To a solution of (2RS,3RS)-2-(4-tert-butoxylbenzyl)-3-(3-chlorophenyl)-3-hydroxypropanoic acid (4.50 g, 14.3 mmol) in tetrahydrofuran (150 ml) were added diphenylphosphoryl azide (3.39 ml, 15.7 mmol) and triethylamine (3.00 ml, 21.4 mmol), and the mixture was heated under reflux for 1 hr. The reaction solution was allowed to cool and the mixture was evaporated under reduced pressure. To the residue was added water (200 ml), and the mixture was extracted with ethyl acetate. The extract was washed with water and saturated brine, dried (anhydrous magnesium sulfate) and evaporated under reduced pressure. The residue was recrystallized from hexane-ethyl acetate to give the objective substance (4.01 g, 80%).
