The above ester (2.5 g, 6.5 mmol) was dissolved in ethanol (20 ml) and 4N sodium hydroxide (4.9 ml) was added. The mixture was stirred at ambient temperature for 3 h and excess concentrated hydrochloric acid was added followed by dichloromethane (300 ml) and water (15 ml). The phases were separated and the organic phase was dried (MgSO4) and the solvent evaporated in vacuo. The residue was re-evaporated with acetone and recrystallised from acetone (180 ml) to give 1.5 g of the title compound as a solid.
