To a solution of trans-4,6,6a,7,9,10a-hexahydro-7-methyl-10a-methyl-1-methoxy-4-(2,4,6-triisopropylphenylsulfonyl)-indolo[3,4-gh][1,4]benzoxazin-8-one (1.9 g, 3.4 mmol) in THF (30 ml) was added, while stirring under ice-cooling, LAH (3 equivalents). The mixture was heated for 3 hours under reflux. After completion of the reaction, ethanol was added to the reaction mixture, and the mixture was then added to an ice-cooled saturated aqueous solution of sodium sulfate. The mixture was subjected to extraction with ethyl acetate. The extract was washed with an aqueous saline solution, and was then dried (anhydrous sodium sulfate). The solvent was distilled off under reduced pressure. The residue was subjected to a silica gel column chromatography, eluting with ethyl acetate to leave 700 mg of a residual substance. To a solution of this residual substance in THF (10 ml) was added, at room temperature in argon streams, a solution of 0.5M naphthalene sodium in THF (10 equivalents). The mixture was stirred for 10 minutes at room temperature, and was added to an ice-cooled saturated aqueous solution of ammonium chloride, followed by extraction with ethyl acetate. The organic layer was washed with an aqueous saline solution, which was dried (anhydrous sodium sulfate). The solvent was distilled off under reduced pressure. The residue was subjected to a silica gel column chromatography, eluting with ethyl acetate to afford 250 mg (27%) of the title compound as crystals, m.p.200°-202° C. (isopropyl ether-ethyl acetate).
