified with 10% NaOH solution and washed with CH2Cl2 (2×50 mL). The aqueous layer was then acidified with 1 N HCl and extracted with EtOAc (4×100 mL). The combined organic layer was washed with water (100 mL), brine (100 mL), dried and filtered. After removal of solvent, the desired compound was obtained (4.5 g, 95%) as an off white solid.
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