A solution of the compound (2) (0.43 g, 1.09 mmol) obtained above in 1N hydrochloric acid (3.28 ml) and tetrahydrofuran (2 ml) was heated under reflux for 3 hours. Thereto was added additional 1N hydrochloric acid (2.18 ml) and the mixture was further heated for 1.5 hours. The reaction mixture was poured into a saturated aqueous solution of sodium hydrogencarbonate, extracted with methylene chloride, dried over anhydrous magnesium sulfate and evaporated. The residue was purified by column chromatography on silica gel to give the title compound (Compound 1). Yield 0.15 g (39%).
