2.17 g (6.09 mmol) of the Intermediate 86 are dissolved in 200 ml of acetone. 1.95 ml (13.99 mmol) of triethylamine are added and the solution is cooled to 0° C. A solution of 0.89 ml (6.84 mmol) of isobutyl chloroformiate in 15 ml of acetone is dropped into the system. After 30′ at 0° C. a solution of 0.99 g (15.23 mmol) of sodium azide in 10 ml of water is slowly added, and the stirring at 0° C. is prosecuted for an additional period of 30 min. Excess water is added, the system is extracted with ethyl ether which is washed with water, dried and concentrated at room temperature. The residue is dissolved in 15 ml of toluene and this solution added slowly to 150 ml of refluxing toluene. The reflux is prosecuted for an additional hour and the solution is concentrated. The residue is dissolved in 15 ml of dioxane, 35 ml of 5N HCl are added and the system is stirred at 100° C. for 30′. The solution is neutralised with 2N NaOH and is extracted with ethyl ether. The ethereal layer is washed with water, dried and concentrated. The residue is chromatographied on silicagel eluting with ethyl acetate/methanol 10:1 then 6:1 giving 1.46 g (72%) of yellowish oil.
