To a 3.0 M solution of lithium diisopropylamide in tetrahydrofuran [prepared from diisopropylamine (0.56 ml), tetrahydrofuran (5 ml) and a 1.4 M solution of butyllithium in hexane (2.2 ml)] was added dropwise 0.41 ml of ethyl isobutyrate at -70° C., and the mixture was stirred at that temperature for 40 minutes. To it was added dropwise a solution of 0.26 g of the benzyl chloride compound (prepared as described in Reference Example 2) in 2.8 ml of a mixture of HMPA and tetrahydrofuran (1:1) at -70° C., and the mixture was stirred at that temperature for 2 hours, and then at room temperature for one hour. The reaction mixture was poured into a saturated aqueous solution of ammonium chloride, and extracted with diethyl ether. The extract was washed with a saturated aqueous solution of sodium chloride, dried over sodium sulphate and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel using a mixture of cyclohexane and ethyl acetate (2:1) as eluent to give 0.27 g of the title compound having the following physical characteristics:
