To 99.8 mg(0.42 mmol) of (1S,3S,3aS,4aS,8aR,9aS)-1-methoxy-3-methyl-4-methylene-dodecahydronaphtho[2,3-c]furan in 10 ml of dehydrated tetrahydrofuran solution were added dropwise 633.4 μl (1.5 equivalents) of borane-tetrahydrofuran complex(1M) under cooling with ice and under an atmosphere of argon, and the mixture was stirred for 4.5 hours while raising temperature naturally. The reaction mixture was cooled with ice and 1 ml of water was added to stop the reaction. Then, 0.50 ml of 30% aqueous hydrogen peroxide and 0.50 ml of 10% aqueous solution of sodium hydroxide were added, which was stirred for 30 minutes. Solvent was distilled off and 20 ml of water were poured to the residue, which was extracted with methylene chloride(10 ml×3). The organic layer was dried over anhydrous magnesium sulfate, filtered and solvent was distilled off under reduced pressure. The residue was purified by means of silica gel column chromatography(hexane:ethyl acetate=4:1, then 1:1) to obtain 86.7 mg of (1S,3S,3aR,4R,4aS,8aR,9aS)-4-hydroxymethyl-1-methoxy-3-methyl-dodecahydronaphtho[2,3-c]furan (yield 81%) and 11.7 mg of (1S,3S,3aR,4S,4aS,8aR,9aS)-4-hydroxymethyl-1-methoxy-3-methyl-dodecahydronaphtho[2,3-c]furan (yield 11%). (1S,3S,3aR,4R,4aS,8aR,9aS)-4-hydroxymethyl-1-methoxy-3-methyl-dodecahydronaphtho[2,3-c]furan.
